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DNV CONSULTING Reg.1 Reg.2 Reg.3 Reg.4 Reg.5 Reg.6 Reg.7 Reg.8 Reg.9 Reg.10 6220000 6240000 6260000 6280000 6300000 6320000 6340000 6360000 6380000 6400000 Nord Yme Gamma Yme Beta Kogge Albuskjell Tor Ekofisk 2/4A Eldfisk A Eldfisk B Valhall Nordflanke Valhall Valhall Sørflanke Hod Trym Tambar Gyda Ula Embla 2/7D Environmental Monitoring Region I, 2005, Main Report: Report for BP Norge AS Report no.: 2006-0187 Rev 01, 27 March 2006

tema.miljodirektoratet.no · DNV CONSULTING Reg.1 Reg.2 Reg.3 Reg.4 Reg.5 Reg.6 Reg.7 Reg.8 Reg.9 Reg.10 6220000 6240000 6260000 6280000 6300000 6320000 6340000 6360000 6380000 6400000

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DNV CONSULTING

Reg.1

Reg.2

Reg.3

Reg.4

Reg.5

Reg.6

Reg.7

Reg.8

Reg.9

Reg.10

6220000

6240000

6260000

6280000

6300000

6320000

6340000

6360000

6380000

6400000

Nor

d

Yme Gamma

Yme Beta

Kogge

Albuskjell Tor

Ekofisk 2/4A

Eldfisk AEldfisk B

Valhall NordflankeValhall

Valhall Sørflanke Hod

Trym

Tambar

Gyda

Ula

Embla 2/7D

Environmental Monitoring Region I, 2005, Main Report:

Report for BP Norge AS Report no.: 2006-0187 Rev 01, 27 March 2006

31 March 2006 Environmental Monitoring Region I, 2005, Main Report 2006-0187 (rev 01) BP Norge AS DNV CONSULTING

Page i Reference to part of this report which may lead to misinterpretation is not permissible.

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Environmental Monitoring Region I, 2005, Main Report for

BP Norge AS Godesetdalen 8 Postboks 197 Forus 4065 STAVANGER

Client ref:

Ingvild Anfinsen/Kristin Ravnaas/Eimund Garpestad

DET NORSKE VERITAS AS Veritasveien 1

1322 HøvikTel: +47 67 57 99 00Fax: +47 67 57 99 11Registered in NorwayNO 945 748 931 MVA

Report No.:

2006-0187

Subject Group:

Marine Monitoring

Indexing terms:

Sediments, macrofauna, hydrocarbons, monitoring, survey

Prepared by: Sam-Arne Nøland, Project Manager Signature Siri Mordal Bakke

Ingegerd Rustad

Karen M. Brinchmann

Verified by: Name and position Tor Jensen, Leader Environmental Team

Signature

Approved by: Name and position Magne Tørhaug, Director

Signature

Date of issue:

27 March 2006

Project No:

66110757

No distribution without permission from the client or responsible organisational unit (however, free distribution for internal use within DNV after 3 years)

No distribution without permission from the client or responsible organisational unit

Strictly confidential

Unrestricted distribution

All copyrights reserved Det Norske Veritas AS. This publication or parts thereof may not be reproduced or transmitted in any form or by any means, including photocopying or recording, without the prior written consent of Det Norske Veritas AS.

31 March 2006 Environmental Monitoring Region I, 2005, Main Report 2006-0187 (rev 01) BP Norge AS DNV CONSULTING

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Contents:

1.0 Resumé .............................................................................................................1

2.0 Introduction ......................................................................................................9 2.1 The Ekofisk Region ............................................................................................9 2.2 Valhall ..............................................................................................................11 2.3 Valhall Nordflanke og Sørflanke.......................................................................11 2.4 Hod ..................................................................................................................12 2.5 Ula....................................................................................................................13 2.6 Gyda ................................................................................................................13 2.7 Tambar.............................................................................................................14 2.8 Ekofisk Centre and 2/4B&K..............................................................................14 2.9 Ekofisk 2/4 A ....................................................................................................16 2.10 Albuskjell 1/6 A ................................................................................................17 2.11 Eldfisk 2/7 A/FTP .............................................................................................17 2.12 Eldfisk 2/7 B .....................................................................................................18 2.13 Embla 2/7 D .....................................................................................................18 2.14 Tor 2/4 E ..........................................................................................................19 2.15 Yme..................................................................................................................20 2.16 Kogge...............................................................................................................21 2.17 Trym.................................................................................................................21

3.0 Materials and Methods ..................................................................................22 3.1 Field work.........................................................................................................22 3.1.1 Sampling strategy........................................................................................................ 22 3.1.2 Execution of field work................................................................................................. 22 3.2 Macrobenthic analyses ....................................................................................23 3.2.1 Macrobenthic analyses – an introduction .................................................................... 23 3.2.2 Sorting and species identification ................................................................................ 24 3.2.3 Analytical methods ...................................................................................................... 24 3.2.4 Comparison of taxonomical data between years......................................................... 24 3.2.5 Quality assurance........................................................................................................ 25 3.3 Chemical analyses and physical characterization of the sediments.................26 3.3.1 Sediment characterization ........................................................................................... 26 3.3.2 Chemical analysis........................................................................................................ 29 3.3.2.1 Hydrocarbons, esters, ethers and selected hydrocarbons .......................................... 29 3.3.2.2 PFOS (perfluorooctyl sulphonate) ............................................................................... 32 3.3.2.3 Metals .......................................................................................................................... 33 3.3.2.4 Determination and quantification limits........................................................................ 33 3.3.3 Limit of contamination.................................................................................................. 34 3.4 Quality assurance ............................................................................................35 3.5 Deviations from the activities regulations .........................................................35

4.0 Results and Discussion.................................................................................37 4.1 Regional stations .............................................................................................37 4.1.1 Sediment characterization ........................................................................................... 37 4.1.2 Chemical analyses ...................................................................................................... 38

31 March 2006 Environmental Monitoring Region I, 2005, Main Report 2006-0187 (rev 01) BP Norge AS DNV CONSULTING

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4.1.3 Limit of contamination (LSC) ....................................................................................... 45 4.1.4 Biological analyses...................................................................................................... 50 4.1.5 Conclusions................................................................................................................. 59 4.2 Valhall ..............................................................................................................61 4.2.1 Sediment characterization ........................................................................................... 61 4.2.2 Chemical analyses ...................................................................................................... 62 4.2.3 Biological analyses...................................................................................................... 69 4.2.4 Conclusions................................................................................................................. 78 4.3 Valhall Nordflanke............................................................................................80 4.3.1 Sediment characterization ........................................................................................... 80 4.3.2 Chemical analyses ...................................................................................................... 81 4.3.3 Biological analyses...................................................................................................... 86 4.3.4 Conclusions................................................................................................................. 92 4.4 Valhall Sørflanke..............................................................................................94 4.4.1 Sediment characterization ........................................................................................... 94 4.4.2 Chemical analyses ...................................................................................................... 95 4.4.3 Biological analyses.................................................................................................... 100 4.4.4 Conclusions............................................................................................................... 106 4.5 Hod ................................................................................................................108 4.5.1 Sediment characterization ......................................................................................... 108 4.5.2 Chemical analyses .................................................................................................... 109 4.5.3 Biological analyses.................................................................................................... 116 4.5.4 Conclusion................................................................................................................. 122 4.6 Ula..................................................................................................................124 4.6.1 Sediment characterization ......................................................................................... 124 4.6.2 Chemical analyses .................................................................................................... 125 4.6.3 Biological analyses.................................................................................................... 132 4.6.4 Conclusion................................................................................................................. 139 4.7 Gyda ..............................................................................................................141 4.7.1 Sediment characterization ......................................................................................... 141 4.7.2 Chemical analyses .................................................................................................... 142 4.7.3 Biological analyses.................................................................................................... 148 4.7.4 Conclusion................................................................................................................. 154 4.8 Tambar...........................................................................................................156 4.8.1 Sediment characterization ......................................................................................... 156 4.8.2 Chemical analyses .................................................................................................... 157 4.8.3 Biological analyses.................................................................................................... 162 4.8.4 Conclusion................................................................................................................. 167 4.9 Ekofisk Center and 2/4 B&K...........................................................................169 4.9.1 Sediment characterization ......................................................................................... 169 4.9.2 Chemical analyses .................................................................................................... 170 4.9.3 Biological analyses.................................................................................................... 178 4.9.4 Conclusion................................................................................................................. 185 4.10 Ekofisk 2/4 A ..................................................................................................187 4.10.1 Sediment characterization ......................................................................................... 187 4.10.2 Chemical analyses .................................................................................................... 188 4.10.3 Ekofisk 2/4 A drill cuttings pile – Core sample VC-2 ................................................. 196 4.10.4 Total organic matter (TOM) ....................................................................................... 197 4.10.5 Biological analyses.................................................................................................... 206 4.10.6 Conclusion................................................................................................................. 213

31 March 2006 Environmental Monitoring Region I, 2005, Main Report 2006-0187 (rev 01) BP Norge AS DNV CONSULTING

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4.11 Eldfisk 2/7 A/FTP ...........................................................................................216 4.11.1 Sediment characterization ......................................................................................... 216 4.11.2 Chemical analyses .................................................................................................... 217 4.11.3 Biological analyses.................................................................................................... 222 4.11.4 Conclusion................................................................................................................. 227 4.12 Eldfisk 2/7 B ...................................................................................................229 4.12.1 Sediment characterization ......................................................................................... 229 4.12.2 Chemical analyses .................................................................................................... 229 4.12.3 Biological analyses.................................................................................................... 236 4.12.4 Conclusion................................................................................................................. 241 4.13 Embla 2/7 D ...................................................................................................243 4.13.1 Sediment characterization ......................................................................................... 243 4.13.2 Chemical analyses .................................................................................................... 243 4.13.3 Conclusion................................................................................................................. 244 4.14 Tor 2/4 E ........................................................................................................245 4.14.1 Sediment characterization ......................................................................................... 245 4.14.2 Chemical analyses .................................................................................................... 245 4.14.3 Biological analyses.................................................................................................... 251 4.14.4 Conclusion................................................................................................................. 256 4.15 Yme Gamma..................................................................................................258 4.15.1 Sediment characterization ......................................................................................... 258 4.15.2 Chemical analyses .................................................................................................... 259 4.15.3 Biological analyses.................................................................................................... 270 4.15.4 Conclusion................................................................................................................. 277 4.16 Yme Beta .......................................................................................................280 4.16.1 Sediment characterization ......................................................................................... 280 4.16.2 Chemical analyses .................................................................................................... 281 4.16.3 Biological analyses.................................................................................................... 289 4.16.4 Conclusion................................................................................................................. 295 4.17 Kogge.............................................................................................................298 4.17.1 Sediment characterization ......................................................................................... 298 4.17.2 Chemical analyses .................................................................................................... 298 4.17.3 Biological analyses.................................................................................................... 301 4.17.4 Conclusion................................................................................................................. 304 4.18 Trym...............................................................................................................305 4.18.1 Sediment characterization ......................................................................................... 305 4.18.2 Chemical analyses .................................................................................................... 306 4.18.3 Biological analyses.................................................................................................... 310 4.18.4 Conclusion................................................................................................................. 314 5.0 Regional Trends and Conclusions .............................................................316 5.1 Chemical analyses and grain size distribution ...............................................316 5.1.1 Grain size distribution ................................................................................................ 317 5.1.2 Total organic matter (TOM) ....................................................................................... 318 5.1.3 Hydrocarbons ............................................................................................................ 318 5.1.4 Esters ........................................................................................................................ 319 5.1.5 PFOS (perfluorooctyl sulphonate) ............................................................................. 319 5.1.6 Barium ....................................................................................................................... 320 5.1.7 Metals ........................................................................................................................ 320 5.1.8 Drill cuttings pile at Ekofisk 2/4 A – Core samples VC-2 ........................................... 320

31 March 2006 Environmental Monitoring Region I, 2005, Main Report 2006-0187 (rev 01) BP Norge AS DNV CONSULTING

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5.1.9 Installation Centre at Yme fields................................................................................ 321 5.2 Benthic communities ......................................................................................321 5.2.1 Factors which impact the composition of the benthic communities........................... 321 5.2.2 Effects of enrichment on benthic communities .......................................................... 322 5.2.2.1 The significance of Myriochele oculata and other dominating species...................... 322 5.3 Contaminated area.........................................................................................326 5.4 Conclusion Region I .......................................................................................329

6.0 Recommendations.......................................................................................331

7.0 References....................................................................................................332

31 March 2006 Environmental Monitoring Region I, 2005, Main Report 2006-0187 (rev 01) BP Norge AS DNV CONSULTING

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Preface The environmental survey at Region I in 2005 has been carried out jointly by Det Norske Veritas and Molab, on behalf of the operators in the region; BP, ConocoPhillips, Statoil, Shell, Talisman and Exxon. The work has been coordinated through BP and ConocoPhillips. Representation from the oil companies have been: BP: Ingvild Anfinsen ConocoPhillips: Eimund Garpestad, Britt Brun Statoil: Karl Henrik Bryne Shell: Øivind Hille Talisman: Hans Jacob Beck Exxon: Jan Erik Jensen Personnel Field work: Tor Jensen (survey leader), Sam-Arne Nøland, Thomas Møskeland, Amund Ulfsnes and Øyvind Fjukmoen (all DNV) and Håkon Larsen and Tore Trulsen (both Molab). Sediment analyses: Grain size distribution: Stein-Tore Bogen, Terje Kolberg, Eli Ellingsen TOM analysis: Gaute Botten, Håkon E. Larsen Metal analyses: Andreas Parslow, Karina E. Ødegård, Håkon E. Larsen THC analysis: Mariam Bouzga, Gaute Botten, Frøydis Oreld, Tove Kristin

Dokka Torstensen Selected hydrocarbon analyses: Tove Kristin Dokka Torstensen PCB Analyses: Tove Kristin Dokka Torstensen PFOS (perfluorooctyl sulphonate): Urs Berger, Norwegian Institute for Air Research, Tromsø The chemical analyses are performed at Molab AS, section Oslo. The grain size distribution is analysed at Molab AS, section Glomfjord. Biological analyses: Species identification: Siri Mordal Bakke, DNV (Polychaeta, varia) Thomas Møskeland, DNV (Crustacea) Amund Ulfsnes, DNV (Echinodermata) Mikkel Petersen, DNV (Polychaeta, varia) Per Bie Wikander, Molltax (Mollusca) Øystein Stokland, Marine Bunndyr (Polychaeta, varia) Sorting has taken place at DNV’s Biology Laboratory. Karen M. Brinchmann and Mikkel Petersen have been in charge of the sorting. Univariate analyses: Thomas Møskeland, Siri M. Bakke Multivariate analyses: Siri Mordal Bakke, Lise Heier

31 March 2006 Environmental Monitoring Region I, 2005, Main Report 2006-0187 (rev 01) BP Norge AS DNV CONSULTING

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Report preparation: Chemistry: Ingegerd Rustad Biology: Siri Mordal Bakke, Karen M. Brinchmann, Sam-Arne Nøland Main Report: Sam-Arne Nøland Verification: Tor Jensen Project Manager: Sam-Arne Nøland

Molab AS is accredited by Norwegian Accreditation to perform chemical analyses, accreditation number Test 032. The accreditation is according to NS-EN ISO/IEC 17025. The accreditation includes methods for determination of total hydrocarbon content (THC), polycyclic aromatic hydrocarbons (PAH), polychlorinated biphenyls (PCB), selected hydrocarbons (NPD), metals and total organic matter (TOM).

NR: P083

DNV’s Biology laboratory (DNV Consulting) is accredited by Norwegian Accreditation for sampling of marine sediments for chemical and biological analyses, and to perform biological analyses, accreditation number TEST 083. Accreditation is according to NS-EN ISO/IEC 17025.

31 March 2006 Environmental Monitoring Region I, 2005, Main Report 2006-0187 (rev 01) BP Norge AS

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1.0 Resumé This report presents the results from the environmental survey in the EKOFISK region (Region I) in 2005. Det Norske Veritas and Molab As carried out the survey jointly, on the behalf of BP, ConocoPhillips, Statoil, Shell, Talisman and Exxon. The report presents results from the regional stations and from the following installations: Valhall, Valhall Flanke Nord og Sør, Hod, Ula, Gyda, Tambar, Ekofisk Centre and 2/4 B&K, Ekofisk 2/4 A, Eldfisk 2/7 A/FTP, Eldfisk 2/7 B, Embla, Tor, Yme Gamma, Yme Beta, Kogge and Trym. The results from the 2005 survey in Region I show: • Generally, the results from the 2005 survey at Region I show that the levels of THC, Ba

and metals have decreased compared to the 2002 survey. • The sediments at Region I consist mainly of fine sand. • The total organic matter (TOM) contents in the sediments are low and range from 0.4 % to

1.5 %. • The chemical results are in agreement with the drilling history. • The regional stations and the reference stations are still unaffected by the drilling chemicals

- no contamination or elevated concentrations are found in these sediments. • The Kogge and Trym areas are not polluted by THC, Ba or metals from oil activity. • Relatively high THC levels are still found at most of the fields. However, the concentrations

are, with a few exceptions, distinctly lower compared to the 2002 survey. • Base liquids from pseudo-oil based drilling mud (olefins) are observed at most stations

where these systems are used. • Base liquids from ester based drilling mud are found in low concentrations at Ekofisk 2/4 A

(Finagreen) and Yme Gamma (Petrofree). • At Tor, ethers from ether based drilling mud (Aquamul B and Aquamul BII) were found for

all the stations analysed. These ethers are in addition observed at Ula and Ekofisk Centre and 2/4 B&K. Thus, the ether compounds are not degrading as fast as previously anticipated.

• Three stations in Region I are analysed for PFOS (PerFluoroOctyl Sulphonate). The highest content is found at Yme Gamma Central in 120° direction and 100m distance. At Valhall the PFOS concentration was considerably lower, and at the station analysed at Ekofisk Centre and 2/4 B&K no PFOS was detected.

• Dispersions of drill cuttings and mud are illustrated by the barium results. Elevated Ba concentrations are found at most of the stations. Though, generally the Ba concentrations are similar or slightly lower compared to the 2002 survey. For some stations at Valhall Flanke Nord and Sør and at Ula the content of Ba has increased, in agreement with their discharge history.

• The concentrations of the heavy metals are low, and elevated levels are only found at some stations.

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• Two core samples from the drill cuttings pile at Ekofisk 2/4 A are analysed. Elevated concentrations of all the chemical parameters analysed, except esters and PCB, are found to 130 cm depth. The levels of THC in the core samples are generally higher in 2005 than in 2002.

• Samples from the Installation Centre at Yme Gamma and at Yme Beta are analysed. High concentrations of THC and Ba are found, but the content is distinctly lower compared to the 2002 survey.

• The fauna community in the central part of the Ekofisk region is disturbed to varying extents. This is a consequence of physical disturbances, the activities in the area and a diffuse organic load from various sources affecting the North Sea.

• The Ekofisk region is exposed to some general temporal and geographical changes. The great variations in the presence of M. oculata from 1996 to 2005 have complicated the faunal picture. Adding the 2005 results to the trend data has made it possible to obtain a pattern in the overall temporal variations in the entire region.

• The biodiversity and numbers of species have increased. An increase in the numbers of individuals on the expense of M. oculata indicates a general improvement in the fauna community in the Ekofisk region.

• There has been a distinct improvement in the fauna at least 500 m from the field centers. At a radius of 250 m no clear trend is observed from the last survey in 2002, except at Ekofisk A where some stations have improved.

• The organic load is highest around regional stations 2 and 6 and the improvement of the fauna communities seems to be slowest around the fields Ula, Gyda, Tambar and Tor. However, the densities of individuals in the region still indicate a relatively high, though decreasing supply of organic matter to the macrofauna.

• In 2005 an area about 100 km2 have THC concentrations higher than the LSC (4.6 mg/kg). The estimate is considered to be more reliable than the 2002 calculations (somewhere between 61 and 266 km2). For limits of 10 and 50 mg/kg the corresponding estimated areas are 24 and 1.4 respectively.

• All in all, the statistical analyses show increasing biodiversity indices and increasing numbers of species. Some increase in the numbers of individuals on the expense of M. oculata reveals a general improvement in the fauna community in the Ekofisk region. Species that are numerous all over the region in 2005 are the brittle star Amphiura filiformis and the bristle worms Paramphinome jeffreysii and Apistobranchus tullbergi. In general the fauna communities are dominated by suspension feeders (M. oculata, Ditrupa arietina, A.filiformis, Thyasira species, hydroids and anthozoa species) and carnivore species like P. jeffreysii. The trend analyses reveal a distinct improvement in the fauna until at least 500 m from the field centers. At a radius of 250 m from the field centers the trend is somewhat diffuse and does not reveal any improving trend from the last survey in 2002. An exception is the Ekofisk A field in 2005, where some stations have improved.

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The main parameters and the variation at each field: Regional stations Variation Main characteristics

THC (mg/kg)

Ba (mg/kg)

No. of species (S)

No. of individuals (N)

Diversity (H’)

Evenness (J)

E100

1.3 – 5,8

4 – 72

55 – 82

341 – 2495

2,7 – 5,1

0,4 – 0,8

17 – 38

The concentrations of THC, Ba and metals are low. No elevated levels are found. Four of the regional stations located in the central part of the region, are somewhat disturbed. There are indications of improvements since 2002.

The high abundance of M. oculata which had a peak in 2002 has to some extent been replaced by other species in 2005.

Valhall Variation Main characteristics

THC (mg/kg)

Ba (mg/kg)

No. of species (S)

No. of individuals (N)

Diversity (H’)

Evenness (J)

E100

4.3 – 130

28 – 5587

60 – 93

1334 – 2300

2,5 – 3,79

0,63 – 0,47

18 – 24

Elevated levels of THC and Ba out to 1000m. Also slightly elevated levels of THC out to 2000m. Olefins from Novaplus discharged in 1996 are found at 500m. Indications of a positive trend in the fauna. Two of the 500m distance stations are slightly disturbed, correlated to the variations in the levels of THC, Ba and Cu. Large amounts of yellow granules were found in the samples at all the Valhall stations.

Valhall Nordflanke Variation Main characteristics

THC (mg/kg)

Ba (mg/kg)

No. of species (S)

No. of individuals (N)

Diversity (H’)

Evenness (J)

E100

4.3 – 8,4

28 – 468

66 – 91

934 – 1921

2,98 - 4,18

0,47 – 0,66

20 – 29

The contents of THC are considered to be within the natural levels. Elevated Ba levels are found at all stations, this means out to 500m. The content of Ba is higher or at the same level compared to 2002.

The biodiversity indices have increased considerably, which is partly due to a significant decline in the abundance of the bristle worm M. oculata. None of the stations are considered affected by field activities. Yellow granules (see Valhall for details) were found at most of the stations.

Valhall Sørflanke Variation Main characteristics

THC (mg/kg)

Ba (mg/kg)

No. of species (S)

No. of individuals (N)

Diversity (H’)

Evenness (J)

E100

3.6 - 5.3

28 - 190

59 – 69

614 – 2384

2,64 – 4,53

0,43 – 0,77

18 – 30

The content of THC is considered to be within the background level. Elevated levels of Ba are found out to 500m in the 74° directions and limited to 250m in the 254° direction. The content of Ba is higher or at the same level compared to 2002. For most of the other stations the Ba concentration found is below the limit of contamination.

The biodiversity has increased considerably since the baseline survey in 2001, primarily due do a significant

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decline in the abundance of the bristle worm M. oculata. Two stations (250 and 500m) considered somewhat disturbed.

Yellow granules (see Valhall for details) were found in several of the samples.

Hod Variation Main characteristics

THC (mg/kg)

Ba (mg/kg)

No. of species (S)

No. of individuals (N)

Diversity (H’)

Evenness (J)

E100

4.3 – 36

32 – 900

56 – 84

539 – 1516

3,6 – 4,0

0,6

24 – 28

Elevated THC values are found at HOD8 164°/500m. For the other stations the THC levels are low. Olefins are found at the six stations analysed. Probably originating from discharges of Novasol and Novaplus in 1994/1995. Elevated Ba levels are found at all the stations. That is maximum range out to 1000m in the 164° direction, and to 250m in the 344° direction.

The biodiversity has increased since 2002 because of a significant decline in M. oculata, indicating a positive trend in the area.

Ula Variation Main characteristics

THC (mg/kg)

Ba (mg/kg)

No. of species (S)

No. of individuals (N)

Diversity (H’)

Evenness (J)

E100

3.9 - 58

35 - 4172

68 – 81

944 – 5193

1,4 – 4,4

0,2 – 0,7

10 – 30

Elevated THC levels are found out to 500m in 45° and 135° direction and to 250m in the 120° and 225° direction. For the other stations the THC level are low. Elevated levels of Ba for all the stations, this means out to 500m (45° and 135°) and limited to 250m for the other directions. The levels of Ba have increased since 2002. The base oil Aquamul BII (ethers) is found at some stations. The positive trend observed in the fauna community from 1996 to 1999 has not continued and the stations sampled in 2005 (250 and 500 m) are considered to be disturbed. This is supported by visual observations and chemical results from the deeper sediment layers.

Gyda Variation Main characteristics

THC (mg/kg)

Ba (mg/kg)

No. of species (S)

No. of individuals (N)

Diversity (H’)

Evenness (J)

E100

4.0 - 43

36 - 1566

20 – 89

249 – 6446

1,3 – 3,0

0,2 – 0,6

10 – 21

High THC contents at the stations at 250m in 45°, 135° and 225° directions. Elevated levels of Ba for all the stations investigated. High Ba contents at stations 250m from the platform in the 45° and 225° directions. High contents of heavy metals for GYDA18, 135°/250m. The results at the other stations are similar to previous surveys. The biodiversity indices indicate a general disturbance in the fauna at Gyda in 2005. One of the 250m station consists of anoxic sediment and is clearly disturbed. There are indications that the fauna is influenced by the field activities. Variations in the fauna between years seem to coincide with the variations in Ba, Pb, TOM and pelite.

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Tambar Variation Main characteristics

THC (mg/kg)

Ba (mg/kg)

No. of species (S)

No. of individuals (N)

Diversity (H’)

Evenness (J)

E100

3.3 – 15.2

106 - 563

75 – 85

2735 – 4130

2,14 – 2,63

0,34 – 0,41

15 – 18

The THC concentration is generally low and elevated levels are only found at TAMBAR5, 135°/250m. Elevated Ba contents are found at all the stations, this means out to 250m for all directions investigated. The Ba contents are lower or at the same level as in the 2002 survey. The fauna community at 250m stations indicates some disturbance, possibly influenced by field activities.

The results indicate no major alterations in the state of the fauna community since 2002. A decline in M. oculata is not observed.

Ekofisk Centre and 2/4 B&K

Variation Main characteristics

THC (mg/kg)

Ba (mg/kg)

No. of species (S)

No. of individuals (N)

Diversity (H’)

Evenness (J)

E100

3.5 – 188

46 – 3860

58 – 78

1385 – 3175

2,8 – 3,8

0,4 – 0,6

18 – 22

THC contents have decreased distinctly and are, for many of the stations investigated, only slightly above or below the limit of contamination. The highest concentrations are found at EKO14, 140°/850m. Elevated Ba concentrations are found at all stations. This means out to maximum range 1800m from 2/4T in the 84° direction. The concentrations are similar or slightly lower compared to previous surveys. Olefins and ethers (Aquamul B) are found, and are in accordance with reported discharges.

The fauna community has improved since 2002. The four stations located closest to 2/4 W are still somewhat disturbed. The decline in M. oculata partly explains the improvement in the fauna community. The changes in the fauna during the years are not directly related to variations in investigated sediment characteristics or chemical data.

Ekofisk 2/4 A Variation Main characteristics

THC (mg/kg)

Ba (mg/kg)

No. of species (S)

No. of individuals (N)

Diversity (H’)

Evenness (J)

E100

8 – 106

887 - 5110

62 – 105

944 – 3693

2,2 – 4,2

0,4 – 0,6

13 – 29

Elevated levels of THC out to 2000m. Olefins and esters (Finagreen) are found. THC generally increases going down in the sediment. The highest THC concentration found is 1031 mg/kg at EKOA5, 67°/100m in the 3-6 cm layer. Elevated levels of Ba are found at all stations, this means out to 500m in all the directions measured. Elevated levels of heavy metals at most of the stations. Drill cuttings piles, corers to 130 cm depth: Elevated levels of hydrocarbons, Ba and heavy metals in all layers. Higher concentrations in the deeper layers. The THC concentrations are higher and the Ba concentrations are lower in the 2005 survey compared to 2002.

The fauna community has in general improved and there has been a significant decrease in the number of M. oculata since 2002. There are disturbances in the fauna at three of the 100 m stations, and the

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disturbance seems to be related to the activity at the field. There is a good correlation between the fauna and the complex of the parameters THC, Ba, Cd, TOM and gravel.

Eldfisk 2/7 A/FTP Variation Main characteristics

THC (mg/kg)

Ba (mg/kg)

No. of species (S)

No. of individuals (N)

Diversity (H’)

Evenness (J)

E100

4.3 - 120

590 – 1700

63 – 90

1677 – 3580

2,4 – 3,4

0,4 – 0,6

16 – 23

High THC contents at ELDA4, 360°/250m. Slightly elevated out to 370m and 250m in the 180° and 90° directions. However, the THC content is low at most stations, either below or just above the limit of contamination. Elevated Ba levels are found at all stations analysed. This means out to maximum 625m in the 360° direction. Olefins are found, but the content has decreased since 2002. Mainly, the results agree with the drilling history.

There are indications of some disturbance in the fauna community out to 625 m from the field centre. A decline in the numbers of M. oculata as described at several other fields in the area has not been the case at Eldfisk A and the biodiversity indices are almost unchanged since 2002. However, a shift in the fauna community is observed, indicating a slow improvement.

Eldfisk 2/7 B Variation Main characteristics

THC (mg/kg)

Ba (mg/kg)

No. of species (S)

No. of individuals (N)

Diversity (H’)

Evenness (J)

E100

5.8 - 30

644 – 1706

82 – 95

2086 – 3196

3,0 – 3,2

0,5

19 - 22

The THC content has decreased since 2002. The highest THC content is found at three stations at 250m. Slightly elevated level out to 500m in 90° direction. The level is lower or just above limit of contamination for the other stations. Low content of olefins are found. Decalins are detected. Elevated Ba levels for all the stations out to 500m. Level similar to 2002 survey. The results mainly agree with the drilling history.

A slightly disturbed fauna was observed at all sampled 500m stations. The biodiversity in the fauna community has in general increased slightly since 2002. The improvement is, however, slow. A general decline in the numbers of M. oculata as described at several other fields in the area is not the case at Eldfisk B.

Embla 2/7 D Variation Main characteristics

THC (mg/kg)

Ba (mg/kg)

3.9 - 18.2

Lowest THC concentrations in the Ekofisk area and slightly elevated levels are only found out to 250m in the 90° and 180°direction. No discharges since 1999.

Tor 2/4 E Variation Main characteristics

THC (mg/kg)

Ba (mg/kg)

6.6 - 20

341 - 1505 Elevated levels of THC/ethers out to 500m (180°) and out to 250m (90° and 360°). Elevated Ba levels out to 500m in the 180° direction. Ethers from the base oil Aquamul B,

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No. of species (S)

No. of individuals (N)

Diversity (H’)

Evenness (J)

E100

85 – 93

1107 – 4092

2,52 – 4,36

0,39 – 0,68

19 – 29

discharged in 1990, are found,.

A general improvement in the fauna community is seen at both the 500m station and the 250 m station. The abundance of M. oculata, higher levels of THC and metals combined with field observations of oil film/black spots, still indicate some disturbance at 250 m.

Yme Gamma Variation Main characteristics

THC (mg/kg)

Ba (mg/kg)

No. of species (S)

No. of individuals (N)

Diversity (H’)

Evenness (J)

E100

2.4 - 32

10 – 4490

62 – 99

213 – 1852

2,97 – 5,27

0,49 – 0,89

18 – 43

Elevated THC levels out to 250m in the 120° direction. Elevated levels of Ba are found for all stations, this means out to maximum range 500m in the 120° direction. The Olefin and ester contents are low and are lower or similar to the 2002 survey. Olefins and esters from Petrofree. The results agree with the drilling history. Installation Centre: High silt and clay content. High THC, olefins and Ba levels (up to ~0.6 %). Elevated metal levels. The silt and clay content has increased, so has the contents of THC, NPD, PAH, decalins, Cd and Cr to varying degrees.

In general, the structure in the fauna community at Yme Gamma indicates a healthy environment. A slight improvement in the fauna community since 2002, also at the 100 m stations, even though these stations still are characterized as disturbed. Based on observations from the sampling and a qualitative analysis the Installation Centre is characterized as heavily disturbed.

Yme Beta Variation Main characteristics

THC (mg/kg)

Ba (mg/kg)

No. of species (S)

No. of individuals (N)

Diversity (H’)

Evenness (J)

E100

0.3 – 5.8

11 – 520

48 – 91

232 – 581

4,45 – 5,46

0,76 – 0,86

32 – 44

No elevated THC concentrations. Ba level below the limit of contamination in the 330° direction. Elevated Ba levels are found at 250m in the other directions. Lower concentrations than at Yme Gamma. The results agree with the drilling history. Installation Centre: Less silt and clay contents than at Yme Gamma. High THC, olefins, Ba and metals levels at 0°/0m. Lower levels at the 100m stations. The structure in the fauna community and the biodiversity indices characterize a healthy fauna community. There are indications of general improvements. However, the 100 m stations and Installation Centre are still characterized as disturbed.

During sampling there were observed large amounts of yellow granules (similar to findings at Valhall) in the samples from the Installation Centre and the 100m stations.

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Kogge Variation Main characteristics

THC (mg/kg)

Ba (mg/kg)

No. of species (S)

No. of individuals (N)

Diversity (H’)

Evenness (J)

E100

0.5

3 – 4

78 – 88

448 – 609

5,1 – 5,2

0,8

39

Low contents of THC and Ba. The Kogge area is not polluted by THC or metals from oil activity. The study has shown that the Kogge field is not contaminated by hydrocarbons nor metals, and the fauna at the two Kogge stations are characterised as diverse and healthy.

Trym Variation Main characteristics

THC (mg/kg)

Ba (mg/kg)

No. of species (S)

No. of individuals (N)

Diversity (H’)

Evenness (J)

E100

1.7 – 3.8

14 - 42

64 – 83

937 – 2040

3,25 – 4,54

0,5 – 0,7

22 – 30

Low contents of THC and Ba. The Trym area is not polluted by THC or metals from oil activity.

The baseline study at Trym revealed a relatively healthy fauna community, not influenced by field activities. However, the fauna community seems to be slightly disturbed, which is probably due to the high energy environment together with a general diffuse organic enrichment in the central parts of the Ekofisk region.

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2.0 Introduction

2.1 The Ekofisk Region

This report presents results from the environmental survey in the EKOFISK region (Region I) in 2002. The main subject in regional monitoring is to study any environmental effects from petroleum activities in larger areas. Regional environmental monitoring has been carried out since 1996.

The report presents results from 16 different field/installations within the region. Fields and installations included in the regional monitoring are listed in Table 2.7.1. An overview of the region including installations is shown in Figure 2.7.1. Background information for each field in Region I is given in the following sections. Table 2.7.1. Fields and installations included in the regional monitoring 2005. Field/Installation Operator Ula BP Valhall BP Hod BP Tambar BP Ekofisk Centre and 2/4B&K ConocoPhillips Ekofisk 2/4 A ConocoPhillips Eldfisk 2/7 A/FTP ConocoPhillips Eldfisk 2/7 B ConocoPhillips Embla 2/7 D ConocoPhillips Tor ConocoPhillips Albuskjell (separate report) ConocoPhillips Yme Gamma Statoil Yme Beta Statoil Gyda Talisman Trym Shell Kogge Exxon

The survey programme has been prepared according to the Activities Regulation Appendix 1 – Requirements to Environmental Monitoring of the Petroleum Activities on the Norwegian Shelf. (Ptil, SFT, SHdir 2005). The selection of sampling stations at the various fields are based on the results from the survey conducted in 2002 and the drilling- and discharge history after the previous survey (in 2002), see Program for sedimentovervåking Region I – Ekofisk 2005 version 3, January 2005 (enclosed in Appendix E).

The Ekofisk region is limited to the Norwegian Continental shelf from 56º02’N to 57º52’N and from 02º46’E to 04º32’E, i.e. the southern part of the Norwegian sector in the North Sea. The depth varies from approximately 65m in the south to 90m in the north. The tidal current direction in the area is in the NE – SW direction while the residual current direction is in the SE direction. The report is divided into three main sections; the Summary Report (rep. no. 2006-0353)/Sammendragsrapport (rep. nr. 2006-0354) where the main results are presented, the Main Report (rep. no. 2006-0187) which gives detailed results and the Appendix Report (rep. no. 2006-0512) consisting of field report, analyses report and other details. Stations for each field are shown in fold-out maps in the main report.

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There are no additional regional stations included in the 2005 survey compared to the previous survey in 2002. Previous surveys has shown that depth, sediment characteristics and carbon content are very homogenous in the region and the existing regional stations represent the general features of the region in a fulfilling way.

Reg.1

Reg.2

Reg.3

Reg.4

Reg.5

Reg.6

Reg.7

Reg.8

Reg.9

Reg.10

480000 500000 520000 540000 560000 580000

Øst

6220000

6240000

6260000

6280000

6300000

6320000

6340000

6360000

6380000

6400000

Nor

d

Yme Gamma

Yme Beta

Kogge

Albuskjell Tor

Ekofisk 2/4A

Eldfisk AEldfisk B

Valhall NordflankeValhall

Valhall Sørflanke Hod

Trym

Tambar

Gyda

Ula

Embla 2/7D

Figure 2.7.1 Regional stations (1 – 10) and an overview of fields included in the 2005 survey, Region I – Ekofisk.

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Table 2.7.2. Regional stations, Region I 2005. Station no. North East Reg. 1 (= ref. st. Ula) 57°09.01' 02°46.67' Reg. 2 56°55’ 03°20’ Reg. 3 (= ref. st. Ekofisk) 56°32.97' 03°27.42' Reg. 4 56°15’ 03°50’ Reg. 5 57°00’ 02°30’ Reg. 6 56°45’ 02°40 Reg. 7 56°30’ 02°45 Reg. 8 (= ref. st. Hod) 56°02,54’ 03°27,80’ Reg. 9 57°07.50’' 03°10.89' Reg. 10 57°51.63' 04°04.35'

2.2 Valhall

The Valhall field is situated in blocks 2/8 and 2/11. The production at the field started in 1982. The oil is transported in pipeline to Ekofisk and the gas to Emden in Germany.

Earlier activities in the area

There has been continuous drilling and production on the Valhall field since the previous survey in 2002. There were no drilling discharges from 1998 to 2003, but discharges from the top section in 2004. Since previous survey there have been no acute discharges of oil based mud, but some smaller acute discharges of oil and diesel. Drill cuttings and oil-containing chalk are re-injected in the field. A summary of drilling and discharge history at Valhall is given in Table 2.7.3.

Table 2.7.3. Summary of recent drilling and discharge history at Valhall. Discharges/ activity

1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005*

No. of wells drilled 4 3 4 6 8 8 3 21) 3 4 3 1 4** Discharges (tonnes):

Barite 0 0 535 1518 3692 0 0 0 0 0 0 14494) 0 Cuttings 0 0 2173 2566 0 0 0 0 0 0 0 3358 0 Base oil 0 0 1172) 15702) 0 0 0 0 0 0 0 0 0 Oil in produced water

8.2 3.7 5.0 1.5/0 0.4 2 3 3 5.5 6.6 5.1 7 2

Other oil discharges/spills

1.9 0.8 30.5 0.9 0 0.15 0.85 0.14 0.93 1.12 0.034 2.43) 0.9155)

1) Includes two side-track operations; 2) linear olefin C16-C18; 3) acute discharges of produced water + leakage from PCP; 4) top section at IP *1. half ** Number of wells drilled for the year 2005! 5) acute discharge from slop (20 ltr), sement spacer (795 ltr) and diesel (100 ltr.)

In order to calculate contaminated area this year’s survey included some additional sampling stations located closer to the installation than in 2002.

2.3 Valhall Nordflanke og Sørflanke

A baseline survey was conducted at Valhall Nordflanke and Sørflanke in 2001. Production commenced in 2003, hence Valhall flanke was not included in the regional survey in 2002. The history of discharges is shown in Table 2.7.4 and Table 2.7.5.

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Table 2.7.4. Summary of discharges at Valhall Sørflanke. Discharges/activity 2003 2004 2005, 1- half No. of wells drilled 5+ top hole 1+top hole 7 (year 2005) Discharges (tonnes): Barite 1166 43 0 Cuttings 5179 4609 0 Base oil 0 0 0 Oil in produced water 0 0 0 Other oil discharges/spills 0.9761) 0 0.009²)

1) Acute discharge of oil based mud ²) Acute discharge of oil based mud Table 2.7.5. Summary of discharges at Valhall Nordflanke

Discharges/activity 2003 2004 2005, 1- half No. of wells drilled 3 + top hole 5 0 Discharges (tonnes): Barite 1050 0 0 Cuttings 7039 0 0 Base oil 0 0 0 Oil in produced water 0 0 0 Other oil discharges/spills 0 0 0

The results from the baseline surveys showed no major signs of contamination, and the discharge history does not indicate major changes outside the 500 m zone. The scope of sampling is thus reduced compared to the 2001 survey; i.e. the 1000 m stations are analysed for THC only and the 2000 m stations are excluded from the sampling programme.

2.4 Hod

The Hod field is situated in block 2/1 and production at the field started in 1990. The oil and gas are transported in pipelines to Valhall for further treatment.

Earlier activities in the area

There has not been any drilling activity on Hod since the previous survey in 2002. The history of discharges is shown in Table 2.7.6 Table 2.7.6. Summary of recent drilling and discharge history at Hod. Discharges/ activity

1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005*

No. of wells drilled 4 1 0 0 0 0 0 0 0 0 0 0 Discharges (tonnes):

0 0 0 0

Barite 1471 552 0 0 0 0 0 0 0 0 0 0 Cuttings 3020 1120 0 0 0 0 0 0 0 0 0 0 Base oil 3371) 852) 0 0 0 0 0 0 0 0 0 0 Oil in produced water

0 0 0 0 0 0 0 0 0 0

Other oil discharges/spills

1.4 0 0 0 0 0 0 0.17 3) 0 0 0

1) Polyalphaolefin, 2) Linear olefin C16-C18, 3) discharge of hydraulic oil *: 1. half

There has been no drilling activity since 1995, and any increase of contaminated area is therefore not expected. The sampling programme is thus somewhat reduced compared to previous survey.

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2.5 Ula

The Ula field, situated in block 7/12, was discovered by BP in 1976. The production commenced in October 1986. The gas and oil are transported to Ekofisk in pipelines.

Earlier activities in the area

Ula is a mature oil field where there has been low activity in recent years. The drilling is carried out with oil based mud and all cuttings are re-injected. 80-90% of the production water is re-injected to the reservoir for pressure support.

Three wells have been drilled since 2002. There have not been any discharges to sea from the drilling operations. There was one acute discharge of oil based mud (1.5 m3) in 2002, see Table 2.7.7. Table 2.7.7. Summary of recent drilling and discharge history at Ula. Discharges/activity 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005* No. of wells drilled 3 2 5 1 1 0 0 1 2 2 1 0 2 Discharges (tonnes): Barite 3100 960 900 0 0 0 0 0 0 0 0 0 0 Cuttings 320 0 0 0 0 0 0 0 0 0 0 Base oil 0 0 0 0 0 0 0 0 0 0 0 0 0 Oil in produced water

62 164 60.7 70 37.5 30 25 23 7 7 9 8 4

Other oil discharges/spills

0 0 0 0 3.471 0 1.52 0 1.25³

1 two acute discharges of oil based mud; 1 and 0,47 m3 and acute discharge of produced water (2 m3 oil). 2 Acute discharge of oil based mud ³ acute discharges of produced water (1 m3 crude) and acute discharge of diesel (250 litres) *: 1. half

The sampling programme has focussed on stations close to the installation in order to calculate contaminated area.

2.6 Gyda

The Gyda field, situated in block 2/1, was discovered by BP in 1980. Production at the field started in 1990, and the oil is transported in pipelines to Ekofisk and further to Teeside.

Earlier activities in the area

Gyda is a mature oil field where the drilling activity has been declining in recent years. Drilling is performed with oil based mud and the cuttings are re-injected. Some water based drilling fluid is discharged in connection with drilling of top sections, see Table 2.7.8.

The results from 2002 showed no impact on the benthic fauna and low levels of THC, hence the sampling program in 2005 has been reduced.

Table 2.7.8. Summary of recent drilling and discharge history at Gyda.

Discharges/activity 1993 1994 1995 1996 1997 1998 1999 No. of wells drilled 6 5 3 3 1 1 0 Discharges (tonnes):

Barite 460 1440 260 1080 468 202 0 Cuttings 550 0 0 0 0 Base oil 0 0 0 0 Oil in produced water

4.3 6.0 10.8 20 18 20 20

Other oil discharges/spills

0 0 0 0

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Table 2.7.8. cont. Discharges/activity 2000 2001 2002 2003 2004 2005

1. half No. of wells drilled 0 0 0 0 0 2 Discharges (tonnes): Barite 0 0 0 0 0 0 Cuttings 0 0 0 0 0 0 Base oil 0 0 0 0 0 0 Oil in produced water

11.5 14.7 18.4 51 32 4.7

Other oil discharges/spills

0 0 0.16 0 0 160 litres crude oil

2.7 Tambar The Tambar field is situated in block 1/3 in the middle of the Ekofisk area. The well head platform is unmanned with three production wells producing through a multiphase pipeline to Ula.

Earlier activities in the area

Since the baseline survey in 1999 two new wells have been drilled. There have been discharges of water based drilling mud in upper sections. The lower sections have been drilled with oil based mud, which was transported to Gyda for re-injection. Discharges are shown in Table 2.7.1. Table 2.7.1. Summary of recent drilling and discharge history at Tambar. Discharges/activity 1998 1999 2000 2001 2002 2003 2004 2005* No. of wells drilled 1 0 0 2 0 0 0 0 Discharges (tonnes): 0 0 0 0 Barite 2065 0 0 432 0 0 0 0 Cuttings 0 0 0 0 0 0 0 0 Base oil 0 0 0 0 0 Oil in produced water 0 0 0 0 Other oil discharges/spills 1.51 0 0 0.52 0 0 0 0 1 Acute discharge of oil based mud 2 Discharge of hydraulic oil *: 1. half

The 1999 survey showed elevated levels of THC at some stations, caused by acute discharges in 1998. The THC level was significantly lower in 2002. Since 2001 there have been no discharges and alterations in the dispersion pattern compared with 2002 are not to be expected. The sampling programme has focussed on stations close to the installation.

2.8 Ekofisk Centre and 2/4B&K The Ekofisk field is situated in block 2/4 and was discovered by Phillips Petroleum in 1979. Oil production started at the field in 1971. In 1990 there were 12 installations on the Ekofisk Centre and 2/4 B&K. The production had its peak in 1980.

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2/4-T is the field centre (the Ekofisk Tank) of the old Ekofisk I (see figure above). The activity has now been moved in the south-east direction to the wellhead platform 2/4 X (drilling) and process platform 2/4 J (production). All waste from drilling is re-injected at 2/4 X. 2/4-T is closed down and the discharges of produced water are therefore moved to 2/4-J. 2/4-T is still kept as centre of the sampling stations.

Earlier activities in the area

Drilling activities have taken place at 2/4-B&K, 2/4 X and 2/4 W and continuous production at Ekofisk Centre and 2/4 B/K since previous survey in 1999. There has been increasing discharges of from drilling activities in 2001, 2002 and 2003. Table 2.8.1. Summary of recent drilling and discharge history at Ekofisk Centre and 2/4 B&K. Discharges/activity 1993 1994 1995 1996 1997 1998 1999 2000 2001 No. of wells drilled 7 12 4 1 8 111 32 1

(2/4X) 6 + 1 sections

(total of 20 sections)

Discharges (tonnes): Barite 12167 11469 2566 365 620 2709 512 0 1398 Cuttings 5614 7068 4472 346 760 2631 914 0 465

(discharges from 2 top sections)

Base oil (with cuttings) 624 2135/390 380 1816 0 0 0 0 0,787

Oil in produced water 31.7 36 57 84 105 58 54 81,9 87 Other oil discharges/spills 0 0.42 0.90 0 2.5 4.5 2.0 0.75 1.8 Cont.

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Table 2.8.1. cont. Discharges/activity 2002 2003 2004 2005 (1. half) No. of wells drilled 11 wells

(40 sections) 12 wells + 2 sections (total 45 sections)

9+ 8 sections (37 sections)

34 sections

Discharges (tonnes): Barite 845,2 380 09 09 Cuttings 1350.8

(discharges from 4 top sections)

7716.8 (discharges from 10 top sections)

5990 (discharges from 8 top sections)

1154.2 (discharges from 4 top sections)

Base oil (with cuttings) 0 0 0 0 Oil in produced water 117 99.4 113.5 82.17 Other oil discharges/spills 0,58 5.6 1.55 0.3 11 well 2/4-K, 10 wells 2/4-X. 2 2 wells 2/4-X, 1 well 2/4-W 4PAO Polyalphaolefin: figure represents 22% of total mud discharged with cutting 5Esterdrill: figure represents 29% of total mud discharged with cuttings 6Novaplus I.O. (2/4-X) 7Acute Discharge of Barite and Carbosea (oil based base oil) from 1 well at 2/4-B and 1 at 2/4-X. 8 including acute Discharge of Barite and Carbosea (oil based base oil) from 1 well at 2/4-B and 1 at 2/4-X.

Located close to each other with overlapping stations the Ekofisk Centre og 2/4 B&K are regarded as one single field in the sampling programme.

2/4-T is the field centre (Ekofisk Tank) in the old Ekofisk. The activity has been moved in south-east direction with the well-head platform 2/4 X (drilling) and the processing platform 2/4 J (production). All drilling waste is re-injected at 2/4 X. 2/4-T is closed down and the discharges of produced water are moved to 2/4-J. 2/4-T is kept as the centre of the station map.

The sampling programme has focussed on stations found to be affected in 2002, and some stations with low levels of THC have been excluded.

2.9 Ekofisk 2/4 A Ekofisk 2/4A is a drilling/production platform located 2.9 km south of the Ekofisk centre.

Earlier activities in the area

Ekofisk 2/4A was established in 1972, and production commenced in 1974. The platform is an unmanned well head platform and included in the Ekofisk Cessation Project (ECP), but still in production. It is not yet decided when the Ekofisk 2/4 A will be shut down.

Ekofisk 2/4-A is the largest of the Ekofisk I drill cuttings piles, and was therefore in 1999 selected to represent Ekofisk I drill cuttings piles regarding environmental monitoring in the decommissioning phase. In 1999 and 2002 stations as close as 100m from the platform centre were sampled to study the development of the fauna and chemical parameters upon the actual cuttings pile. There are no plans of activities including new discharges. The monitoring therefore continues in the same way as in 1999, but there have been collected additional sediment samples from the cuttings pile.

Ekofisk 2/4 A is included in the ordinary environmental monitoring. However, the results from the cuttings pile survey are reported separately.

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Table 2.9.1. Summary of recent drilling and discharge history at Ekofisk 2/4 A. Discharges/activity 1993 1994 1995 1996 1997 1998No. of wells drilled 4 4 0 0 0 0Discharges (tonnes): Barite 6953 3823 0 0 0 0 Cuttings 5547 3050 0 0 0 0 Base oil (with cuttings) 344 10906/ 3257 0 0 0 0 Oil in produced water 0 0 0 0 0 0 Other oil discharges/spills 0 50 643 10.5 0 40Cont Table 2.9.1. cont. Discharges/activity 1999 2000 2001 2002 2003 2004 2005 (1. half)No. of wells drilled 0 0 0 0 0 0 0Discharges (tonnes): Barite 0 0 0 0 0 0 0 Cuttings 0 0 0 0 0 0 0 Base oil (with cuttings) 0 0 0 0 0 0 0 Oil in produced water 0 0 0 0 0 0 0 Other oil discharges/spills 0 0 0.0077 0.015 0.01785 0.051 0.036 PAO Polyalphaolefin: figure represents 22% of total mud discharged with cutting 7 Esterdrill: figure represents 29% of total mud discharged with cuttings

2.10 Albuskjell 1/6 A Albuskjell 1/6A is a drilling/production platform located 21 km west of the Ekofisk centre. The platform was established in 1976, and production commenced in 1979. The installation was closed down in 1998, and the production facilities have been cleaned. The Plugging of the wells was completed in March 2005. Albuskjell 1/6A may be removed prior to the next regional survey, and an extensive sampling programme was therefore included in this survey. A survey will also be carried out prior to removal and also a follow-up survey after removal.

2.11 Eldfisk 2/7 A/FTP Eldfisk 2/7 A/FTP consists of the wellhead platform 2/7-A, the process platform 2/7-FTP and the water injection platform 2/7 E (new in 2000). Eldfisk is situated south of the Ekofisk Centre. Production at the field started in 1977.

Earlier activities in the area

Drilling with Esterdrill took place in 1994 and 1995. In the period 1997 to 1999 there has been no discharges from Eldfisk A. In 2000 three wells were drilled and there were discharges of synthetic drilling fluids attached to cuttings from two of the wells. The third well was re-injected when the re-injection installation was started in second half of 2001. There were no discharges connected to the four wells drilled in 2001. Table 2.11.1. Summary of recent drilling and discharge history at Eldfisk 2/7 A/FTP.

Discharges/activity 1993 1994 1995 1996 1997 1998 1999 2000 No. of wells drilled 0 1 3 4 0 0 0 3 Discharges (tonnes): Barite 0 955 1925 401 0 0 0 306.8 Cuttings 0 589 3354 343 0 0 0 1542.2 Base oil (with cuttings) 0 788/0 2588 2359 0 0 0 1439.710 Oil in produced water 1.5 0.8 0 0 0 0.15 1.09 1 Other oil discharges/spills 0.09 0.021

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Table 2.11.1. Cont. Discharges/activity 1999 2000 2001 2002 2003 2004 2005

(1. half) No. of wells drilled 0 3 3 (no top

sections) 2 (no top sections)

3 (no top sections)

4 (no top sections)

0

Discharges (tonnes): Barite 0 306.8 0 0 0 0 0 Cuttings 0 1542.2 0 0 0 0 0 Base oil (with cuttings) 0 1439.710 0 0 0 0 0 Oil in produced water 1.09 1 3.9 10.08 10.5 9.6 3.5 Other oil discharges/spills 0.09 0.021 0.01 2.56 0.077 0.094 0.094

8 Esterdrill: figure represents 29% of total mud discharged with cuttings 9 Novaplus |I.O. 10 Isoteq (isomerolefin): figure represents 5% of total mud discharged with cuttings

Some of the stations have been excluded from the sampling programme based on the results from 2002.

2.12 Eldfisk 2/7 B The Eldfisk 2/7 B is situated south of the Ekofisk Centre. Production at the field started in 1979.

Earlier activities in the area

Drilling with Polyalphaolefin took place in 1994. Barite, drill cuttings and some synthetic drilling fluid were discharged in 2000 when two wells were drilled. Drill cuttings/mud from other wells drilled in 2000 and four wells drilled in 2001 were re-injected. Table 2.12.1. Summary of recent drilling and discharge history at Eldfisk 2/7 B

Discharges/activity 1993 1994 1995 1996 1997 1998 1999 2000 No. of wells drilled 2 3 0 1 3 0 0 4 Discharges (tonnes): Barite 3476 2867 0 420 1900 0 0 217.4 Cuttings 1604 1767 0 346 2720 0 0 1614.7 Base oil 0 15211 0 131812 134513 0 0 21.814 Oil in produced water 3.3 0.5 0 84 0 0.24 1.6 1.9 Other oil discharges/spills 0 0.080 0 0 0.087

Cont Table 2.12.1. cont.

Discharges/activity 2001 2002 2003 2004 2005 (1. half) No. of wells drilled 4 (no top

sections) 1 (no top sections)

1 (no top sections)

1 (no top sections)

5 sections (no top sections)

Discharges (tonnes): Barite 0 0 0 0 0 Cuttings 0 0 0 0 0 Base oil 0 0 0 0 0 Oil in produced water 2.7 4 7.55 7.2 3.86 Other oil discharges/spills 0 0.038 13.7 0.17 0

11 PAO Polyalpahaolefin; figure represents 22 % of total mud discharged with cuttings. 12 Novaplus I.O. 13 Novaplus PAO 14 Isoteq (isomerolefin): figure represents 1,2% of total mud discharged with cuttings

The sampling programme was somewhat reduced based on the discharge history and previous results.

2.13 Embla 2/7 D The Embla field is situated at block 2/7, south of the Ekofisk Centre. Drilling at Embla started in 1988, while production started in 1993. The production from the unmanned well head platform is sent to Eldfisk A/FTP.

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Earlier activities in the area

There were no discharges from Embla in the period 1993-1999. In 1999, however, one well was drilled and there were discharges of barite and cuttings related to drilling with water based mud in the top section. The remaining sections were drilled with oil based mud. Contaminated cuttings were transported to 2/4 X for re-injection. There have been no discharges since 1999. The sampling programme has focussed on stations close to the installation. Table 2.13.1. Summary of recent drilling and discharge history, Embla. Discharges/ activity

1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 (1. half)

No. of wells drilled 0 0 0 0 0 0 1 0 0 0 0 0 0

Discharges (tonnes):

Barite 0 0 0 0 0 0 294 0 0 0 0 0 0 Cuttings 0 0 0 0 0 0 586 0 0 0 0 0 0 Base oil 0 0 0 0 0 0 0 0 0 0 0 0 0 Oil in produced water 0 0 0 0 0 0 0 0 0 0 0 0 0

Other oil discharges/spills 0 0 0 0 0 0 0 0 0 0.19 0.04 0 0

2.14 Tor 2/4 E The Tor field is situated north-east of the Ekofisk Center at block 2/4 and 2/5. Production started in 1977. It is a manned platform producing oil and gas and utilise injected seawater as pressure support.

Earlier activities in the area

There have only been minor discharges of produced water during the recent years; no discharges from drilling in the period 1993 – 2001 and only minor discharges in the period 2002-2004. Table 2.14.1. Summary of recent drilling and discharge history at Tor 2/4 E. Discharges/ activity

1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 (1. half)

No. of wells drilled 0 0 0 0 0 0 0 0 0 0 0 0 0

Discharges (tonnes):

Barite 0 0 0 0 0 0 0 0 0 0 0 0 0 Cuttings 0 0 0 0 0 0 0 0 0 0 0 0 0 Base oil 0 0 0 0 0 0 0 0 0 0 0 0 0 Oil in produced water 12 8 9 9 5 4.12 5 6.1 8.2 5 4.11 1.23 0.13

Other oil discharges/spills 0 0.15 0 0 0.075 0 0 0 0 0.034 0 0.085 0

The sampling programme has been reduced compared to the previous survey based on the discharge history and low THC concentrations in 2002.

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2.15 Yme The Yme field is situated in block 9/2, northeast of Ekofisk. The oil was discovered in 1987, and the field is built with a jackup drilling platform at Yme Gamma and a foundation frame at Yme Beta. Production at the field started in the beginning of 1996 and ended in spring 2001.

Yme Gamma

Earlier activities in the area

The Yme Gamma template was removed in the summer of 2001. There were no drilling activities at Yme Gamma in 2001. The discharges of barite were related to the closing activities. Discharges from Yme Gamma are shown in Table 2.15.1. Table 2.15.1.Summary of recent drilling and discharge history at Yme Gamma.

Utslipp Yme Gamma 1996 1997 1998 1999 2000 2001

No. of wells 4 2 1 ( 2 side step) (3 side step) 0

Discharges:

Barite (tonnes) 2834 *) 2421*) 111 1130 *) 153 249

Cuttings (m3) 2117 3723 810 264 1437 0

Oil based mud (m3) 0 0 0 0 0 0

Synthetic mud (m3) 244 420 79 71 528 0

Water based mud (m3) 6992 1615 ? 0 0 0

Cementing chemicals (tonnes) 95 *) 3 *) 0,6 *) 12,8 *) 10.4 26

Completion chemicals (tonnes) 771 *) 179 *) 325,9 *) 1051 *) 5 0

Oil in water 34 kg 3 tonn 9 tonn 4 tonn 5.1 tonn 3.5 tonn *) Both Yme Gamma and Yme Beta included

The 2002 survey showed that THC had declined, and the sampling programme was somewhat reduced.

The removal of the template made it possible to conduct an additional study, including stations close to the centre, in 2002. These stations have also been sampled in 2005, including centre positions.

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Yme Beta

The template on Yme Beta was removed the summer of 2001. There has been no drilling activity on Yme Beta in 2000 and 2001. Discharges for the period 1996 – 2001 are shown in Table 2.15.2. Table 2.15.2. Summary of recent drilling and discharge history at Yme Beta. Utslipp Yme Beta 1996 1997 1998 1999 2000 2001 No. of wells 1 1 0 1 0 0

Discharges: 2834 *) 2421 *) 0 1130 *) 0 0

Barite (tonnes) 358 2407 0 1479 0 0

Cuttings (m3) 0 0 0 0 0 0

Oil based mud (m3) 0 48 0 290 0 0

Synthetic mud (m3) 2288 1594 0 840 0 0

Water based mud (m3) 95 *) 3 *) 0,6 *) 12,8 *) 0 4

Cementing chemicals (tonnes) 771 *) 179 *) 325.9 *) 1051 *) 0 0

Completion chemicals (tonnes) 0 0 0 0 0 0 *) Both Yme Gamma and Yme Beta included

Based on the results from 2002 the sampling programme has focussed on the stations close to the centre.

The removal of the template has made it possible to conduct an additional study, including stations located 100m from the centre and the former centre itself (as in 2002).

2.16 Kogge In connection with exploration drilling at Kogge, located between Yme and Ula, two stations were sampled. The purpose was to verify the sea bed characteristics in the area.

2.17 Trym In connection with the development of block 3/7 at Trym a baseline survey was carried out. The development includes one well which will be connected by a pipeline to Harald in the Danish sector.

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3.0 Materials and Methods

3.1 Field work

3.1.1 Sampling strategy

The selection of sampling stations at the various fields are based on the results from the survey conducted in 2002 and the drilling- and discharge history after the previous survey (in 2002), see Program for sedimentovervåking Region I – Ekofisk 2005 version 3, January 2005 (enclosed in Appendix E).

The following criteria have been used:

• Stations shown to be contaminated or biologically affected in 2002 are included in 2005

• In order to obtain an estimate of contaminated area, stations located one step further along the transect from the centre are included

• At fields consisting of several sub-sea installations one or more installations are selected for a more extensive sampling programme than the others

• Biology samples are included at stations previously shown to contain > 50 mg THC/kg

• Stations including biology samples are also analysed for metals

Numbers of replicate samples at the reference stations is reduced from 10 to 5. The reason is that several surveys in the Ekofisk region have shown that no major changes in the species/area curve are to be expected. The conclusions from previous surveys are that even 10 grab samples are not sufficient to obtain the total number of species found in the region.

3.1.2 Execution of field work

The field work was performed by DNV in cooperation with MOLAB using the vessel Nothern River in the period 31st of May to 10th of June 2005 and the vessel Troll Viking from 10th to 15th of June. Sampling and analysis were carried out with reference to activity regulation (OD, SFT, Hi, 2003), appendix 1, Requirement to Environmental Monitoring of the Petroleum Activity on the Norwegian Continental Shelf – technical appendix 2, Sediment Monitoring and DNV procedures for this kind of work. Deviation from the regulations is described in chapter 3.5. It is prepared a separate survey report, see appendix A in the Appendix report (DNV report 2006 – 0512). The survey report contains details from the sampling survey.

Samples for chemical and biological analysis were collected with van Veen grabs (surface area 0.1 m2). For chemical analysis the surface sediment (0-1 cm) from three replicate grab samples were collected on each location. On selected stations additional samples were collected from the 1-3 and 3-6 cm layers. Five grab samples were collected for fauna analyses on each location.

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The main equipment used was:

• van Veen grabs

• Reception table for grab in stainless steel

• Washing table for biological samples

• two sets of sieves for washing of biological samples

• Munsels colour chart Sampling was carried out in accordance with accredited procedures described in Handbook for the Biology laboratory quality system; sampling of marine sediment and soft bottom analyses. It was emphasized that the sediment surface in the samples should be undisturbed and that the washing/sieving of the fauna samples was carried out gently. Animals were fixed in formalin (4 % neutralized with hexamine), added pink Bengal and stored in 3.7 l plastic buckets. All samples were double marked and packed in solid boxes to avoid damage to the sample packing.

The field work was carried out in accordance to the survey program. Some adjustments in the program was however necessary because of other activities in the fields (seismology shooting), or because of interference with cables and chains. In cases where larger modification was necessary in accordance to the planed program, this is indicated in the beginning of each result chapter for the different fields.

Details are given in the Appendix report. In accordance with the activity instructions, sampling is to be taken inside a radius of 50 m round the station. In cases where it was necessary to sample outside this radius, the station was recorded as a new station. The vessel was provided with dynamic positioning equipment. This means very precise positioning, and that the vessel can be kept in the exact same position over time. The variance in positioning was better than ±1 m.

3.2 Macrobenthic analyses

3.2.1 Macrobenthic analyses – an introduction

The macrobenthic fauna considered in this survey is found living either in, or on sand, silt or clay sediments. This fauna comprises the following main taxonomic groups: Polychaeta, Crustacea, Mollusca, Echinodermata and Varia (remaining groups). Only animals more than 1 mm (macrobenthos) are included in the analysis.

Macrobenthic fauna are traditionally included in offshore environmental monitoring. The reason for this is that the study of benthic communities can give an indication of the effects of pollution from offshore activities, while chemical monitoring of sediments is aimed at assessing the dispersion and concentration levels of pollutants in the vicinity of offshore installations. The benthic fauna is a suitable biological parameter for monitoring the effects of pollution since most of the species have limited mobility and changes in species composition and densities of individuals can therefore easily be identified. The distribution of the fauna can be related to natural variations in environmental parameters such as depth and type of sediment, but also anthropogenic factors such as discharges of drilling fluids, cuttings and others, including accidental releases of oil and physical disturbances.

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3.2.2 Sorting and species identification

In the laboratory the samples were washed on 1 mm sieves with (circular holes) to remove formaldehyde and remaining fine sediment, and then sorted by hand under a magnifying glass. The animals were split into the major taxonomic groups; Echinodermata, Polychaeta, Crustacean, Mollusca and Varia and transferred to 70% ethanol before further identification was undertaken.

The literature used for species identification is recommended in the Appendix 1 to the Activities Regulations (Requirements for Environmental Monitoring of the Petroleum Activities on the Norwegian Continental Shelf) (2001). Apart from the exceptions detailed below, all animals were identified to the lowest possible taxonomic level (i.e. generally to species level) and the number of individuals per taxon in each sample was recorded.

In accordance with the Activities Regulations, Nematoda, Foraminifera and colonial organisms (i.e. Porifera and Bryozoa), were excluded from any data analyses. Some taxa (i.e. Platyhelminthes, Nemertini, Tunicata and Tanaidacea) were quantified but were not identified further. A number of representative specimens of each of the species/taxa identified were included in our reference collection.

3.2.3 Analytical methods

The statistical and mathematical methods utilised to aid interpretation of the benthic fauna data are summarised below.

• Abundance ratio

• Shannon-Wiener's diversity index, H' (Shannon & Weaver 1963)

• Evenness calculated by Pielou's "evenness" J' (Pielou 1969)

• Expected number of species in a sample of 100 individuals (ES100)

• Fauna similarity between stations by Bray-Curtis dissimilarity index d (Bray & Curtis 1957). The resulting similarity matrix was utilised in multivariate analyses in order to group stations and assess gradients in the benthic communities. These methods were: hierarchical agglomerative classification with group-average sorting (Lance & Williams 1966), ordination with non-metric Multi-Dimensional Scaling (MDS), (Shepard 1962, Kruskal 1964).

Classification and MDS ordination were carried out using the programme-package PRIMER (Plymouth Routines In Multivariate Ecological Research).

Formulas and further explanations are given in APPENDIX D.

The relation between the fauna composition and the environmental variables on all available data was assessed by principal components analysis, using the Brodgar software. For details, see Appendix D.

The raw data is stored in MOD; MiljøOvervåkingsDatabasen (Environmental Monitoring Database).

3.2.4 Comparison of taxonomical data between years

Comparison of data at species level between years (trend analyses) involves taxonomic sources of errors which have to be minimized in order to get consistent data when using e.g. multivariate analyses. Comparison of univariate data, such as biodiversity indices between years does not raise the same problem and gives minimal or small fluctuations. Main sources

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of errors when using multiple data sets at species level are sampling methodology and variations between taxonomists.

Species-level identification of all specimens is practically not possible. A number of obstacles are always present, e.g. the state of knowledge of the taxonomy of infaunal species. Some groups are comparatively well known, while others are relatively unknown. A substantial number of unrecognized species may be assumed to be present in the samples. These factors, along with various levels of experience and areas of expertise among taxonomists, are present in any survey of this kind, and will directly impact the survey results (Montagne & Bergen, 1996).

Taken this into account the similarity analyses between years (trend analyses) have been performed at family level to get consistent data.

3.2.5 Quality assurance

Procedures including routines for quality assurance related to sorting, species identification and recording of macrobenthos samples are given in DNV’s Biolaboratoriets Kvalitetssystem, Prøvetaking av marint sediment og bløtbunnsanalyser. A brief summary is given here:

All samples are recorded and double-labelled during fieldwork, and transported in wooden boxes in a steel container. During sorting in the laboratory all relevant information about each sample is recorded (who sorted what and when, time spent, number of bottles etc.). After sorting, each sediment sample is examined for remaining organisms by approved personnel. Each identifier establishes a separate reference collection of species for comparison purpose. To maintain traceability each identifier signs a log to keep track over which grab samples and animal group(s) he or she has been working on. The project reference collection is kept at DNV, Høvik.

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3.3 Chemical analyses and physical characterization of the sediments The sediments have been analysed as described in Table 3.3.1 Table 3.3.1. Analytical methods and physical characterization. Analytical method Parameter Sediment characterization • Grain size distribution - Distribution of pelit (< 63 µm) and sand (> 63 µm) - Cumulative weight% distribution 63-2000 µm - Median particle diameter (Mdφ), deviation (SDφ), skewness

(Skφ) and kurtosis (Kφ) • Total organic matter - % TOM in the sediment Chemical analysis • Hydrocarbons - THC, sum C12-C35 - NPD, naphtalene, phenanthrene/anthracene and

dibenzothiophene and their C1-C3 alkylated derivatives. Sum and single compounds.

- PAH, 16 EPA compounds. Sum and single compounds.

- Decalins, sum of C5-C8 alkyl decalins - Olefins, compounds in the area C14H28 to C20H42 • Esters - Petrofree and Finagreen • Ethers - Aquamul B • Chlorinated biphenyls PBC, 7 congeners • Perfluorooctyl sulphonate - PFOS • Metals - Ba, Cd, Cr, Cu, Hg, Pb, Zn

3.3.1 Sediment characterization

Grain size distribution The method for grain size distribution analysis is described in Buchanan (1984). The analysis includes a fast mechanical separation of the sand fraction (> 63 µm) from the silt and clay fraction. The sand fraction is then dried and sieved over a series of graded sieves.

From each station three sub samples (0-5 cm) from separate grab samples were mixed and homogenized, and one homogenized sample from each station was analysed. Approximately 10 g of the sample was weighed to the nearest 0.01 g before wet sieving on a 63 µm sieve. The fraction passing this sieve was transferred to a plastic bottle. A separate sample was weighed and dried for dry weight determination. The percentage of silt and clay (< 63 µm) of total dry weight in the sample was then calculated.

The fraction > 63 µm was dried at 100 °C for 12 hrs and sieved over a series of Wenthworth graded sieves (Endecott Test Sieves, London) with mesh sizes ranging from 2000 to 63 µm. The sample was shaken on a Retsch KG testing sieve shaker for ten minutes. The weight retained upon each sieve was determined to the nearest 0.01 g. The weight of all size fractions was used to prepare cumulative weight% distribution tables for each sampling site. This table was then used in calculating the median particle diameter and deviation, skewness and kurtosis of the particle size distribution. As the grain size distribution was not determined for the fraction < 63 µm, the φ-value for this fraction was given the value 8. The values for Mdφ, SDφ, Skφ, and Kφ should therefore be considered as extrapolated results.

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The mathematical expressions are given below.

Mdφ (median particle diameter):

Mdφ = the φ-value of the midpoint (i.e. 50 %) of the cumulative % weight curve. This measures the central tendency of the size frequency distribution.

SDφ (standard deviation):

SDφ estimated as:

6.6595

416-84SD φφφφφ −

+=

SDφ gives a measure of the spread in particle size around the Mdφ, and thus is a measure of the degree of sorting of the particles.

Skφ (skewness):

Skφ estimated as:

( ) ( )5952Md2955

16842Md28416Sk

φφφφφ

φφφφφφ

−−+

+−−+

=

Skφ describes the symmetry of the spread in distribution around the Mdφ. A completely symmetrical distribution will have Skφ = 0, negative values indicate displacement of the distribution curve towards coarser sediment, and positive Skφ indicates displacement towards finer sediment.

Kurtosis, Kφ:

Kφ estimated as:

( )257544.25-95Kφφ

φφφ−

=

Kφ describes the toppedness of the distribution, i.e. how heavy the tails are (expressed by the φ5 and φ95 fractions) compared to the central portion of the distribution. For a normal distribution the expression above will give a Kφ value of 1.00.

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Interpretation tables are enclosed in Table 3.3.2 and Table 3.3.3. Table 3.3.2. Grain size distribution. Interpretation of descriptive indiced (Buchanan, 1984). Parameter Index value Verbal classification Standard deviation (SDφ) < 0.35 Very well sorted 0.25-0.50 Well sorted 0.50-0.70 Moderately well sorted 0.70-1.00 Moderately sorted 1.00-2.00 Poorly sorted 2.00-4.00 Very poorly sorted > 4.00 Extremely poorly sorted Skewness (Skφ) +1.00 to +0.30 Strongly fine skewed +0.30 to +0.10 Fine skewed +0.10 to -0.10 Symmetrical -0.10 to -0.30 Coarse skewed -0.30 to -1.00 Strongly coarse skewed Kurtosis (Kφ) <0.67 Very platykurtic 0.67-0.90 Platykurtic 0.90-1.11 Mesokurtic (nearly normal) 1.11-1.50 Leptokurtic 1.50-3.00 Very leptokurtic

Table 3.3.3. Grain size distribution. Mesh sizes used and Wentworth grade classification (Buchanan, 1984). Mesh diameter (µm) φ Description 4000 -2 Gravel 2000 -1 Very coarse sand 1000 0 Coarse sand 500 +1.0 355 +1.5 Medium sand 250 +2.0 180 +2.5 Fine sand 125 +3.0 90 +3.5 Very fine sand 63 +4.0 <63 >+4.5 Silt and clay (pelite)

The silt and clay fraction was given the φ-value of 8. Total organic matter 30-40 g of wet sediment was weighed into a porcelain dish. The sample was heated at 105 °C for minimum 20 hours, cooled and weighed, and then heated to 480 °C for minimum 16 hours. The percent weight loss after the combustion was then calculated, and this value represents the total organic matter content (TOM) in the sediment. Two sediment standards with known TOM and calcium carbonate were heated together with the sediment samples. The calcium carbonate was used as a cross check on potential weight loss due to the conversion of carbonate to oxide.

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3.3.2 Chemical analysis

3.3.2.1 Hydrocarbons, esters, ethers and selected hydrocarbons

The chemical analysis comprises determination of the total hydrocarbon content from n-C12 to n-C35 (THC), olefins (Novasol/Novaplus/Ultidril), esters (Petrofree and Finagreen), decalins). The analytical steps are shown in Figure 3.1. The sediment samples were prepared by saponification, followed by extraction with dichloromethan.

The samples in which esters should be determined were prepared by soxhlet extraction. The extract was then separated in a non-polar and a polar fraction using a silica column. The non-polar fractions were analysed for hydrocarbons by use of gas chromatography (GC).

Preparation procedure:

The sediment samples were kept in Rilsan bags. Homogenization was performed by stirring in the Rilsan bag, and small portions of the wet sample were taken randomly giving a total weight of about 50 g. Benthic animals were avoided if possible. Internal standards were added, 5 µg each of naphthalene-d8, biphenyl-d10, phenanthrene-d10, pyrene-d10, chrysene-d12 and perylene-d12. 100 µg diocthylether was added if ether should be determined.

Saponification: The sample was refluxed with 50 ml 0.5 N KOH in methanol for 2 hours. The mixture was then extracted by 80 mL dichloromethane.

Soxhlet extraction: The internal standard ethyl stearate (100 µg) was added in addition to the internal standards for the hydrocarbons, and the sample was refluxed with 200 mL methanol for 2.5 hour. The methanol was then decanted, and the sample was further extracted by refluxing with 200 mL of dichloromethane over night. The metanol extract was diluted with water, extracted with dichloromethane and the dichloromethane extracts were combined.

The extract was evaporated to approximately 1 mL, re-dissolved in hexane and fractionated (clean up) on Bond-Elut silica columns (Isolute, International Sorbent Technology). Fraction I, hexane, was concentrated and analysed for hydrocarbons. Fraction II, hexane/ dichloromethane 70:30, was concentrated and analysed for esters. An aliquot of the wet and homogenized sediment was weighed out and dried for 48 hours at 105 °C, for determination of the dry weight.

PCB and selected hydrocarbons in the core samples: Due to high content of THC the samples were prepared in a different way prior to the quantification. 4-8 g sediment was weighed, internal standards were added (25 µg each of naphthalene-d8, biphenyl-d10, phenanthrene-d10, pyrene-d10, chrysene-d12 and perylene-d12 and 2.5 µg PCB-30). 20 mL of dichloromethane and 20 mL of MeOH:H20 (1:1) were added. The samples were treated 30 min in an ultrasonic bath and shaken for 1 hour. The samples were centrifuged, and the dichloromethane-fraction was analyzed for PCB and selected hydrocarbons. An aliquot of the wet and homogenized sediment was weighed out and dried for 48 hours at 105 °C, for determination of the dry weight.

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Quantification:

THC (total hydrocarbon content) was determined by gas chromatography with flame ionization detector, in the boiling range of n-C12 alkane to n-C35 alkane. The quantification was carried out according to an external standard of the reference oil, HDF 200, a drilling mud base oil. The reported values were corrected for background levels from procedural blanks.

The ester compounds were determined by gas chromatography according to the internal standard ethyl stearate. Compounds in the drilling fluids Petrofree (main compound 2-ethylhexyl dodecanoate) and Finagreen (main compound 2-ethylhexyl oleate) were quantified. Response factors were established by analysis of reference samples.

The ether determination was carried out before the extracts were fractioned on Bond-Elut silica columns. The ether compounds were determined by gas chromatography using diocthylether as internal standard and quantification of the main component in baseliquid Aquamul B II (2-methyl-1.1 – propandiol, di-ethylheksylether). Response factors were established by analysis of reference samples.

NPD, PAH and decalins were determined by gas chromatography/mass spectrometry operated in the selected ion recording mode (SIR). The quantification was carried out according to the added internal standards and integration of the molecular ions. The following compounds were determined: Naphthalene, phenanthrene/anthracene, dibenzothiophene and their C1-, C2- and C3-alkylated derivatives, acenaphtene, acenaphthylene, fluorene, pyrene/fluoranthene, chrysene/ triphenylene, benzo(a)anthracene, benzo(a)pyrene, benzo(b)fluoranthene/ benzo(j)fluoranthene/ benzo(k)fluoranthene, benzo(g,h,i)perylene, indeno(1,2,3-cd)pyrene and dibenzo(a,h)anthracene. In addition the sum of selected bicyclic alkanes, C5 - C8 alkyl decalins, was determined.

Reference compounds were available for all the aromatic compounds. For each of the C1 - C3 alkyl homologue groups one of the isomers was used as reference in the quantification. For the bicyclic alkanes, C5 - C8 alkyl decalins, reference compounds were missing, and a response factor was calculated from n-octylcyclohexane with the assumption that the response of the molecular ions are similar. The reported values were corrected for background levels from procedural blanks.

Chlorinated biphenyls were determined by gas chromatography/mass spectrometry operated in the selected ion recording mode (SIR). The quantification was carried out according to the added internal standard and integration of the molecular ions. The following compounds were determined: PCB 28, PCB 52, PCB 101, PCB 118, PCB 153, PCB 138 and PCB 180, this is the 7-dutch-compounds.

GC-FID conditions: Gas chromatograph : Perkin Elmer Autosystem XL Column : 12 m x 0.20 mm i.d., fused silica, crosslinked with

dimethyl silicone Temperatures: Column : 50 °C (2 min) - 20 °C/min - 350 °C (8 min) Injector : 320 °C Detector : 350 °C Carrier gas : Helium Injection volume : 1 µL Data system : TotalChrom 6.2 HDF 200 : 0.1 – 10 mg/mL hexane

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GC/MS conditions: Mass spectrometer : Clarus 500 Mass Spectrometer, Perkin Elmer Data system : TurboMass Gas chromatograph : Clarus 500 Gas Chromatograph, Perkin Elmer Column: : 30 m fused silica, 0.25 µm DB-5ms Temperatures:

Ion source : 40 °C (2 min) - 20 °C/min - 120 °C 10 °C/min - 300 °C (15 min)

Column : 300 °C Injector : 180 °C Carrier gas : Helium Ionization : Electron impact, 70 eV Masses (m/z) C0-C3 naphthalene : 128, 141, 156, 170 C0-C3 phenanthrene : 178, 192, 206, 220 C0-C3 dibenzothiophene : 184, 198, 212, 226 PAH : 152, 153, 166, 202, 228, 252, 276, 278 C5-C8 decalins : 208, 222, 236, 250 n-octyl cyclohexane : 196 Deuterated standards : 136, 164, 188, 212, 240, 264 Injection volume : 1 µL

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sediment

homogenization

addition of internalstandard

saponification or soxlet extraction

hydrocarbonenriched extract

determination of total hydrocarbon (THC) by gas chromatography

(GC-FID)

determination of selectedaromatic hydrocarbons

and decalins (NPD, PAH) by gas chromatography /

mass spectrometry(GC/MS)

separation polar/unpolarby chromatography

determination of ethersby gas chromatography

determination of estersby gas chromatography

sediment

homogenization

addition of internalstandard

saponification or soxlet extraction

hydrocarbonenriched extract

determination of total hydrocarbon (THC) by gas chromatography

(GC-FID)

determination of selectedaromatic hydrocarbons

and decalins (NPD, PAH) by gas chromatography /

mass spectrometry(GC/MS)

separation polar/unpolarby chromatography

determination of ethersby gas chromatography

determination of estersby gas chromatography

Figure 3.3.1. Flow scheme of essential steps in the hydrocarbon analyses of sediments. 3.3.2.2 PFOS (perfluorooctyl sulphonate)

PFOS is considered as a hazardous environmental substance, which has recently become in focus. Among the most important areas of use for PFOS-related substances in Norway appear to be fire fighting in the offshore industry. In 2005, the Pollution Control Authority decided to make a survey of PFOS-retaled substances in fire fighting foams and emissions from this source.

The sediment was freeze-dried and the dry weight was determined. The samples were prepared with NaOH prior to the extraction with methanol and clean-up with activated carbon. 18O2-PFOS was added as internal standard. PFOS were determined by liqiud chromatography/mass spectrometry. A procedural blank was prepared and show no sign of PFOS.

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3.3.2.3 Metals

The metal analyses include determination of Ba, Cd, Cr, Cu, Hg, Pb and Zn after digestion with nitric acid (NS 4770).

The wet sediment sample was dried at 40 °C for two days, homogenized and sieved through a 500 µm nylon sieve. The fractions larger and less than 0.5 mm were weighed. 1 g of the fraction less than 0.5 mm was extracted with 20 mL 7 M nitric acid in a Pyrex decomposition bottle in an autoclave at 120 °C for 30 min. After cooling, 80 mL of distilled water was added to the Pyrex bottle. The clear solution was decanted into a polyethylene bottle until analysis.

Ba, Cr, Cu, Pb and Zn were determined by inductively coupled plasma atomic emission spectrometry (ICP-AES). Cd was determined by atomic absorption, graphite furnace technique (GF-AAS). Hg was determined by atomic adsorption cold vapour technique (CV-AAS) based on NS 4768.

ICP-AES:

Instrument: Thermo Jarrel Ash Iris Advantage

Analytical lines:

Ba: 493.409 nm, Cr: 267.716 nm, Cu: 324.754 nm, Pb: 220.353 nm, Zn: 213.856 nm

GFAAS:

Instrument: Perkin Elmer AAnalyst 600.

Analytical line: Cd: 228.8 nm

The element was measured with a hollow cathode lamp. Ammonium phosphate was used as a modifier.

CVAAS:

Instrument: Perkin Elmer 3100.

Hg was determined at 253.7 nm by use of stannous chloride in hydrochloric acid.

3.3.2.4 Determination and quantification limits

The limit of detection (LOD) and limit of quantification (LOQ) for THC and metals are calculated as 3 SD (standard deviation) and 10 SD above the measured average blank values respectively. This is according to Guidelines for Data Acquisition and Data Quality Evaluation in Environmental Chemistry, Anal.chem. 52 (1980) p. 2242-2249. The limit of detection (LOD) and limit of quantification (LOQ) for NPD, PAH and decalins are based upon the lowest standard that gives sufficient concentration recovery. The limit of detection (LOD) and limit of quantification (LOQ) for olefins, esters and ethers are based upon the lowest standard that gives sufficient concentration recovery and the actual background noise in the samples.

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Table 3.3.4. Limit of detection (LOD) and limit of quantification (LOQ), hydrocarbons. Analytical parameter LOD LOQ Blank samples mg/kg mg/kg Number THC 1 5 23 Sum NPD 0.01 0.03 - Sum PAH 0.005 0.02 - Sum decalins 0.1 0.3 - Olefins 0.3-0.5 1-2 - Esters 0.2 0.7 - Ethers 1 3 - PCB 0.1 0.3

Table 3.3.5. Limit of detection (LOD) and limit of quantification (LOQ), metals. Ba Cd Cr Cu Hg Pb Zn ICP GFAAS ICP ICP CVAAS ICP ICP LOD mg/kg 1 0.01 0.2 0.5 0.01 0.5 1 LOQ mg/kg 3 0.04 0.7 2 0.03 2 3

3.3.3 Limit of contamination

Natural background levels of THC, NPD, PAH and metals will always be present in the sediments. Statistical treatment of the analytical results allows the determination of specific levels above which a sediment sample may be said to contain higher levels than the background levels.

Esters, ethers and olefins that are included in the drilling mud base liquids, are not present in uncontaminated sediments. If these compounds are observed, the sediments are considered to be contaminated.

For the content of THC, NPD, PAH and metals in the sediments a limit of contamination (an impurity level) is calculated. This level is called LSC (Limit of Significant Contamination). A multivariate analysis is performed as a basis for treatment of Region I in possible sub-regions. For this reason a principal component analysis (PCA analysis) is performed on the chemical data from the Regional stations and the additional reference stations at Region I. The PCA analysis is performed using the data both from the present 2005 survey and from the period 1996 - 2005.

The statistical calculations of limit of significant contamination are based on a normal (Gaussian) distribution of the data and a one-tailed t-test at a confidence level of 95 %. Data from uncontaminated regional stations and reference stations from 1996, 1999, 2002 and 2005 are used. Calculations are not performed for Cd, Hg and decalins as these compounds are not found or found close to the detection limits at these stations.

Expressions used:

LSC : x middle + t 0.05, n-1*SD *(1+1/N)1/2 x mean : mean of regional stations and reference stations SD : standard deviation, SD² = Σ (x - x mean)² / (n-1) T : t-value, from tables with degree of freedom (n-1) and confidence level (95 %) N : number of samples N : number of stations

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3.4 Quality assurance Accreditation Molab AS is accredited by Norsk Akkreditering to perform chemical analyses, accreditation number Test 032. The accreditation is according to NS-EN ISO/IEC 17025.

Quality assurance for grain size distribution Six different laboratory reference sediments (from the 2003 survey) were chosen as a control for the grain size distribution.

Quality assurance for total organic matter Together with the samples, calcium carbonate and two in-house standards were heated to 480 °C. The calcium carbonate was used as a control of loss of carbonate from the sediment samples. The in-house standards have known TOM (0.88 and 8.31 %). If the results of one or both in-house standards were outside the accepted range of variation, the samples were reanalysed. The results of the analyses are given in Appendix C.

Quality assurance for hydrocarbons The instruments are regularly calibrated by use of appropriate standards, and instrument performance is checked regularly. The analytical procedures are regularly controlled by analyses of standards, blank samples and quality assurance samples. Standards of mineral oil are analysed together with the THC samples. For NPD, PAH and decalins reference samples containing known amounts of the different compounds are analysed to establish response factors due to differences in extraction, volatility and GC/MS response compared to the internal standards.

In-house standards are analysed regularly. The accuracy of the THC analysis is documented by participation in the international intercalibration exercise SETOC. The accuracy is also controlled by analysis of sediments containing certified amount of THC

The accuracy of the NPD and PAH analysis is controlled by analysis of in-house standards.

The accuracy of PCB determination is controlled by the analysis of reference material.

Quality assurance for metals All reagents are of pro analysis grade. In-house reference and blank samples are included in the analyses. Accuracy and reproducibility are controlled by the results obtained for the in-house reference materials.

3.5 Deviations from the activities regulations The survey has been performed according to the Activities Regulations (Requirements for Environmental Monitoring of the Petroleum Activities on the Norwegian Continental Shelf) (2001).

The regional surveys conducted since 1996 have shown a considerable reduction in the area contaminated with hydrocarbones. Today biological impacts rarely are seen more than 500 m, in some cases 1000 m from the installation centre.

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The sampling stations have been selected based on the following critera:

o Stations shown to be contaminated or biologically affected in 2002 are included in the 2005 survey.

o In order to measure contaminated/affected area, one station (along the same transect) outside the contaminated/affected stations from 2002 are included.

o At fields consisting of many subsea installations one or more of the installations are selected as typical examples, including a more extensive sampling program than the others.

o Biology analyses are included at stations previously shown to have THC concentrations > 50 mg/kg.

o Metals are included at biology stations.

o Based on experiences from several previous surveys in the area and the assumption that no major changes in the species-area curve are expected, the number of replicate biology samples is reduced from ten to five. The conclusions from previous surveys are that not even 10 grab samples provide sufficient material to obtain the total number of species in the region.

o In some cases the position of the sampling stations deviates from the planned positions because of possible interference with pipelines, cables etc. (see Survey Report). Such deviations are not metioned in the main report unless they are considered to have significant effect on the interpretation of the results.

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4.0 Results and Discussion The locations of the sampling stations are shown in station maps in the back of this report. The maps can be folded out.

4.1 Regional stations

4.1.1 Sediment characterization

Grain size distribution The grain size distribution is shown in Table 4.1.1, together with the results from the previous survey in 2002.

The sediments consist mainly of fine sand. The content of sand ranges from 95 % to 99 %, the content of silt and clay from 1.0 % to 5.3 % and the content of gravel is generally low, below 0.3 %. The median particle diameter ranges from 2.27 to 2.97φ. In average the median particle diameter is 2.72φ and the average sediment consists of 96.8 % sand, 3.1 % silt and clay and 0.06 % gravel.

In general the grain size distribution is similar to the previous surveys. The results from the complete grain size distribution are given in Appendix C. Table 4.1.1 Regional stations, grain size distribution. Station Median

diameter Classification Grain size distrib. 2005

(%) Grain size 2002 (%)

Mdφ Silt and clay

Sand Gravel Silt and clay

Sand

REG1 ULA Ref. 2.78 Fine sand 4.3 95.7 0.0 5.3 94.7 REG2 2.76 Fine sand 2.2 97.5 0.1 2.4 97.4 REG3 EKO Ref. 2.78 Fine sand 2.6 97.3 0.1 2.6 97.4 REG4 2.71 Fine sand 4.8 94.9 0.3 5.5 94.5 REG5 2.97 Fine sand 5.2 94.7 0.1 4.1 94.6 REG6 2.84 Fine sand 4.3 95.7 0.0 4.5 95.4 REG7 2.75 Fine sand 3.3 96.7 0.0 3.8 96.1 REG8 HOD Ref. 2.66 Fine sand 1.0 99.0 0.0 3.0 96.2 REG9 2.63 Fine sand 1.9 98.1 0.0 2.3 97.7 REG10 2.27 Fine sand 1.6 98.4 0.0 1.0 99.0 Mean 2.72 3.1 96.8 0.06 3.5 96.3 Standard deviation 0.18 1.47 1.50 0.10 1.4 1.5

Total organic matter (TOM) The TOM results are shown in Table 4.1.2. The content of TOM in the sediments is low and only small variations are found at the Regional stations. TOM ranges from 0.7 % (REG9 and REG10) to 1.0 % (REG7) and the content corresponds to the grain size distribution. The results are similar to the previous surveys.

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Table 4.1.2 Regional stations, total organic matter (% of dry sediment). Station 2005, 0-5 cm Mean 2002 Mean 1999 Mean1996 REG1. ULA ref. 0.84 0.86 1.06 0.82 REG2 0.85 0.84 0.94 0.95 REG3. EKO ref. 0.88 0.82 0.95 0.86 REG4 0.86 0.87 0.93 0.95 REG5 0.98 0.92 1.14 0.94 REG6 1.02 0.92 1.13 0.95 REG7 1.05 0.89 1.11 0.93 REG8. HOD ref. 0.78 0.78 0.71 0.92 REG9 0.68 0.61 0.78 REG10 0.69 0.68 0.85

4.1.2 Chemical analyses

Parameters analysed in the 0-1 cm sediment layer at the regional stations:

• THC

• NPD, PAH, decalins

• Metals (Ba, Cd, Cr, Cu, Hg, Pb, Zn), work up by nitric acid.

Three replicate samples from the top 0-1 cm sediment layer at each Regional station and five replicate samples at the field reference stations are analysed.

THC The THC results are shown in Table 4.1.3. The corresponding THC data from the previous surveys in 2002, 1999 and 1996 are also included for comparison. Bar diagram of the THC content is given in Figure 4.1.3.

In 1999 the THC concentrations ranged from 1.4 mg/kg (REG9) to 5.5 mg/kg (REG3). The THC concentrations found in the 2002 survey was quite similar and ranged from 1.6 mg/kg (REG9) to 5.9 mg/kg (REG3).

In the present survey the THC concentrations vary from 1.3 mg/kg (REG10) to 5.8 mg/kg (REG3). The concentrations are similar to the previous surveys. None of the stations are contaminated by THC.

Gas chromatograms from each regional station are shown in Appendix C.

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Table 4.1.3. Regional stations, total hydrocarbon content (mg/kg dry sediment). Station Grab

#1 Grab

#2 Grab

#3 Grab

#4 Grab

#5 Mean SD Mean SD Mean SD

2005 2005 2002 2002 1999 1999REG1 ULA ref. 3.3 4.1 5.2 3.7 3.5 3.9 0.7 3.3 0.3 4.1 0.5 REG2 2.4 2.4 2.6 2.5 0.1 2.8 0.4 2.6 0.1 REG3 EKO ref. 6.2 5.3 4.4 6.1 7.1 5.8 1.0 5.9 0.7 5.5 0.5 REG4 4.7 4.2 6.5 5.1 1.2 5.4 0.7 5.3 0.4 REG5 2.5 2.6 2.3 2.5 0.2 3.7 0.2 3.6 0.3 REG6 2.4 1.9 2.4 2.3 0.3 4.0 0.3 4.1 0.5 REG7 3.0 3.8 3.4 3.4 0.4 5.0 0.4 4.3 0.8 REG8 HOD ref. 3.9 4.8 3.2 3.8 5.8 4.3 1.0 4.1 0.2 3.9 0.6 REG9 2.1 3.0 1.5 2.2 0.7 1.6 0.3 1.4 0.0 REG10 1.2 1.3 1.3 1.3 0.1 1.9 0.4 1.9 0.2

The THC results for the additional reference stations, Gyda, Valhall and Yme Gamma, are shown in Table 4.1.4. The THC concentrations are at the same level as the regional stations, and vary from 2.7 mg/kg to 4.3 mg/kg. Table 4.1.4 Additional reference stations, total hydrocarbon content (mg/kg dry sediment). Station Grab #1 Grab #2 Grab #3 Grab #4 Grab #5 Mean SD Mean SD

2005 2005 2002 2002 GYDA ref. 2.9 4.8 2.6 6.5 3.3 4.2 1.6 3.8 0.8 VAL ref. 3.8 3.8 4.9 4.7 4.1 4.3 0.5 4.8 0.5 YMEG ref. 3.0 2.7 3.3 2.7 1.9 2.7 0.5 1.8 0.3

Figure 4.1.1 shows the THC concentrations in 1999, 2002 and 2005 as a bar diagram, including LSC (see Table 4.1.3 for details).

Regionale, THC 2005

0

1

2

3

4

5

6

7

8

9

10

Reg1 Reg2 Reg3 Reg4 Reg5 Reg6 Reg7 Reg8 Reg9 Reg10

station

mg/kg

199920022005LSC BLSC A

B

A

Figure 4.1.1 Bar diagram of the THC content in the sediments at the Regional stations 1999 – 2005.

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NPD, PAH and decalins The results are shown in Table 4.1.5. Included are also results from previous surveys.

The NPD, PAH and decalin levels are low at all the regional stations. NPD is only found in some of the grab samples (REG4, REG7 and REG8). The mean NPD concentrations vary from below 0.01 mg/kg to 0.02 mg/kg (REG8). The mean PAH concentrations vary from 0.018 mg/kg (REG10) to 0.062 mg/kg (REG7). The PAH levels are similar to the levels found in the previous surveys. Small amounts of decalins are detected in some of the grab samples (REG3 and REG8). Table 4.1.5 Regional stations, sum NPD. PAH and decalins (mg/kg dry sediment).

Station Grab #1

Grab #2

Grab #3

Grab #4

Grab #5

Mean SD Mean SD Mean SD Mean

2005 2005 2002 2002 1999 1999 1996NPD REG1 ULA Ref. nd nd nd nd nd nd 0.022 0.004 0.022 0.01 0.012REG2 nd nd nd nd 0.015 0.006 0.008 0.001 REG3 EKO Ref. nd nd nd nd nd nd 0.021 0.004 0.010 0.001 0.026REG4 0.01 0.01 0.021 0.01 0.008 0.025 0.004 0.016 0.002 REG5 nd nd nd nd 0.019 0.004 0.016 0.004 REG6 nd nd nd nd 0.026 0.01 0.012 0.001 REG7 0.012 0.01 0.01 0.01 0.002 0.020 0.003 0.012 0.004 REG8 HOD Ref. 0.031 0.01 0.014 0.011 0.015 0.02 0.01 0.019 0.003 0.013 0.002 0.020REG9 nd nd nd nd 0.019 0.02 0.004 0.001 REG10 nd nd nd nd 0.008 0.002 0.005 0.001 PAH REG1 ULA Ref. 0.024 0.031 0.031 0.032 0.027 0.029 0.003 0.041 0.006 0.034 0.004 0.054REG2 0.033 0.026 0.029 0.030 0.004 0.042 0.010 0.023 0.002 REG3 EKO Ref. 0.045 0.038 0.043 0.031 0.036 0.039 0.005 0.048 0.006 0.035 0.006 0.045REG4 0.036 0.061 0.074 0.057 0.019 0.056 0.006 0.041 0.006 REG5 0.046 0.056 0.046 0.049 0.006 0.052 0.005 0.051 0.015 REG6 0.051 0.058 0.048 0.052 0.005 0.057 0.010 0.047 0.002 REG7 0.083 0.051 0.052 0.062 0.018 0.051 0.007 0.043 0.010 REG8 HOD Ref. 0.052 0.046 0.041 0.041 0.054 0.047 0.006 0.046 0.007 0.038 0.006 0.081REG9 0.020 0.015 0.021 0.019 0.003 0.018 0.002 0.016 0.001 REG10 0.017 0.017 0.020 0.018 0.002 0.018 0.004 0.018 0.002 Decalins* REG3 EKO Ref. 0.028 0.23 0.24 0.038 0.006 0.11 0.12 nd nd nd REG8 HOD Ref. 0.76 0.011 0.27 0.077 0.082 0.24 0.3 nd nd nd *:Decalins are not detected for the other regional stations (<0.1 mg/kg). Limit of detection: NPD 0.01 mg/kg, PAH 0.005 mg/kg, decalins 0.1 mg/kg.

The result of the analyses of NPD, PAH and decalins for the additional reference stations Gyda, Valhall and Yme Gamma are shown in Table 4.1.6. The concentrations are at the same level as the regional stations. NPD concentrations range from less than 0.01 mg/kg to 0.037 mg/kg, and the PAH concentrations range from 0.013 mg/kg to 0.051 mg/kg. Small amounts of decalins are detected in some of the grab samples. None of the stations are considered contaminated by NPD, PAH or decalins.

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Table 4.1.6. Additional reference stations, sum NPD. PAH and decalins (mg/kg dry sediment).

Station Grab #1

Grab #2

Grab #3

Grab #4

Grab #5

Mean SD Mean SD

2005 2005 2002 2002 NPD GYDA ref. 0.003 0.125 0.052 0.004 0.001 0.037 0.054 0.013 0.001 VAL ref. 0.007 0.027 0.004 0.003 0.024 0.013 0.011 0.015 0.003 YMEG ref. nd nd nd nd nd nd 0.006 0.001 PAH GYDA ref. 0.027 0.036 0.038 0.031 0.028 0.032 0.005 0.035 0.003 VAL ref. 0.044 0.050 0.040 0.039 0.081 0.051 0.017 0.035 0.005 YMEG ref. 0.020 0.013 0.012 0.010 0.009 0.013 0.004 0.011 0.003 Decalins GYDA ref. 0.002 0.010 1.79 0.071 0.010 0.38 0.79 nd VAL ref. 0.063 0.67 0.019 0.004 0.099 0.17 0.28 nd YMEG ref. 0.34 nd nd nd nd <0.3 nd Limit of detection: NPD 0.01 mg/kg, PAH 0.005 mg/kg, decalins 0.3 mg/kg.

Metals The results are shown in Table 4.1.7. In Table 4.1.8 the mean values are compared with data from the previous surveys in 2002, 1999 and 1996. Bar diagram of the Ba content in the sediments is shown in Figure 4.1.2.

In 1999 the Ba concentrations ranged from 5 mg/kg (REG10) to 67 mg/kg (REG4). In 2002 the Ba concentrations ranged from 7 mg/kg (REG10) to 72 mg/kg (REG3).

In the present survey the concentration of Ba was low at all stations, and varied from 4 mg/kg (REG10) to 72 mg/kg (REG4). The concentrations are similar to the previous surveys. None of the stations are considered contaminated by Ba.

The concentrations of the heavy metals are also low and similar to the level in 2002. As in 2002 the highest Cr and Zn concentrations are found at REG10. Cd and Hg concentrations are close to the detection limit.

The metal results for the additional reference stations for Gyda, Valhall and Yme Gamma are shown in Table 4.1.8. The Ba concentrations at GYDA and VAL are at the same level as the majority of the regional stations, 36 mg/kg and 28 mg/kg respectively. At YMEG the Ba concentration is low, 10 mg/kg, and similar to REG9 and REG10. The following variations are found at Regional stations in the top layer, 0-1 cm. The values are given in mg/kg:

Regional: REG1 – REG10 Ba: 4.1 – 72 Cr: 5.8 – 9.1 Cu: ≤0.05 Pb: 4.0 – 7.2 Zn: 3.1 – 6.8 Cd: <0.01 – 0.2 Hg: <0.01

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Table 4.1.7. Regional stations, metals (mg/kg dry sediment). Station Sample Ba Cd Cr Cu Hg Pb Zn 2005 2005 2005 2005 2005 2005 2005 REG1 1 37 <0.01 6.9 0.5 <0.01 6.2 5.4 ULA Ref. 2 34 <0.01 6.9 <0.5 <0.01 5.9 5.6

3 19 <0.01 6.8 <0.5 <0.01 5.7 5.0 4 29 <0.01 6.8 <0.5 <0.01 5.6 5.1 5 54 <0.01 7.6 <0.5 <0.01 7.7 6.2 mean 35 <0.01 7.0 <0.5 <0.01 6.2 5.4 SD 13 0.3 0.9 0.5

REG2 1 18 <0.01 7.1 <0.5 0.01 4.6 5.9 2 18 <0.01 6.9 <0.5 0.01 4.7 4.3 3 17 <0.01 6.7 <0.5 0.01 4.9 4.5 mean 18 <0.01 6.9 <0.5 0.01 4.7 4.9 SD 1 0.2 0.0 0.1 0.9

REG3 1 52 <0.01 7.7 <0.5 <0.01 6.6 5.6 ECO Ref. 2 77 <0.01 8.0 0.5 <0.01 6.3 5.8

3 37 <0.01 7.5 <0.5 <0.01 6.4 5.0 4 36 <0.01 7.4 <0.5 <0.01 5.5 5.6 5 29 <0.01 7.4 <0.5 <0.01 5.7 4.9 mean 46 <0.01 7.6 <0.5 <0.01 6.1 5.4 SD 19 0.3 0.5 0.4

REG4 1 32 <0.01 6.8 <0.5 <0.01 6.9 5.0 2 66 0.29 2.2 <0.5 <0.01 7.5 5.7 3 117 0.30 7.5 0.5 <0.01 7.1 6.6 mean 72 0.20 7.1 <0.5 <0.01 7.2 5.7 SD 43 0.17 0.3 0.3 0.8

REG5 1 30 0.3 6.7 0.5 <0.01 6.0 6.1 2 42 0.3 7.3 <0.5 <0.01 7.8 6.6 3 32 <0.01 7.4 <0.5 <0.01 6.5 6.1 mean 35 0.20 7.1 <0.5 <0.01 6.7 6.3

SD 7 0.17 0.4 1.0 0.3

REG6 1 33 <0.01 7.9 0.5 <0.01 6.5 6.5 2 30 <0.01 7.2 <0.5 <0.01 5.9 5.8 3 30 <0.01 7.5 <0.5 <0.01 5.9 5.9 Mean 31 <0.01 7.5 <0.5 <0.01 6.1 6.0 SD 2 0.3 0.3 0.4

REG7 1 88 <0.01 8.5 <0.5 <0.01 6.8 7.0 2 38 <0.01 7.7 <0.5 <0.01 6.0 5.9 3 40 <0.01 8.4 <0.5 <0.01 7.4 6.3 Mean 55 <0.01 8.2 <0.5 <0.01 6.8 6.4 SD 28 0.4 0.7 0.6

REG8 1 40 <0.01 7.3 <0.5 <0.01 5.9 6.1 HOD Ref 2 31 <0.01 6.9 <0.5 <0.01 5.9 6.3

3 27 <0.01 7.1 <0.5 <0.01 5.6 5.8 4 33 <0.01 7.3 <0.5 <0.01 5.8 5.8 5 30 <0.01 7.2 <0.5 <0.01 5.6 5.7 Mean 32 <0.01 7.1 <0.5 <0.01 5.8 5.9 SD 5 0.2 0.1 0.3

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Table 4.1.7. cont. Station Sample Ba Cd Cr Cu Hg Pb Zn 2005 2005 2005 2005 2005 2005 2005 REG9 1 5 <0.01 5.8 <0.5 <0.01 3.9 3.3

2 6 <0.01 5.7 <0.5 <0.01 4.0 3.0 3 7 <0.01 5.9 <0.5 <0.01 4.0 3.0 Mean 6 <0.01 5.8 <0.5 <0.01 4.0 3.1 SD 1 0.1 0.1 0.1

REG10 1 5 <0.01 9.1 <0.5 <0.01 5.9 6.8 2 4 <0.01 9.0 <0.5 <0.01 5.0 6.7

3 4 <0.01 9.0 <0.5 <0.01 5.2 6.9 Mean 4 <0.01 9.1 <0.5 <0.01 5.4 6.8 SD 1 0.1 0.5 0.1

Table 4.1.8..Regional stations, metals (mg/kg dry sediment), comparing with earlier surveys. Station Ba Ba Ba Ba Cd Cd Cd Cr Cr Cr 2005 2002 1999 1996 2005 2002 1999 2005 2002 1999 REG1 ULA Ref 35 29 33 52 <0.01 <0.02 <0.02 7.0 6.9 6.9 REG2 18 18 13 23 <0.01 <0.01 <0.02 6.9 6.3 6.1 REG3 EKO Ref 46 72 41 68 <0.01 <0.01 <0.02 7.6 7.7 7.1 REG4 72 67 67 102 0.2 <0.01 <0.03 7.1 6.7 7.5 REG5 35 35 28 42 0.2 <0.01 <0.01 7.1 6.5 6.2 REG6 31 27 31 35 <0.01 <0.01 <0.02 7.5 7.3 7.0 REG7 55 48 31 58 <0.01 <0.01 <0.02 8.2 7.4 7.4 REG8 HOD Ref 32 45 31 51 <0.01 <0.04 <0.02 7.1 6.9 6.6 REG9 6 8 6 <0.01 <0.01 <0.02 5.8 5.8 5.8 REG10 4 7 5 <0.01 <0.01 <0.02 9.1 9.1 9.2

Table 4.1.8. cont. Station Cu Cu Cu Hg Hg Hg Pb Pb Pb Zn Zn Zn 2005 2002 1999 2005 2002 1999 2005 2002 1999 2005 2002 1999REG1 ULA Ref <0.5 1.3 0.6 <0.01 <0.01 <0.01 6.2 6.1 7.3 5.4 6.2 5.6 REG2 <0.5 0.8 0.4 <0.01 <0.01 <0.01 4.7 4.6 4.5 4.9 4.9 3.6 REG3 EKO Ref <0.5 1.0 0.8 <0.01 <0.01 <0.01 6.1 6.3 5.8 5.4 5.6 4.7 REG4 <0.5 1.0 0.6 <0.01 <0.01 0.02 7.2 6.9 7.2 5.7 5.9 6.7 REG5 <0.5 1.0 0.5 <0.01 <0.01 0.02 6.7 6.8 6.8 6.3 7.4 5.3 REG6 <0.5 1.2 0.6 <0.01 <0.01 0.02 6.1 6.1 6.9 6.0 6.0 5.9 REG7 <0.5 1.1 0.5 <0.01 <0.01 0.02 6.8 7.0 7.3 6.4 6.4 5.4 REG8 HOD Ref <0.5 1.0 0.4 <0.01 <0.01 <0.01 5.8 6.1 6.3 5.9 6.0 5.3 REG9 <0.5 0.9 <0.3 <0.01 <0.01 <0.02 4.0 3.7 3.9 3.1 3.5 2.7 REG10 <0.5 1.0 0.5 <0.01 <0.01 <0.01 5.4 6.0 6.4 6.8 8.2 6.7

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Table 4.1.9. Additional reference stations, metals (mg/kg dry sediment). Station Sample Ba Cd Cr Cu Hg Pb Zn 2005 2002 2005 2002 2005 2002 2005 2002 2005 2002 2005 2002 2005 2002GYDA 1 52 <0.01 7.2 <0.5 <0.01 6.2 5.2 Ref. 2 25 <0.01 6.8 <0.5 <0.01 5.3 4.6 3 35 <0.01 7.2 <0.5 <0.01 6.0 5.4 4 25 <0.01 6.9 <0.5 <0.01 5.4 4.7 5 43 <0.01 6.9 <0.5 <0.01 6.2 4.5 Mean 36 40 <0.01 0.01 7.0 6.7 <0.5 1.3 <0.01 0.01 5.8 5.8 4.9 5.7 SD 12 9 0.00 0.2 0.3 0.3 0.00 0.4 0.3 0.4 1.3 VAL 1 25 <0.01 7.6 <0.5 <0.01 6.4 6.6 5.6 Ref. 2 27 <0.01 7.7 <0.5 <0.01 6.0 6.6 5.6 3 26 <0.01 7.0 <0.5 <0.01 7.6 7.9 5.8 4 35 <0.01 7.6 <0.5 <0.01 6.1 6.6 5.7 5 27 <0.01 7.7 <0.5 <0.01 6.6 6.1 5.5 Mean 28 35 <0.01 <0.01 7.7 7.7 <0.5 1.2 <0.01 0.01 6.5 6.8 5.6 6.3 SD 4 10 0.1 0.2 0.7 0.00 0.6 0.7 0.1 0.4 YMEG 1 18 <0.01 6.9 <0.5 <0.01 7.2 6.2 7.3 Ref. 2 7 <0.01 7.6 <0.5 <0.01 8.2 6.7 7.8 3 7 <0.01 6.9 <0.5 <0.01 7.4 5.6 7.6 4 13 <0.01 7.8 <0.5 <0.01 8.7 10.8 7.4 5 5 <0.01 7.2 <0.5 <0.01 7.2 5.9 7.3 Mean 10 6 <0.01 <0.01 7.3 6.9 <0.5 0.8 <0.01 <0.01 7.7 7.5 7.0 7.5 SD 5 1 0.4 0.2 0.1 0.7 0.2 2.1 0.2

Figure 4.1.2 shows the Barium concentrations in 1999, 2002 and 2005 as a bar diagram, including LSC (see 4.1.3 for details).

Regionale, Ba 2005

0

10

20

30

40

50

60

70

80

90

100

Reg1 Reg2 Reg3 Reg4 Reg5 Reg6 Reg7 Reg8 Reg9 Reg10

station

mg/kg

199920022005LSC BLSC A

A

B

Figure 4.1.2. Bar diagram of the Ba content in the sediments at the Regional stations 1999 – 2005.

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4.1.3 Limit of contamination (LSC)

For the content of THC, NPD, PAH and metals in the sediments LSC (Limit of Significant Contamination) has been calculated.

PCA As a basis for treatment of Region I in possible subregions a PCA analysis (Principal Component Analysis) has been performed by use of THC, NPD, PAH, Ba, Cr, Cu, Pb and Zn data at the Regional and reference stations from the surveys in 1996, 1999, 2002 and 2005. The analyses are based on the mean values of each parameter from the present survey and from the period 1996-2005, see Table 4.1.10 and

Table 4.1.11. To give equal weight to the different parameters, the mean value and standard deviation are calculated for each parameter, and the concentrations (mean value) are divided with the standard deviation. Table 4.1.10. Regional and reference stations, chemical parameters Region I 2005. Basis for PCA, (mean values: mg/kg dry sediment).

THC THC/ NPD NPD/ PAH PAH/ Ba Ba/ Cr Cr/ Cu Cu/ Pb Pb/ Zn Zn/ SD SD SD SD SD SD SD SD

REG1 ULA 3.9 3.0 0.003 0.3 0.029 1.8 35 1.8 7.0 8.8 0.3 3.0 6.2 6.2 5.4 4.9 REG2 2.5 1.9 0.004 0.4 0.030 1.9 18 0.9 6.9 8.6 0.2 2.0 4.7 4.7 4.9 4.5 REG3 EKO

5.8 4.5 0.006

0.6 0.039

2.4 46 2.4 7.6 9.5 0.3 3.0 6.1 6.1 5.4 4.9

REG4 5.1 3.9 0.013 1.3 0.057 3.6 72 3.7 7.1 8.9 0.3 3.0 7.2 7.2 5.7 5.2 REG5 2.5 1.9 0.006 0.6 0.049 3.1 35 1.8 7.1 8.9 0.4 4.0 6.7 6.7 6.3 5.7 REG6 2.3 1.8 0.005 0.5 0.052 3.2 31 1.6 7.5 9.4 0.4 4.0 6.1 6.1 6 5.5 REG7 3.4 2.6 0.010 1.0 0.062 3.9 55 2.8 8.2 10.3 0.3 3.0 6.8 6.8 6.4 5.8 REG8 HOD

4.3 3.3 0.016

1.6 0.047

2.9 32 1.6 7.1 8.9 0.2 2.0 5.9 5.9 5.9 5.4

REG9 2.2 1.7 0.002 0.2 0.019 1.2 6 0.3 5.8 7.3 0.1 1.0 4 4.0 3.1 2.8 REG10 1.3 1.0 0.0001 0.01 0.018 1.1 4 0.2 9.1 11.4 0.1 1.0 5.4 5.4 6.8 6.2 GYDA 4.2 3.2 0.037 3.8 0.032 2.0 36 1.9 7 8.8 0.2 2.0 5.8 5.8 5.7 5.2 VAL 4.3 3.3 0.013 1.3 0.051 3.2 28 1.4 7.7 9.6 0.1 1.0 6.8 6.8 6.3 5.7 YMEG 2.7 2.1 0.002 0.2 0.013 0.8 10 0.5 7.3 9.1 0.1 1.0 7.5 7.5 7.5 6.8 Mean 3.4 0.009 0.038 31 7.3 0.2 6.1 5.8 SD 1.3 0.010 0.016 19 0.8 0.1 1.0 1.1

Table 4.1.11. Regional and reference stations, chemical parameters Region I 1996-2005. Basis for PCA (mean values: mg/kg dry sediment).

THC THC/ NPD NPD/ PAH PAH/ Ba Ba/ Cr Cr/ Cu Cu/ Pb Pb/ Zn Zn/ SD SD SD SD SD SD SD SD

REG1 ULA

3.9 3.0 0.015 3.2 0.039 2.9 39 1.9 6.9 8.7 0.7 6.8 6.7 5.5 5.8 5.3

REG2 3.0 2.3 0.009 2.0 0.032 2.4 18 0.8 6.4 8.0 0.5 5.0 4.6 3.9 4.0 3.6REG3 EKO

5.9 4.5 0.016 3.4 0.042 3.1 56 2.7 7.5 9.3 0.7 6.8 6.1 5.1 4.7 4.2

REG4 5.6 4.3 0.019 4.1 0.051 3.8 77 3.6 7.1 8.9 0.7 6.8 7.2 6.0 5.9 5.3REG5 4.2 3.2 0.015 3.2 0.051 3.8 35 1.7 6.5 8.1 0.6 6.3 6.9 5.8 5.9 5.3REG6 4.3 3.3 0.016 3.3 0.052 3.9 31 1.5 7.2 9.0 0.6 6.3 6.4 5.3 5.5 5.0REG7 4.2 3.3 0.015 3.1 0.051 3.8 48 2.3 7.6 9.5 0.5 5.3 7.0 5.9 5.7 5.1REG8 HOD

4.4 3.4 0.018 3.8 0.053 3.9 39 1.8 6.9 8.6 0.6 5.8 6.1 5.1 5.2 4.7

Cont.

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Table 4.1.11. cont. THC THC/ NPD NPD/ PAH PAH/ Ba Ba/ Cr Cr/ Cu Cu/ Pb Pb/ Zn Zn/ SD SD SD SD SD SD SD SD

REG9 1.7 1.3 0.010 2.0 0.018 1.3 7 0.3 5.8 7.3 0.5 4.8 3.9 3.2 3.1 2.8REG10 1.8 1.3 0.005 1.1 0.018 1.3 6 0.3 9.2 11.5 0.6 6.3 6.0 5.0 7.3 6.7GYDA 4.4 3.3 0.021 4.4 0.040 3.0 46 2.2 6.9 8.7 0.7 6.5 6.0 5.0 5.6 5.1VAL 5.0 3.8 0.018 3.9 0.046 3.4 44 2.1 7.9 9.8 0.6 6.3 7.2 6.0 5.6 5.0YMEG 2.9 2.3 0.008 1.7 0.020 1.5 7 0.3 8.1 10.1 0.6 5.5 8.5 7.1 6.8 6.1Mean 3.9 0.014 0.039 35 7.2 0.6 6.4 5.4 SD 1.3 0.005 0.013 21 0.8 0.1 1.2 1.1

The results of the PCA analyses are given in Figure 4.1.3 (2005 data) and Figure 4.1.4 (1996-2005 data). The figures (top) show that the stations can be divided into three groups. These are Yme and Regional 10 in one group, Regional 2 and Regional 9 in a second group and a third main group with the remaining nine stations. In Figure 4.1.4 which includes data from 1996-2002, the stations within each group are closer than in Figure 4.1.3 with the 2005 data, however the essential features are the same.

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-4

-3

-2

-1

0

1

2

3

4

-5 -4 -3 -2 -1 0 1 2 3 4 5

PC2

PC1

PCA Scores 2005 data

Reg 1 UlaReg 2 Reg 3 Eko Reg 4

Reg 5Reg 6Reg 7

Reg 8 Hod

Reg 9

Reg 10

Gyda

Valhall

Yme

-0,20

-0,10

0,00

0,10

0,20

0,30

0,40

0,50

0,60

0,00 0,10 0,20 0,30 0,40

PC

2

PC1

PCA Loadings 2005 data

THC

NPDPAH

Ba

Cr

Cu

Pb

Zn

Figure 4.1.3 Results of the PCA analysis of the mean values 2005 of each chemical parameter at the Regional stations and reference stations at Region I.

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-4

-3

-2

-1

0

1

2

3

4

-6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6

PC

2

PC1

PCA Scores 1996-2005 data

Reg 1 Ula

Reg 2

Reg 3 EkofReg 4Reg 5Reg 6Reg 7

Reg 8 Hod

Reg 9

Reg 10

Gyda

Valhall

Yme

-0,20

-0,10

0,00

0,10

0,20

0,30

0,40

0,50

0,60

0,00 0,10 0,20 0,30 0,40

PC

2

PC1

PCA Loadings 1996-2005 data

THC

NPDPAH

Ba

Cr

Cu

Pb

Zn

Figure 4.1.4 Results of the PCA analysis of the mean values 1996-2005 of each chemical parameter at the Regional stations and reference stations at Region I.

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The figures (Figure 4.1.3 and Figure 4.1.4) also show that the parameters THC, Ba, PAH and NPD are situated in the same area, which means that it is a good correlation between these parameters. On the other hand, neither Cr nor Cu or Zn or Pb seems to have any relation to Ba and THC. These observations are in agreement with the results obtained from environmental surveys offshore through many years.

Subregions identified:

Subregion A: Regional 1, Regional 3, Regional 4, Regional 5, Regional 6, Regional 7, Regional 8, Gyda ref. and Valhall ref.

Subregion B: Regional 10 and Yme ref. Subregion C: Regional 2 and Regional 9.

LSC The PCA results are taken into account in the LSC assessments. Subregions A and B are used further. Subregion C is not representative for any of the fields, and is thus omitted from the LSC calculations.

It is important, however, to realise that the different parameters are given equal weight in the PCA analyses. But for the contamination of the fields caused by the drill cuttings discharges, THC and Ba are far more important than the heavy metals. Looking at the concentrations of THC, NPD, PAH and Ba, Regional 9 and Regional 10 are very similar. Thus, it seems reasonable to classify Regional 9 in Subregion B together with Regional 10 and Yme. Nevertheless we have chosen to use the Subregions A and B as given by the PCA analysis. In fact calculations including Regional 9 in Subregion B resulted in only small differences in the LSC values.

The LSC calculations are based on data from the period 1996 - 2005. The calculation is performed with 95 % confidence level. For each parameter the mean value for each year (1996, 1999, 2002 and 2005) is used, and a new mean value and standard deviation are calculated. The formula used is given in Section 3.3.3. The results are shown in Table 4.1.12.

For Cu the LSC value of 1.3 mg/kg is not relevant. This low value results from the fact that the Cu concentrations at the Regional and reference stations are just above the detection limit and thus very similar. Thus the standard deviation is also low, and so is the LSC value. Cu concentrations around 1.0 mg/kg are not considered to be elevated. Table 4.1.12 LSC values Region I 2005 (mg/kg dry sediment). 95 % confidence level, one-tailed t-test. Parameter Subregion A Subregion B (Yme fields)

Mean SD LSC Mean SD LSC THC 4.6 1.1 6.6 2.4 0.9 4.6 Ba 44.9 17.5 76.2 6.4 2.3 12.1 Cr 7.2 0.5 8.0 8.3 1.1 11.1 Cu 0.7 0.3 1.3 0.6 0.3 1.4 Pb 6.5 0.5 7.4 6.6 1.0 9.0 Zn 5.8 0.6 6.9 7.2 0.6 8.8 NPD 0.016 0.008 0.030 0.004 0.003 0.012 PAH 0.045 0.009 0.061 0.016 0.003 0.024

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4.1.4 Biological analyses

A total of 186 species and 11734 individuals were sampled at 10 stations. Greatest abundance (68.6 %) was found among the polychaetes, of which the species Myriochele oculata constitutes 52.5 % and Paramphinome jeffreysii constitutes about 19.1 % of the total number of Polychaeta, see Table 4.1.13. Table 4.1.13. Number of species and individuals distributed between the main groups, Regional stations 2005.

Individuals Species Main animal groups Number % Number %

Varia 418 3.6 19 10.2Polychaeta 8044 68.6 84 45.2- Paramphinome jeffreysii 1533 19.1 - Myriochele oculata 4226 52.5 Crustacea 277 2.4 29 15.6Mollusca 1120 9.5 40 21.5Echinodermata 1875 16.0 14 7.5- Amphiura filiformis 1337 71.3 Total 11734 100.0 186 100.0

Figure 4.1.5 shows the numbers of species and individuals sampled at each station and variations between grab samples.

020406080

100

Reg-01

Reg-02

Reg-03

Reg-04

Reg-05

Reg-06

Reg-07

Reg-08

Reg-09

Reg-10

Stations

No.

of s

peci

es (S

)

0

500

1000

1500

2000

2500

Reg-01

Reg-02

Reg-03

Reg-04

Reg-05

Reg-06

Reg-07

Reg-08

Reg-09

Reg-10

Stations

No.

of i

ndiv

idua

ls (N

)

Ex. P. jeffreysii

0500

1000150020002500

Reg-01

Reg-02

Reg-03

Reg-04

Reg-05

Reg-06

Reg-07

Reg-08

Reg-09

Reg-10

Stations

No.

of i

ndiv

idua

ls (N

)

Ex. P. jeffreysii and M. oculata

0500

1000150020002500

Reg-01

Reg-02

Reg-03

Reg-04

Reg-05

Reg-06

Reg-07

Reg-08

Reg-09

Reg-10

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No.

of i

ndiv

idua

ls (N

)

Figure 4.1.5. Numbers of species (S) and individuals (N) per 0.5 m2 (incl./excl. P. jeffreysii and M. oculata), mean values per grab sample and standard deviation, Regional stations 2005.

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The standard deviation was in general dramatically reduced when the two species P. jeffreysii and M. oculata were removed. This is evident since the two species constitute 49.1 % of the total number of individuals.

Diversity and dominant species

The dominant species varied from 11.7 % at REG-10 to 58.7 % at REG-6. The 10 most abundant species made up from 57.2 % at REG-10 to 89.7 % at REG-6, see Table 4.1.14. The bristle worms M. oculata and P. jeffreysii together with the brittle star Amphiura filiformis were in general dominating species in the Ekofisk region. Other frequently found species were amongst other the bristle worms Chaetozone setosa, Scoloplos armiger and Goniada spp. (mainly G. maculata) together with the Crustacean Harpinia antennaria and the mussel Mysella bidentata and Abra prismatica. M. oculata, A. filiformis, Mysella bidentata and A. prismatica are suspension feeders while C. setosa and S. armiger are characterized as both suspension- and deposit feeeding (Word 1978, 1980a &1980b) P. jeffreysii and Goniada species are mainly carnivore species, often feeding on larva. According to Ernst & Dietrich (2006) the Harpinia family is composed of mobile diggers and they feed on organic matter. They are generally scavengers, but can sometimes act as deposit feeders. The Harpinia family is sensitive to oil spills. M. bidentata is a very small (ca 3 mm) bivalve. Ockelmann & Muus (1978) reported a significant association between M. bidentata and A. filiformis. The bivalve lives in the oxidized layers around the brittle star's burrow. Several of these species, and in particular the most numerous species, have a planktotrophic larval development stage (Eckert 2003), and are able to settle in large numbers. Most of these species are known indicators of organic pollution when they are found in high numbers. Simboura & Zenetos (2002) have described almost all of the populations of species mentioned above, according to ecological quality. Most of these populations, may respond to disturbances, in particular organic enrichment, with an increase in density. Table 4.1.14. The 10 most abundant species, Regional stations 2005 (excl. juv.).

10 most dominating species Reg-01 No. % Cum. % Reg-02 No. % Cum. % Myriochele oculata 210 22.3 22.3 Myriochele oculata 1140 45.7 45.7 Mysella bidentata 128 13.6 35.8 Paramphinome jeffreysii 347 13.9 59.6 Amphiura filiformis 105 11.1 46.9 Amphiura filiformis 235 9.4 69.0 Paramphinome jeffreysii 84 8.9 55.8 Echinoidea spp.juv. 210 8.4 77.4 Chaetozone setosa 48 5.1 60.9 Mysella bidentata 105 4.2 81.6 Levinsenia gracilis 32 3.4 64.3 Scoloplos armiger 55 2.2 83.9 Scoloplos armiger 25 2.7 67.0 Spiophanes bombyx 36 1.4 85.3 Abra prismatica 22 2.3 69.3 Goniada spp. 30 1.2 86.5 Phoronis muelleri 17 1.8 71.1 Abra prismatica 26 1.0 87.5 Spiophanes wigleyi 17 1.8 72.9 Ophelia borealis 24 1.0 88.5 Cont.

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Table 4.1.14. cont. 10 most dominating species

Reg-03 No. % Cum. % Reg-04 No. % Cum. % Myriochele oculata 851 46.1 46.1 Myriochele oculata 240 25.9 25.9 Echinoidea spp.juv. 205 11.1 57.1 Paramphinome jeffreysii 207 22.3 48.2 Amphiura filiformis 154 8.3 65.5 Amphiura filiformis 123 13.3 61.4 Paramphinome jeffreysii 113 6.1 71.6 Scoloplos armiger 54 5.8 67.2 Scoloplos armiger 50 2.7 74.3 Chaetozone setosa 29 3.1 70.4 Goniada spp. 38 2.1 76.4 Phoronis muelleri 24 2.6 73.0 Spiophanes bombyx 36 2.0 78.3 Corymorpha nutans 23 2.5 75.4 Abra prismatica 35 1.9 80.2 Echinoidea spp.juv. 20 2.2 77.6 Chaetozone setosa 34 1.8 82.0 Goniada spp. 19 2.1 79.6 Eudorellopsis deformis 32 1.7 83.8 Caudofoveata spp. 18 1.9 81.6 Reg-05 No. % Cum. % Reg-06 No. % Cum. % Paramphinome jeffreysii 121 16.2 16.2 Myriochele oculata 1330 58.7 58.7 Amphiura filiformis 115 15.4 31.6 Paramphinome jeffreysii 278 12.3 71.0 Ditrupa arietina 71 9.5 41.1 Amphiura filiformis 154 6.8 77.8 Myriochele oculata 55 7.4 48.5 Levinsenia gracilis 78 3.4 81.2 Mysella bidentata 53 7.1 55.6 Spiophanes bombyx 47 2.1 83.3 Goniada spp. 23 3.1 58.6 Aonides paucibranchiata 39 1.7 85.0 Eudorellopsis deformis 20 2.7 61.3 Chaetozone setosa 34 1.5 86.5 Harpinia antennaria 17 2.3 63.6 Goniada spp. 24 1.1 87.6 Nephtys longosetosa 16 2.1 65.7 Prionospio cirrifera 24 1.1 88.7 Antalis entale 14 1.9 67.6 Apistobranchus tullbergi 23 1.0 89.7 Reg-07 No. % Cum. % Reg-08 No. % Cum. % Paramphinome jeffreysii 208 24.1 24.1 Amphiura filiformis 180 34.0 34.0 Myriochele oculata 180 20.9 45.0 Myriochele oculata 85 16.1 50.1 Amphiura filiformis 151 17.5 62.5 Paramphinome jeffreysii 59 11.2 61.3 Montacuta substriata 36 4.2 66.7 Sthenelais limicola 22 4.2 65.4 Goniada spp. 26 3.0 69.7 Harpinia antennaria 21 4.0 69.4 Scoloplos armiger 24 2.8 72.5 Eudorellopsis deformis 17 3.2 72.6 Mysella bidentata 18 2.1 74.6 Goniada spp. 17 3.2 75.8 Levinsenia gracilis 18 2.1 76.7 Scoloplos armiger 13 2.5 78.3 Caudofoveata spp. 13 1.5 78.2 Chaetozone setosa 13 2.5 80.7 Montacuta tenella 12 1.4 79.6 Nephtys longosetosa 12 2.3 83.0 Reg-09 No. % Cum. % Reg-10 No. % Cum. % Myriochele oculata 125 16.1 16.1 Edwardsia sp. 40 11.7 11.7 Paramphinome jeffreysii 99 12.8 28.9 Antalis entale 28 8.2 19.9 Amphiura filiformis 92 11.9 40.8 Amphiura filiformis 28 8.2 28.2 Mysella bidentata 65 8.4 49.2 Nephtys longosetosa 18 5.3 33.4 Abra prismatica 53 6.8 56.0 Paramphinome jeffreysii 17 5.0 38.4 Goniada spp. 38 4.9 60.9 Scoloplos armiger 16 4.7 43.1 Spiophanes bombyx 35 4.5 65.4 Spiophanes kroyeri 14 4.1 47.2 Chaetozone setosa 27 3.5 68.9 Spiophanes bombyx 14 4.1 51.3 Aonides paucibranchiata 27 3.5 72.4 Myriochele oculata 10 2.9 54.3 Scoloplos armiger 26 3.4 75.7 Echinoidea spp.juv. 10 2.9 57.2

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The number of species varied from 53 at REG-8 to 82 at REG-1. The number of individuals varied from 327 at REG-10 to > 2250 at REG-2 and REG-6. The Shannon Wiener diversity index varied from 2.9 at REG-2 to 5.1 at REG-10 and the Hurlberts index (ES100) varied from 17 (REG-6) to 38 at REG-10 including M. oculata. Removal of M. oculata from the data gave indices above 4 except for station REG-02, -07 and -08 and the ES100 indices ranged from 25 to 39.

Indices above 4 indicate a relative undisturbed fauna. Indices between 3 and 4 indicate a slight disturbance, while indices between 2 and 3 indicate a disturbance in the fauna. In general ES100 indices above 20 characterize a relatively normal fauna community.

The indices at several of these stations indicate a slightly disturbed fauna, especially in the areas around station REG-02, -03 and -06 which are located in the central part of the Ekofisk region, see Figure 4.1.5. However, the levels of THC and metals in the sediments were low. The regional stations are located far from all fields and should not be influenced by any field activities. Table 4.1.15. Numbers of individuals (N) and species (S), depth, Shannon-Wiener diversity index (H’), Pielou’s evenness index (J), and expected number of species per 100 individuals (ES100) for each station at Regional stations 2005 (excl. juv.).

H' ES100 Station Direction ° Distance m Depth S N Incl.

M. o. Excl. M. o.

J Incl. M. o.

Excl. M. o.

Reg-01 315 6000 73 82 944 4.4 4.7 0.7 30 33.3Reg-02 68 73 2278 2.9 3.9 0.5 18 24.7Reg-03 90 15000 70 75 1635 3.2 4.4 0.5 22 29.6Reg-04 72 59 908 3.7 4.0 0.6 23 26.1Reg-05 72 77 744 4.7 4.7 0.7 33 33.4Reg-06 70 72 2265 2.7 4.0 0.4 17 26.6Reg-07 73 66 862 3.9 3.9 0.6 25 27.4Reg-08 180 15000 70 53 527 3.7 3.6 0.6 23 25.0Reg-09 69 64 773 4.4 4.5 0.7 27 28.2Reg-10 87 67 327 5.1 5.1 0.8 38 39.2

M. o.= M. oculata

Classification and ordination The dendrogram from the cluster analysis and the MDS plot from the ordination analysis based on station level are presented in Figure 4.1.6 and Figure 4.1.7. REG-10 separates at about 45 % similarity from the rest of the regional stations. REG-10 differs from the other stations mainly because of a smaller number of individuals of the most common species. The remaining regional stations separate into three main groups at a ~55 % similarity:

- Group 1: REG-05 and -08 - Group 2: REG-01, -07 and -09 - Group 3: REG-02, -03, -04 and -06

The distribution of the regional stations in groups reflects to a lesser degree the geographical distribution. However, the stations REG-02, -03 and -06 (from group 2), which also differed with somewhat lower biodiversity indices, are situated in the central part of the region. The species that contribute the most to the differences between the groups are significantly higher numbers of the bristle worm M. oculata, somewhat higher numbers of the bristle worm P. jeffreysii and the brittle star A. filiformis together with high numbers of juvenile echinoidea in group 3. These stations also have reduced biodiversity indices. Compared to the other groups, group 1 differs with higher numbers of the bristle worm Ditrupa arietina and the crustacean H. antennaria.

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Group 2 have a relatively higher number of the mussel M. bidentata in the fauna. The fauna community at all stations where in a high degree dominated by suspension feeders which indicate organic material in suspension.

REG-10 differs from the other stations with somewhat larger depth and slightly coarser sediment than the other stations. The other regional stations have about the same depth. PCA of the chemical data (see Figure 4.1.3) showed that REG-02 and REG-09 were not representative for the region, i.e. the two stations differed significantly from the other regional stations. This is not the case in the biological analyses.

The Bioenv analysis reveals a correlation of 0.7 between the fauna and the grain size, which reflects that the stations are placed in different parts of the region with varying sediment structure.

The distribution of the most common species in the area is not a main function of geographical distribution. The similarity analysis and the biodiversity indices indicate that the fauna at stations belonging to group 3, which are located in the central part of the region, are somewhat influenced. However, the influence can not be directly connected to the activities in the area. According to McGlade (2002) both offshore and land-based activities have a significant effect on the North Sea.

R eg-

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80

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40

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Group 1 Group 2 Group 3 Figure 4.1.6. Dendrogram of Regional stations 2005 (excl. juv.).

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Reg-01

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Reg-04

Reg-05

Reg-06

Reg-07

Reg-08

Reg-09Reg-10

Stress: 0,09

Gruppe 1

Gruppe 2

Gruppe 3

Figure 4.1.7. MDS plot of Regional stations 2005 (excl. juv.).

Comparison with 1996, 1999, 2002 and 2005 In Figure 4.1.8 the results from the present study are compared to the results from previous surveys. The numbers of species and individuals include the bristle worms M. oculata and P. jeffreysii for all the years. The numbers of species vary somewhat, but are at approximately the same level as in 2002. The numbers of individuals have decreased significantly, in particular at REG-3 but also at REG-04 since last survey. At REG-02 and -06 there have been a small increase in the numbers of M. oculata. At the other stations the numbers are slightly decreasing or unaltered since last survey. In general the biodiversity indices reveal an increase since last survey indicating a continuous improvement in the fauna1.

020406080

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)

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0

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ndiv

idua

ls (N

)

1996 1999 2002 2005

Figure 4.1.8. Numbers of species (S) and individuals (N) per 0.5 m2 and diversity (H’) (incl.P. jeffreysii and M. oculata, excl. juv.) Regional stations 1996, 1999, 2002 and 2005.

1 The great variations in the presence of M. oculata from 1996 to 2005 have complicated the faunal picture, making

it difficult to draw conclusions about the state of the fauna community. Adding the 2005 results to the trend data have, however, strengthened the data set, and has made it possible to obtain a pattern in the overall temporal variations in the entire region, see Chapter 5.2 - General Trends in the Region.

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0123456

Reg-01

Reg-02

Reg-03

Reg-04

Reg-05

Reg-06

Reg-07

Reg-08

Reg-09

Reg-10

Stations

H'

1996 1999 2002 2005

Figure 4.1.8. cont. Classification and ordination analyses

The stations from all the years have been analysed at family level∗. The dendrogram (Figure 4.1.9) from the cluster analysis reveals that REG-10 (all years) differs somewhat from the other stations which divide into two main groups at about 60 % similarity:

Group 1 - Stations sampled in 1996 Group 2 - stations sampled in 1999 – 2005

Group 2 differ from REG-10 and group 1 with significantly higher numbers of species from the families Owenidae (mainly M. oculata), Amphinomidae (mainly P. jeffreysii) and Amphiuridae (mainly A. filiformis).

The stations in group 1 have higher numbers of Cirratulidae (mainly C. setosa) than group 2 and station REG-10. The analyses indicate a disturbed fauna community at stations in group 2, but also the stations in group 1 have a structure in the fauna indicating disturbances. The somewhat disturbed fauna is presumably due to several factors; the high energy environment and the general organic enrichment of the central parts of the North Sea and the activities in this area for over 30 years. Organic enrichment gives the chance for opportunistic species to flourish. However, the bristle worm C. setosa which dominated the fauna in 1996 is a stronger indicator of organic load and disturbances than M. oculata, which flourished in the region to a peak in 2002 (but have in general decreased somewhat in 2005). M. oculata is known as a transition species between polluted and healthy environment and this pattern could reflect an environment in general continuous improvement.

The same main pattern of classification is seen when excluding M. oculata from the data. However, when analyzing without M. oculata group 2 could be further subdivided into 3 subgroups based on years. The stations in group 2 (incl. M. oculata) also divides into 3 subgroups, but not entirely based on year:

∗ Necessary when comparing between years, to avoid significant source of error due to both different years and

different taxonomists.

0123456

Reg-01

Reg-02

Reg-03

Reg-04

Reg-05

Reg-06

Reg-07

Reg-08

Reg-09

Reg-10

Stations

H'

1996 1999 2002 2005Excl. M. oculata

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Group 2:

- Subgroup a: REG-1 (1999), REG-5 (1999), REG-6 (1999), REG-7 (1999), REG-8 (1999), REG- 9 (1999, 2002)

- Subgroup b: REG-2 (1999, 2002, 2005), REG-3 (1999, 2002, 2005), REG-4 (1999, 2002), REG-6 (2002, 2005), REG-8 (2002)

- Subgroup c: REG-1 (2002, 2005), REG-4 (2005), REG-5 (2002, 2005), REG-7 (2002, 2005), REG-8 (2005), REG-9 (2005)

REG-2 and -3 (1999, 2002, 2005) and station REG-6 (2002, 2005) form subgroup b, indicating small changes in the fauna community and at the same high disturbance level at these stations since 1999 and 2002. REG-4 (2005) in subgroup c differs from REG-4 sampled in 1999 and 2002 (subgroup b). Station REG-8 is included in all 3 subgroups in different years, from a (1999) via b (2002) to c (2005). The changes at stations REG-4 and -8 indicate positive changes in the fauna community at these stations since 2002.

REG-1, -5 and -7 (2002, 2005) cluster together with REG-9 (05) in subgroup c. REG-1, -5 and -7 (1999) and REG-9 (1999, 2002) are included in subgroup a. The results indicate minor changes at stations REG-1, -5 and -7 and changes in the fauna at station REG-9 since 2002. However, shift from subgroup a to c does not indicate any increased disturbance of the fauna.

The similarity analysis indicates a positive trend with reduced disturbance in the fauna community at REG-4 and -8 since 2002. At REG-2, -3 and –6 there have not been any improvement or reduced disturbance in the fauna community since 1999. At the other regional stations there have been some changes since 1999 and 2002, but the changes are not related to increased disturbance of the fauna community.

Reg-

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Group 1 (1996) Group 2 (1999 - 2005)

2a 2b 2c

Figure 4.1.9. Dendrogram showing similarity between Regional stations 1996, 1999, 2002 and 2005. Family level, incl. M. oculata, excl. juv., sq. root transformation.

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The Bioenv analysis gave some correlation (0.4) between the fauna and the combination of the environmental factors THC, Ba, Zn, pelite and TOM. This indicates that there is only a weak relationship between the environmental factors and the changes in the fauna in the period 1996 to 2005. Furthermore the Bioenv analysis on the group 2 data (1999 – 2005) gave a higher correlation (0.5) between the fauna and the environment complex THC, Ba, Zn and TOM, indicating a slight relationship. The correlation factor between environmental factors and fauna when excluding M. oculata from the data was slightly higher, but not significant.

To analyse the data more thorough a PCA analyses (in BRODGAR) for the data (1999 – 2005) with environmental variables and the most common species superimposed was performed. The result is presented below in Figure 4.1.10.

The fauna at REG- 01, -05, -07 and -09 are slightly disturbed, but are increasingly influenced by Amphinomidae (mainly P. jeffreysii) and Apistobranchidae (mainly A. tullbergi) over the years. The fauna at station REG-02, -03, -04 and -06 are more disturbed, and in 2002 they contained large numbers of Oweniidae (mainly M. oculata). Oweniidae are to an increasing degree being replaced by Amphiuridae (mainly A. filiformis), Amphinomidae (mainly P. jeffreysii) and Apistobranchidae (mainly A. tullbergi) in 2005. The fauna at station 10 is not disturbed and have no dominating species. There is no obvious correlation between the dominating families and the chemical parameters, although the analysis indicates a connection between THC and Oweniidae.

Reg0199

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Reg1005 THC

BaCuPb

Zn

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Am phinom idae

Am phiuridae

ApistobranchidaeLasaeidae

Leuconidae

Ow eniidae

axis 1-1 0 1

axis

2

-1

0

1

Figure 4.1.10. PCA plot showing the distribution of the regional stations (1999 – 2005) with regards to species composition. Environmental variables and selected families are superimposed on the plot. The first two digits give the station number, and the last two digits specify the year.

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4.1.5 Conclusions

The sediments at the Regional stations consist mainly of fine sand, and the sand contents vary from 95 % to 99 %. The gravel contents are low, and only small amounts are found at four of the stations. The silt and clay contents are in general similar to previous observations. The total organic matter contents in the sediments are low and only small variations are found at the Regional stations, from 0.7 % to 1.1 %. The contents correspond to the grain size distribution with low pelite contents. The results are similar to the previous surveys in 2002, 1999 and 1996.

The concentrations of hydrocarbons, barium and heavy metals are low, and the sediments are not contaminated. The THC concentrations in the sediments vary from 1.3 mg/kg to 5.8 mg/kg. The NPD concentrations vary from below 0.01 mg/kg to 0.02 mg/kg, and the PAH concentrations vary from 0.013 mg/kg to 0.051 mg/kg. Small amount of decalins are detected in some of the grab samples. The concentrations of Ba vary from 4 mg/kg to 72 mg/kg. The concentrations of the heavy metals are similar to previous surveys. Three subregions are identified from Region I:

- Subregion A: Regional 1, Regional 3, Regional 4, Regional 5, Regional 6, Regional 7, Regional 8, Gyda ref. and Valhall ref.

- Subregion B: Regional 10 and Yme ref. - Subregion C: Regional 2 and Regional 9. For Subregion A and for Subregion B a limit of contamination value (LSC) is calculated for each parameter. Subregion C is not representative for any of the fields, and thus no LSC is calculated. The calculated LSC values are: Parameter Subregion A Subregion B*

LSC mg/kg LSC mg/kg THC 6.6 4.6 Ba 76.2 12.1 Cr 8.0 11.1 Cu 1.3 1.4 Pb 7.4 9.0 Zn 6.9 8.8 NPD 0.030 0.012 PAH 0.061 0.024 * Yme fields

The similarity analysis and the biodiversity indices indicate that the fauna at stations REG-02, -03, -04 and -06, located in the central part of the region, are somewhat disturbed.

The trend analysis indicates that the fauna community at REG-10 has been unaltered since at least 1999. At Reg-04 and -08, which are located south in the Valhall and Hod area, the fauna is improving, indicating a higher ecological quality in this area than earlier. The fauna at REG-2, -3 and -6 is still somewhat disturbed and there are signs of reduced ecological quality. There are, however, indications of improvements since the previous surveys. At the other regional stations there have been changes in the fauna community over the years, but the changes can not be related to increased disturbances of the fauna.

The high abundance of M. oculata which had a peak in 2002 seems to some extent to have been replaced by Amphiuridae (mainly A. filiformis), Amphinomidae (mainly P. jeffreysii) and Apistobranchidae (mainly A. tullbergi) in 2005, indicating a general positive trend in some areas.

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The results reflect that the Ekofisk region is exposed to some general temporal and geographical changes. The great variations in the presence of M. oculata from 1996 to 2005 have complicated the faunal picture, making it difficult to draw conclusions about the state of the fauna community. Adding the 2005 results to the trend data have, however, strengthened the data set, and has made it possible to obtain a pattern in the overall temporal variations in the entire region (see General Trends in the Region).

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4.2 Valhall Stations VAL9, 10 and -23 from the the sampling programme had to be relocated slightly because of interference with subsea cables/pipelines. The new stations are located somewhat more than 50 m from the planned sampling stations, and are therefore renamed; VAL109, -110 and -123 respectively. The three stations are, however, considered not to deviate significantly from the originally planned stations, and the results are compared with historical data from the old stations.

4.2.1 Sediment characterization

Grain size distribution The grain size distribution from the present survey is given in Table 4.2.1 together with the silt and clay content from the previous surveys in 2002, 1999 and 1996.

The sediments at Valhall consist mainly of fine sand, and the sand content varies from 85 % at VAL21, 344°/500m, to 98 % at VAL reference station, 254°/15000m. The maximum gravel content found is 4 % at VAL8, 164°/500 m. Gravel is only found at four of the stations. The silt and clay content is similar or somewhat higher than previously observed. The average silt and clay concentration found is 8.7 % and the average medium particle diameter is 2.78φ.

At the VAL reference station, 254°/15000m, the sediment is characterized as fine sand with 98 % sand and a median particle diameter of 2.63φ. The silt and clay content is somewhat lower compared to previous surveys. The results from the complete grain size distribution are given in Appendix C. Table 4.2.1. Valhall 2005, grain size distribution. Station Median

diameterClassification Grain size distrib. 2005

(%) 2002 (%)

1999 (%)

1996 (%)

Mdφ Silt and clay

Sand Gravel Silt and clay

Silt and clay

Silt and clay

VAL2 74°/500m 2.78 Fine sand 7.5 92.5 0.0 VAL3 74°/1000m 2.74 Fine sand 6.0 93.5 0.5 5.8 VAL8 164°/500m 2.75 Fine sand 7.7 88.1 4.2 7.6 VAL109 160°/1000m 2.76 Fine sand 6.0 93.9 0.1 5.8* 4,1* 4,7* VAL15 254°/500m 2.80 Fine sand 9.9 90.1 0.0 VAL21 344°/500m 2.82 Fine sand 14.9 85.1 0.0 6.1 VAL ref. 254°/15000m 2.63 Fine sand 1.6 98.3 0.1 4.2 3.2 4.7 Mean (excl. ref. station) 2.78 Fine sand 8.7 90.5 0.80 Standard deviation 0.03 3.4 3.4 1.7 *: VAL-9 (164°/1000m)

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Total organic matter (TOM) The TOM results are shown in Table 4.2.2. The content of TOM in the sediments is low and only small variations are found at the field. The minimum content, 0.8 %, is found at VAL reference station, 254°/15000m, and the maximum content, 1.5 %, is found at VAL15, 254°/500m. Only small variations are found compared to the previous surveys in 2002, 1999 and 1996. The content corresponds to the grain size distribution. Table 4.2.2. Valhall 2005, total organic matter (% of dry sediment). Station 2005, 0-5 cm Mean

2002 SD

2002 Mean1999

Mean 1996

VAL2 74°/500 m 1.04 VAL3 74°/1000 m 0.97 1.01 0.07 VAL8 164°/500 m 1.13 1.20 0.14 0.41 0.87 VAL109 160°/1000 m 0.89 0.94* 0.04 0.90* 1.09* VAL15 254°/500 m 1.52 VAL21 344°/500 m 0.95 0.89 0.08 VAL ref. 254°/15000 m 0.82 0.72 0.03 *: VAL-9 (164°/1000m)

4.2.2 Chemical analyses

Parameters analysed in the sediments at Valhall:

• THC • NPD, PAH, decalins • PFOS (perfluorooctyl sulphonate) • Metals (Ba, Cd, Cr, Cu, Hg, Pb, Zn)

Three replicate samples at each station and five replicate samples at the reference station are analysed. The samples are taken from the top 0-1 cm sediment layer. In addition the 1-3 cm and 3- 6 cm sediment layers are sampled at two stations and the reference station.

This year’s survey included some additional sampling stations closer to the installation than in 2002.

THC The THC results are shown in Table 4.2.3. The corresponding THC data from the previous surveys in 2002, 1999 and 1996 are also included for comparison. Bar diagram of the THC content in the sediments is shown in Figure 4.2.1. Two new stations at 500m distance is included in the present survey, VAL2, 74°/500m and VAL15, 254°/500m.

In 1999 the THC concentrations in the top 0-1 cm layer ranged from 5.1 mg/kg at VAL reference station, 254°/15000m to 65 mg/kg at VAL9, 60°/1000m. Olefins were not detected in any of the samples. In 2002 the THC in the top 0-1 cm layer ranged from 4.8 mg/kg (VAL Ref.) to 274 mg/kg (VAL8, 164°/500m). Olefins were found in the sediments at VAL8. The gas chromatograms clearly showed peaks similar to Novaplus olefins, C16H32/C18H36. These findings were in agreement with the discharge of 1570 tonnes of olefin based mud attached to cuttings during the second half of 1996.

In the present survey the THC concentrations in the top 0-1 cm layer vary from 4.3 mg/kg at VAL reference station to 130 mg/kg at VAL2. VAL2 was not analysed in 2002. The concentration of THC has decreased distinctly at all stations since last survey in 2002. Relative high concentrations of THC are found for VAL8 and VAL15 at 500m distance from the platform,

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about 75 mg/kg. Generally the concentration of THC is higher in the deeper layers. The maximum concentration found is 726 mg/kg in the 1-3 cm at VAL8. The concentration in the 3-6 cm layer is 83 mg/kg. The concentrations found in the deeper samples at VAL109 are 40-50 mg/kg.

All the stations except for VAL16, 254°/2000m and the reference station have elevated THC levels, some stations just slightly elevated. The VAL reference station is still uncontaminated, and the mean THC concentration of five replicate samples is 4.3 mg/kg.

Small amounts of olefins are also found in the sediments at VAL8 (164°/500m), as can be seen from the gas chromatograms.

Representative gas chromatograms are given in Appendix C. These include VHAL2 (74°/500m), VHAL8 (164°/500m), VHAL109 (160°/1000m), VHAL15 (254°/500m), VHAL 16* (254°/1000m), VHAL16 (254°/2000m) and VHAL reference station (254°/15000m). Table 4.2.3. Valhall 2005, total hydrocarbon content (mg/kg dry sediment). Station Grab

#1 Grab

#2 Grab

#3 Grab

#4 Grab

#5 Mean SD Mean Mean Mean

2005 2005 2002 1999 1996 VAL2 74°/500m 130 172 88 130 42 VAL3 74°/1000m 15.4 24.4 23.3 21 5 61 VAL4 74°/2000m 9.1 8.6 8.0 8.5 0.5 12.7 10.8 14.9 VAL8 164°/500m 102 72 60 78 22 274

1-3 cm 726 313 3-6 cm 83 396

VAL109 160°/1000m 15.6 13.7 11.3 13.5 2.2 271 651 421 1-3 cm 41 711 801 511 3-6 cm 49 741 491 11.41

VAL110 160°/2000m 6.5 6.5 7.5 6.8 0.5 12.82 11.02 13.22 VAL15 254°/500m 106 18.4 99 75 49 VAL16* 254°/1000m 7.2 6.8 9.7 7.9 1.6 16.5 34 137 VAL16 254°/2000m 5.8 4.8 6.1 5.6 0.7 7.9 10.2 VAL21 344°/500m 7.3 6.8 9.9 8.0 1.6 17.2 VAL22 344°/1000m 7.3 8.1 8.5 8.0 0.6 12.1 14.9 22 VAL123 340°/2000m 7.7 8.3 6.3 7.4 1.0 8.23 8.23 8.73 VAL ref. 254°/15000m 3.8 3.8 4.9 4.7 4.1 4.3 0.5 4.8 5.1 6.1

1-3 cm 8.6 5.6 6.4 3.7 3-6 cm 6.8 6.9 7.2 5.5

LSC, Subregion A 6.6 6.4 9 1: VAL-9 (164°/1000m) 2: VAL-10 (164°/2000m) 3: VAL-23 (344°/2000m)

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Valhall, THC 2005

0

20

40

60

80

100

120

140

VHAL2

VHAL3

VHAL4

VHAL8

VHAL109

*

VHAL110

*

VHAL15

VHAL16*

VHAL16

VHAL21

VHAL22

VHAL23

VHALref

station

mg/kg

1999

2002

2005

LSC A

274±35,

Figure 4.2.1. Bar diagram of the THC content in the sediments at Valhall, 1999-2005.

NPD, PAH and decalins Two stations are analysed in addition to the reference station, VAL8, 164°/500m and VAL109, 160°/1000m. Also included for analysis are station VAL2, 74°/500m and VAL15, 254°/500m, as these stations have a THC content >50 mg/kg. The results are shown in Table 4.2.4. In 1999 elevated levels of NPD, PAH and decalins were found at VAL9. In 2002 elevated levels of NPD, PAH and decalins were found at VAL8 and VAL9, also in the deeper sections. The decalin concentrations were high at VAL8 in the top layer and in the deeper layers. The maximum concentration was found in the 3-6 cm layer, 12.4 mg/kg.

In the present survey elevated levels of NPD, PAH and decalins are found at VAL2, VAL8 and VAL15 and for VAL8 also in the vertical layers. The content of NPD varies from 0.4 to 0.6 mg/kg, of PAH from 0.1 to 0.2 mg/kg and of decalins from 0.8 to 2.7 mg/kg. Highest concentration of NPD is found at VAL8 in the 1-3 cm layer (2.9 mg/kg). High concentrations of decalins are also found in the vertical layers of VAL8 with respectively 11.1 mg/kg in the 1-3 cm layer and 6.8 mg/kg in the 3-6 cm layer. The content of decalins has, however, decreased significantly in the top layer.

At VAL109 the content of NPD, PAH and decalins has decreased since last survey to about the level of significant contamination. The distribution of NPD, PAH and decalins are relatively patchy, particularly at VAL15. The same trend is observed for THC. Elevated levels are not found at the reference station.

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Table 4.2.4. Valhall 2005, sum NPD, PAH and decalins (mg/kg dry sediment). Historical data shown as VAL109 are from VAL9 (164°/1000m).

Station Grab #1

Grab #2

Grab #3

Grab #4

Grab #5

Mean SD Mean SD Mean SD Mean

2005 2005 2002 2002 1999 1999 1996NPD VAL2 74°/500m 0.45 0.54 0.17 0.39 0.19 VAL8 164°/500m 0.53 0.15 1.09 0.59 0.48 0.78 0.054 - 1-3 cm 2.89 1.11 - 3-6 cm 1.90 1.15 - VAL109 160°/1000m 0.06 0.03 0.04 0.04 0.01 0.084 0.026 0.084 0.024 0.078 1-3 cm 0.13 0.12 0.11 0.14 3-6 cm 0.08 0.19 0.090 0.054VAL15 254°/500m 0.66 0.040 3.02 1.24 1.6 VAL Ref 254°/15000m 0.007 0.027 0.004 0.003 0.024 0.01 0.01 0.015 0.003 0.015 0.001 0.028 1-3 cm 0.018 0.018 0.020 0.054 3-6 cm 0.016 0.026 0.026 0.051LSC Subregion A 0.030 0.026 0.040 PAH VAL2 74°/500m 0.096 0.125 0.064 0.095 0.03 VAL8 164°/500m 0.16 0.095 0.117 0.13 0.034 0.17 0.039 1-3 cm 0.15 0.16 3-6 cm 0.20 0.21 VAL109 160°/1000m 0.077 0.052 0.056 0.062 0.013 0.11 0.065 0.080 0.020 0.074 1-3 cm 0.12 0.095 0.16 0.096 3-6 cm 0.17 0.12 0.17 0.12VAL15 254°/500m 0.19 0.031 0.42 0.21 0.20 VAL Ref 254°/15000m 0.044 0.050 0.040 0.039 0.081 0.051 0.017 0.035 0.005 0.048 0.004 0.049 1-3 cm 0.057 0.046 0.063 0.059 3-6 cm 0.067 0.074 0.085 0.085LSC Subregion A 0.061 0.062 0.090 Decalins VAL2 74°/500m 0.48 5.9 1.6 2.7 2.9 VAL8 164°/500m 1.6 0.29 0.54 0.80 0.7 7.9 1.8 1-3 cm 11.1 7.4 3-6 cm 6.8 12.4 VAL109 160°/1000m nd nd nd nd 0.28 0.2 0.78 0.85 0.48 1-3 cm 0.31 0.89 2.04 1.31 3-6 cm 0.14 1.42 1.32 0.19VAL15 254°/500m 3.0 0.29 0.33 1.22 1.6 VAL Ref 254°/15000m 0.063 0.67 0.019 0.004 0.1 0.17 0.3 nd nd 0.055 1-3 cm 0.26 nd nd 0.12 3-6 cm nd nd nd 0.056nd: not detected. Limit of detection for NPD is 0.01 mg/kg, for PAH 0.005 mg/kg and for decalins 0.1 mg/kg.

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PFOS (perfluorooctyl sulphonate)

One station is analysed, VAL8, 164°/500m. The result is shown in Table 4.2.5. The PFOS content at VAL8 was 1.25 µg/kg. Some acute discharges of PFOS occurred because of release failure on tanks during a few years after start-up at Valhall. The estimates of previous discharges are quite uncertain. Table 4.2.5. Valhall 2005, PFOS (perfluorooctyl sulphonate), µg/kg dry sediment. Station PFOS VAL8 74°/500m 1.32 1.05 1.38 Mean 1.25 SD 0.14 Limit of detection: 0.1 µg/kg

Metals

The results are shown in Table 4.2.6. For comparison the mean values from the present survey together with the data from previous survey in 2002 and 1999 are shown in

Table 4.2.7. Hg was only determined for some of the stations. Bar diagram of the Ba content in the sediments is shown in Figure 4.2.2.

In 1999 the Ba concentrations ranged from 47 mg/kg at VAL reference station, (254°/15000m) to 2160 mg/kg at VAL9, (164°/1000m) and in 2002 ranged from 35 mg/kg at VAL reference station to 5120 mg/kg at VAL8 (164°/500m).

Elevated Ba concentrations are found at all stations, except for the reference station. Thus elevated levels of Ba are found out to 1000m in the 74° and 160° direction and out to 500m in the 254° and 344° directions. In general the Ba levels are similar to previous measured levels. High Ba concentrations are also found in the deeper sections at VAL8 and VAL9.

The highest concentrations of the heavy metals are found at VAL2 (74°/500m), and elevated concentrations are observed. Slightly elevated concentrations are also found at the other stations. The levels are similar or slightly lower than previous surveys.

The following variations are found at Valhall in the top layer, 0-1 cm. The values are given in mg/kg: Valhall: VAL2 – VAL21 VAL Ref. station Ba: 653 – 5587 28 Cr: 7.8 – 10.5 7.7 Cu: <0.5 – 9.6 <0.5 Pb: 9.9 – 19.1 6.5 Zn: 7.8 – 32.5 5.6 Cd: <0.01 – 0.03 <0.01 Hg: <0.01 – 0.02 <0.01

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Table 4.2.6. Valhall 2005, metals (mg/kg dry sediment). Station Sample Ba Cd Cr Cu Hg Pb Zn 2005 2005 2005 2005 2005 2005 2005 VAL2 74°/500m 1 5410 0.03 10.3 10.2 19.0 34.5 2 6336 0.03 11.5 10.7 21.7 37.3 3 5015 0.02 9.3 8.0 16.6 25.7 mean 5587 0.03 10.4 9.6 19.1 32.5 SD 678 1.1 1.4 2.5 6.0 VAL3 74°/1000m 1 1779 <0.01 8.4 1.3 10.4 10.0 2 1133 <0.01 7.8 1.3 10.2 8.8 3 2268 <0.01 8.3 1.7 10.5 10.9 mean 1727 <0.01 8.2 1.4 10.3 9.9 SD 569 0.3 0.2 0.1 1.1 VAL8 164°/500m 1 4091 0.02 8.2 3.9 0.02 10.7 14.5 2 4015 0.01 7.3 3.2 0.01 10.4 11.8 3 3910 0.01 8.0 4.6 0.01 10.9 14.9 mean 4005 0.01 7.8 3.9 0.02 10.7 13.7 SD 91 0.5 0.7 0.00 0.2 1.7 1-3 cm 1 5077 0.12 8.6 3.7 0.02 21.2 29.6 3-6 cm 1 4583 0.07 9.2 2.8 0.02 17.1 24.4 VAL109 160°/1000m 1 1883 <0.01 8.1 1.2 0.01 9.1 8.1 2 1082 <0.01 9.0 <0.5 <0.01 15.2 8.0 3 1154 <0.01 7.2 <0.5 <0.01 9.0 7.3 mean 1373 <0.01 8.1 <0.5 <0.01 11.1 7.8 SD 443 0.9 3.6 0.5 1-3 cm 1 2787 0.02 8.9 1.4 0.02 12.0 11.2 3-6 cm 1 1346 0.02 9.6 1.4 0.01 12.2 11.1 VAL15 254°/500m 1 3627 0.05 13.7 4.1 17.7 28.0 2 2007 0.01 8.2 1.5 9.8 9.7 3 2498 0.01 9.6 2.3 12.3 14.8 mean 2711 0.03 10.5 2.6 13.3 17.5 SD 831 0.02 2.8 1.3 4.1 9.5 VAL21 344°/500m 1 694 <0.01 8.1 1.3 9.0 7.6 2 616 0.02 9.8 1.1 11.0 10.3 3 650 <0.01 8.2 1.2 9.7 8.0 mean 653 <0.01 8.7 1.2 9.9 8.7 SD 39 1.0 0.1 1.0 1.4 VAL ref. 254°/15000m 1 25 <0.01 7.6 <0.5 <0.01 6.4 5.6 2 27 <0.01 7.7 <0.5 <0.01 6.0 5.6 3 26 <0.01 7.0 <0.5 <0.01 7.6 5.8 4 35 <0.01 7.6 <0.5 <0.01 6.1 5.7 5 27 <0.01 7.7 <0.5 <0.01 6.6 5.5 mean 28 <0.01 7.7 <0.5 <0.01 6.5 5.6 SD 4 0.1 0.6 0.1 LSC Subregion A 76.2 8.0 1.3 7.4 6.9

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Valhall, Ba 2005

0

1000

2000

3000

4000

5000

6000

VHAL2 VHAL3 VHAL8 VHAL109* VHAL15 VHAL21 VHALref

station

mg/kg

1999

2002

2005

LSC A

Figure 4.2.2. Bar diagram of the Ba content in the sediments at Valhall 1999- 2005. Table 4.2.7. Valhall 2005, metals (mg/kg dry sediment), comparing mean values with previous surveys. Historical data shown as VAL109 are from VAL9 (164°/1000m). Station Ba Cd Cr 2005 2002 1999 2005 2002 1999 2005 2002 1999 VAL2 74°/500m 5587 0.03 10.4 VAL3 74°/1000m 1727 2120 <0.01 0.02 8.2 7.6 VAL8 164°/500m 4005 5120 0.01 0.08 7.8 8.5 1-3 cm 5077 5266 0.12 0.16 8.6 8.6 3-6 cm 4583 1041 0.07 0.05 9.2 9.0 VAL109 160°/1000m 1373 1060 2160 <0.01 0.01 <0.02 8.1 6.5 7.8 1-3 cm 2787 1548 1910 0.02 0.02 <0.02 8.9 6.4 8.0 3-6 cm 1346 2164 989 0.02 0.02 0.02 9.6 7.4 9.6 VAL15 254°/500m 2711 0.03 10.5 VAL21 344°/500m 653 840 <0.01 0.01 8.7 7.5 VAL ref. 254°/15000m 28 35 47 <0.01 <0.01 <0.02 7.7 7.7 8.1 cont.

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Table 4.2.7. cont. Cu Hg Pb Zn 2005 2002 1999 2005 2002 1999 2005 2002 1999 2005 2002 1999VAL2 74°/500m 9.6 19.1 32.5 VAL3 74°/1000m 1.4 2.9 10.3 11.8 9.9 12.3 VAL8 164°/500m 3.9 7.8 0.02 0.03 10.7 19.5 13.7 31.8 1-3 cm 3.7 6.4 0.02 0.03 21.2 23.5 29.6 36.5 3-6 cm 2.8 2.6 0.02 0.02 17.1 11.1 24.4 18.7 VAL109 160°/1000m <0.5 1.8 1.2 <0.01 0.01 0.02 11.1 8.4 10.8 7.8 9.0 8.7 1-3 cm 1.4 3.2 1.1 0.02 0.02 0.02 12.0 8.7 11.3 11.2 6.8 10.0 3-6 cm 1.4 2.2 1.2 0.01 0.02 0.03 12.2 11.0 11.4 11.1 12.7 11.7 VAL15 254°/500m 2.6 13.3 17.5 VAL21 344°/500m 1.2 2.2 9.9 9.4 8.7 10.9 VAL ref. 254°/15000m <0.5 1.2 0.5 <0.01 0.01 0.02 6.5 6.8 8.1 5.6 6.3 6.1

4.2.3 Biological analyses

A total of 141 species and 12142 individuals were sampled at 9 stations. Greatest abundance (82 %) was found among the polychaetes, of which the species Paramphinome jeffreysii constitutes 36.0 % and Myriochele oculata constitutes 32.6 %, see Table 4.2.8. Table 4.2.8. Number of species and individuals distributed between the main groups, Valhall 2005.

Individuals Species Main animal groups Number % Number %

Varia 861 7.1 15 10.6Polychaeta 9958 82.0 57 40.4- Paramphinome jeffreysii 3582 36.0 - Myriochele oculata 3245 32.6 Crustacea 224 1.8 28 19.9Mollusca 539 4.4 31 22.0Echinodermata 560 4.6 10 7.1- Amphiura filiformis 395 70.5 Total 12142 100.0 141 100.0

Figure 4.2.3 shows the numbers of species and individuals sampled at each station and variations between grab samples.

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0

20

40

60

80

100VAL-02VAL-03VAL-08

VAL-109VAL-15VAL-21

VAL-REF

Stations

No.

of s

peci

es (S

)

Station º/m VAL-02 74/500 VAL-03 74/1000 VAL-08 164/500 VAL-109 160/1000

VAL-15 254/500

VAL-21 344/500

VAL-REF 254/15000

0

500

1000

1500

2000

2500

VAL-02VAL-03VAL-08

VAL-109VAL-15VAL-21

VAL-REF

Stations

No.

of i

ndiv

idua

ls (N

) Ex. P. jeffreysii and M. oculata

0500

1000150020002500

VAL-02VAL-03VAL-08

VAL-109VAL-15VAL-21

VAL-REF

Stations

No.

of i

ndiv

idua

ls (N

)

Figure 4.2.3. Numbers of species (S) and individuals (N) per 0.5 m2 (incl./excl. P. jeffreysii and M. oculata), mean values per grab sample and standard deviation, Valhall 2005.

The standard deviation was in general dramatically reduced when the two species P. jeffreysii and M. oculata were removed from the data set. This is evident since the two species constitute 56.2 % of the total number of individuals. An exception was VAL-02, where the standard deviation was slightly increased. This is due to the differences between the five grabs sampled at each station.

Diversity and dominant species

The dominant species varied from 27.3 % at VAL-03 (74°/1000m) to 63.7 % at the reference station (254°/15000m). The 10 most abundant species made up from 79.4 % at VAL-15 (254°/500m) to 88.3 % at the reference station, see Table 4.2.9. The bristle worms P. jeffreysii and M. oculata dominated the fauna at the Valhall field. Other frequently found species were among others the bristle worms Apistobranchus tullbergi, Chaetozone setosa, the brittle star Amphiura filiformis and the ribbon worm Nemertea spp. P. jeffreysii is mainly a carnivore species and the ribbon worm is a deposit feeder. The other mentioned species are either suspension feeders or both suspension- and deposit feeders. Most of these species are known indicators of organic pollution when they are found in large amounts. However several of the above mentioned species have a planktonic developmental stage and are able to settle in large numbers.

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Table 4.2.9. The 10 most abundant species at each station, Valhall 2005. 10 most dominating species

VAL-02 No. % Cum. % VAL-03 No. % Cum. % Paramphinome jeffreysii 567 39.57 39.6 Paramphinome jeffreysii 397 27.27 27.3 Nemertea spp. 157 10.96 50.5 Myriochele oculata 250 17.17 44.4 Chaetozone setosa 157 10.96 61.5 Apistobranchus tullbergi 194 13.32 57.8 Jasmineira caudata 77 5.37 66.9 Chaetozone setosa 122 8.38 66.1 Caudofoveata spp. 57 3.98 70.8 Nemertea spp. 98 6.73 72.9 Myriochele oculata 45 3.14 74.0 Levinsenia gracilis 52 3.57 76.4 Amphiura filiformis 33 2.3 76.27 Scoloplos armiger 36 2.47 78.91 Tharyx sp. 26 1.8 78.1 Jasmineira caudata 26 1.8 80.7 Thyasira c.f. sarsii 23 1.61 79.7 Diplocirrus glaucus 24 1.65 82.4 Trichobranchus roseus 19 1.33 81.0 Tharyx sp. 20 1.37 83.7 VAL-08 No. % Cum. % VAL-109 No. % Cum. % Paramphinome jeffreysii 1023 44.06 44.1 Myriochele oculata 700 36.05 36.1 Myriochele oculata 440 18.95 63.0 Paramphinome jeffreysii 507 26.11 62.2 Chaetozone setosa 99 4.26 67.3 Apistobranchus tullbergi 170 8.75 70.9 Amphiura filiformis 66 2.84 70.1 Nemertea spp. 66 3.4 74.3 Apistobranchus tullbergi 52 2.24 72.4 Echinoidea spp.juv. 42 2.16 76.5 Nemertea spp. 49 2.11 74.5 Amphiura filiformis 42 2.16 78.6 Scoloplos armiger 48 2.07 76.53 Levinsenia gracilis 31 1.6 80.23 Jasmineira caudata 42 1.8 78.3 Ditrupa arietina 27 1.4 81.6 Thyasira c.f. sarsii 35 1.51 79.8 Hemichordata spp. 23 1.18 82.8 Goniada maculata 34 1.46 81.3 Cerianthus lloydii 21 1.08 83.9 VAL-15 No. % Cum. % VAL-21 No. % Cum. % Paramphinome jeffreysii 398 29.7 29.7 Myriochele oculata 645 34.4 34.4 Apistobranchus tullbergi 284 21.19 50.9 Paramphinome jeffreysii 529 28.21 62.6 Nemertea spp. 125 9.33 60.2 Apistobranchus tullbergi 106 5.65 68.3 Levinsenia gracilis 55 4.1 64.3 Amphiura filiformis 77 4.11 72.4 Amphiura filiformis 51 3.81 68.1 Levinsenia gracilis 45 2.4 74.8 Chaetozone setosa 47 3.51 71.6 Chaetozone setosa 44 2.35 77.1 Myriochele oculata 35 2.61 74.25 Nemertea spp. 40 2.13 79.25 Jasmineira caudata 24 1.8 76.0 Scoloplos armiger 33 1.8 81.0 Terebellides stroemi 24 1.79 77.8 Hemichordata spp. 28 1.49 82.5 Thyasira c.f. sarsii 21 1.57 79.4 Cerianthus lloydii 27 1.44 84.0 VAL-REF No. % Cum. % Myriochele oculata 1130 63.7 63.7 Paramphinome jeffreysii 161 9.08 72.8 Amphiura filiformis 110 6.2 79.0 Nemertea spp. 33 1.86 80.8 Chaetozone setosa 33 1.86 82.7 Aonides paucibranchiata 25 1.41 84.1 Harpinia antennaria 22 1.24 85.34 Eudorellopsis deformis 18 1.0 86.4 Apistobranchus tullbergi 18 1.01 87.4 Cerianthus lloydii 17 0.96 88.3

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The number of species varied from 60 at VAL-03 (74°/1000m) to 93 at VAL-08 (164°/500m). The number of individuals varied from 1334 at VAL-15 (254°/500m) to 2300 at VAL-08 (164°/500m). The Shannon Wiener diversity index varied from 2.5 at the reference station (254°/15000m) to 3.8 at VAL-15 and the Hurlberts index (ES100) varied from 18 (reference station) to 24 (VAL-02, 74°/500m) including M. oculata. Removal of M. oculata from the data gave minor changes to the indices in 2005. A main reason is that in general, this species shows a significant decrease in the central part of the Ekofisk region, including Valhall. Indices above 4 indicate a relatively undisturbed fauna. Indices between 3 and 4 indicate a slight disturbance, while indices between 2 and 3 indicate a disturbance in the fauna. In general ES100 indices above 20 characterize a relatively normal fauna community. Some of the indices reflect slight disturbances, see Table 4.2.10.

The biodiversity indices indicate small general disturbances in the fauna community at Valhall. However the fauna at the reference station (254°/15000m) seems to be somewhat more disturbed than at the other stations. The disturbance does not seem to be related to the activity at the field. Table 4.2.10. Numbers of individuals (N) and species (S), depth, Shannon-Wiener diversity index (H’), Pielou’s evenness index (J), and expected number of species per 100 individuals (ES100) for each station at Valhall 2005 (excl. juv.).

H' ES100 Station Direction ° Distance m Depth S N Incl.

M. o. Excl. M. o.

J Incl. M. o.

Excl. M. o.

VAL-02 74 500 74 69 1424 3.6 3.6 0.6 24 23VAL-03 74 1000 74 60 1439 3.7 3.7 0.6 21 23VAL-08 164 500 73 93 2300 3.4 3.4 0.5 23 26VAL-109 160 1000 72 79 1900 3.3 3.8 0.5 21 27VAL-15 254 500 74 66 1334 3.8 3.7 0.6 24 24VAL-21 344 500 75 76 1864 3.4 3.8 0.5 22 27VAL-REF 254 15000 72 63 1771 2.5 4.3 0.4 18 30M. o.= M. oculata

Classification and ordination

The dendrogram from the cluster analysis and the MDS plot from the ordination analysis based on station level are presented in Figure 4.2.4 and Figure 4.2.5. The reference station (254°/15000m) separates from the other stations at Valhall which form a group at about 70 %. The cluster analysis is well supported by the ordination analysis. The reference station also differs with somewhat lower biodiversity indices than the other stations. The similarity analysis reveals that the differences are caused mainly by significantly higher numbers of M. oculata combined with small numbers of P. jeffreysii and A. tullbergi at the reference station. The reference station had slightly coarser sediment and contained low levels of THC and metals in the sediment. The Valhall field stations could be further subdivided into three groups. VAL-02 (74°/500m) and -08 (164°/500m) make up the first group. The second group consists of VAL-109 (160°/1000m) and -21 (344°/500m) and the third group consists of VAL-03 (74°/1000m) and -15 (254°/500m). The similarity analysis shows that the species which contribute the most to the differences among the Valhall field stations were higher numbers of M. oculata at VAL-109 and -21, higher numbers of P. jeffreysii at VAL-02 and -08 and higher numbers of A. tullbergi at VAL-03 and 15. Both M. oculata and P. jeffreysii are known indicator species when appearing in large numbers, while A. tullbergi is characterized as a more sensitive species.

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Photo 1 Granules from the field sampling.

Photo 2 Granules from the sorting process. During sampling there were observed large amounts of yellow granules in the sediment samples from VAL-02, -15 and -21 (Photo 2). The samples from VAL-15 and -21 had a smell of H2S. During the processing of samples in the laboratory the granules were observed at all Valhall stations, also in other colours (Photo 2). Analyses of the granules (Photo 3) showed that they contain 33-34% Al, 34-35% Si, 27-29% O, ca.1,4 % Ti and 1,3-1,7% Fe.

Photo 3 Photo taken of a granule through an electron microcope.

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Oily substances were observed at VAL-02 (Photo 4), -08 and -15, which correponds to the stations with highest concentrations of THC. Of these stations only VAL-08 was analysed in the deeper sediment layers. The observations correspond well with the results from 1-3 cm sediment depth, showing elevated concentrations of THC as well as NPD and decalins.

The Bioenv analysis reveals a correlation of 0.8 between the fauna and the environmental factors THC, Ba1, Cu and average grain size, indicating that the variations in the fauna can be explained by variations in THC, Ba1 and Cu.

The similarity analysis indicates a slight disturbance in the fauna at the stations VAL-02 (74°/500m) and -08 (164°/500m) related to THC and the metals listed above. There were also observed black spots in the sediment during sampling at the two stations. The reference station (254°/15000m) differs with slightly coarser sediment type which also affects the fauna composition.

1 Ba and the other metals are not degradable and will not disappear from the sediments. These metals may

presumable not have any effect on the fauna in itself, but could be regarded as trace elements for other degradable substances.

Photo 4 Valhall sample VAL-02. Photo taken during field sampling.

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VAL-

R EF

VAL-

02

VAL-

0 8

VAL-

109

VAL-

2 1

VAL-

03

VAL-

15

100

90

80

70

60

50Si

mila

rity

Valhall field stations

74/500m 164/500m 160/1000m 344/500m 74/1000m 254/500m254/15000m

Figure 4.2.4. Dendrogram of stations from Valhall 2005 (excl. juv.).

VAL-02

VAL-03

VAL-08

VAL-109

VAL-15

VAL-21

VAL-REF

Stress: 0,01

Valhall field stations74/500m, 164/500m

160/1000m, 344/500m

74/1000m, 254/500m

254/15000m

Figure 4.2.5. MDS plot of stations from Valhall 2005 (excl. juv.).

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Comparison with 1996, 1999, 2002 and 2005

In Figure 4.2.6 the results from the present survey are compared with the results from previous surveys. Data for comparison of VAL-02 and VAL-15 were not available. The number of species and individuals includes the bristle worms M. oculata and P. jeffreysii for all the years. The numbers of species have decreased since earlier surveys at VAL-03 (74°/1000m), -21 (344°/500m) and the reference station (254°/15000m).

At VAL-08 (164°/500m) and -109 (160°/1000m) the number of species has increased. The numbers of individuals have decreased in particular at VAL-109, Val-21, Val-03 and Val-ref and in some lesser degree at Val-08. The biodiversity indices have increased significantly at VAL-03, -09, -21 and at the reference station. At Val-08 the index is almost unaltered since the last survey.

The great variations in the presence of M. oculata from 1996 to 2005 have complicated the faunal picture, making it difficult to draw conclusions about the state of the fauna community. Adding the 2005 results to the trend data has, however, strengthened the data set, and has made it possible to obtain a pattern in the overall temporal variations in the entire region. On the basis of this the full data set, i.e. including M. oculata, has been emphasized when drawing conclusions. Thus we recommend reading Chapter 5.2 - General Trends in the Region which forms a basis for the conclusions for each of the fields.

020406080

100

VAL-02

VAL-03

VAL-08

VAL-109

VAL-15

VAL-21

VAL-Ref

Stations

No.

of s

peci

es (S

)

1996 1999 2002 2005

Station º/m

VAL-02 74/500 VAL-03 74/1000 VAL-08 164/500 VAL-109 160/1000 VAL-15 254/500 VAL-21 344/500 VAL-REF 254/15000

0

1000

2000

3000

4000

5000

VAL-02

VAL-03

VAL-08

VAL-109

VAL-15

VAL-21

VAL-Ref

Stations

No.

of i

ndiv

idua

ls (N

)

1996 1999 2002 2005

012345

VAL-02

VAL-03

VAL-08

VAL-109

VAL-15

VAL-21

VAL-Ref

Stations

H'

1996 19991999-ex. M. oculata 20022002-ex. M. oculata 20052005-ex. M. oculata

Figure 4.2.6. Numbers of species (S) and individuals (N) per 0.5 m2 and diversity (H’), incl.P. jeffreysii and M. oculata, excl. juv), Valhall 1996, 1999, 2002 and 2005. Historical data shown as VAL109 are from VAL9 (164°/1000m).

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Classification and ordination analyses

The sampled stations from all the years have been analysed at family level∗. The dendrogram from the cluster analysis reveals that most of the stations separate into two main groups at about 55 % similarity, based on years. The stations sampled in 2002 and 2005 group together and the stations sampled in 1996 and 1999 group together. The species that contributes the most to the differences were, among others, species within the families Oweniidae (mainly M. oculata), Amphinomidae (mainly P. jeffreysii) and Apistobranchidae (mainly A.tullbergi). These species were found in greater amounts in 2002 and 2005 than in 1996 and 1999. The 2002 and 2005 group could be subdivided further based on sampling years. An exception is the reference station in 2005 which is clustering together with the 2002 stations.

The differences between the subgroups of the 2002 stations (including reference station 2005) and the 2005 stations are mainly due to significant decreases in the numbers of species within the family Oweniidae (mainly M. oculata) and an increase in numbers of species within the families Amphinomidae (mainly P. jeffreysii) and Apistobranchidae (mainly A.tullbergi) from 2002 to 2005.

The Bioenv analysis gave some correlation (0.5) between fauna and the environmental factors Ba, Cu, Pb and pelite indicating some relationship between the environmental factors and the development in the fauna over the years.

VAL-

09-2

005

VAL-

21-2

005

VAL-

03-2

005

VAL-

15-2

005

VAL-

02-2

0 05

VAL-

08-2

0 05

VAL-

08-2

0 02

VAL-

09-2

002

VAL-

03-2

002

VAL-

21-2

002

VAL-

24A-

200 5

V AL-

24A-

2002

VAL-

24B-

2002

VAL-

24A-

1996

VAL-

09-1

996

VAL-

09-1

999

VAL-

24A-

1 999

VAL-

24B-

1999

100

90

80

70

60

50

Sim

ilarit

y

2002 and 2005 stations 1996 and 1999 stations

2005 2002 + ref. station 2005

Figure 1.5.3. Dendrogram showing similarity between Valhall stations 1996, 1999, 2002, 2005. Family level, incl. M. oculata, excl. juv., sq. root transformation. VAL109 from 2005 shown as VAL9-2005.

4.2.4 Conclusions

The sediments at Valhall consist mainly of fine sand, and the sand content varies from 85 % at VAL8 (164°/500m) to 98 % at VAL reference station (254°/15000m). The gravel content is low. ∗ Necessary when comparing between years, to avoid significant source of error due to both different years and

different taxonomists.

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The silt and clay content is similar or slightly higher than previously observed. The total organic matter content in the sediments is low, and only small variations are found at the field, from 0.8 % to 1.5 %. The results are similar to the previous surveys in 2002, 1999 and 1996.

The mean THC concentrations in the top 0-1 cm layer vary from 4.3 mg/kg at VAL reference station to 130 mg/kg at VAL2, 74°/500m. VAL2 was not analysed in 2002. The concentration of THC has decreased distinctly for all stations since last survey. Relative high concentrations of THC are found for VAL8 and VAL15 at 500m distance from the platform, about 75 mg/kg. Generally, the concentration of THC is higher in the deeper layers. The maximum concentration found is 726 mg/kg in the 1-3 cm at VAL8. All stations except for VAL16, 254°/2000m and the reference station have elevated THC levels. However, some stations just slightly elevated.

As in the survey of 2002, small amounts of olefins were found at VAL 8, (164°/500m), but not quantified.

Elevated levels of NPD and PAH are found at VAL8, 164°/500m, both in the top layer and in the deeper layers. The maximum concentration of NPD is found in the 1-3 cm layer (2.9 mg/kg). High concentrations of decalins are found in the deeper layers with maximim 11.1 mg/kg, while the content of decalins has decreased significantly in the top layer. At VAL109 the content of NPD, PAH and decalins has decreased since last survey to about the level of significant contamination.

Station VAL8, 164°/500m was analysed for PFOS (perfluorooctyl sulphonate). The content was found to be 1.25 µg/kg.

Elevated Ba concentrations are found at all stations, except for the reference station. In general the Ba levels are similar to previous surveys. High Ba concentrations are also found in the deeper sections at VAL8 and VAL9.

The highest concentrations of the heavy metals are found at VAL2, 74°/500m and elevated concentrations are observed. Slightly elevated concentrations are also found at the other stations. The levels are similar or slightly lower than previous surveys.

The chemical results are in correspondence with the drilling history at Valhall.

The biodiversity indices are relatively high compared to several other fields in the central Ekofisk region. However, they indicate a small general disturbance in the fauna community which presumably reflects physical disturbance as well as a diffuse organic load in the area. The fauna at the reference station (254°/15000m) has slightly lower biodiversity indices than the other stations. The station also differs with a slightly coarser type of sediment. The similarity analysis indicates a slight disturbance at VAL-02 (74°/500m) and -08 (164°/500m) correlated to THC, Ba and Cu. The samples from stations VAL-02, -08 and -15 contained oil lumps. The observation from VAL-08 corresponds with the elevated concentrations of THC, NPD and decalins in the deeper sections of the sample (1-6 cm).

In general, the biodiversity at Valhall (including M. oculata1), has increased significantly since 2002, indicating a positive trend in the fauna community.

The sediment characteristics and thus the fauna composition at the Valhall reference station deviates somewhat from the field stations and should be considered replaced.

1 On the basis of trend analyses of the entire region the data including M. oculata has been emphasized, see also Chapter 5.2 - General Trends in the Region.

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Large amounts of yellow granules were found in the samples at all the Valhall stations. BP has established an investigation group to find out more about the origin and properties of the observed granules.

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4.3 Valhall Nordflanke Stations VAN6 and -7 from the the sampling programme had to be relocated slightly because of interference with subsea cables/pipelines. The new stations are located somewhat more than 50 m from the planned sampling stations, and are therefore renamed; VAN106 and -107 respectively. The two stations are, however, considered not to deviate significantly from the originally planned stations, and the results are compared with historical data from the old stations.

4.3.1 Sediment characterization

Grain size distribution

The grain size distribution from the present survey is given in Table 4.3.1 together with the grain size distribution from the baseline survey in 2001.

The sediments at Valhall Nordflanke consist mainly of fine sand, and the sand contents vary from 92.8 % at VAN10, 254°/500m, to 99.7 % at VAN2, 74°/500m. The average sand content is 95.6 %. The gravel content is low, and only small amounts are found at two of the stations. The silt and clay content is also low. The average silt and clay concentration found is 4.4 %.

The results from the complete grain size distribution are given in Appendix C. Table 4.3.1. Valhall Nordflanke 2005, grain size distribution. Station Median

diameter Classification Grain size distrib. 2005

(%) Grain size distrib. 2001

(%) Baseline survey

Mdφ Silt and clay

Sand Gravel Silt and clay

Sand Gravel

VAN1 74°/250m 2.73 Fine sand 3.4 96.6 0.0 2.7 97.3 0.0 VAN2 74°/500m 2.68 Fine sand 0.3 99.7 0.0 4.7 95.3 0.0 VAN5 164°/250m 2.72 Fine sand 3.3 96.7 0.0 5.3 94.7 0.0 VAN106 155°/500m 2.73 Fine sand 3.8 96.2 0.0 4.1 95.9 0.0 VAN9 254°/250m 2.75 Fine sand 4.8 95.1 0.1 1.8 98.2 0.0 VAN10 254°/500m 2.75 Fine sand 7.1 92.8 0.1 4.1 95.6 0.2 VAN13 344°/250m 2.72 Fine sand 5.7 94.3 0.0 4.0 96.0 0.0 VAN14 344°/500m 2.73 Fine sand 6.4 93.6 0.0 4.3 95.7 0.0 Mean 2.73 Fine sand 4.4 95.6 0.03 3.9 96.1 0.0 Standard deviation 0.02 2.2 2.2 0.05 1.1 1.1 0.1 VAL Ref. 254°/5000m 2.63 Fine sand 1.6 98.3 0.1 4.2 3.2 4.7

Total organic matter (TOM)

The content of TOM is low and at the same level at both fields. The content ranges from 0.8 % to 0.9 %. This is as expected as the sediments consist of homogeneous, fine sand.

The results are given inTable 4.3.2.

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Table 4.3.2. Valhall Nordflanke 2005, total organic matter (% of dry sediment). Station 2005, 0-5 cm Mean

2001 SD

2001 VAN1 74°/250m 0.81 0.9 0.03 VAN2 74°/500m 0.78 0.8 0.03 VAN5 164°/250m 0.90 0.9 0.06 VAN106 155°/500m 0.87 0.8 0.02 VAN9 254°/250m 0.90 0.8 0.04 VAN10 254°/500m 0.90 0.8 0.07 VAN13 344°/250m 0.91 0.7 0.02 VAN14 344°/500m 0.90 0.8 0.03 Mean 0.87 0.8 Standard deviation 0.05 0.06 VAL Ref. 254°/15000m 0.82 0.7 0.07

4.3.2 Chemical analyses

Parameters analysed in the sediments at Valhall Nordflanke:

• THC • NPD, PAH, decalins • Metals (Ba, Cd, Cr, Cu, Hg, Pb, Zn)

Three replicate samples at each station and five replicate samples at the reference station are analysed. The samples are taken from the top 0-1 cm sediment layer. In addition the 1-3 cm and 3-6 cm sediment layers are sampled at one station and the reference station.

The baseline survey showed that the Flanke Nord field had no major signs of contamination, and the discharge history does not indicate major changes outside the 500m zone. The number of stations in this year survey was thus reduced compared to 2001.

THC

The THC results are shown in Table 4.3.3. The corresponding THC data from the baseline survey in 2001 are also included for comparison. Bar diagram of the THC content in the sediments is shown in Figure 4.3.1.

The concentrations of hydrocarbons are low and at the same level as in 2001 baseline survey. In the present investigation the THC concentration in the top 0-1 cm layer vary from 5.1 mg/kg at VAN14 344°/500m to 8.4 mg/kg at VAN11 254°/1000m.

At one station the sediment layers at 1-3 cm and 3-6 cm are analysed. A tendency of slightly higher concentrations down in the sediments is observed.

The content of THC is considered to be within the natural level at Valhall Nordflanke. None of the stations are contaminated. The limit of contamination is 6.6 mg/kg.

Representative gas chromatograms are given in Appendix C, including VHAN1 (74°/250m), VHAN 5 (164°/250m), VHAN9 (254°/250m) and VHAN15 (344°/1000m).

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Valhall Flanke Nord, THC 2005

0

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

VHAN1

VHAN2

VHAN3

VHAN5

VHAN106

VHAN107

VHAN8

VHAN9

VHAN10

VHAN11

VHAN13

VHAN14

VHAN15

station

mg/kg

2001

2005

LSC A

Figure 4.3.1. THC in the sediments, Valhall Nordflanke, 2001-2005. VHAL = VAN. Table 4.3.3. Valhall Nordflanke 2005, total hydrocarbon content (mg/kg dry sediment). Station Grab

#1 Grab

#2 Grab

#3 Mean 2005

SD 2005

Mean 2001

SD 2001

VAN1 74°/250m 6.4 8.3 7.6 7.5 1.0 6.7 0.5 VAN2 74°/500m 5.4 5.4 4.9 5.2 0.3 6.5 0.2 VAN3 74°/1000m 5.1 5.6 5.1 5.3 0.3 9.8 2.8 VAN5 164°/250m 5.4 6.4 8.7 6.8 1.7 7.8 0.6 1-3 cm 7.7 8.4 3-6 cm 12.1 7.8 VAN106 155°/500m 4.9 6.0 5.9 5.6 0.6 8.0 0.5 VAN107 155°/850m 6.1 7.3 5.8 6.4 0.8 8.2 0.3 VAN8 164°/2000m 7.0 5.7 5.7 6.2 0.8 7.3 0.3 VAN9 254°/250m 5.5 6.1 5.7 5.8 0.3 7.6 0.7 VAN10 254°/500m 5.7 5.1 6.4 5.7 0.6 7.0 0.3 VAN11 254°/1000m 10.2 10.0 5.0 8.4 2.9 7.1 0.6 VAN13 344°/250m 5.4 5.2 6.8 5.8 0.9 7.6 0.3 VAN14 344°/500m 5.6 5.4 4.6 5.1 0.6 8.1 0.1 VAN15 344°/1000m 5.1 5.4 6.1 5.6 0.5 7.7 0.8 VAL Ref. 254°/15000m 4.3 0.4 6.1 0.6 LSC, Subregion A 6.6 6.4 9

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NPD, PAH and decalins

One station is analysed in addition to the reference station at Valhall Nordflanke, VAN5, 164°/250m. The results are shown in Table 4.3.4. The corresponding data from the baseline survey in 2001 are also included for comparison.

The level of NPD, PAH and decalins is low for the station investigated. The content is below or just about the limit of contamination. Elevated levels are not found at the reference station. Table 4.3.4 Valhall Nordflanke 2005, sum NPD, PAH and decalins (mg/kg dry sediment).

Station Grab #1

Grab #2

Grab #3

Grab #4

Grab #5

Mean SD Mean SD

2005 2005 2001 2001NPD VAN5 164°/250m 0.014 0.011 0.017 0.014 0.003 0.017 0.003 1-3 cm 0.017 0.032 3-6 cm 0.034 0.023 VAL Ref. 254°/15000m 0.007 0.027 0.004 0.003 0.024 0.013 0.01 0.011 0.003 1-3 cm 0.018 0.012 3-6 cm 0.016 0.030 LSC Subregion A 0.030 PAH VAN5 164°/250m 0.043 0.037 0.049 0.043 0.006 0.053 0.08 1-3 cm 0.060 0.075 3-6 cm 0.102 0.066 VAL Ref. 254°/15000m 0.044 0.050 0.040 0.039 0.081 0.051 0.017 0.040 0.007 1-3 cm 0.057 0.040 3-6 cm 0.067 0.053 LSC Subregion A 0.061 Decalins VAN5 164°/250m 0.045 0.10 0.080 nd nd 1-3 cm 0.1 3-6 cm 0.1 VAL Ref. 254°/15000m 0.063 0.67 0.019 0.004 0.099 0.17 0.3 nd 1-3cm 0.26 nd 3-6cm nd nd nd: not detected. Limit of detection for NPD is 0.01 mg/kg, for PAH 0.005 mg/kg and for decalins 0.1mg/kg.

Metals

The results are shown in Table 4.3.5. For comparison the mean values from the present survey together with the data from the baseline survey in 2001 are shown in Table 4.3.6. Bar diagram of the Ba content in the sediments is shown in Figure 4.3.2.

In the present investigation the concentration of Ba varies from 94 mg/kg at VAN10, 254°/500m to 468 mg/kg at VAN9, 254°/250m.

Elevated Ba concentrations are found at all stations, except for the reference station. Thus elevated levels of Ba are found out to 500m in all directions. High Ba concentrations are also found in the vertical sections at VAN5 and the Ba concentration increases going down in the sediments.

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The concentration of heavy metals are low and at the same level as found in the baseline survey.

Valhall Flanke Nord, Ba 2005

0

50

100

150

200

250

300

350

400

450

500

550

600

VHAN1 VHAN2 VHAN5 VHAN106 VHAN9 VHAN10 VHAN13 VHAN14

station

mg/kg

2001

2005

LSC A

468±518

Figure 4.3.2. Ba in the sediments, Valhall Nordflanke, 2001- 2005. VHAL = VAN. The following variation is found at Valhall Nordflanke in the top layer, 0-1 cm. The values are given in mg/kg: Valhall Nordflanke VAN1 – VAN14 VAL Reference station Ba: 94 – 468 28 Cr: 7.6 – 9.4 7.7 Cu: <0.5 <0.5 Pb: 6.9 – 8.5 6.5 Zn: 6.0 – 7.7 5.6 Cd: <0.01 <0.01 Hg: <0.01 <0.01

Table 4.3.5. Valhall Nordflanke 2005, metals (mg/kg dry sediment). Station Sample Ba Cd Cr Cu Hg Pb Zn 2005 2005 2005 2005 2005 2005 2005 VAN1 74°/250m 1 297 0.01 8.5 0.8 8.6 7.2 2 245 <0.01 7.6 0.7 7.7 6.1 3 202 <0.01 8.9 0.7 7.7 7.3 mean 248 <0.01 8.3 0.7 8.0 6.9 SD 48 0.7 0.0 0.5 0.6 cont.

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Table 4.3.5. cont. Station Sample Ba Cd Cr Cu Hg Pb Zn 2005 2005 2005 2005 2005 2005 2005 VAN2 74°/500m 1 107 <0.01 8.3 0.5 6.9 6.7 2 242 <0.01 8.5 0.6 7.8 6.7 3 147 <0.01 7.6 0.7 6.5 6.2 mean 166 <0.01 8.1 0.6 7.0 6.5 SD 69 0.5 0.1 0.7 0.3 VAN5 164°/250m 1 169 <0.01 8.8 0.8 <0.01 8.3 8.2 2 79 <0.01 7.9 0.5 <0.01 7.4 6.0 3 84 <0.01 8.0 0.6 <0.01 7.6 6.1 mean 111 <0.01 8.2 0.6 <0.01 7.8 6.8 SD 51 0.5 0.2 0.5 1.3 1-3 cm 1 225 <0.01 9.4 0.7 <0.01 8.9 8.6 3-6 cm 1 317 <0.01 9.1 0.8 <0.01 8.9 7.7 VAN106 155°/500m 1 211 <0.01 9.4 0.6 8.8 7.4 2 146 <0.01 8.9 0.7 8.4 7.4 3 126 <0.01 8.6 0.8 7.6 7.4 mean 205 <0.01 9.1 0.7 8.5 7.7 SD 75 0.4 0.1 0.5 0.5 VAN9 254°/250m 1 1063 <0.01 9.6 1.2 9.2 9.9 2 122 <0.01 8.2 0.7 7.9 6.6 3 219 <0.01 7.7 0.7 8.4 6.8 mean 468 <0.01 8.5 0.9 8.5 7.7 SD 518 - 1.0 0.3 0.7 1.8 VAN10 254°/500m 1 59 <0.01 7.4 0.5 6.0 5.8 2 107 <0.01 7.5 0.7 7.1 6.1 3 115 <0.01 7.9 0.6 7.7 6.2 mean 94 <0.01 7.6 0.6 6.9 6.0 SD 30 0.2 0.1 0.8 0.2 VAN13 344°/250m 1 135 <0.01 8.1 0.7 7.9 6.5 2 101 <0.01 7.9 0.7 7.9 6.4 3 129 <0.01 7.9 0.8 7.9 7.1 mean 122 <0.01 7.9 0.7 7.9 6.7 SD 18 0.1 0.1 0.0 0.4 VAN14 344°/500m 93 <0.01 7.3 0.6 7.7 5.8 88 <0.01 7.8 0.6 8.1 6.4 323 <0.01 8.0 0.6 7.1 6.0 mean 168 <0.01 7.7 0.6 7.6 6.1 SD 134 0.4 0.0 0.5 0.3 VAL Ref. 254°/15000m 1 25 <0.01 7.6 0.5 <0.01 6.4 5.6 2 27 <0.01 7.7 <0.5 <0.01 6.0 5.6 3 26 <0.01 7.0 <0.5 <0.01 7.6 5.8 4 35 <0.01 7.6 <0.5 <0.01 6.1 5.7 5 27 <0.01 7.7 0.5 <0.01 6.6 5.5 mean 28 <0.01 7.7 <0.5 <0.01 6.5 5.6 SD 4 0.1 0.6 0.1 LSC Subregion A 76.2 8.0 1.3 7.4 6.9

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Table 4.3.6. Valhall Nordflanke 2005, metals (mg/kg dry sediment), comparing mean values with the baseline survey in 2001. Station Ba Ba Cd Cd Cr Cr Cu Cu Hg Hg Pb Pb Zn Zn 2005 2001 2005 2001 2005 2001 2005 2001 2005 2001 2005 2001 2005 2001VAN1 74°/250m 248 106 <0.01 0.03 8.3 7.6 0.7 0.6 8.0 7.4 6.9 6.3 VAN2 74°/500m 166 132 <0.01 <0.01 8.1 7.8 0.6 0.6 7.0 7.9 6.5 6.5 VAN5 164°/250m 111 111 <0.01 <0.01 8.2 7.8 0.6 0.7 <0.01 <0.01 7.8 7.6 6.8 6.4 1-3 cm 225 209 <0.01 <0.01 9.4 8.3 0.7 0.7 <0.01 <0.01 8.9 8.4 8.6 7.7 3-6 cm 317 467 <0.01 <0.01 9.1 8.8 0.7 0.8 <0.01 0.01 8.9 9.2 7.7 8.1 VAN106 155°/500m 205 133 <0.01 <0.01 9.1 8.1 0.7 0.6 8.5 8.0 7.7 6.8 VAN9 254°/250m 468 78 <0.01 <0.01 8.5 7.8 0.9 0.7 8.5 7.7 7.7 6.0 VAN10 254°/500m 94 94 <0.01 <0.01 7.6 7.6 0.6 0.6 6.9 7.3 6.0 5.8 VAN13 344°/250m 122 100 <0.01 <0.01 7.9 7.9 0.7 0.6 7.9 7.9 6.7 6.1 VAN14 344°/500m 168 110 <0.01 <0.01 7.7 8.1 0.6 0.7 7.6 7.9 6.1 6.7 VAL Ref 254°/15000m 28 53 <0.01 <0.01 7.7 8.1 <0.5 0.5 <0.01 <0.01 6.5 7.7 5.6 6.6

4.3.3 Biological analyses

A total of 146 species and 11994 individuals were sampled at 8 stations. Greatest abundance (70.9 %) was found among the polychaetes, of which the species Myriochele oculata constitutes 60.6 % and Paramphinome jeffreysii constitutes 14.7 %, see Table 4.3.7. Table 4.3.7. Number of species and individuals distributed between the main groups, Valhall Nordflanke 2005.

Individuals Species Main animal groups Number % Number %

Varia 603 5.0 14 9.6Polychaeta 8502 70.9 61 41.8- Paramphinome jeffreysii 1254 14.7 - Myriochele oculata 5150 60.6 Crustacea 325 2.7 26 17.8Mollusca 862 7.2 36 24.7Echinodermata 1702 14.2 9 6.2- Amphiura filiformis 1107 65.0 Total 11994 100.0 146 100.0

Figure 4.3.3 shows the numbers of species and individuals sampled at each station and variations between grab samples.

0

20

40

60

80

100

VAN-01VAN-02VAN-05

VAN-106

VAN-09VAN-10VAN-13VAN-14

VAL-REF

Stations

No.

of s

peci

es (S

)

Station º/m VAN-01 74/250 VAN-02 74/500 VAN-05 164/250 VAN-106 155/500 VAN-09 254/250 VAN-10 254/500 VAN-13 344/250 VAN-14 344/500 VAN-REF 254/15000

Figure 4.3.3. Numbers of species (S) and individuals (N) per 0.5 m2 (incl./excl. P. jeffreysii and M. oculata), mean values per grab sample and standard deviation, Valhall Nordflanke 2005.

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0400800

1200160020002400

VAN-01VAN-02VAN-05

VAN-106

VAN-09VAN-10VAN-13VAN-14

VAL-REF

Stations

No.

of i

ndiv

idua

ls (N

) Ex. P. jeffreysii and M. oculata

0400800

1200160020002400

VAN-01VAN-02VAN-05

VAN-106

VAN-09VAN-10VAN-13VAN-14

VAL-REF

Stations

No.

of i

ndiv

idua

ls (N

)

Figure 4.3.3. cont.

The standard deviation decrease dramatically when P. jeffreysii and M. oculata are removed from the number of individuals, this is evident since the two species constitute 53.4 % of the total number of individuals. An exception is at station VAN-10, where the standard deviation was only slightly reduced. This is due to relatively large differences between the five grabs sampled at each station.

Diversity and dominant species

The dominant species at each station varied from 25.2 % at VAN-13 (344°/250m) to 55.8 % at VAN-106 (155°/500m). The 10 most abundant species made up from 73.0 % at VAN-02 (74°/500m) to 81.9 % at VAN-1(74°/250m), see table 4.14.8. The bristle worms M. oculata and P. jeffreysii together with the brittle star Amphiura filiformis dominated the fauna, but also juvenile Echinoidea were found in relatively high amounts. Other frequently found species were the bristle worms Chaetozone setosa, Levinsenia gracilis, Goniada maculata and also the ribbon worm Nemertea spp. P. jeffreysii is mainly a carnivore species and the ribbon worm is a deposit feeder. The other mentioned species are both suspension- and deposit feeders. Most of these species are known indicators of organic pollution when they are found in high numbers. Several of the above mentioned species have, however, a planktonic development stage and are able to settle in large numbers. Table 4.3.8. The 10 most abundant species at each station,Valhall Nordflanke 2005. 10 most dominating species VAN-01 No. % Cum. % VAN-02 No. % Cum. %Myriochele oculata 860 44.7 44.7 Myriochele oculata 300 29.1 29.1Paramphinome jeffreysii 203 10.6 55.3 Paramphinome jeffreysii 123 11.9 41.0Amphiura filiformis 143 7.4 62.7 Echinoidea spp.juv. 91 8.8 49.8Echinoidea spp.juv. 86 4.5 67.2 Amphiura filiformis 72 7.0 56.8Chaetozone setosa 70 3.6 70.8 Chaetozone setosa 49 4.8 61.5Levinsenia gracilis 62 3.2 74.1 Levinsenia gracilis 28 2.7 64.2Nemertea spp. 41 2.1 76.2 Sthenelais limicola 24 2.3 66.6Corymorpha nutans 40 2.1 78.3 Corymorpha nutans 24 2.3 68.9Caudofoveata spp. 35 1.8 80.1 Goniada maculata 21 2.0 70.9Aonides paucibranchiata 35 1.8 81.9 Eudorellopsis deformis 21 2.0 73.0

Cont.

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Table 4.3.8. cont. VAN-05 No. % Cum. % VAN-106 No. % Cum. %Myriochele oculata 1030 51.2 51.2 Myriochele oculata 960 55.8 55.8Amphiura filiformis 199 9.9 61.1 Amphiura filiformis 120 7.0 62.8Paramphinome jeffreysii 184 9.2 70.3 Paramphinome jeffreysii 120 7.0 69.7Echinoidea spp.juv. 89 4.4 74.7 Echinoidea spp.juv. 53 3.1 72.8Levinsenia gracilis 63 3.1 77.8 Caudofoveata spp. 42 2.4 75.3Chaetozone setosa 54 2.7 80.5 Levinsenia gracilis 40 2.3 77.6Nemertea spp. 35 1.7 82.3 Chaetozone setosa 30 1.7 79.3Goniada maculata 31 1.5 83.8 Phoronis muelleri 26 1.5 80.8Caudofoveata spp. 28 1.4 85.2 Nemertea spp. 25 1.5 82.3Phoronis muelleri 25 1.2 86.4 Goniada maculata 24 1.4 83.7 VAN-09 No. % Cum. % VAN-10 No. % Cum. %Myriochele oculata 560 39.6 39.6 Myriochele oculata 790 45.3 45.3Paramphinome jeffreysii 165 11.7 51.3 Amphiura filiformis 167 9.6 54.9Amphiura filiformis 131 9.3 60.6 Paramphinome jeffreysii 152 8.7 63.6Caudofoveata spp. 54 3.8 64.4 Echinoidea spp.juv. 84 4.8 68.5Levinsenia gracilis 43 3.0 67.5 Levinsenia gracilis 48 2.8 71.2Chaetozone setosa 38 2.7 70.1 Caudofoveata spp. 46 2.6 73.8Harpinia antennaria 32 2.3 72.4 Mysella bidentata 43 2.5 76.3Echinoidea spp.juv. 27 1.9 74.3 Chaetozone setosa 35 2.0 78.3Goniada maculata 24 1.7 76.0 Montacuta substriata 33 1.9 80.2Abra prismatica 23 1.6 77.6 Harpinia antennaria 28 1.6 81.8 VAN-13 No. % Cum. % VAN-14 No. % Cum. %Myriochele oculata 270 25.2 25.2 Myriochele oculata 380 35.2 35.2Amphiura filiformis 167 15.6 40.8 Paramphinome jeffreysii 140 13.0 48.2Paramphinome jeffreysii 167 15.6 56.3 Amphiura filiformis 108 10.0 58.2Echinoidea spp.juv. 64 6.0 62.3 Caudofoveata spp. 41 3.8 62.0Caudofoveata spp. 34 3.2 65.5 Levinsenia gracilis 39 3.6 65.6Harpinia antennaria 31 2.9 68.4 Echinoidea spp.juv. 38 3.5 69.1Goniada maculata 26 2.4 70.8 Goniada maculata 25 2.3 71.5Sthenelais limicola 26 2.4 73.2 Chaetozone setosa 23 2.1 73.6Chaetozone setosa 24 2.2 75.5 Scoloplos armiger 22 2.0 75.6Abra prismatica 23 2.2 77.6 Harpinia antennaria 17 1.6 77.2

The number of species varied from 70 at station VAN-09 (254°/250m) to 91 at VAN-01 (74°/250m). The number of individuals varied from 934 at VAN-10 (254°/500m) to 1921 at VAN-13 (344°/250m). The Shannon Wiener diversity index varied from 3.0 at station VAN-05 (164°/250m) and -106 (155°/500m) to 4.2 at station VAN-02 (74°/500m) and the Hurlberts index (ES100) varied from 20 at VAN-05 to 29 at VAN-02 including M. oculata. Removal of M. oculata from the data gave indices above 4 and from 29 to 34 respectively. Indices above 4 indicate a relatively undisturbed fauna. Indices between 3 and 4 indicate a slight disturbance, while indices between 2 and 3 indicate a distinct disturbance in the fauna. In general ES100 indices above 20 characterize a relatively normal fauna community, see Table 4.3.9.

The biodiversity at Valhall Nordflanke is in general relatively high compared to the rest of the central Ekofisk region. However, excluding the reference station at Valhall, the fauna community at VAN-05 (164°/250m) and also VAN-13 (344°/250m) differ with slightly lower indices than the rest of the Valhall nordflanke stations. Field observations indicate a possible disturbance at VAN-05.

Similar to the Valhall sediments small, mostly yellowish granules were observed in nearly all samples (see Valhall for details).

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Table 4.3.9. Numbers of individuals (N) and species (S), depth, Shannon-Wiener diversity index (H’), Pielou’s evenness index (J), and expected number of species per 100 individuals (ES100) for each station at Valhall Nordflanke 2005 (excl. juv.).

H' ES100 Station Direction ° Distance m Depth S N Incl.

M. o. Excl. M. o.

J Incl. M. o.

Excl. M. o.

VAN-01 74 250 71 91 1833 3.5 4.6 0.5 24 32VAN-02 74 500 70 66 1657 3.3 4.8 0.6 22 34VAN-05 164 250 71 80 1666 3.0 4.3 0.5 22 29VAN-106 155 500 71 71 1007 4.0 4.8 0.7 26 34VAN-09 254 250 69 70 1038 3.8 4.6 0.6 26 32VAN-10 254 500 70 82 934 4.2 4.4 0.7 29 29VAN-13 344 250 70 77 1921 3.0 4.3 0.5 20 30VAN-14 344 500 70 79 1381 3.7 4.6 0.6 25 32VAL-REF 254 15000 72 63 1771 2.5 4.3 0.4 18 29M. o.= M. oculata

Classification and ordination

The dendrogram from the cluster analysis and the MDS plot from the ordination analysis based on station level are presented in Figure 4.3.4 and Figure 4.3.5. The reference station (254°/15000m) separates from the Valhall Nordflanke stations at 70 % similarity. There was significantly higher abundance of M. oculata (suspension feeder) at the reference station and somewhat higher numbers of the bristle worm L. gracilis (suspension/deposit feeders) and the Caudofoveatas at the field stations. Caudofoveata are small primitive deep sea molluscs. They are worm-like and lack shells and distinct muscular feet. Instead they have scales and calcareous spines for movement. They live by burrowing through soft sediment, and eat passing organic detritus.

The field stations divide into subgroups at about 75 %. At this level VAN-02 (74°/500m) does not cluster with any other stations. In a subgroup apart from the other field stations, we find VAN-13 (344°/250m) and -14 (344°/500m). VAN-02 differs from the other stations because of fewer numbers of Caudofoveata (mollusca) and the brittle star A. filiformis. The three stations VAN-02, -13 and -14 differ from the other field stations because of significantly smaller abundances of M. oculata. The main reason for a slightly different fauna at VAN-02 is probably somewhat coarser sediment than at the other stations.

The Bioenv analysis reveals a correlation of 0.8 between the fauna and a combination of the environmental factors THC, Ba1, pelite and average grain size, indicating that the fauna and these parameters are varying in about the same manner at the field. This relationship is not considered relevant as the THC concentrations are generally low and uniform.

1 Ba and the other metals are not degradable and will not disappear from the sediments. These metals may

presumable not have any effect on the fauna in itself, but could be regarded as trace elements for other degradable substances.

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VAL-

REF

VAN-

02

VAN-

1 3

V AN-

14

VAN-

01

VAN-

10

VAN-

0 5

VAN-

1 06

VAN-

09

100

95

90

85

80

75

70Si

mila

rity

Valhall Nordflanken field stations

344/250m 344/500m 74/250m 254/500m 164/250m 155/500m 254/250m74/500m

Figure 4.3.4. Dendrogram of stations from Valhall Nordflanke 2005 (excl. juv.).

VAN-01

VAN-02

VAN-05

VAN-106

VAN-09VAN-10

VAN-13

VAN-14

VAL-REF

Stress: 0,05

74/250m, 254/500m, 164/250m, 155/500m, 254/250m

74/500m

344/250m, 344/500m

Figure 4.3.5. MDS plot of stations from Valhall Nordflanke 2005 (excl. juv.).

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Comparison 2001 and 2005

In Figure 4.3.6 the results from the present survey are compared to the results from the baseline survey in 2001. The numbers include the bristle worms M. oculata and P. jeffreysii. There are no major changes in numbers of species between years. The numbers of individuals have decreased significantly since the baseline survey in 2001. The decrease is mainly due to a decline in the abundance of M. oculata after a peak in 2001/20021. As a consequence the biodiversity indices (incl. M. oculata) have increased significantly at all stations during the same period.

020406080

100

VAN-01

VAN-02

VAN-05

VAN-106

VAN-09

VAN-10

VAN-13

VAN-14

Stations

No.

of s

peci

es (S

)

2001 2005

Station º/m

VAN-01 74/250 VAN-02 74/500 VAN-05 164/250 VAN-106 155/500 VAN-09 254/250 VAN-10 254/500 VAN-13 344/250 VAN-14 344/500

01000200030004000

VAN-01

VAN-02

VAN-05

VAN-106

VAN-09

VAN-10

VAN-13

VAN-14

Stations

No.

of i

ndiv

idua

ls (N

)

2001 2005

0123456

VAN-01

VAN-02

VAN-05

VAN-106

VAN-09

VAN-10

VAN-13

VAN-14

Stations

H'

2001 2001-ex. M. oculata2005 2005-ex. M. oculata

Figure 4.3.6. Numbers of species (S) and individuals (N) per 0.5 m2 and diversity (H’), incl. P. jeffreysii and M. oculata, excl. juv.), Valhall Nordflanke 2001 and 2005.

Classification and ordination analyses

The data from 2001 and 2005 were analysed at family level∗. The dendrogram (Figure 4.3.7) from the cluster analysis reveals that the stations divide into two main groups, based on years, at about 60 % similarity. The species that contributes the most to the differences were species within the familiy Oweniidae (mainly M. oculata), which were found in significantly higher numbers in 2001. Other contributors were higher abundance of species within the families

1 Adding the 2005 data to historical data from the region has made it possible to interpret the great variations of M.

oculata in the period 1996 to 2005, thus obtaining a pattern in the overall temporal variations in the entire region which again forms the basis for the conclusions for each of the fields, see Chapter 5.2 - General Trends in the Region for details.

∗ Necessary when comparing between years to avoid significant source of error due to different years and different taxonomists.

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Amphinomidae (mainly P. jeffreysii), Amphiuridae (mainly A. filiformis) and Corymorphidae (mainly Corymorpha nutans) in 2005. The same pattern was found at Valhall Sørflanke.

The Bioenv analysis gave a correlation of 0.6 between fauna and the environmental factors THC, Ba1, TOM and pelite, which could indicate some relationship between the environmental factors and the development in the fauna over the years.

VAN-

11-2

001

VAN-

0 7-2

001

VAN-

06-2

001

VAN-

03-2

001

VAN-

05-2

001

V AN-

08-2

0 01

VAN-

01-2

001

VAN-

0 2-2

001

VAN -

13-2

001

VAN-

0 9-2

001

VAN-

1 4-2

001

VAN-

1 0-2

001

VAN-

15-2

001

VAN-

02-2

005

VAN -

13-2

005

VAN -

14-2

005

VAN-

01-2

005

V AN-

09-2

0 05

VAN -

05-2

005

VAN-

06-2

005

VAN -

10-2

005

100

90

80

70

60

Sim

ilarit

y

2001 2002 Figure 4.3.7. Dendrogram showing the similarity between Valhall Nordflanke 2001 and 2005. Family level, incl. M. oculata, excl. juv., sq. root transformation.

4.3.4 Conclusions

The sediments at Valhall Nordflanke consist mainly of fine sand, and the sand content varies from 93 % at VAN10, 254°/500m, to ~100 % at VAN2, 74°/500m. The average sand content is 95.6 %. The gravel content is low, and small amounts are only found at two of the stations. The silt and clay content is also low. The average silt and clay concentration found is 4.4 %. The total organic matter is low. The values vary from 0.8 % to 0.9%. This is in accordance with the sediments of homogeneous, fine sand.

The concentrations of hydrocarbons are low and at the same level as in the 2001 baseline survey. In the present investigation the THC concentrations in the top 0-1 cm layer vary from 5.1 mg/kg at VAN14 344°/500 m to 8.4 mg/kg at VAN11 254°/1000 m. At one station the sediment layers, 1-3 cm and 3-6 cm are analysed. A tendency of slightly higher concentrations of THC down in the sediments is observed. The content of THC is considered to be within the natural level at Valhall Nordflanke and none of the stations are contaminated.

1 Ba and the other metals are not degradable and will not disappear from the sediments. These metals may

presumable not have any effect on the fauna in itself, but could be regarded as trace elements for other degradable substances.

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The concentrations of NPD, PAH and decalins are low for the one station investigated, VAN5 164°/250m. The content is below or just about the limit of contamination.

In the present survey the Ba concentrations vary from 94 mg/kg at VAN10, 254°/500m to 468 mg/kg at VAN9, 254°/250m. Elevated Ba concentrations are found at all stations, except for the reference station. Thus elevated levels of Ba are found out to 500m in all directions. High Ba concentrations are also found in the vertical sections at VAN5 and the Ba concentration increases downwards in the sediments. The content of Ba has increased since the 2001 survey. This is in accordance with discharge of barite and cuttings in 2003.

The concentration of heavy metals are low and at the same level as found in the baseline survey. The chemical results are in correspondence with the drilling history at Valhall Nordflanke

The biodiversity indices are relatively high compared to several other fields in the central Ekofisk region. However, they indicate a small disturbance in the fauna community which presumably reflects a general physical disturbance as well as a diffuse organic load in the area.

Since the baseline survey the THC levels have decreased at Valhall Nordflanke and the biodiversity indices (incl. M. oculata) have increased considerably since the baseline survey in 2001, which is partly due to a significant decline in the abundance of the bristle worm M. oculata.

Yellow granules (see Valhall for details) were found at most of the stations.

None of the stations are considered affected by field activities.

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4.4 Valhall Sørflanke Station VAS13 from the the sampling programme had to be relocated slightly because of interference with subsea cables/pipelines. The new station is located somewhat more than 50 m from the planned station, and are therefore renamed; VAsS113. The station is, however, considered not to deviate significantly from the originally planned station, and the results are compared with historical data from the old station.

4.4.1 Sediment characterization

Grain size distribution

The grain size distribution from the present survey is shown in Table 4.4.1 together with the grain size distribution from the baseline survey in 2001.

The sediments at Valhall Sørflanke consist mainly of fine sand, and the sand content varies from 93.1 % at VAS113, 325°/250m, to 97.4 % at VAS10, 254°/500m. The average sand content is 95.4 %. The gravel content is low, and small amounts are only found at three of the stations. The silt and clay content is also low. The average silt and clay concentration found is 4.3 %.

The results from the complete grain size distribution are given in Appendix C. Table 4.4.1. Valhall Sørflanke 2005, grain size distribution. Station Median

diameter Classification Grain size distrib. 2005

(%) Grain size distrib. 2001

(%) Baseline survey

Mdφ Silt and clay

Sand Gravel Silt and clay

Sand Gravel

VAS1 74°/250m 2.70 Fine sand 5.0 95.5 0.0 2.8 97.2 0.0 VAS2 74°/500m 2.68 Fine sand 2.5 96.7 0.8 3.0 97.0 0.0 VAS5 164°/250m 2.69 Fine sand 3.5 95.7 0.8 0.7 99.3 0.0 VAS6 164°/500m 2.71 Fine sand 6.6 93.4 0.0 2.0 98.0 0.0 VAS9 254°/250m 2.70 Fine sand 3.7 95.1 1.2 0.8 99.2 0.0 VAS10 254°/500m 2.69 Fine sand 2.6 97.4 0.0 2.8 97.7 0.0 VAS113 325°/250m 2.72 Fine sand 6.8 93.1 0.0 4.5 95.5 0.0 VAS14 344°/500m 2.72 Fine sand 3.9 96.1 0.0 3.8 96.2 0.0 Mean 2.70 Fine sand 4.3 95.4 0.4 2.6 97.5 0.0 Standard deviation 0.01 1.7 1.5 0.5 1.3 1.3 0.0 VAL Ref. 254°/5000m 2.63 Fine sand 1.6 98.3 0.1 4.2 3.2 4.7

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Total organic matter (TOM)

The content of TOM is low and at the same level at both fields. The content ranges from 0.6 % to 0.8 %. This is as expected as the sediments consist of homogeneous, fine sand.

The results are shown in Table 4.4.2. Table 4.4.2. Valhall Sørflanke 2005, total organic matter (% of dry sediment). Station 2005, 0-5 cm Mean 2001 SD 2001 VAS1 74°/250m 0.64 0.7 0.04 VAS2 74°/500m 0.72 0.7 0.05 VAS5 164°/250m 0.70 0.7 0.05 VAS6 164°/500m 0.70 0.7 0.02 VAS9 254°/250m 0.72 0.6 0.01 VAS10 254°/500m 0.76 0.7 0.01 VAS113 325°/250m 0.66 0.7 0.07 VAS14 344°/500m 0.78 0.7 0.03 Mean 0.71 0.7 Standard deviation 0.04 0.03 VAL Ref. 254°/15000m 0.82 0.7 0.07

4.4.2 Chemical analyses

Parameters analysed in the sediments at Valhall Sørflanke:

• THC • NPD, PAH, decalins • Metals (Ba, Cd, Cr, Cu, Hg, Pb, Zn)

Three replicate samples at each station and five replicate samples at the reference station are analysed. The samples are taken from the top 0-1 cm sediment layer. In addition the 1-3 cm and 3- 6 cm sediment layers are sampled at one station and the reference station.

The baseline survey showed that the Flanke Sør field had no major signs of contamination, and the discharge history does not indicate major changes outside the 500m zone. The number of stations in this year survey was thus reduced compared to 2001.

THC

The THC results are shown in Table 4.4.3. The corresponding THC data from the baseline survey in 2001 are also included for comparison. Bar diagram of the THC content in the sediments is shown in Figure 4.4.1.

The concentrations of hydrocarbons are low and at the same level as in 2001 baseline survey. In the present investigation the THC concentrations in the top 0-1 cm layer vary from 3.6 mg/kg at VAS7 164°/1000 m to 5.3 at VAS1 74°/250 m. At one station the sediment layers at 1-3 cm and 3-6 cm are analysed. A tendency of slightly higher concentrations down in the sediments is observed.

The content of THC is considered to be within the natural level at Valhall Sørflanke. None of the stations are contaminated. The limit of contamination is 6.6 mg/kg.

Representative gas chromatograms are given in Appendix C, including VHAS1 (74°/250m), VHAS5 (164°/250m), VHAS9 (254°/250m) and VHAS15 (344°/1000m).

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Valhall Flanke Sør, THC 2005

0

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

VHAS1

VHAS2

VHAS3

VHAS5

VHAS6

VHAS7

VHAS9

VHAS10

VHAS11

VHAS113

VHAS14

VHAS15

VHALref

station

mg/kg

2001

2005

LSC A

Figure 4.4.1. Bar diagram of the THC content in the sediments at Valhall Sørflanke 2001-2005. Table 4.4.3. Valhall Sørflanke 2005, total hydrocarbon content (mg/kg dry sediment). Station Grab

#1 Grab

#2 Grab

#3 Mean 2005

SD 2005

Mean 2001

SD 2001

VAS1 74°/250m 7.8 4.2 3.9 5.3 2.1 6.4 0.6 VAS2 74°/500m 4.1 3.8 4.7 4.2 0.4 6.0 0.6 VAS3 74°/1000m 3.9 4.9 3.7 4.1 0.6 6.4 0.3 VAS5 164°/250m 4.6 5.1 4.6 4.8 0.3 5.3 0.7 1-3 cm 5.7 5.5 3-6 cm 5.1 VAS6 155°/500m 3.9 3.7 4.3 4.0 0.3 6.0 0.4 VAS7 164°/1000m 4.2 2.9 3.7 3.6 0.7 5.2 0.2 VAS9 254°/250m 4.3 4.8 5.8 5.0 0.8 6.2 0.7 VAS10 254°/500m 4.5 4.8 4.3 4.6 0.3 6.2 0.7 VAS11 254°/1000m 4.7 4.2 4.7 4.5 0.3 VAS113 325°/250m 4.8 4.7 4.7 4.7 0.1 7.1 0.8 VAS14 344°/500m 4.1 4.6 5.0 4.6 0.4 6.9 0.4 VAS15 344°/1000m 5.5 4.8 4.2 4.8 0.7 6.4 0.5 VAL Ref. 254°/15000m 4.3 0.4 6.1 0.6 LSC, Subregion A 6.6 6.4 9

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NPD, PAH and decalins

One station is analysed in addition to the reference station at Valhall Sørflanke, VAS5, 164°/250m. The results are shown in Table 4.4.4. The corresponding data from the baseline survey in 2001 are also included for comparison.

The level of NPD, PAH and decalins is low for the station investigated. The content is below or just about the limit of contamination. Elevated levels are not found at the reference station. Table 4.4.4. Valhall Sørflanke 2005, sum NPD, PAH and decalins (mg/kg dry sediment).

Station Grab #1

Grab #2

Grab #3

Grab #4

Grab #5

Mean SD Mean SD

2005 2005 2001 2001NPD VAS5 164°/250m 0.003 0.005 0.007 nd 0.010 0.001 1-3 cm 0.013 0.012 3-6 cm 0.014 0.019 VAL Ref. 254°/15000m 0.007 0.027 0.004 0.003 0.024 0.013 0.01 0.011 0.003 1-3 cm 0.018 0.012 3-6 cm 0.016 0.030 LSC Subregion A 0.030 PAH VAS5 164°/250m 0.014 0.025 0.022 0.020 0.006 0.034 0.005 1-3 cm 0.043 0.041 3-6 cm 0.061 0.058 VAL Ref. 254°/15000m 0.044 0.050 0.040 0.039 0.081 0.051 0.017 0.040 0.007 1-3 cm 0.057 0.040 3-6 cm 0.067 0.053 LSC Subregion A 0.061 Decalins VAS5 164°/250m 0.008 0.012 0.019 nd nd 1-3 cm 0.0 3-6 cm 0.0 VAL Ref. 254°/15000m 0.063 0.67 0.019 0.004 0.099 0.17 0.3 nd 1-3cm 0.26 nd 3-6cm nd nd nd: not detected. Limit of detection for NPD is 0.01 mg/kg, for PAH 0.005 mg/kg and for decalins 0.1mg/kg.

Metals

The results are shown in Table 4.4.5. For comparison the mean values from the present survey together with the data from the baseline survey in 2001 are given in Table 4.4.6. Bar diagram of the Ba content in the sediments is shown in Figure 4.4.2.

In the present investigation the concentration of Ba varies from 43 mg/kg at VAS6, 164°/500m to around 190 mg/kg at VAS1, 74°/250m and VAS9, 254°/250m.

Elevated Ba concentrations are only found at VAS1, 74°/250m, VAS2, 74°/500m and VAS9, 254°/250m. Thus elevated levels of Ba are only found out to 500m in the 74° directions and limited to 250m in the 254° direction. For the other stations the Ba concentration found is below the limit of contamination. Elevated Ba concentrations are also found in the vertical section 3-6 cm at VAS5. The Ba concentration increases downwards in the sediments. The content of Ba

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has increased at VHAS1, 74°/250m, VHAS2, 74°/500m and VHAS9, 254°/250m since the 2001 survey.

The concentration of heavy metals are low and at the same level as found in the baseline survey.

Valhall Flanke Sør, Ba 2005

0

25

50

75

100

125

150

175

200

225

250

275

300

VHAS1 VHAS2 VHAS5 VHAS6 VHAS9 VHAS10 VHAS113 VHAS14 VHALref

station

mg/kg

2001

2005

LSC A

Figure 4.4.2. Bar diagram of the Ba content in the sediments at Valhall Sørflanke, 2001- 2005. The following variation is found at Valhall Sørflanke in the top layer, 0-1 cm. The values are given in mg/kg: Valhall Sørflanke: VAS1 – VAS14 VAL Reference station Ba: 43 – 194 28 Cr: 6.3 – 7.2 7.7 Cu: <0.5 <0.5 Pb: 5.9 – 7.4 6.5 Zn: 4.9 – 5.8 5.6 Cd: <0.01 <0.01 Hg: <0.01 <0.01

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Table 4.4.5. Valhall Sørflanke 2005, metals (mg/kg dry sediment). Station Sample Ba Cd Cr Cu Hg Pb Zn 2005 2005 2005 2005 2005 2005 2005 VAS1 74°/250m 1 235 <0.01 6.6 <0.5 5.7 5.4 2 151 <0.01 6.8 0.6 6.0 5.7 3 193 <0.01 6.8 0.6 6.9 5.5 mean 193 <0.01 6.7 0.6 6.2 5.6 SD 42 0.1 0.6 0.2 VAS2 74°/500m 1 131 <0.01 6.9 0.6 6.8 6.0 2 220 <0.01 6.5 0.6 6.7 5.8 3 173 <0.01 6.5 1.0 6.3 5.4 mean 175 <0.01 6.6 0.7 6.6 5.7 SD 44 0.2 0.2 0.3 0.3 VAS5 164°/250m 1 39 <0.01 6.9 <0.5 0.02 6.4 5.4 2 74 <0.01 6.9 <0.5 <0.01 6.0 5.8 3 54 <0.01 6.6 0.5 0.01 5.9 5.4 mean 56 <0.01 6.8 <0.5 0.01 6.1 5.5 SD 17 0.2 0.3 0.2 1-3 cm 1 75 <0.01 6.6 0.5 0.01 6.4 5.9 3-6 cm 1 150 <0.01 7.8 0.6 <0.01 7.7 6.5 VAS6 164°/500m 1 41 <0.01 6.3 <0.5 6.0 4.9 2 45 <0.01 6.2 <0.5 5.6 4.8 3 41 <0.01 6.3 <0.5 6.0 5.0 mean 43 <0.01 6.3 <0.5 5.9 4.9 SD 2 0.1 0.2 0.1 VAS9 254°/250m 1 268 <0.01 7.5 0.5 7.7 5.8 2 120 <0.01 7.2 <0.5 6.2 5.4 3 192 <0.01 7.0 0.6 8.3 6.2 mean 194 <0.01 7.2 0.5 7.4 5.8 SD 74 0.2 1.1 0.4 VAS10 254°/500m 1 43 <0.01 6.9 0.5 7.0 5.7 2 54 <0.01 7.2 <0.5 6.3 5.5 3 75 <0.01 7.2 <0.5 6.6 5.5 mean 57 <0.01 7.1 <0.5 6.7 5.5 SD 16 0.2 0.3 0.1 VAS113 325°/250m 1 46 <0.01 6.5 <0.5 5.6 4.9 2 96 <0.01 7.4 <0.5 6.7 5.8 3 46 <0.01 6.9 <0.5 5.1 5.3 mean 63 <0.01 6.9 <0.5 5.8 5.3 SD 29 0.5 0.8 0.5 VAS14 344°/500m 1 40 <0.01 7.2 0.5 7.3 5.3 2 73 <0.01 7.4 <0.5 6.6 5.3 3 46 <0.01 7.1 <0.5 6.7 5.2 mean 53 <0.01 7.2 <0.5 6.9 5.3 SD 18 0.2 0.4 0.1 cont.

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Table 4.4.5. cont. Station Sample Ba Cd Cr Cu Hg Pb Zn 2005 2005 2005 2005 2005 2005 2005 VAL Ref. 254°/15000m 1 25 <0.01 7.6 0.5 <0.01 6.4 5.6 2 27 <0.01 7.7 <0.5 <0.01 6.0 5.6 3 26 <0.01 7.0 <0.5 <0.01 7.6 5.8 4 35 <0.01 7.6 <0.5 <0.01 6.1 5.7 5 27 <0.01 7.7 0.5 <0.01 6.6 5.5 mean 28 <0.01 7.7 <0.5 <0.01 6.5 5.6 SD 4 0.1 0.6 0.1 LSC Subregion A 76.2 8.0 1.3 7.4 6.9

Table 4.4.6. Valhall Sørflanke 2005, metals (mg/kg dry sediment), comparing mean values with the baseline survey in 2001. Station Ba Ba Cd Cd Cr Cr Cu Cu Hg Hg Pb Pb Zn Zn 2005 2001 2005 2001 2005 2001 2005 2001 2005 2001 2005 2001 2005 2001

VAS1 74°/250m 193 38 <0.01 <0.01 6.7 6.9 0.6 0.5 6.2 6.2 5.6 5.2 VAS2 74°/500m 175 36 <0.01 <0.01 6.6 6.9 0.7 0.4 6.6 6.3 5.6 5.3 VAS5 164°/250m 56 33 <0.01 <0.01 6.8 6.8 <0.5 0.4 0.01 <0.01 6.1 6.1 5.5 5.4 1-3 cm 75 51 <0.01 <0.01 6.6 7.4 0.5 0.9 0.01 <0.01 6.4 6.7 5.9 6.8 3-6 cm 150 79 <0.01 <0.01 7.8 7.3 0.6 0.6< <0.01 <0.01 7.7 6.3 6.5 5.6 VAS6 164°/500m 43 36 <0.01 <0.01 6.3 6.6 <0.5 0.4 5.9 6.0 4.9 5.2 VAS9 254°/250m 194 38 <0.01 0.01 7.2 7.1 0.5 0.4 7.4 6.5 5.8 5.4 VAS10 254°/500m 57 41 <0.01 <0.01 7.1 7.4 <0.5 0.5 6.7 6.5 5.5 5.4 VAS113 325°/250m 63 68 <0.01 <0.01 6.9 7.3 <0.5 0.5 5.8 6.7 5.3 6.0 VAS14 344°/500m 53 70 <0.01 <0.01 7.2 7.4 <0.5 0.5 6.9 6.5 5.3 5.7 VAL Ref 254°/15000m 28 53 <0.01 <0.01 7.7 8.1 <0.5 0.5 <0.01 <0.01 6.5 7.7 5.6 6.6

4.4.3 Biological analyses

A total of 134 species and 8785 individuals were sampled at 8 stations. Greatest abundance (61.9 %) was found among the polychaetes, of which the species Myriochele oculata constitutes 54.9 % and Paramphinome jeffreysii constitutes 18.4 %, see Table 4.4.7. Table 4.4.7. Number of species and individuals distributed between the main groups, Valhall Sørflanke 2005.

Individuals Species Main animal groups Number % Number %

Varia 572 6.5 13 9.7Polychaeta 5442 61.9 48 35.8- Paramphinome jeffreysii 1001 18.4 - Myriochele oculata 2985 54.9 Crustacea 306 3.5 30 22.4Mollusca 823 9.4 32 23.9Echinodermata 1642 18.7 11 8.2- Amphiura filiformis 1259 76.7 Total 8785 100.0 134 100.0

Figure 4.4.3 shows the numbers of species and individuals sampled at each station and variations between grab samples.

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0

20

40

60

80

100VAS-01VAS-02VAS-05VAS-06VAS-09VAS-10

VAS-113

VAS-14VAL-R

EF

Stations

No.

of s

peci

es (S

) Station º/m VAS-01 74/250 VAS-02 74/500 VAS-05 164/250 VAS-06 164/500 VAS-09 254/250 VAS-10 254/500 VAS-113 325/250 VAS-14 344/500 VAL-REF 254/15000

0400800

1200160020002400

VAS-01VAS-02VAS-05VAS-06VAS-09VAS-10

VAS-113

VAS-14VAL-R

EF

Stations

No.

of i

ndiv

idua

ls (N

) Ex. P. jeffreysii and M. oculata

0400800

1200160020002400

VAS-01VAS-02VAS-05VAS-06VAS-09VAS-10

VAS-113

VAS-14VAL-R

EF

Stations

No.

of i

ndiv

idua

ls (N

)

Figure 4.4.3. Numbers of species (S) and individuals (N) per 0.5 m2 (incl./excl. P. jeffreysii and M. oculata), mean values per grab sample and standard deviation, Valhall Sørflanke 2005.

The standard deviation was in general dramatically reduced when the two species P. jeffreysii and M. oculata were removed from the data. This is evident since the two species constitute 45.4 % of the total number of individuals. An exception is at stations VAS-09 and VAS-113, where the standard deviations were only slightly reduced. This is due to relatively large differences between the five grabs sampled at each station.

As for Valhall and Valhall Nordflanke yellowish granules were found in several of the grab samples at Valhall Sørflanke.

Diversity and dominant species

The dominant species at each station varied from 16.2 % at station VAS-06 (164°/500m) to 60.3 % at VAS-01 (74°/250m). The 10 most abundant species made up from 67.8 % at VAS-06 to 87.4 % at VAS-01, see Table 4.4.8. The bristle worms M. oculata and P. jeffreysii together with the brittle star Amphiura filiformis dominated the fauna in general at Valhall Sørflanke. Other frequently found species were the bristle worms Chaetozone setosa, Scoloplos armiger and Goniada maculata together with the hydroid Corymorpha nutans. This hydroid is usually found in sand or gravel sediments. Almost all of these species are suspension feeders or both suspension- and deposit feeders. P. jeffreysii is mainly a carnivore species. Most of these species are known indicators of organic pollution when they are found in high amounts. However, several of the above mentioned species have a planktonic developmental stage and are able to settle in large numbers.

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Table 4.4.8.The 10 most abundant species at each station,Valhall Sørflanke 2005. 10 most dominating species

VAS-01 No. % Cum. % VAS-02 No. % Cum. % Myriochele oculata 1460 60.3 60.3 Myriochele oculata 560 41.7 41.7Paramphinome jeffreysii 194 8.0 68.3 Amphiura filiformis 218 16.2 58.0Amphiura filiformis 186 7.7 76.0 Paramphinome jeffreysii 126 9.4 67.4Chaetozone setosa 49 2.0 78.0 Corymorpha nutans 47 3.5 70.9Ditrupa arietina 46 1.9 79.9 Aonides paucibranchiata 33 2.5 73.3Aonides paucibranchiata 41 1.7 81.6 Echinoidea spp.juv. 25 1.9 75.2Nemertea spp. 39 1.6 83.2 Caudofoveata spp. 23 1.7 76.9Phoronis muelleri 39 1.6 84.8 Chaetozone setosa 22 1.6 78.5Echinoidea spp.juv. 34 1.4 86.3 Scoloplos armiger 21 1.6 80.1Eudorellopsis deformis 28 1.2 87.4 Goniada maculata 17 1.3 81.4 VAS-05 No. % Cum. % VAS-06 No. % Cum. % Myriochele oculata 170 24.3 24.3 Amphiura filiformis 101 16.2 16.2Amphiura filiformis 90 12.9 37.2 Paramphinome jeffreysii 96 15.4 31.6Paramphinome jeffreysii 50 7.2 44.4 Myriochele oculata 55 8.8 40.4Montacuta substriata 44 6.3 50.6 Corymorpha nutans 41 6.6 47.0Corymorpha nutans 29 4.2 54.8 Scoloplos armiger 34 5.5 52.4Goniada maculata 28 4.0 58.8 Aonides paucibranchiata 28 4.5 56.9Echinoidea spp.juv. 26 3.7 62.5 Montacuta substriata 20 3.2 60.1Eudorellopsis deformis 23 3.3 65.8 Goniada maculata 19 3.0 63.1Cylichna cylindracea 18 2.6 68.4 Caudofoveata spp. 15 2.4 65.5Sthenelais limicola 17 2.4 70.8 Nemertea spp. 14 2.2 67.8 VAS-09 No. % Cum. % VAS-10 No. % Cum. % Myriochele oculata 195 19.2 19.2 Amphiura filiformis 182 21.6 21.6Amphiura filiformis 191 18.8 38.1 Myriochele oculata 160 19.0 40.7Paramphinome jeffreysii 165 16.3 54.3 Paramphinome jeffreysii 99 11.8 52.4Echinoidea spp.juv. 86 8.5 62.8 Echinoidea spp.juv. 63 7.5 59.9Chaetozone setosa 29 2.9 65.7 Montacuta substriata 41 4.9 64.8Eudorellopsis deformis 26 2.6 68.2 Sthenelais limicola 25 3.0 67.8Goniada maculata 26 2.6 70.8 Scoloplos armiger 23 2.7 70.5Nemertea spp. 25 2.5 73.3 Chaetozone setosa 22 2.6 73.1Corymorpha nutans 21 2.1 75.4 Eudorellopsis deformis 20 2.4 75.5Cylichna cylindracea 20 2.0 77.3 Goniada maculata 17 2.0 77.5 VAS-113 No. % Cum. % VAS-14 No. % Cum. % Myriochele oculata 185 18.5 18.5 Myriochele oculata 200 23.6 23.6Amphiura filiformis 170 17.0 35.6 Paramphinome jeffreysii 135 16.0 39.6Montacuta substriata 145 14.5 50.1 Amphiura filiformis 121 14.3 53.9Paramphinome jeffreysii 136 13.6 63.7 Echinoidea spp.juv. 46 5.4 59.3Echinoidea spp.juv. 54 5.4 69.1 Chaetozone setosa 24 2.8 62.2Scoloplos armiger 25 2.5 71.6 Goniada maculata 22 2.6 64.8Corymorpha nutans 22 2.2 73.9 Antalis entale 19 2.3 67.0Cylichna cylindracea 22 2.2 76.1 Phoronis muelleri 19 2.3 69.3Goniada maculata 20 2.0 78.1 Eudorellopsis deformis 18 2.1 71.4Antalis entale 17 1.7 79.8 Abra prismatica 18 2.1 73.5

The number of species varied from 59 at station VAS-06 (164º/500m) to 69 at VAS-01 (74º/250m). The numbers of individuals varied from 614 at VAS-06 to 2384 at VAS-01. The Shannon Wiener diversity index varied from 2.5 at the Valhall reference station (254º/15000m) and 2.6 at station VAS-01 to 4.5 at station VAS-06 and the Hurlberts index (ES100) varied from 18 (reference station and station VAS-01) to 30 (station VAS-06) including M. oculata.

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In general, removing M. oculata from the data gives somewhat higher indices, but not significantly. Indices above 4 indicate a relatively undisturbed fauna. Indices between 3 and 4 indicate a slight disturbance, while indices between 2 and 3 indicate a definite disturbance in the fauna. In general ES100 indices above 20 characterize a relatively normal fauna community.

The biodiversity at Valhall Sørflanke is in general relatively high compared to the rest of the Ekofisk region when including M. oculata. However, some of the biodiversity indices indicate a small disturbance in the fauna community see Table 4.4.9. The fauna at the reference station (254º/15000m) and at VAS-01 deviates from the others with the lowest indices. Traces of oil were observed in one of the VAS-01 grab samples. Table 4.4.9. Numbers of individuals (N) and species (S), depth, Shannon-Wiener diversity index (H’), Pielou’s evenness index (J), and expected number of species per 100 individuals (ES100) for each station at Valhall Sørflanke 2005 (excl. juv.).

H' ES100 Station Direction ° Distance m Depth S N Incl.

M. o. Excl. M. o.

J Incl. M. o.

Excl. M. o.

VAS-01 74 250 68 69 2384 2.6 4.3 0.4 18 28VAS-02 74 500 68 61 1316 3.4 4.2 0.6 22 29VAS-05 164 250 68 60 668 4.3 4.7 0.7 28 31VAS-06 164 500 68 59 614 4.5 4.5 0.8 30 30VAS-09 254 250 68 69 925 4.0 4.1 0.7 26 28VAS-10 254 500 68 64 778 4.0 4.2 0.7 27 29VAS-113 325 250 69 63 942 3.9 3.9 0.7 24 25VAS-14 344 500 69 67 799 4.1 4.4 0.7 27 30VAL-REF 254 15 000 72 63 1771 2.5 4.3 0.4 18 29M. o.= M. oculata

Classification and ordination

The dendrogram from the cluster analysis and the MDS plot from the ordination analysis based on station level are presented in Figure 4.4.4 and Figure 4.4.5.

The Valhall Sørflanke stations including the Valhall reference station (254°/15000m) split into two main groups at a similarity of about 65 %. The reference station forms a group together with VAS-01 (74°/250m) and VAS-02 (74°/500m). The other group consists of the remaining field stations. The differences between the groups are caused by high numbers of the bristle worms M. oculata, P. jeffreysii and Ditrupa arietina together with the brittle star A. filiformis at the reference station and VAS-01 and VAS-02 compared to the other stations. The suspension feeders M. oculata, A. filiformis and D. arietina are, according to Simboura & Zenetos (2002), not sensitive species, i.e. they are tolerant to disturbance and may respond to organic enrichment. There are also high numbers of the mussel M. substriata at the other Valhall Sørflanke stations. Group 1 is further subdivided at about 75 % similarity. The differences between these subgroups are caused by high numbers of M. oculata, P. jeffreysii and A. filiformis at VAS-09 (254°/250m) and VAS-14 (344°/500m) and higher numbers of the mussel M. substriata in the fauna at the other VAS stations. M. oculata, P. jeffreysii and A. filiformis are all known as indicator species when appearing in large amounts. However, these species are found in larger numbers at the reference station and there is not any clear correlation between the variation in the fauna and the measured environmental factors.

The Bioenv analysis reveals a correlation of 0.6 between the fauna and a combination of the environmental factors Cd and Cu, thus indicating a relationship. The Cd and Cu levels are, however, low and uniform, and the correlation factor can be considered an artifact caused by uniform conditions in the sampled area. However, observations of oil and organic matter in the VAS-01 sample under processing probably originated from deeper layers of the sediment.

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VAS-

0 9

VAS-

14

VAS-

113

VAS-

05

VAS-

0 6

VAS-

10

VAL-

REF

VAS -

01

VAS-

02

100

90

80

70

60Si

mila

rity

Group 1 Group 2

254/250m 344/500m 325/250m 164/250m 164/500m 254/500m 254/15000m 74/250m 74/500m

Figure 4.4.4. Dendrogram of stations from Valhall Sørflanken 2005 (excl. juv.).

VAS-01

VAS-02

VAS-05

VAS-06

VAS-09

VAS-10

VAS-113

VAS-14

VAL-REF

Stress: 0,04

254/15000m, 74/250m, 74/500m

Group 1 Group 2

254/250m, 344/500m

325/250m, 164/250m, 164/500m, 254/500m

Figure 4.4.5. MDS plot of stations from Valhall Sørflanke 2005 (excl. juv.).

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Comparison 2001 and 2005

In Figure 4.4.6 the results from the present study are compared to the results from the baseline survey in 2001. The numbers of individuals are shown inclusive and exclusive the bristle worms M. oculata and P. jeffreysii. There are some increases in the numbers of species at some stations since 2001. With the exception of station VAS-01 (74/250m), the numbers of individuals have decreased significantly since the baseline study in 2001. The decrease is mainly due to a decline of M. oculata after a peak in 2001/20021. As a consequence the biodiversity indices (incl. M. oculata) have increased significantly at all stations in the same period. Whitout M. oculata there is a general decrease in the biodiversity since 2001.

020406080

VAS-01

VAS-02

VAS-05

VAS-06

VAS-09

VAS-10

VAS-113

VAS-14

Stations

No.

of s

peci

es (S

)

2001 2005

Station º/m

VAS-01 74/250 VAS-02 74/500 VAS-05 164/250 VAS-06 164/500 VAS-09 254/250 VAS-10 254/500 VAS-113* 325/250 VAS-14 344/500 *: Historical data from VAS-13.

Cont.

0

1000

2000

3000

VAS-01

VAS-02

VAS-05

VAS-06

VAS-09

VAS-10

VAS-113

VAS-14

Stations

No.

of i

ndiv

idua

ls (N

)

2001 2005

0123456

VAS-01

VAS-02

VAS-05

VAS-06

VAS-09

VAS-10

VAS-113

VAS-14

Stations

H'

2001 2001ex. M.oculata2005 2005-ex. M. oculata

Figure 4.4.6. Numbers of species (S) and individuals (N) per 0.5 m2 and diversity (H’), incl. P. jeffreysii and M. oculata, excl. juv.), Valhall Sørflanke 2001 and 2005.

Classification and ordination analyses

The sampled stations from 2001 and 2005 have been analysed at family level∗. The dendrogram from the cluster analysis reveals two main groups at about 55 % similarity, based on years. The differences between years are caused by the decline of species within the family Oweniidae (mainly M. oculata) from 2001 to 2005. Also high abundances of species within the families Amphinomidae (mainly P. jeffreysii), Amphiuridae (mainly A. filiformis) and

1 The great variations in the presence of M. oculata from 1996 to 2005 are dicussed in Chapter 5.2 - General Trends

in the Region. ∗ Necessary when comparing between years, to avoid significant source of error due to both different years and

different taxonomists.

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Corymorphidae (mainly Corymorpha nutans) in 2005 contributed to the difference between the two groups.

The Bioenv analysis only gave a weak correlation (0.4) between the fauna and the environmental factors THC, Ba and average grain size. This does not indicate any major relationship between the environmental factors and the development in the fauna over the years.

VAS-

05-2

001

VAS -

07-2

001

VAS-

08-2

001

VAS -

12-2

001

VAS-

15-2

001

VAS-

03-2

001

VAS-

04-2

0 01

V AS-

13-2

001

V AS-

09-2

001

VAS-

10-2

0 01

VAS -

14-2

001

VAS-

01-2

0 01

VAS-

0 2-2

001

VAS-

06-2

001

VAS-

09- 2

005

VAS-

14- 2

005

VAS-

06-2

005

VAS -

113-

2005

VAS-

05-2

005

VAS-

10-2

005

VAS -

01-2

005

VAS-

02-2

0 05

100

90

80

70

60

50

Sim

ilarit

y

a b

Figure 4.4.7. Dendrogram showing similarity between Valhall Sørflanke stations 2001 and 2005. Family level, incl. M. oculata, excl. juv., sq. root transformation.

4.4.4 Conclusions

The sediments at Valhall Sørflanke consist mainly of fine sand, and the sand content varies from 93.1 % at VAS113, 325°/250m, to 97.4 % at VAS10, 254°/500m. The average sand content is 95.4 %. The gravel content is low, and only small amounts are found at three of the stations. The silt and clay content is also low. The average silt and clay concentration found is 4.3 %. The total organic matter is low, varying from 0.6 % to 0.8 %. This is in accordance with sediments of homogeneous, fine sand.

The concentrations of hydrocarbons are low and at the same level as in the 2001 baseline survey. In the present survey the THC concentrations in the top 0-1 cm layer vary from 3.6 mg/kg at VAS7 164°/1000m to 5.3 mg/kg at VAS1 74°/250m.At one station the deeper layers, 1-3 cm and 3-6 cm, are analysed. A tendency of slightly higher concentrations of THC down in the sediments is observed. The content of THC is considered to be within the natural level at Valhall Sørflanke and none of the stations are contaminated.

The concentrations of NPD, PAH and decalins are low for the station investigated, VAS5 at 164°/250m. The contents are just below or above the limit of contamination.

In the present investigation the Ba concentrations vary from 43 mg/kg at VAS6, 164°/500m to around 190 mg/kg at VAS1, 74°/250m and VAS9, 254°/250m. Elevated Ba concentrations are

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only found at VAS1, 74°/250m, VAS2, 74°/500m and VAS9, 254°/250m. Thus elevated levels of Ba are found out to 500m in the 74° directions and limited to 250m in the 254° direction. For the other stations the Ba concentration is below the limit of contamination. Elevated Ba concentrations are also found in the deeper section 3-6 cm at VAS5. The Ba concentrations increase downwards in the sediments. The content of Ba has increased at VHAS1, VHAS2 and VHAS9 since the 2001 survey. This is in accordance with discharge of barite and cuttings in 2003 and 2004.

The concentration of heavy metals are low and at the same level as in the baseline survey.

The chemical results are in correspondence with the drilling history at Valhall Sørflanke.

The biodiversity indices are relatively high compared to several other fields in the central Ekofisk region. However, they indicate a small disturbance in the fauna community which presumably reflects a physical disturbance as well as a general diffuse organic load in the area. The fauna community at station VAS-01 (74/250m) in particular, but also station VAS-02 (74/500) differed slightly from the other stations in the similarity analysis and also showed somewhat lower biodiversity indices. The levels of metals and THC in the sediments were not elevated at these stations. The oil and organic matter that was observed in the VAS-01- and -02 samples, probably originated from somewhat deeper layers of the sediment.

The indices have increased considerably since the baseline survey in 2001 and the reason for this is partly a significant decline in the abundance of the bristle worm M. oculata since 2001. In general the levels of THC and metals in the sediments have decreased since 2001.

Yellow granules (see Valhall for details) were found in most of the samples.

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4.5 Hod

4.5.1 Sediment characterization

Grain size distribution

The grain size distribution from the present survey is shown in Table 4.5.1 together with the silt and clay content from the previous surveys in 2002, 1999 and 1996.

The sediments at Hod consist mainly of fine sand, and the sand content ranges from 91.2 % at HOD13 (164°/1000m) to 97.3 % at HOD19 (54°/500m). The median particle diameter is 2.74φ. The average silt and clay concentration is 6.2 % compared to 3.0 % in 2002, 3.6 % in 1999 and 5.8 % in 1996 for the same stations. The gravel content is generally low, below 0.6 mg/kg. At the Hod reference station (180°/15000m) the sediment is characterized as fine sand with 99 % sand and a median particle diameter of 2.66φ. The silt and clay content is slightly lower than the content found in previous surveys.

The sediments at Hod are quite similar to the sediments at Valhall, the neighbouring field situated north of Hod. The results from the complete grain size distribution are given in Appendix C. Table 4.5.1. Hod 2005, grain size distribution. Station Median

diameter Classification Grain size distrib. 2005 (%) 2002

(%) 1999 (%)

1996 (%)

Mdφ Silt and clay

Sand Gravel Silt and clay

Silt and clay

Silt and clay

HOD2 74°/ 500m 2.76 Fine sand 7.8 91.6 0.6 6.0 7.1HOD8 74°/500m 2.74 Fine sand 5.6 94.4 0.0 5.2 4.8HOD13 164°/1000m 2.74 Fine sand 8.6 91.2 0.2 6.0 4.7 9.7HOD19 254°/500m 2.71 Fine sand 2.7 97.3 0.0 4.6 5.8Mean 2.74 6.2 93.6 0.2 5.5 4.8 7.5St. dev. 0.02 2.6 2.8 0.3 0.7 0.1 2.0 HOD Ref.

180°/15000m 2.66 Fine sand 1.0 99.0 0.0 3.0 3.6 5.8

Total organic matter (TOM)

The TOM results are shown in Table 4.5.2. The content of TOM in the sediments is low and only small variations are found at the field. The minimum content, 0.78 %, is found at HOD reference station (180°/15000m) and the maximum content, 1.3 %, is found at HOD8 (74°/500m). The TOM content is similar to results from previous surveys in 2002, 1999 and 1996. Table 4.5.2. Hod 2005, total organic matter (% of dry sediment). Station 2005. 0-5 cm Mean

2002 Sd

2002 Mean 1999

Mean 1996

HOD2 74°/ 500m 1.08 1.02 0.08 1.13 HOD8 74°/500m 1.27 0.93 0.13 1.05 1.18 HOD13 164°/1000m 1.04 HOD19 254°/500m 0.96 HOD Ref. 180°/15000m 0,78 0.78 0.05 0.71 0.92

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4.5.2 Chemical analyses

Parameters analysed in the sediments at Hod:

• THC • Olefins • NPD, PAH, decalins • Metals (Ba, Cd, Cr, Cu, Hg, Pb, Zn)

Three replicate samples at each station and five replicate samples at the reference station are analysed. The samples are taken from the top 0-1 cm sediment layer. In addition the 1-3 cm and 3- 6 cm sediment layers are sampled at two stations and the reference station.

There has been no drilling activity since 1995, and any increase of contaminated area is therefore not expected. The sampling program is somewhat reduced compared to previous survey. However the 250m station, HOD19, not investigated since 1996, is included in this survey.

THC and olefins

The THC results including olefins are shown in Table 4.5.3, and olefins are shown separately in Table 4.5.4. The corresponding THC and olefin data from the previous surveys in 2002, 1999 and 1996 are also included for comparison. One station at 250m distance is included in the present survey, HOD19 (344°/250m). This station was last analysed in the 1996 survey.

Bar diagram of the THC content in the sediments is shown in Figure 4.5.1.

In 1999 the mean concentration of THC in the top layer ranged from 3.9 mg/kg at the HOD reference station (180°/15000m) to 135 mg/kg at HOD8 (164°/500m). Olefins were detected at the four stations analysed, and ranged from 1.2 mg/kg at HOD3 (74°/1000m) to 7.8 mg/kg at HOD8 (164°/500m).

In 2002 the mean concentrations ranged from 4.1 mg/kg at the HOD reference station to 165 mg/kg at HOD2 (74°/500m). Olefins were detected at the six stations analysed, and ranged from 0.8 mg/kg at HOD15 (254°/1000m) to 17.1 mg/kg at HOD2 (74°/500m). In the present survey the mean concentration of THC varies from 4.3 mg/kg at the reference station, to 36 mg/kg at HOD8 (164°/500m). Olefins are detected at the six stations analysed, from 0.7 mg/kg (HOD3, 74°/1000m) to 7.1 mg/kg (HOD8, 164°/500m).

HOD2 was the most contaminated station, concerning THC and olefins in the 2002 survey. Compared to the 2002 survey the concentrations of THC have decreased from 165 mg/kg almost to the background level and the content of olefins from 17.6 mg/kg to 0.9 mg /kg.

At HOD8 the concentration of THC in the top 0-1 cm layer is unchanged since the 2002 survey. However a distinct decrease is observed in the deeper layers, in the 1-3 cm layer from 210 mg/kg to 41 mg/kg and in the 3-6 cm layer from 27 mg/kg to 11 mg/kg.

At the other stations the concentrations are similar to the previous surveys. The olefin concentrations have decreased compared to previous surveys for all the stations investigated. This is also in agreement with the results observed for THC.

No discharges of olefins have taken place since 1994 (337 tonnes of Novasol) and 1995 (85 tonnes of Novaplus). The olefin concentration is low and at the same level for all the stations, in average 1 mg/kg. An exception is observed for HOD8 with an olefin concentration of 7 mg/kg.

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Elevated THC levels are found at HOD8, 164°/500m. The stations HOD2, 74°/500m and HOD13, 254°/315m are only slightly elevated. The other stations have THC content below the the limit of contamination for this region.

The HOD reference station, 180°/15000m, is still uncontaminated, and the mean THC concentration of five replicate samples is 4.3 mg/kg.

Representative gas chromatograms are given in Appendix C. These include HOD3 (74°/1000m), HOD8, (164°/500m) all three layers, HOD9 (164°/1000m), HOD13 (254°/315m) and the HOD reference station (180°/15000m).

Hod, THC 2005

0

10

20

30

40

50

60

70

80

90

100

HOD2 HOD3 HOD8 HOD9 HOD13 HOD14 HOD19 HOD20 HOD ref

station

mg/kg

1999

2002

2005

LSC A

165±196 135±48,3

Figure 4.5.1. Bar diagram of the THC content in the sediments at Hod 1999-2005.

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Table 4.5.3. Hod 2005, total hydrocarbon content (mg/kg dry sediment). Station Grab

#1 Grab

#2 Grab

#3 Grab

#4 Grab

#5 Mean SD Mean Mean Mean

2005 2005 2002 1999 1996 HOD2 74°/500m 10.9 6.6 5.9 7.8 2.7 165 18.1 HOD3 74°/1000m 3.7 6.9 2.7 4.5 2.2 10.6 13.2 7.6 HOD8 164°/500m 29.7 25.8 52.4 36 14 37 135 65 1-3 cm 41.4 210 59 54 3-6 cm 10.6 27 47 89 HOD9 164°/1000m 6.7 5.8 6.3 6.2 0.5 9.6 12.6 39

1-3 cm 5.6 10.5 3-6 cm 5.4 17

HOD13 254°/315m 9.0 11.3 5.2 8.5 3.1 HOD14 254°/500m 4.7 5.3 6.1 5.4 0.7 9.6 55 HOD19 344°/250m 4.8 4.2 4.5 4.5 0.3 10.9 HOD20 344°/500m 6.5 3.6 5.9 5.3 1.5 8.1 10.3 12.7 HOD Ref. 180°/15000m 3.9 4.8 3.2 3.8 5.8 4.3 1.0 4.1 3.9 5.3

1-3 cm 3.8 5.3 3.8 6.2 3-6 cm 5.4 6.0 6.2 7.2

LSC Region A 6.6 6.4 9 Table 4.5.4. Hod 2005, olefins (mg/kg dry sediment). Station Grab #1 Grab #2 Grab #3 Mean SD Mean Mean Mean

2005 2005 2002 1999 1996 HOD2 74°/500m 0.9 0.9 0.9 0.9 0.0 17.6 1.7 HOD3 74°/1000m 0.5 1.1 0.5 0.7 0.4 1.7 1.2 0.3 HOD8 164°/500m 6.3 6.5 8.4 7.1 1.2 11.2 7.8 2.2 1-3 cm 6.0 3-6 cm 0.8 HOD9 164°/1000m 1.0 0.7 1.0 0.9 0.1 1.5 1.5 3.6

1-3 cm 0.6 3-6 cm 0.5

HOD13 254°/315m 1.3 1.5 0.7 1.1 0.4 2.0 11.9 HOD14 254°/500m 0.9 0.8 1.0 0.9 0.1 1.3 1.3 0.3

NPD, PAH and decalins

Two stations are analysed in addition to the HOD reference station (180°/15000m), HOD8 (164°/500m) and HOD9 (164°/1000m). The results are shown in Table 4.5.5.

In 1999 elevated levels of NPD, PAH and decalins were found at HOD8, and the concentrations in the deeper sections were relatively high. In 2002 elevated levels of NPD, PAH and decalins were found at HOD2, HOD8 and in the layers at HOD9. The concentration of decalins was relatively high, and thus confirmed the presence of drilling mud base oil in the sediments.

In the present survey the NPD concentrations vary from 0.016 mg/kg at the reference station to 0.085 mg/kg at HOD8. Elevated concentrations of NPD are found at HOD8 in all three layers and in the vertical sections of HOD9. The NPD concentrations are similar or lower compared to the 2002 survey.

The PAH concentrations vary from 0.047 mg/kg at the reference station to 0.23 mg/kg in the 3-6 cm layer at HOD8 and HOD9. The top sediment layer at HOD8 and HOD9 has PAH

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concentrations just at the limit of contamination, while the PAH content in the layers are above this limit. No change is observed since the previous survey.

The decalin concentrations vary from below 0.01 mg/kg at HOD9 and HOD Ref to 1.6 mg/kg in the 1-3 cm layer at HOD8. Comparing to the 2002 survey, the decalin content is slightly higher in the top 0-1 cm layer, considerably lower in the 1-3 cm layer and unchanged in the 3-6 cm layer.

Elevated levels are not found at the reference station. Table 4.5.5. Hod 2005, sum NPD, PAH and decalins (mg/kg dry sediment). Station Grab

#1 Grab

#2 Grab

#3 Grab

#4 Grab

#5 Mean SD Mean SD Mean SD Mean

2005 2005 2002 2002 1999 1999 1996NPD HOD8 164°/500m 0.056 0.083 0.12 0.085 0.03 0.066 0.02 0.22 0.07 0.33 1-3 cm 0.18 0.54 0.13 0.43 3-6 cm 0.064 0.086 0.14 0.47HOD9 164°/1000m 0.032 0.023 0.021 0.025 0.01 0.026 0.002 1-3 cm 0.042 0.030 3-6 cm 0.067 0.058 HOD Ref. 180°/15000m 0.031 0.009 0.014 0.011 0.015 0.016 0.01 0.019 0.003 0.013 0.002 0.020 1-3 cm 0.016 0.037 0.014 0.024 3-6 cm 0.020 0.033 0.25 0.029LSC Subregion A 0.030 0.026 0.040 PAH HOD8 164°/500m 0.072 0.044 0.078 0.065 0.018 0.064 0.02 0.074 0.014 0.089 1-3 cm 0.18 0.15 0.16 0.085 3-6 cm 0.23 0.20 0.20 0.14HOD9 164°/1000m 0.075 0.095 0.061 0.077 0.017 0.058 0.005 1-3 cm 0.12 0.071 3-6 cm 0.23 0.123 HOD Ref. 180°/15000m 0.052 0.046 0.041 0.041 0.054 0.047 0.006 0.046 0.007 0.038 0.006 0.081 1-3 cm 0.070 0.076 0.040 0.10 3-6 cm 0.080 0.074 0.32 0.11LSC Subregion A 0.061 0.062 0.090 Decalins HOD8 164°/500m 0.4 0.6 1.8 0.91 0.7 0.49 0.15 4.71 1.30 3.39 1-3 cm 1.6 8.31 2.11 4.34 3-6 cm 0.4 0.36 1.48 2.11HOD9 164°/1000m nd nd nd nd nd 1-3 cm nd nd 3-6 cm nd 0.095 HOD Ref. 180°/15000m 0.76 0.011 0.27 0.077 0.082 0.24 0.3 nd nd 0.047 1-3 cm nd nd nd 0.061 3-6 cm nd nd nd 0.075nd: not detected. Limit of detection for NPD is 0.01 mg/kg, for PAH 0.005 mg/kg and for decalins 0.1 mg/kg.

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Metals

The results are shown in Table 4.5.6. Data from the previous surveys in 2002 and 1999 are also included for comparison in Table 4.5.7. Bar diagram of the Ba content in the sediments is shown in Figure 4.5.2.

In 1999 the Ba concentrations ranged from 31 mg/kg (HOD Ref., 180°/15000m) to 1600 mg/kg (HOD8, 164°/500m) and in 2002 from 45 mg/kg (HOD Ref.) to 1520 mg/kg (HOD2, 74°/500m).

In the present investigation the Ba concentrations vary from 32 mg/kg at HOD reference station to 900 mg/kg at HOD2.

Elevated Ba concentrations are found at all stations, except for the reference station. This means out to 1000m in the 164° direction, to 500m in the 74° direction, to 315m in the 254° direction and to 250m in the 344° direction. In general the Ba levels are similar to the levels found in previous surveys. Elevated Ba concentrations are found in the deeper sections at HOD8 and HOD9, and the concentration increase downwards in the sediments.

The concentrations of the heavy metals are low, and similar to the 2002 and 1999 survey. Elevated concentrations of Cr and Cu are not found. Slightly elevated concentrations of Pb and Zn are found at almost all stations. The highest concentrations are found at HOD2. Cd and Hg concentrations are below the detection limit.

Hod, Ba 2005

0

500

1000

1500

2000

2500

HOD2 HOD8 HOD9 HOD13 HOD19 HOD ref

station

mg/kg

1999

2002

2005

LSC A

Figure 4.5.2. Bar diagram of the Ba content in the sediments at Hod 1999-2005.

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The following variation is found at Hod in the top layer, 0-1 cm. The values are given in mg/kg: Hod: HOD2 – HOD19 HOD Reference stationBa: 187 - 901 32 Cr: 6.9 – 8.9 7.1 Cu: 0.6 – 1.0 <0.5 Pb: 7.4 – 10.5 5.8 Zn: 6.5 – 8.6 5.9 Cd: <0.01 <0.01 Hg: <0.01 <0.01

Table 4.5.6. Hod 2005, metals (mg/kg dry sediment). Station Sample Ba Cd Cr Cu Hg Pb Zn 2005 2005 2005 2005 2005 2005 2005 HOD2 74°/500m 1 715 <0.01 7.4 0.8 9.3 7.4 2 792 <0.01 7.7 0.9 10.6 8.6 3 1196 0.01 8.9 1.1 11.6 9.8 mean 901 <0.01 8.0 0.94 10.5 8.6 SD 259 - 0.8 0.14 1.2 1.2HOD8 164°/500m 1 727 <0.01 7.4 1.1 0.01 8.5 7.3 2 751 <0.01 7.3 0.8 <0.01 9.5 7.2 3 703 <0.01 7.3 1.2 <0.01 8.6 7.0 mean 727 <0.01 7.3 1.0 <0.01 8.9 7.2 SD 24 0.1 0.2 0.5 0.2 1-3 cm 1 1227 0.02 8.2 1.4 0.01 11.0 10.6 3-6 cm 1 1660 0.07 12.6 2.6 0.02 18.3 20.8HOD9 164°/1000m 1 217 <0.01 8.1 0.7 <0.01 8.0 8.3 2 150 <0.01 7.1 0.5 <0.01 8.4 6.6 3 194 <0.01 7.6 0.6 0.01 11.0 7.2 mean 187 <0.01 7.6 0.6 <0.01 9.1 7.4 SD 34 0.5 0.11 1.6 0.9 1-3 cm 1 250 <0.01 7.6 0.8 0.01 8.7 7.4 3-6 cm 1 422 0.01 8.8 1.0 <0.01 9.6 9.3HOD13 254°/315m 1 426 <0.01 6.8 0.8 8.4 6.7 2 578 <0.01 6.9 0.8 9.3 7.2 3 575 <0.01 7.0 0.8 8.4 7.4 mean 527 <0.01 6.9 0.8 8.7 7.1 SD 87 0.1 0 0.5 0.4HOD19 344°/250m 1 239 <0.01 6.7 0.6 7.0 6.5 2 434 <0.01 7.2 0.7 7.7 6.8 3 187 <0.01 6.7 0.5 7.6 6.1 mean 287 <0.01 6.9 0.6 7.4 6.5 SD 130 0.3 0.1 0.4 0.4Cont.

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Table 4.5.6. cont. HOD Ref. 180°/15000m 1 40 <0.01 7.3 <0.5 <0.01 5.9 6.0 2 31 <0.01 6.9 <0.5 <0.01 5.9 6.3 3 27 <0.01 7.1 <0.5 <0.01 5.6 5.7 4 33 <0.01 7.3 <0.5 <0.01 5.8 5.8 5 30 <0.01 7.2 <0.5 <0.01 5.6 5.7 mean 32 <0.01 7.1 <0.5 <0.01 5.8 5.9 SD 5 <0.01 0.2 0.1 0.3 1-3 cm 45 <0.01 7.8 <0.5 <0.01 6.5 6.7 3-6 cm 86 <0.01 7.6 <0.5 <0.01 8.2 7.4LSC Subregion A 76.2 8.0 1.3 7.4 6.9 Table 4.5.7. Hod 2005, metals (mg/kg dry sediment), comparing mean values with previous surveys. Station Ba Ba Ba Ba Cd Cd Cd Cr Cr Cr 2005 2002 1999 1996 2005 2002 1999 2005 2002 1999HOD2 74°/500m 901 1520 1180 <0.01 0.04 8.0 7.1

HOD8 164°/500m 727 762 1600 1990 <0.01 <0.01 0.02 7.3 7.0 7.8

1-3 cm 1227 1330 1680 0.02 0.03 0.03 8.2 8.9 8.8 3-6 cm 1660 1252 1780 0.07 0.04 0.04 12.6 9.6 9.9 HOD13 254°/315m 527 <0.01 6.9 HOD9 164°/1000m 187 320 332 515 <0.01 <0.01 <0.02 7.6 7.2 7.8 1-3 cm 250 854 <0.01 0.02 7.6 8.4 3-6 cm 422 839 0.01 0.03 8.8 9.4 HOD19 344°/250m 287 <0.01 6.9 HOD Ref. 180°/15000m 32 45 31 48 <0.01 <0.04 <0.02 7.1 6.9 6.6 1-3 cm 45 51 29 <0.01 <0.01 <0.02 7.8 7.0 6.8 3-6 cm 86 89 53 <0.01 <0.01 <0.02 8.4 7.2 7.2 Cont. Table 4.5.7 cont. Station Cu Cu Cu Hg Hg Hg Pb Pb Pb Zn Zn Zn 2005 2002 1999 2005 2002 1999 2005 2002 1999 2005 2002 1999HOD2 74°/500m 0.9 1.9 10.5 14.2 8.6 12.6 HOD8 164°/500m 1.0 1.5 1.1 <0.01 0.02 0.03 8.9 9.4 11.7 7.2 7.7 11.2 1-3 cm 1.4 2.3 1.3 0.01 0.02 0.03 11.0 12.2 12.9 10.6 18.7 13.1 3-6 cm 2.6 2.5 1.4 0.02 0.02 0.04 18.3 13.0 13.3 20.8 14.3 17.4 HOD9 164°/1000m 0.6 1.8 0.6 <0.01 0.01 9.1 8.7 7.3 7.4 8.4 7.5 1-3 cm 0.8 1.8 0.01 0.02 8.7 11.1 7.4 11.6 3-6 cm 1.0 2.8 <0.01 0.02 9.6 12.7 9.3 12.9 Cont.

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Table 4.5.7 cont. Station Cu Cu Cu Hg Hg Hg Pb Pb Pb Zn Zn Zn 2005 2002 1999 2005 2002 1999 2005 2002 1999 2005 2002 1999HOD13 254°/315m 0.8 8.7 7.1 HOD19 344°/250m 0.6 7.4 6.5 HOD Ref. 180°/15000m <0.5 1.0 0.4 <0.01 0.01 0.01 5.8 6.1 6.2 5.9 6.0 5.3 1-3 cm <0.5 1.1 0.4 <0.01 0.01 0.01 6.5 6.1 6.3 6.7 6.6 5.3 3-6 cm <0.5 1.2 0.5 <0.01 0.02 0.01 8.2 6.9 6.7 7.4 6.8 5.9 4.5.3 Biological analyses

A total of 134 species and 5701 individuals were sampled at 5 stations. Greatest abundance (70.7 %) was found among the polychaetes, of which the species Paramphinome jeffreysii and Myriochele oculata constitutes about 49.1 % and 17.6 % respectively of the total number of Polychaeta, see Table 4.5.8. There were also relative high abundances of echinoderms, mostly due to the newly settled brittle star Amphiura filiformis. Table 4.5.8. Number of species and individuals distributed between the main groups, Hod 2005.

Individuals Species Main animal groups Number % Number %

Varia 249 4.4 17 12.7Polychaeta 4028 70.7 64 47.8- Paramphinome jeffreysii 1978 49.1 - Myriochele oculata 710 17.6 Crustacea 350 6.1 21 15.7Mollusca 351 6.2 21 15.7Echinodermata 723 12.7 11 8.2- Amphiura filiformis 680 94.1 Total 5701 100.0 134 100.0

Figure 4.5.3 shows the numbers of species and individuals sampled at each station and variations between grab samples.

0

20

40

60

80

100

HOD-02

HOD-08

HOD-13

HOD-19HOD-R

ef

Stations

No.

of s

peci

es (S

)

Station º/m HOD-02 74/500 HOD-08 164/500 HOD-13 254/315 HOD-19 344/250 HOD-Ref 180/15000

Figure 4.5.3. Numbers of species (S) and individuals (N) per 0.5 m2 (incl./excl. P. jeffreysii and M. oculata), mean values per grab sample and standard deviation, incl. juv., HOD 2005.

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0

400

800

1200

1600

HOD-02

HOD-08

HOD-13

HOD-19HOD-R

ef

Stations

No.

of i

ndiv

idua

ls (N

) Ex. P . je f fre ys ii a nd M . o c ula ta

0200400600800

HOD-02

HOD-08

HOD-13

HOD-19HOD-R

ef

Stations

No.

of i

ndiv

idua

ls (N

)

Figure 4.5.3. Cont.

The standard deviation was dramatically reduced when the two species P. jeffreysii and M. oculata were removed. This is evident since the two species constitute 47.2 % of the total number of individuals.

Diversity and dominant species

The dominant species at each station varied from 31.8 % at HOD-13 (254°/315m) to 43.3 % at HOD-2 (74°/500m). The 10 most abundant species shown in Table 4.5.9 constituted from 75.4 % of the total number of individuals at HOD-19 (344°/250m) to 83.1 % of the total number of individuals at the reference station (180°/15000). The bristle worm P. jeffreysii was the dominating species at most of the stations. The exception was the reference station where the brittle star A. filiformis dominated the fauna community. The three species P. jeffreysii, M. oculata and A. filiformis were dominating the fauna at almost all stations. Other frequently found species were the bristle worms Apistobranchus tullbergi, Scoloplos armiger, Levinsenia gracilis and the ribbon worms (Nemertea). Most of these species are known as indicators of organic pollution when they are found in high numbers. However, several of these species have a planktonic developmental stage and are able to settle in large numbers.

The amount of juvenile species was low and they do not contribute to the top ten list, these individuals are therefore not removed from the dataset prior to analyses. Table 4.5.9. The 10 most abundant species at each station, Hod 2005.

10 most dominating species HOD-2 No. % Cum.% HOD-8 No. % Cum.% Paramphinome jeffreysii 657 43.3 43.3 Paramphinome jeffreysii 420 36.4 36.4 Myriochele oculata 185 12.2 55.5 Myriochele oculata 150 13.0 49.4 Apistobranchus tullbergi 106 7.0 62.5 Apistobranchus tullbergi 128 11.1 60.4 Amphiura filiformis 79 5.2 67.7 Amphiura filiformis 105 9.1 69.5 Montacuta substriata 72 4.8 72.5 Levinsenia gracilis 42 3.6 73.2 Scoloplos armiger 44 2.9 75.4 Scoloplos armiger 27 2.3 75.5 Levinsenia gracilis 33 2.2 77.6 Ampelisca diadema/tenuicornis 24 2.1 77.6 Nemertea spp. 27 1.8 79.4 Trichobranchus roseus 19 1.7 79.2 Ampelisca diadema/tenuicornis 25 1.7 81.0 Goniada maculata 15 1.3 80.5 Trichobranchus roseus 21 1.4 82.4 Nemertea spp. 14 1.2 81.7 Cont.

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Table 4.5.9. cont. 10 most dominating species

HOD-13 No. % Cum.% HOD-19 No. % Cum.% Paramphinome jeffreysii 424 31.8 31.8 Paramphinome jeffreysii 418 36.1 36.1 Myriochele oculata 180 13.5 45.4 Amphiura filiformis 153 13.2 49.3 Amphiura filiformis 163 12.2 57.6 Myriochele oculata 100 8.6 57.9 Apistobranchus tullbergi 132 9.9 67.5 Harpinia antennaria 77 6.6 64.5 Scoloplos armiger 37 2.8 70.3 Scoloplos armiger 34 2.9 67.5 Cerianthus lloydii 29 2.2 72.5 Apistobranchus tullbergi 29 2.5 70.0 Nemertea spp. 27 2.0 74.5 Ampelisca diadema/tenuicornis 17 1.5 71.4 Levinsenia gracilis 26 2.0 76.4 Antalis entale 16 1.4 72.8 Ampelisca diadema/tenuicornis 25 1.9 78.3 Siphonoecetes kroeyeranus 15 1.3 74.1 Eudorellopsis deformis 19 1.4 79.7 Montacuta substriata 15 1.3 75.4 HOD-Ref No. % Cum.% Amphiura filiformis 180 33.4 33.4 Myriochele oculata 95 17.6 51.0 Paramphinome jeffreysii 59 11.0 62.0 Sthenelais limicola 22 4.1 66.1 Harpinia antennaria 21 3.9 69.9 Eudorellopsis deformis 17 3.2 73.1 Goniada maculata 16 3.0 76.1 Scoloplos armiger 13 2.4 78.5 Chaetozone setosa 13 2.4 80.9 Nephtys longosetosa 12 2.2 83.1 Table 4.5.10. Numbers of individuals (N) and species (S), depth, Shannon-Wiener diversity index (H’), Pielou’s evenness index (J) and expected number of species per 100 individuals (ES100), Hod 2005.

H' ES100 Station Direction ° Distance m Depth S N Incl.

M. o. Excl. M. o.

J Incl. M. o.

Excl. M. o.

HOD-2 74 500 73 78 1516 3.6 3.4 0.6 24 24.4HOD-8 164 500 72 68 1155 3.7 3.6 0.6 24 24.8HOD-13 254 315 73 84 1332 3.9 3.8 0.6 25 26.4HOD-19 344 250 74 80 1159 4.0 3.9 0.6 28 28.2HOD-Ref 180 15000 70 56 539 3.7 3.7 0.6 24 25.2M. o.= M. oculata

The number of species varied from 56 at the reference station (180°/15000m)) to 84 at HOD-13 (254°/315m). The number of individuals varied from 539 at the reference station to 1516 at HOD-2 (74°/500m). The Shannon Wiener diversity index varied from 3.6 at HOD-2 (74°/500m) to 4.0 at HOD-19 (344°/250m) and the Hurlberts index (ES100) varied from 24 (HOD-2, 8 and reference) to 28 (HOD-19) including M. oculata. Removing M. oculata from the data gives minor changes to the indices in 2005. This species shows a significant decrease in abundance in areas of the southern part of the Ekofisk region since 2002. Indices above 4 indicate a relatively undisturbed fauna, while indices between 3 and 4 indicate a slight disturbance. In general ES100 indices above 20 characterize a relatively normal fauna community. The observed indices, however, reflect a slight disturbance, see Table 4.5.10.

In general the indices reflect a slightly disturbed benthic fauna in the Hod area, which is difficult to relate to direction or distance from the field centre. The indices are, however, relatively high compared to other fields in the central Ekofisk region.

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Classification and ordination

The dendrogram from the cluster analysis and the MDS plot from the ordination analysis based on grab samples are presented in Figure 4.5.4 and Figure 4.5.5. Because the data set contains only 4 stations and the analysis at station level show the same pattern as the grab level, only the dendrogram and MDS plot from grab level are presented. The reference station (180°/15000m) deviates from the other samples, with a dissimilarity of about 60 %. The other stations separate further into two subgroups at a similarity of almost 60 %. The grabs from station HOD-2 (74°/500m), HOD-8 (164°/500m) and HOD-13 (254°/315m) forms a separate subgroup, while the grabs from HOD-19 (344°/250) cluster in another subgroup. The cluster analysis is well supported by the ordination analysis.

HOD-

REF-

4

HOD-

REF-

2

HOD-

REF-

5

H OD-

REF-

1

HOD -

REF-

3

H OD-

13-3

HOD-

13-2

H OD-

13-4

HOD -

02-5

HOD-

02-1

H OD-

08-1

HOD-

02-3

HOD-

13-1

HOD-

02-4

HOD -

08-2

HOD-

08-4

HOD-

02-2

HOD-

13-5

HOD-

08- 3

HOD -

08-5

HOD -

19-1

HOD -

19-5

HOD-

19- 2

HOD-

19-3

HOD-

19-4

100

80

60

40

Sim

ilarit

y

Reference station (180/15000m)Station HOD-19 (344/250m)Station HOD-2 (74/500m), 8 (164/500m) and 13 (254/315m)

HOD field stations Figure 4.5.4. Dendrogram of grab samples from Hod 2005.

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HOD-02-1

HOD-02-2

HOD-02-3

HOD-02-4

HOD-02-5

HOD-08-1HOD-08-2

HOD-08-3HOD-08-4

HOD-08-5

HOD-13-1

HOD-13-2

HOD-13-3

HOD-13-4

HOD-13-5

HOD-19-1

HOD-19-2

HOD-19-3

HOD-19-4

HOD-19-5

HOD-REF-1

HOD-REF-2

HOD-REF-3

HOD-REF-4

HOD-REF-5

Stress: 0,14

HOD field stationsStation HOD-19 (344/250m)

Station HOD-2 (74/500m), 8 (164/500m/) and 13 (254/315m)

Reference station (180/15000m)

Figure 4.5.5. MDS plot of grab samples from Hod 2005.

A Simper analysis (Primer package) has been performed to examine which species contribute most to the differences between groups and subgroups. The difference between the reference station (180°/15000m) and the Hod field stations was in general due to higher numbers of the bristle worms P. jeffreysii, M. oculata and A. tullbergi at the Hod field stations. The reference station contained larger amounts of the brittle star A. filiformis and the Crustacea Harpinia antennata compared to the field stations.

The differences among the field stations were mainly due to considerably higher numbers of the former mentioned bristle worms at HOD-2 (500m/74°), HOD-8 (500m/164°) and HOD-13 (315m/254°) compared to station HOD-19 (250m/344°). HOD-19 contained higher numbers of the crustacean H. antennata compared to the other field stations.

A Bioenv analysis (Primer package) which connects the variations in the biological data with the variations in the chemical and physical data was performed. Bioenv calculates the combination of environmental (chemical and physical) factors which best correlate with the biological data. The results from the analysis gave a high correlation between the fauna composition and grain size (>0.9) indicating none or minor influence from THC and metals.

Comparison with 1991, 1996, 1999, 2002 and 2005

In Figure 4.5.6 the results from the present survey are compared to the results from previous surveys. The numbers of M. oculata are drastically reduced since 2002 and the total number of individuals is thus reduced. The numbers of the bristle worm P. jeffreysii, but also the bristle worm A. tullbergi and the echinoderm A. filiformis have increased considerably since 2002 and are dominating species at Hod together with M. oculata.

The biodiversity in the fauna community at Hod has increased relatively much since 2002 at HOD-2, HOD-8 and the reference station (including M. oculata). At these and the other comparable stations the biodiversity indices (including M. oculata) approach the results from

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surveys before 20021. Removal of M. oculata from the data gives the opposite pattern, a reduced diversity over years.

020406080

100

HOD-02

HOD-08

HOD-13

HOD-19

HOD-24A

Stations

No.

of s

peci

es (S

)

1991 1996 1999 2002 2005

Station º/m

HOD-02 74/500 HOD-08 164/500 HOD-13 254/315 HOD-19 344/250 HOD-24A 180/15000

0500

10001500200025003000

HOD-02

HOD-08

HOD-13

HOD-19

HOD-24A

Stations

No.

of i

ndiv

idua

ls (N

)

1991 1996 1999 2002 2005

0123456

HOD-02

HOD-08

HOD-13

HOD-19

HOD-24A

Stations

H'

1991 1996 19991999-ex. M. o cula ta 2002 2002-ex. M. o cula ta2005 2005-ex. M. o cula ta

Figure 4.5.6. Numbers of species (S) and individuals (N) per 0.5m2 and diversity (H’), incl. P. jeffreysii, M. oculata and juv, Hod 1999, 2001, 2002 and 2005. Hod 24A=HOD.REF.

Classification and ordination analyses

The sampled stations from all years have been analysed at family level2. The dendrogram from the analysis of comparable stations is shown in Figure 4.5.7. Most of the stations divide into two main groups at about 50 % similarity based on year. However the reference station (180°/15000m) in 1999 and 2005 form a separate group (1). This station also has slightly more sandy sediment than the rest of the stations. Stations from 2005 and stations sampled in earlier years form separate groups, group 2 and 3 respectively. Group 3 separates further into subgroups based on years. The similarity analysis reveals that a significant decrease in the number of species within the family Oweniidae (mainly M. oculata) and an increase of species within the family Amphinomidae (mainly P. jeffreysii) in the 2005 group (stations sampled in 2005) contributes to most of the difference between the two main groups.

A Bioenv analysis gave a correlation of 0.4 between the fauna and the combination of the environmental factors Ba, Cu and TOM, showing that the environmental factors have little influence on the variations in the fauna over the years.

1 The great variations in the presence of M. oculata from 1996 to 2005 have complicated the faunal picture, making

it difficult to draw conclusions about the state of the fauna community. Adding the 2005 results to the trend data have, however, strengthened the data set, and has made it possible to obtain a pattern in the overall temporal variations in the entire region. It is recommended to read Chapter X - General Trends in the Region which forms a basis for the conclusions for each of the fields.

2 Necessary when comparing between years, to avoid significant source of error due to both different years and different taxonomists.

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H OD-

24A-

199 9

HOD-

24A-

2005

HOD-

02- 2

005

HOD -

08-2

005

HOD-

13-2

005

HOD -

24A-

1996

HOD-

02-2

002

HOD-

0 8-2

002

HOD-

08-1

999

HOD-

02- 1

996

HOD-

08-1

996

100

90

80

70

60

50Si

mila

rity

Group 1 Group 2 Group 3 Figure 4.5.7. Dendrogram showing similarity between Hod stations 1991, 1996, 1999, 2002 and 2005. Family level, incl. M. oculata and juv., sq. root transformation.HOD-24A=HOD-REF.

4.5.4 Conclusion

The sediments at Hod consist mainly of fine sand, and the sand content varies from 91 % at to 97 %. The gravel content is low. The silt and clay content is similar to previous observations. The total organic matter content in the sediments is low and only small variations are found at the field, from 0.8 % to 1.3 %. The TOM content is similar to the result from the previous surveys in 2002, 1999 and 1996.

The mean THC concentrations vary from 4.3 mg/kg at the HOD reference station, 180°/15000m to 36 mg/kg at HOD8, 164°/500m. HOD2, 74°/500m was the most contaminated station, concerning THC and olefins in the 2002 survey. Compared to this survey the concentrations of THC have now decreased almost to the background level. The content of olefins has also decreased from 17.6 mg/kg to 0.9 mg/kg.

At HOD8, a decrease in the THC concentration is observed in the 0-1 cm top layer, and in the deeper layers 1-3 cm and 3-6 cm compared to previous surveys. At the other stations the concentrations are similar to previous surveys.

Elevated THC levels are found at HOD8, 164°/500m. The stations HOD2, 74°/500m and HOD13, 254°/315m are only slightly elevated. The other stations have THC content below the limit of contamination for this region.

Olefins are detected at the six stations analysed, and varies from 0.7 mg/kg at HOD3, 74°/1000m to 7.1 mg/kg at HOD8, 164°/500m. The olefin concentrations have decreased compared to previous surveys for all the stations investigated. This is also in agreement with the results observed for THC.

No discharges of olefins have taken place since 1994 (337 tonnes of Novasol) and 1995 (85 tonnes of Novaplus). The olefin concentration is low and at the same level for all the stations,

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in average 1 mg/kg. An exception is observed for HOD8 with an olefin concentration of 7 mg/kg.

Elevated concentrations of NPD are found at HOD8, 164°/500m in all three layers and in the deeper sections of HOD9, 164°/1000m. The top sediment layer at HOD8 and HOD9 has PAH concentrations just at the limit of contamination, while the PAH content in the layers are above this limit. The decalin content is similar or lower compared to the 2002 survey.

The Ba concentrations vary from 32 mg/kg at HOD reference station 180°/15000m to 900 mg/kg at HOD2, 74°/500m. Elevated Ba concentrations are found at all stations, except for the reference station. This means out to 1000m in the 164° direction, to 500m in the 74° direction, to 315m in the 254° direction and to 250m in the 344° direction. In general the Ba levels are similar to the levels found in previous surveys. Elevated Ba concentrations are found in the deeper sections at HOD8 and HOD9, and the concentration increases going down in the sediments.

The concentrations of the heavy metals are low, but slightly elevated concentrations of Pb and Zn are found.

No drilling activity has taken place at Hod since the survey in 1996. However, hydrocarbons originating from drilling discharges are still present in the sediments.

In general the indices reflect a slightly disturbed benthic fauna in the Hod area, which is difficult to relate to direction or distance from the field centre. The indices are, however, relatively high compared to other fields in the central Ekofisk region. The fauna at stations HOD-2, -8 and -13 differ somewhat from the others, but the deviations can not be related to the field activities. The fauna at the reference station (180/15000m) differs from the rest of the HOD stations and should be reconsidered as a reference station.

The biodiversity in the fauna community at Hod has increased relatively much since 2002, approaching the results from surveys prior to 2002. There has been a significant decrease in the numbers of species M. oculata and an increase in P. jeffreysii at Hod since 2002. This alteration in the fauna community between years seems to be a general positive trend in some parts of the Ekofisk region.

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4.6 Ula During sampling a few adjustments to the location of the stations were necessary:

- Station ULA16 (315°/500m) is replaced by ULA116 (330°/500m) because of interference with export pipeline.

- Station ULA17 (315°/250m) is replaced by ULA117 (300°/500m) because of interference with cable.

- Station ULA18 was sampled at the original location (135°/250m) (in 2002 it had to me relocated to ULA118 (120°/250m).

- Station ULA119 (125°/500m) is replaced by ULA119 (125°/500m) because of interference with cable.

See survey report (Appendix A) for details.

4.6.1 Sediment characterization

Grain size distribution

The grain size distribution from the present survey is shown in Table 4.6.1 together with the silt and clay content from the previous surveys in 2002, 1999 and 1996.

The sediments at Ula consist mainly of fine sand, and the sand content varies from 95 % to 97 %. The average median diameter is 2.80φ. The gravel content is low (below 1.1 %), and small amounts are found at four of the stations. The silt and clay content is similar to previously observed. The average silt and clay concentration found is 4.0 % compared to 5.6 % in 1999 and 2.7 % in 1996 for the same stations.

At Ula reference station (315°/6000m) the sediment is characterized as fine sand with 96 % sand and a median particle diameter of 2.78φ. The silt and clay content found is the same as for the previous surveys.

The results from the complete grain size distribution are given in Appendix C. Table 4.6.1. Ula 2005, grain size distribution. Station Median

diameter Classification Grain size distrib. 2005 (%) 2002

(%) 1999 (%)

1996 (%)

Mdφ Silt and clay

Sand Gravel Silt and clay

Silt and clay

Silt and clay

ULA5 45°/ 500m 2.79 Fine sand 4.8 95.2 0.0 4.5 2.3 ULA7 225°/250m 2.79 Fine sand 2.9 96.8 0.3 ULA117 300°/250m 2.81 Fine sand 4.1 94.8 1.1 ULA18 135°/250m 2.83 Fine sand 4.8 94.9 0.3 7.5 ULA119 125°/500m 2.77 Fine sand 3.2 95.8 1.0 4.8 3.8 3.0 Mean 2.80 4.0 95.5 0.5 5.6 2.7 St. dev. 0.02 0.8 0.7 0.4 1.4 0.4 ULA ref. 315°/6000m 2.78 Fine sand 4.3 95.7 0.0 4.5 3.6 2.9

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Total organic matter (TOM)

The contents of TOM in the sediments are low. Only small variations are found at the field, from 0.84 % at Ula reference station (315°/6000m) to 1.1 % at ULA18, 135°/250m. The contents correspond to the grain size distribution with low pelite contents. The results are similar to the previous surveys and are shown in Table 4.6.2. Table 4.6.2. Ula 1996-2005. Total organic matter (% of dry sediment).

Station 2005, 0-5 cm Mean 2002

Sd 2002

Mean 1999

Mean 1996

ULA5 45°/ 500m 0.93 0.88 0.06 0.83 ULA7 225°/250m 0.87 ULA117 300°/250m 0.90 ULA18 135°/250m 1.10 0.93 0.03 ULA119 125°/500m 0.91 0.89 0.03 0.74 0.88 Mean 0.94 0.90 0.74 0.86 St. dev. 0.09 0.03 0.04 ULA ref. 315°/6000m 0.84 0.86 0.06 0.71 0.82

4.6.2 Chemical analyses

Parameters analysed in the sediments at Ula:

• THC • NPD, PAH, decalins • Metals (Ba, Cd, Cr, Cu, Hg, Pb, Zn)

Three replicate samples at each station and five replicate samples at the reference station are analysed. The samples are taken from the top 0-1 cm sediment layer. In addition, the 1-3 cm and 3- 6 cm sediment layers are sampled at two stations and the reference station.

This year survey has focused on stations close to the installation in order to calculate contaminated area. Thus two new stations at 250m distance were included in the survey.

THC

The results are shown in Table 4.6.3. The corresponding THC results from the previous surveys in 2002, 1999 and 1996 are also included for comparison. Two new stations at 250m distance are included in the present survey, ULA7, 225°/250m, and ULA17, 300°/250m. Bar diagram of the THC content in the sediments is shown in Figure 4.6.1.

In 1996 the highest THC concentrations were found at the innermost stations at 500 m in the four directions, from 14.1 mg/kg to 40.0 mg/kg. In 1999 only one station at 500 m distance was analysed, ULA119, 125°/500m. At this station the THC concentration in the top 0-1 cm layer had decreased compared to the 1996 survey, from 17.3 mg/kg to 5.0 mg/kg. An elevated level of THC was however found in the 3-6 cm layer at ULA119. The THC concentrations in the sediments and outside 1000 m distance were low. These stations were not contaminated by THC. In the 2002 survey the stations were situated closer to the platform. The THC concentrations in the top 0-1 cm layer ranged from 3.3 mg/kg (ULA Ref) to 143 mg/kg (ULA18, 135°/250m). The maximum concentrations at Ula were found in the deeper layers at ULA18, in average 360 mg/kg.

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In the present survey the concentrations of THC in the top 0-1 cm layers has decreased for the majority of the stations analysed compared to the 2002 survey. The concentrations of THC in the top 0-1 cm layers vary from 3.9 mg/kg (ULA Ref) to 58 mg/kg (ULA18, 135°/250m). The maximum concentrations are found in the 1-3 cm and 3-6 cm layers at ULA18, 336 mg/kg and 416 mg/kg, respectively. The level is similar to the 2002 survey.

At ULA18, 135°/250m, the concentration has decreased from 143 mg/kg to 58 mg/kg. At ULA119, 125°/500m, the concentration has decreased from 25 mg/kg to 13 mg/kg. A decrease is also observed in the 1-3 cm layer. The present level is similar to that found in 1999. The THC contents in the 3-6 cm layers have been unchanged since 1996. At ULA4, 45°/1000m, the concentration has decreased from 11.2 mg/kg to 4.7 mg/kg, the same concentration as in 1999. At ULA5, 45°/500m, the concentration has decreased from 69 mg/kg to 18 mg/kg, as is the level in the 1996 survey.

Elevated levels of THC are found out to 500m in the 45° and 135° directions and out to 250m in the 120° and 225° directions. The other stations have the same levels of THC as the reference station.

Ula reference station, 315°/6000m, is still uncontaminated, and the mean THC concentration of the five replicate samples is 3.9 mg/kg.

In addition to the THC contamination, pronounced peaks corresponding to the drilling fluid Aquamul BII are clearly seen in the gas chromatograms on the top of the THC hump and confirmed by GC/MS analysis. The main compound in Aquamul BII is alkyl ether, C20H42O2. The maximum concentrations are seen in the deeper layers at ULA18, 135°/250m. At this station Aquamul BII gives an important contribution to the THC contents. The results indicate that the base oil Aquamul BII has been used in the drilling activities at Ula. In 1993 this mud system was used in a few wells and was later removed. Obviously Aquamul BII is not degrading as fast as previously anticipated.

Representative gas chromatograms are given in Appendix C. These include ULA4, 45°/1000m, ULA5, 45°/500m, ULA18, 135°/250m, ULA119, 125°/500m and ULA reference station, 315°/6000m.

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Ula, THC 2005

0

10

20

30

40

50

60

70

80

90

100

ULA4 ULA5 ULA7 ULA8 ULA116 ULA117 ULA18 ULA119 ULA20 ULA ref

station

mg/kg

1999

2002

2005

LSC A

143±268,8±4

Figure 4.6.1. Bar diagram of the THC content in the sediments at Ula 1999-2005. Table 4.6.3. Ula 2005, total hydrocarbon content (mg/kg dry sediment). Station Grab

#1 Grab

#2 Grab

#3 Grab

#4 Grab

#5 Mean SD Mean Mean Mean

2005 2005 2002 1999 1996 ULA4 45°/ 1000m 6.3 3.7 4.0 4.7 1.4 11.2 4.4 10.2 ULA5 45°/ 500m 12.6 27.5 13.6 17.9 8.3 69 19.6 ULA7 225°/250m 15.3 9.0 16.0 13.4 3.8 ULA8 225°/500m 4.6 3.9 3.3 3.9 0.6 6.7 40 ULA116 3305°/500m 5.0 3.9 4.0 4.3 0.6 3.9 14.1 ULA117 300°/250m 3.9 4.4 4.0 4.1 0.3 ULA18 135°/250m 79 52 41 58 20 143 1-3 cm 336 359 3-6 cm 416 358 ULA119 125°/500m 9.4 6.2 24 13.1 9.2 25 5.0 17.3 1-3 cm 7.3 19.3 6.8 16.5 3-6 cm 9.6 11.7 10.4 11.0 ULA20 135°/1000m 5.0 4.3 4.7 4.7 0.4 ULA ref. 315°/6000m 3.3 4.1 5.2 3.6 3.5 3.9 0.7 3.3 4.1 4.2 1-3 cm 4.7 3.3 5.0 2.6 3-6 cm 4.8 3.8 4.6 7.1 LSC Subregion A 6.6 6.4 9

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NPD, PAH and decalins

Two stations are analysed in addition to the reference station; ULA18, 135°/250m and ULA119, 125°/500m. The results are shown in Table 4.6.4.

In 1999 the NPD and PAH concentrations were low, and elevated levels were not observed. Decalins were found in one sample, in the 3-6 cm layer at station ULA119, 125°/500m.

In 2002 elevated levels of NPD, PAH and decalins were found at ULA5, 45°/500m, and ULA18, 135°/250m, in all three layers. The NPD concentrations ranged from 0.022 mg/kg (Ref station) to 0.30 mg/kg (ULA18). The PAH concentrations ranged from 0,041 mg/kg (Ref station) to 0.12 mg/kg (ULA18).

In the present survey elevated levels of NPD, PAH and decalins are found at ULA18, 135°/250m, in the top 0-1cm layer and in the deeper layers. At ULA119, 125°/500m, levels of NPD and PAH are only slightly above the limit of contamination. The mean NPD concentrations vary from below 0.01 mg/kg (ULA ref) to 0.16 mg/kg (ULA18). The mean PAH concentrations vary from 0.029 mg/kg (ULA ref) to 0.12 mg/kg (ULA18). Maximum content of NPD and PAH is found in the deeper layers at ULA18. The NPD content is ~1.9mg/kg in both layers and the PAH content is 1.3 mg/kg in the 1-3 cm layer and 0.8 mg/kg in the 3-6 cm layer.

ULA18 contains the highest values of decalins, particularly in the deeper layers. The decalin concentrations vary from below 0.1 mg/kg (ULA ref) to 25 mg/kg in the 3-6cm layer at ULA18, 135°/250m. This observation is in accordance with the THC results, as the sediments from these samples show the highest THC concentrations at ULA18. Generally, the level of NPD, PAH and decalins has not changed since the 2002 survey. Table 4.6.4. Ula 2005, sum NPD, PAH and decalins (mg/kg dry sediment).

Station Grab #1

Grab #2

Grab #3

Grab #4

Grab #5

Mean SD Mean SD Mean SD Mean

2005 2005 2002 2002 1999 1999 1996NPD ULA18 135°/250m 0.25 0.11 0.11 0.16 0.08 0.30 0,06 1-3 cm 1.92 0.63 3-6 cm 1.97 0.30 ULA119 125°/500m 0.042 0.01 0.08 0.043 0.04 0.072 0.04 0.020 0.009 0.13 1-3 cm 0.024 0.035 0.022 0.047 3-6 cm 0.024 0.042 0.035 0.030ULA REF 315°/6000m nd nd nd nd 0.022 0.004 0.022 0.011 0.012

1-3 cm nd 0.029 0.021 0.021 3-6 cm nd 0.026 0.026 0.028LSC Subregion A 0.030 0.026 0.040 cont.

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Table 4.6.4. cont.

Station Grab #1

Grab #2

Grab #3

Grab #4

Grab #5

Mean SD Mean SD Mean SD Mean

2005 2005 2002 2002 1999 1999 1996PAH ULA18 135°/250m 0.11 0.19 0.053 0.12 0.070 0.12 0.05 1-3 cm 1.32 0.13 3-6 cm 0.77 0.14 ULA119 125°/500m 0.064 0.024 0.13 0.073 0.054 0.044 0.009 0.029 0.020 0.080 1-3 cm 0.068 0.080 0.038 0.040 3-6 cm 0.10 0.11 0.065 0.217ULA REF 315°/6000m 0.024 0.031 0.031 0.032 0.027 0.029 0.003 0.041 0.006 0.034 0.004 0.054

1-3 cm 0.036 0.045 0.040 0.080 3-6 cm 0.062 0.063 0.057 0.16LSC Subregion A 0.061 0.062 0.090 Decalins ULA18 135°/250m 3.0 2.7 1.5 2.4 0.8 6.1 0.6 1-3 cm 16.7 9.9 3-6 cm 25.1 9.9 ULA119 125°/500m 0.16 0.045 0.37 0.19 0.16 0.71 0.24 nd 0.63 1-3 cm 0.14 0.48 nd 0.20 3-6 cm 0.26 0.35 0.20 0.19nd: not detected. Limit of detection for NPD is 0.01 mg/kg, for PAH 0.005 mg/kg and for decalins 0.1 mg/kg. Decalins are not detected at the reference station.

Metals

The results are shown in Table 4.6.5. Data from the previous survey in 2002 and 1999 are also included. For Ba the results from the 1996 survey are included. Hg is only analysed at some of the stations. A bar diagram of the Ba contents in the sediments is shown in Figure 4.6.2.

In the 1996 survey the maximum concentrations of Ba were found at the innermost stations at 500m in the four directions. The Ba concentrations at these stations ranged from 540 mg/kg to 2440 mg/kg. In the 1999 survey only one station at 500 m distance was analysed, ULA119, 125°/500m. The maximum concentration of Ba was found at this station, 612 mg/kg, which is the 1996 level. In the 2002 survey, the mean Ba concentrations ranged from 29 mg/kg at ULA reference station to 3500 mg/kg at ULA18, 135°/250m. Elevated levels were found at all stations except for at the reference station. Thus elevated levels of Ba are found out to 500m in 45° and 135° direction and out to 250m in the other directions.

In the present survey stations are located closer to the platform. These are ULA18, 135°/250m, (also in the 2002 survey), ULA7, 225°/250m, and ULA117, 300°/250m. The Ba concentrations vary from 461 mg/kg (ULA117) to 4272 mg/kg (ULA18). The Ba concentrations are similar or slightly higher compared to the previous surveys. At ULA18 the Ba concentrations in all three layers are similar. At ULA119 the highest concentration is found in the 1-3 cm layer.

The ULA reference station, 315°/6000m, is still uncontaminated, and the mean Ba concentration of the five replicate samples is 35 mg/kg. Maximum concentrations of the heavy metals are found at ULA18, 135°/250m, and elevated concentrations are observed.

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Slightly elevated concentrations are also found at some of the other stations, except for Cr and Hg. The levels are similar to the previous surveys.

Ula, Ba 2005

0

500

1000

1500

2000

2500

3000

3500

4000

ULA5 ULA7 ULA117 ULA18 ULA119 ULA ref

station

mg/kg

1999

2002

2005

LSC A

4172±219

Figure 4.6.2. Bar diagram of the Ba content in the sediments at Ula 1999-2005. The following variations are found at ULA field in the top layer, 0-1 cm. The values are given in mg/kg: Ula: ULA5 – ULA18 ULA Reference station Ba: 461 - 4172 35 Cr: 6.2 - 8.0 7.0 Cu: 0.7 - 5.5 <0.5 Pb: 6.8 - 16.4 6.2 Zn: 7.1 - 43.3 5.4 Cd: <0.01 <0.01 Hg: <0.01 <0.01

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Table 4.6.5. Ula 2005, metals (mg/kg dry sediment). Station Sample Ba Cd Cr Cu Hg Pb Zn 2005 2005 2005 2005 2005 2005 2005 ULA5 45°/500m 1 3246 <0.01 7.3 1.9 12.6 15.2 2 2678 <0.01 7.8 2.4 12.5 14.2 3 1931 <0.01 7.2 1.6 12.3 14.5 mean 2618 <0.01 7.4 2.0 12.5 14.6 SD 660 - 0.3 0.4 0.2 0.5ULA7 225°/250m 1 1586 <0.01 6.6 1.2 9.8 9.2 2 1661 0.01 7.0 1.4 9.7 24.5 3 1595 <0.01 6.9 1.3 9.7 10.0 mean 1614 <0.01 6.8 1.3 9.8 14.6 SD 41 0.3 0.1 0.1 8.6ULA117 300°/250m 1 406 <0.01 6.4 0.7 7.4 7.3 2 538 <0.01 6.0 0.7 6.8 6.9 3 438 <0.01 6.3 0.8 6.1 6.9 mean 461 <0.01 6.2 0.7 6.8 7.1 SD 69 0.2 0.1 0.6 0.2ULA18 135°/250m 1 3949 0.06 8.4 7.4 0.02 16.7 52.5 2 4180 0.04 7.3 5.9 0.02 18.3 51.2 3 4387 0.03 8.1 3.2 0.02 14.2 26.3 mean 4172 0.05 8.0 5.5 0.02 16.4 43.3 SD 219 0.02 0.6 2.1 - 2.1 14.8 1-3 cm 1 4597 0.07 7.9 8.8 0.01 21.1 46.8 3-6 cm 1 3683 0.06 7.7 4.8 0.02 18.5 41.8ULA119 125°/500m 1 781 0.00 6.9 1.4 <0.01 8.5 8.3 2 1122 0.00 6.9 0.8 <0.01 8.4 7.4 3 572 0.02 7.8 1.4 <0.01 9.4 14.5 mean 825 <0.01 7.2 1.2 <0.01 8.8 10.1 SD 278 0.5 0.3 0.6 3.9 1-3 cm 1 1668 <0.01 7.1 0.9 <0.01 8.7 8.3 3-6 cm 1 648 <0.01 6.9 0.9 <0.01 7.5 7.9ULA Ref. 315°/6000m 1 37 <0.01 6.8 <0.5 <0.01 6.2 5.4 2 34 <0.01 6.9 <0.5 <0.01 5.9 5.6 3 19 <0.01 6.8 <0.5 <0.01 5.7 4.9 4 29 <0.01 6.7 <0.5 <0.01 5.6 5.1 5 54 <0.01 7.6 <0.5 <0.01 7.7 6.2 mean 35 <0.01 7.0 <0.5 <0.01 6.2 5.4 SD 13 0.3 0.9 0.5 1-3 cm 49 <0.01 7.4 <0.5 <0.01 6.6 6.2 3-6 cm 60 <0.01 7.6 <0.5 <0.01 6.6 6.2LSC Subregion A 76.2 8.0 1.3 7.4 6.9

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Table 4.6.6. Ula 2005, metals (mg/kg dry sediment), comparing mean values with previous surveys. Station Ba Ba Ba Ba Cd Cd Cd Cr Cr Cr 2005 2002 1999 1996 2005 2002 1999 2005 2002 1999ULA5 45°/500m 2618 1320 1200 <0.01 0.02 7.4 7.0 ULA7 225°/250m 1614 <0.01 6.8 ULA117 300°/250m 461 <0.01 6.2 ULA18 135°/250m 4172 3500 <0.01 0.08 8.0 6.8 1-3 cm 4597 3750 <0.01 0.10 7.9 8.0 3-6 cm 3683 2250 <0.01 0.06 7.7 7.8 ULA119 125°/500m 825 979 612 704 <0.01 0.02 <0.02 7.2 6.3 6.2 1-3 cm 1668 1120 1150 <0.01 0.04 <0.02 7.1 6.9 5.8 3-6 cm 648 1050 1210 <0.01 0.04 <0.02 6.9 7.3 6.1 ULA Ref. 315°/6000m 35 29 33 60 <0.01 <0.02 <0.02 7.0 6.9 6.9 1-3 cm 49 33 41 <0.01 <0.01 <0.02 7.4 7.0 6.9 3-6 cm 60 48 160 <0.01 <0.01 <0.02 7.6 6.9 7.8 cont. Table 4.6.6. cont. Station Cu Cu Cu Hg Hg Hg Pb Pb Pb Zn Zn Zn 2005 2002 1999 2005 2002 1999 2005 2002 1999 2005 2002 1999ULA5 45°/500m 2.0 3.1 12.5 11.8 14.6 14.5 ULA7 225°/250m 1.3 9.8 14.6 ULA117 300°/250m 0.7 6.8 7.1 ULA18 135°/250m 5.5 7.6 0.02 0.02 16.4 18.5 43.3 56.5 1-3 cm 8.8 7.7 0.01 0.03 21.1 25.1 46.8 58.5 3-6 cm 4.8 4.7 0.02 0.02 18.5 18.5 41.8 49.5 ULA119 125°/500m 1.2 2.0 0.8 <0.01 0.01 0.02 8.8 8.8 9.2 10.1 13.3 8.4 1-3 cm 0.9 2.4 1.1 <0.01 <0.01 0.02 8.7 8.9 9.6 8.3 13.0 9.1 3-6 cm 0.9 2.0 0.9 <0.01 0.01 0.01 7.5 8.7 8.6 7.9 9.5 7.0 ULA Ref. 315°/6000m <0.5 1.3 0.6 <0.01 <0.01 <0.01 6.2 6.1 7.3 5.4 6.2 5.6 1-3 cm <0.5 1.4 0.6 <0.01 0.01 0.01 6.6 6.4 7.4 6.2 7.1 5.9 3-6 cm <0.5 1.5 0.8 <0.01 <0.01 0.02 6.6 6.3 8.4 6.2 6.3 7.4

4.6.3 Biological analyses

A total of 145 species and 21091 individuals were sampled at 6 stations. Greatest abundance (91.0 %) was found among the polychaetes, of which the species Myriochele oculata constitutes 74.2 % and Paramphinome jeffreysii constitutes about 11.8 % of the total number of Polychaeta, see Table 4.6.7.

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Table 4.6.7. Number of species and individuals distributed between the main groups, Ula 2005. Individuals Species Main animal groups

Number % Number % Varia 608 2.9 14 9.7Polychaeta 19199 91.0 76 52.4- Paramphinome jeffreysii 2258 11.8 - Myriochele oculata 14250 74.2 Crustacea 105 0.5 19 13.1Mollusca 666 3.2 29 20.0Echinodermata 513 2.4 7 4.8- Amphiura filiformis 456 88.9 Total 21091 100.0 145 100.0

Figure 4.6.3 shows the numbers of species and individuals sampled at each station and variations between grab samples.

020406080

100

ULA-05

ULA-07ULA-117

ULA-18ULA-119ULA-R

ef

Stations

No.

of s

peci

es (S

)

Station º/m ULA-05 45/500 ULA-07 225/250 ULA-117 300/250 ULA-18 135/250 ULA-119 125/500 ULA-Ref 315/6000

0800

160024003200400048005600

ULA-05

ULA-07ULA-117

ULA-18ULA-11

9ULA-R

ef

Stations

No.

of i

ndiv

idua

ls (N

)

Ex. P. jeffreysii and M. oculata

0800

160024003200400048005600

ULA-05

ULA-07ULA-117

ULA-18ULA-119ULA-R

ef

Stations

No.

of i

ndiv

idua

ls (N

)

Figure 4.6.3 Numbers of species (S) and individuals (N) per 0.5 m2 (incl./excl. P. jeffreysii and M. oculata), mean values per grab sample and standard deviation, Ula 2005.

The standard deviation was in general dramatically reduced when the two species P. jeffreysii and M. oculata were removed. This is evident since the two species constitute 78.3 % of the total number of individuals.

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Diversity and dominant species

The dominant species at each station varied from 22.3 % at the reference station (315°/6000m) to 81.3 % at ULA-119 (125°/500m). The 10 most abundant species made up from 73.1 % at the reference station to 95.8 % at ULA-119, see Table 4.6.8. The bristle worm M. oculata dominated the fauna at the Ula field. Other frequently found species were the bristle worms P. jeffreysii and Chaetozone setosa, the brittle star Amphiura filiformis and the mussel Thyasira flexuosa. P. jeffreysii is mainly a carnivore species. The other mentioned species are either suspension feeders or both suspension- and deposit feeders. Most of these species are known indicators of organic pollution when they are found in high numbers. However, several of the above mentioned species have a planktonic developmental stage and are able to settle in large numbers. Table 4.6.8. The 10 most abundant species at each station, Ula 2005 (incl. juv.). 10 most dominating species ULA-05 No. % Cum. % ULA-07 No. % Cum. % Myriochele oculata 2270 60.8 60.8 Myriochele oculata 2540 69.0 69.0 Paramphinome jeffreysii 603 16.2 76.9 Paramphinome jeffreysii 312 8.5 77.4 Chaetozone setosa 283 7.6 84.5 Chaetozone setosa 267 7.3 84.7 Nemertea spp. 77 2.1 86.6 Apistobranchus tullbergi 62 1.7 86.4 Apistobranchus tullbergi 71 1.9 88.5 Amphiura filiformis 49 1.3 87.7 Phoronis muelleri 56 1.5 90.0 Nemertea spp. 48 1.3 89.0 Goniada maculata 41 1.1 91.1 Goniada maculata 33 0.9 89.9 Amphiura filiformis 28 0.8 91.8 Thyasira flexuosa 31 0.8 90.7 Levinsenia gracilis 27 0.7 92.6 Scoloplos armiger 29 0.8 91.5 Thyasira flexuosa 26 0.7 93.3 Tharyx sp. 26 0.7 92.2 ULA-117 No. % Cum. % ULA-18 No. % Cum. % Myriochele oculata 2970 71.7 71.7 Myriochele oculata 2040 60.1 60.1 Paramphinome jeffreysii 440 10.6 82.4 Paramphinome jeffreysii 410 12.1 72.1 Amphiura filiformis 188 4.5 86.9 Chaetozone setosa 379 11.2 83.3 Chaetozone setosa 126 3.0 90.0 Nemertea spp. 181 5.3 88.6 Goniada maculata 29 0.7 90.7 Apistobranchus tullbergi 59 1.7 90.4 Levinsenia gracilis 28 0.7 91.3 Tharyx sp. 44 1.3 91.7 Caudofoveata spp. 24 0.6 91.9 Thyasira flexuosa 42 1.2 92.9 Nephtys longosetosa 24 0.6 92.5 Goniada maculata 31 0.9 93.8 Thyasira flexuosa 21 0.5 93.0 Scalibregma inflatum 15 0.4 94.3 Nemertea spp. 21 0.5 93.5 Glycera alba 15 0.4 94.7 ULA-119 No. % Cum. % ULA-Ref No. % Cum. % Myriochele oculata 4220 81.3 81.3 Myriochele oculata 210 22.3 22.3 Paramphinome jeffreysii 409 7.9 89.1 Mysella bidentata 128 13.6 35.8 Chaetozone setosa 110 2.1 91.3 Amphiura filiformis 105 11.1 46.9 Amphiura filiformis 76 1.5 92.7 Paramphinome jeffreysii 84 8.9 55.8 Phoronis muelleri 35 0.7 93.4 Chaetozone setosa 50 5.3 61.1 Caudofoveata spp. 30 0.6 94.0 Levinsenia gracilis 32 3.4 64.5 Goniada maculata 29 0.6 94.5 Scoloplos armiger 25 2.7 67.2 Thyasira flexuosa 25 0.5 95.0 Abra prismatica 22 2.3 69.5 Nemertea spp. 25 0.5 95.5 Phoronis muelleri 17 1.8 71.3 Scoloplos armiger 17 0.3 95.8 Spiophanes bombyx 17 1.8 73.1

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The numbers of species varied from 68 at ULA-18 (135°/250m) to 81 at the reference station (315°/6000m). The numbers of individuals varied from 944 at the reference station to 5193 at ULA-119 (125°/500m). The Shannon Wiener diversity index varied from 1.4 at station ULA-119 to 4.4 at the reference station and the Hurlberts indices (ES100) varied from 10 (ULA-119) to 30 (reference station) including M.oculata. Excluding M. oculata from the data gave higher biodiversity/ES100 indices ranging from 3.3 (ULA-18) to 4.7 (reference station) and from 19 (ULA-18) to 33 (reference station) respectively. Indices above 4 indicate a relatively undisturbed fauna. Indices between 3 and 4 indicate a slight disturbance, while indices between 2 and 3 indicate a distinct disturbance in the fauna. In general ES100 indices above 20 characterize relatively normal fauna communities. The observed indices reflect disturbances at all stations, except the reference station, see Table 4.6.9.

The biodiversity indices in general indicate disturbances in the fauna community at Ula. The very low indices are caused by the high abundance of the bristle worm M. oculata1. However, the fauna at the reference station (254°/15000m) is characterized as relatively healthy.

During sampling black spots and lumps were observed in the samples from ULA-5, -7 and -118, see Photo 5. The observations correspond with the chemical data from the deeper layers at this station, showing elevated concentrations of THC, decalins, PAH and NPD. Table 4.6.9. Numbers of individuals (N) and species (S), depth, Shannon-Wiener diversity index (H’), Pielou’s evenness index (J), and expected number of species per 100 individuals (ES100) for each station at Ula 2005.

H' ES100 Station Direction ° Distance m Depth S N Incl.

M. o. Excl. M. o.

J Incl. M. o.

Excl. M. o.

ULA-05 45 500 72 73 3734 2.3 3.4 0.4 14 22ULA-07 225 250 70 79 3684 2.1 4.0 0.3 14 27ULA-117 300 250 73 77 4140 1.9 3.7 0.3 13 25ULA-18 135 250 70 68 3396 2.3 3.3 0.4 13 19ULA-119 125 500 71 78 5193 1.4 3.8 0.2 10 27ULA-Ref 315 6000 73 81 944 4.4 4.7 0.7 30 33M.o.= M. oculata

1 The great variations in the presence of M. oculata from 1996 to 2005 are discussed in Chapter X - General Trends

in the Region.

Photo 5 Photo of sample ULA-5 during field sampling.

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Classification and ordination

The dendrogram from the cluster analysis and the MDS plot from the ordination analysis based on station level are presented in Figure 4.6.4 and Figure 4.6.5. The reference station (315°/6000m) separates from the Ula stations at about 55 % similarity. The differences between the reference stations and the Ula stations were significantly higher abundance of M. oculata and the bristle worms P. jeffreysii and C. setosa at the Ula stations. The reference station contained somewhat higher numbers of the brittle star A. filiformis and the mussel Mysella bidentata in the fauna. The reference station has significantly higher biodiversity indices than the Ula field stations. The field stations group at a similarity at about 70 %, indicating high similarity in the fauna at the field.

The Bioenv analysis indicates that the fauna variations are related to the Ba1 concentrations at Ula. However, there are few stations included in the analysis, and the result should be interpreted with caution. The cluster analysis is well supported by the ordination analysis.

REF

ULA

-18

ULA

-117

ULA

-119

ULA

-5

ULA

-7

100

90

80

70

60

50

Sim

ilarit

y

135/250m 300/250m 125/500m 45/500m 225/250m315/6000m

Ula field stations Figure 4.6.4. Dendrogram of stations from Ula 2005.

1 Ba and the other metals are not degradable and will not disappear from the sediments. These metals may

presumable not have any effect on the fauna in itself, but could be regarded as trace elements for other degradable substances.

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ULA-5

ULA-7

ULA-117

ULA-18

ULA-119

REF

Stress: 0

315/6000m

45/500m, 125/500m, 135/250m, 225/250m, 300/250m, 315/6000m Figure 4.6.5. MDS plot of stations from Ula 2005. Comparison with 1996, 1999, 2002 and 2005 In Figure 4.6.6 the results from the present study are compared to the results from previous surveys. The numbers include the bristle worms M. oculata and P. jeffreysii for all years. The number of species has increased slightly at all comparable stations since 2002, except at ULA-119 (125°/500m) where it has been a slight decrease. The numbers of individuals have increased significantly since 2002 at comparable stations. An exception is the reference station where there is only a minor increase.

The increases are mainly due to higher abundance of the bristle worm M. oculata. The high numbers of individuals are reflected in the biodiversity indices, which in general have decreased at all comparable stations since 2002.

The great variations in the presence of M. oculata from 1996 to 2005 have complicated the faunal picture, making it difficult to draw conclusions about the state of the fauna community. Adding the 2005 results to the trend data have, however, strengthened the data set, and has made it possible to obtain a pattern in the overall temporal variations in the entire region. Temporal changes are discussed in Chapter X - General Trends in the Region which forms a basis for the conclusions for each of the fields.

020406080

100

ULA-05

ULA-07

ULA-17

ULA-118

ULA-19*

ULA-Ref

Stations

No.

of s

peci

es (S

)

1996 1999 2002 2005

Station º/m

ULA-05 45/500 ULA-07 225/250 ULA-117 300/250 ULA-18 135/250 ULA-119 125/500 ULA-Ref 315/6000

Figure 4.6.6. Numbers of species (S) and individuals (N) per 0.5 m2 and diversity (H’), incl. P. jeffreysii and M. oculata), Ula 1996, 1999, 2002 and 2005 (ULA-18 compared with ULA-118 etc.).

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0100020003000400050006000

ULA-05

ULA-07

ULA-17

ULA-118

ULA-19*

ULA-Ref

Stations

No.

of i

ndiv

idua

ls (N

)1996 1999 2002 2005

012345

ULA-05

ULA-07

ULA-17

ULA-11

8

ULA-19

*

ULA-R

ef

Stations

H'

1996 19991999 ex. M. oculata 20022002 ex. M. oculata 20052005 ex M. oculata

Figure 4.6.6. Cont.

Classification and ordination analyses

Stations from all years have been analysed at family level∗. The dendrogram from the cluster analysis reveals that most of the stations divide into two main groups at about 55 % similarity, based on years. The stations sampled in the period 1999 – 2005 cluster together while the stations sampled in 1996 form a separate group. The species that contributed the most to the differences were species within the families Oweniidae (mainly M. oculata), Amphinomidae (mainly P. jeffreysii) and Amphiuridae (mainly A.filiformis). They were found in higher abundances in 1999, 2002 and 2005 than in 1996. Species within the family Cirratulida (mainly Chaetozone species) where found in relative high numbers in the fauna in 1996 compared to later years. Chaetosone setosa is a strong indicator for organic load in an area and the species are able to act as a deposit feeder. M. oculata is a suspension feeder and a moderate indicator, characterised as a transition species. The shift in the fauna community from 1996 to 1999 with a high share of suspension feeders indicated a slight improvement in the environment. However the improvement does not seem to continue in the same degree after 1999 at ULA. The 1999 - 2005 group can be subdivided into sampling years. The differences between the years are mainly due to significant increases in the numbers of M. oculata in particular, but also P. jeffreysii and Chaetozone and Tharyx species from 1999 to 2005, still indicating an organic load in the area.

The Bioenv analysis gave a correlation of 0.7 between fauna and the combination of the environmental factors Ba1 and pelite, indicating that the changes in the fauna community are related to the changes in Ba1 concentrations. However, only few stations where comparable for all the years.

∗ Necessary when comparing between years, to avoid significant source of error due to both different years and

different taxonomists. 1 Ba and the other metals are not degradable and will not disappear from the sediments. These metals may

presumable not have any effect on the fauna in itself, but could be regarded as trace elements for other degradable substances.

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ULA-

08-1

996

U LA-

Ref-1

996

ULA-

05-1

996

ULA-

0 4-1

996

ULA-

21-1

996

ULA-

09-1

996

ULA-

15-1

9 96

ULA-

20-1

996

ULA-

16-1

9 96

U LA-

19-1

996

ULA -

Ref-1

999

ULA-

22-1

999

ULA-

04-1

999

ULA-

14-1

999

ULA-

09-1

999

ULA-

10-1

999

U LA-

21-1

999

ULA-

19-1

9 99

ULA-

20-1

999

ULA -

03-1

999

ULA-

15-1

999

ULA-

Ref-2

002

ULA-

Ref-2

005

U LA-

05-2

002

ULA-

19-2

002

ULA-

15-2

002

ULA -

09-2

002

ULA-

04-2

002

U LA-

08-2

002

ULA-

16-2

002

ULA-

18-2

002

ULA-

1 8-2

005

ULA-

1 7-2

005

ULA-

19-2

005

ULA-

0 5-2

005

ULA-

07-2

005

100

90

80

70

60

50Si

mila

rity

1996 1999 - 2005

1999 2002 2005

Figure 4.6.7. Dendrogram showing similarity between Ula stations 1996, 1999, 2002, 2005. Family level, incl. M. oculata, excl. juv., sq. root transformation.

4.6.4 Conclusion

The sediments at Ula consist mainly of fine sand, and the sand content varies from 95 % to 97 %. The gravel content is low. The silt and clay content is similar or slightly higher than previously observed. The total organic matter content in the sediments is low, and only small variations are found at the field, from 0.84 % to 1.1 %. The results are similar to the previous surveys.

In the present survey the stations are situated closer to the platform than previously. The THC concentrations in the top 0-1 cm layer vary from 3.9 mg/kg at ULA reference station (315°/6000m) to 58 mg/kg at ULA18 (135°/250m). Maximum concentrations are found in the 1-3 cm and 3-6 cm layers at ULA18, 336 mg/kg and 416 mg/kg respectively. The present level is similar to that found in 2002. However, the con centration of THC in the top 0-1 cm layer at ULA18 (135°/250m) has decreased from 143 mg/kg in 2002 to 58 mg/kg in the present survey. Elevated levels of THC are found out to 500m in 45° and 135° direction and out to 250m in the 120° and 225° direction. The other stations have THC content similar to the reference station.

The base oil Aquamul BII is found in the sediments, but not quantified separately. The highest concentrations are observed in the deeper layers at ULA18 (135°/250m). At this station Aquamul BII gives an important contribution to the THC content.

Elevated levels of NPD, PAH and decalins were found at ULA18 (135°/250m) both in the top 0-1cm layer and in the deeper layers. At ULA119 (125°/500m) levels of NPD and PAH are only slightly above the limit of contamination. Highest content of NPD and PAH is found in the deeper layers at ULA18. The NPD content is ~1.9mg/kg in both layers and the PAH content is 1.3 mg/kg in the 1-3 cm layer and 0.8 mg/kg in the 3-6 cm layer. ULA18 has also the highest content of decalins, in the deeper section up to 25 mg/kg. This is in agreement with high THC content for the same station. Generally, the level of NPD, PAH and decalins has not changed since 2002 survey.

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The Ba concentrations vary from 35 mg/kg at ULA reference station to 4170 mg/kg at ULA18 (135°/250m). Elevated levels are found at all stations except for the reference station. Thus, elevated levels of Ba are found out to 500m in 45° and 135° direction and out to 250m in the other directions. The Ba concentrations are similar or higher compared to the previous surveys.

The concentrations of the heavy metals are low. The highest concentrations are found at ULA18 (135°/250m), and elevated concentrations are observed. Slightly elevated concentrations are also found at some of the other stations, except for Cr and Hg.

The chemical results agree with the drilling history. The mud system Aquamul BII was used on a few wells in 1993.

The fauna at Ula is disturbed and have reduced biodiversity indices mainly due to high numbers of the bristle worm M. oculata. This species was found in normal numbers at the Ula reference station, indicating that the fauna is influenced by the field activities. The biodiversity indices have decreased at the field stations since 2002, but increased at the reference station.

There was a shift in the fauna community from 1996 to 1999 which indicated a slight improvement in the environment. However, the improvement does not seem to continue and the fauna community at the sampled stations (250 and 500m) at Ula is considered to be disturbed. This is supported by visual observations and chemical data from the deeper layers, showing elevated concentrations of THC, decalins, PAH and NPD.

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4.7 Gyda

4.7.1 Sediment characterization

Grain size distribution

The grain size distribution from the present survey is shown in Table 4.7.1 together with the silt and clay content from the previous surveys in 2002, 1999 and 1996.

The sediments at Gyda consist mainly of fine sand, and the sand content varies from 94.4 % at GYDA19, 135°/500m to 99.7 % at GYDA reference station, 315°/8000m. The average median diameter is 2.79φ. The gravel contents are low, and small amounts are found only at GYDA19 (0.6 %). The silt and clay contents are similar to those previously observed. The average silt and clay concentration is 4.0 % compared to 4.1 % in 2002 for the same stations. Station GYDA18 station is completely different compared to the other stations. The sediments consist mainly of silt and clay (99.5 %), and a median diameter of 5.88.

At the Gyda reference station, 315°/8000m the sediment is characterized as fine sand with 99.7 % sand and a median particle diameter of 2,77φ. The silt and clay contents are similar to the previous surveys.

The results from the complete grain size distribution are given in Appendix C. Table 4.7.1. Gyda 2005, grain size distribution. Station Median

diameter Classification Grain size distrib. 2005 (%) 2002

(%) 1999 (%)

1996 (%)

Mdφ Silt and clay

Sand Gravel Silt and clay

Silt and clay

Silt and clay

GYDA6 45°/ 250m 2.79 Fine sand 3.2 96.8 0.0 GYDA7 225°/250m 2.79 Fine sand 4.3 95.7 0.0 GYDA8 225°/500m 2.79 Fine sand 3.2 96.8 0.0 5.4 GYDA16 315°/500m 2.79 Fine sand 4.3 95.7 0.0 3.9 3.3 2.1 GYDA18* 135°/250m 5.88 Silt and clay 99.5 0.5 0.0 GYDA19 135°/500m 2.80 Fine sand 5.0 94.4 0.6 2.9 2.5 2.8 Mean 2.79 4.0 95.9 0.12 4.1 2.9 2.5 St. dev. 0.0 0.7 0.9 0.2 1.0 0.4 0.4 GYDA ref. 315°/8000m 2.77 Fine sand 0.3 99.7 0.0 3.0 3.5 2.3 *: not included in the mean value. If GYDA18* is included the mean value of Mdφ is 3.30 ± 1.2

Total organic matter (TOM)

The contents of TOM in the sediments are low and only small variations are found at the field, from 0.62 % to 0.78 %. The content corresponds to the grain size distribution with low pelite (silt and clay) content. The results are similar to the previous surveys and are shown in Table 4.7.2. An exception is GYDA18. This station has a TOM content of 5.3 %, which is in agreement with the high content of pelite found at this station.

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Table 4.7.2.Gyda 2005, total organic matter (% of dry sediment). Station 2005. 0-5 cm Mean

2002 Sd

2002 Mean 1999

Mean 1996

GYDA6 45°/ 250m 0.61 GYDA7 225°/250m 0.78 GYDA8 225°/500m 0.77 0.77 0.03 GYDA16 315°/500m 0.69 0.77 0.07 0.78 0.71 GYDA18 135°/250m 5.3 GYDA19 135°/500m 0.78 0.71 0.03 0.61 0.65 GYDA ref. 315°/8000m 0.75 0.82 0.02 0.74 0.97

4.7.2 Chemical analyses

Parameters analysed in the sediments at Gyda:

• THC • NPD, PAH, decalins • Metals (Ba, Cd, Cr, Cu, Hg, Pb, Zn)

Three replicate samples at each station and five replicate samples at the reference station are analysed. The samples are taken from the top 0-1 cm sediment layer. In addition, the 1-3 cm and 3-6 cm sediment layers are sampled at two stations and the reference station.

The results from 2002 showed no impact on the benthic fauna and low levels of THC, hence the sampling program in 2005 has been reduced.

THC

The results are shown in Table 4.7.3. The corresponding THC data from the previous surveys in 2002, 1999 and 1996 are also included for comparison. Three stations at 250m distance are included in the present survey; GYDA6, 45°/250m, GYDA7, 225°/250m and GYDA18, 135°/250m. Bar diagram of the THC content in the sediments is shown in Figure 4.7.1.

In the 1999 survey the THC concentrations in the top 0-1 cm layer ranged from 3.4 mg/kg at GYDA3, 45°/2000m and GYDA10, 225°/2000m to 9.2 mg/kg at GYDA19, 135°/500m. In the 2002 survey the THC concentrations in the top 0-1 cm layer ranged from 3.4 mg/kg at GYDA21, 135°/2000m to 9.2 mg/kg at GYDA19, 135°/500m. The maximum THC concentration at the field, 22 mg/kg, was found in the deeper layers at GYDA19.

In the present survey the concentrations of THC in the top 0-1 cm layer vary from 4.0 mg/kg at GYDA16, 315°/500m to 43 mg/kg at GYDA7, 225°/250m. One 250m station, GYDA17, 315°/250m was analysed in the 2002 survey and also analysed in the present survey. The contents of THC are unchanged and below the limit of contamination.

Elevated THC concentrations are found for the three new 250m stations, 40 mg/kg at GYDA6, 43 mg/kg at GYDA7 and 18 mg/kg at GYDA18. In general the levels of THC at the other stations are low and similar to those found in 2002 and 1999. Only slightly elevated THC concentrations are found at the 500m stations in the 45°, 135° and 225° directions.

The reference station, 315°/8000m is still uncontaminated, and the mean THC concentration of five replicate samples is 4.2 mg/kg.

Representative gas chromatograms are given in Appendix C. These include GYDA6 (45°/250m), GYDA8 (225°/500m), GYDA18 (135°/250m), GYDA19 (135°/500m) and GYDA reference station (315°/8000m).

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Gyda, THC 2005

0

10

20

30

40

50

60

GYDA5 GYDA6 GYDA7 GYDA8 GYDA16 GYDA17 GYDA18 GYDA19 GYDA ref

station

mg/kg

1999

2002

2005

LSC A

40±28

Figure 4.7.1. Bar diagram of the THC content in the sediments at Gyda 1999-2005. Table 4.7.3. Gyda 2005, total hydrocarbon content (mg/kg dry sediment). Station Grab

#1 Grab

#2 Grab

#3 Grab

#4 Grab

#5 Mean SD Mean Mean Mean

2005 2005 2002 1999 1996 GYDA5 45°/500m 8.1 5.7 10.1 8.0 2.2 6.9 GYDA6 45°/250m 13.2 36 70 40 28 GYDA7 225°/250m 43 50 34 43 8.4 GYDA8 225°/500m 7.2 6.2 9.2 7.5 1.5 7.4 GYDA16 315°/500m 3.8 4.1 4.0 4.0 0.2 5.4 4.1 3.0 GYDA17 315°/250m 3.7 5.1 5.6 4.8 1.0 4.9 GYDA18 135°/250m 18.7 20 14.6 17.9 2.9 GYDA19 135°/500m 6.4 7.5 6.9 6.9 0.6 9.2 9.2 7.4 1-3 cm 23 22 15.0 2.2 3-6 cm 12.5 17.5 16.6 9.9 GYDA ref. 315°/8000m 2.9 4.8 2.6 6.5 4.3 4.2 1.6 3.8 3.7 5.6 1-3 cm 3.4 3.8 3.0 4.4 3-6 cm 5.2 4.6 4.6 7.0 LSC Region A 6.6 6.4 9

NPD, PAH and decalins

One station is analysed in addition to the reference station, GYDA19, 135°/500m. GYDA6, 45°/250m, grab #3, with THC content of >50 mg/kg, was also included for analyses. The results are shown in Table 4.7.4.

Elevated NPD and decalin contents were found in grab #3 at GYDA6. This is in accordance with the high THC content in this sample. The PAH content is low.

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The NPD concentrations in the top layer at GYDA19 are below the limit of contamination. However, the NPD content in the deeper layers are slightly elevated (up to 0.082 mg/kg in the 1-3 cm layer), and the levels are similar or slightly higher compared to 2002. The PAH content in the top layer is low (0.030 mg/kg) and below the limit of contamination. The content of PAH in the deeper layers are slightly elevated, ~0.10 mg/kg. The decalin concentration found at GYDA19, 135°/500m in the 0-1 cm top layer is low and the content has decreased since 2002. The contents of decalins in the deeper layers are however unchanged since 1999 and 2002 survey. The contents are 1.9 mg/kg and 0.8 mg/kg, respectively.

Gyda reference station, 315°/8800m is still considered uncontaminated. Table 4.7.4. Gyda 2005, sum NPD, PAH and decalins (mg/kg dry sediment).

Station Grab #1

Grab #2

Grab #3

Grab #4

Grab #5

Mean SD Mean SD Mean SD Mean

2005 2005 2002 2002 1999 1999 1996NPD GYDA19 135°/500m 0.021 0.021 0.013 0.018 0.004 0.052 0.020 0.043 0.022 0.012 1-3 cm 0.082 0.039 0.19 0.010 3-6 cm 0.037 0.026 0.025 0.035GYDA6* 45°/250m 0.70 0.70 GYDA Ref. 315°/8000m nd 0.13 0.052 nd nd <0.13 0.05 0.013 0.001 0.018 0.004 0.015 1-3 cm 0.012 0.014 0.016 0.026 3-6 cm 0.013 0.015 0.018 0.019LSC Subregion A 0.030 0.026 0.040 PAH GYDA19 135°/500m 0.032 0.037 0.021 0.030 0.008 0.064 0.013 0.028 0.013 0.028 1-3 cm 0.12 0.057 0.16 0.023 3-6 cm 0.10 0.036 0.010 0.17GYDA6* 45°/250m 0.056 GYDA Ref. 315°/8000m 0.027 0.036 0.038 0.031 0.028 0.032 0.005 0.035 0.003 0.038 0.012 0.056 1-3 cm 0.045 0.035 0.031 0.093 3-6 cm 0.080 0.049 0.037 0.078LSC Subregion A 0.061 0.062 0.090 Decalins GYDA19 135°/500m 0.13 0.15 0.12 0.13 0.02 0.33 0.068 0.40 0.43 0.30 1-3 cm 1.9 0.96 0.46 0.50 3-6 cm 0.80 1.0 0.83 1.7 GYDA6* 45°/250m 1.01 GYDA Ref. 315°/8000m nd nd 1.8 nd nd nd nd - nd 0.075 1-3 cm nd nd nd 0.14 3-6 cm nd nd nd 0.074nd: not detected. Limit of detection for NPD is 0.01 mg/kg, for PAH 0.005 mg/kg and for decalins 0.1 mg/kg. *: only grab #3.

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Metals

The results are shown in Table 4.7.5. Data from the previous survey in 2002 and 1999 are also included for comparison in Table 4.7.6. Hg is only analysed for some stations. Bar diagram of the Ba content in the sediments is shown in Figure 4.7.2.

In 1999 the Ba concentrations ranged from 29 mg/kg at the reference station (315°/8000m) to 379 mg/kg at GYDA19 (135°/500m). The Ba concentrations have decreased since 1996.

In 2002 the Ba concentrations ranged from 40 mg/kg at the reference station to 542 mg/kg at GYDA19, 135°/500m. The content of Ba was at the same levels as in the previous surveys.

In the present survey three new stations are included at distance 250 m from the platform. The Ba concentrations vary from 36 mg/kg at GYDA Ref to 1566 mg/kg at GYDA7, 225°/250m. The new stations GYDA6, 45°/250m and GYDA7, 225°/250m are the most contaminated, with respect to Ba, containing 1171 mg/kg and 1566 mg/kg respectively. The new station GYDA18, 135°/250m has the lowest Ba content observed in the Gyda field. However, this station appears different compared to the others, with a high content of silt and clay, a relatively high content of total organic matter and a high level of heavy metals.

Elevated Ba concentrations are found at all stations except for GYDA18, 135°/250m and the reference station. Thus elevated levels of Ba are found out to 500m in the 135°, 225° and 315° direction and to 250m in the 45° direction. Elevated concentrations are also found in the deeper sections at GYDA19.

The concentrations of the heavy metals are low for all stations investigated, except for GYDA18, 135°/250m, which has a high content of heavy metals. Slightly elevated concentrations of Pb and Zn are found at some of the other stations. Cd and Hg concentrations are just above or below the detection limit.

Gyda, Ba 2005

0

200

400

600

800

1000

1200

1400

1600

1800

2000

GYDA6 GYDA7 GYDA8 GYDA16 GYDA18 GYDA19 GYDA ref

station

mg/kg

1999

2002

2005

LSC A

Figure 4.7.2 Bar diagram of the Ba content in the sediments at Gyda 1999- 2005.

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The following variation is found at Gyda in the top layer, 0-1 cm. The values are given in mg/kg: Gyda: GYDA6 – GYDA19 GYDA Reference station Ba: 62 – 1566 36 Cr: 6.5 – 23.8 7.0 Cu: 0.7 – 20.8 <0.5 Pb: 6.5 – 23.8 5.8 Zn: 5.6 – 88 4.9 Cd: <0.01 <0.01 Hg: <0.01 <0.01

Table 4.7.5. Gyda 2005, metals (mg/kg dry sediment). Station Sample Ba Cd Cr Cu Hg Pb Zn 2005 2005 2005 2005 2005 2005 2005GYDA6 45°/250m 1 639 <0.01 5.9 1.3 8.8 9.2 2 1982 0.01 6.5 1.6 9.5 8.7 3 891 0.01 6.4 1.5 9.3 8.9 mean 1171 0.01 6.3 1.4 9.2 8.9 SD 714 0.3 0.2 0.4 0.2 GYDA7 225°/250m 1 1886 <0.01 6.7 1.2 12.1 9.4 2 1339 0.01 6.7 1.3 10.3 9.1 3 1474 <0.01 6.8 1.7 12.6 17.3 mean 1566 <0.01 6.7 1.4 11.7 11.9 SD 285 0.0 0.3 1.2 4.6 GYDA8 225°/500m 1 324 <0.01 6.6 0.9 6.0 5.5 2 348 <0.01 6.5 1.0 7.5 5.5 3 208 <0.01 6.5 0.9 7.0 5.7 mean 294 <0.01 6.5 0.9 6.8 5.6 SD 75 0.0 0.1 0.8 0.2 GYDA16 315°/500m 1 69 <0.01 6.8 0.8 6.5 7.1 2 114 <0.01 7.1 0.7 6.4 6.0 3 84 <0.01 6.8 0.6 6.8 12.6 mean 89 <0.01 6.9 0.7 6.5 8.6 SD 23 0.2 0.1 0.2 3.5 GYDA18 135°/250m 1 59 0.14 51.0 21.0 22.9 89.2 2 68 0.14 44.7 19.9 24.7 87.1 3 60 0.14 48.4 21.4 23.8 87.8 mean 62 0.14 48 21 24 88 SD 5 3.1 0.8 0.9 1.1 GYDA19 135°/500m 1 306 <0.01 7.2 1.5 <0.01 8.3 9.1 2 429 <0.01 7.3 1.4 <0.01 8.1 8.3 3 460 <0.01 6.9 1.4 0.01 8.2 9.5 mean 399 <0.01 7.2 1.4 <0.01 8.2 9.0 SD 81 0.2 0.04 0.1 0.6 1-3 cm 1 994 0.03 8.4 2.1 <0.01 8.6 11.1 3-6 cm 1 409 0.02 8.7 1.2 <0.01 7.3 9.4 Cont.

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Table 4.7.5. cont. Station Sample Ba Cd Cr Cu Hg Pb Zn 2005 2005 2005 2005 2005 2005 2005GYDA Ref. 315°/8000m 1 52 <0.01 7.2 <0.5 <0.01 6.2 5.1

2 25 <0.01 6.8 <0.5 <0.01 5.3 4.6 3 35 <0.01 7.2 <0.5 <0.01 6.0 5.4 4 25 <0.01 6.9 <0.5 <0.01 5.4 4.7 5 43 <0.01 6.9 <0.5 <0.01 6.2 4.5 mean 36 <0.01 7.0 <0.5 <0.01 5.8 4.9 SD 12 0.2 0.4 0.4 1-3 cm 53 0.01 7.5 <0.5 <0.01 5.8 5.6 3-6 cm 111 0.01 8.0 <0.5 0.01 6.5 6.5 LSC Subregion A 76.2 8.0 1.3 7.4 6.9 Table 4.7.6 Gyda 2005, metals (mg/kg dry sediment), comparing mean values with previous surveys. Station Ba Ba Ba Ba Cd Cd Cd Cr Cr Cr 2005 2002 1999 1996 2005 2002 1999 2005 2002 1999 GYDA6 45°/250m 1171 <0.01 6.3 GYDA7 225°/250m 1566 <0.01 6.7 GYDA8 225°/500m 294 382 <0.01 <0.01 6.5 6.1 GYDA16 315°/500m 89 106 84 218 <0.01 <0.01 <0.02 6.9 6.2 GYDA18 135°/250m 62 0.14 48.0 GYDA19 135°/500m 399 542 379 935 <0.01 0.01 <0.02 7.2 5.9 6.1 1-3 cm 994 651 382 0.03 0.02 <0.02 8.4 6.6 6.0 3-6 cm 409 437 320 0.02 0.03 0.03 8.7 7.4 6.5 GYDA Ref. 315°/8000m 36 40 47 63 <0.01 0.01 <0.02 7.0 6.7 7.1 1-3 cm 53 40 46 0.01 <0.01 <0.02 7.5 6.7 6.9 3-6 cm 111 78 112 0.01 0.01 0.02 8.0 6.7 7.7 cont. Table 4.7.6 cont. Station Cu Cu Cu Hg Hg Hg Pb Pb Pb Zn Zn Zn 2005 2002 1999 2005 2002 1999 2005 2002 1999 2005 2002 1999GYDA6 45°/250m 1.4 9.4 8.9 GYDA7 225°/250m 1.4 11.7 11.9 GYDA8 225°/500m 0.9 1.4 6.8 7.1 5.6 9.0 GYDA16 315°/500m 0.7 1.2 0.6 6.5 6.4 7.4 8.6 5.1 5.6 GYDA18 135°/250m 21 24 88 GYDA19 135°/500m 1.4 1.8 0.7 <0.01 0.01 <0.02 8.2 6.7 6.2 9.0 8.1 5.3 1-3 cm 2.1 1.8 0.6 <0.01 0.01 0.01 8.6 7.2 5.7 11.1 7.8 4.6 3-6 cm 1.2 1.6 0.5 <0.01 0.01 0.03 7.3 7.1 5.6 9.4 9.1 6.8 GYDA Ref. 315°/8000m <0.05 1.3 0.5 <0.01 0.01 0.02 5.8 5.8 6.5 4.9 5.7 5.5 1-3 cm <0.05 0.9 0.5 <0.01 <0.01 0.01 5.8 6.1 6.7 5.6 5.2 4.5 3-6 cm <0.05 1.1 0.7 0.01 <0.01 0.02 6.5 6.3 7.1 6.6 6.9 6.7

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4.7.3 Biological analyses

A total of 153 species and 27071 individuals were sampled at 7 stations. Greatest abundance (91.8 %) was found among the polychaetes, of which the species Myriochele oculata constitutes 78.4 % and Paramphinome jeffreysii constitutes 13.0 % of the total number of Polychaeta, see Table 4.7.7. Table 4.7.7 Number of species and individuals distributed between the main groups, Gyda 2005.

Individuals Species Main animal groups Number % Number %

Varia 1026 3.8 15 9.8Polychaeta 24860 91.8 77 50.3- Paramphinome jeffreysii 3240 13.0 - Myriochele oculata 19481 78.4 Crustacea 102 0.4 19 12.4Mollusca 479 1.8 34 22.2Echinodermata 604 2.2 8 5.2- Amphiura filiformis 533 88.2 Total 27071 100.0 153 100.0

Figure 4.7.3 shows the numbers of species and individuals sampled at each station and variations between grab samples.

0

20

4060

80

100

Gyda-0

6Gyd

a-07

Gyda-0

8Gyd

a-16

Gyda-1

8Gyd

a-19

Gyda-R

efA

Stations

No.

of s

peci

es (S

)

Station º/m Gyda-06 45/250 Gyda-07 225/250 Gyda-08 225/500 Gyda-16 315/500 Gyda-18 135/250 Gyda-19 135/500 Gyda-RefA 315/8000

0100020003000400050006000

Gyda-0

6Gyd

a-07

Gyda-0

8Gyd

a-16

Gyda-1

8Gyd

a-19

Gyda-R

efA

Stations

No.

of i

ndiv

idua

ls (N

)

Ex. P. jeffreysii and M. oculata

0100020003000400050006000

Gyda-0

6Gyd

a-07

Gyda-0

8Gyd

a-16

Gyda-1

8Gyd

a-19

Gyda-R

efA

Stations

No.

of i

ndiv

idua

ls (N

)

Figure 4.7.3 Numbers of species (S) and individuals (N) per 0.5 m2 (incl./excl. P. jeffreysii and M. oculata), mean values per grab sample and standard deviation, Gyda 2005. The standard deviation was in general dramatically reduced when the two species P. jeffreysii and M. oculata were removed from the data set. This is evident since the two species constitute 91.4 % of the total number of individuals. An exception is at station Gyda-18

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(135°/250m), where the standard deviation was only slightly reduced. This is due to considerably smaller number of individuals.

Diversity and dominant species

The dominant species at each station varied from 46.6 % at GYDA-18 (135°/250m) to 82.8 % at GYDA-19 (135°/500m). The 10 most abundant species made up from 85.5 % at the reference station (315°/8000) to 97 % at GYDA-06 (45°/250m), see Table 4.7.8. The bristle worm M. oculata dominated the fauna at the Gyda field, followed by P. jeffreysii. Other frequently found species were the brittle star Amphiura filiformis, the bristle worms Chaetozone setosa, Scoloplos armiger, Apistobranchus tullbergi and the ribbon worm Nemertea spp. P. jeffreysii is mainly a carnivore species and the ribbon worm is a deposit feeder. The other mentioned species are either suspension- or both suspension- and deposit feeders. Most of these species are known indicators of organic pollution when they are found in high amounts. However, several of the above mentioned species have a planktonic developmental stage and are able to settle in large numbers. Table 4.7.8 The 10 most abundant species at each station, Gyda 2005. 10 most dominating species Gyda-06 No. % Cum. % Gyda-07 No. % Cum. % Myriochele oculata 3150 68.4 68.4 Myriochele oculata 2690 66.7 66.7 Paramphinome jeffreysii 566 12.3 80.6 Paramphinome jeffreysii 590 14.6 81.3 Chaetozone setosa 337 7.3 88.0 Chaetozone setosa 193 4.8 86.1 Nemertea spp. 195 4.2 92.2 Nemertea spp. 150 3.7 89.8 Apistobranchus tullbergi 78 1.7 93.9 Amphiura filiformis 67 1.7 91.5 Spiophanes bombyx 43 0.9 94.8 Scoloplos armiger 62 1.5 93.0 Scoloplos armiger 37 0.8 95.6 Apistobranchus tullbergi 56 1.4 94.4 Tharyx sp. 30 0.7 96.3 Spiophanes bombyx 34 0.8 95.2 Amphiura filiformis 21 0.5 96.7 Tharyx sp. 19 0.5 95.7 Goniada maculata 13 0.3 97.0 Glycera alba 19 0.5 96.2 Gyda-08 No. % Cum. % Gyda-16 No. % Cum. % Myriochele oculata 4945 76.7 76.7 Myriochele oculata 3360 72.0 72.0 Paramphinome jeffreysii 731 11.3 88.1 Paramphinome jeffreysii 639 13.7 85.7 Amphiura filiformis 176 2.7 90.8 Amphiura filiformis 120 2.6 88.3 Scoloplos armiger 66 1.0 91.8 Phoronis muelleri 58 1.2 89.6 Apistobranchus tullbergi 64 1.0 92.8 Edwardsia sp. 49 1.1 90.6 Nemertea spp. 59 0.9 93.7 Scoloplos armiger 45 1.0 91.6 Phoronis muelleri 54 0.8 94.6 Chaetozone setosa 37 0.8 92.4 Edwardsia sp. 39 0.6 95.2 Nemertea spp. 36 0.8 93.1 Chaetozone setosa 35 0.5 95.7 Apistobranchus tullbergi 24 0.5 93.7 Caudofoveata spp. 26 0.4 96.1 Caudofoveata spp. 23 0.5 94.2 Gyda-18 No. % Cum. % Gyda-19 No. % Cum. % Myriochele oculata 116 46.6 46.6 Myriochele oculata 4070 82.8 82.8 Paramphinome jeffreysii 30 12.1 58.6 Paramphinome jeffreysii 330 6.7 89.5 Limacina retroversa 25 10.0 68.7 Phoronis muelleri 84 1.7 91.2 Spisula subtruncata 24 9.6 78.3 Edwardsia sp. 62 1.3 92.5 Chaetozone setosa 12 4.8 83.1 Chaetozone setosa 57 1.2 93.7 Themisto spp. 11 4.4 87.6 Scoloplos armiger 42 0.9 94.5 Chaetognatha spp. 7 2.8 90.4 Apistobranchus tullbergi 35 0.7 95.2 Glycera alba 5 2.0 92.4 Nemertea spp. 29 0.6 95.8 Abra prismatica 3 1.2 93.6 Caudofoveata spp. 19 0.4 96.2 Ophiura affinis 3 1.2 94.8 Cerianthus lloydii 17 0.4 96.5 Cont.

Table 4.7.8. cont.

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10 most dominating species Gyda-RefA No. % Cum. %Myriochele oculata 1150 53.4 53.4Paramphinome jeffreysii 354 16.4 69.8Amphiura filiformis 140 6.5 76.3Spiophanes bombyx 42 2.0 78.3Scoloplos armiger 35 1.6 79.9Nemertea spp. 27 1.3 81.2Goniada maculata 25 1.2 82.3Pleustidae spp. 24 1.1 83.4Phoronis muelleri 24 1.1 84.5Montacuta substriata 20 0.9 85.5

The number of species varies from 20 at GYDA-18 (135°/250m) to 89 at the reference station (315°/8000m). The numbers of individuals vary from 249 at GYDA-18 to 4915 at GYDA-19 (135°/500m). The Shannon Wiener diversity indices vary from 1.3 at GYDA-19 to 3.0 at the reference station and the Hurlberts indices (ES100) vary from 10 at GYDA-06 (45/250m), GYDA-08 (225/500m) and GYDA-19 to 21 at the reference station. Removal of M. oculata1 from the data gave higher biodiversity indices ranging from 3.0 (GYDA-6) to 4.2 (reference station) and 16 (GYDA-6) to 32 (reference station).

Diversity indices above 4 indicate a relatively undisturbed fauna. Indices between 3 and 4 indicate a slight disturbance, while indices between 2 and 3 indicate a definite disturbance in the fauna. In general ES100 indices above 20 characterize a relatively normal fauna community. The biodiversity indices indicate a general disturbance in the fauna community at Gyda, see Table 4.7.9. The fauna at the reference station (254°/15000m) is less disturbed than at the other stations. Table 4.7.9. Numbers of individuals (N) and species (S), depth, Shannon-Wiener diversity index (H’), Pielou’s evenness index (J), and expected number of species per 100 individuals (ES100) for each station at Gyda 2005.

H' ES100 Station Direction ° Distance m Depth S N Incl.

M. o. Excl. M. o.

J Incl. M. o.

Excl. M. o.

Gyda-06 45 250 67 59 4608 1.9 3.0 0.3 10 16Gyda-07 225 250 63 53 4035 2.0 3.1 0.3 11 17Gyda-08 225 500 64 85 6446 1.6 3.3 0.2 10 22Gyda-16 315 500 68 80 4664 1.8 3.5 0.3 12 25Gyda-18 135 250 65 20 249 2.8 3.3 0.6 14 17Gyda-19 135 500 69 56 4915 1.3 3.7 0.2 10 23Gyda-RefA 315 8000 69 89 2154 3.0 4.2 0.5 21 32M. o.= M. oculata

Classification and ordination

The dendrogram from the cluster analysis and the MDS plot from the ordination analysis based on station level are presented in Figure 4.7.4 and Figure 4.7.5. Station GYDA-18 (135°/250m) differs significantly from the other stations. This is due to considerably smaller numbers of species as well as individuals at GYDA-18. Observations from the sampling show that GYDA-18 was anoxic. The reference station (315°/8000m) separates from the rest of the Gyda stations at about 60 % similarity.

At a similarity of about 70 % the other Gyda stations divide into two groups: 1 See Chapter 5 for a general discussion about the role of M. oculata in the region.

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Group 1: GYDA-06 (45°/250m) and -07 (225°/250m). Group 2: GYDA-08 (225°/500m), -16 (315°/500m) and -19 (135°/500m).

The species that contribute the most to the differences between the reference stations and the field stations (excl. GYDA-18) were significantly higher abundances of M. oculata, C. setosa and Nemertea at the field stations. The fauna in group 2 contained considerably higher numbers of M. oculata and A. filiformis than group 1. The stations in group 1 contained higher numbers of strong indicator species as C. setosa and Nemertea than group 2. The stations in group 2 also differed with lower biodiversity indices than group 1. When removing M. oculata from the data set, the opposite is the case. However, the structure of the fauna communities both at station GYDA-18 and at the other field stations (group 1 and 2) indicates disturbance. High abundances of the above mentioned species also indicate available organic matter in the area.

The Bioenv analysis reveals a correlation of 0.93 between the fauna and the combination of the environmental factors Cr, Cu, TOM and pelite. Station GYDA-18 had a significantly different type of sediment than the other stations and omitting this station from the data set gave a correlation factor of 0.98 which indicates that the variations in the fauna coincide with the variations in the complex comprised of THC, Cu, TOM and pelite.

Gyd

a -18

Gyd

a-Re

fA

Gyd

a-0 6

Gyd

a-07

Gyd

a-1 9

Gyd

a-08

Gyd

a-16

100

80

60

40

20

Sim

ilarit

y

135 /250m 315 /8000m 45 /250m 225 /250m 225 /500m 315 /500m135 /500m

Group 1 Group 2 Figure 4.7.4. Dendrogram of stations from Gyda 2005.

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Gyda-06Gyda-07

Gyda-08Gyda-16

Gyda-18Gyda-19

Gyda-RefA

Stress: 0,01

45 /250m, 225 /250m

135 /500m, 225 /500m, 315 /500m

Figure 4.7.5. MDS plot of stations from Gyda 2005.

Comparison with 1993, 1996, 1999 and 2002

In Figure 4.7.6 the results from the present survey are compared to the results from previous surveys. The numbers include the bristle worms M. oculata and P. jeffreysii for all years. The numbers of individuals have decreased slightly since last survey at GYDA-19 (135°/500m) and the reference station, and are relatively unaltered at GYDA-08 (225°/500m) and -16 (315°/500m). The numbers of species have increased since last survey at GYDA-08 and the reference station. There has been a decrease in number of species at GYDA-19. At GYDA-08 and -16 the indices are unaltered since 2002, while a slight decrease is observed at GYDA-19 and the reference station (315°/8000m). The biodiversity indices exclusive of M. oculata have declined at all comparable stations since 2002.

020406080

100

Gyda-0

6

Gyda-0

7

Gyda-0

8

Gyda-1

6

Gyda-1

8

Gyda-1

9

Gyda-R

efA

Stations

No.

of s

peci

es (S

)

1990 1993 1996 1999 2005

01000200030004000500060007000

Gyda-0

6

Gyda-0

7

Gyda-0

8

Gyda-1

6

Gyda-1

8

Gyda-1

9

Gyda-R

ef

Stations

No.

of i

ndiv

idua

ls (N

)

1990 1993 1996 1999 2002 2005

Figure 4.7.6. Numbers of species (S) and individuals (N) per 0.5 m2 and diversity (H’), incl. P. jeffreysii and M. oculata,), Gyda 1990, 1993, 1996, 1999 and 2005.

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012345

Gyda-0

6

Gyda-0

7

Gyda-0

8

Gyda-1

6

Gyda-1

8

Gyda-1

9

Gyda-R

efA

Stations

H'

1990 1993 1996 1999 2002 2005

012345

Gyda-0

6

Gyda-0

7

Gyda-0

8

Gyda-1

6

Gyda-1

8

Gyda-1

9

Gyda-R

ef

Stations

H'

1999 2002 2005Ex. M. oculataEx. M. oculata

Station º/m Station º/m Station º/m Gyda-06 45/250 Gyda-08 225/500 Gyda-18 135/250 Gyda-07 225/250 Gyda-16 315/500 Gyda-19 135/500 Gyda-RefA 315/8000 Table 4.7.4. Cont.

Classification and ordination analyses

Stations from all years have been analysed at family level∗. The dendrogram from the cluster analysis (Figure 4.7.7) reveals that most of the stations divide into two main groups at about 45 % similarity. The stations sampled in 1999, 2002 and 2005 group together and most of the stations sampled in 1993 and 1996 group together. Stations GYDA-06, -07 and -18 sampled in 1993 separate significantly from the others and form a third group at about 30 % similarity. These stations have high abundances of species within the family Cirratulidae (mainly C. setosa) compared to the rest of the stations in 1993, indicating disturbance at these stations in 1993.

The species that contributed most to the difference between the two main groups were significant higher numbers of species within the family Oweniidae (mainly M. oculata) and higher numbers within the families Amphinomidae (mainly P. jeffreysii) and Serpulidae (mainly D. arietina) in the group 1999 – 2005 compared to the 1993 and 1996 stations1.

The Bioenv analysis gave a correlation of 0.8 between fauna and a combination of the environmental factors Ba2, Pb, TOM and pelite, indicating a relationship between the variations of the environmental factors and the development in the fauna over the years.

∗ Necessary when comparing between years, to avoid significant source of error due to both different years and

different taxonomists. 1 The great variations in the presence of M. oculata from 1996 to 2005 have complicated the faunal picture, making it difficult to draw conclusions about the state of the fauna community. Adding the 2005 results to the trend data have, however, strengthened the data set, and has made it possible to obtain a pattern in the overall temporal variations in the entire region. The changes are discussed in Chapter X - General Trends in the Region which forms a basis for the conclusions for each of the fields. 2 Ba and the other metals are not degradable and will not disappear from the sediments. These metals may

presumable not have any effect on the fauna in itself, but could be regarded as trace elements for other degradable substances.

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Gyd

a-0 6

-93

Gyd

a -07

-93

Gyd

a-18

-93

Gyd

a-Re

fA-0

5G

yda-

0 6-0

5G

yda-

07-0

5G

yda-

19-0

5G

yda-

08 -0

5G

yda-

16- 0

5G

yda-

R efA

-99

Gyd

a-Re

fB-9

9G

yda-

2 1-0

2G

yda-

RefA

-02

Gyd

a-Re

fB-0

2G

yda-

16-0

2G

yda-

1 7-0

2G

y da-

09-0

2G

yda-

04- 0

2G

yda-

05-0

2G

yda -

08 -0

2G

yda-

19-0

2G

yda-

20-0

2G

yda-

21-9

9G

yda-

09-9

9G

yda-

16-9

9G

yda-

03-9

9G

y da-

15-9

9G

yda-

10-9

9G

yda-

04-9

9G

yda-

19-9

9G

yda-

20-9

9G

y da-

RefA

-96

Gyd

a-2 1

-96

Gyd

a-10

-96

Gyd

a-03

-96

Gyd

a-15

-96

Gyd

a-16

-96

Gy d

a-09

-96

Gyd

a-19

-96

Gyd

a-04

-96

Gy d

a-20

-96

Gy d

a-08

-93

Gyd

a-19

-93

Gyd

a-02

-93

Gyd

a-Re

fB-9

3G

yda-

11-9

3G

yda-

RefA

-93

Gyd

a-03

-93

Gyd

a-05

-93

Gyd

a-17

-93

Gyd

a-04

-93

Gyd

a-20

-93

Gyd

a-09

-93

Gyd

a-16

-93

Gyd

a-10

-93

Gyd

a -15

-93

Gyd

a-14

-93

Gyd

a-21

-93100

80

60

40

20Si

mila

rity

1999 - 2005 1993 - 1999 Figure 4.7.7. Dendrogram showing similarity between Gyda stations 1990, 1993, 1996, 1999 and 2005. Family level, incl. M. oculata, sq. root transformation.

4.7.4 Conclusion

The sediments at Gyda consist mainly of fine sand, and the sand content varies from 94.4 % to 99.7 %. The gravel content is low, and small amounts are found only at GYDA19. The silt and clay content is similar to those previously observed. The average silt and clay concentration found is similar to the previous observations. Station GYDA18, 135°/250m appears different from the rest of the stations. The sediments at this station consist mainly of silt and clay (99.5 %).

The total organic matter content in the sediments is low and only small variations are found at the field, from 0.62 % to 0.78 %. The content corresponds to the grain size distribution with low pelite (silt and clay) content. The results are similar to the previous survey. An exception is GYDA18. This station has a content of total organic matter of 5.3%. This is in agreement with the high content of silt and clay found for this station.

Three new stations are included in the present survey at a distance 250 m from the platform. These are GYDA6, 45°/250m, GYDA7, 225°/250m and GYDA18, 135°/250m. Elevated THC concentrations are found at these stations, 40 mg/kg at GYDA6, 43 mg/kg at GYDA7 and 18 mg/kg at GYDA18. In general the THC levels at the other stations are low and similar to those found in 2002 and 1999. Only slightly elevated THC concentrations are found at the 500m stations in the 45°, 135° and 225° directions.

Elevated NPD and decalin contents were found in grab #3 at GYDA6. This is in accordance with high THC content in the same sample. The PAH content is low. The NPD concentrations in the top layer at GYDA19 are below the limit of contamination. However, the NPD content in the deeper layers are slightly elevated and the levels are similar or slightly higher compared to 2002. The PAH levels are low, just at the limit of contamination. The decalin concentrations are still relatively high in the deeper layers, 1.9 mg/kg at 1-3 cm.

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The Ba concentrations vary from 36 mg/kg at GYDA reference station to 1566 mg/kg at GYDA7. The new stations GYDA6 and GYDA7 are the most contaminated, with Ba values of 1171 mg/kg and 1566 mg/kg respectively. The new station GYDA18, 135°/250m contains the lowest values of Ba observed in the Gyda field. However, this station appears different from the others, with high contents of silt and clay, a relatively high content of total organic matter and high levels of heavy metals. The Ba concentration has not changed since 2002. Elevated Ba concentrations are found at all the stations except for GYDA18, 135°/250m and the reference station. Thus elevated levels of Ba are found out to 500m in the 135°, 225° and 315° direction and limited to 250m in the 45° direction. Elevated concentrations are also found in the deeper sections.

The concentrations of the heavy metals are low, except at GYDA18, 135°/250m, which has a high content of heavy metals. Slightly elevated concentrations of Pb and Zn are found at some of the other stations.

The biodiversity indices indicate a general disturbance in the fauna at Gyda in 2005. The fauna at Gyda-18 (135°/250m) differ from the other stations with anoxic sediment and is clearly disturbed. The fauna at the reference station (254°/15000m) is less disturbed than the field stations located 250 m and 500 m from the centre. The similarity analysis revealed that the stations are clustering in a pattern that reflects the distance from the field centre, which indicates that the fauna is influenced by the field activities.

The biodiversity indices show a slight increase since 2002 at the reference station. At GYDA-08 (225°/500m) and -16 (315°/500m), the indices have not changed since 2002, while slight decreases are observed at GYDA-19 (135°/500m). Variations in the fauna between years seem to coincide with the variations in Ba, Pb, TOM and pelite.

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4.8 Tambar

4.8.1 Sediment characterization

Grain size distribution

The grain size distribution from the present survey is shown in Table 4.8.1 together with the silt and clay content from the previous survey in 2002 and 1999.

The sediments at Tambar consist of fine sand, and the sand content varies from 92.6 % at TAMBAR13, 315°/250m to 97.8 % at TAMBAR5, 135°/250m. The average median particle diameter is 2.80φ. Gravel is only found in a small amount (0.5 %) at TAMBAR1, 45°/250m. The silt and clay content is at the same level as in 2002 and the average concentration is 4.1 % compared to 4.4 % in 2002. The mean median particle diameter is 2.80φ. The mean values are similar to the Gyda reference station, 315°/8000m where the sediment is characterized as fine sand with a median particle diameter of 2.77φ. The results from the complete grain size distribution are given in Appendix C. Table 4.8.1. Tambar 2005, grain size distribution. Stations Median

diameter Classification Grain size distrib. 2005

(%) 2002 (%)

1999 (%)

Mdφ Silt and clay Sand Gravel Silt and clay

TAMBAR1 45°/250m 2.80 Fine sand 4.1 95.4 0.5 4.0 4.2 TAMBAR5 135°/250m 2.79 Fine sand 2.6 97.4 0.0 4.0 4.9 TAMBAR9 225°/250m 2.78 Fine sand 2.2 97.8 0.0 5.4 5.3 TAMBAR13 315°/250m 2.82 Fine sand 7.4 92.6 0.0 4.1 5.2 Mean 2.80 Fine sand 4.1 95.8 4.4 4.9 Standard deviation 0.02 2.4 2.4 0.7 0.5 GYDA ref. 315°/8000m 2.77 Fine sand 0.3 99.7 0.0 3.0 3.5

Total organic matter (TOM)

The contents of TOM in the sediments are low, and only small variations are found at the field. The results are shown in Table 4.8.2. Table 4.8.2. Tambar 2005, total organic matter (% of dry sediment). Station 2005. 0-5 cm Mean

2002 Sd

2002 Mean 1999

TAMBAR1 45°/250m 0.85 0.80 0.03 0.76 TAMBAR5 135°/250m 0.95 0.83 0.02 0.75 TAMBAR9 225°/250m 0.83 0.71 0.03 0.84 TAMBAR13 315°/250m 0.81 0.86 0.06 0.72 GYDA ref. 315°/8000m 0.75 0.82 0.02 0.74

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4.8.2 Chemical analyses

Parameters analysed in the 0-1 cm sediment layer at Tambar:

• THC • NPD, PAH, decalins • Metals (Ba, Cd, Cr, Cu, Hg, Pb, Zn)

Three replicate samples at each station are analysed. The samples are taken from the top 0-1 cm sediment layer. In addition the 1-3 cm and 3- 6 cm sediment layers are sampled at two stations.

There have been no discharges since 2001 and alterations in the dispersion pattern compared to 2002 are not to be expected. This year survey has thus focussed on stations close to the installation.

THC

The results are shown in Table 4.8.3. The corresponding THC data from the survey in 2002 and the baseline survey in 1999 are included for comparison. Bar diagram of the THC content in the sediments is shown in Figure 4.8.1.

At the baseline survey in 1999 the THC concentrations ranged from 3.2 mg/kg to 107 mg/kg (TAMBAR9, 225°/250m). The elevated THC concentrations found were residues from an incident of unintentional discharge of base oil during exploration drilling in 1998. In the 2002 survey the mean THC concentrations ranged from 2.9 mg/kg at TAMBAR14, 315°/500m to 15.8 mg/kg at TAMBAR5, 135°/250m.

In the present survey the mean THC concentration vary from 3.3 mg/kg at TAMBAR2, 45°/500m to 15.2 mg/kg at TAMBAR5, 135°/250m. The THC concentrations are generally low, and elevated concentrations are only found at TAMBAR5, in the top 0-1 cm layer. This means out to 250m in the 135° direction. The concentrations of THC have decreased significantly in the deeper sections (TAMBAR5 and TAMBAR6). The concentration of THC at TAMBAR5 indicates that base oil is present at the Tambar field, but that elevated contents of THC are limited to the 250m station in the 135° direction. The base oil found could be residues from an incident of unintentional discharge of base oil during explorational drilling in 1998.

Representative gas chromatograms are given in Appendix C. These include TAMBAR5, 135°/250m, TAMBAR6, 135°/500m and TAMBAR9, 225°/250m and TAMBAR13, 315°/250m.

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Tambar, THC 2005

0

20

40

60

80

100

120

TAMBAR1 TAMBAR2 TAMBAR5 TAMBAR6 TAMBAR9 TAMBAR10 TAMBAR13 TAMBAR14 GYDA ref.

station

mg/kg

1999

2002

2005

LSC A

107±140

Figure 4.8.1. Bar diagram of the THC content in the sediments at Tambar 1999- 2005. Table 4.8.3. Tambar 2005, total hydrocarbon content (mg/kg dry sediment). Station Grab

#1 Grab

#2 Grab

#3 Grab

#4 Grab

#5 Mean SD Mean Mean

2005 2005 2002 1999 TAMBAR1 45°/250m 4.0 3.3 3.1 3.5 0.4 6.2 5.6 TAMBAR2 45°/500m 3.2 3.8 2.9 3.3 0.4 3.7 4.1 TAMBAR5 135°/250m 4.0 23 18.5 15.2 9.9 15.8 50 1-3 cm 3.9 27 9.6 3-6 cm 8.7 17.8 11.5 TAMBAR6 135°/500m 4.5 4.6 5.8 4.9 0.7 5.0 5.3 1-3 cm 4.4 10.5 3-6 cm 3.7 17.6 TAMBAR9 225°/250m 4.1 3.5 4.0 3.8 0.3 4.5 107 TAMBAR10 225°/500m 3.5 4.5 4.7 4.2 0.7 3.2 5.3 TAMBAR13 315°/250m 4.4 4.2 4.2 4.3 0.1 3.0 3.5 TAMBAR14 315°/500m 4.4 4.3 4.2 4.3 0.1 2.9 4.0 GYDA ref. 315°/8000m 2.9 4.8 2.6 6.5 4.3 4.2 1.6 3.8 3.7 1-3 cm 3.4 3.8 3.0 3-6 cm 5.2 4.6 4.6 LSC Subregion A 6.6 6.4 9

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NPD, PAH and decalins Two stations are analysed, TAMBAR5, 135°/250m and TAMBAR6, 135°/500m. The results are shown in Table 4.8.4.

In 1999 and 2002 the concentration of NPD and PAH were below or just about the limit of contamination. Relatively high concentrations of decalins were found at TAMBAR5, 135°/250m in 1999 (3.5 mg/kg) and in 2002 (2.8 mg/kg in the 1-3 cm layer).

In the present survey the levels of NPD and PAH are below the limit of contamination.

The NPD concentrations at the two stations vary from 0.015 mg/kg to 0.030 mg/kg, and the PAH concentrations from 0.039 mg/kg to 0.046 mg/kg. Decalins are found in some of the grab samples. The content is at the same level as in 2002 in the top 0-1 cm layer, as the contents in the deeper layers have decreased. Table 4.8.4. Tambar 2005, sum NPD, PAH and decalins (mg/kg dry sediment).

Station Grab #1

Grab #2

Grab #3

Grab #4

Grab #5

Mean SD Mean SD Mean SD Mean

2005 2005 2002 2002 1999 1999 1996NPD TAMBAR5 135°/250m 0.032 0.024 0.035 0.030 0.006 0.034 0.010 0.032 0.036 1-3 cm n.d 0.036 0.024 3-6cm 0.012 0.036 0.027 TAMBAR6 135°/500m 0.013 0.017 0.015 0.015 0.002 0.014 0.005 1-3 cm 0.01 0.017 3-6cm 0.01 0.037 GYDA REF 315°/8000m nd 0.13 nd nd nd <0.13 0.05 0.013 0.001 0.018 0.004 0.015 1-3 cm 0.012 0.016 0.026 3-6 cm 0.013 0.018 0.019LSC Subregion A 0.030 0.026 0.040 PAH TAMBAR5 135°/250m 0.048 0.038 0.052 0.046 0.007 0.027 0.000 0.036 0.011 1-3 cm 0.017 0.032 0.053 3-6 cm 0.031 0.071 0.062 TAMBAR6 135°/500m 0.028 0.037 0.052 0.039 0.013 0.024 0.001 1-3 cm 0.032 0.025 3-6 cm 0.025 0.059 GYDA Ref. 315°/8000m 0.027 0.036 0.038 0.031 0.028 0.032 0.005 0.035 0.003 0.038 0.012 0.056 1-3 cm 0.045 0.031 0.093 3-6 cm 0.080 0.037 0.078LSC Subregion A 0.061 0.062 0.090 Decalins TAMBAR5 135°/250m n.d 2.3 1.8 1.4 1.2 1.05 0.076 3.5 3.2 1-3 cm 0.06 2.8 0.36 3-6 cm 0.54 1.2 0.41 TAMBAR6 135°/500m 0.02 0.07 0.12 nd 0.19 0.071 1-3 cm 0.08 0.61 3-6 cm nd 1.1 GYDA Ref. 315°/8000m nd nd 1.8 nd nd nd nd nd 0.075 1-3 cm nd nd 0.14 3-6 cm nd nd 0.074nd: not detected. Limit of detection for NPD is 0.01 mg/kg, for PAH 0.005 mg/kg and for decalins 0.1 mg/kg.

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Metals

The results are shown in Table 4.8.5. Data from the 2002 survey and the baseline survey in 1999 are also included for comparison in Table 4.8.6. Hg is only analysed for some stations. Bar diagram of the Ba content in the sediments is shown in Figure 4.8.2.

In 1999 the Ba concentrations ranged from 24 mg/kg to 4040 mg/kg (TAMBAR9, 225°/250m). In 2002 the Ba concentrations ranged from 55 mg/kg to 538 mg/kg (TAMBAR1, 45°/250m).

In the present survey the Ba concentrations vary from 106 mg/kg at TAMBAR13, 315°/250m to 563 mg/kg at TAMBAR5, 135°/250m. The Ba concentrations are lower or at the same level as in the 2002 survey. Elevated Ba concentrations are found at all stations, except for at the reference station. Thus elevated levels are found out to 250m in all directions investigated. The concentrations of heavy metals are low.

Tambar, Ba 2005

0

200

400

600

800

1000

1200

1400

1600

1800

2000

TAMBAR1 TAMBAR5 TAMBAR9 TAMBAR13 GYDA ref.

station

mg/kg

1999

2002

2005

LSC A

4040±2390

Figure 4.8.2. Bar diagram of the Ba content in the sediments at Tambar 1999- 2005. The following variations are found at Tambar in the top layer, 0-1 cm. The values are given in mg/kg: Tambar: TAMBAR6 – TAMBAR19 GYDA Reference station Ba: 106 – 563 36 Cr: 6.8 – 7.4 7.0 Cu: 0.5 – 0.7 <0.5 Pb: 5.3 – 6.8 5.8 Zn: 5.7 – 6.5 4.9 Cd: <0.01 <0.01 Hg: <0.01 <0.01

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Table 4.8.5. Tambar 2005, metals (mg/kg dry sediment). Station Sample Ba Cd Cr Cu Hg Pb Zn 2005 2005 2005 2005 2005 2005 2005 TAMBAR1 45°/250m 1 358 <0.01 6.6 0.61 6.5 6.2 2 199 <0.01 6.9 0.59 7.0 5.5 3 196 <0.01 6.9 0.51 7.0 5.5 Mean 251 <0.01 6.8 0.6 6.8 5.7 SD 93 0.2 0.05 0.3 0.4 TAMBAR5 135°/250m 1 511 <0.01 7.9 0.97 <0.01 6.9 7.1 2 627 <0.01 7.2 0.58 <0.01 6.5 6.5 3 550 <0.01 7.2 0.66 <0.01 6.5 6.0 Mean 563 <0.01 7.4 0.7 <0.01 6.6 6.5 SD 58 0.4 0.2 0.2 0.5 1-3 cm 1 1035 0.02 8.4 1.1 <0.01 8.9 10.8 3-6 cm 1 536 0.01 8.6 0.87 <0.01 8.0 11.2 TAMBAR9 225°/250m 1 117 <0.01 7.0 0.48 6.3 6.3 2 143 <0.01 7.0 0.60 6.1 6.1 3 128 <0.01 6.8 0.49 6.5 5.7 Mean 129 <0.01 6.9 0.5 6.3 6.0 SD 13 0.1 0.07 0.2 0.3 TAMBAR13 315°/250m 1 150 <0.01 7.5 0.56 5.2 6.1 2 93 <0.01 7.2 0.93 5.6 5.9 3 75 <0.01 7.0 0.41 5.2 5.5 Mean 106 <0.01 7.3 0.6 5.3 5.8 SD 39 - 0.3 0.3 0.3 0.3 GYDA Ref. 315°/8000m 1 52 <0.01 7.2 <0.5 <0.01 6.2 5.1 2 25 <0.01 6.8 <0.5 <0.01 5.3 4.6 3 35 <0.01 7.2 <0.5 <0.01 6.0 5.4 4 25 <0.01 6.9 <0.5 <0.01 5.4 4.7 5 43 <0.01 6.9 <0.5 <0.01 6.2 4.5 Mean 36 <0.01 7.0 <0.5 <0.01 5.8 4.9 SD 12 0.2 0.4 0.4 1-3 cm 53 0.01 7.5 <0.5 <0.01 5.8 5.6 3-6 cm 111 0.01 8.0 <0.5 0.01 6.5 6.5 LSC Subregion A 76.2 8.0 1.3 7.4 6.9 Table 4.8.6. Tambar 2005, metals (mg/kg dry sediment), comparing mean values with previous surveys. Station Ba Ba Ba Ba Cd Cd Cd Cr Cr Cr 2005 2002 1999 1996 2005 2002 1999 2005 2002 1999TAMBAR1 45°/250m 251 538 276 <0.01 <0.02 <0.02 6.8 6.5 6.9 TAMBAR5 135°/250m 563 451 677 <0.01 <0.01 <0.02 7.7 6.6 7.5 1-3 cm 1035 473 1890 <0.01 0.01 <0.02 8.4 6.8 7.3 3-6 cm 536 431 489 <0.01 0.03 <0.02 8.6 7.6 8.0 TAMBAR9 225°/250m 129 232 4040 <0.01 <0.01 <0.02 6.9 6.9 8.0 TAMBAR13 315°/250m 106 90 280 <0.01 <0.01 <0.02 7.3 6.8 6.9 GYDA Ref. 315°/8000m 36 40 47 63 <0.01 0.01 <0.02 7.0 6.7 7.1 1-3 cm 53 40 46 0.01 <0.01 <0.02 7.5 6.7 6.9 3-6 cm 111 78 112 0.01 0.01 0.02 8.0 6.7 7.7 Cont.

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Table 4.8.6. cont. Station Cu Cu Cu Hg Hg Hg Pb Pb Pb Zn Zn Zn 2005 2002 1999 2005 2002 1999 2005 2002 1999 2005 2002 1999TAMBAR1 45°/250m 0.6 1.4 0.7 6.8 6.3 6.2 5.7 7.5 5.1 TAMBAR5 135°/250m 0.8 1.4 0.8 <0.01 0.01 <0.01 7.0 5.8 6.3 7.7 6.3 5.7 1-3 cm 1.1 1.6 0.9 <0.01 <0.01 <0.01 8.9 6.1 7.6 10.8 5.5 5.6 3-6 cm 0.9 1.5 1.2 <0.01 0.01 <0.01 8.0 6.8 6.4 11.2 6.8 6.2 TAMBAR9 225°/250m 0.5 1.5 3.5 6.3 5.8 8.5 6.0 7.7 7.5 TAMBAR13 315°/250m 0.6 1.0 2.1 5.3 5.6 5.7 5.8 5.1 5.3 GYDA Ref. 315°/8000m <0.5 1.3 0.5 <0.01 0.01 0.02 5.8 5.8 6.5 4.9 5.7 5.5 1-3 cm <0.5 0.9 0.5 <0.01 <0.01 0.01 5.8 6.1 6.7 5.6 5.2 4.5 3-6 cm <0.5 1.1 0.7 0.01 <0.01 0.02 6.5 6.3 7.1 6.6 6.9 6.7

4.8.3 Biological analyses

A total of 126 species and 13748 individuals were sampled at 4 stations. Greatest abundance (88.8 %) was found among the polychaetes, of which the species Myriochele oculata constitutes 72.5 % and Paramphinome jeffreysii constitutes about 13.5 % of the total number of Polychaeta, see Table 4.8.7. Table 4.8.7. Number of species and individuals distributed between the main groups, Tambar 2005.

Individuals Species Main animal groups Number % Number %

Varia 648 4.7 15 11.9Polychaeta 12213 88.8 62 49.2- Paramphinome jeffreysii 1644 13.5 - Myriochele oculata 8850 72.5 Crustacea 61 0.4 14 11.1Mollusca 346 2.5 29 23.0Echinodermata 480 3.5 6 4.8- Amphiura filiformis 423 88.1 Total 13748 100.0 126 100.0

At Tambar the bristle worm M. oculata constitues a very high percentage of the total number of individuals. This species is found to be very common and often significantly dominant in central parts of the Ekofisk region.

Figure 4.8.3 shows the numbers of species and individuals sampled at each station and variations between grab samples.

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020406080

100TAM-01

TAM-05

TAM-09

TAM-113

Stations

No.

of s

peci

es (S

) Station º/m TAM-01 45/250 TAM-05 135/250 TAM-09 225/250 TAM-113 305/250

0500

10001500200025003000350040004500

TAM-01

TAM-05

TAM-09

TAM-113

Stations

No.

of i

ndiv

idua

ls (N

) Ex. P. jeffreysii and M. oculata

0500

10001500200025003000350040004500

TAM-01

TAM-05

TAM-09

TAM-113

Stations

No.

of i

ndiv

idua

ls (N

)

Figure 4.8.3 Numbers of species (S) and individuals (N) per 0.5 m2 (incl./excl. P. jeffreysii and M. oculata), mean values per grab sample and standard deviation, Tambar 2005.

The standard deviation was in general dramatically reduced when the two species P. jeffreysii and M. oculata were removed. This is evident since the two species constitute 76.3 % of the total number of individuals.

Diversity and dominant species

The dominant species at each station varied from 60.7 % at station TAM-113 (305°/250m) to 69.0 % at TAM-01 (45°/250m). The 10 most abundant species shown in Table 4.8.8 constituted from 88.5 % of the total number of individuals at TAM-113 to 90.3 % of the total number of individuals at TAM-01. The bristle worm M. oculata was the dominating species at all stations. The three species P. jeffreysii, Chaetozone setosa and Amphiura filiformis were also dominating the fauna at all the stations. Other dominating species were the bristle worms Spiophanes bombyx, Scoloplos armiger, Apistobranchus tullberg, and the ribbon worm Nemertea. In general the fauna community is dominated by species which are pure suspension feeders or species which are able to make use of both suspension- and deposit feeding. P. jeffreysii is mainly a carnivore species.

The amount of juvenile species is low and they do not contribute to the top ten list. They are therefore not removed from the data set prior to analyses.

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Table 4.8.8. The 10 most abundant species at each station, Tambar 2005. 10 most dominating species TAM-01 No. % Cum. % TAM-05 No. % Cum. % Myriochele oculata 2420 62.6 62.6 Myriochele oculata 1920 63.6 63.6 Paramphinome jeffreysii 466 12.1 74.7 Paramphinome jeffreysii 328 10.9 74.5 Chaetozone setosa 120 3.1 77.8 Chaetozone setosa 106 3.5 78.0 Amphiura filiformis 109 2.8 80.6 Amphiura filiformis 96 3.2 81.2 Phoronis muelleri 78 2.0 82.6 Spiophanes bombyx 70 2.3 83.5 Spiophanes bombyx 76 2.0 84.6 Nemertea spp. 62 2.1 85.6 Nemertea spp. 72 1.9 86.4 Scoloplos armiger 45 1.5 87.1 Apistobranchus tullbergi 58 1.5 87.9 Phoronis muelleri 41 1.4 88.4 Scoloplos armiger 52 1.4 89.3 Edwardsia sp. 39 1.3 89.7 Caudofoveata spp. 41 1.1 90.3 Caudofoveata spp. 34 1.1 90.9 TAM-09 No. % Cum. % TAM-113 No. % Cum. % Myriochele oculata 2850 69.0 69.0 Myriochele oculata 1660 60.7 60.7 Paramphinome jeffreysii 495 12.0 81.0 Paramphinome jeffreysii 355 13.0 73.7 Amphiura filiformis 100 2.4 83.4 Amphiura filiformis 118 4.3 78.0 Spiophanes bombyx 69 1.7 85.1 Spiophanes bombyx 82 3.0 81.0 Phoronis muelleri 61 1.5 86.6 Scoloplos armiger 41 1.5 82.5 Chaetozone setosa 54 1.3 87.9 Chaetozone setosa 41 1.5 84.0 Scoloplos armiger 48 1.2 89.0 Phoronis muelleri 37 1.4 85.3 Apistobranchus tullbergi 37 0.9 89.9 Goniada maculata 36 1.3 86.7 Nemertea spp. 29 0.7 90.6 Nemertea spp. 26 1.0 87.6 Goniada maculata 28 0.7 91.3 Caudofoveata spp. 24 0.9 88.5

The numbers of species and individuals and relevant indices are shown in Table 4.8.9. The numbers of species vary from 75 at station TAM-05 (135°/250m) to 85 at TAM-113 (305°/250m). The numbers of individuals vary from 2735 at TAM-113 to 4130 at TAM-09 (225°/250m). The Shannon Wiener diversity index varied from 2.1 at TAM-09 to 2.6 at TAM-113 and the Hurlberts index (ES100) varied from 15 (TAM-09) to 18 (TAM-113) including M. oculata. Removing M. oculata from the data gave higher diversity indices (>4) and the ES100 range from 26 to 30 at the 4 stations. Diversity indices above 4 indicate a relatively undisturbed fauna. Indices between 3 and 4 indicate a slight disturbance, while indices between 2 and 3 indicate a distinct disturbance in the fauna. In general ES100 indices above 20 characterise relatively normal fauna communities. The indices including M. oculata indicate disturbances at all sampled stations (250 m) at Tambar, which is supported by field/laboratory observations of traces of oil and black spots in some of the grab samples. Table 4.8.9. Numbers of individuals (N) and species (S), depth, Shannon-Wiener diversity index (H’), Pielou’s evenness index (J), and expected number of species per 100 individuals (ES100) for each station at Tambar 2005.

H' ES100 Station Direction ° Distance m Depth S N Incl.

M. o. Excl. M. o.

J Incl. M. o.

Excl. M. o.

TAM-01 45 250 68 81 3866 2.5 4.2 0.4 17 27TAM-05 135 250 72 75 3017 2.5 4.1 0.4 17 26TAM-09 225 250 69 77 4130 2.1 4.0 0.3 15 28TAM-113 305 250 69 85 2735 2.6 4.2 0.4 18 30M. o.= M. oculata

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Classification and ordination

The dendrogram from the cluster analysis and the MDS plot from the ordination analysis based on grab level are presented in Figure 4.8.4 and Figure 4.8.5. The similarity between the grabs from the 4 stations is 70 % and the grabs are not further divided into groups. The exception is grab # 4 from station TAM-113 which differs somewhat from the other grabs.

The Bioenv analysis reveals a correlation of 0.8 between the variations in the fauna and the variations in the complex of the chemical parameters Ba and Pb. However, it is difficult to see a pattern in the distribution of the grab samples in the dendrogram, i.e. the grab samples do not cluster in stations. Hence the correlation is not relevant.

T AM

113-

4

TAM

113-

2

TAM

5-4

TAM

5-5

TAM

113 -

3

TAM

9-1

TAM

5-2

TAM

113-

1

T AM

9-2

TAM

9-3

TAM

1-3

TAM

9 -4

TAM

113-

5

TAM

5-1

TAM

5-3

TAM

1-1

TAM

1-5

TAM

1-2

T AM

1-4

TAM

9-5100

90

80

70

60

Sim

ilarit

y

Figure 4.8.4. Dendrogram of grab samples from Tambar 2005.

TAM1-1

TAM1-2

TAM1-3

TAM1-4TAM1-5

TAM5-1

TAM5-2

TAM5-3

TAM5-4

TAM5-5

TAM9-1

TAM9-2

TAM9-3TAM9-4

TAM9-5

TAM113-1

TAM113-2

TAM113-3

TAM113-4

TAM113-5

Stress: 0,22

Figure 4.8.5. MDS plot of grab samples from Tambar 2005.

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Comparison with 1999, 2002 and 2005

In Figure 4.8.6 the results from the present survey are compared to the results from the previous surveys. The numbers of species and individuals include the bristle worms M. oculata and P. jeffreysii for all the years, unless otherwise stated. The numbers of species have increased somewhat at all stations since 2002. The numbers of individuals have increased considerably at all stations since both 1999 and 2002. The increases are mainly due to higher numbers of the bristle worm M. oculata in the fauna. When comparing the numbers of individuals exclusive M. oculata, the numbers are about the same as in the previous surveys.

The Shannon-Wiener diversity indices (H’) have increased slightly or remained the same since 2002 (including the M. oculata1). When excluding this species the indices decrease from the 2002 survey.

02040

6080

100

TAM-01

TAM-05

TAM-09

TAM-113

Stations

No.

of s

peci

es (S

)

1999 2002 2005

Station º/m

TAM-01 45/250 TAM-05 135/250 TAM-09 225/250 TAM-113 305/250

0500

10001500200025003000350040004500

TAM-01

TAM-05

TAM-09

TAM-113

Stations

No.

of i

ndiv

idua

ls (N

)

1999 2002 2005

012345

TAM-01

TAM-05

TAM-09

TAM-113

Stations

H'

1999 20022002-ex M. oculata 20052005-ex M. oculata

Figure 4.8.6 Numbers of species (S) and individuals (N) per 0.5 m2 and diversity (H’), incl. P. jeffreysii and M. oculata), Tambar 1999, 2002 and 2005.

Classification and ordination analyses

The sampled stations from all the years have been analysed at family level∗ and are shown in Figure 4.8.7. The dendrogram from the cluster analysis reveals that the stations divide into three main groups at about 65 % similarity, based on years. The stations sampled in 2002 and 2005 are the most similar splitting at about 80 % similarity. The species that contribute the

1 The great variations in the presence of M. oculata from 1996 to 2005 are discussed in Chapter X - General Trends in the Region which forms a basis for the conclusions for each of the fields. ∗ Necessary when comparing between years, to avoid significant source of error due to both different years and

different taxonomists.

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most to the differences were species within the families Oweniidae (mainly M. oculata) and Amphinomidae (mainly P. jeffreysii). These were found in increasing numbers in the fauna over the years from 1999 to 2005.

The great variations in the presence of M. oculata from 1996 to 2005 have complicated the faunal picture, making it difficult to draw conclusions about the state of the fauna community. Adding the 2005 results to the trend data have, however, strengthened the data set, and has made it possible to obtain a pattern in the overall temporal variations in the entire region. This is discussed in Chapter 5.2 - General Trends in the Region, which forms a basis for the conclusions for each of the fields.

In 2002 the fauna at Tambar was characterised as healthy, due to the masking effects of M. oculata which flourished in the region. In 2005 the abundance of M. oculata is seen to decrease in the region and it is possible to see trends in the data. The positive trend observed at several other fields is, however, not observed at Tambar, and the 250 m stations are considered to be somewhat disturbed.

The Bioenv analysis showed no relevant correlation between the variations in the fauna and variations in abiotic factors over years.

TAM

-13-

99

TAM

-09-

99

TAM

- 01-

99

TAM

-05-

99

TAM

-01-

05

TAM

-09-

05

TAM

-05-

05

TAM

-13-

05

TAM

-13-

02

TAM

-09-

0 2

TAM

-01-

0 2

TAM

- 05-

02

100

90

80

70

60

Sim

ilarit

y

1999 2005 2002 Figure 4.8.7. Dendrogram showing similarity between Tambar stations 1999, 2002 and 2005. Family level, incl. M. oculata, sq. root transformation.

4.8.4 Conclusion

The sediments at Tambar consist of fine sand, and the sand content varies from 92.6 % at TAMBAR13, 315°/250m to 97.8 % at TAMBAR5, 135°/250m. Gravel is only found in small amounts at TAMBAR1, 45°/250m. The average silt and clay content is similar to the previous survey in 2002. The total organic matter content in the sediments is low; approximately 0.85 %. Only small variations are found at the field. The results are similar to the previous surveys.

The concentration of THC is generally low, and elevated concentrations that might originate from an incident in 1998 are limited to the 250m station in the 135° direction (TAM5). The

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concentration in the top 0-1 cm layer is unchanged since 2002, however, a significant reduction is observed in the deeper layers.

Two stations are analysed for NPD, PAH and decalins, TAMBAR5, 135°/250m and TAMBAR6, 315°/500m. The levels of NPD and PAH are below the limit of contamination. The NPD concentrations at the two stations vary from 0.015 mg/kg to 0.030 mg/kg, and the PAH concentrations from 0.039 mg/kg to 0.046 mg/kg. Decalins are found in some of the grab samples. The content is at the same level as in 2002 in the top 0-1 cm layer, and the content in the deeper layers has decreased.

The Ba concentrations vary from 106 mg/kg at TAMBAR13, 315°/250m to 563 mg/kg at TAMBAR5, 135°/250m. The Ba concentrations are lower or at the same level as in 2002. Elevated Ba concentrations are found at all stations, except for the reference station. Thus elevated levels are found out to 250m in all directions investigated.

The concentrations of heavy metals are low.

The chemical results are in correspondence with the drilling history at Tambar.

The results indicate no major alterations in the state of the fauna community since 2002. The decline in M. oculata which is observed in several fields in the region, is not observed at Tambar. The fauna community at the Tambar 250m stations are somewhat disturbed, possibly influenced by the field activities. However, the diversity indices (H’) have increased slightly at some stations possibly indicating a positive development.

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4.9 Ekofisk Center and 2/4 B&K

4.9.1 Sediment characterization

Grain size distribution

The grain size distribution from the present survey is given in Table 4.9.1 together with the silt and clay content from the previous surveys in 2002, 1999 and 1996.

The sediments at Ekofisk Centre consist mainly of fine sand. The sand contents vary from 90.6 % at EKO15, 175°/500m to 97.4 % at EKO42 reference station, 90°/15000m. The average median diameter is 2.88φ. The gravel content is low. The silt and clay content is at the same level as the 2002 survey and the average silt and clay concentration is 6.8 % compared to 8.1 % in 1999 and 4.9 % in 1996.

EKO14 appears different compared to the other stations, with 35 % silt and clay content,

65 % sand content and a median particle diameter of 3.29φ.

At the Ekofisk reference station, EKO42, 90°/15000m, the sediment is characterized as fine sand with 97 % sand and a median particle diameter of 2.88φ. The silt and clay content is similar to the 2002 survey.

The results from the complete grain size distribution are given in Appendix C. Table 4.9.1. Ekofisk Centre and 2/4 B&K 2005, grain size distribution. Station Median

diameter Classification Grain size distrib. 2005

(%) 2002

(%) 1999 (%)

1996 (%)

Mdφ Silt and clay

Sand Gravel Silt and clay

Silt and clay

Silt and clay

EKO8 84°/1800m 2.95 Fine sand 7.7 91.9 0.4 7.5 6.3 4.6 EKO9 94°/800m 2.84 Fine sand 6.1 93.8 0.1 8.4 6.2 EKO9a 70°/500m 2.91 Fine sand 7.4 89.4 3.2 8.6 EKO13 146°/1300m 2.86 Fine sand 5.4 94.3 0.3 6.9 5.3 5.1 EKO14* 140°/850m 3.29 Fine sand 35.2 64.8 0.0 9.5 3.2 5.6 EKO15 175°/500m 2.93 Fine sand 9.4 90.6 0.0 13.0 EKO32 180°/500m 2.91 Fine sand 8.7 91.2 0.1 8.4 4.3 5.2 EKO Ref. 42 90°/15000m 2.78 Fine sand 2.6 97.3 0.1 2.6 5.3 2.9 Mean (excl. ref. station) 2.88 Fine sand 6.8 92.6 8.1 4.9 4.9 Standard deviation 0.06 2.3 2.7 2.9 1.2 1.1 * not included in the mean value

Total organic matter (TOM)

The contents of TOM in the sediments are low, and the concentrations range from 0.88 % at EKO42 reference station, 90°/15000m to 1.28 % at EKO15, 175°/500m. The concentrations are similar to the previous surveys. The results correspond to the grain size distribution, and are given in Table 4.9.2.

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Table 4.9.2. Ekofisk Centre and 2/4 B&K 2005, total organic matter (% of dry sediment). Station 2005, 0-5 cm Mean

2002 Sd

2002 Mean 1999

Mean 1996

EKO8 84°/1800m 1.05 1.19 0.08 1.03 1.06 EKO9 94°/800m 0.89 1.40 0.17 1.03 EKO9a 70°/500m 0.98 1.36 0.12 EKO13 146°/1300m 1.18 1.32 0.07 1.14 1.11 EKO14 140°/850m 1.21 1.67 0.14 0.99 1.31 EKO15 175°/500m 1.28 2.10 0.08 EKO32 180°/500m 1.10 1.28 0.32 1.07 1.29 EKO Ref. 42 90°/15000m 0.88 0.82 0.02 0.95 0.86

4.9.2 Chemical analyses

Parameters analysed in the sediments at Ekofisk Centre 2/4 B&K:

• THC • Olefins • NPD, PAH, decalins • PFOS (perfluorooctyl sulphonate) • Metals (Ba, Cd, Cr, Cu, Hg, Pb, Zn)

Three replicate samples at each station and five replicate samples at the reference station are analysed. The samples are taken from the top 0-1 cm sediment layer. In addition the 1-3 cm and 3-6 cm sediment layers are sampled at three stations and the reference station.

This year survey has focussed on stations found not to be affected in 2002, and some of the stations with low levels of THC have been excluded.

THC and olefins

The THC results including olefins are shown in Table 4.9.3, and olefins separately are shown in Table 4.9.4. The corresponding THC data from the previous surveys in 2002, 1999 and 1996 are also included for comparison. Bar diagram of the THC content in the sediments is shown in Figure 4.9.1.

In 1999 the mean THC concentrations ranged from 5.5 mg/kg at the reference station, EKO42, 90°/15000m to 51.6 mg/kg at EKO14, 140°/850m. Olefins were also detected at the four stations analysed, and the concentration ranged from 0.9 mg/kg to 2.9 mg/kg. In 2002 the mean THC concentrations ranged from 5.9 mg/kg at the reference station (EKO42) to 601 mg/kg at EKO14. Olefins were also detected at the five stations analysed, and the concentration ranged from 2.0 mg/kg to 361 mg/kg.

In the present investigation the mean THC concentrations vary from 5.8 mg/kg at EKO42 to 188 mg/kg at EKO14. The THC content has decreased distinctly, for all the stations, since 2002. The highest concentrations are found at EKO14, in all three layers, with respectively 188 mg/kg (top layer), 408 mg/kg (1-3 cm) and 152 mg/kg (3-6 cm). Relatively high content of THC are also found at EKO15, 175°/500m, with a mean value of 34 mg/kg.

Thus, elevated levels of THC are found out to 1000m in the 90° and 180° direction, out to 800-850m in the 94° and 140° direction and out to 500m in the 70° direction. The other stations are either below or slightly above the limit of contamination for the region.

Olefins are found at the four stations analysed, from 1.1 mg/kg at EKO9a, 70°/500m and EKO13, 146°/1300m to 86 mg/kg at EKO14, 140°/850m. The content of olefins has decreased

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distinctly since the last survey. The olefin results reported for Ekofisk Centre are a mixture of olefins and ethers. Comparing the GC/MS analysis on samples from EKO14, 140°/850m with a reference sample of the drilling fluid Aquamul B (didecyl ethers) shows that the MS spectra of the compounds in the “olefin area” are identical to Aquamul B.

This agrees with the fact that ether containing drilling mud has been discharged during drilling at 2/4-W, 260 tonnes with cuttings in 1990 and 1991. Stations EKO14 and EKO15 are situated close to these wells. Obviously Aquamul B is not degrading as fast as previously anticipated. However, the content of olefins has decreased considerably during the last three years. This observation agrees with the situation at Ula. At Ula the ether based drilling fluid Aquamul B was used in 1993, and the ether compounds are still present in the sediments. Thus a major part (approx 45 %) of the elevated THC concentrations found at EKO14 results from didecyl ethers in Aquamul B. It is, however, important to realise that the sediments are not analysed for ether compounds. Thus, we can not estimate the total concentrations of Aquamul B in the sediment due to possible losses during sample preparation.

The gas chromatograms from the stations at Ekofisk Centre and 2/4 B&K are quite complex, and they show different profiles with additional compounds in the HDF 200 area, in the olefin areas and in the heavier hydrocarbon area. In addition ether compounds originating from Aquamul B are identified in the olefin area.

The reference station, EKO42 90°/15000m, is still uncontaminated, and the mean THC concentration is 5.8 mg/kg. The concentrations found in vertical layers are slightly above the limit of contamination, but additional THC compounds are not observed in the gas chromatograms.

Representative gas chromatograms are given in Appendix C. These include EKO8 (84°/1800m), EKO9 (94°/800m), EKO9a (70°/500m), EKO13 (146°/1300m), EKO14 (140°/850m), EKO15 (175°/500m), EKO28 (360°/1000m), EKO32 (180°/500m) and reference station EKO42 (90°/15000m).

Ekofisk Centre, THC 2005

0

20

40

60

80

100

120

140

160

180

200

EKOC7

EKOC8

EKOC9

EKOC9a

EKOC11

EKOC12

EKOC13

EKOC14

EKOC15

EKOC18

EKOC19

EKOC21

EKOC22

EKOC23

EKOC28

EKOC29

EKOC32

EKOC33

EKOC34

EKOC39

EKOC Ref.

42

station

mg/kg

1999

2002

2005

LSC A

188±8

Figure 4.9.1. THC in the sediments at Ekofisk Centre 2/4 B&K 1999-2005. EKOCx=EKOx.

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Table 4.9.3 Ekofisk Centre and 2/4 B&K 2005, total hydrocarbon content (mg/kg dry sediment). Station Grab

#1Grab

#2 Grab

#3 Mean SD Mean Mean Mean

2005 2005 2002 1999 1996 EKO7 74°/3900m 2/4 T 6.5 7.4 8.4 7.4 1.0 EKO8 84°/1800m " 7.2 8.1 7.1 7.5 0.6 14.3 12.2 10.4 EKO9 94°/800m " 17.9 15.5 15.1 16.1 1.5 60 17.3 EKO9a 70°/500m " 17.9 18.3 19.7 18.6 0.9 40 EKO11 144°/4400m " 7.6 6.8 7.9 7.4 0.6 9.6 9.7 8.3 EKO12 148°/2500m " 8.7 10.5 6.9 8.7 1.8 15.8 16.4 15.9 EKO13 146°/1300m " 10.2 9.6 9.8 9.9 0.3 18.0 16.0 15.3 1-3 cm “ 12.9 21 3-6 cm “ 17.9 25 EKO14 140°/850m " 282 156 127 188 83 601 52 26 1-3 cm “ 408 47 204 3-6 cm “ 152 100 246 EKO15 175°/500m " 37 33 32 34 2.6 105 EKO18 208°/2500m " 7.0 5.6 10.9 7.8 2.7 10.9 12.3 18.3 EKO19 200°/1200m " 8.1 8.9 7.2 8.1 0.8 19.1 20 EKO21 287°/4000m " 5.1 5.5 5.0 5.2 0.3 EKO22 288°/1900m " 4.8 3.5 2.3 3.5 1.3 14.6 15.7 EKO23 290°/1000m " 6.8 7.7 10.5 8.3 1.9 19.6 13.8 21 EKO28 360°/1000m 3.9 4.9 5.0 4.6 0.6 35 12.0 EKO29 360°/500m " 4.1 5.6 3.2 4.3 1.2 EKO32 180°/500m 14.0 18.5 16.2 16.3 2.2 38 19.4 38 1-3 cm 18.0 39 4.0 54 3-6 cm 41 46 5.7 30 EKO33 180°/1000m " 4.8 12.8 14.2 10.6 5.1 19.6 13.3 44 EKO34 270°/1000m " 5.9 6.4 8.2 6.8 1.2 11.6 11.9 12.3 EKO39 90°/1000m " 12.1 10.9 12.2 11.7 0.7 16.2 16.7 16.7 EKO Ref. 42 90°/15000m “ 6.2 5.3 4.4 5.8 1.0 5.9 5.5 6.4

1-3 cm " 7.3 7.9 9.0 10.0 3-6 cm " 7.6 8.5 5.9 8.7

LSC Subregion A 6.6 6.4 9 Table 4.9.4. Ekofisk Centre and 2/4 B&K 2005, olefins (mg/kg dry sediment). Station Grab

#1 Grab

#2 Grab

#3 Mean SD Mean Mean

2005 2005 2002 1999 EKO9a 70°/500m 2/4 T 1.0 0.8 1.4 1.1 0.3 3.5 EKO13 146°/1300m " 0.9 1.1 1.2 1.1 0.1 2.1 1-3 cm “ 1.5 3.0 3-6 cm “ 2.1 4.1 EKO14 140°/850m " 126 72 59 86 35 361 1-3 cm “ 275 867 3-6 cm “ 98 830 EKO32 180°/500m 1.0 1.2 1.0 1.4 0.1 3.9 2.9 1-3 cm 1.4 4.9 3-6 cm 6.7 5.1

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NPD, PAH and decalins Three stations are analysed in addition to the reference station; EKO13, 146°/1300m, EKO14, 140°/850m and EKO32, 180°/500m. The results are given in Table 4.8.5.

The present survey shows that the concentration of NPD, PAH and decalins has decreased for all three stations since 2002. Maximum concentrations of NPD, PAH and decalins are found at station EKO14, particular in the vertical layer 1-3 cm.

The NPD concentrations in the top 0-1 cm layer vary from not detected at the reference station EKO42 to 0.20 mg/kg at EKO14. The concentration of NPD in the 1-3 cm layer at EKO14 is 0.43 mg/kg. Only slightly elevated levels of NPD are found at EKO13 and EKO32 in the top 0-1 cm layer and in the 1-3 cm layer. However, the concentration increases for these stations going down in the sediment and elevated levels are found in the 3-6 cm.

The PAH concentrations vary from 0.039 mg/kg at the reference station to 0.10 mg/kg at EKO14. Highest level of PAH is found in the vertical sections, up to 1.3 mg/kg at EKO14 in the 1-3 cm layer. Only slightly elevated levels of PAH is found in the top 0-1 cm layer at EKO13 and EKO32.

The decalin concentrations vary from 0.11 mg/kg at the reference station to 7.7 mg/kg at EKO14. Elevated level of decalins is also found in the 1-3 cm layer at EKO14 (4.2 mg/kg).The high content of decalins at EKO14 are in accordance with the THC content at the same stations and represent ~4 %. Table 4.9.5. Ekofisk Centre and 2/4 B&K, sum NPD, PAH and decalins (mg/kg dry sediment).

Station Grab #1

Grab #2

Grab #3

Grab #4

Grab #5

Mean SD Mean SD Mean SD Mean

2005 2005 2002 2002 1999 1999 1996NPD EKO13 146°/1300m 0.041 0.023 0.027 0.031 0.01 0.094 0.017 1-3 cm 0.034 0.072 3-6 cm 0.10 0.080 EKO14 140°/850m 0.26 0.21 0.13 0.20 0.07 0.35 0.118 0.026 0.002 0.25 1-3 cm 0.43 0.27 0.058 0.12 3-6 cm 0.09 0.27 0.17 0.072EKO32 180°/500m 0.11 0.10 0.03 0.08 0.04 0.15 0.055 0.060 0.045 0.15 1-3 cm 0.07 0.19 0.010 0.17 3-6 cm 0.35 0.10 0.043 0.068

90°/15000m 0.008 0.008 0.008 0.003 0.004 nd 0.021 0.004 0.010 0.001 0.026EKO42 Ref 1-3 cm nd 0.028 0.032 0.079 3-6 cm 0.014 0.033 0.015 0.049LSC Subregion A 0.030 0.026 0.040 PAH EKO13 146°/1300m 0.10 0.058 0.058 0.073 0.025 0.12 0.03 - 1-3 cm 0.087 0.095 3-6 cm 0.21 0.13 EKO14 140°/850m 0.088 0.11 0.11 0.10 0.011 0.22 0.063 0.055 0.014 0.50 1-3 cm 1.25 0.24 0.10 0.16 3-6 cm 0.11 0.085 0.29 0.34EKO32 180°/500m 0.088 0.074 0.065 0.076 0.011 0.092 0.049 0.042 0.015 0.12 1-3 cm 0.14 0.081 0.008 0.098Cont. 3-6 cm 0.57 0.090 0.008 0.12Table 4.9.5. cont.

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Station Grab #1

Grab #2

Grab #3

Grab #4

Grab #5

Mean SD Mean SD Mean SD Mean

2005 2005 2002 2002 1999 1999 1996PAH cont. EKO42 Ref 90°/15000m 0.045 0.038 0.043 0.031 0.036 0.039 0.005 0.048 0.006 0.035 0.006 0.045 1-3 cm 0.049 0.068 0.094 0.091 3-6 cm 0.080 0.081 0.048 0.19LSC Subregion A 0.061 0.062 0.090 Decalins EKO13 146°/1300m 0.19 0.074 0.097 0.12 0.06 0.12 0.025 1-3 cm 0.12 0.11 3-6 cm 0.29 0.12 EKO14 140°/850m 10.7 8.2 4.2 7.7 3.3 13.6 8.2 0.23 0.064 0.17 1-3 cm 4.2 8.1 0.094 0.20 3-6 cm 0.82 1.42 0.048 0.25EKO32 180°/500m 0.15 0.49 0.13 0.26 0.2 0.39 0.17 0.16 0.081 0.45 1-3 cm 0.32 0.34 nd 1.12 3-6 cm 0.88 0.50 0.12 0.54EKO42 Ref 90°/15000m 0.028 0.23 0.25 0.038 0.006 0.11 0.1 nd nd 0.053 1-3 cm nd nd nd 0.075 3-6 cm nd nd nd 0.088nd: not detected. Limit of detection for NPD is 0.01 mg/kg, for PAH 0.005 mg/kg and for decalins 0.1 mg/kg.

PFOS (perfluorooctyl sulphonate)

One station is analysed at Ekofisk Center and 2/4 B&K, EKO32, 180°/500m. The result is given in Table 4.9.6. PFOS was not detected at EKO32. Table 4.9.6. Ekofisk Centre and 2/4 B&K 2005, PFOS (perfluorooctyl sulphonate), µg/kg dry sediment. Station PFOS (one grab sample)EKO32 180°/500m <0.1 Limit of detection: 0.1 µg/kg

Metals

The results are given in Table 4.9.7. For comparison, data from the present survey and previous surveys in 2002, 1999 and 1996 are included in Table 4.9.8. Hg is analysed for some stations. Bar diagram of the Ba content in the sediments is given in Figure 4.9.2.

In 1999 the mean Ba concentrations ranged from 41 mg/kg at EKO reference station, 90°/15000m to 1920 mg/kg at EKO32, 180°/500m. In 2002 the mean Ba concentrations ranged from 72 mg/kg at the reference station to 4680 mg/kg at EKO14, 140°/850m.

In the present survey the mean Ba concentrations vary from 46 mg/kg at the reference station to 3860 mg/kg at EKO15, 175°/500m.

Elevated Ba concentrations are found at all stations, except for the reference station. Thus elevated levels are observed out to 1800m in the 84° direction and limited to 500m in the 74°, 175° and 180° direction. The concentrations are similar or slightly lower compared to previous surveys.

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High Ba concentrations are also found in the 1-3 cm and 3-6 cm layers, similar or higher concentrations than in the top 0-1 cm layer.

The concentrations of the heavy metals are low, however concentrations above the limit of contaminations are found at most of the stations. Highest concentrations are found at EKO14, 140°/850m and EKO15, 175°/500m.

Ekofisk Centre, Ba 2005

0

500

1000

1500

2000

2500

3000

3500

4000

4500

5000

EKOC8 EKOC9 EKOC9a EKOC13 EKOC14 EKOC15 EKOC32 EKOC Ref. 42

station

mg/kg

1999

2002

2005

LSC A

Figure 4.9.2. Ba content in the sediments at Ekofisk Centre 2/4 B&K 1999-2005. EKOCx=EKOx. The following variations are found at Ekofisk Centre and 2/4 B&K in the top layer, 0-1 cm. The values are given in mg/kg: Ekofisk Centre and 2/4 B&K: EKO8 – EKO32 EKO42 Reference station Ba: 669 – 3861 46 Cr: 5.6 – 11.7 7.6 Cu: <0.05 – 5.3 <0.5 Pb: 6.7 – 22.2 6.1 Zn: 7.6 – 48 5.4 Cd: <0.01 – 0.09 <0.01 Hg: <0.01 – 0.07 <0.01

Table 4.9.7. Ekofisk Centre and 2/4 B&K 2005, metals (mg/kg dry sediment). Station Sample Ba Cd Cr Cu Hg Pb Zn 2005 2005 2005 2005 2005 2005 2005 EKO8 84°/1800m 1 537 0.01 5.7 0.5 7.2 7.4 2 789 <0.01 6.4 0.6 7.7 8.0 3 682 <0.01 5.6 <0.5 5.2 7.3 Mean 669 <0.01 5.9 <0.5 6.7 7.6 SD 126 0.4 1.3 0.4 cont.

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Table 4.9.7. cont. Station Sample Ba Cd Cr Cu Hg Pb Zn 2005 2005 2005 2005 2005 2005 2005 EKO9 94°/800m 1 1262 0.01 7.5 1.2 12.8 13.1 2 1879 0.02 8.0 1.7 12.9 17.1 3 1764 0.01 7.4 1.4 13.3 13.6 Mean 1635 0.01 7.6 1.5 13.0 14.6 SD 328 0.001 0.3 0.2 0.3 2.2 EKO9a 74°/500m 1 3576 0.09 10.8 3.5 20.5 33.2 2 2538 0.08 8.8 2.9 18.7 46.5 3 3524 0.09 10.3 3.8 19.1 34.8 Mean 3213 0.08 10.0 3.4 19.4 38 SD 585 0.007 1.1 0.4 1.0 7.3 EKO13 146°/1300m 1 732 0.03 8.8 0.9 0.01 11.9 13.4 2 749 0.02 7.8 0.9 <0.01 10.8 10.9 3 1119 0.01 8.2 1.0 0.01 10.6 10.9 Mean 867 0.02 8.3 1.0 0.01 11.1 11.7 SD 218 0.006 0.5 0.1 0.7 1.4 1-3 cm 1 1633 0.05 9.7 1.0 0.02 13.3 14.2 3-6 cm 1 2744 0.09 10.6 1.3 0.03 16.5 18.2 EKO14 140°/850m 1 2818 0.03 8.7 3.0 0.02 17.4 19.2 2 3557 0.04 11.6 3.2 0.17 18.3 31.1 3 3053 0.04 9.3 3.5 0.02 16.7 25.3 Mean 3142 0.03 9.9 3.2 0.07 17.5 25 SD 378 0.005 1.5 0.3 0.08 0.8 6.0 1-3 cm 1 4184 0.07 10.0 4.9 0.18 27.4 42.8 3-6 cm 1 5255 0.11 10.7 4.6 0.02 45.0 59.3 EKO15 175°/500m 1 3872 0.11 11.6 5.3 25.9 54.7 2 3283 0.08 12.0 5.9 19.2 41.5 3 4428 0.09 11.4 4.8 21.5 46.7 Mean 3861 0.09 11.7 5.3 22.2 48 SD 573 0.02 0.3 0.5 3.4 6.7 EKO32 180°/500m 1 3818 0.02 8.7 1.9 0.02 15.1 16.2 2 2552 0.02 8.8 1.0 0.01 12.5 12.6 3 2771 0.02 8.1 1.2 0.01 12.2 13.6 Mean 3047 0.02 8.5 1.4 0.02 13.3 14.1 SD 677 0.004 0.3 0.5 - 1.6 1.9 1-3 cm 1 4037 0.05 9.5 3.1 0.03 23.2 25.1 3-6 cm 1 4226 0.08 10.2 2.5 0.03 27.8 29.2 EKO Ref. 90°/15000m 1 52 <0.01 7.7 <0.5 0.01 6.6 5.6 2 77 <0.01 8.0 0.5 <0.01 6.3 5.8 3 37 <0.01 7.5 <0.5 <0.01 6.4 5.0 4 36 <0.01 7.4 <0.5 0.01 5.5 5.6 5 29 <0.01 7.4 <0.5 <0.01 5.7 4.9 Mean 46 <0.01 7.6 <0.5 <0.01 6.1 5.4 SD 19 0.3 0.5 0.4 1-3 cm 1 50 <0.01 8.1 <0.5 <0.01 6.4 5.8 3-6 cm 1 72 <0.01 8.0 <0.5 <0.01 6.6 5.8 LSC Subregion A 76.2 8.0 1.3 7.4 6.9

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Table 4.9.8. Ekofisk Centre and 2/4 B&K 2005, metals (mg/kg dry sediment), comparing mean values with previous surveys. Station Ba Ba Ba Ba Cd Cd Cd Cr Cr Cr 2005 2002 1999 1996 2005 2002 1999 2005 2002 1999 EKO8 84°/1800m 669 840 1030 1510 <0.01 0.02 <0.02 5.9 7.7 8.8 EKO9 94°/800m 1635 3750 3240 0.01 0.05 7.6 9.6 EKO9a 74°/500m 3213 3200 0.08 0.08 10.0 9.4 EKO13 146°/1300m 867 1550 1310 1540 0.02 0.02 <0.02 8.3 8.4 9.0 1-3 cm 1633 2590 0.05 0.05 9.7 9.4 3-6 cm 2744 2620 0.09 0.06 10.6 9.7 EKO14 140°/850m 3142 4680 1490 2410 0.03 0.14 <0.02 9.9 10.1 7.4 1-3 cm 4184 4708 2740 0.07 0.11 0.02 10.0 9.3 8.0 3-6 cm 5255 4673 3700 0.11 0.13 0.04 10.7 8.9 6.7 EKO15 175°/500m 3861 4180 0.09 0.16 11.7 14.4 EKO32 180°/500m 3047 2900 1920 3700 0.02 0.04 0.02 8.5 8.4 7.2 1-3 cm 4037 3830 1370 0.05 0.08 0.02 9.5 9.7 4.6 3-6 cm 4226 2780 563 0.08 0.07 <0.02 10.2 9.5 4.6 EKO Ref. 90°/15000m 46 72 41 67 <0.01 <0.01 <0.02 7.6 7.7 7.1 1-3 cm 50 88 50 <0.01 <0.01 <0.02 8.1 7.7 7.2 3-6 cm 72 331 141 <0.01 0.01 <0.02 8.0 8.1 7.8 cont. Table 4.9.8. cont. Station Cu Cu Cu Hg Hg Hg Pb Pb Pb Zn Zn Zn 2005 2002 1999 2005 2002 1999 2005 2002 1999 2005 2002 1999EKO8 84°/1800m <0.5 1.6 1.1 6.7 11.5 13.4 7.6 10.0 7.1 EKO9 94°/800m 1.5 6.1 13.0 18.4 14.6 31 EKO9a 74°/500m 3.4 4.9 19.4 20.6 38.2 32 EKO13 146°/1300m 1.0 1.9 1.4 0.01 0.02 11.1 11.6 16.3 11.7 12.2 11.5 1-3 cm 1.0 3.0 0.02 0.03 13.3 15.3 14.2 17.0 3-6 cm 1.3 2.5 0.03 0.03 16.5 16.8 18.2 20.3 EKO14 140°/850m 3.2 70.1 2.0 0.07 0.05 0.02 17.5 15.3 9.2 25.2 65 12.2 1-3 cm 4.9 10.0 2.1 0.18 0.05 0.02 15.4 36.4 10.6 42.8 65 15.0 3-6 cm 4.6 5.4 1.9 0.02 0.04 0.02 45.0 43.3 14.0 59.3 81 17.6EKO15 175°/500m 5.3 14.1 22.2 30.5 47.6 82 EKO32 180°/500m 1.4 3.4 1.8 0.02 0.04 0.02 13.3 16.9 11.8 14.1 20.9 17.6 1-3 cm 3.1 4.5 0.5 0.03 0.05 <0.01 23.2 29.8 3.3 25.1 35.6 5.5 3-6 cm 2.5 3.2 0.4 0.03 0.03 <0.01 27.8 21.1 3.2 29.2 27.5 4.0 EKO Ref. 90°/15000m <0.5 1.0 0.5 <0.01 <0.01 <0.01 6.1 6.3 6.1 5.4 5.6 4.7 1-3 cm <0.5 1.1 0.5 <0.01 0.01 <0.01 6.4 6.3 6.0 5.8 5.6 5.1 3-6 cm <0.5 1.8 0.8 <0.01 <0.01 <0.01 6.6 7.2 7.3 5.8 6.9 5.8

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4.9.3 Biological analyses

A total of 180 species and 18165 individuals were sampled at 8 stations. Greatest abundance (71.4 %) was found among the polychaetes, of which the species Myriochele oculata constitutes 39.9 % and Paramphinome jeffreysii constitutes 16.7 %, see Table 4.9.9. Table 4.9.9. Number of species and individuals distributed between the main groups, Ekofisk Center and 2/4 B&K 2005.

Individuals Species Main animal groups Number % Number %

Varia 105 0.6 19 10.6Polychaeta 12974 71.4 75 41.7- Paramphinome jeffreysii 3040 16.7 - Myriochele oculata 7245 39.9 Crustacea 149 0.8 36 20.0Mollusca 278 1.5 37 20.6Echinodermata 140 0.8 13 7.2- Amphiura filiformis 4 0.0 Total 18165 100.0 180 100.0

Figure 4.9.3 shows the numbers of species and individuals sampled at each station and variations between grab samples.

0

20

40

60

80

100

EKO-8EKO-9

EKO-9aEKO-13EKO-14EKO-15EKO-32

EKO-REF 42

Stations

No.

of s

peci

es (S

)

Station º/m

EKO8 84/1800 EKO9 94/800 EKO9a 70/500 EKO13 146/1300EKO14 140/850 EKO15 175/500 EKO32 180/500 EKOREF 90/15000

0

800

1600

2400

3200

EKO-8EKO-9

EKO-9aEKO-13EKO-14EKO-15EKO-32

EKO-REF 42

Stations

No.

of i

ndiv

idua

ls (N

)

Ex. P. jeffreysii and M. oculata

0

800

1600

2400

3200

EKO-8EKO-9

EKO-9aEKO-13EKO-14EKO-15EKO-32

EKO-REF 42

Stations

No.

of i

ndiv

idua

ls (N

)

Figure 4.9.3. Numbers of species (S) and individuals (N) per 0.5 m2 (incl./excl. P. jeffreysii and M. oculata incl. juv.), mean values per grab sample and standard deviation, Ekofisk Center and 2/4 B&K 2005.

The standard deviation was dramatically reduced when the two species P. jeffreysii and M. oculata were removed. This is evident since the two species constitute 56.6 % of the total number of individuals.

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Diversity and dominant species

The dominant species at each station varied from 20.2 % at station EKO-15 (175°/500m) to 58.3 % at EKO-8 (84°/1800m) and 58 % at EKO-32 (180°/500m). The 10 most abundant species made up from 83.2 % at EKO-9a (70°/500m) to 89.1 % at EKO-14 (140°/850), see Table 4.9.10. In general the bristle worm M. oculata dominated the fauna at the Ekofisk C field, followed by the bristle worm P. jeffreysii and the brittle star Amphiura filiformis. However, at the reference station the ribbon worm (Nemertea spp.) dominated the fauna. Juvenile echinoidea were found in relatively high amounts at the reference station (90°/15000m) and at the following stations; EKO-8 (84°/1800m), EKO-9 (94°/800m) and EKO-13 (146°/1300m). Other frequently found species were the bristle worms Chaetozone setosa, Scoloplos armiger and Goniada spp. and the mussel Thyasira flexuosa. M. oculata and A. filiformis are suspension feeders, while the C. setosa, S. armiger, Goniada spp. and T. flexuosa all have the possibility to act as both suspension and deposit feeders. P. jeffreysii is mainly a carnivore species and the ribbon worms are deposit feeders. Most of these species are known indicators of organic pollution when they are found in vast amounts. However, several of the above mentioned species have a planktonic developmental stage and are able to settle in large numbers. Table 4.9.10. The 10 most abundant species at each station, Ekofisk Center and 2/4 B&K 2005. 10 most dominating species EKO-8 No. % Cum. % EKO-9 No. % Cum. % Myriochele oculata 1850 58.3 58.3 Myriochele oculata 745 30.0 30.0 Paramphinome jeffreysii 210 6.6 64.9 Paramphinome jeffreysii 626 25.2 55.2 Amphiura filiformis 168 5.3 70.2 Amphiura filiformis 300 12.1 67.2 Echinoidea spp.juv. 160 5.0 75.2 Echinoidea spp.juv. 114 4.6 71.8 Thyasira flexuosa 94 3.0 78.2 Mysella bidentata 78 3.1 75.0 Scoloplos armiger 64 2.0 80.2 Nemertea spp. 74 3.0 78.0 Corymorpha nutans 57 1.8 82.0 Scoloplos armiger 72 2.9 80.9 Goniada spp. 51 1.6 83.6 Thyasira flexuosa 52 2.1 82.9 Caudofoveata spp. 49 1.5 85.1 Goniada spp. 44 1.8 84.7 Phoronis muelleri 36 1.1 86.3 Phoronis muelleri 36 1.5 86.2 EKO-9a No. % Cum. % EKO-13 No. % Cum. % Myriochele oculata 350 25.3 25.3 Myriochele oculata 1025 35.3 35.3 Paramphinome jeffreysii 304 22.0 47.2 Paramphinome jeffreysii 697 24.0 59.3 Nemertea spp. 159 11.5 58.7 Amphiura filiformis 240 8.3 67.5 Amphiura filiformis 121 8.7 67.4 Echinoidea spp.juv. 122 4.2 71.7 Chaetozone setosa 61 4.4 71.8 Scoloplos armiger 113 3.9 75.6 Apistobranchus tullbergi 46 3.3 75.2 Thyasira flexuosa 107 3.7 79.3 Thyasira flexuosa 34 2.5 77.6 Eudorella truncatula/emarginata 63 2.2 81.5 Mysella bidentata 33 2.4 80.0 Goniada spp. 59 2.0 83.5 Arctica islandica 22 1.6 81.6 Phoronis muelleri 45 1.6 85.1 Scoloplos armiger 22 1.6 83.2 Nemertea spp. 42 1.5 86.5 cont.

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Table 4.9.10. cont. 10 most dominating species EKO-14 No. % Cum. % EKO-15 No. % Cum. % Myriochele oculata 650 30.0 30.0 Nemertea spp. 335 20.2 20.2 Paramphinome jeffreysii 519 24.0 54.0 Myriochele oculata 300 18.1 38.2 Amphiura filiformis 209 9.7 63.7 Paramphinome jeffreysii 257 15.5 53.7 Apistobranchus tullbergi 186 8.6 72.3 Amphiura filiformis 159 9.6 63.3 Nemertea spp. 138 6.4 78.7 Chaetozone setosa 80 4.8 68.1 Echinoidea spp.juv. 60 2.8 81.4 Levinsenia gracilis 67 4.0 72.1 Thyasira flexuosa 46 2.1 83.6 Apistobranchus tullbergi 64 3.9 76.0 Goniada spp. 46 2.1 85.7 Pholoe baltica 44 2.7 78.6 Chaetozone setosa 45 2.1 87.8 Thyasira flexuosa 40 2.4 81.0 Levinsenia gracilis 29 1.3 89.1 Scoloplos armiger 40 2.4 83.4 EKO-32 No. % Cum. % EKO-REF No. % Cum. % Myriochele oculata 1475 58.0 58.0 Myriochele oculata 850 46.0 46.0 Paramphinome jeffreysii 314 12.4 70.4 Echinoidea spp.juv. 209 11.3 57.3 Amphiura filiformis 69 2.7 73.1 Amphiura filiformis 154 8.3 65.7 Thyasira flexuosa 54 2.1 75.2 Paramphinome jeffreysii 113 6.1 71.8 Scoloplos armiger 51 2.0 77.2 Scoloplos armiger 50 2.7 74.5 Echinoidea spp.juv. 48 1.9 79.1 Goniada spp. 38 2.1 76.6 Goniada spp. 44 1.7 80.8 Spiophanes bombyx 36 2.0 78.5 Chaetozone setosa 40 1.6 82.4 Abra prismatica 35 1.9 80.4 Caudofoveata spp. 26 1.0 83.4 Chaetozone setosa 34 1.8 82.2 Hippomedon denticulatus 26 1.0 84.4 Eudorellopsis deformis 32 1.7 84.0

The numbers of species vary from 70 at station EKO-15 (175°/500m) to 97 at EKO-8 (84°/1800m). The numbers of individuals vary from 1361 at EKO-9a (70°/500m) to 3011 at EKO-8. The Shannon Wiener diversity indices vary from 2.8 at EKO-8 to 3.8 at EKO-15 and the Hurlberts indices (ES100) vary from 18 at EKO-14 (140°/850m) to 22 at EKO-9a and the reference station (90°/15000) including M.oculata. Removal of M. oculata from the data gave minor changes for most of the stations except for EKO-8, EKO-32 and the reference station. Indices above 4 indicate a relatively undisturbed fauna, while indices between 3 and 4 indicate a slight disturbance. In general ES100 indices above 20 characterize a relatively normal fauna community. However these indices are relative high compared to several other fields in the central parts of the Ekofisk region, see Table 4.9.11.

The biodiversity indices are somewhat lower at EKO-8 (84°/1800m) and EKO-32 (180°/500m) than at the other stations.

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Table 4.9.11. Numbers of individuals (N) and species (S), depth, Shannon-Wiener diversity index (H’), Pielou’s evenness index (J), and expected number of species per 100 individuals (ES100) for each station at Ekofisk Center and 2/4 B&K 2005 (excl. juv.).

H' ES100 Station Direction ° Distance m Depth S N Incl.

M. o. Excl. M. o.

J Incl. M. o.

Excl. M. o.

EKO-8 84 1800 78 97 3011 2.8 4.8 0.4 20 34EKO-9 94 800 98 76 2356 3.3 3.6 0.5 20 23EKO-9a 70 500 81 73 1361 3.7 3.9 0.6 22 25EKO-13 146 1300 80 96 2775 3.3 3.8 0.5 20 25EKO-14 140 850 80 81 2097 3.3 3.5 0.5 18 21EKO-15 175 500 80 70 1641 3.8 3.9 0.6 21 23EKO-32 180 500 78 90 2491 2.9 4.6 0.4 21 34EKO-REF 90 15000 70 76 1634 3.2 4.6 0.5 22 32M. o.= M. oculata

Classification and ordination

The dendrogram from the cluster analysis and the MDS plot from the ordination analysis based on station level are presented in Figure 4.9.4 and Figure 4.9.5. The analysis based on grab level show the same pattern as the analysis based on station level. The stations divide into two main groups at a similarity of about 60 %. The stations in group 1 had in general somewhat higher values of the measured chemical parameters. At EKO8, -9, 14 and -15 black spots were registered in the sediment during sampling. During sample processing it was also observed small, soft oily pellets in the samples from EKO14 and -15. Group 1 is separated into two subgroups at a similarity of almost 70 %. In group 2 the reference station differs somewhat from the 3 other stations which divide and form a subgroup at about 70 %. The cluster analysis is well supported by the ordination analysis.

EKO

-9

E KO

-14

EKO

-9a

EKO

-15

EKO

-REF

EKO

-32

EKO

-8

EKO

-13100

90

80

70

60

50

Sim

il arit

y

94/800m, 140/850m 70/500m, 175/500m 90/15000m 180/500m 84/1800m 146/1300m

Group 1 Group 2 Figure 4.9.4. Dendrogram - station level, Ekofisk Center and 2/4 B&K 2005 (excl. juv.). ECB-x = EKOx.

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ECB-8

ECB-9

ECB-9a

ECB-13

ECB-14

ECB-15 ECB-32

ECB-REF

Stress: 0,02

Group 1 Group 2

94/800m, 140/850m

70/500m, 175/500m

180/500m, 84/500m, 146/1300m

90/15000m

Figure 4.9.5. MDS plot – station level, Ekofisk Center and 2/4 B&K 2005 (excl. juv.). ECB-x = EKOx.

A Simper analysis (Primer package) was performed to examine which species contributes most to the differences between the groups and subgroups. The differences between the two main groups were mainly due to a significantly higher numbers of the bristle worm M. oculata in group 2, and higher numbers of P. jeffreysii and the ribbon worm Nemertea spp. in group 1. Furthermore the differences between the subgroups in group 1 are mainly due to higher numbers of M. oculata and P. jeffreysi at EKO-9 (94°/800m) and EKO-14 (140°/800m) and higher numbers of Nemertea spp. at stations EKO-9a (70°/500m) and EKO-15 (175/500m). In group two the differences are mainly due to smaller numbers of M. oculata, P. jeffreysi and the mussel T. flexuosa at the reference station (90°/1500m). All these species are known as indicator species. However, there are no clear patterns in the distribution of the species according to the levels of hydrocarbons or metals in the sediment.

A Bioenv-analysis which connects the variations in the biological data to the variations in the chemical and physical data was performed on the data. The results from the analysis gave a high correlation (0.8) between the fauna composition and the combination of the metals Cu, Pb and Zn.

Comparison with 1990, 1991, 1992, 1996, 1999, 2002 and 2005

In Figure 4.14.6, the results from the present survey are compared to the results from previous surveys. In general the numbers of species and individuals are increasing over the years.

The biodiversity (incl. M. oculata) at Ekofisk C has increased since 2002. This is also the case for EKO-9, -9a, -14 and -15, which were characterized as disturbed in the 2002 survey. Excluding M. oculata from the data show no obvious trend in the same period. The number of M. oculata has increased over the years to a peak in 2002 and declined somewhat in 2005, while the numbers of P. jeffreysii and A. filiformis have been increasing up to 2005.

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0

204060

80100

EKOC-8

EKOC-9

EKOC-9a

EKOC-13

EKOC-14

EKOC-15

EKOC-32

EKOC-REF42

Stations

No.

of s

peci

es (S

)1990 1991 1992 1996 1999 2002 2005

0500

100015002000250030003500

EKOC-8

EKOC-9

EKOC-9a

EKOC-13

EKOC-14

EKOC-15

EKOC-32

EKOC-REF42

Stations

No.

of i

ndiv

idua

ls (N

)

1990 1991 1992 1996 1999 2002 2005

0123456

EKOC-8

EKOC-9

EKOC-9a

EKOC-13

EKOC-14

EKOC-15

EKOC-32

EKOC-REF42

Stations

H'

1990 1991 1992 1996 1999 2002 2005

0123456

EKOC-8

EKOC-9

EKOC-9a

EKOC-13

EKOC-14

EKOC-15

EKOC-32

EKOC-REF42

Stations

H'

1999 2002 2005Excl. M. oculata

Station º/m Station º/m Station º/m Station º/m EKO8 84/1800 EKO9a 70/500 EKO14 140/850 EKO32 180/500 EKO9 94/800 EKO13 146/1300 EKO15 175/500 EKOREF 90/15000

Figure 4.9.6. Numbers of species (S) and individuals (N) per 0.5 m2 and diversity (H’), incl. P. jeffreysii and M. oculata, excl. juv., Ekofisk Center and 2/4 B&K 1990, 1991, 1992, 1996, 1999, 2002 and 2005.

The numbers of the bristle worm P. jeffreysii in particular, but also the bristle worm Apistobranchus tullbergi and the echinoderm A. filiformis have increased considerably since the 2002 survey and represent the dominating species at Ekofisk C together with M. oculata. M. oculata, P. jeffreysii and A. filiformis all have life cycles including a planktonic larval stage and have the opportunity to wide dispersal and establish relatively large populations. A. tullbergi probably also has a planctonic larval stage, because of great dispersal ability and amount of individuals at the Ekofisk region.

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Classification and ordination analyses

The sampled stations from all years have been analysed at family level∗. In general the stations from 1996 - 2005 are grouping together in group 2, while the others (from earlier years) form group 1. The dendrogram from the analysis of comparable stations is shown in Figure 4.9.7.

EKO

-42A

-199

3EK

O-4

2A-1

992

EKO

-42A

-19 9

6EK

O-4

2B-1

996

E KO

-08-

1993

EKO

-09 -

1993

EKO

-13-

1 993

EKO

-09-

1992

E KO

-14-

1992

EKO

-15-

199 2

EKO

-08-

199 2

EKO

-13-

1992

EKO

-32-

1993

EKO

-14-

1993

EKO

-15-

1993

EKO

-15-

1991

EKO

-14 -

1991

EKO

-08-

1991

EKO

-09-

1991

EKO

-13-

1991

EKO

-32-

1 990

EKO

-15-

199 0

EKO

-14-

1990

EKO

-08-

1990

EKO

-09-

1 990

EKO

-13-

1990

EKO

-09A

-200

2EK

O-1

5-20

02EK

O-0

9-20

02EK

O-1

4-20

02EK

O-3

2-19

96EK

O-0

8 -19

96EK

O-0

9-19

96EK

O-1

3-19

96EK

O-1

4-19

9 6EK

O-1

4-19

99EK

O-3

2-19

99EK

O-0

8-19

99EK

O-1

3-19

99EK

O-4

2A-2

002

EKO

-42B

-200

2EK

O-4

2A- 1

999

E KO

-42B

-199

9EK

O-1

3-20

02EK

O-0

8-20

02EK

O-3

2 -20

02EK

O-0

9-20

05EK

O-1

4-20

05EK

O-0

9A-2

005

EKO

-15-

2005

EKO

-42 A

-200

5E K

O-3

2-20

05EK

O-0

8-20

05EK

O-1

3-20

05

100

80

60

40

Sim

ilarit

y

Group 1 Group 2

Ref. 1992-1996 1990 - 1993 Ref.1999-20022002 1996 - 1999 2002-2005

Figure 4.9.7. Dendrogram showing similarity between 8 stations, Ekofisk Center and 2/4 B&K 1990, 1991, 1992, 1996, 1999, 2002 and 2005. Family level, ex. juv., sq. root transformation.

A similarity analysis has been performed on the data set. The results reveal a significant increase in group 2 (stations sampled 1996 - 2005) of species within the families Oweniidae (mainly M. oculata) and Amphinomidae (mainly P. jeffreysii) and the ribbon worm (Nemertea spp.). They also show a decrease in the number of species within the family Cirratulidae (mainly C. setosa). These changes in the number of species contribute most to the differences between group 1 (stations sampled 1990 – 1993) and group 2. Further the two groups can be divided in subgroups. In group 1, the reference station sampled in 1992, -93 and -96 separates from the other stations (stations sampled in 1990 – 1993). In group 2 most of the stations sampled in 2002 and 2005 (incl. the reference station) are clustering together, except for 4 stations sampled in 2002 (EKO-9 (94°/800m), EKO-9a (70°/500m), EKO-14 (140°/800m) and EKO-15 (175/500m)) with high numbers of individuals within the families Oweniidae and Amphiuridae. EKO-9, -9A, -14 and -15 were also sampled in 2005, and are now a part of the main subgroup of 2002 and 2005 stations. The change of subgroup indicates improvements in the fauna at these stations.

Furthermore, the stations sampled in 1996 and 1999 are clustering together. Comparing the reference stations between years reveals that the number of M. oculata has increased over the years to a peak in 2002 and declined somewhat in 2005, while the numbers of P. jeffreysii and A. filiformis have increased up to 2005.

The great variations in the presence of M. oculata from 1996 to 2005 have complicated the faunal picture, making it difficult to draw conclusions about the state of the fauna community.

∗ Necessary when comparing between years, to avoid significant source of error due to both different years and

different taxonomists.

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Adding the 2005 results to the trend data have, however, strengthened the data set, and has made it possible to obtain a pattern in the overall temporal variations in the entire region. Based on this more attention has been drawn to the fluctuations in the numbers of M. oculata and species replaced by or replacing M. oculata. For more background information it is recommended to read Chapter X - General Trends in the Region which forms a basis for the conclusions for each of the fields.

A Bioenv analysis reveals a correlation of 0.4 between fauna and the combination of the environmental factors barium, lead and organic material. The results indicate a negligible relationship between the variation of abiotic factors and the variation in the fauna over the years.

4.9.4 Conclusion

The sediments at Ekofisk Centre consist mainly of fine sand, and the sand content varies from 90.6 % at EKO15, 175°/500m to 97.4 % at the reference station EKO42, 90°/15000m. The gravel content is low. The silt and clay content is at the same level as the 2002 survey. The average silt and clay concentration found is 6.8 % compared to 8.1 % in 1999 and 4.9 % in 1996 for the same stations. EKO14 appears different compared to the other stations, with 35 % silt and clay content, 65 % sand content and a median particle diameter of 3,29φ. The total organic matter content in the sediments is low, and the concentrations vary from 0.88 % to 1.28 %. The concentrations are similar to previous surveys.

The mean THC concentrations (including ether drilling fluid) vary from 5.8 mg/kg at the reference station, EKO42, 90°/15000m to 188 mg/kg at EKO14, 140°/850m. The THC content has decreased considerably, for all the stations analysed, since the last survey.

Maximum concentrations are found at EKO14, 140°/850m, both at the surface and in the deeper layers, with respectively 188 mg/kg (top layer), 408 mg/kg (1-3 cm) and 152 mg/kg (3-6 cm). Relatively high THC concentrations are also found at EKO15, 175°/500m, a mean value of 34 mg/kg. Thus, elevated levels of THC are observed out to 1000m in the 90° and 180° direction, out to 800-850m in the 94° and 140° direction and out to 500m in the 70° direction. The other stations are either below or slightly above the limit of contamination for the region.

Gas chromatograms from previous surveys have shown that the major part of the elevated THC concentrations observed at EKO14 results from didecyl ethers in Aquamul B drilling fluid. Olefins/ethers are found at the four stations analysed, from 1.1 mg/kg at EKO9a, 70°/500m and EKO13, 146°/1300m to 86 mg/kg at EKO14, 140°/850m. The content of olefins has also decreased distinctly since the last survey. The contribution from ethers could not be estimated, since the sediments are not analysed for ether compounds. Thus a major part (approx 45 %) of the elevated THC concentrations found at EKO14 results from didecyl ethers in Aquamul B. It is, however, important to realise that the sediments are not analysed for ether compounds. Thus, we can not estimate the total concentrations of Aquamul B in the sediment due to possible losses during sample preparation.

The gas chromatograms from the stations at Ekofisk Centre and 2/4 B&K are quite complex, and they show different profiles with additional compounds in the HDF 200 area, in the olefin areas and in the heavier hydrocarbon area. In addition ether compounds originating from Aquamul B are identified in the olefin area.

The concentration of NPD, PAH and decalins has decreased for all three stations analysed since the survey in 2002. Highest concentration of NPD, PAH and decalins are found at station EKO14, 140°/850m, particular in the 1-3 cm layer.

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PFOS (perfluorooctyl sulphonate) was not detected at the one station analysed, EKO32, 180°/500 m.

The mean Ba concentrations vary from 46 mg/kg at EKO42 reference station, 90°/15000m to 3860 mg/kg at EKO15, 175°/500m. Elevated Ba concentrations are found at all stations, except for the reference station. Thus elevated levels are observed out to 1800m in the 84° direction and limited to 500m in the 74°, 175° and 180° direction. The concentrations are similar or slightly lower compared to previous surveys. High concentrations of Ba are also found in the 1-3 cm and 3-6 cm layers, similar or higher concentrations than in the top 0-1 cm layer.

The concentrations of the heavy metals are low, however concentrations above the limit of contaminations are found at most of the stations. Highest concentrations are found at EKO14, 140°/850m and EKO15, 175°/500m.

The chemical results agree with the drilling history at Ekofisk Centre and 2/4 B&K. Smaller amounts of barite and cuttings have been discharged related to drilling of top sections with water based mud since the previous survey in 2002. The ether based drilling fluid Aquamul B was discharged in 1990/1991. The ether content is decreasing, but obviously these ether compounds are not degrading as fast as previously anticipated.

The biodiversity indices at Ekofisk C are in general slightly lower than 4, but relatively high compared to several other fields in the central parts of the Ekofisk region. The stations EKO-9, -9A, -14 and -15, which where characterised as disturbed in 2002, separates somewhat in the similarity analyses. It should also be noted that the four stations are closest to the discharge point, 2/4 W (i.e. the distances are shorter than the station names, referring to 2/4 T, indicate). However, the biodiversities have increased, and are not lower than the other stations. The stations are still considered to be disturbed, which is strongly supported by visual observations from sampling and sample processing, but showing a positive trend.

The 2005 data show a good correlation between the variations in the fauna composition and the variations in the concentrations of the metal complex Cu, Pb and Zn. The levels of these metals are relatively low, but above LSC. The highest concentrations are found at EKO-14 and -15. It should, however, be noted that the the correspondance analyses only includes the results from the sediment surface, while considerably higher consentrations of organic and inorganic parameters are found in the deeper layers.

The biodiversity in the fauna community at Ekofisk C has increased since 2002 (data including M. oculata) also at the stations characterised as disturbed in 2002. The decline in M. oculata partly explains the increased biodiversity indices. The changes in the fauna during the years are not directly related to variations in investigated sediment characteristics or chemical data from the sediment surface, see Chapter X for Regional Trends.

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4.10 Ekofisk 2/4 A

4.10.1 Sediment characterization

Grain size distribution

The main results of the grain size distribution are shown in Table 4.10.1. The sediments consist of fine sand. The content of sand ranges from 82.9 % to 97.3 %, the content of silt and clay from 2.6 % to 16.8 % and the content of gravel is below 1.3 % (including the reference station). The median particle diameter ranges from 2.70 to 3.06. In average the median particle diameter is 2.86 and the average sediment consist of 91.8 % sand, 8.0 % silt and clay and 0.2 % gravel.

The complete set of results for the grain size distribution is given in Appendix C.

Total organic matter (TOM)

The TOM results are shown in Table 4.10.2. TOM ranges from 0.76 % (EKOA1) to 1.50 % (EKOA13*), with a mean value of 1.16 % and a median value of 1.18 %. The median value was measured to 1.15 % in 2002 and 1.05 % in 1999.

Table 4.10.1. Ekofisk 2/4 A, grain size distribution.

Median

diameter Grain size distribution 2005 (%) Station MDΦ Classification Silt and clay Sand Gravel EKOA1, 337°/100m 2.70 Fine sand 3.8 94.9 1.3 EKOA2, 337°/250m 2.87 Fine sand 5.6 94.4 0.0 EKOA3, 337°/500m 2.86 Fine sand 5.9 93.7 0.4 EKOA5, 67°/100m 2.81 Fine sand 10.0 89.5 0.5 EKOA6, 67°/250m 2.91 Fine sand 8.0 91.9 0.1 EKOA7, 67°/500m 2.89 Fine sand 8.2 91.8 0.0 EKOA9, 157°/100m 3.06 Fine sand 16.8 82.9 0.3 EKOA10, 157°/250m 2.88 Fine sand 8.8 91.2 0.0 EKOA11, 157°/500m 2.83 Fine sand 5.4 94.6 0.0 EKOA13*, 247°/100m 2.81 Fine sand 8.8 91.1 0.1 EKOA14, 247°/250m 2.91 Fine sand 10.7 89.3 0.0 EKOA15, 247°/500m 2.88 Fine sand 8.8 91.2 0.0 EKOA REF, 90°/15000m 2.78 Fine sand 2.6 97.3 0.1 Mean 2.87 7.96 91.83 0.21 SD 0.08 3.58 3.54 0.37

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Table 4.10.2. Ekofisk 2/4 A, silt and clay and TOM (%). Silt and clay TOM Station 2005 2002 1999 2005 2002 1999 EKOA1 337°/100m 3.8 5.4 9.1 0.76 0.77 1.00 EKOA1B 337°/150m 8.4 1.09 EKOA1C 337°/200m 7.2 1.01 EKOA2 337°/250m 2.9 8.2 7.3 1.04 1.21 0.90 EKOA3 337°/500m 2.9 5.4 5.5 1.22 1.05 0.90 EKOA4 337°/1000m 6.5 7.0 1.26 1.00 EKOA5 67°/100m 2.9 14.3 9.9 1.31 1.31 1.70 EKOA5B 67°/150m 19.6 1.86 EKOA5C 67°/200m 13.2 1.58 EKOA6 67°/250m 2.9 11.1 8.3 1.40 1.20 EKOA7 67°/500m 2.9 7.2 6.7 1.08 1.17 1.00 EKOA8 67°/1000m 7.2 4.5 1.08 1.10 EKOA9 157°/100m 3.1 18.2 7.9 1.36 2.06 1.30 EKOA9B 157°/150m 12.1 1.90 EKOA9C 157°/200m 13.0 1.55 EKOA10 157°/250m 2.9 8.8 5.2 1.33 1.33 1.30 EKOA11 157°/500m 2.8 8.8 5.2 1.24 0.97 1.00 EKOA12 157°/1000m 6.2 6.4 0.91 1.40 EKOA12A 157°/2000m 6.4 0.91 EKOA13* 247°/100m 2.8 14.8 1.50 1.54 EKOA13B 247°/150m 11.9 1.40 EKOA13C 247°/200m 10.5 1.13 EKOA14 247°/250m 2.9 8.5 6.9 1.14 1.04 1.20 EKOA15 247°/500m 2.9 7.9 5.5 1.10 0.95 1.10 EKOA16 247°/1000m 8.0 2.4 0.91 0.70 EKOA REF 90°/15000m 2.6 2.6 5.3 0.88 0.82 1.00

4.10.2 Chemical analyses

In the sediments from Ekofisk 2/4 A, the following parameters are determined:

• THC and olefins • Esters • NPD, PAH and decalins • Metals (Ba, Cd, Cr, Cu, Hg, Pb and Zn)

Three replicate samples from the top layer are analyzed. In addition, samples from deeper layers (down to 6-20 cm) are analyzed for some parameters. For the 0-1 cm layer, only the mean values are given.

The monitoring program continues in the same way as in 2002, but there have been collected additional sediment samples from the cutting pile.

The reference station named EKOA REF is the Ekofisk refrence station EKOC Ref. 42, 90°/15000m.

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THC and olefins

The results for the determination of THC and olefins are shown in Table 4.10.3.

The concentration of THC in the 0-1 cm layer ranges from 8 mg/kg (EKOA12A) to 195 mg/kg (EKOA5). The concentration at the reference station, EKOA REF, is 6 mg/kg. The mean concentration is 32 mg/kg and the median 17 mg/kg, when EKOA REF is excluded. In 2002 the median concentration was found to be 24 mg/kg, and in 1999 16 mg/kg.

The highest measured concentration of THC is 1030 mg/kg in the 3-6 cm layer at EKOA5.

As can be seen in Figure 4.10.1, the levels of THC generally increase from the upper 0-1 cm layer to the 6-9 cm layers.

EKO

A1EK

OA1

bEK

OA1

cEK

OA2

EKO

A3EK

OA

4E

KOA5

EKO

A5b

EKO

A5c

EKO

A6EK

OA7

EKO

A8EK

OA1

9EK

OA

9EK

OA9

bEK

OA9

cEK

OA1

0E

KOA1

1EK

OA

12EK

OA1

2aEK

OA1

3*EK

OA1

3bEK

OA1

3cEK

OA1

4E

KOA1

5EK

OA1

6EK

OA1

7

0-1cm

6-9cm

15-20cm

0

100

200

300

400

500

600

700

800

900

1000

mg/kg

station

Ekofisk 2/4 A, THC 2005

0-1cm 1-3cm 3-6cm 6-9cm 9-12cm12-15cm15-20cm

Figure 4.10.1. Ekofisk 2/4 A, concentrations of THC in the 2005 survey. Ekofisk 2/4A, THC 2005

0

50

100

150

200

250

EKOA1

EKOA2

EKOA3

EKOA4

EKOA5

EKOA6

EKOA7

EKOA8

EKOA19

EKOA9

EKOA10

EKOA11

EKOA12

EKOA12a

EKOA13*

EKOA14

EKOA15

EKOA16

EKOA17

EKOA REF

station

mg/kg

1999

2002

2005

LSC A

384±238 311±41 189±85

Figure 4.10.2. Ekofisk 2/4 A, concentrations of THC.

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Generally, the levels of THC appear to decrease from 1999 to 2005 in the 0-1 cm layer (Figure 4.10.2). This is also the case for the olefins from 2002 to 2005 (Figure 4.10.3).

The concentration of olefins in the 0-1 cm layer ranges from 2 mg/kg (EKOA1C and EKOA9C) to 61 mg/kg (EKOA5), with a mean value of 12 mg/kg and a median value of 5 mg/kg. In 2002 the mean and median value was 31 mg/kg and 35 mg/kg, respectively.

The highest concentration of olefins is 465 mg/kg in the 3-6 cm layer at EKOA5.

The 1-6 cm layers at EKOA5 have distinctly higher concentrations of THC and olefins in 2005 than in 2002. This is most likely due to a heterogeneous distribution of the contamination at EKOA5.

0

10

20

30

40

50

60

70

mg/kg

EKO

A1

EKO

A1B

EKO

A1C

EKO

A5

EKO

A5B

EKO

A5C

EKO

A9

EKO

A9B

EKO

A9C

EKO

A13

*

EKO

A13

B

EKO

A13

C

station

Ekofisk 2/4 A olefins

20052002

Figure 4.10.3. Ekofisk 2/4 A, concentrations of olefins. Table 4.10.3. Ekofisk 2/4 A, THC and olefins (mg/kg dry sediment). layer THC Olefin Station cm 2005 2002 1999 2005 2002 EKOA1 337°/100m 0-1 17 28 49 5 8 1-3 25 35 7 11 3-6 39 58 14 17 6-9 20 EKOA1B 337°/150m 0-1 16 24 3 6 1-3 24 32 3-6 23 55 6-9 28 35 9-12 11 42 EKOA1C 337°/200m 0-1 13 15 2 3 1-3 30 24 3-6 22 61 6-9 34 93 9-12 18 64 EKOA2 337°/250m 0-1 18 20 12 EKOA3 337°/500m 0-1 12 12 11

Cont.

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Table 4.10.3. cont. layer THC Olefin Station cm 2005 2002 1999 2005 2002 EKOA4 337°/1000m 0-1 11 16 14 EKOA5 67°/100m 0-1 195 141 384 61 54 1-3 409 152 168 60 3-6 1031 92 465 12 EKOA5B 67°/150m 0-1 106 146 20 51 1-3 213 3-6 216 6-9 200 9-11 132 EKOA5C 67°/200m 0-1 42 125 7 44 1-3 51 3-6 84 6-9 52 9-12 10 EKOA6 67°/250m 0-1 29 83 58 EKOA7 67°/500m 0-1 13 16 9 EKOA8 67°/1000m 0-1 12 16 13 EKOA19 67°/2000m 0-1 9 EKOA9 157°/100m 0-1 73 119 311 16 46 1-3 246 155 77 43 3-6 245 50 74 8 6-9 649 9-12 476 12-15 407 15-20 18 EKOA9B 157°/150m 0-1 24 109 3 34 1-3 52 285 3-6 73 104 6-9 35 60 9-12 8 30 EKOA9C 157°/200m 0-1 17 88 2 22 1-3 44 110 3-6 44 52 6-9 26 23 9-12 14 EKOA10 157°/250m 0-1 22 41 59 1-3 54 46 114 3-6 61 54 69 EKOA11 157°/500m 0-1 11 16 16 1-3 8 16 3-6 10 21 EKOA12 157°/1000m 0-1 10 10 14 EKOA12A 157°/2000m 0-1 8 8

Cont.

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Table 4.10.3. cont. EKOA13* 247°/100m 0-1 90 93 14 35 1-3 142 205 24 97 3-6 307 111 14 26 6-9 122 9-12 8 12-15 6 15-25 12 EKOA13B 247°/150m 0-1 33 125 4 54 1-3 82 3-6 73 6-9 80 9-12 20 EKOA13C 247°/200m 0-1 24 36 3 12 1-3 131 3-6 31 6-9 20 9-12 13 EKOA14 247°/250m 0-1 21 24 189 EKOA15 247°/500m 0-1 12 13 18 EKOA16 247°/1000m 0-1 10 11 10 EKOA17 247°/2000m 0-1 9 EKOA REF 90°/15000m 0-1 6 6 6 1-3 7 8 9 3-6 8 9 6

Esters

The concentrations of esters are shown in Table 4.10.4. The content of esters is generally very low and close to the detection limits. Small amount of esters are found at EKOA5 (3 mg/kg) and EKOA9 (1-3 mg/kg). Table 4.10.4. Ekofisk 2/4 A, esters (mg/kg dry sediment). layer Ester Station cm 2005 2002 EKOA1 337°/100m 0-1 <1 <1 1-3 <1 <1 3-6 <1 <1 6-9 <1 EKOA1B 337°/150m 0-1 <1 EKOA1C 337°/200m 0-1 <1 EKOA5 67°/100m 0-1 3 1 1-3 3 <1 3-6 3 <1 EKOA5B 67°/150m 0-1 1 EKOA5C 67°/200m 0-1 <1 EKOA9 157°/100m 0-1 3 2 1-3 2 <1 3-6 1 <1 EKOA9B 157°/150m 0-1 1

Cont.

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Table 4.10.4. cont. EKOA9C 157°/200m 0-1 <1 EKOA13* 247°/100m 0-1 1 1-3 <1 3-6 <1 EKOA13B 247°/150m 0-1 <1 EKOA13C 247°/200m 0-1 <1

NPD, PAH and decalins

The results from the determination of NPD, PAH and decalins are shown in Table 4.10.5.

The concentration of NPD ranges from 0.02 mg/kg (0-1 cm at EKOA1C) to 1.42 mg/kg (1-3 cm at EKOA5), with a mean concentration of 0.41 mg/kg and a median of 0.31 mg/kg. The mean and median value in 2002 was 0.61 mg/kg and 0.29 mg/kg, respectively. At EKOC Ref. 42 the concentration of NPD is from 0.01 mg/kg and below.

The concentration of PAH ranges from 0.029 mg/kg (0-1 cm at EKOA1) to 1.54 mg/kg (1-3 cm at EKOA5), with a mean concentration of 0.172 mg/kg and a median of 0.102 mg/kg. The mean and median value in 2002 was 1.08 mg/kg and 0.146 mg/kg, respectively. At EKOA REF the concentration of PAH is from 0.039 mg/kg to 0.080 mg/kg.

The concentration of decalins ranges from below 0.1 mg/kg to 27.9 mg/kg (6-9 cm at EKOA9), with a mean concentration of 1.9 mg/kg and a median of 0.4 mg/kg. The mean and median in 2002 was 0.7 mg/kg and 0.6 mg/kg, respectively. At EKOA REF the concentration of decalins is from 0.1 mg/kg and below. Table 4.10.5. Ekofisk 2/4 A, NPD, PAH and decalins (mg/kg dry sediment). NPD PAH Decalins

Station cm 2005

2002

1999 2005 2002 1999 2005 2002 1999

EKOA1 337°/100m 0-1 0.03 0.08 0.029 0.088 <0.1 0.2 1-3 0.05 0.10 0.040 0.141 <0.1 0.2 3-6 0.06 0.14 0.045 0.119 0.1 0.5 EKOA1B 337°/150m 0-1 0.03 0.12 0.066 0.092 <0.1 EKOA1C 337°/200m 0-1 0.02 0.11 0.056 0.128 <0.1 EKOA5 67°/100m 0-1 0.94 0.67 0.170 0.179 0.9 0.9 1-3 1.42 0.49 1.54 0.162 1.2 1.3 3-6 1.12 0.32 0.102 0.285 3.2 1.0 EKOA5B 67°/150m 0-1 0.72 0.50 0.248 0.218 0.7 1.2 1-3 0.56 0.109 1.2 3-6 0.53 0.326 4.1 6-9 0.64 0.161 4.1

9-12 0.80 0.516 2.2

EKOA5C 67°/200m 0-1 0.24 0.31 0.083 0.336 0.2 1.3 1-3 0.19 0.068 0.2 EKOA9 157°/100m 0-1 0.53 0.72 0.126 0.322 0.2 1.3 1-3 0.44 8.17 0.140 23.4 1.1 1.4 3-6 0.48 0.26 0.127 0.309 3.0 0.6 6-9 1.18 0.155 27.9

Cont.

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Table 4.10.5. cont. EKOA9B 157°/150m 0-1 0.27 0.54 0.118 0.475 0.4 0.9 1-3 0.32 0.069 0.4 3-6 0.31 0.278 1.8 EKOA9C 157°/200m 0-1 0.24 0.49 0.100 0.181 0.1 0.5 EKOA10 157°/250m 0-1 0.16 0.21 0.15 0.080 0.092 0.065 0.2 0.2 0.4 1-3 0.69 0.18 0.17 0.188 0.132 0.067 0.4 0.3 1.1 3-6 0.16 0.41 0.20 0.189 0.362 0.367 0.5 0.4 2.6 EKOA11 157°/500m 0-1 0.03 0.07 0.074 0.064 <0.1 0.1 1-3 0.03 0.06 0.065 0.074 <0.1 0.1 3-6 0.03 0.08 0.069 0.106 <0.1 0.1 EKOA13* 247°/100m 0-1 0.37 0.27 0.090 0.106 0.4 0.5 1-3 0.40 0.54 0.104 0.137 1.5 1.6 3-6 1.01 0.43 0.271 0.097 8.1 1.3 6-9 0.27 0.080 3.8 EKOA13B 247°/150m 0-1 0.09 0.32 0.092 0.150 0.1 1.5 EKOA13C 247°/200m 0-1 0.04 0.19 0.060 0.191 0.1 0.3 EKOA REF

90°/15000m 0-1

<0.01 0.02 0.01 0.039 0.048 0.035 0.1

1-3 <0.01 0.03 0.03 0.049 0.068 0.094 <0.1

3-6 0.01 0.03 0.02 0.080 0.081 0.048 <0.1

Metals

The results from the determination of metals are shown in Table 4.10.6.

The concentration of Ba in the 0-1 cm layer ranges from 890 mg/kg (EKOA11) to 5110 mg/kg (EKOA13*), with a mean concentration of 2950 mg/kg and a median of 3070 mg/kg. In 2002 the mean and median concentration for the same stations was 2920 mg/kg and 2320 mg/kg, respectively. In 1999 EKOA13* was not sampled. The mean and median concentration was then 3240 mg/kg and 2990 mg/kg, respectively. The highest measured concentration of Ba in 2005 is 5940 mg/kg in the 1-3 cm layer at EKOA9. The concentration of Ba at EKOA REF is 46-72 mg/kg. No general trend is obvious for the concentrations of Ba from 1999 to 2005 (Figure 4.10.4). Table 4.10.6. Ekofisk 2/4 A, metals (mg/kg dry sediment). layer Ba Cd Cr Cu Hg Pb Zn Station cm 2005 2002 1999 2005 2005 2005 2005 2005 2005 EKOA1 337°/100m 0-1 1120 2330 3750 0.04 4.7 1.4 0.01 9.0 11.5 1-3 2120 4500 0.04 6.7 2.2 0.01 15.4 17.2 3-6 4340 4980 0.06 6.9 2.7 0.02 16.8 22.3 EKOA1B 337°/150m 0-1 1820 EKOA1C 337°/150m 0-1 2290 EKOA2 337°/250m 0-1 2480 1690 2430 0.02 8.9 1.7 20.4 13.2 EKOA3 337°/500m 0-1 925 945 739 0.01 6.4 0.8 9.7 8.5 EKOA4 337°/1000m 0-1 896 1170 EKOA5 67°/100m 0-1 4320 4740 5680 0.40 10.0 13.2 0.12 40.2 154 1-3 5400 4950 0.72 14.0 18.6 0.17 66.0 273 3-6 5130 4310 0.73 15.8 20.7 0.39 115 272 EKOA5B 67°/150m 0-1 4960

Cont.

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Table 4.10.6. cont. layer Ba Cd Cr Cu Hg Pb Zn Station cm 2005 2002 1999 2005 2005 2005 2005 2005 2005 EKOA5C 67°/200m 0-1 4150 EKOA6 67°/250m 0-1 4730 4480 4340 0.12 11.5 5.9 29.2 39.5 EKOA7 67°/500m 0-1 2280 2290 1860 0.02 6.8 2.0 14.4 10.6 EKOA8 67°/500m 0-1 1190 1310 EKOA9 157°/100m 0-1 4150 4260 4710 0.12 7.8 6.5 0.07 28.0 57.3 1-3 5940 5620 0.27 11.5 15.5 0.08 55.1 139 3-6 4340 4820 0.81 10.5 19.5 0.29 120 302 EKOA9B 157°/100m 0-1 5470 EKOA9C 157°/100m 0-1 3400 EKOA10 157°/250m 0-1 3650 4340 2990 0.03 9.5 2.6 0.03 24.3 21.9 1-3 3070 6060 5240 0.04 10.1 2.7 0.02 28.3 24.8 3-6 4230 5180 4810 0.08 10.7 3.2 0.04 31.9 34.6 EKOA11 157°/500m 0-1 887 1350 1670 0.02 9.3 1.1 0.02 14.4 11.6 1-3 820 2970 0.04 10.1 1.0 0.01 10.8 10.3 3-6 1320 4480 0.06 10.3 1.2 0.01 11.0 11.3 EKOA12 157°/1000m 0-1 476 605 EKOA12A 157°/2000m 0-1 268 EKOA13* 247°/100m 0-1 5110 4350 0.2 14.2 17.5 0.09 51.7 125 1-3 5330 5790 0.33 14.3 18.4 6.64 59.9 152 3-6 4770 4290 0.53 16.8 42.1 0.15 113 263 EKOA13*B 247°/150m 0-1 4790 EKOA13*C 247°/200m 0-1 3460 EKOA14 247°/250m 0-1 4000 2300 4540 0.07 11.9 17.4 29.7 39.4 EKOA15 247°/500m 0-1 1690 1960 2900 0.02 6.6 4.7 13.2 11.0 EKOA16 247°/500m 0-1 957 567 EKOA REF 90°/15000m 0-1 46 72 41 <0.01 7.6 <0.5 <0.01 6.1 5.4 1-3 50 88 50 <0.01 8.1 <0.5 <0.01 6.4 5.8 3-6 72 331 141 <0.01 8.0 <0.5 <0.01 6.6 5.8

The concentration of Cd in the 0-1 cm layer ranges from 0.01 mg/kg (EKOA3) to 0.40 mg/kg (EKOA5), with a mean concentration of 0.09 mg/kg and a median of 0.04 mg/kg. This is the same mean and median found for the same stations in 1999 and 2002. The highest measured concentration of Cd in 2005 is 0.81 mg/kg in the 3-6 cm layer at EKOA9. Cd is not detected at EKOA REF.

The concentration of Cr in the 0-1 cm layer ranges from 4.7 mg/kg (EKOA1) to 14.2 mg/kg (EKOA13*), with a mean and median concentration of 9.0-9.1 mg/kg. This is virtually the same mean and median found for the same stations in 1999 and 2002. The highest measured concentration of Cr in 2005 is 16.8 mg/kg in the 3-6 cm layer at EKOA13*. The concentration of Cr at EKOA REF is 7.6-8.1 mg/kg.

The concentration of Cu in the 0-1 cm layer ranges from 0.8 mg/kg (EKOA3) to 17.5 mg/kg (EKOA13*), with a mean concentration of 6.2 mg/kg and a median of 3.7 mg/kg. This is virtually the same mean and median found for the same stations in 1999 and 2002. The highest measured concentration of Cu in 2005 is 42.1 mg/kg in the 3-6 cm layer at EKOA13*. Cu is not detected at EKOA REF.

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Ekofisk 2/4A, Ba 2005

0

500

1000

1500

2000

2500

3000

3500

4000

4500

5000

5500

6000

EKOA1 EKOA2 EKOA3 EKOA5 EKOA6 EKOA7 EKOA REF

station

mg/kg

1999

2002

2005

LSC A

5682±473

Figure 4.10.4. Ekofisk 2/4 A, the concentrations of Ba.

The concentration of Hg in the 0-1 cm layer ranges from 0.01 mg/kg (EKOA1) to 0.12 mg/kg (EKOA5), with a mean and median concentration of 0.05-0.06 mg/kg. This is virtually the same mean and median found for the same stations in 1999 and 2002. The highest measured concentration of Hg in 2005 is 6.64 mg/kg in the 1-3 cm layer at EKOA13*. Hg is not detected at EKOA REF. Please note that Hg is not analyzed in samples from EKOA2, EKOA3, EKOA6, EKOA7, EKOA14 and EKOA15.

The concentration of Pb in the 0-1 cm layer ranges from 9.0 mg/kg (EKOA1) to 51.7 mg/kg (EKOA13*), with a mean and median concentration of 22.4-23.7 mg/kg. The mean concentration has decreased from 33.1 mg/kg in 1999 to 29.2 mg/kg in 2002 to 23.7 mg/kg in 2005. The median concentration has decreased from 26.7 mg/kg in 1999, to 25.9 mg/kg in 2002 to 22.4 mg/kg in 2005. In reality, this is virtually the same levels. The highest measured concentration of Pb in 2005 is 120 mg/kg in the 3-6 cm layer at EKOA9. The concentration of Pb at EKOA REF is 6.1-6.6 mg/kg.

The concentration of Zn in the 0-1 cm layer ranges from 8.5 mg/kg (EKOA3) to 153 mg/kg (EKOA5), with a mean concentration of 41.9 mg/kg and median of 17.6 mg/kg. This is virtually the same mean found for the same stations in 1999 and 2002. The highest measured concentration of Zn in 2005 is 302 mg/kg in the 3-6 cm layer at EKOA9. The concentration of Zn at EKOA REF is 5.4-5.8 mg/kg.

4.10.3 Ekofisk 2/4 A drill cuttings pile – Core sample VC-2

Sediment characterization and chemical analyses

The monitoring of the drill cutting pile continues in the same way as in 1999 and 2002, but there have been collected additional sediment samples from the pile.

Two core samples were investigated. The core sample is analyzed for the same parameters as the Ekofisk 2/4 A field and in addition PCB. Thus the following parameters are included in the

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survey: Grain size distribution, TOM, THC, Olefins, Esters, NPD, PAH, Decalins, PCB and metals (Ba, Cd, Cr, Cu, Hg, Pb, Zn).

Core samples VC-2

The core samples investigated were 130 cm and 115 cm long respectively. The two core samples were black and uniform all the way. However, a difference could be observed below approximately 40 cm for VC-2 (I) with mostly sand as VC-2 (II) had had a layer of fine sand between 40-45 cm. It was decided to cut the corer mainly into 5 cm layers from the top. VC-2 (I) was cut in 9 layers of 5 cm down to 60 cm, then in a 50-60 cm and 90-130 cm layer. VC-2 (II) was cut in 10 layers of 5 cm down to 65 cm and then in a 80-115 cm layer. Grain size distribution The main results of the grain size distribution are shown in Table 4.10.7 and visualized in Figure 4.10.5. The sediments consist mainly of silt and clay down to 40 cm depth. From 40 cm and down, different classifications of sand are found in both VC-2 (I) and VC-2 (II). From 45 to 130 cm depth, different layers are analyzed in the two samples, and a comparison is therefore not straightforward.

4.10.4 Total organic matter (TOM)

The TOM results are shown in Table 4.10.8. TOM (2005) ranges from 5.3-5.4 % in the bottom layer to 12.0-13.8 % in the 40-45 cm layer. The TOM content is 10.0-12.4 % in the top layer (0-5 cm), and decreases to 6.7-6.9 % in the 10-15 cm layer. It then increases to 12.0-13.8 % in the 40-45 cm layer. The TOM content then decreases to 5.3-5.4 % at 80-130 cm.

The 2005 TOM results are quite different from the 2002 results. In 2002 the TOM content was 1.4 % at 40-45 cm, compared to 12.0-13.8 % in 2005. The TOM results are generally higher in 2005 than in 2002. Table 4.10.7. Ekofisk 2/4 A drill cuttings pile, grain size distribution.

layer Median

diameter Grain size distribution 2005

(%) Station cm MDΦ Classification Silt and clay Sand Gravel VC-2 (I) 0-5 5.77 Silt and clay 89.7 8.7 1.6 5-10 5.86 Silt and clay 93.5 5.4 1.1 10-15 5.82 Silt and clay 91.6 7.1 1.3 15-20 5.67 Silt and clay 85.9 11.8 2.3 20-25 5.40 Silt and clay 76.9 21.0 2.1 25-30 5.81 Silt and clay 91.3 7.6 1.1 30-35 5.75 Silt and clay 89.0 7.5 3.5 35-40 5.26 Silt and clay 72.9 14.0 13.1 40-45 -0.38 Coarse sand 32.7 24.9 42.4 50-60 2.46 Medium sand 42.7 35.7 21.6 90-130 3.78 Very fine sand 48.9 46.5 4.6

Cont.

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Table 4.10.7. cont.

layer Median

diameter Grain size distribution 2005

(%) Station cm MDΦ Classification Silt and clay Sand Gravel VC-2 (II) 0-5 4.60 Silt and clay 58.8 21.9 19.3 5-10 5.88 Silt and clay 94.1 5.2 0.7 10-15 5.85 Silt and clay 93.0 6.8 0.2 15-20 5.61 Silt and clay 83.6 10.5 5.9 20-25 5.74 Silt and clay 88.6 9.7 1.7 25-30 5.77 Silt and clay 89.8 9.9 0.3 30-35 5.84 Silt and clay 92.6 7.1 0.3 35-40 5.44 Silt and clay 78.1 15.0 6.9 40-45 2.61 Fine sand 47.6 21.8 30.6 45-65 5.23 Silt and clay 72.2 18.6 9.2 80-115 5.13 Silt and clay 69.7 24.7 5.6 Mean 4.95 76.51 15.52 7.97 SD 1.55 18.80 10.62 11.12

Table 4.10.8. Ekofisk 2/4 A drill cuttings pile, silt and clay and TOM (%). 2005(I), 2005 (II) and 2002 denotes the VC-2(I), VC-2(II) and VC-2 corer sampled and analyzed in 2005 and 2002 respectively.

corer layer /cm 2005(I) 50-60 90-130 2005(II) 45-65 80-115

parameter 2002 0-5 5-10 10-15 15-20 20-25 25-30 30-35 35-40 40-45

45-58 Silt and clay 2005(I) 89.7 93.5 91.6 85.9 76.9 91.3 89.0 72.9 32.7 42.7 48.9 2005(II) 58.8 94.1 93.0 83.6 88.6 89.8 92.6 78.1 47.6 72.2 69.7 2002 36.6 47.7 63.5 34.5 14.2 9.3 8.0 47.2 6.2 7.3 TOM 2005(I) 10.0 8.52 6.87 7.45 8.39 9.18 11.0 9.38 12.0 6.97 5.42 2005(II) 12.4 9.30 6.65 7.33 7.13 9.40 9.58 9.21 13.8 6.37 5.29 2002 6.26 10.4 9.24 8.70 5.17 4.47 3.83 2.71 1.40 1.27

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0 % 10 % 20 % 30 % 40 % 50 % 60 % 70 % 80 % 90 % 100 %

0-5 cm

5-10 cm

10-15 cm

15-20 cm

20-25 cm

25-30 cm

30-35 cm

35-40 cm

40-45 cm

50-60 cm

90-130 cm

dept

hVC-2(I)

0 % 10 % 20 % 30 % 40 % 50 % 60 % 70 % 80 % 90 % 100 %

0-5 cm

5-10 cm

10-15 cm

15-20 cm

20-25 cm

25-30 cm

30-35 cm

35-40 cm

40-45 cm

45-65 cm

80-115 cm

dept

h

VC-2(II)Silt and claySand Gravel

0 % 10 % 20 % 30 % 40 % 50 % 60 % 70 % 80 % 90 % 100 %

0-5 cm

5-10 cm

10-15 cm

15-20 cm

20-25 cm

25-30 cm

30-35 cm

35-40 cm

40-45 cm

50-60 cm

90-130 cm

dept

h

0 % 10 % 20 % 30 % 40 % 50 % 60 % 70 % 80 % 90 % 100 %

0-5 cm

5-10 cm

10-15 cm

15-20 cm

20-25 cm

25-30 cm

30-35 cm

35-40 cm

40-45 cm

50-60 cm

90-130 cm

dept

hVC-2(I)

0 % 10 % 20 % 30 % 40 % 50 % 60 % 70 % 80 % 90 % 100 %

0-5 cm

5-10 cm

10-15 cm

15-20 cm

20-25 cm

25-30 cm

30-35 cm

35-40 cm

40-45 cm

45-65 cm

80-115 cm

dept

h

0 % 10 % 20 % 30 % 40 % 50 % 60 % 70 % 80 % 90 % 100 %

0-5 cm

5-10 cm

10-15 cm

15-20 cm

20-25 cm

25-30 cm

30-35 cm

35-40 cm

40-45 cm

45-65 cm

80-115 cm

dept

h

VC-2(II)Silt and claySand Gravel

Silt and claySand Gravel

Figure 4.10.5. Ekofisk 2/4 A drill cuttings pile, grain size distribution for the two corer samples.

THC, olefins, esters, PCB, NPD, PAH and decalins

The concentrations of THC, esters, PCB, NPD, PAH and decalins are shown in Table 4.10.9.

The concentrations of THC in the 2005 survey ranges from 998-1150 mg/kg in the 45-65 cm layers to 77400 mg/kg in the 20-25 cm layer in VC-2(I) and 88100 mg/kg in the 0-5 cm layer in VC-2(II). The levels of THC in the core samples are generally higher in 2005 than in 2002. The maximum in the 2002 sample is 71900 mg/kg in the 10-15 cm layer (see Figure 4.10.6), while the maxima in the 2005 samples are 88100 mg/kg in the 0-5 cm layer and 77400 mg/kg in the 20-25 cm layer. The depth profile for 2005(I) and 2002 show the same pattern, except for higher levels and also at deeper layers for the 2005 (I) sample. The 2005 (II) sample seems to be more heterogeneous than the other samples.

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0 10000 20000 30000 40000 50000 60000 70000 80000 90000

THCmg/kg

0-5 cm

5-10 cm

10-15 cm

15-20 cm

20-25 cm

25-30 cm

30-35 cm

35-40 cm

40-45 cm

45-65* cm

80-130* cm

dept

hVC-2

THC concentrations

2005(I)2005(II)2002

Figure 4.10.6. Ekofisk 2/4 A drill cuttings pile. THC concentrations (mg/kg dry sediment): a depth profile for VC-2 in 2005 and 2002. *) 90-130 cm for VC-2 (I) / 80-115 cm for VC-2 (II).

The concentrations of olefins in the 2005 survey ranges from 170-565 mg/kg in the 45-65 cm layers to 44400 mg/kg in the 20-25 cm layer in VC-2(I) and 52500 mg/kg in the 0-5 cm layer in VC-2(II). The levels of olefins in the samples are generally higher in 2005 than in 2002 and are in correlation with THC. The depth profiles are shown in Figure 4.10.7.

0 10000 20000 30000 40000 50000 60000

olefinsmg/kg

0-5 cm

5-10 cm

10-15 cm

15-20 cm

20-25 cm

25-30 cm

30-35 cm

35-40 cm

40-45 cm

45-65* cm

80-130* cm

dept

h

VC-2olefin concentrations

2005(I)2005(II)2002

Figure 4.10.7. Ekofisk 2/4 A drill cuttings pile. Olefin concentrations (mg/kg dry sediment): a depth profile for VC-2 in 2005 and 2002.*) 90-130 cm for VC-2 (I) / 80-115 cm for VC-2 (II).

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In 2005 no ester or PCB was found in the corer samples. The limit of detection in 2005 for ester and PCB are higher than in 2002, and this fact can explain the differences for PCB between the two surveys. For esters this is not the case, as the ester content in the 2002 samples are far higher than the detection limit in the 2005 survey. Table 4.10.9. Ekofisk 2/4 A drill cuttings pile, THC, olefins, ester, PCB, NPD, PAH and decalins (mg/kg dry sediment). 2005(I), 2005 (II) and 2002 denotes the VC-2 (I), VC-2 (II) and VC-2 corer sampled and analyzed in 2005 and 2002, respectively.

corer layer /cm

2005(I) 50-60 90-130

2005(II) 45-65 80-115

para

met

er

2002 0-5

5-10

10-1

5

15-2

0

20-2

5

25-3

0

30-3

5

35-4

0

40-4

5

45-58 THC 2005(I) 48141 56670 20013 71677 77422 41228 49377 12540 15956 1153 1855 2005(II) 88088 46341 41455 49648 43848 69221 44943 37754 4378 998 7811 2002 5480 35000 71900 19600 994 934 883 1360 55 58 Olefin 2005(I) 26400 32771 11546 36771 44397 29054 31464 7405 10568 565 <5 2005(II) 52487 25660 23577 28369 22817 38828 23099 19143 2066 170 <5 2002 3040 24200 54700 14600 277 200 116 n.d 13 36 Ester 2005(I) <15 <15 <15 <15 <15 <15 <15 <15 <15 <15 <15 2005(II) <15 <15 <15 <15 <15 <15 <15 <15 <15 <15 <15 2002 1500 1210 45 33 13 9 6 3 1 3 PCB 2005(I) <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 2005(II) <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 2002 0.012 <0.01 <0.01 <0.01 0.064 0.139 0.776 0.711 0.078 0.004 NPD 2005(I) 69.0 72.4 37.2 54.5 52.0 22.9 31.2 10.4 9.3 5.4 68.7 2005(II) 80.5 42.5 48.0 53.2 43.4 53.5 30.8 21.4 5.7 13.1 35.8 2002 21.5 10.1 5.5 11.2 13.1 12.7 14.0 40.9 1.2 0.3 PAH 2005(I) 18.0 14.9 6.7 18.9 14.9 13.8 22.4 1.5 1.4 0.4 1.8 2005(II) 3.4 2.7 2.9 3.4 17.6 14.5 13.8 8.9 0.9 0.7 1.0 2002 0.6 1.3 0.5 0.8 0.6 0.9 0.8 1.1 0.3 0.1 Decalins 2005(I) 48.3 41.0 18.1 36.7 73.4 36.5 67.1 4.6 3.9 2.3 63.3 2005(II) 105 19.6 21.9 20.4 37.6 76.6 48.2 32.9 2.2 6.3 39.5 2002 22.5 22.5 29.1 37.3 8.1 18.5 36.1 77.5 0.9 0.5

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0 10 20 30 40 50 60 70 80 90

NPDmg/kg

0-5 cm

5-10 cm

10-15 cm

15-20 cm

20-25 cm

25-30 cm

30-35 cm

35-40 cm

40-45 cm

45-65* cm

80-130* cm

dept

hVC-2

NPD concentrations

2005(I)2005(II)2002

Figure 4.10.8. Ekofisk 2/4 A drill cuttings pile. NPD concentrations (mg/kg dry sediment): a depth profile for VC-2 in 2005 and 2002. *) 90-130 cm for VC-2 (I) / 80-115 cm for VC-2 (II).

0 5 10 15 20 25

PAHmg/kg

0-5 cm

5-10 cm

10-15 cm

15-20 cm

20-25 cm

25-30 cm

30-35 cm

35-40 cm

40-45 cm

45-65* cm

80-130* cm

dept

h

VC-2PAH concentrations

2005(I)2005(II)2002

Figure 4.10.9. Ekofisk 2/4 A drill cuttings pile. PAH concentrations (mg/kg dry sediment): a depth profile for VC-2 in 2005 and 2002. *) 90-130 cm for VC-2 (I) / 80-115 cm for VC-2 (II).

The concentration of NPD in the 2005 survey ranges from 5.4-13.1 mg/kg in the 40-65 cm layers to 42.5-80.5 mg/kg in the 0-10 cm layers. The levels of NPD in the samples are generally higher in 2005 than in 2002. The depth profiles for NPD (Figure 4.10.8.) show maxima in the top (0-10 cm) and bottom layers (80-130 cm in 2005, 35-40 cm in 2002).

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0 20 40 60 80 100 120

decalinsmg/kg

0-5 cm

5-10 cm

10-15 cm

15-20 cm

20-25 cm

25-30 cm

30-35 cm

35-40 cm

40-45 cm

45-65* cm

80-130* cm

dept

hVC-2

decalin concentrations

2005(I)2005(II)2002

Figure 4.10.10. Ekofisk 2/4 A drill cuttings pile. Decalin concentrations (mg/kg dry sediment): a depth profile for VC-2 in 2005 and 2002. *) 90-130 cm for VC-2 (I) / 80-115 cm for VC-2 (II).

The uncertainty in the measurements of the concentrations of NPD, PAH and decalins are, however, rather large in these measurements, caused by the large concentrations of THC in the core samples. Hence, a definite conclusion should not be stated.

The concentration of PAH in the 2005 survey ranges from 0.4 mg/kg to 22.4 mg/kg. The levels are generally higher in 2005 than in 2002. The PAH concentrations for the 2002 sample were evenly distributed down through the sediment layers (Figure 4.10.9). In 2005 the VC-2 (I) sample has maxima in the 0-10 cm, 15-20 cm and 30-35 cm layers, while the VC-2 (II) sample has a maximum in the 20-35 cm layers.

The concentration of decalins in the 2005 survey ranges from 2.2 mg/kg to 105 mg/kg. The levels of decalins are generally higher in 2005 than in 2002. A closer look at the depth profiles reveals an impression that the decalins are layered in the corer samples. In 2002 the maxima are found in the 15-20 cm and the 35-40 cm layers. In 2005 the maxima are found in the 0-5 cm, 20-30 cm and 80-130 cm layers.

Metals

The results are shown in Table 4.10.10.

The Ba concentrations in VC-2 (I) ranges from 343 mg/kg in the 35-40 cm layer to 2100 mg/kg in the 15-20 cm layer. In VC-2 (II) the concentrations ranges from 313 mg/kg in the 40-45 cm layer to 1500 mg/kg in the 80-115 cm layer. Compared to 2002 the concentrations are generally lower. In VC-2 (I) the Ba is distributed with maxima in the 10-20 cm, 25-30 cm and the 40-45 cm layers (Figure 4.10.11). In VC-2 (II) the Ba is distributed with maxima in the 10-15 cm, 20-25 cm and 80-115 cm layers. In the 2002 sample the maxima were found in the 0-5 cm, 25-30 cm and the 40-45 cm layers. The differences between VC-2 (I) and VC-2 (II) suggest that the Ba is very heterogeneous distributed in the sediment layers. The 2002 results strengthen that impression.

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Table 4.10.10. Ekofisk 2/4 A drill cuttings pile, metals (mg/kg dry sediment). 2005(I), 2005 (II) and 2002 denotes the VC-2 (I), VC-2 (II) and VC-2 corer sampled and analyzed in 2005 and 2002, respectively.

corer layer /cm 2005(I) 50-60 90-130 2005(II) 45-65 80-115

parameter 2002 0-5 5-10 10-15 15-20 20-25 25-30 30-35 35-40 40-45

45-58 Ba 2005(I) 958 930 2079 2104 808 2069 576 343 1088 693 358 2005(II) 640 847 1432 807 1148 558 650 480 313 573 1502 2002 2280 1440 1660 2450 3010 3440 2970 1870 3700 815 Cd 2005(I) 0.47 0.46 0.39 0.37 0.73 0.47 0.58 0.31 0.09 0.46 11.3 2005(II) 0.40 0.44 0.56 0.26 0.38 0.63 0.48 0.43 0.34 0.80 1.29 2002 0.40 0.20 2.80 0.40 0.50 0.60 1.40 12.60 0.20 <0.2 Cr 2005(I) 40.6 37.9 36.7 40.4 35.0 40.6 43.2 38.7 13.0 46.2 183 2005(II) 50.0 40.8 38.8 42.2 36.1 48.0 42.2 43.3 28.0 40.8 66.9 2002 36.1 31.8 28.4 32.1 52.1 43.7 63.1 125 9.8 10.8 Cu 2005(I) 55 83 79 77 75 51 46 32 20 57 103 2005(II) 68 77 81 66 73 81 54 47 37 49 37 2002 62 74 74 52 56 66 107 136 4 2 Hg 2005(I) 0.09 0.09 0.09 0.14 0.47 0.23 0.11 0.21 0.04 0.13 1.70 2005(II) 0.06 0.08 0.11 0.10 0.22 0.28 0.26 0.18 0.08 0.21 0.37 2002 0.18 0.19 0.61 0.27 0.18 0.18 0.47 2.52 0.14 0.03 Pb 2005(I) 54 67 57 70 209 98 129 60 23 138 1201 2005(II) 75 70 46 61 130 103 103 101 49 237 272 2002 56 76 181 120 123 142 211 1300 60 9 Zn 2005(I) 112 128 103 133 551 244 271 170 59 230 2173 2005(II) 123 102 135 118 187 299 265 244 259 390 432 2002 138 146 373 354 567 535 746 2080 50 12

The concentration of Cd in 2005 ranges from 0.09 mg/kg (40-45 cm layer, VC-2 (I)) to 11.3 mg/kg (90-130 cm, VC-2 (I)). The concentration of Cr in 2005 ranges from 13.0 mg/kg (40-45 cm layer, VC-2 (I)) to 183 mg/kg (90-130 cm, VC-2 (I)). The concentration of Cu in 2005 ranges from 20.4 mg/kg (40-45 cm layer, VC-2 (I)) to 103 mg/kg (90-130 cm, VC-2 (I)). The concentration of Hg in 2005 ranges from 0.04 mg/kg (40-45 cm layer, VC-2 (I)) to 1.70 mg/kg (90-130 cm, VC-2 (I)). The concentration of Pb in 2005 ranges from 23 mg/kg (40-45 cm layer, VC-2 (I)) to 1200 mg/kg (90-130 cm, VC-2 (I)). The concentration of Zn in 2005 ranges from 59 mg/kg (40-45 cm layer, VC-2 (I)) to 2170 mg/kg (90-130 cm, VC-2 (I)).

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0 500 1000 1500 2000 2500 3000 3500 4000

Bamg/kg

0-5 cm

5-10 cm

10-15 cm

15-20 cm

20-25 cm

25-30 cm

30-35 cm

35-40 cm

40-45 cm

45-65* cm

80-130* cm

dept

hVC-2

Ba concentrations

2005(I)2005(II)2002

Figure 4.10.11. Ekofisk 2/4 A drill cuttings pile. Ba concentrations (mg/kg dry sediment): a depth profile for VC-2 in 2005 and 2002. *) 90-130 cm for VC-2 (I) / 80-115 cm for VC-2 (II).

The concentration profiles for Cd, Cr, Cu, Hg, Pb and Zn in the corer samples are shown in Figure 4.10.12. The 2002 sample has a maximum at 35-40 cm, while the 2005 samples have a maximum at 80-130 cm.

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0 1 2 3

Hgmg/kg

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h

0 2 4 6 8 10 12 14

Cdmg/kg

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h

2005(I)

2005(II)

2002

0 20 40 60 80 100 120 140 160 180 200

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h

0 20 40 60 80 100 120 140

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h

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Figure 4.10.12. Ekofisk 2/4 A drill cuttings pile. Cd, Cr, Cu, Hg, Pb and Zn concentrations (mg/kg dry sediment): a depth profile for VC-2 in 2005 and 2002. *) 90-130 cm for VC-2 (I) / 80-115 cm for VC-2 (II).

4.10.5 Biological analyses

A total of 173 species and 26986 individuals were sampled at 12 stations. Greatest abundance (73 %) was found among the polychaetes, of which the species Myriochele oculata constitutes 60.8 % and Paramphinome jeffreysii constitutes 16.7 %, Table 4.10.11.

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Table 4.10.11. Number of species and individuals distributed between the main groups, Ekofisk 2/4 A 2005.

Individuals Species Main animal groups Number % Number %

Varia 1960 7.3 15 8.7Polychaeta 19707 73.0 70 40.5- Paramphinome jeffreysii 3311 16.8 - Myriochele oculata 11986 60.8 Crustacea 708 2.6 31 17.9Mollusca 1668 6.2 45 26.0Echinodermata 2943 10.9 12 6.9- Amphiura filiformis 1721 58.5 Total 26986 100.0 173 100.0

Figure 4.10.13 shows the numbers of species and individuals sampled at each station and variations between grab samples.

0800

1600240032004000

EKOA-01EKOA-02EKOA-03EKOA-05EKOA-06EKOA-07EKOA-09EKOA-10EKOA-11

EKOA-13*EKOA-14EKOA-15

Stations

No.

of i

ndiv

idua

ls (N

)

020406080

100

EKOA-01EKOA-02EKOA-03EKOA-05EKOA-06EKOA-07EKOA-09EKOA-10EKOA-11

EKOA-13*EKOA-14EKOA-15

Stations

No.

of s

peci

es (S

)

Ex. P. jeffreysii

0800

1600240032004000

EKOA-01EKOA-02EKOA-03EKOA-05EKOA-06EKOA-07EKOA-09EKOA-10EKOA-11

EKOA-13*EKOA-14EKOA-15

Stations

No.

of i

ndiv

idua

ls (N

)

Ex. P. jeffreysii and M. oculata

0800

1600240032004000

EKOA-01EKOA-02EKOA-03EKOA-05EKOA-06EKOA-07EKOA-09EKOA-10EKOA-11

EKOA-13*EKOA-14EKOA-15

Stations

No.

of i

ndiv

idua

ls (N

)

Station º/m Station º/m Station º/m Station º/m EKOA1 337/100 EKOA5 67/100 EKOA9 157/100 EKOA13* 247/100 EKOA2 337/250 EKOA6 67/250 EKOA10 157/250 EKOA14 247/250 EKOA3 337/500 EKOA7 67/500 EKOA11 157/500 EKOA15 247/500

Figure 4.10.13. Numbers of species (S) and individuals (N) per 0.5 m2 (incl./excl. P. jeffreysii and M. oculata), mean values per grab sample and standard deviation, Ekofisk 2/4 A 2005.

The standard deviation was in general dramatically reduced when the two species P. jeffreysii and M. oculata were removed. This is evident since the two species constitute 56.7 % of the total number of individuals.

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At stations EKOA-02 and EKOA-11 the standard deviation was only slightly reduced, and at EKOA-13*, the standard deviation actually increased. This is due to relatively large differences between the five grabs sampled at each station.

Diversity and dominant species

The dominant species at each station varied from 29.2 % at EKOA-01 (337°/100m) to 66 % at EKOA-05 (67°/100m). The 10 most abundant species made up from 73.6 % at EKOA-14 (247°/250m) to 94.1 % at EKOA-05, see Table 4.10.12. In general the bristle worm M. oculata dominated the fauna at the Ekofisk A field, often followed by the bristle worm P. jeffreysii and the brittle star Amphiura filiformis. At EKOA-01 P. jeffreysii was the dominating species followed by M. oculata. Other frequently found species were the ribbon worm (Nemertea spp.), the bristle worms Scoloplos armiger and Chaetozone setosa and the mussel Thyasira flexuosa. M. oculata and A. filiformis are suspension feeders, while C. setosa, S. armiger and the mussel T. flexuosa all have the possibility to act as both suspension and deposit feeders. P. jeffreysii is mainly a carnivore species and the ribbon worms are deposit feeders. Most of these species are known indicators of organic pollution when they are found in high numbers. However several of the above mentioned species have a planktonic developmental stage and are able to settle in large amounts. Table 4.10.12. The 10 most abundant species at each station, Ekofisk 2/4 A 2005 (excl. juv.). 10 most dominating species EKOA-01 No. % Cum. % EKOA-02 No. % Cum. %Paramphinome jeffreysii 276 29.2 29.2 Myriochele oculata 670 33.7 33.7Myriochele oculata 128 13.6 42.8 Paramphinome jeffreysii 387 19.5 53.2Echinoidea spp.juv. 89 9.4 52.2 Amphiura filiformis 176 8.9 62.0Nemertea spp. 82 8.7 60.9 Scoloplos armiger 71 3.6 65.6Scoloplos armiger 57 6.0 67.0 Thyasira flexuosa 56 2.8 68.4Amphiura filiformis 56 5.9 72.9 Echinoidea spp.juv. 40 2.0 70.4Chaetozone setosa 50 5.3 78.2 Corymorpha nutans 40 2.0 72.4Echinocardium flavescens 18 1.9 80.1 Goniada pallida 35 1.8 74.2Glycera alba 18 1.9 82.0 Caudofoveata spp. 33 1.7 75.9Montacuta substriata 15 1.6 83.6 Eudorella truncatula/emarginata 24 1.2 77.1 EKOA-03 No. % Cum. % EKOA-05 No. % Cum. %Myriochele oculata 721 36.5 36.5 Myriochele oculata 2439 66.0 66.0Paramphinome jeffreysii 252 12.8 49.3 Nemertea spp. 284 7.7 73.7Amphiura filiformis 194 9.8 59.1 Paramphinome jeffreysii 228 6.2 79.9Harpinia antennaria 74 3.8 62.8 Scoloplos armiger 175 4.7 84.7Echinoidea spp.juv. 65 3.3 66.1 Chaetozone setosa 159 4.3 89.0Eudorella t t l / i t

59 3.0 69.1 Thyasira flexuosa 49 1.3 90.3Corymorpha nutans 50 2.5 71.7 Amphiura filiformis 39 1.1 91.3Thyasira flexuosa 49 2.5 74.1 Pholoe baltica 38 1.0 92.4Caudofoveata spp. 48 2.4 76.6 Echinoidea spp.juv. 35 1.0 93.3Scoloplos armiger 45 2.3 78.8 Glycera alba 30 0.8 94.1 Cont.

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Table 4.10.12. cont. EKOA-06 No. % Cum. % EKOA-07 No. % Cum. %Myriochele oculata 1050 44.3 44.3 Myriochele oculata 790 42.4 42.4Paramphinome jeffreysii 277 11.7 56.0 Paramphinome jeffreysii 262 14.1 56.5Amphiura filiformis 189 8.0 64.0 Echinoidea spp.juv. 122 6.6 63.1Echinoidea spp.juv. 114 4.8 68.8 Amphiura filiformis 86 4.6 67.7Scoloplos armiger 103 4.4 73.1 Thyasira flexuosa 58 3.1 70.8Thyasira flexuosa 97 4.1 77.2 Scoloplos armiger 56 3.0 73.8Nemertea spp. 40 1.7 78.9 Corymorpha nutans 49 2.6 76.4Chaetozone setosa 37 1.6 80.5 Eudorella truncatula/emarginata 34 1.8 78.3Goniada maculata 27 1.1 81.6 Goniada pallida 32 1.7 80.0Hemichordata spp. 24 1.0 82.6 Trichobranchus roseus 25 1.3 81.3 EKOA-09 No. % Cum. % EKOA-10 No. % Cum. %Myriochele oculata 1546 52.5 52.5 Myriochele oculata 730 37.7 37.7Paramphinome jeffreysii 312 10.6 63.1 Paramphinome jeffreysii 246 12.7 50.4Nemertea spp. 195 6.6 69.7 Amphiura filiformis 162 8.4 58.7Amphiura filiformis 169 5.7 75.4 Echinoidea spp.juv. 139 7.2 65.9Scoloplos armiger 125 4.2 79.7 Scoloplos armiger 58 3.0 68.9Apistobranchus tullbergi 123 4.2 83.8 Thyasira flexuosa 50 2.6 71.5Thyasira flexuosa 100 3.4 87.2 Chaetozone setosa 46 2.4 73.8Chaetozone setosa 49 1.7 88.9 Corymorpha nutans 43 2.2 76.1Goniada pallida 30 1.0 89.9 Trichobranchus roseus 36 1.9 77.9Echinoidea spp.juv. 23 0.8 90.7 Goniada pallida 34 1.8 79.7 EKOA-11 No. % Cum. % EKOA-13* No. % Cum. %Myriochele oculata 1020 44.5 44.5 Myriochele oculata 1553 47.1 47.1Paramphinome jeffreysii 240 10.5 55.0 Nemertea spp. 482 14.6 61.7Echinoidea spp.juv. 206 9.0 64.0 Paramphinome jeffreysii 426 12.9 74.6Amphiura filiformis 184 8.0 72.0 Chaetozone setosa 163 4.9 79.6Scoloplos armiger 53 2.3 74.3 Scoloplos armiger 128 3.9 83.5Eudorella truncatula/emarginata 45 2.0 76.3 Amphiura filiformis 125 3.8 87.3Caudofoveata spp. 37 1.6 77.9 Apistobranchus tullbergi 59 1.8 89.1Thyasira flexuosa 32 1.4 79.3 Levinsenia gracilis 37 1.1 90.2Chaetozone setosa 31 1.4 80.7 Thyasira flexuosa 35 1.1 91.2Sthenelais limicola 24 1.1 81.7 Pectinaria auricoma 35 1.1 92.3 EKOA-14 No. % Cum. % EKOA-15 No. % Cum. %Myriochele oculata 529 32.4 32.4 Myriochele oculata 810 39.5 39.5Paramphinome jeffreysii 187 11.5 43.9 Amphiura filiformis 219 10.7 50.2Amphiura filiformis 122 7.5 51.4 Paramphinome jeffreysii 218 10.6 60.8Scoloplos armiger 92 5.6 57.0 Echinoidea spp.juv. 120 5.9 66.7Corymorpha nutans 63 3.9 60.9 Corymorpha nutans 80 3.9 70.6Echinoidea spp.juv. 62 3.8 64.7 Scoloplos armiger 62 3.0 73.6Thyasira flexuosa 53 3.3 67.9 Trichobranchus roseus 33 1.6 75.2Chaetozone setosa 37 2.3 70.2 Chaetozone setosa 30 1.5 76.7Trichobranchus roseus 29 1.8 72.0 Thyasira flexuosa 27 1.3 78.0Goniada pallida 27 1.7 73.6 Goniada pallida 27 1.3 79.3

The number of species varied from 65 at station EKOA-01 (337°/100m) to 103 at EKOA-10 (157°/250m). The number of individuals varied from 851 at EKOA-01 to 3658 at EKOA-05 (67°/100m). The Shannon Wiener diversity index varied from 2.2 at EKOA-05 to 4.2 at EKOA-14 (247°/250m) and the Hurlberts index (ES100) varied from 13 at EKOA-05 to 29 at EKOA-14 including M. oculata. Indices above 4 indicate a relatively undisturbed fauna. Indices between 3 and 4 indicate a slight disturbance, while indices between 2 and 3 indicate a disturbance in the fauna. In general ES100 indices above 20 characterize a relatively normal

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fauna community. Thus some of the observed indices reflect a slight disturbance, see Table 4.10.13.

The biodiversity results indicate somewhat more disturbances in the fauna at most of the 100 m stations (EKOA-05 (67°/100m), EKOA-09 (157°/100m) and EKOA-13* (247°/100m)) than at the other stations. Table 4.10.13. Numbers of individuals (N) and species (S), depth, Shannon-Wiener diversity index (H’), Pielou’s evenness index (J), and expected number of species per 100 individuals (ES100) for each station at Ekofisk 2/4 A 2005 (excl. juv.).

H' ES100 Station Direction ° Distance m Depth S N Incl.

M. o. Excl. M. o.

J Incl. M. o.

Excl. M. o.

EKOA-01 337 100 78 65 851 3.7 3.7 0.6 23 24EKOA-02 337 250 77 100 1943 3.9 4.5 0.6 27 35EKOA-03 337 500 78 84 1902 3.8 4.6 0.6 25 31EKOA-05 67 100 76 69 3658 2.2 3.7 0.4 13 21EKOA-06 67 250 76 84 2245 3.4 4.5 0.5 23 31EKOA-07 67 500 77 81 1736 3.5 4.5 0.5 24 32EKOA-09 157 100 76 79 2915 2.9 4.0 0.5 17 23EKOA-10 157 250 76 103 1796 3.8 4.8 0.6 27 35EKOA-11 157 500 76 84 2081 3.4 4.7 0.5 24 35EKOA-13* 247 100 77 61 3295 2.8 3.5 0.5 15 19EKOA-14 247 250 77 93 1559 4.2 4.9 0.6 29 36EKOA-15 247 500 77 93 1923 3.7 4.6 0.6 25 34M. o.= M. oculata

Classification and ordination

The dendrogram from the cluster analysis and the MDS plot from the ordination analysis based on station level are presented in Figure 4.10.14 and Figure 4.10.15. The analysis based on grab level shows the same patterns as the analysis based on station level. The stations divide into two main groups at a similarity of about 60 %. Station EKOA-01 (337°/100m) separates from the two main groups. Group 1, consisting of EKOA-05 (67°/100m), EKOA-09 (157°/100m) and EKOA-13* (247°/100m), differ from the other group with somewhat lower biodiversity indices and significantly higher numbers of M. oculata and ribbon worms (Nemertea spp.). These stations also had the highest levels of THC, barium and the other metals in the sediments. The similarities within the main groups are about 75 % and the groups are not further subdivided. Station EKOA-01 differs with somewhat more sand and gravel in the sediment than the other stations. The fauna at this station contains significantly smaller numbers of the bristle worm M. oculata, the mussel T. flexuosa and the brittle star A. filiformis than the other stations. The cluster analysis is well supported by the ordination analysis.

The Bioenv analysis reveals a correlation factor of 0.9 between the fauna and the complex of the parameters THC, Ba1, Cd, TOM and gravel, indicating that the variations in the fauna composition can be explained by these parameters. This is supported by observations of black oily spots in some of the samples during field work and processing of the samples.

The similarity analysis indicates disturbances in the fauna due to higher levels of THC and metals in the sediments at the stations EKOA-05 (67°/100m), EKOA-09 (157°/100m) and EKOA-13* (247°/100m).

1 Ba and the other metals are not degradable and will not disappear from the sediments. These metals may

presumable not have any effect on the fauna in itself, but could be regarded as trace elements for other degradable substances.

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EKO

A -01

E KO

A-05

EKO

A-09

EKO

A-13

*

EKO

A-06

EKO

A-02

EKO

A-10

EKO

A-07

EKO

A-1 4

EKO

A-15

EKO

A-03

EKO

A-11

100

90

80

70

60

50Si

mila

rity

Group 1 Group 2

67/100m 157/100m 247/100m 67/250 337/250 157/250 67/500 247/250 247/500 337/500 157/500

Figure 4.10.14. Dendrogram of stations from Ekofisk 2/4 A 2005 (excl. juv.).

EKOA-01

EKOA-02

EKOA-03

EKOA-05

EKOA-06

EKOA-07

EKOA-09

EKOA-10EKOA-11

EKOA-13*

EKOA-14EKOA-15

Stress: 0,03

Group 1

Group 2

Figure 4.10.15 MDS plot of stations from Ekofisk 2/4 A 2005 (excl. juv.).

Comparison with 1999, 2002 and 2005

In Figure 4.10.16, the results from the present survey are compared to the results from previous surveys. The numbers of species and individuals include the bristle worms M. oculata and P. jeffreysii for all the years, unless otherwise stated. The numbers of species have in general increased since 1999 and 2002 and the numbers of individuals have decreased since 2002. At station EKOA-01 (337°/100m) the number of species has decreased since 2002. At station EKOA-13* (247°/100m), the number of species has decreased while the number of individuals has increased. The number of individuals has also increased at station EKOA-05 (67°/100m) since 2002.

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The biodiversity has in general increased since 2002 and are at the same level or higher than in 1999. However, at stations EKOA-05 and EKOA-13* the diversity indices have declined since 2002.

020406080

100120

EKOA-01

EKOA-02

EKOA-03

EKOA-05

EKOA-06

EKOA-07

EKOA-09

EKOA-10

EKOA-11

EKOA-13*

EKOA-14

EKOA-15

Stations

No.

of s

peci

es (S

)

1999 2002 2005

010002000300040005000

EKOA-01

EKOA-02

EKOA-03

EKOA-05

EKOA-06

EKOA-07

EKOA-09

EKOA-10

EKOA-11

EKOA-13*

EKOA-14

EKOA-15

Stations

No.

of i

ndiv

idua

ls (N

1999 2002 2005

012345

EKOA-01

EKOA-02

EKOA-03

EKOA-05

EKOA-06

EKOA-07

EKOA-09

EKOA-10

EKOA-11

EKOA-13*

EKOA-14

EKOA-15

Stations

H'

1999 2002 2005

0123456

EKOA-01

EKOA-02

EKOA-03

EKOA-05

EKOA-06

EKOA-07

EKOA-09

EKOA-10

EKOA-11

EKOA-13*

EKOA-14

EKOA-15

Stations

H'

1999 2002 2005Excl. M. oculata

Station º/m Station º/m Station º/m Station º/m EKOA-01 337/100 EKOA-05 67/100 EKOA-09 157/100 EKOA-13* 247/100 EKOA-02 337/250 EKOA-06 67/250 EKOA-10 157/250 EKOA-14 247/250 EKOA-03 337/500 EKOA-07 67/500 EKOA-11 157/500 EKOA-15 247/500

Figure 4.10.16. Numbers of species (S) and individuals (N) per 0.5 m2 and diversity (H’). (Incl.P. jeffreysii and M. oculata, excl. juv.), Ekofisk 2/4 A 1999, 2002 and 2005.

Classification and ordination analyses

The sampled stations from all years have been analysed at family level∗. The dendrogram from the cluster analysis reveals that most of the stations divide into three main groups at about 65 % similarity, based on years. Station EKOA-01 (337°/100m) sampled in 2005 differs from the other stations. A similarity analysis has been performed on the data, and the results reveal a significant decrease in the number of species within the family Oweniidae (mainly M. oculata) and an increase in the number of species within Amphinomidae (mainly P. jeffreysii) in the 2005 group (stations sampled in 2005). The changes in the numbers of species in the 2005 group contribute the most to the differences between 2005 and 2002. From 1999 to 2002 there was a great increase in the number of the species M. oculata1.

Both M. oculata and P. jeffreysii have life cycles including a planktonic larval stage and have the opportunity to wide dispersal and establish relatively large populations.

∗ Necessary when comparing between years, to avoid significant source of error due to both different years and

different taxonomists. 1 The great variations in the presence of M. oculata from 1996 to 2005 are discussed in Chapter X - General Trends

in the Region which forms a basis for the conclusions for each of the fields.

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EKO

A-01

-200

5EK

OA-

06-2

005

EKO

A-03

-200

5EK

OA-

11- 2

005

EKO

A-0 7

-200

5E K

OA-

14-2

0 05

EKO

A-15

-200

5

EKO

A-0 2

-200

5EK

OA-

10-2

005

EKO

A-0 5

-200

5EK

OA-

09-2

005

EKO

A-13

-200

5

EKO

A -05

-200

2EK

OA-

13-2

002

EKO

A-01

-200

2EK

OA-

11-2

002

EKO

A-02

-200

2EK

OA-

10-2

002

EKO

A-07

- 200

2

EKO

A-14

-200

2EK

OA-

03-2

002

EKO

A-15

-200

2

EKO

A-06

-200

2EK

OA-

09-2

002

EKO

A-14

-199

9EK

OA-

01-1

999

E KO

A-09

-19 9

9EK

OA-

05-1

999

EKO

A-06

-199

9EK

OA-

02-1

999

EKO

A-0 3

-199

9EK

OA-

07-1

999

EKO

A-15

-199

9

EKO

A-1 0

-199

9EK

OA-

11-1

999

100

90

80

70

60

50Si

mila

rity

2005 2002 1999 Figure 4.10.17. Dendrogram showing similarity between Ekofisk 2/4 A stations 1999, 2002, 2005. Family level, incl. M. oculata, excl. juv., sq. root transformation.

The Bioenv analysis gave some correlation (0.4) between fauna and a combination of the environmental factors THC, Cd, Pb and TOM, which indicates a poor relevance for the development over the years.

4.10.6 Conclusion

The sediments at Ekofisk 2/4 A consist of fine sand. The content of sand in the top 0-1 cm layer ranges from 82.9 % to 97.3 %, the content of silt and clay from 2.6 % to 16.8 % and the content of gravel is below 1.3 %, including the Ekofisk reference station. In average the median particle diameter is 2.86 and the average sediment consist of 91.8 % sand, 8.0 % silt and clay and 0.2 % gravel.

The total organic matter (TOM) ranges from 0.76 % at 337°/100 m to 1.50 % at 247°/100 m, with a mean value of 1.16 % and a median value of 1.18 %. The median value was measured to 1.15 % in 2002 and 1.05 % in 1999.

THC in the 0-1 cm layer is below 50 mg/kg from 67°/200 m, 157°/150 m, 247°/150 m and 337°/<100 m. This means that the area with a THC concentration larger than 50 mg/kg has decreased since 2002. However, to a distance at least 200 m from the centre, the THC concentrations in the deeper layers are somewhat higher.

The concentration of THC in the 0-1 cm layer ranges from 8 mg/kg at 157°/2000 m to 195 mg/kg at 67°/100 m. The concentration at the reference station at 90°/15000 m is 6 mg/kg. The mean concentration is 32 mg/kg and the median 17 mg/kg. In 2002 the median concentration was found to be 24 mg/kg, and in 1999 16 mg/kg.

Generally, the levels of THC appear to decrease from 1999 to 2005 in the 0-1 cm layer. This is also the case for the olefins from 2002 to 2005. However, the level of THC generally increases from the upper 0-1 cm layer to the 1-9 cm layers.

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The concentration of olefins in the 0-1 cm layer ranges from 2 mg/kg to 61 mg/kg, with a mean value of 12 mg/kg and a median value of 5 mg/kg. In 2002 the mean and median value was 31 mg/kg and 35 mg/kg, respectively.

The highest measured concentration of THC and olefins is 1030 mg/kg and 465 mg/kg, respectively, in the 3-6 cm layer at 67°/100 m.

The content of esters is generally very low and close to the detection limits. Small amount of esters are found at 67°100 m (3 mg/kg) and at 157°/100 m (1-3 mg/kg).

Elevated concentrations of NPD and PAH are found at all stations analyzed.

The concentration of Ba in the 0-1 cm layer ranges from 890 mg/kg at 157°/500 m to 5110 mg/kg at 247°/100 m, with a mean concentration of 2950 mg/kg and a median of 3070 mg/kg. The highest measured concentration of Ba in 2005 is 5940 mg/kg in the 1-3 cm layer at 157°/100 m. No general trend is obvious for the concentrations of Ba from 1999 to 2005.

Elevated levels of heavy metals are found at most of the stations.

The chemical results agree with the drilling history of at Ekofisk 2/4 A. Olefins and esters are found in the sediments due to discharges in 1994.

In general the biodiversity indices are relatively high compared to several other fields in the central Ekofisk region. However, the fauna at EKOA-05 (67°/100m), EKOA-09 (157°/100m) and EKOA-13* (247°/100m) differ from the other stations at Ekofisk A and the disturbance in the fauna at these 100 m stations seem to be related to field activities.

The Bioenv analysis reveals a high correlation (0.9) between the fauna and the complex of the parameters THC, Ba, Cd, TOM and gravel, indicating that the variations in the fauna composition could be explained by the variations of these parameters.

The biodiversity at Ekofisk A has in general increased and there has been a significant decrease in the numbers of M. oculata since 2002.

Drill cuttings pile at Ekofisk 2/4 A – Corer VC-2

The sediment in the two corer samples consist mainly of silt and clay down to 40 cm depth. From 40 cm and down, different classifications of sand are found in both VC-2 (I) and VC-2 (II).

TOM ranges from 5.3-5.4 % in the deepest layers to 12.0-13.8 % in the 40-45 cm layer. The TOM content is 10.0-12.4 % in the top layer (0-5 cm), and decreases to 6.7-6.9 % in the 10-15 cm layer. It then increases to 12.0-13.8 % in the 40-45 cm layer, followed by a decrease to 5.3-5.4 % at 80-130 cm.

The 2005 TOM results are quite different from the 2002 results. In 2002 the TOM content was 1.4 % at 40-45 cm, compared to 12.0-13.8 % in 2005. The TOM results are generally higher in 2005 than in 2002.

The concentrations of THC in the corer samples from the 2005 survey ranges from 998-1150 mg/kg in the 45-65 cm layers to 77400 mg/kg in the 20-25 cm layer in VC-2 (I) and 88100 mg/kg in the 0-5 cm layer in VC-2 (II). The levels of THC in the 2005 samples are generally higher than in 2002. The maximum in the 2002 sample is 71900 mg/kg in the 10-15 cm layer, while the maxima in the 2005 samples are 88100 mg/kg in the 0-5 cm layer and 77400 mg/kg in the 20-25 cm layer. The depth profile for one of the 2005 samples and the one sampled in 2002 show the same pattern, except for higher levels and also at deeper layers for the 2005 sample. The other 2005 sample seems to be more heterogeneous than the others.

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The concentrations of olefins in the 2005 survey ranges from 170-565 mg/kg in the 45-65 cm layers to 44400 mg/kg in the 20-25 cm layer in VC-2 (I) and 52500 mg/kg in the 0-5 cm layer in VC-2 (II). The levels of olefins in the samples are generally higher in 2005 than in 2002 and are in correlation with THC.

A large share of the THC is olefins. This is not the case, however, for the deepest layers.

In 2005 no ester or PCB was found in the corer samples. This was not the case in 2002, when both ester and PCB were detected.

The levels of NPD in the samples are generally higher in 2005 than in 2002. The depth profiles for NPD show maxima in the top (0-10 cm) and bottom layers (80-130 cm in 2005, 35-40 cm in 2002).

The levels of PAH in the samples are generally higher in 2005 than in 2002. The PAH concentrations for the 2002 sample are evenly distributed down the sediment layers.

In 2005 the VC-2 (I) sample has maxima in the 0-10 cm, 15-20 cm and 30-35 cm layers, while the VC-2 (II) sample has a maximum in the 20-35 cm layers.

The levels of decalins in the samples are generally higher in 2005 than in 2002. A closer look at the depth profiles reveals an impression that the decalins are layered in the corer samples. In 2002 the maxima are found in the 15-20 cm and the 35-40 cm layers. In 2005 the maxima are found in the 0-5 cm, 20-30 cm and 80-130 cm layers.

The Ba concentrations in VC-2 (I) ranges from 343 mg/kg in the 35-40 cm layer to 2100 mg/kg in the 15-20 cm layer. In VC-2 (II) the concentrations ranges from 313 mg/kg in the 40-45 cm layer to 1500 mg/kg in the 80-115 cm layer. Compared to 2002 the concentrations are generally lower. In VC-2 (I) the Ba is distributed with maxima in the 10-20 cm, 25-30 cm and the 40-45 cm layers. In VC-2 (II) the Ba is distributed with maxima in the 10-15 cm, 20-25 cm and 80-115 cm layers. In the 2002 sample the maxima were found in the 0-5 cm, 25-30 cm and the 40-45 cm layers. The differences between VC-2 (I) and VC-2 (II) suggest that the Ba is very heterogeneous distributed in the sediment layers. The results from 2002 strengthen that impression.

Elevated concentrations of heavy metals are found in most of the samples, with the highest concentrations in the deepest layers.

The chemical results mainly agree with the drilling history. Olefins and esters were discharged in 1994. Only small discharges have taken place since 1994. As ester drilling fluids were discharged in 1994, only lower concentrations could be expected, due to the relatively easy degradation of ester compounds. This is in agreement with that the ester content has decreased considerably since last survey and could not be detected in this survey.

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4.11 Eldfisk 2/7 A/FTP Station ELDA6 was in 2002 described as 180°/500m, but was actually sampled at 180°/370m. In 2005 this station was included as ELDA6 (180°/370m). An additional station, ELDA106, was sampled (THC only) at 180°/500m.

4.11.1 Sediment characterization

Grain size distribution

The grain size distribution from the present survey is shown in Table 4.11.1 together with the silt and clay content from the previous surveys in 2002, 1999 and 1996. The sediments at Eldfisk 2/7 A/FTP consist of fine sand, and the sand content varies from 92 % to 97%. The average median diameter is 2.74φ. Gravel content is zero. The silt and clay content is similar to the previous surveys and the average silt and clay content is 5.7 %, compared to 5.2% in 2002.

The results from the complete grain size distribution are given in Appendix C. Table 4.11.1. Eldfisk 2/7 A/FTP 2005, grain size distribution. Station Median

diameterClassification Grain size distrib. 2005

(%) 2002

(%) 1999 (%)

1996 (%)

Mdφ Silt and clay

Sand Gravel Silt and clay

Silt and clay

Silt and clay

ELDA3 360°/625m 2.72 Fine sand 4.0 96.0 0.0 4.9 ELDA6 180°/370m 2.74 Fine sand 5.3 94.7 0.0 5.1 5.7 4.2 ELDA11 270°/500m 2.75 Fine sand 5.0 95.0 0.0 ELDA14 90°/500m 2.76 Fine sand 8.3 91.7 0.0 5.5 EKO Ref. 42 90°/15000m 2.78 Fine sand 2.6 97.3 0.1 2.6 5.3 2.9 Mean (excl. ref. station) 2.74 Fine sand 5.7 94.4 5.2 5.5 3.6 Standard deviation 0.017 1.9 1.9 0.3

Total organic matter (TOM)

The content of TOM in the sediments is low. Only small variations are found at the field, from 0.88 % to 0.97 %. The concentrations are similar to the previous surveys in 2002, 1999 and 1996, and the content corresponds to the grain size distribution. The results are shown in Table 4.11.2. Table 4.11.2. Eldfisk 2/7 A/FT 2005, total organic matter (% of dry sediment). Station 2005, 0-5 cm Mean 2002 SD

2002 Mean 1999 Mean

1996 ELDA3 360°/625m 0.88 0.76 0.05 ELDA6 180°/370m 0.97 0.89 0.08 0.81 0.86 ELDA11 270°/500m 0.97 ELDA14 90°/500m 0.94 0.90 0.09 EKO Ref. 42 90°/15000m 0.88 0.82 0.02 0.95 0.86

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4.11.2 Chemical analyses

Parameters analysed in the sediments at Eldfisk 2/7 A/FTP:

• THC • Olefins • NPD, PAH, decalins • Metals (Ba, Cd, Cr, Cu, Hg, Pb, Zn)

Three replicate samples at each station are analysed. The samples are taken from the top 0-1 cm sediment layer. In addition the 1-3 cm and 3- 6 cm sediment layers are sampled at one station. The 2000m stations have been excluded from this year survey based on the results from 2002. ELDA11 at 500m distance is however included in the investigation.

THC and olefins

The THC results including olefins are shown in Table 4.11.3, and olefins separately are given in Table 4.11.4. The corresponding THC data from the previous surveys in 2002, 1999, 1996 and 1995 are also included for comparison. Bar diagram of the THC content in the sediments is given in Figure 4.11.1.

One new station at 500m distance is included in the present survey, ELDA11, 270°/500m. Four stations at 250m distance, which have not been analysed since 1995, are also included. These are ELDA4 (360°), ELDA5 (180°), ELDA12 (270°) and ELDA13 (90°).

In 1999 the THC concentrations ranged from 8.9 mg/kg at ELDA15, 180°/2000m to 16.3 mg/kg at ELDA6, 180°/500m. Olefins were also detected at the three stations analysed, and ranged from 0.4 mg/kg to 0.9 mg/kg. In 2002 the mean THC concentrations ranged from 6.1 mg/kg at ELDA8, 180°/2000m to 33 mg/kg at ELDA6, 180°/500m. Olefins were also detected at the four stations analysed, and ranged from 0.9 mg/kg to 1.3 mg/kg.

In the present survey the content of THC has decreased for all the stations analysed, compared to with previous surveys. The mean concentrations of THC vary from 4.3 mg/kg (ELDA7, 180°/870m) to 120 mg/kg (ELDA4, 360°/250m). The THC concentrations are low at most of the stations, either below or just above the limit of contamination. However, elevated concentrations are found at ELDA4, 360°/250m (120 mg/kg), at ELDA6, 180°/370m (11.2 mg/kg) and ELDA13, 90°/250m (14 mg/kg). Elevated THC concentrations are also found in the vertical sections at ELDA6; 20 mg/kg and 23 mg/kg respectively. Thus elevated levels of THC are observed out to 370m in the 180° direction and to 250m in the 90° and 360°.

Olefins are also detected at two stations analysed, from 0.5 mg/kg at ELDA6, 180°/370m to 0.6 mg/kg at ELDA14, 90°/500m. The concentrations have decreased since the previous survey in 2002. The last discharge of olefins was reported in 2000.

Representative gas chromatograms are given in Appendix C. These include ELDA4, 360°/250m, ELDA6, 180°/370m (all three layers), ELDA12, 270°/250m, ELDA13, 90°/250m and the reference station EKOC42, 90°/15000m.

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Eldfisk A, THC 2005

0

10

20

30

40

50

60

70

ELDA3 ELDA4 ELDA5 ELDA6 ELDA7 ELDA12 ELDA11 ELDA13 ELDA14 ELDA106 ECOC Ref.42

station

mg/kg

1999

2002

2005

LSC A

120±160

Figure 4.11.1. Bar diagram of the THC content in the sediments at Eldfisk 2/7 A/FTP 1999-2005. Table 4.11.3. Eldfisk 2/7 A/FTP 2005, total hydrocarbon content (mg/kg dry sediment).

Station Grab #1

Grab #2

Grab #3 Mean SD Mean Mean Mean Mean

2005 2005 2002 1999 1996 1995 ELDA3 360°/625m 5.0 4.7 4.7 4.8 0.2 8.3 ELDA4 360°/250m 34 21 306 120 160 5.9 ELDA5 180°/250m 2.9 13.1 8.4 8.2 5.1 21.5 ELDA6 180°/370m 13.9 8.3 11.2 11.2 2.8 33 16.3 18.8 1-3 cm 20 48 3-6 cm 23 52 ELDA7 180°/870m 3.1 4.2 5.8 4.3 1.4 7.6 11.8 10.2 ELDA12 270°/250m 12.8 8.1 4.0 8.3 4.4 6.9 ELDA11 270°/500m 7.5 7.6 4.5 6.6 1.8 ELDA13 90°/250m 9.6 17.2 15.3 14.0 3.9 73.1 ELDA14 90°/500m 9.0 7.3 6.8 7.7 1.1 16.9 ELDA106 180°/500m 5.8 5.4 5.8 5.7 0.2

90°/15000m 6.2 5.3 4.4 5.8 1.0 5.9 5.5 6.4 ECOC Ref. 42 LSC Subegion A 6.6 6.4 9

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Table 4.11.4. Eldfisk 2/7 A/FTP 2005, olefins (mg/kg dry sediment). Station Grab #1 Grab #2 Grab #3 Mean SD Mean Mean

2005 2005 2002 1999 ELDA6 180°/370m 0.7 <0.5 <0.5 0.5 1.3 0.9 1-3 cm 0.5 <0.6 0.9 3-6 cm 0.6 <0.6 0.9 ELDA11 270°/500m <0.5 <0.5 <0.5 <0.5 ELDA14 90°/500m 0.7 0.6 0.5 0.6 0.1 1.3

NPD, PAH and decalins One station is analysed, ELDA6, 180°/500m. Also incuded for analysis are grab sample #3 at station ELDA4, 360°/250m, as this has a THC content >50 mg/kg. The results are shown in Table 4.11.5.

In 1999 elevated concentrations of NPD and decalins were found at ELDA6, 180°/500m. Elevated concentrations of PAH were not found. In 2002 the concentrations of NPD and PAH were similar to the 1999 survey. The content of decalins had increased considerably to 2.5 mg/kg in the top layer, 4.2 mg/kg in the 1-3 cm layer and 4.6 mg/kg in the 3-6 cm layer.

In the present survey the mean NPD and PAH concentrations at ELDA6 have only increased slightly since 2002 to 0.10 mg/kg of NPD and 0.22 mg/kg of PAH (due to high concentration in one grab sample).

The content of decalins has decreased in the same period for all three layers. The concentration in the top layer has decreased to 0.6 mg/kg. However, an elevated level of decalins in the vertical layers is still observed (2.5 mg/kg in the 1-3 cm layer). These trends are in agreement with the THC results.

Elevated levels of NPD (0.21 mg/kg) and decalins (33 mg/kg) are observed at ELDA4 (grab #3). The relatively high concentration of decalins (33 mg/kg) confirms the high level of THC (306 mg/kg) found in this sample. The content of PAH in this sample is low, below the limit of contamination. Table 4.11.5. Eldfisk 2/7 A/FTP 2005, sum NPD, PAH and decalins (mg/kg dry sediment). Station Grab #1 Grab #2 Grab #3 Mean SD Mean SD Mean SD Mean 2005 2005 2002 2002 1999 1999 1996 NPD ELDA6 180°/370m 0.25 0.03 0.03 0.10 0.13 0.051 0.01 0.062 0.00 0.076 1-3cm 0.05 0.071 0.043 0.080 3-6cm 0.08 0.057 0.042 0.14 ELDA4 360°/250m 0.21 LSC Subregion A 0.030 0.026 0.040 PAH ELDA6 180°/370m 0.55 0.06 0.06 0.22 0.3 0.053 0.01 0.064 0.01 0.042 1-3cm 0.094 0.064 0.049 0.083 3-6cm 0.16 0.060 0.053 0.076 ELDA4 360°/250m 0.024 LSC Subregion A 0.061 0.062 0.090 Decalins ELDA6 180°/370m 0.5 0.74 0.75 0.6 0.2 2.5 1.7 0.084 0.02 0.17 1-3cm 2.5 4.2 0.10 0.12 3-6cm 1.4 4.6 0.12 0.20 ELDA4 360°/250m 32.8

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Metals

The results are shown in Table 4.11.6. For comparison, data from the present survey and previous surveys in 2002, 1999 and 1996 are included in Table 4.11.7. Bar diagram of the Ba content in the sediments is shown in Figure 4.11.2.

In 1999 the Ba concentrations ranged from 189 mg/kg at ELDA1, 360°/2000m to 1130 mg/kg at ELDA6, 180°/500m and in 2002 the Ba concentrations ranged from 111 mg/kg at ELDA8, 180°/2000m to 1540 mg/kg at ELDA14, 90°/500m.

In the present survey the Ba concentrations vary from 590 mg/kg at ELDA3, 360°/625m to 1699 mg/kg at ELDA11, 270°/500m. Elevated Ba concentrations are found at all stations, except for the reference station. This means out to 625m in the 360° direction, to 500m in the 90° and 270° and to 370m in the 180° directions. The concentrations are similar to previous surveys. This is also in agreement with the drilling history. No discharge of barite has taken place since 2000. As in 2002 the highest Ba concentrations were found in the 1-3 cm layer and 3-6 cm layer at ELDA6, 180°/500m, 1820 mg/kg and 2600 mg/kg respectively. The concentrations of the heavy metals are low, and no increases are observed since 2002. Slightly elevated concentrations of Pb and Zn are found, also in the vertical layers.

Eldfisk A, Ba 2005

0

200

400

600

800

1000

1200

1400

1600

1800

2000

ELDA3 ELDA6 ELDA11 ELDA14 EKOC42 Ref.

station

mg/kg

1999

2002

2005

LSC A

1699±5751130±90

Figure 4.11.2. Bar diagram of the Ba content in the sediments at Eldfisk 2/7 A/FTP 1999- 2005. The following variation is found at Eldfisk 2/7 A/FTP in the top layer, 0-1 cm. The values are given in mg/kg: Eldfisk 2/7 A/FTP: ELDA3 – ELDA14 EKO42 Reference station Ba: 590 - 1699 46 Cr: 6.7 – 7.6 7.6 Cu: 0.7 – 1.4 <0.5 Pb: 9.7 – 13.5 6.1 Zn: 7.6 – 11.7 5.4 Cd: <0.01 <0.01 Hg: ~0.03 <0.01

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Table 4.11.6. Eldfisk 2/7 A/FTP 2005, metals (mg/kg dry sediment). Station Sample Ba Cd Cr Cu Hg Pb Zn 2005 2005 2005 2005 2005 2005 2005 ELDA3 360°/625m 1 363 <0.01 6.6 0.8 10.0 7.2 2 537 <0.01 7.1 0.7 9.6 8.1 3 869 <0.01 6.6 0.6 9.5 7.4 Mean 590 <0.01 6.7 0.7 9.7 7.6 SD 257 0.3 0.1 0.3 0.5 ELDA6 180°/370m 1 1435 <0.01 7.3 1.1 <0.01 10.2 10.0 2 544 <0.01 7.2 1.1 0.06 9.9 9.3 3 1041 <0.01 7.6 1.2 0.01 10.9 10.9 Mean 1007 <0.01 7.3 1.2 0.03 10.3 10.1 SD 446 0.2 0.1 0.5 0.8 1-3 cm 1 1820 0.02 8.5 1.6 0.03 12.3 13.5 3-6 cm 1 2599 0.03 9.1 2.0 0.02 15.8 21.8 ELDA11 270°/500m 1 1404 0.01 7.0 1.0 9.3 9.1 2 2362 <0.01 7.7 1.5 11.6 12.8 3 1332 <0.01 7.1 0.8 11.9 8.6 Mean 1699 <0.01 7.2 1.1 10.9 10.2 SD 575 0.4 0.4 1.4 2.3 ELDA14 90°/500m 1 1719 <0.01 7.3 1.4 13.8 10.9 2 1458 <0.01 7.6 1.4 13.5 12.5 3 1760 <0.01 7.7 1.5 13.2 11.6 Mean 1646 7.6 1.4 13.5 11.7 SD 164 0.2 0.1 0.3 0.8

90°/15000m 1 52 <0.01 7.7 <0.5 0.01 6.6 5.6 EKO42 Ref. 2 77 <0.01 8.0 0.5 <0.01 6.3 5.8 3 37 <0.01 7.5 <0.5 <0.01 6.4 5.0 4 36 <0.01 7.4 <0.5 0.01 5.5 5.6 5 29 <0.01 7.4 <0.5 <0.01 5.7 4.9 Mean 46 <0.01 7.6 <0.5 <0.01 6.1 5.4 SD 19 0.3 0.5 0.4 1 50 <0.01 8.1 <0.5 <0.01 6.4 5.8 1 72 <0.01 8.0 <0.5 <0.01 6.6 5.8 LSC, Subregion A 76.2 8.0 1.3 7.4 6.9 Table 4.11.7. Eldfisk 2/7 A/FTP 2005, metals (mg/kg dry sediment), comparing mean values with previous surveys. Station Ba Ba Ba Ba Cd Cd Cd Cr Cr Cr 2005 2002 1999 1996 2005 2002 1999 2005 2002 1999 ELDA3 360°/625m 590 593 <0.01 0.01 6.7 6.7 ELDA6 180°/370m 1007 1150 1130 2390 <0.01 0.02 <0.03 7.3 7.2 7.8 1-3 cm 1820 2330 1280 0.02 0.04 <0.02 8.5 7.9 7.2 3-6 cm 2599 2600 2740 0.03 0.04 0.03 9.1 7.6 8.0 ELDA11 270°/500m 1699 <0.01 7.2 ELDA14 90°/500m 1646 1540 <0.01 0.02 7.6 7.5 EKO42 Ref. 90°/15000m 46 72 41 67 <0.01 <0.01 <0.02 7.6 7.7 7.1 1-3 cm 50 88 50 <0.01 <0.01 <0.02 8.1 7.7 7.2 3-6 cm 72 331 141 <0.01 0.01 <0.02 8.0 8.1 7.8 cont.

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Table 4.11.7. cont. Station Cu Cu Cu Hg Hg Hg Pb Pb Pb Zn Zn Zn

2005 2002 1999 2005 2002 1999 2005 2002 1999 2005 2002 1999ELDA3 360°/625m 0.7 1.5 9.7 9.3 7.6 10.2 ELDA6 180°/370m 1.2 2.4 1.4 0.03 0.02 0.02 10.3 10.2 14.5 10.1 10.6 13.7 1-3 cm 1.6 2.7 1.1 0.03 0.02 0.04 12.3 14.6 14.3 13.5 18.8 12.1 3-6 cm 2.0 2.7 1.9 0.02 0.03 0.03 15.8 15.3 17.5 21.8 19.0 20.7 ELDA11 270°/500m 1.1 10.9 10.2 ELDA14 90°/500m 1.4 2.4 13.5 14.0 11.7 12.5

EKO42 Ref. 90°/15000m <0.5 1.0 0.5 <0.01 <0.01 <0.01 6.1 6.3 6.1 5.4 5.6 4.7 1-3 cm <0.5 1.1 0.5 <0.01 0.01 <0.01 6.4 6.3 6.0 5.8 5.6 5.1 3-6 cm <0.5 1.8 0.8 <0.01 <0.01 <0.01 6.6 7.2 7.3 5.8 6.9 5.8

4.11.3 Biological analyses

A total of 143 species and 11171 individuals were sampled at 4 stations. Greatest abundance (78.7 %) was found among the polychaetes, of which the species Myriochele oculata constitutes 64.9 %, see Table 4.11.8. There were also high abundances of the brittle star Amphiura filiformis which constituted 76.8 % of the total number of Echinodermata. The bristle worm Paramphinome jeffreysii constituted 13.9 % of the total number of Polychaeta, which is a relatively high abundance. Table 4.11.8. Number of species and individuals distributed between the main groups, including juv., Eldfisk 2/7 A/FTP/E 2005.

Individuals Species Main animal groups Number % Number %

Varia 535 4.8 11 7.7Polychaeta 8789 78.7 65 45.5- Paramphinome jeffreysii 1223 13.9 - Myriochele oculata 5700 64.9 Crustacea 116 1.0 27 18.9Mollusca 780 7.0 31 21.7Echinodermata 951 8.5 9 6.3- Amphiura filiformis 730 76.8 Total 11171 100.0 143 100.0

Figure 4.11.3 shows the numbers of species and individuals sampled at each station and variations between grab samples.

0

20

40

60

80

100

ELDA-03

ELDA-06

ELDA-11

ELDA-14

Stations

No.

of s

peci

es (S

)

Station º/m ELDA-03 360/625 ELDA-06 180/370 ELDA-11 270/500 ELDA-14 90/500

Figure 4.11.3. Numbers of species (S) and individuals (N) per 0.5 m2 (incl./excl. P. jeffreysii and M. oculata), mean values per grab sample and standard deviation, Eldfisk 2/7 A/FTP/E 2005.

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0

800

1600

2400

3200

4000

ELDA-03

ELDA-06

ELDA-11

ELDA-14

Stations

No.

of i

ndiv

idua

ls (N

) Ex. P. jeffreysii and M. oculata

01000200030004000

ELDA-03

ELDA-06

ELDA-11

ELDA-14

Stations

No.

of i

ndiv

idua

ls (N

)

Figure 4.11.3. Cont.

The standard deviation is dramatically reduced when the two species P. jeffreysii and M. oculata are removed. This is evident since the two species constitute 62.0 % of the total number of individuals. Though, at station ELDA-06 the standard deviation actually increased slightly. This is due to relatively large differences between the numbers of individuals in the five grabs sampled.

Diversity and dominant species

The dominant species at each station varied from 32.0 % at ELDA-06 (180°/370m) to 65.7 % at ELDA-14 (90°/500m). The 10 most abundant species made up from 82.2 % at ELDA-11 (270°/500m) to 91.6 % at ELDA-06, see Table 4.11.9. The bristle worm M. oculata dominated the fauna at the Eldfisk A field, followed by the bristle worms P. jeffreysii and Apistobranchus tullbergi and the brittle star A. filiformis. Other frequently found species were the bristle worms Ditrupa arietina and Chaetozone setosa and the ribbon worms (Nemertea). D. arietina, M. oculata and A. filiformis are suspension feeders, while A. tullbergi and C. setosa are known as mixed feeders (both suspension and deposit feeders). P. jeffreysii is mainly a carnivore species and the ribbon worms are deposit feeders. M. oculata, C. setosa, P. jeffreysii, Nemertea and A. filiformis are all known indicators of organic pollution when they are found in high numbers. D. arietina and A. tullbergi are known as more sensitive species. However, several of the above mentioned species have a planktonic developmental stage and are able to settle in large numbers. Juvenile Echinoidea were also present in relatively vast amounts at three of the stations (ELDA-03, ELDA-11 and ELDA-14). Thus in further analyses, these are excluded because they are not representative of the benthic fauna. Table 4.11.9. The 10 most abundant species at each station, Eldfisk 2/7 A/FTP/E 2005. 10 most dominating species ELDA-03 No. % Cum. % ELDA-06 No. % Cum. %Myriochele oculata 2300 62.7 62.7 Myriochele oculata 800 32.0 32.0Paramphinome jeffreysii 412 11.2 73.9 Apistobranchus tullbergi 339 13.6 45.6Ditrupa arietina 183 5.0 78.9 Ditrupa arietina 274 11.0 56.5Amphiura filiformis 180 4.9 83.8 Paramphinome jeffreysii 260 10.4 66.9Echinoidea spp.juv. 66 1.8 85.6 Amphiura filiformis 255 10.2 77.1Scoloplos armiger 43 1.2 86.8 Nemertea spp. 180 7.2 84.3Phoronis muelleri 33 0.9 87.7 Scalibregma inflatum 56 2.2 86.6Cerianthus lloydii 26 0.7 88.4 Chaetozone setosa 49 2.0 88.5Trichobranchus roseus 23 0.6 89.0 Tharyx sp. 44 1.8 90.3Chaetozone setosa 23 0.6 89.6 Tunicata spp. 33 1.3 91.6 Cont.

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Table 4.11.9. Cont. ELDA-11 No. % Cum. % ELDA-14 No. % Cum. %Myriochele oculata 700 40.9 40.9 Myriochele oculata 1900 65.7 65.7Paramphinome jeffreysii 292 17.1 57.9 Paramphinome jeffreysii 259 9.0 74.7Amphiura filiformis 234 13.7 71.6 Amphiura filiformis 61 2.1 76.8Apistobranchus tullbergi 38 2.2 73.8 Apistobranchus tullbergi 59 2.0 78.8Echinoidea spp.juv. 28 1.6 75.5 Echinoidea spp.juv. 56 1.9 80.8Goniada maculata 28 1.6 77.1 Chaetozone setosa 39 1.4 82.1Chaetozone setosa 27 1.6 78.7 Nemertea spp. 30 1.0 83.2Thyasira flexuosa 23 1.3 80.0 Mysella bidentata 27 0.9 84.1Trichobranchus roseus 21 1.2 81.3 Phoronis muelleri 26 0.9 85.0Scoloplos armiger 17 1.0 82.2 Thyasira flexuosa 25 0.9 85.9

The number of species varied from 63 at ELDA-06 (180°/370m) to 90 at ELDA-11 (270°/500m). The number of individuals varied from 1677 at ELDA-11 to 3580 at ELDA-3 (360°/625m). The Shannon Wiener diversity index varied from 2.4 at ELDA-3 to 3.4 at ELDA-11 and the Hurlberts index (ES100) varied from 16 (ELDA-3 and ELDA-6) to 23 (ELDA-11) including M. oculata. Removal of M. oculata from the data gave higher biodiversity indices ranging from respectively 3.6 (ELDA-06) to 4.8 (ELDA-14 (90°/500m) and 16 (ELDA-03 and -06) to 35 (ELDA-14). Indices above 4 indicate a relatively undisturbed fauna, while indices between 3 and 4 indicate a slight disturbance. Indices between 2 and 3 reflect distinct disturbances. In general ES100 indices above 20 characterize a relatively normal fauna. The observed indices, however, reflect a disturbance, see Table 4.11.10, also indicated by visual observations in field and during sample processing. Table 4.11.10. Numbers of individuals (N) and species (S), depth, Shannon-Wiener diversity index (H’), Pielou’s evenness index (J), and expected number of species per 100 individuals (ES100) for each station at Eldfisk 2/7 A/FTP/E 2005 (excl. juv.).

H' ES100 Station Direction ° Distance m Depth S N Incl.

M. o. Excl. M. o.

J Incl. M. o.

Excl. M. o.

ELDA-03 360 625 74 88 3580 2.4 4.2 0.4 16 30ELDA-06 180 370 75 63 2486 3.3 3.6 0.6 16 18ELDA-11 270 500 74 90 1677 3.4 4.2 0.5 23 32ELDA-14 90 500 74 83 2833 2.5 4.8 0.4 19 35M. o.= M. oculata

In general the reduced biodiversity indices at Eldfisk A reflect some disturbance in the fauna community, which are probably due to both a physical disturbance as well as a diffuse organic load in the area affecting the biodiversity.

Classification and ordination

The dendrogram from the cluster analysis and the MDS plot from the ordination analysis based on grab samples are presented in Figure 4.11.4 and Figure 4.11.5. Only the dendrogram and MDS plot from grab level are shown, because the data set contains only 4 stations and the analysis at station level show the same pattern as the grab level. The grabs divides in three groups mainly based on stations, at about 55 % similarity. The grab samples from ELDA-6 (180°/370m) in group 1 (similarity of about 70 %) differ most from the other grabs. Also the samples from ELDA-11 (270°/500m) form one group, group 3 (similarity of about 60 %). ELDA-3 (360°/625m) and ELDA-14 (90°/500m) are clustering together in group 2 at about 65 % similarity. The cluster analysis is well supported by the ordination analysis, see MDS plot in Figure 4.11.5.

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ELDA

6-1

ELDA

6-3

ELDA

6-5

E LDA

6-2

ELDA

6-4

ELDA

14-2

ELDA

1 4-4

ELDA

3-2

ELDA

3-4

ELD A

3-3

ELDA

3-1

ELDA

3-5

ELDA

14-3

ELDA

14-1

ELDA

14-5

ELDA

11- 2

ELDA

11-4

ELDA

11-5

E LDA

11-1

ELD A

11-3

100

90

80

70

60

50Si

mila

rity

Group 1 Group 2 Group 3Station ELDA-6(180/370m) Station ELDA-3(360/625m) and ELDA-14(90/500m) Station ELDA-11(270/500m)

Figure 4.11.4. Dendrogram of grab samples from Eldfisk 2/7 A/FTP/E 2005 (excl. juv.).

ELDA3-1

ELDA3-2

ELDA3-3

ELDA3-4ELDA3-5

ELDA6-1

ELDA6-2

ELDA6-3

ELDA6-4

ELDA6-5

ELDA11-1

ELDA11-2

ELDA11-3ELDA11-4

ELDA11-5

ELDA14-1

ELDA14-2

ELDA14-3

ELDA14-4ELDA14-5

Stress: 0,16

Group 1Station ELDA-6(180/370m)

Group 3Station ELDA-11(270/500m)

Group 2Station ELDA-3(360/625m) andELDA-14(90/500m)

Figure 4.11.5. MDS plot of grab samples from Eldfisk 2/7 A/FTP/E 2005.

A Simper analysis (Primer package) was performed to examine which species contributes most to the differences between the groups. The difference between ELDA-3 (360°/625m) and ELDA-14 (90°/500m) in group 2 and ELDA-6 (180°/370m) and ELDA-11 (270°/500m) in group 1 and 3 respectively is mainly due to significantly higher numbers of the bristle worm M. oculata at ELDA-3 and ELDA-14 in group 2. ELDA-6 differs from the others mainly because of a greater number of the bristle worms A. tullbergi and D. arietina and the ribbon worms Nemertea.

A Bioenv-analysis which connects the biological data with the chemical and physical data was performed on the data set. Bioenv calculates the combination of environmental factors which

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best correlates to the biological data. The results from the analysis gave a very high correlation between the fauna composition and a combination of total organic matter and the grain size (>0.9).

Comparison with 1996, 1999, 2002 and 2005

In Figure 4.11.6 the results from the present survey are compared to the results from previous surveys. The number of the bristle worm M. oculata is reduced at several fields since 2002 in the Ekofisk region. However, at Eldfisk A there has been a slight increase of this species since 2002. The biodiversity indices show minor changes since the last survey, see Figure 4.11.6.

The great variations in the presence of M. oculata from 1996 to 2005 have complicated the faunal picture, making it difficult to draw conclusions about the state of the fauna community. Adding the 2005 results to the trend data have, however, strengthened the data set, and has made it possible to obtain a pattern in the overall temporal variations in the entire region. This is described in Chapter X - General Trends in the Region, which forms a basis for the conclusions for each of the fields.

020406080

100

ELDA-03

ELDA-06

ELDA-11

ELDA-14

Stations

No.

of s

peci

es (S

)

1996 1999 2002 2005

Station º/m ELDA-03 360/625 ELDA-06 180/370 ELDA-11 270/500 ELDA-14 90/500

0

1000

2000

3000

4000

ELDA-03

ELDA-06

ELDA-11

ELDA-14

Stations

No.

of i

ndiv

idua

ls (N

)

1996 1999 2002 2005

0123456

ELDA-03

ELDA-106

ELDA-11

ELDA-14

Stations

H'

1996 19991999-ex.M.oculata 20022002-ex.M.oculata 20052005-ex.M.oculata

Figure 4.11.6. Numbers of species (S) and individuals (N) per 0.5 m2 and diversity (H’), incl. P. jeffreysii and M. oculata, excl. juv., Eldfisk 2/7 A/FTP/E 1996, 1999, 2002 and 2005∗.

Classification and ordination analyses

The sampled stations from all years have been analysed at family level∗. Most of the stations divide into two main groups at about 50 % similarity. The stations sampled in 2002 and 2005 are clustering together in group 1, while the other stations sampled in the earlier years form

∗ Indices from 1990 and 1993 are not available. ∗ Necessary when comparing between years, to avoid significant source of error due to both different years and

different taxonomists.

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group 2. The results from the similarity analysis reveal significant increases in the numbers of species within the families Oweniidae (mainly M. oculata), Amphinomidae (mainly P. jeffreysii) and the ribbon worm Nemertea in 2002 and 2005, together with a decrease in the numbers of species within the family Cirratulida (mainly C. setosa).

The temporal variations contribute the most to the differences between the two groups, indicating a shift in the fauna community to transition species (like M. oculata) which are somewhat less tolerant to organic enrichment. The dendrogram from the analysis of comparable stations is shown in Figure 4.11.7.

The numbers of individuals of the bristle worm P. jeffreysii in particular, but also the bristle worm A. tullbergi and the echinoderm A. filiformis have increased considerably since 2002, and are dominating the fauna at Eldfisk together with M. oculata in 2005. M. oculata, P. jeffreysii and A. filiformis all have a life cycle including a planktonic larval stage and are able to establish large populations. Also A. tullbergi probably has a planktonic larval stage, considering the great dispersal ability and abundance in the Ekofisk region.

ELDA

-06-

2002

E LDA

-03-

200 2

ELD A

-14-

2002

ELDA

-06-

2005

ELDA

-11-

2005

E LDA

-03-

200 5

ELD A

-14-

2005

ELD A

-06-

1996

ELDA

-06-

1 999

E LDA

-11-

199 0

ELDA

-03-

1990

ELDA

-06-

1990

ELD A

-14-

1990

ELDA

-03-

1993

E LDA

-06-

199 3

ELDA

-11-

1993

ELDA

-14-

1993

100

80

60

40

Sim

ilar it

y

Group 1 Group 2 Figure 4.11.7. Dendrogram showing similarity between Eldfisk A stations 1990, 1993, 1996, 1999, 2002 and 2005. Family level, incl. M. oculata, excl. juv., sq. root transformation.

4.11.4 Conclusion

The sediments at Eldfisk 2/7 A/FTP consist of fine sand, and the sand content varies from 92 % to 97 %. The gravel content is zero. The silt and clay content is similar to the previous surveys and the average silt and clay concentration is 5.7 %. The total organic matter content in the sediments is low. Only small variations are found at the field, from 0.88 % to 0.97 %. The concentrations are similar to the previous surveys and the content corresponds to the grain size distribution.

The THC content has decreased for all the stations analysed, compared to previous surveys. The mean THC concentrations vary from 4.3 mg/kg (ELDA7) to 120 mg/kg (ELDA4). Elevated

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THC concentrations are found at ELDA4, 360°/250m (120 mg/kg), at ELDA6, 180°/370m (11.2 mg/kg) and ELDA13, 90°/250m (14 mg/kg). Relatively high concentrations of THC are also found in the vertical sections at ELDA6; 20 mg/kg and 23 mg/kg respectively. Thus elevated levels of THC are observed out to 370m in the 180° direction and to 250m in the 90° and 360°. For the other stations, the THC content is low, either below or slightly above the limit of contamination.

Olefins are also detected at the two stations analysed, from 0.5 mg/kg at ELDA6, 180°/370m to 0.6 mg/kg at ELDA14, 90°/500m. The concentrations have decreased since the previous survey in 2002. The last discharge of olefins is reported in 2000.

The NPD and PAH concentrations at ELDA6, 180°/370m have only increased slightly since 2002 to 0.10 mg/kg of NPD and 0.22 mg/kg of PAH. The content of decalins has decreased in the same period for all three layers. However, elevated level of decalins in the vertical layers is still observed. These trends are in agreement with the THC results.

Elevated levels of NPD and decalins are observed at ELDA4 (grab #3). The relatively high concentration of decalins (33 mg/kg) confirms the high level of THC (306 mg/kg) found in this sample. The content of PAH in this sample is low, below the limit of contamination.

The Ba concentrations vary from 590 mg/kg at ELDA3, 360°/625m to 1699 mg/kg at ELDA11, 270°/500m. Elevated Ba concentrations are found at all stations. This means out to 625m in the 360° direction, to 500m in the 90° and 270° and to 370m in the 180° directions. The concentrations are similar to the previous surveys. This is in agreement with the drilling history. No discharge of barite has taken place since 2000.

The concentrations of the heavy metals are low, and no increases are observed since 2002. Slightly elevated concentrations of Pb and Zn are found, also in the deeper layers.

Mainly the chemical results are in correspondence with the drilling history at Eldfisk 2/7 A/FTP. No barite has been discharged since 2000.

In general the reduced biodiversity indices at Eldfisk A reflect some disturbance in the fauna community in 2005 out to 625 m from the field centre. A decline in the numbers of M. oculata in 2005 as described at several other fields in the area has not been the case at Eldfisk A and the biodiversity indices are almost unchanged since the survey in 2002. Taking the general trend in the region into account, the positive trend seems to go somewhat slower at Eldfisk A. However, there has been a shift in the fauna community from a fauna where C. setosa, a strong indicator species able to act as a deposit feeder, was the dominating species in the 1990’s towards a fauna community where the transition species M. oculata dominates the fauna together with a higher share of other suspenison feeding species. This development in the fauna indicates a slow improvement in the environment at Eldfisk A.

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4.12 Eldfisk 2/7 B

4.12.1 Sediment characterization

Grain size distribution

The grain size distribution from the present survey is given in Table 4.12.1 together with the silt and clay content from the previous surveys in 2002, 1999 and 1996.

The sediments at Eldfisk 2/7 B consist of fine sand, and the sand content is almost at the same level, varies from 95 % to 97 %. The gravel content is zero or very low. Silt and clay content is similar to the previous surveys. The average silt and clay concentration is 4.1 % compared to 5.6 % in 2002, 4.7 % in 1999 and 4.7 % in 1996 for the same stations. The results from the complete grain size distribution are given in Appendix C. Table 4.12.1. Eldfisk 2/7 B 2005, grain size distribution. Station Median

diameter Classification Grain size distrib. 2005

(%) 2002

(%) 1999 (%)

1996 (%)

Mdφ Silt and clay

Sand Gravel Silt and clay

Silt and clay

Silt and clay

ELDB3 360°/500m 2.78 Fine sand 4.0 96.0 0.0 4.5 5.6 ELDB6 180°/500m 2.80 Fine sand 4.3 95.7 0.0 5.4 5.1 4.7 ELDB11 270°/500m 2.75 Fine sand 3.6 96.4 0.0 6.4 4.5 ELDB14 90°/500m 2.79 Fine sand 4.6 95.3 0.1 6.1 3.6 EKO Ref. 42

90°/15000m 2.78 Fine sand 2.6 97.3 0.1 2.6 5.3 2.9

Mean (excl. ref. station) 2.78 Fine sand 4.1 95.9 5.6 4.7 4.7 Standard deviation 0.02 0.4 0.5 0.8 0.9

Total organic matter (TOM)

The content of TOM in the sediments is low. Only small variations are found at the field, from 0.88 % to 1.02 %. The concentrations are similar to the previous surveys. The content corresponds to the grain size distribution. The results are shown in Table 4.12.2. Table 4.12.2. Eldfisk 2/7 B 2005, total organic matter (% of dry sediment). Station 2005, 0-5 cm Mean 2002 SD

2002 Mean 1999 Mean

1996 ELDB3 360°/500m 0.88 0.98 0.01 0.75 ELDB6 180°/500m 0.92 0.96 0.01 1.07 0.78 ELDB11 270°/500m 1.02 0.88 0.09 0.81 ELDB14 90°/500m 0.89 0.88 0.11 0.81 EKO Ref. 42 90°/15000m 0.88 0.82 0.02 0.95 0.86

4.12.2 Chemical analyses

Parameters analysed in the sediments at Eldfisk 2/7 B:

• THC • Olefins • NPD, PAH, decalins • Metals (Ba, Cd, Cr, Cu, Hg, Pb, Zn)

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Three replicate samples at each station are analysed. The samples are taken from the top 0-1 cm sediment layer. In addition the 1-3 cm and 3- 6 cm sediment layers are sampled at three stations.

The sampling program was somewhat reduced based on the discharge history and previous results. The survey has focussed on stations close to the installation and four new stations at 250m were included.

THC and olefins

The THC results including olefins are shown in Table 4.12.3, and olefins are shown separately in Table 4.12.4. The corresponding THC data from the previous surveys in 2002, 1999 and 1996 are also included for comparison. Four new stations at a distance 250m from the platform are included in the survey. These are ELDB4, 360°/250m, ELDB5, 180°/250m, ELDB12, 270°/250m and ELDB13, 90°/250m. A bar diagram of the THC content in the sediments is shown in Figure 4.12.1.

In 1999 the mean THC concentrations ranged from 6.7 mg/kg at ELDB2, 360°/1000m to 22.0 mg/kg at ELDB6, 180°/500m. Olefins were detected at the four stations analysed, and ranged from 0.7 mg/kg at ELDB7, 180°/1000m and ELDB11, 270°/500m to 3.8 mg/kg at ELDB6, 180°/500m. In 2002 the mean THC concentrations ranged from 7.8 mg/kg at ELDB8, 180°/2000m to 16.4 mg/kg at ELDB14, 90°/500m. Olefins were detected at the four stations analysed, and ranged from 0.8 mg/kg at ELDB11, 270°/500m to 1.1 mg/kg at ELDB14, 90°/500m.

In the present survey the mean THC concentrations vary from 5.8 mg/kg at ELDB11, 270°/500m to 30 mg/kg at ELDB13, 90°/250m. Elevated THC content is observed at three of the new stations, respectively 15.8 mg/kg at ELDB5, 13.2 mg/kg at ELDB12 and 30 mg/kg at ELDB13. Thus elevated levels of THC are observed out to 500m in the 90° direction and to 250m in the 180° and 270° direction. For the other stations, the THC content is below or just above the limit of contamination. The THC content for these stations has decreased since 2002. Elevated THC concentrations are observed in the deeper sections at ELDB6 and ELDB13.

Olefins are detected at the three stations analysed, from 0.5 mg/kg at ELDB14 to 0.9 mg/kg at ELDB13. The content of olefins has decreased since the last survey. Similar to Eldfisk 2/7 A/FTP, additional hydrocarbons in the drilling mud base oil area is seen in some of the gas chromatograms. Olefins are seen in all the gas chromatograms. Representative gas chromatograms are given in Appendix C. These include, ELDB5, 180°/250m, ELDB6, 180°/500m, ELDB13, 90°/250m, ELDB14, 90°/500m and the reference station, EKO42, 90°/15000m.

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Eldfisk B, THC 2005

0

10

20

30

40

50

ELDB3 ELDB4 ELDB5 ELDB6 ELDB11 ELDB12 ELDB13 ELDB14 ECOC Ref.42

station

mg/kg

1999

2002

2005

LSC A

Figure 4.12.1. Bar diagram of the THC content in the sediments at Eldfisk 2/7 B 1999-2005. Table 4.12.3. Eldfisk 2/7 B 2005, total hydrocarbon content (mg/kg dry sediment). Station Grab

#1 Grab

#2 Grab

#3 Mean SD Mean Mean Mean

2005 2005 2002 1999 1996 ELDB3 360°/500m 5.8 6.2 7.6 6.5 1.0 11.6 8.5 ELDB4 360°/250m 7.9 7.2 7.5 7.5 0.3 ELDB5 180°/250m 22 15.1 10.5 15.8 5.7 1-3 cm 18.9 3-6 cm 23 ELDB6 180°/500m 6.2 5.8 6.5 6.1 9.3 15.0 22 12.7 1-3 cm 8.8 21 13.9 18.9 3-6 cm 22 23 19.2 26 ELDB11 270°/500m 6.0 6.3 5.2 5.8 0.6 12.2 11.9 ELDB12 270°/250m 16.0 11.6 12.1 13.2 2.4 ELDB13 90°/250m 22 32 37 30 8 1-3 cm 54 3-6 cm 76 ELDB14 90°/500m 10.0 12.5 11.1 11.2 1.3 16.4 14.1 ECOC Ref. 42 90°/15000m 6.2 5.3 4.4 5.8 1.0 5.9 5.5 6.4 LSC Subregion A 6.6 6.4 9

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Table 4.12.4. Eldfisk 2/7 A/FTP 2005, olefins (mg/kg dry sediment). Station Grab

#1 Grab

#2 Grab

#3 Mean SD Mean Mean

2005 2005 2002 1999 ELDB6 180°/500m 0.7 0.6 0.6 0.6 0.03 0.9 3.8 1-3 cm 1.0 3-6 cm 1.7 ELDB13 90°/250m 1.1 1.2 0.6 0.9 0.3 1-3 cm 2.8 3-6 cm 1.9 ELDB14 90°/500m <0.5 0.5 0.5 0.5 1.1 1.2

NPD, PAH and decalins

Three stations are analysed; ELDB5, 180°/250m, ELDB6, 180°/500m and ELDB13, 90°/250m. The results are shown in Table 4.12.5. Stations ELD5B and ELDB13 have not been analysed in previous surveys.

In 1999 elevated concentrations of NPD, PAH and decalins were found at ELDB6, 180°/500m.

In 2002 the content of NPD and PAH had decreased considerably at ELDB6, PAH to levels below the limit of contamination and NPD to levels slightly elevated. The content of decalins had increased from ~0.09 mg/kg in previous survey to 0.6 mg/kg in 2002. At ELDB6, high contents of decalins were also found in the deeper layers.

In the present survey low concentrations of NPD, PAH and decalins are found at ELDB6. The content of NPD and PAH in the top layer, 0-1 cm, is below the limit of contamination. However, elevated level of decalins is found in the deeper layers, particular in the 3-6 cm layer (0.7 mg/kg). The content of NPD, PAH and decalins has decreased considerably since 2002. NPD and PAH concentrations are also low at ELDB5 and ELDB13, but the content increases slightly down in the sediment. The content of decalins is relatively high, 0.52 mg/kg at ELDB5, 180°/250m and 1.8 mg/kg at ELDB13, 90°/250m. Relatively high contents are also found in the deeper layers, up to 2.6 mg/kg at ELDB13 in the 1-3 cm layer.

Usually high content of decalins is related to the THC content, as the base oil and diesel contain decalins. Thus, the relatively high content of decalins found is in agreement with the relatively high content of THC observed at stations ELDB5 and ELDB13.

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Table 4.12.5. Eldfisk 2/7 B 2005, sum NPD, PAH and decalins (mg/kg dry sediment).

Station Grab #1

Grab #2

Grab #3

Mean SD Mean SD Mean SD Mean

2005 2005 2002 2002 1999 1999 1996NPD ELDB5 180°/250m 0.08 0.07 0.07 0.07 0.01 1-3 cm 0.09 3-6 cm 0.07 ELDB6 180°/500m 0.04 0.02 0.03 0.03 0.01 0.060 0.018 0.44 0.66 0.062 1-3 cm 0.04 0.061 0.070 0.095 3-6 cm 0.07 0.070 0.078 0.093ELDB13 90°/250m 0.15 0.10 0.10 0.12 0.03 1-3 cm 0.11 3-6 cm 0.16 LSC Subregion A 0.030 0.026 0.040 PAH

ELDB5 180°/250m 0.09 0.06 0.07 0.07 0.018

1-3 cm 0.11 3-6 cm 0.08

ELDB6 180°/500m 0.03 0.03 0.03 0.03 0.004 0.056 0.008 0.86 1.250 0.058

1-3 cm 0.06 0.061 0.11 0.068

3-6 cm 0.12 0.102 0.129 0.095

ELDB13 90°/250m 0.08 0.07 0.07 0.07 0.006

1-3 cm 0.11 3-6 cm 0.17

LSC Subregion A 0.061 0.062 0.090

Decalins ELDB5 180°/250m 0.50 0.85 0.20 0.52 0.32 1-3 cm 0.69 3-6 cm 0.74

ELDB6 180°/500m 0.05 0.06 0.08 0.07 0.01 0.63 0.357 0.091 0.044 0.088

1-3 cm 0.14 0.99 0.058 0.16

3-6 cm 0.69 0.48 0.11 0.53 ELDB13 90°/250m 1.52 2.26 1.63 1.80 0.40 1-3 cm 2.57 3-6 cm 1.65 Limit of detection for NPD is 0.01 mg/kg, for PAH 0.005 mg/kg and for decalins 0.1mg/kg.

Metals

The results are shown in Table 4.12.6. For comparison, data from the present survey and previous surveys in 2002, 1999 and 1996 are included in Table 4.12.7. Bar diagram of the Ba content in the sediments is given in Figure 4.12.2.

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In 1999 the Ba concentrations ranged from 221 mg/kg at ELDB8, 180°/2000m to 1740 mg/kg at ELDA14, 90°/500m. In 2002 the Ba concentrations ranged from 213 mg/kg at ELDB8, 180°/2000m to 1850 mg/kg at ELDB14, 90°/500m.

In the present survey the Ba concentrations vary from 644 mg/kg at ELDB3, 360°/500m to 1706 mg/kg at ELD14, 90°/500m. The content of Ba is similar to the previous survey, and elevated concentrations are found at all stations. This means out to 500m in all directions investigated. Maximum Ba concentration (2674 mg/kg) is found in the 3-6 cm layer at ELDB6, 180°/500m.

The concentrations of the heavy metals are low, and no increase is observed since 2002. Slightly elevated concentrations of Pb and Zn are found, also in the deeper layers.

Eldfisk B, Ba 2005

0

500

1000

1500

2000

2500

ELDB3 ELDB6 ELDB11 ELDB14 EKOC42 Ref

station

mg/kg

1999

2002

2005

LSC A

Figure 4.12.2. Bar diagram of the Ba content in the sediments at Eldfisk 2/7 B 1999-2005. The following variation is found at Eldfisk 2/7 B in the top layer, 0-1 cm. The values are given in mg/kg: Eldfisk 2/7 B: ELDB3 – ELDB14 EKO42 Reference station Ba: 644 - 1706 46 Cr: 4.8 – 7.2 7.6 Cu: 0.7 – 1.2 <0.5 Pb: 7.0 – 14.4 6.1 Zn: 5.8 – 10.4 5.4 Cd: <0.01 <0.01 Hg: <0.01 <0.01

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Table 4.12.6. Eldfisk 2/7 B 2005, metals (mg/kg dry sediment). Station Sample Ba Cd Cr Cu Hg Pb Zn 2005 2005 2005 2005 2005 2005 2005 ELDB3 360°/500m 1 683 <0.01 7.3 0.9 8.9 7.4 2 664 <0.01 7.2 0.7 9.7 7.0 3 586 <0.01 7.2 0.8 9.1 8.0 mean 644 <0.01 7.2 0.8 9.2 7.5 SD 52 0.0 0.1 0.4 0.5 ELDB6 180°/500m 1 1030 <0.01 6.2 0.9 <0.01 9.8 7.9 2 872 <0.01 5.9 0.7 0.02 9.6 7.5 3 1344 <0.01 7.2 2.1 <0.01 12.9 9.6 mean 1082 <0.01 6.4 1.2 <0.01 10.8 8.3 SD 240 0.7 0.8 1.9 1.1 1-3 cm 1 1109 <0.01 6.7 0.9 <0.01 10.7 8.2 3-6 cm 1 2674 0.02 7.7 1.6 0.01 15.2 12.6 ELDB11 270°/500m 1 114 <0.01 0.7 0.1 1.0 0.8 2 1491 <0.01 6.8 1.0 10.2 8.3 3 1412 <0.01 7.0 1.0 9.9 8.2 mean 1005 <0.01 4.8 0.7 7.0 5.8 SD 773 3.6 0.5 5.2 4.3 ELDB14 90°/500m 1 1247 <0.01 7.1 1.2 13.6 10.5 2 1588 <0.01 7.2 1.0 14.5 10.5 3 2283 0.01 7.1 1.5 14.9 10.2 mean 1706 <0.01 7.2 1.2 14.4 10.4 SD 528 0.0 0.2 0.6 0.2 EKO42 Ref. 90°/15000m 1 52 <0.01 7.7 <0.5 0.01 6.6 5.6 2 77 <0.01 8.0 0.5 <0.01 6.3 5.8 3 37 <0.01 7.5 <0.5 <0.01 6.4 5.0 4 36 <0.01 7.4 <0.5 0.01 5.5 5.6 5 29 <0.01 7.4 <0.5 <0.01 5.7 4.9 Mean 46 <0.01 7.6 <0.5 <0.01 6.1 5.4 SD 19 0.3 - 0.5 0.4 1 50 <0.01 8.1 <0.5 <0.01 6.4 5.8 1 72 <0.01 8.0 <0.5 <0.01 6.6 5.8 LSC Subregion A 76.2 8.0 1.3 7.4 6.9 Table 4.12.7. Eldfisk 2/7 B 2005, metals (mg/kg), comparing mean values with previous surveys. Station Ba Ba Ba Ba Cd Cd Cd Cr Cr Cr

2005 2002 1999 1996 2005 2002 1999 2005 2002 1999ELDB3 360°/500m 644 1020 1000 <0.01 0.01 <0.02 7.2 6.9 6.2 ELDB6 180°/500m 1082 1480 1460 1630 <0.01 0.02 <0.02 6.4 6.1 7.1 1-3 cm 1109 1730 1500 <0.01 0.03 0.02 6.7 6.1 6.6 3-6 cm 2674 2740 2930 0.02 0.03 0.03 7.7 7.0 6.9 ELDB11 270°/500m 1005 1210 1450 <0.01 0.01 <0.02 4.8 ELDB14 90°/500m 1706 1850 1740 <0.01 0.02 <0.02 7.2 6.8 7.3 EKO42 Ref. 90°/15000m 46 72 41 67 <0.01 <0.01 <0.02 7.6 7.7 7.1 1-3 cm 50 88 50 <0.01 <0.01 <0.02 8.1 7.7 7.2 3-6 cm 72 331 141 <0.01 0.01 <0.02 8.0 8.1 7.8 cont.

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Table 4.12.7. cont. Station Cu Cu Cu Hg Hg Hg Pb Pb Pb Zn Zn Zn 2005 2002 1999 2005 2002 1999 2005 2002 1999 2005 2002 1999ELDB3 360°/500m 0.8 1.7 0.6 9.2 9.5 8.7 7.5 9.3 6.2 ELDB6 180°/500m 1.2 1.9 1.2 0.01 0.02 0.03 10.8 10.3 12.6 8.3 13.6 13.1 1-3 cm 0.9 1.9 1.1 <0.01 0.02 0.02 10.7 11.1 12.3 8.2 9.7 12.3 3-6 cm 1.6 3.7 1.2 0.01 0.03 0.04 15.2 15.3 13.5 12.6 19.0 12.1ELDB11 270°/500m 0.7 1.9 1.1 7.0 10.6 12.8 5.8 10.7 9.3 ELDB14 90°/500m 1.2 2.5 1.4 14.4 15.6 17.3 10.4 14.3 11.4EKO42 Ref.

90°/15000m <0.5 1.0 0.5 <0.01 <0.01 <0.01 6.1 6.3 6.1 5.4 5.6 4.7

1-3 cm <0.5 1.1 0.5 <0.01 0.01 <0.01 6.4 6.3 6.0 5.8 5.6 5.1 3-6 cm <0.5 1.8 0.8 <0.01 <0.01 <0.01 6.6 7.2 7.3 5.8 6.9 5.8

4.12.3 Biological analyses

A total of 141 species and 10227 individuals were sampled at 4 stations. Greatest abundance (80.4 %) was found among the polychaetes, of which the species Myriochele oculata constitutes about 58.2 % see Table 4.12.8. There was also high abundance of the brittle star Amphiura filiformis which constituted 70.2 % of the total number of Echinodermata. The bristle worm Paramphinome jeffreysii constituted 20.1 % of the total number of Polychaeta, which is a relatively high abundance. Table 4.12.8. Number of species and individuals distributed between the main groups, Eldfisk 2/7 B 2005.

Individuals Species Main animal groups Number % Number %

Varia 448 4.4 10 7.1Polychaeta 8220 80.4 69 48.9- Paramphinome jeffreysii 1651 20.1 - Myriochele oculata 4780 58.2 Crustacea 100 1.0 23 16.3Mollusca 644 6.3 30 21.3Echinodermata 815 8.0 9 6.4- Amphiura filiformis 572 70.2 Total 10227 100.0 141 100.0

Figure 4.12.3 shows the numbers of species and individuals sampled at each station and variations between grab samples.

0

800

1600

2400

3200

4000

ELDB-03

ELDB-06

ELDB-11

ELDB-14

Stations

No.

of i

ndiv

idua

ls (N

)

020406080

100120

ELDB-03

ELDB-06

ELDB-11

ELDB-14

Stations

No.

of s

peci

es (S

)

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Ex. P. jeffreysii

0800

1600240032004000

ELDB-03

ELDB-06

ELDB-11

ELDB-14

Stations

No.

of i

ndiv

idua

ls (N

)

Ex. P. jeffreysii and M. oculata

0800

1600240032004000

ELDB-03

ELDB-06

ELDB-11

ELDB-14

Stations

No.

of i

ndiv

idua

ls (N

)

Station º/m Station º/m ELDB-03 360/500 ELDB-11 270/500

ELDB-06 180/500 ELDB-14 90/500 Figure 4.12.3. Numbers of species (S) and individuals (N) per 0.5 m2 (incl./excl. P. jeffreysii and M. oculata), mean values per grab sample and standard deviation, Eldfisk 2/7 B 2005.

The standard deviation was dramatically reduced when the two species P. jeffreysii and M. oculata were removed. This is evident since the two species constitute 62.9 % of the total number of individuals.

Diversity and dominant species

The dominant species at each station varied from 41.1 % at station ELDB-11 (270°/500m) to 52.3 % at ELDB-06 (180°/500m). The 10 most abundant species made up from 82.4 % at ELDB-06 to 87.3 % at ELDB-03 (360°/500m), see Table 4.12.9. The bristle worm M. oculata dominated the fauna at the Elda B field followed by the bristle worm P. jeffreysii and the brittle star A. filiformis, except at ELDB-03 where number of A.filiformis was exceeded by the bristle worm Ditrupa arietina. Other frequently found species were amongst others the bristle worms Apistobranchus tullbergi, Chaetozone setosa, Scoloplos armiger and Levinsenia gracilis, the ribbon worms (Nemertea) and the Phoronid (worm) Phoronis mulleri. P. mulleri, D. arietina, M. oculata and A. filiformis is suspension feeders, while A. tullbergi, S. armiger, C. setosa and L. gracilis are known as mixed feeders (both suspension and deposit feeders). P. jeffreysii is mainly a carnivore species and the ribbon worms are deposit feeders. M. oculata, C. setosa, S. armiger, P. jeffreysii, Nemertea and A. filiformis are all known indicators of organic pollution when they are found in high numbers. D. arietina and A. tullbergi are known as more sensitive species. However several of the above mentioned species have a planktonic developmental stage and are able to settle in large numbers. Juvenile Echinoidea were also present in relatively vast amounts at three of the stations (ELDA-03, ELDA-11 and ELDA-14). These are excluded from further analyses because they are not representative for the benthic fauna. Table 4.12.9. The 10 most abundant species at each station, Eldfisk 2/7 B 2005. 10 most dominating species ELDB-03 No. % Cum. % ELDB-06 No. % Cum. % Myriochele oculata 1650 50.4 50.4 Myriochele oculata 1100 52.3 52.3 Paramphinome jeffreysii 410 12.5 62.9 Paramphinome jeffreysii 304 14.5 66.8 Ditrupa arietina 287 8.8 71.7 Amphiura filiformis 104 5.0 71.7 Amphiura filiformis 203 6.2 77.9 Scoloplos armiger 38 1.8 73.6 Echinoidea spp.juv. 75 2.3 80.2 Chaetozone setosa 35 1.7 75.2 Levinsenia gracilis 62 1.9 82.1 Apistobranchus tullbergi 34 1.6 76.8 Apistobranchus tullbergi 52 1.6 83.7 Trichobranchus roseus 31 1.5 78.3

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Nemertea spp. 43 1.3 85.0 Levinsenia gracilis 29 1.4 79.7 Phoronis muelleri 38 1.2 86.2 Thyasira flexuosa 28 1.3 81.0 Scoloplos armiger 38 1.2 87.3 Phoronis muelleri 28 1.3 82.4 ELDB-11 No. % Cum. % ELDB-14 No. % Cum. % Myriochele oculata 950 41.1 41.1 Myriochele oculata 1080 46.7 46.7 Paramphinome jeffreysii 468 20.3 61.4 Paramphinome jeffreysii 469 20.3 67.0 Amphiura filiformis 173 7.5 68.9 Amphiura filiformis 92 4.0 71.0 Echinoidea spp.juv. 84 3.6 72.5 Apistobranchus tullbergi 83 3.6 74.6 Apistobranchus tullbergi 75 3.3 75.8 Levinsenia gracilis 51 2.2 76.8 Levinsenia gracilis 53 2.3 78.1 Nemertea spp. 43 1.9 78.6 Chaetozone setosa 50 2.2 80.2 Chaetozone setosa 42 1.8 80.5 Nemertea spp. 47 2.0 82.3 Echinoidea spp.juv. 41 1.8 82.2 Scoloplos armiger 44 1.9 84.2 Thyasira flexuosa 37 1.6 83.8 Phoronis muelleri 42 1.8 86.0 Phoronis muelleri 32 1.4 85.2

Table 4.12.10. Numbers of individuals (N) and species (S), depth, Shannon-Wiener diversity index (H’), Pielou’s evenness index (J), and expected number of species per 100 individuals (ES100) for each station at Eldfisk 2/7 B 2005 (excl. juv.).

H' ES100 Station Direction ° Distance m Depth S N Incl.

M. o. Excl. M. o.

J Incl. M. o.

Excl. M. o.

ELDB-03 360 500 75 95 3196 3.0 4.2 0.5 19 28.1ELDB-06 180 500 76 86 2086 3.1 4.6 0.5 22 34.4ELDB-11 270 500 75 88 2222 3.2 4.1 0.5 20 27.0ELDB-14 90 500 76 82 2269 3.1 4.1 0.5 20 28.7M. o.= M. oculata

The number of species varied from 82 at station ELDB-14 (90°/500m) to 95 at ELDB-03 (360°/500m). The number of individuals varied from 2086 at ELDB-06 (180°/500m) to 3196 at station ELDB-03. The Shannon Wiener diversity index varied from 3.0 at ELDB-03 to 3.2 at ELDB-11 (270°/500m). Indices above 4 indicate a relative undisturbed fauna, while indices between 3 and 4 indicate a slight disturbance.

The Hurlberts index (ES100) varied from 19 (ELDB-03) to 22 (ELDB-06). In general indices above 20 characterise a relatively normal fauna community, thus these indices reflect a slight disturbance, see Table 4.12.10. In general the indices reflect a slightly disturbed benthic fauna in the Eldfisk B-area, which is difficult to relate to direction or distance from the field centre. The results presumably reflect both a physical disturbance as well as a more diffuse organic load in the area.

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Classification and ordination

The dendrogram from the cluster analysis and the MDS plot from the ordination analysis based on grab samples are presented in Figure 4.12.4 and Figure 4.12.5. Only the dendrogram and the MDS plot from grab level are shown because the data contains only 4 stations and the analysis at station level shows the same pattern as the grab level. Most of the grab samples divide into two main groups at a similarity of about 62 %. An exception is the 4th grab sample from ELDB-06 (180°/500m). The similarity between group 1 and 2 is about 65 %. The grab samples from ELDB-03(360°/500m) separates into group 1, while the samples from the 3 other stations (direction 90°, 180° and 270°/ distance 500m) divide into group 2. The cluster analysis is supported by the ordination analysis (Figure 4.12.5).

ELDB

6-4

ELDB

3-1

ELDB

3-2

ELDB

3-4

ELD B

3-3

ELDB

3-5

ELDB

6-3

ELDB

6-5

ELDB

6-2

E LDB

14-2

ELDB

11-2

ELDB

1 1-4

ELDB

1 4-4

E LDB

14-3

ELDB

6-1

ELDB

1 4-1

ELDB

11-1

ELDB

14-5

ELDB

11-3

ELDB

1 1-5

100

90

80

70

60

Sim

ilari

ty

Group 1 Group 2ELDB-3 (360/500m ELDB-14 (90/500m), ELDB-6 (180/500m), ELDB-11 (270/500m)

Figure 4.12.4. Dendrogram of grab samples from Eldfisk 2/7 B 2005 (excl. juv.).

ELDB3-1

ELDB3-2

ELDB3-3

ELDB3-4

ELDB3-5ELDB6-1

ELDB6-2

ELDB6-3ELDB6-4

ELDB6-5

ELDB11-1

ELDB11-2

ELDB11-3

ELDB11-4

ELDB11-5

ELDB14-1

ELDB14-2

ELDB14-3

ELDB14-4

ELDB14-5

Stress: 0,21

Group 2ELDB-14 (90/500m), ELDB-6 (180/500m), ELDB-11 (270/500m)

Group 1ELDB-3 (360/500m)

Figure 4.12.5. MDS plot of grab samples from Eldfisk 2/7 B 2005 (excl. juv.).

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A Simper analysis (Primer package) was performed to examine which species contributes most to the differences between the two groups. The differences between the ELDB-03 (360°/500m) and the stations in group 2 were mainly due to a significantly higher number of the bristle worm D. arietina, a higher number of the brittle star A. filiformis and a slightly higher number of M. oculata in the fauna at station ELDB-03, all suspension feeders.

A bioenv-analysis which connects the variations in the biological data with the variations in the chemical and physical data was performed on the datasets. Bioenv calculates the combination of environmental factors which best correlates to the biological data. The results from the analysis gave a poor correlation between the fauna composition and the environmental factors.

Comparison with 1996, 1999, 2002 and 2005

In Figure 4.12.6 the results from the present survey are compared to the results from previous surveys.

Numbers of species and individuals have increased in 2005 compared to earlier years. The biodiversity (incl. M. oculata1) in the fauna community at Eldfisk B has in general increased slightly since the survey in 2002, indicating a positive trend.

020406080

100

ELDB-03

ELDB-06

ELDB-11

ELDB-14

Stations

No.

of s

peci

es (S

)

1996 1999 2002 2005

Station º/m ELDB-03 360/500 ELDB-06 180/500 ELDB-11 270/500 ELDB-14 90/500

0500

100015002000250030003500

ELDB-03

ELDB-06

ELDB-11

ELDB-14

Stations

No.

of i

ndiv

idua

ls (N

) 1996 1999 2002 2005

0123456

ELDB-03

ELDB-06

ELDB-11

ELDB-14

Stations

H'

1996 19991999-ex. M. oculata 20022002-ex. M. oculata 20052005-ex. M. oculata

Figure 4.12.6. Numbers of species (S) and individuals (N) per 0.5 m2 and diversity (H’) incl. P. jeffreysii and M. oculata, excl. juv., Eldfisk 2/7 B 1996, 1999, 2002 and 2005.

1 The significance of the temporal fluctuations of M. oculata is discussed in Chapter X - General Trends in the Region which also forms a basis for the conclusions for each of the fields.

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Classification and ordination analyses

The sampled stations from all the years have been analysed at family level∗. The stations divide into two main groups at 60 % similarity. Group 1 consists of stations sampled in 2002 and 2005, which could be further subdivided into subgroups based on year at about 70 % similarity. The one 1996 station in group 2 differ somewhat from the 1999 stations. The dendrogram from the analysis of comparable stations is shown in Figure 4.12.7

A similarity analysis was performed on the data, and the results revealed a significant increase in the numbers of species within the families Oweniidae (mainly M. oculata), Amphinomidae (mainly P. jeffreysii) and also A. tullbergi in 2002 and 2005 compared to earlier surveys. These increases contribute most to the differences between the two groups. The difference between 2002 and 2005 is mainly due to higher numbers of species within the family Amphinomidae (mainly P. jeffreysii) and the family Amphiuridae (mainly A. filiformis) in 2005. The numbers of these species seems to be increasing in the area.

ELDB

-06-

2002

ELDB

-14-

2002

ELDB

-03-

2002

ELDB

-11 -

2002

ELDB

-03-

2005

ELDB

-06-

200 5

ELDB

-11-

2005

ELDB

-14-

200 5

ELD B

-06-

1996

ELDB

-06-

199 9

ELD B

-14-

1999

ELD B

-03-

1999

ELDB

-11-

1 999

100

90

80

70

60

Sim

ilarit

y

Group 1 Group 2

2002 2005

Figure 4.12.7. Dendrogram showing similarity between Eldfisk B stations 1996, 1999, 2002 and 2005. Family level, incl. M. oculata excl. juv., sq. root transformation.

A Bioenv analysis was performed on the data. The results gave a correlation of 0.6 between a combination of the environmental factors Cu and pelite and fauna over the years, which indicate some relation in the variations between the years, which may be explained by a decline in the Cu concentrations.

4.12.4 Conclusion

The sediments at Eldfisk 2/7 B consist of fine sand, and the sand content is almost at the same level, varies from 95 % to 97 %. The gravel content is zero or very low. Silt and clay content is similar to previous surveys. The total organic matter content in the sediments is low. Only small

∗ Necessary when comparing between years, to avoid significant source of error due to both different years and

different taxonomists.

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variations are found at the field, from 0.88 % to 1.02 %. The content corresponds to the grain size distribution.

The mean THC concentrations vary from 5.8 mg/kg at ELDB11, 270°/500m to 30 mg/kg at ELDB13, 90°/250m. Elevated THC content is observed for three stations, respectively 15.8 mg/kg at ELDB5, 180°/250m, 13.2 mg/kg at ELDB12, 270°/250m and 30 mg/kg at ELDB13, 90°/250m. Thus elevated levels of THC are observed out to 500m in the 90° direction and to 250m in the 180° and 270° direction. For the other stations the THC content is below or just above the limit of contamination. The THC content for these stations has decreased since 2002. Elevated THC concentrations are observed in the vertical sections at ELDB6 and ELDB13.

Olefins are detected at the three stations analysed, from 0.5 mg/kg at ELDB14, 90°/500m to 0.9 mg/kg at ELDB13, 90°/250m. The content of olefins has decreased since the last survey.

Low concentrations of NPD and PAH are found for ELDB5, 180°/250m, ELDB6, 180°/500m and ELDB13, 90°/250m, but the content is increasing slightly going down in the sediment. The content of decalins is relatively high, 0.52 mg/kg at ELDB5, 180°/250m and 1.8 mg/kg at ELDB13, 90°/250m. The content is also high in the deeper layers, up to 2.6 mg/kg at ELDB13 in the 1-3 cm layer. At ELDB6 the decalin content is low and has decreased considerably since the 2002 survey. A relatively high content is also found in the deeper layers, up to 2.6 mg/kg at ELDB13 in the 1-3 cm layer. The relatively high contents of decalins found are in agreement with the relatively high contents of THC observed at ELDB5 and ELDB13.

The Ba concentrations vary from 644 mg/kg at ELB3, 360°/500m to 1706 mg/kg at ELD14, 90°/500m. The Ba concentrations are similar to the previous survey, and elevated concentrations are found at all stations. This means out to 500m in all directions. The highest Ba concentrations are found in the 3-6 cm layer at ELDB6, 180°/500m, 2674 mg/kg.

The concentrations of the heavy metals are low, and no increases are observed since 2002. Slightly elevated concentrations of Pb and Zn are found, also in the vertical layers.

The chemical results are mainly in correspondence with the drilling history at Eldfisk 2/7 B. Pseudo-oil based drilling fluids (olefins) and barite are not discharged since the last survey in 2002.

The biological analysis at Eldfisk B reveals a slightly disturbed fauna at the sampled stations (all located 500 m from the field centre). There was no significant correlation between the fauna composition and the chemical parameters. The biodiversity in the fauna community has in general increased slightly since the survey in 2002, together with an ongoing shift in the fauna community. C. setosa which is a strong indicator species able to act as deposit feeder, was the dominating species in the fauna in the 1990’s. In 2002 this species decreased and M. oculata, a transition species, dominated the fauna together with a higher share of other suspension feeding species which has increased towards 2005. However, a general decline in the numbers of M. oculata as described at several other fields in the area in 2005 has not been the case at Eldfisk B. However, the development in the fauna could indicate a slowly improvement in the environment at Eldfisk B.

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4.13 Embla 2/7 D

4.13.1 Sediment characterization

Grain size distribution

The grain size distribution has not been determined in the present survey. Previous surveys in 2002, 1999 and 1996 have shown that sediments at Embla consist of fine sand. The sand content ranged from 94 to 97 %. The gravel content was low. The average silt and clay concentration was ~4.3 %.

Total organic matter (TOM)

The total organic matter content has not been determined in the present survey. Previous surveys in 2002, 1999 and 1996 have shown that the total organic matter in the sediments is low. The content is in average ~0.85 %.

4.13.2 Chemical analyses

Only THC was analysed in the sediments at Embla, three replicate samples from the top 0-1 cm sediment layer at each station. There have been no discharges since 1999, thus the present survey has focused on stations close to the installation.

THC

The THC results are shown in

Table 4.13.1 for four stations at 250 m from the field centre. These stations have not been sampled since 1993. A bar diagram of the THC content in the sediments is shown in Figure 4.13.1. In the present survey the mean THC concentrations vary from 3.9 mg/kg (EMBLA4) to 18.2 mg/kg (EMBLA5). Concentrations above the limit of contamination for the region are found at station EMBLA5 and EMBLA13. Thus elevated levels of THC are observed out to 250m in the 90° and 180° directions. The content of THC is below the limit of contamination at EMBLA4 and EMBLA12. Representative gas chromatograms are given in Appendix C. These include EMBLA4, 360°/250 m, EMBLA5, 180°/250m and EMBLA13, 90°/250m.

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Embla, THC 2005

0

10

20

30

40

50

EMBLA4 EMBLA5 EMBLA12 EMBLA13 ECOC Ref. 42

station

mg/kg

1999

2002

2005

LSC A

Figure 4.13.1. Bar diagram of the THC content in the sediments at Embla 2/7 2005. Table 4.13.1. Embla 2/7 D 2005, total hydrocarbon content (mg/kg dry sediment). Station Grab

#1 Grab

#2 Grab

#3 Mean SD

2005 2005 EMBLA4 360°/250m 3.2 3.7 4.8 3.9 0.8 EMBLA5 180°/250m 18.2 15.6 21 18.2 2.5 EMBLA12 270°/250m 4.3 5.4 3.4 4.4 1.0 EMBLA13 90°/250m 12.3 17.5 15.2 15.0 2.6 EKO Ref. 42 90°/15000m 6.2 5.3 4.4 5.8 1.0 LSC Subregion A 6.6

4.13.3 Conclusion

Previous surveys show that the sediments at Embla 2/7 D consist of fine sand and that the gravel content is low. The total organic matter content in the sediments is also low, in average ~0.85 %. The mean THC concentrations vary from 3.9 mg/kg at EMBLA4, 360°/250m to 18.2 mg/kg at EMBLA5, 180°/250m. Concentrations above the limit of contamination are found for station EMBLA5, 180°/250m and EMBLA13, 90°/250m. For EMBLA4, 360°/250m and EMBLA12, 270°/250m, the content of THC is below the limit of contamination for the region. The chemical results agree with the drilling history. No discharges have taken place at Embla 2/7 D since 1999, except for some small amounts of oil discharges/spills in 2002 and 2003.

Based on the results biological analyses should be included at Embla in the next monitoring survey.

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4.14 Tor 2/4 E

4.14.1 Sediment characterization

Grain size distribution

The grain size distribution from the present survey is shown in Table 4.14.1 together with the silt and clay content from the previous surveys in 2002, 1999 and 1996.

The sediments at Tor 2/4 E consist of fine sand, and the sand content is in average 97.5 %. The gravel content is low. The silt and clay content is similar to the previous survey and the average concentration is 2.4 % compared to 4.1 % in 2002, 3.6 % in 1999 and 2.8 % in 1996 for the two stations investigated. The results from the complete grain size distribution are given in Appendix C. Table 4.14.1. Tor 2/4 E 2005, grain size distribution. Station Median

diameter Classification Grain size distrib. 2005

(%) 2002

(%) 1999 (%)

1996 (%)

Mdφ Silt and clay

Sand Gravel Silt and clay

Silt and clay

Silt and clay

TOR5 180°/250m 2.82 Fine sand 1.6 98.1 0.3 4.1 3.5 1.9 TOR6 180°/500m 2.83 Fine sand 3.1 96.9 0.0 4.0 3.6 3.7 EKO Ref. 42 90°/15000m 2.78 Fine sand 2.6 97.3 0.1 2.6 5.3 2.9 Mean (excl. ref. station) 2.83 Fine sand 2.4 97.5 4.1 3.6 2.8 Standard deviation 0.007 1.1 0.8 0.07 0.07 1.3

Total organic matter (TOM)

The content of TOM in the sediments is low. Only small variations are found at the field, and are respectively 0.86% and 0.93 % for the two stations sampled. The content is at the same level as the 2002 survey. The content corresponds to the grain size distribution. The results are shown in Table 4.14.2. Table 4.14.2. Tor 2/4 E 2005, total organic matter (% of dry sediment). Station 2005, 0-5 cm Mean 2002 SD

2002 Mean 1999 Mean

1996 TOR5 180°/250m 0.93 0.96 0.07 0.80 0.80 TOR6 180°/500m 0.86 0.92 0.04 0.77 0.84 EKO Ref. 42 90°/15000m 0.88 0.82 0.02 0.95 0.86

4.14.2 Chemical analyses

The parameters analysed in the sediments at Tor are:

• THC • NPD, PAH, decalins • Ethers • Metals (Ba, Cd, Cr, Cu, Hg, Pb, Zn)

Three replicate samples at each station are analysed. The samples are taken from the top 0-1 cm sediment layer. In addition the 1-3 cm and 3- 6 cm sediment layers are sampled at two stations. The sampling program has been reduced compared to the previous survey based on

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the discharge history and low THC concentrations in 2002. Thus the present survey has focused on stations close to the installation.

THC and ethers

The THC results are shown in Table 4.14.3. The corresponding THC data from the previous surveys in 2002, 1999 and in 1996 are also included for comparison. The ether results are shown in Table 4.14.4. In Table 4.14.3 we have also included the sum of THC and ethers in the present survey. Bar diagram of the THC content in the sediments is shown in Figure 4.14.1.

In 2002 the mean THC concentrations ranged from 8.5 mg/kg (TOR6 180°/500m) to 31 mg/kg (TOR5, 180°/250m). Maximum concentrations were found in the 1-3 cm and 3-6 cm layers at TOR5, 122 mg/kg and 238 mg/kg, respectively.

In the present survey the mean content of THC varies from 6.6 mg/kg at TOR12, 270°/250m to 20 mg/kg at TOR5, 180°/250m. It was revealed in the 2002 survey that the major part of the elevated THC values found at Tor was due to the presence of Aquamul B (didecyl ethers). This ether based drilling fluid Aquamul was used in 1990. At TOR5, 180°/250m, these additional peaks represented approx. 80% of the THC value in the deeper layers and approx. 50 % in the top 0-1 cm layer. At TOR6, 180°/500m the additional peaks represented approx. 10 % of the THC value. It is, however, important to realise that the concentrations of Aquamul B in the sediments could not be estimated, since the ether compounds might be partly lost during the sample preparation of the sediments. With this in mind, the content of ether was analysed in the present survey.

Ethers were found at all the stations analysed. The mean concentrations vary from 1.3 mg/kg at TOR12, 270°/250m to 28 mg/kg at TOR4, 360°/250m. Grab # 3 at TOR4 showed ether content of 75 mg/kg. The highest concentrations of THC and ethers were found in the 1-3 cm and 3-6 cm layers at TOR5. The 1-3 cm layer contained 23 mg/kg THC and 93 mg/kg ethers. Corresponding, the 3-6 cm layer contained 23 mg/kg THC and 56 mg/kg ethers. TOR12, 270°/250m has a low content of THC (or sum THC plus ether), close to the limit of contamination. For the other stations elevated levels of THC (or THC plus ethers) are observed. Thus elevated levels of THC (or THC/ether) are observed out to 500m in the 180° direction and to 250m in the 90 and 360° direction. These Aquamul B results are similar to that found at Ekofisk Centre. It is likely that the Aquamul B drilling fluid is more stable than previously anticipated, and that the ether concentrations in the sediment results from discharges performed in 1990.

Representative gas chromatograms are given in Appendix C. These include TOR5, 180°/250m (all three layers), TOR6, 180°/500m (all three layers) and TOR12, 270°/250m.

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Tor, THC 2005

0

10

20

30

40

50

TOR4 TOR5 TOR6 TOR12 TOR13 EKOC Ref. 42

station

mg/kg

1999

2002

2005

LSC A

46±24

Figure 4.14.1. Bar diagram of the THC content in the sediments at Tor 2/4 E 1999-2005. Aqual B ethers are included. Table 4.14.3. Tor 2/4 E 2005, total hydrocarbon content (mg/kg dry sediment). Station Grab

#1 Grab

#2 Grab

#3 Mean SD Mean Mean* Mean* Mean*

2005 2005 2005 THC + ethers

2002 1999 1996

TOR4 360°/250m 7.2 6.2 10.5 8.0 2.2 36 TOR5 180°/250m 11.4 38 11.3 20 15 37 31 46 35 1-3 cm 23 116 122 174 69 3-6 cm 23 79 238 192 33 TOR6 180°/500m 6.2 18.1 4.2 9.5 7.5 11.5 8.5 19 13 1-3 cm 7.5 9.8 9.3 3-6 cm 21 23 13 TOR12 270°/250m 6.0 7.0 6.7 6.6 0.5 7.9 TOR13 90°/250m 9.7 11.7 11.9 11.1 1.2 22 EKO Ref. 42

90°/15000m 6.2 5.3 4.4 5.8 1.0 5.9 5.5 6.4

LSC Subregion A 6.6 6.4 9 * The ether drilling fluid Aquamul B was included in the THC values in the previous surveys.

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Table 4.14.4. Tor 2/4 E 2005, ether content (mg/kg dry sediment). Station Grab #1 Grab #2 Grab #3 Mean SD

2005 2005 TOR4 360°/250m 5.1 4.9 75 28 40 TOR5 180°/250m 10.3 24 6.7 17 15 1-3 cm 93 3-6 cm 56 TOR6 180°/500m 3.7 1.5 1.3 2 1 1-3 cm 2.3 3-6 cm 2.4 TOR12 270°/250m 1.3 1.4 1.3 1.3 0.03 TOR13 90°/250m 11.0 9.5 10.6 10.4 0.7

NPD, PAH and decalins

Two stations are analysed, TOR5, 180°/250m and TOR6, 180°/500m. The results are shown in Table 4.12.4.

In 1999 elevated mean NPD and PAH concentrations were found at both stations (TOR5 and TOR7), and in the 1-3cm and 3-6 cm layers as well. Elevated content of decalins were found at TOR5, 180°/250m and in the 3-6 cm layer at TOR7, 180°/1000m. In 2002 elevated NPD concentrations were found at TOR5, 180°/250m and at TOR6, 180°/500m. At TOR5, the concentrations were similar to 1999. Decalins were also found at TOR5. The decalin concentrations are higher in the sediment layers at 1-3 cm and 3-6 cm than in the top layer. The concentrations are similar to 1999 level. Elevated concentrations of PAH were not found.

In the present survey slightly elevated NPD concentrations are found at TOR5, 180°/250m and at TOR6, 180°/500m, mean values of 0.065 mg/kg and 0.039 mg/kg, respectively. At TOR5, elevated levels of NPD are also found in the deeper layers, with highest concentration in the 1-3 cm layer (0.25 mg/kg). Concentration of NPD is low in the deeper layers at TOR6, (below the limit of contamination) and has decreased since 2002.

The PAH content has increased slightly since 2002 survey. The mean concentration of PAH is 0.053 mg/kg at TOR5 and 1.6 ± 2.5 mg/kg at TOR6. The elevated level at TOR6 is mainly due to grab #3. Thus the standard deviation for the mean value at TOR6 is high. Significant differences between replicates are also observed earlier for this region. Elevated content of PAH is also observed for the deeper layers, with highest content in the 1-3 cm layer, 1.0 mg/kg and 0.8 mg/kg at TOR5 and TOR6, respectively.

Decalins are not found in the top layer at any of the stations. Small amounts are found in the deeper layers at TOR5 (0.17mg/kg and 0.12 mg/kg). Thus the level of decalin has decreased at TOR5 since 2002.

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Table 4.14.5. Tor 2/4 E 2005, sum NPD, PAH and decalins (mg/kg dry sediment).

Station Grab #1

Grab #2

Grab #3

Grab #4

Grab #5

Mean SD Mean SD Mean SD Mean

2005 2005 2002 2002 1999 1999 1996NPD TOR5 180°/250m 0.05 0.11 0.034 0.065 0.04 0.12 0.019 0.13 0.07 0.29 1-3 cm 0.25 0.13 0.16 0.19 3-6 cm 0.065 0.16 0.20 0.11TOR6 180°/500m 0.029 0.077 0.011 0.039 0.03 0.048 0.018 1-3 cm 0.016 0.026 3-6 cm 0.023 0.061 LSC Subregion A 0.030 0.026 0.040 PAH TOR5 180°/250m 0.044 0.066 0.048 0.053 0.01 0.045 0.011 0.17 0.214 0.30 1-3 cm 1.04 0.039 0.097 0.03 3-6 cm 0.27 0.046 0.050 0.04TOR6 180°/500m 0.11 0.067 4.5 1.6 2.5 0.043 0.003 1-3 cm 0.77 0.052 3-6 cm 0.095 0.11 LSC Subregion A 0.061 0.062 0.090 Decalins TOR5 180°/250m nd nd nd nd 0.072 0.016 0.15 0.074 0.19 1-3 cm 0.17 0.21 0.38 0.39 3-6 cm 0.12 0.57 0.46 0.24TOR6 180°/500m nd nd nd nd nd 1-3 cm nd nd 3-6 cm nd 0.056 nd: not detected. Limit of detection is for NPD 0.01 mg/kg, for PAH 0.005 mg/kg and for decalins 0.1 mg/kg.

Metals

The results are shown in Table 4.12.5. For comparison, data from the present survey and previous surveys in 2002, 1999 and 1996 are included in Table 4.12.6. Bar diagram of the Ba content in the sediments is shown in Figure 4.12.2.

In 1999 the Ba concentrations ranged from 92 mg/kg at TOR8, 180°/2000m to 1470 mg/kg at TOR5, 180°/250m. In 2002 the Ba concentrations ranged from 123 mg/kg at TOR3, 360°/500m to 1420 mg/kg at TOR5, 180°/250m. In the present survey the Ba concentrations vary from 341 mg/kg at TOR6, 180°/500m to 1505 mg/kg at TOR5, 180°/250m. The Ba content at the EKO42 reference station is 46 mg/kg.

Elevated Ba concentrations are found at the two stations analysed; out to 500m in the 180° direction. The concentrations are similar to the 2002 and 1999 survey. High concentrations are found in the 0-1 cm and 3-6 cm layers at TOR5, 180°/250m, 2744 mg/kg and 3501 mg/kg, respectively.

The concentrations of the heavy metals are low. However some elevated concentrations of heavy metals are found, particularly at TOR5, 180°/250m in the three layers analysed. The content has not changed since the 2002 survey.

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Tor, Ba 2005

0

500

1000

1500

2000

2500

TOR5 TOR6 EKOC Ref. 42

station

mg/kg

1999

2002

2005

LSC A

Figure 4.14.2. Bar diagram of the Ba content in the sediments at Tor 2/4 E 1999- 2005. The following variation is found at Tor in the top layer, 0-1 cm. The values are given in mg/kg: Tor: TOR5 – TOR6 ECOC42 Reference station Ba: 341 – 1505 46 Cr: 8.4 – 8.5 7.6 Cu: 0.7 – 2.3 <0.5 Pb: 10.4 – 18.3 6.1 Zn: 10.0 – 19 5.4 Cd: 0.01 – 0.03 <0.01 Hg: <0.01 – 0.05 <0.01

Table 4.14.6. Tor 2/4 E 2005, metals (mg/kg dry sediment). Station Sample Ba Cd Cr Cu Hg Pb Zn 2005 2005 2005 2005 2005 2005 2005 TOR5 180°/250m 1 1563 0.02 8.3 2.1 0.02 18.3 16.9 2 1363 0.03 8.7 2.6 0.11 17.9 17.7 3 1589 0.03 8.6 2.1 0.02 18.7 22.4 mean 1505 0.03 8.5 2.3 0.05 18.3 19.0 SD 124 0.006 0.2 0.3 0.06 0.4 2.9 1-3 cm 1 2744 0.04 9.3 3.2 0.03 24.0 26.1 3-6 cm 1 3501 0.11 10.1 3.9 0.04 28.8 48.5 TOR6 180°/500m 1 328 0.02 8.8 0.9 0.01 11.1 14.8 2 532 0.01 8.6 0.8 0.01 11.5 8.3 3 162 <0.01 7.7 0.6 <0.01 8.5 6.9 mean 341 0.01 8.4 0.7 <0.01 10.4 10.0 SD 186 0.003 0.6 0.2 1.6 4.2 1-3 cm 1 674 0.02 9.0 0.9 0.01 11.8 11.0 Cont. 3-6 cm 1 1195 0.04 9.9 1.1 0.01 10.7 11.8

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Table 4.14.6. cont. EKO Ref. 90°/15000m 1 52 <0.01 7.7 <0.5 0.01 6.6 5.6

2 77 <0.01 8.0 0.5 <0.01 6.3 5.8 3 37 <0.01 7.5 <0.5 <0.01 6.4 5.0 4 36 <0.01 7.4 <0.5 0.01 5.5 5.6 5 29 <0.01 7.4 <0.5 <0.01 5.7 4.9 mean 46 <0.01 7.6 <0.5 <0.01 6.1 5.4 SD 19 0.3 0.5 0.4 1-3 cm 1 50 <0.01 8.1 <0.5 <0.01 6.4 5.8 3-6 cm 1 72 <0.01 8.0 <0.5 <0.01 6.6 5.8 LSC, Subregion A 76.2 8.0 1.3 7.4 6.9 Table 4.14.7. Tor 2/4 E 2005, metals (mg/kg dry sediment), comparing mean values with previous surveys. Station Ba Ba Ba Ba Cd Cd Cd Cr Cr Cr 2005 2002 1999 1996 2005 2002 1999 2005 2002 1999 TOR5 180°/250m 1505 1420 1470 2590 0.03 0.04 0.06 8.5 7.9 6.6 1-3 cm 2744 2110 2350 0.04 0.09 0.03 9.3 8.4 8.0 3-6 cm 3501 2330 2190 0.11 0.06 0.20 10.1 7.9 8.9 TOR6 180°/500m 341 448 385 1300 0.01 0.02 <0.02 8.4 8.0 7.2 1-3 cm 674 1390 0.02 0.03 9.0 9.0 3-6 cm 1195 1090 0.04 0.05 9.9 9.8 EKO Ref.

90°/15000m 46 72 41 67 <0.01 <0.01 <0.02 7.6 7.7 7.1

1-3 cm 50 88 50 <0.01 <0.01 <0.02 8.1 7.7 7.2 3-6 cm 72 331 141 <0.01 0.01 <0.02 8.0 8.1 7.8 cont. Table 4.14.7. cont. Station Cu Cu Cu Hg Hg Hg Pb Pb Pb Zn Zn Zn 2005 2002 1999 2005 2002 1999 2005 2002 1999 2005 2002 1999TOR5 180°/250m 2.3 1.5 0.7 0.05 0.04 0.03 18.3 24.3 15.3 19.0 25.3 26.5 1-3 cm 3.2 4.2 0.03 0.05 0.06 24.0 26.6 21.0 26.1 40.9 40.2 3-6 cm 3.9 2.7 0.04 0.03 0.04 28.8 21.9 31.3 48.5 32.1 126 TOR6 180°/500m 0.7 1.9 0.9 <0.01 0.02 10.4 12.6 11.9 10.0 9.0 9.5 1-3 cm 0.9 2.1 0.01 0.02 11.8 14.4 11.0 12.4 3-6 cm 1.1 2.5 0.01 0.02 10.7 10.3 11.8 13.5 EKO Ref. 90°/15000m <0.5 1.0 0.5 <0.01 <0.01 <0.01 6.1 6.3 6.1 5.4 5.6 4.7

1-3 cm <0.5 1.1 0.5 <0.01 0.01 <0.01 6.4 6.3 6.0 5.8 5.6 5.1 3-6 cm <0.5 1.8 0.8 <0.01 <0.01 <0.01 6.6 7.2 7.3 5.8 6.9 5.8

4.14.3 Biological analyses

A total of 125 species and 5909 individuals were sampled at 2 stations. Greatest abundance (66.4 %) was found among the polychaetes, of which the species Myriochele oculata constitutes 73.7 % and Paramphinome jeffreysii constitutes about 7.4 % of the total number of Polychaeta, see Table 4.14.8.

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Table 4.14.8.Number of species and individuals distributed between the main groups, Tor 2005. Individuals Species Main animal groups

Number % Number % Varia 478 8.1 13 10.4Polychaeta 3922 66.4 56 44.8- Paramphinome jeffreysii 291 7.4 - Myriochele oculata 2890 73.7 Crustacea 127 2.1 21 16.8Mollusca 312 5.3 27 21.6Echinodermata 1070 18.1 8 6.4- Amphiura filiformis 343 32.1 Total 5909 100.0 125 100.0

Figure 4.14.3 shows the numbers of species and individuals sampled at each station and variations between grab samples.

04080

120160200

TOR-05

TOR-06

Stations

No.

of s

peci

es (S

)

Station º/m TOR-05 180/250 TOR-06 180/500

0800

16002400320040004800

TOR-05

TOR-06

Stations

No.

of i

ndiv

idua

ls (N

)

Ex. P. jeffreysii and M. oculata

0800

16002400320040004800

TOR-05

TOR-06

Stations

No.

of i

ndiv

idua

ls (N

)

Figure 4.14.3. Numbers of species (S) and individuals (N) per 0.5 m2 (incl./excl. P. jeffreysii and M. oculata), mean values per grab sample and standard deviation, Tor 2005.

The standard deviation was dramatically reduced at station TOR-05 (180º/250m) when the two species P. jeffreysii and M. oculata were removed. This is evident since the two species constitute 53.8 % of the total number of individuals. At station TOR-06 (180°/500m) the standard deviation was only slightly reduced. This is due to large differences between the five grabs sampled at the station.

Diversity and dominant species

The dominant species at each station varied from 18.1 % at TOR-06 (180°/500m) to 59.3 % at TOR-05 (180°/250m). The 10 most abundant species made up from 76.4 % at TOR-06 to 87.2

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% at TOR-05, see Table 4.14.9. Juvenile Echinoidea were the second most dominating species at the TOR field after the bristle worm M. oculata. Other dominating species were the brittle star Amphiura filiformis, the hydroid Corymorpha nutans and the bristle worm P. jeffreysii. P. jeffreysii is mainly a carnivore species and the other mentioned species are either suspension- or both suspension- and deposit feeders. Most of these species are known indicators of organic pollution when they are found in high numbers. However, several of the above mentioned species have a planktonic developmental stage and are able to settle in large numbers. Table 4.14.9. The 10 most abundant species at each station,Tor 2005. 10 most dominating species TOR-05 No. % Cum. % TOR-06 No. % Cum. % Myriochele oculata 2700 59.3 59.3 Echinoidea spp.juv. 246 18.1 18.1 Echinoidea spp.juv. 442 9.7 69.0 Amphiura filiformis 198 14.6 32.7 Corymorpha nutans 340 7.5 76.5 Myriochele oculata 190 14.0 46.8 Amphiura filiformis 145 3.2 79.7 Paramphinome jeffreysii 188 13.9 60.6 Paramphinome jeffreysii 103 2.3 81.9 Montacuta substriata 43 3.2 63.8 Chaetozone setosa 60 1.3 83.2 Eudorellopsis deformis 37 2.7 66.5 Scoloplos armiger 48 1.1 84.3 Scoloplos armiger 36 2.7 69.2 Phoronis muelleri 47 1.0 85.3 Goniada maculata 35 2.6 71.8 Eudorellopsis deformis 44 1.0 86.3 Spiophanes bombyx 33 2.4 74.2 Goniada maculata 41 0.9 87.2 Levinsenia gracilis 30 2.2 76.4

Including the bristle worm M. oculata, the number of species varied from 85 at TOR-06 (180°/500m) to 93 at TOR-05 (180°/250m). The number of individuals varied from 1107 at TOR-06 to 4092 at TOR-05. The Shannon Wiener diversity index varied from 2.5 at TOR-05 to 4.4 at TOR-06 and the Hurlberts index (ES100) varied from 19 at TOR-05 to 29 at TOR-06. Excluding M. oculata from the data resulted in diversity indices above 4 and ES100 from 29 to 30 respectively. Diversity indices above 4 indicate a relatively undisturbed fauna. Indices between 3 and 4 indicate a slight disturbance, while indices between 2 and 3 indicate a disturbance in the fauna. In general Hurlberts indices above 20 characterize a relatively normal fauna community, see Table 4.14.10.

The indices excluding M. oculata indicate a relative healthy fauna community at Tor. However, when including M. oculata, the indices at TOR-05 reflect disturbances, which are supported by field observations of oil film in the samples from TOR-05. Table 4.14.10. Numbers of individuals (N) and species (S), depth, Shannon-Wiener diversity index (H’), Pielou’s evenness index (J), and expected number of species per 100 individuals (ES100) for each station at Tor 2005 (excl. juv.).

H' ES100 Station Direction ° Distance m Depth S N Incl.

M. o. Excl. M. o.

J Incl. M. o.

Excl. M. o.

TOR-05 180 250 69 93 4092 2.5 4.4 0.4 19 30 TOR-06 180 500 69 85 1107 4.4 4.3 0.7 29 29 M. o.= M. oculata

Classification and ordination

The dendrogram from the cluster analysis and the MDS plot from the ordination analysis based on grab level are presented in Figure 4.14.4 and Figure 4.14.5. The grab samples cluster in stations at about 55 % similarity. The overall pattern was the same inclusive and exclusive M. oculata. There were significantly higher numbers of the bristle worm M. oculata and the hydrozoan C. nutans at TOR-05 (180°/250m) and somewhat higher numbers of the bristle

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worm P. jeffreysii at TOR-06 (180°/500m). M. oculata and C. nutans are mainly suspension feeders, while P. jeffreysii is known as a carnivore species.

The Bioenv analysis has not been performed because the field consists of two stations only. However, the values of THC and the metals are higher in the sediment at station TOR-05.

T OR

-05-

4

TOR

- 05-

5

TOR

-05-

3

TOR

-05-

1

TOR

-05-

2

TOR

-06-

5

TOR

-06-

2

TOR

-06-

1

TOR

- 06-

3

TOR

-06 -

4100

90

80

70

60

50

Sim

ilarit

y

TOR-05 (180/250m) TOR-06 (180/500m) Figure 4.14.4. Dendrogram of grab samples from Tor 2005 (excl. juv.).

TOR-05-1TOR-05-2

TOR-05-3

TOR-05-4TOR-05-5TOR-06-1

TOR-06-2

TOR-06-3TOR-06-4

TOR-06-5

Stress: 0,05

TOR-05 (180/250m)

TOR-06 (180/500m)

Figure 4.14.5. MDS plot of grab samples from Tor 2005 (excl. juv.).

Comparison with 1992, 1996, 1999, 2002 and 2005

In Figure 4.14.6 the results from the present study are compared to the results from previous surveys. The numbers of species have increased at both stations since 1992. At TOR-06 (180º/500m) the number of species has only increased slightly since the last survey. The number of individuals has increased sligthly at TOR-05 (180°/250m). At TOR-06, the number of individuals has decreased significantly since the last survey in 2002, mainly due to a decrease in the numbers of M. oculata. The biodiversity indices have increased at both stations

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(including M. oculata)1. At TOR-06, the diversity index including M. oculata is more than 4. The biodiversity indices excl. M. oculata shows a decreasing trend since last survey.

020

4060

80100

TOR-05

TOR-06

Stations

No.

of s

peci

es (S

)

1992 1996 1999 2002 2005

Station º/m TOR-05 180/250 TOR-06 180/500

0600

120018002400300036004200

TOR-05

TOR-06

Stations

No.

of i

ndiv

idua

ls (N

)

1992 1996 1999 2002 2005

0123456

TOR-05

TOR-06

Stations

H'

1992 19961999 20022002-ex M.oculata 20052005-ex. M. oculata

Figure 4.14.6. Numbers of species (S) and individuals (N) per 0.5 m2 and diversity (H’), incl.P. jeffreysii and M. oculata, excl. juv., Tor 1992, 1996, 1999, 2002 and 2005.

Classification and ordination analyses

The sampled stations from all years have been analysed at family level∗. The dendrogram from the cluster analysis reveals that most of the stations divide into three main groups. The 1992 and the 1996 stations form separate groups based on years while the 1999-2005 stations cluster together at about 60 % similarity. The differences between groups are caused by significantly higher abundances of the bristle worms within the family Oweniidae (mainly M. oculata) and higher numbers of species within the family Serpulidae (D. arietina) and Hydrozoans within the family Corymorphidae (Corymorpha nutans) in the 1999-2005 group. This group can be subdivided based on years. The 1996 group differs with higher numbers of the bristle worms within the families Spionidae and Cirratulidae (mainly C. setosa) compared to the other two groups. The 1992 group differs with higher abundances of species within the family Lasaiidea (mussel). The number of the bristle worm M. oculata had a peak in 2002 and decreased significantly at TOR-06 (180º/500m) in 2005. A weaker decline is revealed at TOR- 1 The great variations in the presence of M. oculata from 1996 to 2005 have complicated the faunal picture, making it difficult to draw conclusions about the state of the fauna community. Adding the 2005 results to the trend data have, however, strengthened the data set, and has made it possible to obtain a pattern in the overall temporal variations in the entire region. Thus it is recommended to read Chapter X - General Trends in the Region which forms a basis for the conclusions for each of the fields. ∗ Necessary when comparing between years, to avoid significant source of error due to both different years and

different taxonomists.

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05 (180º/250m) in 2005. The numbers of D. arietina were highest in 1999 at these two stations. The pattern indicates an improvement, in particular at TOR-06 in 2005 compared to 2002.

The Bioenv analysis (excluding the 1992 stations) gave a correlation of 0.7 between fauna and the combination of the environmental factors Cu and pelite, indicating some relationship between these environmental factors and the changes in the fauna over the years from 1996 - 2005. The variations in the Cu concentrations are, however, small and the results do not reflect any significant trend in the data.

TOR

-01-

92

TOR

-18-

92T O

R-2

0-92

TOR

-03 -

92TO

R-0

2-92

TOR

-04-

92

TOR

-11-

92T O

R-1

4-92

TOR

-05-

92

TOR

-19 -

92TO

R-1

3-92

TOR

-17-

92TO

R-1

2-92

TOR

-06-

92TO

R-1

5-92

T OR

-10-

92

TOR

-07-

92T O

R-1

6-92

TOR

-08-

92TO

R- 0

9-92

TOR

-05-

96TO

R-1

4 -96

TOR

-10-

96TO

R-1

5-96

TOR

-03-

96

TOR

-07-

96TO

R-0

6-96

TOR

-04-

96

TOR

-11-

96TO

R-0

5-05

TOR

-06-

05TO

R-0

5-99

TOR

-08-

99TO

R-0

3-99

TOR

-11-

99TO

R-1

4-99

TOR

-06-

99

TOR

-07 -

99TO

R-0

3-02

TOR

-11-

0 2TO

R-0

7-02

TOR

-14-

02TO

R-0

5-02

TOR

-06-

02

100

80

60

40

Sim

ilarit

y

1992 1996 1999-2005 Figure 4.14.7. Dendrogram showing similarity between Tor stations 1992, 1996, 1999, 2002 and 2005. Family level, incl. M. oculata, excl. juv., sq. root transformation.

4.14.4 Conclusion

The sediments at Tor 2/4 E consist of fine sand, and the sand content is in average 97.5 %. The gravel content is low. The silt and clay content is similar to the previous survey. The total organic matter content in the sediments is low. Only small variations are found at the field, from 0.86 % to 0.93 % for the two stations sampled. The content is at the same level as found in the 2002 survey.

The mean THC concentrations vary from 6.6 mg/kg at TOR12, 270°/500m to 20 mg/kg at TOR5, 180°/250m.

Ethers were found at all the stations analysed. The mean concentrations varied from 1.3 mg/kg at TOR12 to 28 mg/kg at TOR4. Grab # 3 at TOR4 showed ether content of 75 mg/kg. The highest concentrations of THC and ethers were found in the 1-3 cm and 3-6 cm layers at TOR5. The 1-3 cm layer contained 23 mg/kg THC and 93 mg/kg ethers. Corresponding, the 3-6 cm layer contained 23 mg/kg THC and 56 mg/kg ethers. Station TOR12 has a content of THC (or sum THC plus ether) close to the limit of contamination. The other stations analysed show elevated levels of THC (or THC plus ethers). Thus elevated levels of THC (or THC/ether) are observed out to 500m in the 180° direction and to 250m in the 90 and 360° direction.

Slightly elevated NPD concentrations are found at the two stations analysed, TOR5, 180°/250m and TOR6, 180°/500m. At TOR5, elevated levels of NPD are also found in the deeper layers. At TOR6 the concentration of NPD is low in the deeper layers and has decreased since 2002. The PAH content has increased slightly since 2002 survey. The mean concentration of PAH is 0.053 mg/kg at TOR5 and 1.6 ± 2.5 mg/kg at TOR6. The elevated

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level at TOR6 is mainly due to grab #3. Therefore the standard deviation for the mean value at TOR6 is high. Significant differences between replicates have been observed earlier for this region. Decalins are not found in the top 0-1 cm layer of the stations. Small amount is, however, found in the deeper layers at TOR5.

The Ba concentrations vary from 341 mg/kg at TOR6, 180°/500m to 1505 mg/kg at TOR5, 180°/250m. Elevated Ba concentrations are found at the two stations analysed; out to 500m in the 180° direction. The concentrations are similar to the 2002 and 1999 survey. High concentrations are also found in the 0-1 cm and 3-6 cm layers at TOR5, 180°/250m, 2744 mg/kg and 3501 mg/kg respectively.

The concentrations of the heavy metals are low, however some elevated concentrations of heavy metals are found, particularly at TOR5, 180°/250m and in the layer samples as well. No increases are observed since 2002.

The chemical results agree with the drilling history. No drilling activities has taken place at Tor 2/4 E since 1990 and only minor discharges has taken place in the periode 2002-2005. In 1990 the drilling fluid Aquamul B was added as a lubricant in the water based mud drilling.

The fauna community at station TOR-06 (180º/500m) is characterized as relatively healthy, independent of the abundance of M. oculata. The biodiversity indices have increased at both stations since the last survey, indicating improvement in the fauna community. However, the decline in M. oculata observed at TOR-06 was not observed at TOR-05, located 250m from the centre. The abundance of M. oculata, higher levels of THC and metals combined with field observations of oil film/black spots, still indicate some disturbance.

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4.15 Yme Gamma

4.15.1 Sediment characterization

Grain size distribution

The grain size distribution from the present shown is given in Table 4.15.1 together with the silt and clay content from the previous surveys in 2002, 1999 and 1996.

The sediments at the regular Yme Gamma monitoring stations consist of medium sand, and the sand content varies from 94 % at YMEG5, 120°/500m to 98 % at reference station YMEG18, 300°/10000m. The gravel content is low, and small amounts are found at some stations. The silt and clay content is similar to previous surveys.

As in the 2002 survey samples from the Installation Centre, YMEG Central (0°/0m) and from stations at 100m distance are included. At the centre 0°/0m the sediments consist of 81 % silt and clay. High contents of silt and clay are also found at YMEGII, 120°/100m (38 %) and at YMEG-III, 210°/100m (25 %). At YMEG-I, 30°/100m and YMEG-IV, 300°/100m, the silt and clay content is similar to the regular monitoring stations at Yme Gamma. The sand content varies from 93.6 % at YMEG-IV to 94.9 % at YMEG-I. The sediments at the 100m stations are characterized as medium sand. The highest gravel content is found at YMEG-IV, 6.1%.

At the reference station, YMEG18, the sediment is characterized as medium sand with 98.3 % sand and a median particle diameter of 1.71φ. The results from the complete grain size distribution are given in Appendix C. Table 4.15.1. Yme Gamma 2005, grain size distribution. Station Median

diameterClassification Grain size distrib. 2005

(%) 2002

(%) 1999 (%)

1996 (%)

Mdφ Silt and clay

Sand Gravel Silt and clay

Silt and clay

Silt and clay

YMEG1 30°/250m 1.75 Medium sand 3.8 95.4 0.8 3.0 2.4 YMEG5 120°/250m 1.79 Medium sand 6.1 93.9 0.0 4.5 5.6 2.0 YMEG6 120°/500m 1.74 Medium sand 2.9 96.6 0.5 5.2 2.9 2.2 YMEG10 210°/250m 1.73 Medium sand 2.9 96.8 0.3 2.0 1.5 YMEG14 300°/250m 1.75 Medium sand 3.4 96.5 0.1 1.6 2.8 Mean (excl. ref. station) 1.75 3.8 95.8 0.34 3.3 4.3 2.2 Standard deviation 0.02 1.3 1.2 0.32 1.6 1.9 0.5 YMEG Cent.* 0°/0m 5.53 Silt and clay 81.1 15.5 3.4 75.4 YMEG-I 30°/100m 1.73 Medium sand 4.6 94.9 0.5 11.1 YMEG-II 120°/100m 2.16 Medium sand 38 60.8 1.2 16.2 YMEG-III 210°/100m 1.93 Medium sand 25.3 74.4 0.3 9.3 YMEG-IV 300°/100m 1.65 Medium sand 0.3 93.6 6.1 10.2 YMEG18 ref. 300°/10000m 1.71 Medium sand 1.6 98.3 0.1 0.5 2.8 0.9 Mean (excl. ref. station) 1.84 14.0 84.4 1.6 9.5 Standard deviation 0.21 16.8 16.2 2.5 5.7 * not included in the mean value

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Total organic matter (TOM)

The content of TOM in the sediments is low at the regular monitoring stations. The concentrations range from 0.52 % (YMEG10 and YMEG18 Ref.) to 0.69 % (YMEG5). The results are similar to the previous surveys. At the Installation Centre 0°/0m the TOM content is high, 5.6 %. Relatively high TOM contents are also found at YMEG-II and YMEG-III, 2.8 % and 2.4 % respectively. The results are similar to the 2002 survey. The results correspond to the grain size distribution, and they are shown in Table 4.15.2. Table 4.15.2. Yme Gamma 2005, total organic matter (% of dry sediment). Station 2005, 0-5 cm

One sampleMean 2002 SD

2002 Mean 1999 Mean

1996 YMEG1 30°/250m 0.52 0.65 0.07 0.74 YMEG5 120°/250m 0.69 0.93 0.13 0.86 0.96 YMEG6 120°/500m 0.56 0.70 0.02 0.64 0.90 YMEG10 210°/250m 0.55 0.53 0.06 0.68 YMEG14 300°/250m 0.57 0.61 0.02 0.73 YMEG Cent. 0°/0m 5.61 6.58 0.82 YMEG-I 30°/100m 0.78 1.28 0.43 YMEG-II 120°/100m 2.81 6.58 7.55 YMEG-III 210°/100m 2.43 1.39 0.23 YMEG-IV 300°/100m 0.68 2.82 3.77 YMEG18 ref. 300°/10000m 0.52 0.63 0.11 0.59 0.67

4.15.2 Chemical analyses

Parameters analysed in the sediments at Yme Gamma:

• THC • Olefins • Esters • NPD, PAH, decalins • PFOS (perfluorooctyl sulphonate) • Metals (Ba, Cd, Cr, Cu, Hg, Pb, Zn)

Three replicate samples at each station and five replicate samples at the reference station are analysed. The samples are taken from the top 0-1 cm sediment layer. In addition the 1-3 cm and 3-6 cm sediment layers are sampled at two stations. Station YMEG Central is analysed for additional five layers; 1-3 cm, 3-6 cm, 6-9 cm, 9-12 cm and 12-15 cm.

Based on the 2002 survey, the sampling programme has been somewhat reduced to only focussing on stations close to the centre. The removal of the template made it possible to conduct an additional study, including stations close to the centre in 2002. These stations have also been sampled in 2005, including centre positions.

THC and olefins

The THC results including olefins are shown in Table 4.15.3, and olefins separately in Table 4.15.4. The corresponding data from the previous surveys in 2002, 1999 and 1996 are also included for comparison. Bar diagrams of the THC content in the sediments are shown in Figure 4.15.1 and Figure 4.15.2.

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In 1999 the concentration of THC ranged from 1.9 mg/kg (YMEG18 Ref.) to 173 mg/kg (YMEG5) and the concentration of olefins varied correspondingly from less than 0.2 mg/kg to 35 mg/kg. In 2002, the concentration ranged from 1.8 mg/kg to 87 mg/kg. The olefin concentrations varied from less than 0.2 mg/kg to 9.9 mg/kg (YMEG1).

In the present survey, the mean THC concentrations at the regular monitoring stations varied from 2.4 mg/kg at YMEG10, 210°/250m to 32 mg/kg at YMEG5, 120°/250m. The concentration of olefins varied correspondingly from <0.4 mg/kg to 2.5 mg/kg. The maximum concentrations of THC were found at YMEG5, with 32 mg/kg in the top 0-1 cm layer, 53 mg/kg in the 1-3 cm layer and 91 mg/kg in the 3-6 cm layer. Thus, the THC concentration increases downwards in the sediment. At YMEG5 and YMEG1, the concentration of THC in the top 0-1 cm layer has decreased distinctly since the 2002 survey. At YMEG5 the THC concentration has decreased from 87 mg/kg to 32 mg/kg and at YMEG1 from 39 mg/kg to 5.7 mg kg. At the other stations the THC concentrations are low, with contents at about the limit of contamination. Thus elevated THC concentrations are only observed out to 250m in 120°direction. The THC content in the deeper layers has not changed since 2002.

Generally, the olefins are closely related to the THC content and thus a similar trend might be observed. At YMEG5, the olefin concentration in the top 0-1 cm layer has decreased from 35 mg/kg in 1999 to 4.8 mg/kg in 2002 to 2.5 mg/kg in 2005. The olefin concentrations in the layers increase downwards in the sediments. The maximum concentration is found in the 3-6 cm layer. Correspondingly, the concentrations of olefins at YMEG1 has decreased from 9.9 mg/kg in 2002 to not detected (<0.4 mg/kg) in the present survey. At the other stations the concentrations of olefins are low (<0.4 mg/kg).

At the Installation Centre 0°/0m the THC concentration is high, 4510 mg/kg. However, the concentration in the top 0-1 cm layer has decreased distinctly compared to the 2002 survey where a THC content of 1.3% was found. Deeper sections down to 15 cm depth are investigated. It is observed that the THC concentrations decrease gradually downwards in the sediments (from 4510 mg/kg in the top 0.1 cm layer to 650 mg/kg in the 12-15 cm layer). The content of the THC in the deeper layers is similar to the 2002 level. High concentrations are also found at the 100 m stations in the 30°, 120° and 210° directions, where the mean concentrations vary from 34 mg/kg in the 30° direction to 706 mg/kg in the 120° direction. The THC concentration is only 8.5 mg/kg in the 300° direction. Compared to the 2002 survey the THC content has decreased significantly for all the directions.

The sediments from the Installation centre also contain olefins. However, these are not quantified. The olefins found at Yme Gamma consist mainly of C14 and C16 olefins. This is in agreement with the reported discharges of about 78 tonnes of Ultidril (C14 and C16 olefins) in 1999 prior to the 1999 survey.

The YMEG18, reference station, 300°/10000m is still uncontaminated, and the mean THC concentration of five replicate samples is 2.7 mg/kg.

Representative gas chromatograms are given in Appendix C. These include YMEG1, 30°/250m, YMEG5, 120°/250m (layers: 0-1cm and 3-6 cm), YMEG central, 0°/0m, YMEG-I, 30°/100m, YMEG-IV, 300°/100m and YMEG18, reference station, 300°/10000m.

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Yme Gamma, THC 2005

0

20

40

60

80

100

120

140

160

180

200

YMEG1 YMEG5 YMEG6 YMEG10 YMEG14 YMEG18 Ref

station

mg/kg

1999

2002

2005

LSC A

Figure 4.15.1. Bar diagram of the THC content in the sediments at Yme Gamma 1999-2005.

Yme Gamma, THC 2005

0

2000

4000

6000

8000

10000

12000

14000

YMEG Cent. YMEG-I YMEG-II YMEG-III YMEG-IV

station

mg/kg

2002

2005

LSC A

13100±5403

Figure 4.15.2. Bar diagram of the THC content in the sediments at Yme Gamma Central 2002-2005.

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Table 4.15.3. Yme Gamma 2005, total hydrocarbon content (mg/kg dry sediment). Station Grab

#1 Grab

#2 Grab

#3 Grab

#4 Grab

#5 Mean SD Mean Mean Mean

2005 2005 2002 1999 1996 YMEG1 30°/250m 5.5 5.0 6.5 5.7 0.8 39 YMEG5 120°/250m 43 23 30 32 10 87 173 25 1-3 cm 53 97 73 7.2 3-6 cm 91 69 26 6.5 YMEG6 120°/500m 8.1 6.4 7.3 7.2 0.8 6.5 18 8.4 1-3 cm 6.4 3.8 3-6 cm 8.5 5.0 YMEG10 210°/250m 2.7 2.1 2.3 2.4 0.3 4.1 6.7 YMEG14 300°/250m 5.5 4.4 2.8 4.2 1.4 6.7 6.9 YMEG Cent. 0°/0m 3980 5330 4230 4510 716 13100 1-3 cm 4620 6180 3-6 cm 1710 1100 6-9 cm 1040 635 9-12 cm 1240 12-15 cm 650 YMEG-I 30°/100m 38 38 26 34 6.5 567 YMEG-II 120°/100m 470 895 755 706 217 537 YMEG-III 210°/100m 273 190 502 322 161 1257 YMEG-IV 300°/100m 9.4 7.1 8.9 8.5 1.2 6500 YMEG18 ref. 300°/10000m 3.0 2.7 3.3 2.7 1.9 2.7 0.5 1.8 1.9 3.6 1-3 cm 3.1 3-6 cm 1.4 LSC Subregion B 4.6 5.1 Table 4.15.4. Yme Gamma 1999, 2002 and 2005, olefins (mg/kg dry sediment). Station Grab

#1 Grab

#2 Grab

#3 Mean SD Mean Mean

2005 2005 2002 1999 YMEG1 30°/250m <0.4 <0.4 <0.4 <0.4 9.9 YMEG5 120°/250m 4.5 <0.4 2.7 2.5 2.1 4.8 35 1-3 cm 6.4 15.9 1.6 3-6 cm 10.0 3.9 <0.1 YMEG6 120°/500m <0.4 <0.4 <0.4 <0.4 0.7 2.3 1-3 cm <0.4 0.4 3-6 cm <0.4 0.3 YMEG10 210°/250m <0.4 <0.4 <0.4 <0.4 0.3 YMEG14 300°/250m <0.4 <0.4 <0.4 <0.4 0.3

Esters

Two stations are analysed, YMEG5, 120°/250m and YMEG6, 120°/500m. The ester analysis includes Finagreen and Petrofree, and the results are shown in Table 4.15.5. The corresponding ester data from the previous surveys in 2002, 1999 and 1996 are also included for comparison.

In 1996 Petrofree dominated, and the concentrations varied below 0.01 mg/kg (YMEG18 Ref.) to 312 mg/kg (YMEG5). The Finagreen concentrations were lower and varied from below 0.01 mg/kg to 17.8 mg/kg (YMEG5). In 1999 Petrofree 16.4 mg/kg was found at YMEG5 and 0.9

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mg/kg at YMEG6. A decrease was observed since 1996. Finagreen was not detected. In 2002 the Petrofree concentrations were further reduced to 4.3 mg/kg (YMEG5) to 0.4 mg/kg (YMEG6). Finagreen was not detected.

In the present survey the Petrofree concentrations are similar to the 2002 survey. The concentration is 3.4 mg/kg at YMEG5, 120°/250m and 0.5 mg/kg at YMEG6, 120°/500m. As in 1999 and 2002 surveys, Finagreen is not detected. The results correspond with the discharge history and with the relatively easy degradation of ester compounds. In 1996 Petrofree was discharged prior to the survey, and high concentrations were observed in the sediments. Since the 1996 survey discharges of Petrofree have taken place in 1997 (371 tonnes) and in 1998 (44 tonnes). Finagreen has not been discharged since 1994. Gas chromatogram of YMEG5, 120°/250m is given in Appendix C. Table 4.15.5. Yme Gamma 2005, esters (mg/kg dry sediment). Station Grab

#1Grab

#2Grab

#3Mean SD Mean Mean Mean

2005 2005 2002 1999 1996YMEG5 120°/250m 5.4 2.5 2.4 3.4 1.7 4.3 16.4 312 1-3 cm 4.7 2.5 12.8 3-6 cm 6.1 3.6 4.5 YMEG6 120°/500m 0.7 0.4 0.4 0.5 0.2 0.4 0.9 9.0 1-3 cm 0.5 0.6 3-6 cm 0.4 0.5

NPD, PAH and decalins

Two stations in the 120° direction, the Installation Centre and the reference station are analysed. In addition, stations with content of THC >50 mg/kg are analysed. These are the additional layers at the Installation Centre, (6-9 cm, 9-12 cm and 12-15 cm), and two stations at 100m distance (YMEG-II, 120°/100m and YMEG-III, 210°/100m). The results are shown in Table 4.15.6.

Elevated levels of NPD, PAH and decalins are found at YMEG5, 120°/250m. The NPD and PAH concentrations have increased since 2002. The decalin concentrations have decreased, but the level is still relatively high in the 3-6 cm layer (1.93 mg/kg). Only slightly elevated NPD and PAH concentrations are found at YMEG6, 120°/500m. Decalins are not detected. The mean NPD concentrations vary from <0.01 mg/kg (limit of detection) at the reference station to 0.66 mg/kg at YMEG5. Correspondingly the PAH concentrations vary from 0.13 mg/kg to 0.44 mg/kg. The decalin concentrations vary from <0.1mg/kg (limit of detection) to 0.17 mg/kg.

At the Installation Centre 0°/0m the concentrations of NPD, PAH and decalins are high (8.7 mg/kg of NPD, 1.9 mg/kg of PAH and 186 mg/kg of decalins). High concentration of NPD, PAH and decalins is also found in all the deeper layers in the 1-15 cm section, where the NPD content varies from 7.3 mg/kg to 13.7 mg/kg, the PAH content from 1.1 mg/kg to 1.5 mg/kg and the decalin content from 6.7 mg/kg to 174 mg/kg.

High levels of NPD, PAH and decalins at the 100m stations are also found. The decalin concentrations are in accordance with the THC content and represent 2~4 %.

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Table 4.15.6. Yme Gamma 2005, sum NPD, PAH and decalins (mg/kg dry sediment).

Station Grab #1

Grab #2

Grab #3

Grab #4

Grab #5

Mean SD Mean SD Mean SD Mean

2005 2005 2002 2002 1999 1999 1996NPD YMEG5 120°/250m 1.05 0.23 0.72 0.66 0.41 0.40 0.19 1.77 2.49 0.19 1-3 cm 0.53 0.24 0.41 0.047 3-6 cm 0.50 0.22 0.19 0.086YMEG6 120°/500m 0.05 0.06 0.05 0.05 0.01 0.027 0.008 1-3 cm 0.11 0.022 3-6 cm 0.23 0.029 YMEG Cent. 0°/0m 8.09 9.68 8.33 8.70 0.86 16.4 3.94 1-3 cm 9.10 12.8 3-6 cm 7.26 4.97 6-9 cm 9.88 3.45 9-12 cm 13.7 12-15 cm 9.13 YMEG-II 120°/100m 3.75 5.54 5.07 4.79 0.93 1.83 0.98 YMEG-III 210°/100m 2.56 2.66 2.72 2.65 0.08 1.67 0.72 YMEG Ref 300°/10000m nd nd nd nd nd nd 0.006 0.001 0.005 0.001 0.018 1-3 cm nd 0.006 0.004 0.005 3-6 cm 0.021 0.006 0.007 0.005LSC Subregion B 0.012 0.024 0.040 PAH YMEG5 120°/250m 0.51 0.057 0.755 0.44 0.35 0.12 0.041 0.29 0.20 0.066 1-3 cm 0.14 0.062 0.12 0.059 3-6 cm 0.11 0.078 0.068 0.033YMEG6 120°/500m 0.049 0.031 0.026 0.035 0.012 0.046 0.008 1-3 cm 0.039 0.051 3-6 cm 0.061 0.046 YMEG Cent. 0°/0m 1.50 2.62 1.62 1.92 0.62 2.51 0.70 1-3 cm 1.42 1.38 3-6 cm 1.52 0.99 6-9 cm 1.36 0.72 9-12 cm 1.24 12-15 cm 1.07 YMEG-II 120°/100m 0.84 1.37 1.21 1.14 0.27 0.47 0.24 YMEG-III 210°/100m 0.51 0.84 0.70 0.69 0.17 0.32 0.067 YMEG Ref 300°/10000m 0.020 0.013 0.012 0.010 0.009 0.013 0.004 0.011 0.003 0.015 0.001 0.039 1-3 cm 0.013 0.011 0.015 0.020 3-6 cm 0.036 0.010 0.025 0.018LSC Subregion B 0.024 0.048 0.090 cont.

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Table 4.15.6. cont. Station Grab

#1 Grab

#2 Grab

#3 Grab

#4 Grab

#5 Mean SD Mean SD Mean SD Mean

2005 2005 2002 2002 1999 1999 1996Decalins YMEG5 120°/250m 0.23 0.14 0.13 0.17 0.06 2.72 1.57 1.87 2.11 0.37 1-3 cm 0.46 2.85 0.98 0.12 3-6 cm 1.93 2.38 0.30 0.094YMEG6 120°/500m nd nd nd nd 0.10 0.051 1-3 cm nd 0.11 3-6 cm nd 0.10 YMEG Cent. 0°/0m 166 246 146 186 53 201 29 1-3 cm 174 163 3-6 cm 44 38 6-9 cm 11.5 13.8 9-12 cm 10.2 12-15 cm 6.7 YMEG-II 120°/100m 12.6 25.6 15.6 17.9 6.8 15 12 YMEG-III 210°/100m 11.8 7.3 24.7 14.6 9.0 32 14 YMEG Ref 300°/10000m 0.34 0.008 0.009 0.004 0.004 <0.3 nd nd 0.039 1-3 cm nd nd nd 0.034 3-6 cm 1.17 nd nd 0.039nd: not detected. Limit of detection for NPD is 0.01 mg/kg, for PAH 0.005 mg/kg and for decalins 0.1mg/kg.

PFOS (perfluorooctyl sulphonate)

One station is analysed at Yme Gamma Central, YMEG-II, 120°/100m. The result is shown in Table 4.15.7. YMEG-II has a content of PFOS 25.8 µg/kg. Table 4.15.7. Yme Gamma 2005, PFOS (perfluorooctyl sulphonate), µg/kg dry sediment. Station PFOS YMEG-II 120°/100m 19.4 21.7 36.3 Mean 25.8 SD 7.5 Limit of detection: 0.1 µg/kg

Metals

The results are shown in Table 4.15.8. For comparison, data from the present survey and previous surveys in 2002, 1999 and 1996 are included in Table 4.15.9. Bar diagrams of the Ba content in the sediments are shown in Figure 4.15.3 and Figure 4.15.4.

In 1999 the mean Ba concentrations at the regular monitoring stations ranged from 6 mg/kg at the reference station, YMEG18 Ref., 300°/10000m to 4520 mg/kg at YMEG5, 120°/250m. High Ba concentrations, 994 mg/kg, were also found at YMEG6, 120°/500m. Compared to 1996 the Ba concentrations increased at most stations, particularly at YMEG5, 120°/250m. In 2002 the mean Ba concentrations varied from 6 mg/kg at YMEG18 to 4350 mg/kg at YMEG5. High Ba concentrations were also found at YMEG6, 120°/500m.

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In the present survey the mean Ba concentrations vary from 10 mg/kg YMEG18 to 4489 mg/kg at YMEG5. High Ba concentrations are also found at YMEG1, 30°/250m, YMEG6, 120°/500m, respectively 1778 mg/kg and 1466 mg/kg. The Ba concentrations are similar or slightly lower compared to the 2002 and 1999 results. The results agree with the drilling activity in the period since the last survey.

At the Yme fields the background levels of Ba are less than at the other fields of Region I. The Yme fields are included in Subregion B with an LSC (limit of contamination) value for Ba of 12.1 mg/kg. Thus elevated Ba concentrations are found at all stations, except for the reference station, out to 500m in the 120° direction and 250m in the other directions.

The concentrations of the heavy metals are low and unchanged since the 2002 survey.

At the Installation Centre 0°/0m the Ba concentration has decreased from 6050 mg/kg in 2002 to 705 mg/kg in this survey. The same decrease is observed in the deeper layers 1–3 cm and 3-6 cm. High concentrations of Ba are found at the 100m stations in all four directions, ranging from 2247 mg/kg in the 300° direction to 5630 mg/kg in the 210° direction. Elevated levels of heavy metals are found both at 0°/0m and at the 100m stations.

Yme Gamma, Ba 2005

0

500

1000

1500

2000

2500

3000

3500

4000

4500

5000

YMEG1 YMEG5 YMEG6 YMEG10 YMEG14 YMEG18 Ref

station

mg/kg

1999

2002

2005

LSC A

Figure 4.15.3. Bar diagram of the Ba content in the sediments at Yme Gamma 1999-2005.

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Yme Gamma, Ba 2005

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

YMEG Cent. YMEG-I YMEG-II YMEG-III YMEG-IV

station

mg/kg

2002

2005

LSC A

Figure 4.15.4. Bar diagram of the Ba content in the sediments at Yme Gamma Central 2002-2005. The following variations are found at Yme Gamma in the top layer, 0-1 cm, at the Installation Centre and at a distance of 100m, given in mg/kg: Yme Gamma: YMEG1 – YMEG14 YMEG0 – YMEG-IV YMEG18 Reference station Ba: 181 – 4489 705 – 5630 10 Cr: 5.8 – 9.5 3.8 – 50 7.3 Cu: 1.0 – 20 5.2 – 78 <0.5 Pb: 5.5 – 11 7.8 – 99 7.7 Zn: 7.8 – 56 12.7 – 168 7.0 Cd: <0.01 – 0.02 <0.01 – 0.52 <0.01 Hg: <0.01 0.14 <0.01

Table 4.15.8. Yme Gamma 2005, metals (mg/kg dry sediment). Station Sample Ba Cd Cr Cu Hg Pb Zn 2005 2005 2005 2005 2005 2005 2005 YMEG1 30°/250m 1 1693 <0.01 5.8 3.3 7.2 12.8 2 2076 <0.01 6.1 4.0 8.0 14.6 3 1564 <0.01 5.5 2.2 7.2 9.8 mean 1778 <0.01 5.8 3.2 7.4 12.4 SD 267 - 0.3 0.9 0.5 2.5 YMEG5 120°/250m 1 4322 0.01 8.7 6.3 <0.01 11.6 20 2 4606 <0.01 8.5 5.0 <0.01 11.1 19.0 3 4540 <0.01 8.0 7.7 <0.01 10.3 16.4 mean 4489 <0.01 8.4 6.3 <0.01 11.0 18.6 SD 148 - 0.3 1.4 - 0.6 2.0 1-3 cm 1 4105 <0.01 7.7 5.1 <0.01 9.8 15.4 3-6 cm 1 6521 0.04 9.9 5.5 0.01 14.7 25 Cont.

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Table 4.15.8. cont. Station Sample Ba Cd Cr Cu Hg Pb Zn 2005 2005 2005 2005 2005 2005 2005 YMEG6 120°/500m 1 1374 <0.01 6.6 1.1 <0.01 5.9 8.1 2 1531 <0.01 6.7 1.1 <0.01 5.7 8.6 3 1492 <0.01 6.6 0.9 <0.01 5.0 6.8 mean 1466 <0.01 6.6 1.0 <0.01 5.5 7.8 SD 82 - 0.1 0.1 - 0.4 0.9 1-3 cm 1 1534 <0.01 6.4 1.2 <0.01 7.1 7.8 3-6 cm 1 2616 <0.01 7.2 2.0 0.02 8.2 9.5 YMEG10 210°/250m 1 186 0.06 13.6 38 8.7 104 2 79 <0.01 8.4 17.1 4.7 46 3 277 <0.01 6.6 5.5 5.6 18.2 mean 181 0.02 9.5 20.3 6.3 56 SD 99 0.04 3.6 16.6 2.1 44 YMEG14 300°/250m 1 423 <0.01 5.6 1.7 6.9 9.4 2 861 <0.01 6.1 1.5 6.9 8.6 3 261 <0.01 5.5 0.9 6.4 7.2 mean 515 <0.01 5.8 1.4 6.8 8.4 SD 310 - 0.3 0.4 0.3 1.1 YMEG Cent. 0°/0m 1 714 0.56 49 88 0.11 103 143 2 775 0.50 46 80 0.10 98 130 3 624 0.49 53 69 0.22 96 128 mean 705 0.52 50 78 0.14 99 134 SD 76 0.04 3.4 8.3 0.07 3.7 8.4 1-3 cm 524 0.80 48 84 0.09 179 136 3-6 cm 517 0.33 50 81 0.06 156 103 YMEG-I 30°/100m 1 4681 0.02 4.9 5.6 9.1 22 2 5076 0.03 5.4 19.3 9.8 16.0 3 4128 0.06 4.3 6.2 7.0 11.9 mean 4628 0.03 4.9 10.4 8.6 16.6 SD 476 0.02 0.6 7.8 1.5 5.0 YMEG-II 120°/100m 1 2984 0.33 38 88 100 187 2 2956 0.18 30 54 69 109 3 2463 0.30 42 91 100 209 mean 2801 0.27 37 18.1 90 168 SD 293 0.08 6.1 31 18 53 YMEG-III 210°/100m 1 5671 0.03 11.2 14.4 18.1 35 2 5679 0.05 16.4 40 24 45 3 5542 0.05 13.2 21 24 40 mean 5631 0.04 13.6 25 22 40 SD 77 0.01 2.6 13.4 3.5 4.6 YMEG-IV 300°/100m 1 2476 <0.01 3.7 4.8 7.9 11.7 2 2475 <0.01 3.4 6.2 8.0 14.2 3 1790 <0.01 4.4 4.6 7.5 12.1 mean 2247 <0.01 3.8 5.2 7.8 12.7 SD 396 - 0.5 0.9 0.2 1.3 cont.

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Table 4.15.8. cont. Station Sample Ba Cd Cr Cu Hg Pb Zn 2005 2005 2005 2005 2005 2005 2005 YMEG18 Ref. 300°/10000m 1 18 <0.01 6.9 <0.5 <0.01 7.2 6.2 2 7 <0.01 7.6 <0.5 <0.01 8.2 6.6 3 7 <0.01 6.9 <0.5 <0.01 7.4 5.6 4 13 <0.01 7.8 <0.5 <0.01 8.7 10.8 5 5 <0.01 7.2 <0.5 <0.01 7.2 5.9 mean 10 <0.01 7.3 <0.5 <0.01 7.7 7.0 SD 5 - 0.4 <0.5 0.7 2.1 1-3 cm 5 5 <0.01 7.1 <0.5 <0.01 6.8 5.8 3-6 cm 5 13 <0.01 7.3 <0.5 <0.01 6.9 6.5 LSC Subregion B 12.1 11.1 1.4 9.0 8.8 Table 4.15.9. Yme Gamma 2005, metals (mg/kg dry sediment), comparing mean values with previous surveys. Station Ba Ba Ba Ba Cd Cd Cd Cr Cr Cr 2005 2002 1999 1996 2005 2002 1999 2005 2002 1999YMEG1 30°/250m 1778 1240 2420 <0.01 0.01 5.8 5.4 YMEG5 120°/250m 4489 4350 4520 1110 <0.01 0.03 0.03 8.4 7.9 6.9 1-3 cm 4105 5206 4760 <0.01 0.02 0.05 7.7 9.5 7.4 3-6 cm 6521 3170 4690 0.04 0.02 0.02 9.9 6.9 7.5 YMEG6 120°/500m 1466 2100 994 426 <0.01 <0.01 <0.02 6.6 6.6 5.9 1-3 cm 1534 2378 <0.01 <0.01 6.4 6.0 3-6 cm 2616 2483 <0.01 0.01 7.2 7.1 YMEG10 210°/250m 181 387 662 0.02 0.01 9.5 5.6 YMEG14 300°/250m 515 771 464 <0.01 <0.01 5.8 6.0 YMEG Cent 0°/0m 705 6050 0.52 0.49 50 39 1-3 cm 524 4966 0.80 0.46 48 41 3-6 cm 517 4736 0.33 0.17 50 38 YMEG-I 30°/100m 4628 5700 0.03 0.09 4.9 8.9 YMEG-II 120°/100m 2801 7410 0.27 0.14 37 17.7 YMEG-III 210°/100m 5631 5790 0.04 0.09 13.6 11.2 YMEG-IV 300°/100m 2247 4080 <0.01 0.13 3.8 15.8 YMEG18 Ref. 300°/10000m 10 6 6 6 <0.01 <0.01 <0.2 7.3 6.9 9.8 1-3 cm 5 6 9 <0.01 <0.01 <0.02 7.1 6.9 9.7 3-6 cm 13 9 14 <0.01 0.01 <0.02 7.3 6.8 9.2 cont.

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Table 4.15.9. cont. Station Cu Cu Cu Hg Hg Hg Pb Pb Pb Zn Zn Zn 2005 2002 1999 2005 2002 1999 2005 2002 1999 2005 2002 1999YMEG1 30°/250m 3.2 4.2 7.4 8.0 12.4 14.4 YMEG5 120°/250m 6.3 5.2 7.2 <0.01 0.01 0.02 11.0 10.4 11.9 18.6 18.8 19.7 1-3 cm 5.1 4.5 6.6 <0.01 0.01 0.02 9.8 9.9 11.8 15.4 17.6 28 3-6 cm 5.5 3.9 3.6 0.01 0.01 0.02 14.7 8.3 9.0 25 19.0 10.1YMEG6 120°/500m 1.0 2.7 2.1 <0.01 0.02 5.5 6.8 6.7 7.8 10.2 10.1 1-3 cm 1.2 1.8 <0.01 0.03 7.1 6.9 7.8 7.5 3-6 cm 2.0 2.0 0.02 0.01 8.2 7.8 9.5 10.2 YMEG10 210°/250m 20.3 4.5 6.3 7.2 56 17.2 YMEG14 300°/250m 515 3.1 6.8 7.2 8.4 11.2 YMEG Cent 0°/0m 78 76 0.14 0.16 99 95 134 136

1-3 cm 84 59 0.09 0.15 179 63 136 115 3-6 cm 81 39 0.06 0.04 156 31 103 77 YMEG-I 30°/100m 4628 5700 0.03 0.09 4.9 8.9 YMEG-II 120°/100m 2801 7410 0.27 0.14 37 17.7 YMEG-III 210°/100m 5631 5790 0.04 0.09 13.6 11.2 YMEG-IV 300°/100m 2247 4080 <0.01 0.13 3.8 15.8 YMEG18 Ref 300°/10000m <0.5 0.8 0.3 <0.01 <0.01 <0.05 7.7 7.5 9.9 7.0 5.4 7.4

1-3 cm <0.5 0.8 0.4 <0.01 <0.01 0.03 6.8 7.2 10.1 5.8 5.1 7.6 3-6 cm <0.5 1.4 0.7 <0.01 0.01 0.03 6.9 7.7 9.2 6.5 5.7 7.8

4.15.3 Biological analyses

A total of 219 species and 9139 individuals were sampled at 10 stations. Greatest abundance (72.5 %) was found among the polychaetes, of which the species Paramphinome jeffreysii constitutes 32.5 % and Myriochele oculata constitutes about 4.6 % of the total number of Polychaeta, see Table 4.15.10. Table 4.15.10. Number of species and individuals distributed between the main groups, Yme Gamma 2005.

Individuals Species Main animal groups Number % Number %

Varia 1137 12.4 22 10.0Polychaeta 6625 72.5 94 42.9- Paramphinome jeffreysii 2153 32.5 - Myriochele oculata 304 4.6 Crustacea 473 5.2 45 20.5Mollusca 622 6.8 47 21.5Echinodermata 282 3.1 11 5.0- Amphiura filiformis 84 29.8 Total 9139 100.0 219 100.0

The sampling programme included biological analyses from the Installation Centre, YMEG Central (0°/0m). The sediment samples were, however, greasy with oil, and not suitable for sieving. Some of the material was brought to the laboratory for a qualitative analysis. Only one species was found; Capitella capitata. This polychaete is a well known indicator species of oil

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contamination. Based on observations from the sampling and in the laboratory this station is characterized as heavily disturbed.

Figure 4.15.5 shows the numbers of species and individuals sampled at each station and variations between grab samples.

0250500750

10001250150017502000

YMEG-01YMEG-05YMEG-6

YMEG-10YMEG-14

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No.

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-01

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5YM

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Station º/m Station º/m Station º/m Station º/m Station º/m YMEG-01 30/250 YMEG-6 120/500 YMEG-14 300/250 YMEG-I 30/100 YMEG-III 210/100 YMEG-05 120/250 YMEG-10 210/250 YMEG-Ref 300/10000 YMEG-II 120/100 YMEG-IV 300/100

Figure 4.15.5. Numbers of species (S) and individuals (N) per 0.5 m2 (incl./excl. P. jeffreysii and M. oculata), mean values per grab sample and standard deviation, Yme Gamma 2005.

The standard deviation was only slightly reduced when the two species P. jeffreysii and M. oculata were removed. This is due to the fact that the two species constitute only 26.9 % of the total number of individuals, and that there are large differences between the five grabs sampled at each station.

Diversity and dominant species

The dominant species at each station varied from 9.2 % at the Yme Gamma reference station (300°/1000m) to 45.8 % at station YMEG-II (120°/100m). The 10 most abundant species made up from 51.4 % at the Yme Gamma reference station to 89.3 % at YMEG-II, Table 4.15.11. The bristle worms Exogone verugera, M. oculata and P. jeffreysii together with the anthozoan Edwardsia sp. dominated the fauna. Other frequently found species were the bristle worms Ampharete falcate and Ditrupa arietina and also the ribbon worm Nemertea spp., the echinoderm Amphiura filiformis and the mussel Arctica islandica. P. jeffreysii and E. verugera are mainly carnivore species and the ribbon worm is a deposit feeder. The other mentioned

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species are either suspension- or both suspension- and deposit feeders. The structure in the fauna community in general indicates a healthy environment. Table 4.15.11. The 10 most abundant species at each station, Yme Gamma 2005. 10 most dominating species YMEG-01 No. % Cum. % YMEG-05 No. % Cum. %Exogone verugera 220 26.8 26.8 Chaetozone setosa 138 16.7 16.7Paramphinome jeffreysii 79 9.6 36.4 Nemertea spp. 86 10.4 27.2Myriochele oculata 65 7.9 44.3 Paramphinome jeffreysii 77 9.3 36.5Echinoidea spp.juv. 27 3.3 47.6 Natatolana borealis juv. 62 7.5 44.0Arctica islandica 27 3.3 50.9 Tharyx sp. 53 6.4 50.4Nemertea spp. 25 3.0 53.9 Exogone verugera 45 5.5 55.9Edwardsia sp. 24 2.9 56.8 Arctica islandica 30 3.6 59.5Ampharete falcata 21 2.6 59.4 Timoclea ovata 22 2.7 62.2Amphiura filiformis 18 2.2 61.6 Paradoneis lyra 20 2.4 64.6Spiophanes kroyeri 17 2.1 63.6 Glycera alba 19 2.3 66.9 YMEG-06 No. % Cum. % YMEG-10 No. % Cum. %Exogone verugera 131 20.0 20.0 Exogone verugera 101 17.9 17.9Melita obtusata 55 8.4 28.4 Paramphinome jeffreysii 55 9.8 27.7Paramphinome jeffreysii 52 7.9 36.3 Echinoidea spp.juv. 30 5.3 33.0Edwardsia sp. 28 4.3 40.6 Myriochele oculata 30 5.3 38.3Spiophanes kroyeri 25 3.8 44.4 Nemertea spp. 25 4.4 42.7Nemertea spp. 24 3.7 48.1 Amphiura filiformis 20 3.6 46.3Myriochele oculata 21 3.2 51.3 Edwardsia sp. 16 2.8 49.1Echinoidea spp.juv. 18 2.8 54.1 Glycera alba 15 2.7 51.8Cerianthus lloydii 16 2.4 56.5 Glycera lapidum 13 2.3 54.1Jasmineira caudata 13 2.0 58.5 Spiophanes bombyx 13 2.3 56.4 YMEG-14 No. % Cum. % YMEG-Ref No. % Cum. %Exogone verugera 149 18.5 18.5 Edwardsia sp. 20 9.2 9.2Paramphinome jeffreysii 100 12.4 31.0 Paramphinome jeffreysii 17 7.8 17.0Myriochele oculata 55 6.8 37.8 Spiophanes bombyx 14 6.4 23.4Nemertea spp. 34 4.2 42.0 Antalis entale 11 5.1 28.4Edwardsia sp. 30 3.7 45.8 Aonides paucibranchiata 10 4.6 33.0Amphiura filiformis 26 3.2 49.0 Exogone verugera 10 4.6 37.6Spiophanes kroyeri 26 3.2 52.2 Spiophanes kroyeri 9 4.1 41.7Notomastus sp. 25 3.1 55.4 Amphiura filiformis 7 3.2 45.0Spiophanes bombyx 24 3.0 58.3 Nemertea spp. 7 3.2 48.2Scoloplos armiger 17 2.1 60.5 Spiophanes wigleyi 7 3.2 51.4 YMEG-I No. % Cum. % YMEG-II No. % Cum. %Paramphinome jeffreysii 507 30.8 30.8 Paramphinome jeffreysii 849 45.8 45.8Ditrupa arietina 299 18.2 48.9 Nemertea spp. 337 18.2 63.9Chaetozone setosa 128 7.8 56.7 Ampharete falcata 225 12.1 76.1Nemertea spp. 71 4.3 61.0 Pholoe baltica 69 3.7 79.8Exogone verugera 51 3.1 64.1 Chaetozone setosa 56 3.0 82.8Heteromastus filiformis 42 2.6 66.7 Glycera alba 34 1.8 84.6Thyasira sarsii 41 2.5 69.2 Caprellidae spp. 30 1.6 86.3Tharyx sp. 31 1.9 71.0 Tharyx sp. 20 1.1 87.3Thyasira flexuosa 29 1.8 72.8 Caudofoveata spp. 19 1.0 88.4Ampharete falcata 27 1.6 74.4 Cerianthus lloydii 17 0.9 89.3 Cont.

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Table 4.15.11. cont. YMEG-III No. % Cum. % YMEG-IV No. % Cum. %Paramphinome jeffreysii 376 35.6 35.6 Exogone verugera 104 15.0 15.0Chaetozone setosa 127 12.0 47.6 Ditrupa arietina 53 7.7 22.7Ampharete falcata 73 6.9 54.5 Myriochele oculata 51 7.4 30.1Nemertea spp. 60 5.7 60.2 Nemertea spp. 48 6.9 37.0Pholoe baltica 43 4.1 64.2 Paramphinome jeffreysii 41 5.9 42.9Caudofoveata spp. 32 3.0 67.3 Chaetozone setosa 36 5.2 48.1Myriochele oculata 31 2.9 70.2 Tharyx sp. 32 4.6 52.8Tharyx sp. 29 2.7 72.9 Cerianthus lloydii 26 3.8 56.5Glycera alba 24 2.3 75.2 Spiophanes bombyx 24 3.5 60.0Ampelisca diadema/tenuicornis 20 1.9 77.1 Glycera alba 22 3.2 63.2

The number of species varied from 62 at YMEG-14 (300°/250m) to 99 at YMEG-10 (210°/250m). The number of individuals varied from 213 at YMEG-14 to 1852 at YMEG-II (120°/100m). The Shannon Wiener diversity index varied from 3.0 at YMEG-II to 5.3 at YMEG-14 and the Hurlberts index (ES100) varied from 18 at YMEG-II to 43 at YMEG-14. Indices above 4 indicate a relatively undisturbed fauna. Indices between 3 and 4 indicate a slight disturbance, while indices between 2 and 3 indicate a disturbance in the fauna. In general, ES100 indices above 20 characterize a relatively normal fauna community, see Table 4.15.12.

The biodiversity indices indicate disturbances in the fauna at the 100 m station YMEG-II, but also the 100 m stations YMEG-I and III had somewhat lower indices than the rest of the stations in the area, though the indices were above 4 and 20 respectively. Table 4.15.12. Numbers of individuals (N) and species (S), depth, Shannon-Wiener diversity index (H’), Pielou’s evenness index (J), and expected number of species per 100 individuals (ES100) for each station at Yme Gamma 2005, (excl. juv.). Station Direction ° Distance m Depth S N H' J ES100 YMEG-01 30 250 94 97 788 4.7 0.7 36YMEG-05 120 250 95 88 757 4.8 0.7 34YMEG-06 120 500 95 94 533 5.2 0.8 42YMEG-10 210 250 95 99 789 5.0 0.8 38YMEG-14 300 250 95 62 213 5.3 0.9 43YMEG-Ref 300 10000 90 90 633 5.0 0.8 39YMEG-I 30 100 93 89 1643 4.1 0.6 28YMEG-II 120 100 94 66 1852 3.0 0.5 18YMEG-III 210 100 93 85 1052 4.0 0.6 27YMEG-IV 300 100 94 84 686 5.0 0.8 35

Classification and ordination

The dendrogram from the cluster analysis and the MDS plot from the ordination analysis on station level are presented in Figure 4.15.6 and Figure 4.15.7. The reference station (300°/10000m) separates at 40 % similarity from the Yme Gamma field stations, having significantly smaller numbers of the most common species in the Yme Gamma area. Furthermore the field stations can be divided in two main groups at about 50 % similarity:

Group 1: YMEG-1 (30°/250m), -6 (120°/500m), -10 (210°/250m), -14 (300°/250m) and –IV (300°/100m) Group 2: YMEG-I (30°/100m), -II (120°/100m), -III (210°/100m), -5 (120°/250m)

In general, group 1 contains the stations located farthest away (250 and 500 m) from the field centre and group 2 contains the stations located 100 m from the field centre. The exception is station YMEG-IV and YMEG-5 which are included in group 1 and 2 respectively.

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The similarity analysis reveals that the stations belonging to group 2 contain higher numbers of the most common species in the area; the bristle worms P. jeffreysii, C. setosa, E.verugera, D.arietina and M. oculata together with the ribbon worm Nemertea. Most of these are known as indicator species for organic materials in the environment, indicating some disturbance in the fauna at the stations in group 2.

The Bioenv analysis reveals a good correlation (0.9) between the fauna and the complex of the chemical parameters THC, Ba1, and TOM, indicating that the variations in the fauna are related to the variations in THC, Ba1 and TOM. This is also supported by field observations (oil and oily smell) at the 100m stations.

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300 /100m 210 /250m 30 /250m 120 /500m 300 /250m120 /100m 120/250m 30 /100m 210 /100m300/10000m Figure 4.15.6. Dendrogram of stations from Yme Gamma 2005 (excl. juv.).

YG-01

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Stress: 0,01

300 /100m, 210 /250m, 30 /250m, 120 /500m, 300 /250m

120 /100m, 120/250m, 30 /100m, 210 /100m

300/10000m

Figure 4.15.7. MDS plot of stations from Yme Gamma 2005 (excl. juv.).

1 Ba and the other metals are not degradable and will not disappear from the sediments. These metals may

presumable not have any effect on the fauna in itself, but could be regarded as trace elements for other degradable substances.

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Comparison with 1994, 1996, 1999, 2002 and 2005

In Figure 4.15.8 the results from the present survey are compared with the results from the previous surveys. All data include the bristle worms M. oculata and P. jeffreysii for all years. Since the last survey, the numbers of species have increased in general. An exception is the reference station (300°/10000m), where the decrease is significant, almost 40 %. The numbers of individuals have increased significantly at stations YMEG-14 (300°/250m), -I (30°/100m) and –II (120°/100m) since the previous surveys. At YMEG-01 (30°/250m), -05 (120°/250m) and -06 (120°/500m), there are slight increases. Slight decreases in the numbers of individuals are observed at YMEG-III (210°/100m), -IV (300°/100m) and at the reference station. At station YMEG-10, the numbers of individuals are unchanged.

At stations YMEG-01, -I, -II, -III and -IV, there were observed oily components in the sediment during sampling and sample processing.

In general the numbers of individuals are smaller than at many of the other fields in Region I. The main reason for this is that the field contains significantly less of M. oculata which are flourishing at other fields in the more central parts of the Ekofisk region. The Shannon-Wiener diversity indices (H’) reflect at slight, general increase at most of the stations. The decline observed at YMEG-01, -06, -II and the reference station are very small. Two stations have significant increases, stations YMEG-III and -IV.

020406080

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YMEG-06

YMEG-10

YMEG-14

YMEG18-Ref

YMEG-I

YMEG-II

YMEG-III

YMEG-IV

Stations

No.

of s

peci

es (S

)

1994 1996 1999 2002 2005

Station º/m

YMEG-01 30/250 YMEG-05 120/250 YMEG-6 120/500 YMEG-10 210/250 YMEG-14 300/250 YMEG-Ref 300/10000 YMEG-I 30/100 YMEG-II 120/100 YMEG-III 210/100 YMEG-IV 300/100

0250500750

10001250150017502000

YMEG-01

YMEG-05

YMEG-06

YMEG-10

YMEG-14

YMEG18-Ref

YMEG-I

YMEG-II

YMEG-III

YMEG-IV

Stations

No.

of i

ndiv

idua

ls (N

)

1994 1996 1999 2002 2005

0123456

YMEG-01

YMEG-05

YMEG-06

YMEG-10

YMEG-14

YMEG18-Ref

YMEG-I

YMEG-II

YMEG-III

YMEG-IV

Stations

H'

1994 1996 1999 2002 2005

Figure 4.15.8. Numbers of species (S) and individuals (N) per 0.5 m2 and diversity (H’), (incl. P. jeffreysii and M. oculata, excl. juv.), Yme Gamma 1994, 1996, 1999, 2002 and 2005.

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Classification and ordination analyses

The stations from all years have been analysed at family level∗. The dendrogram from the cluster analysis reveals that most of the stations divide into three main groups at about 50% similarity. However, the reference station in 2005 (300º/10000m) and YMEG-05 (120º/250m) and -06 (120º/500m) separate from these groups. Stations sampled in 1994 and 1996 cluster together and most of the stations sampled in 1999, 2002 and 2005 (the same stations as sampled in earlier years) group together. However the 100 m stations YMEG-I (30º/100m), -II (120º/100m) and -III (210º/100m) sampled for first time in 2002 and then in 2005, in addition to station -IV (300º/100m) from 2002 separates from the other stations sampled in 2002 and 2005. Station YMEG-IV 2005 is included into group 2 with the rest of the 2002 and 2005 samples. The results indicate a positive trend since 2002.

Group 1: 1994 and 1996 stations Group 2: 2002 and 2005 stations + YMEG-IV (300°/100m) in 2005 Group 3: 2002-2005 - YMEG-I (30°/100m), -II (120°/100m), -III (210°/100m) and -05 120°/250m). YMEG -IV (300°/100m) in 2002.

Group 3 (stations located near the field centre) separates with the highest numbers of indicator species for organic enrichment such as the ribbon worm (Nemertea), the bristle worms within the families Capitellidae (mainly Capitella capitata), Cirratulidae (mainly C. setosa) and Amphinomidae (mainly P. jeffreysii).

The differences between group 1 (1994-1996) and 2 (1999-2005) are smaller, but the numbers of species within the families Capitellidae, Spionidae and Amphiuridae have decreased over the years while the numbers of ribbon worms have increased somewhat. These changes could indicate a slight improvement in the fauna over the years.

The Bioenv analyses gave a good correlation (0.8) between the fauna community and the combination of the complex of the chemical parameters THC, Ba1 and Cu. This indicates that the chemical parameters have had some impact on the fauna community over the years.

∗ Necessary when comparing between years, to avoid significant source of error due to both different years and

different taxonomists. 1 Ba and the other metals are not degradable and will not disappear from the sediments. These metals may

presumable not have any effect on the fauna in itself, but could be regarded as trace elements for other degradable substances.

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YG-0

5-99

YG-0

6 -99

YG-R

e fA-

-05

YG-R

efA-

96YG

-05-

96YG

-06-

96YG

-07-

9 6YG

-08 -

96YG

-02-

96YG

-01-

96YG

-14-

96YG

-10-

96YG

-11 -

96YG

-15-

9 6YG

-05-

-94

YG-0

1-- 9

4

YG-0

6--9

4YG

-Ref

A -94

YG-R

efB-

94Y G

-02-

-94

YG- 0

3--9

4Y G

-14-

-94

YG- 1

6--9

4YG

-10-

- 94

YG-0

7--9

4YG

-11 -

-94

YG-1

5-- 9

4YG

-08-

-94

YG-1

2--9

4Y G

-IV-0

5YG

-10-

-05

YG-0

6 --0

5YG

-01-

-05

YG-1

4 --0

5YG

-06-

-02

YG-0

1--0

2YG

-10-

-02

YG-1

4--0

2YG

-Ref

A-99

Y G-R

efB-

99YG

-11-

99YG

-02-

99Y G

-07-

99YG

-15-

99YG

-Ref

A-02

YG-1

8 B--0

2YG

-02-

-02

YG-0

7--0

2YG

-11-

-02

YG-1

5--0

2YG

- III-0

2YG

-IV-0

2YG

-II-0

2YG

-05-

-02

YG-I-

02YG

-05-

-05

Y G-I-

05YG

-II-0

5YG

-III-0

5100

80

60

40Si

mila

rity

Group 1 (1994-1996) Group 2 (1999-2005) Group 3 Figure 4.15.9. Dendrogram showing similarity between Yme Gamma stations 1994, 1996, 1999, 2002 and 2005. Family level, incl. M. oculata, excl. juv., sq. root transformation.

4.15.4 Conclusion

The sediments at the regular monitoring stations at Yme Gamma consist of medium sand, and the sand content varies from 94 % at YMEG5, 120°/500m to 98 % at YMEG18, reference station, 300°/10000m. The gravel content is low, only small amounts are found at some stations. The silt and clay content is similar to the previous surveys.

Samples were also taken from the Installation Centre and from stations at 100m distance. At the Centre, 0°/0m, the sediment consists of 81 % silt and clay. High contents of silt and clay are found at YMEGII, 120°/100m and YMEGIII, 210°/100m with 38 % and 25 % respectively. At YMEGI, 30°/100m and YMEGIV, 300°/100m, the silt and clay content is more similar to the regular Yme Gamma monitoring stations and the sand content varies from 93.6 % to 94.9 %. The sediments at the 100m stations are characterized as medium sand.

The total organic matter content outside 100m distance is low. The concentrations vary from 0.52 % to 0.69 %. The results are similar to previous surveys. At the Installation Centre 0°/0m the TOM content is high, 5.6 %. Relatively high TOM contents are also found for YMEGII, 2.8 % and YMEGIII, 2.4 %. The results are similar to the 2002 survey and they correspond to the grain size distribution.

The mean THC concentrations at the regular monitoring stations vary from 2.4 mg/kg at YMEG10, 210°/250m to 32 mg/kg at YMEG5, 120°/250m. Correspondingly, the concentrations of olefins vary from <0.4 mg/kg to 2.5 mg/kg. The maximum concentrations of THC found are at YMEG5, with 32 mg/kg in the top 0-1 cm layer, 53 mg/kg in the 1-3 cm layer and 91 mg/kg in the 3-6 cm layer. Thus, the THC concentrations increase downwards in the sediment. This seems also to be the pattern for YMEG6 (120°/250m), increasing slightly from 7.2 mg/kg in the top 0-1 cm layer to 8.5 mg/kg in the 3-6 cm layer.

At stations YMEG5 and YMEG1, the concentration of THC in the top 0-1 cm layer has decreased distinctly since the 2002 survey, YMEG5 from 87 mg/kg to 32 mg/kg and YMEG1 from 39 mg/kg to 5.7 mg/kg. At the other stations the THC concentrations are low, with

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contents around the limit of contamination. Thus elevated THC concentrations are only observed out to 250m in 120°direction. The THC content in the vertical deeper investigated has not changed since 2002.

Generally, the olefins are closely related to the THC contents and thus a similar pattern might be observed. At YMEG5, the olefin concentration in the top 0-1 cm layer has decreased from 35 mg/kg in 1999 to 4.8 mg/kg in 2002 to 2.5 mg/kg in 2005. The olefins concentrations in the layers increase downwards in the sediments. The maximum concentration is found in the 3-6 cm layer. The concentrations of olefins at YMEG1 have decreased from 9.9 mg/kg in 2002 to not detectable (<0.4 mg/kg) in the present survey. At the other stations investigated the concentrations of olefins are low (<0.4 mg/kg).

At the Installation Centre, 0°/0m, the THC concentration is high (4510 mg/kg). However, the concentration in the top 0-1 cm layer has decreased considerably compared to the 2002 survey where a THC content of 1.3% was found. Vertical sections to 15 cm depth have been sampled, and the THC concentrations decrease gradually downwards. The level of the THC concentration in the deeper layers is similar to the 2002 level.

High concentrations are also found at the 100 m stations in the 30°, 120° and 210° directions. The mean concentrations vary from 34 mg/kg in the 30° direction to 706 mg/kg in the 120° direction. The THC concentration is only 8.5 mg/kg in the 300° direction. However, the THC content has decreased distinctly for all directions compared to the 2002 survey.

The mean olefin concentration at the regular monitoring stations is low and vary from not detectable (<0.4 mg/kg) to 2.5 mg/kg at YMEG5, 120°/250m. At YMEG5 the olefin concentration in the top 0-1 cm layer has decreased from 35 mg/kg in 1999 to 4.8 mg/kg in 2002 to 2.5 mg/kg in 2005. The olefin concentrations in the layers increase downwards in the sediments. The maximum concentration is found in the 3-6 cm layer. At YMEG1, 30°/250m the concentration of olefins decreased from 9.9 mg/kg in 2002 to not detectable (<0.4 mg/kg) in 2005.

The sediments from the central station also contain olefins, however these are not quantified. The olefins found agree with the constituents of the pseudo-oil based drilling fluid Ultidril, C14 and C16 olefins.

The ester based drilling fluid Petrofree is found at the two stations analysed, 3.4 mg/kg at YMEG5, 120°/250m and 0.5 mg/kg at YMEG6, 120°/500m. The Petrofree concentrations are similar to the 2002 survey. Finagreen is not detected. The results correspond with the discharge history and with the relatively easy degradation of ester compounds.

Elevated levels of NPD, PAH and decalins are found at YMEG5, 120°/250m. The NPD and PAH concentrations have increased since 2002. The decalin concentrations have decreased. Only slightly elevated NPD and PAH concentrations are found at YMEG6, 120°/500m. Decalins are not detectable. The mean NPD concentrations vary from not detectable at the reference station to 0.66 mg/kg at YMEG5. Correspondingly the PAH concentrations vary from 0.013 mg/kg to 0.44 mg/kg. The decalin concentrations vary from not detectable to 0.17 mg/kg.

At the installation Centre the concentrations of NPD, PAH and decalins are high (8.7 mg/kg of NPD, 1.9 mg/kg of PAH and 186 mg/kg of decalins). High concentrations of NPD, PAH and decalins are also found for all the deeper layers in the 1-15 cm section, where the NPD content varies from 7.3 mg/kg to 13.7 mg/kg, the PAH content from 1.1 mg/kg to 1.5 mg/kg and the decalins content from 6.7 mg/kg to 174 mg/kg. High levels of NPD, PAH and decalins at the 100m stations are also found. The decalins concentrations are in accordance with the THC contents and represent 2-4 %.

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PFOS (perfluorooctyl sulphonate) is analysed at one station at Yme Gamma Central, YMEG-II, 120°/100m. The PFOS content at YMEG-II was 25.8 µg/kg.

The mean Ba concentrations at the regular monitoring stations vary from 10 mg/kg at YMEG18 reference station, 300°/10000m to 4489 mg/kg at YMEG5, 120°/250m. High Ba concentrations are also found at YMEG1, 30°/250m, YMEG6, 120°/500m, 1778 mg/kg and 1466 mg/kg respectively. The Ba concentrations are similar or slightly lower compared to the 2002 and 1999 surveys. Elevated Ba concentrations are found at all stations, except for at the reference station. This is out to 500m in the 120° direction and out to 250m in the other directions. The concentrations of the heavy metals are low and unchanged since 2002.

At the Installation Centre the Ba concentration has decreased from 6050 mg/kg in 2002 to 705 mg/kg in this survey. The same decrease is observed in the layers 1–3 cm and 3-6 cm. High concentrations of Ba are observed at the 100m stations in all four directions, ranging from 2247 mg/kg in the 300° direction to 5630 mg/kg in the 210° direction. Elevated levels of heavy metals are found both at 0°/0m and at the 100m stations.

Generally the results agree with the drilling history at Yme Gamma.

In general, the structure in the fauna community at Yme Gamma indicates a healthy environment. However, the biodiversity indices together with the similarity analyses indicate slight disturbances in the fauna at station YMEG-II (120°/100m), and also at YMEG-I (30°/100m) and -III (210°/100m). This is supported by the observations from the field work and during the sample processing. Also YMEG-05 (120°/250m) differs somewhat in the similarity analyses. Based on observations from the sampling and a qualitative analysis the Installation Centre (0°/0) is characterized as heavily disturbed.

The biodiversity indices reflect slight increases at most of the stations since 2002. The similarity analyses indicate a slight overall improvement since 2002, particularly at the 100 m station YMEG-IV (300°/100m). YMEG-II is the only station that has a noticably lower diversity index than the other stations. This station seems to have only small improvements in just some of the biological and chemical parameters measured.

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4.16 Yme Beta

4.16.1 Sediment characterization

Grain size distribution

The grain size distribution from the present survey is shown in Table 4.16.1 together with the silt and clay content from the previous surveys in 2002, 1999 and 1996.

The sediments at the Yme Beta field consist of medium sand, and the sand contents vary from 97.7 % at YMEB1, 60°/250m to 99.8 % at YMEB12, 330°/250m. The average median diameter is 1.70φ. The gravel content is low (<0.3 %). The silt and clay content is similar to the previous surveys. In the present survey samples from the Installation Centre and from stations at 100m distance are included in the investigation. At the centre 0°/0m the sediments consist of 70 % sand and 30 % silt and clay. The medium diameter for YMEB Central is 2.52φ and thus this sediment is characterized as fine sand. At the 100m stations the silt and clay content is similar to the regular Yme Beta monitoring stations, and the sand content varies from 95.2 % at YMEB-II, 150°/100m to 99.3 % at YMEB-IV, 330°/100m. The sediments are characterized as medium sand. The results from the complete grain size distribution are given in Appendix C. Table 4.16.1. Yme Beta 2005, grain size distribution. Station Median

diameterClassification Grain size distrib. 2005

(%) 2002

(%) 1999 (%)

1996 (%)

Mdφ Silt and clay

Sand Gravel Silt and clay

Silt and clay

Silt and clay

YMEB1 60°/250m 1.69 Medium sand

2.3 97.7 0.0 1.2 0.4

YMEB4 150°/250m 1.69 Medium sand

0.7 99.3 0.0 1.9 2.9 0.4

YMEB9 240°/250m 1.69 Medium sand

0.2 99.5 0.3 2.4 0.7

YMEB12 330°/250m 1.67 Medium sand

0.2 99.8 0.0 1.5 0.5

YMEB Cent.*

0°/0m 2.52 Fine sand 29.9 70.1 0.0 19.2

YMEB-I 60°/100m 1.69 Medium sand

1.9 98.0 0.1 1.1

YMEB-II 150°/100m 1.78 Medium sand

4.7 95.2 0.1 1.4

YMEB-III 240°/100m 1.69 Medium sand

1.0 99.0 0.0 4.6

YMEB-IV 330°/100m 1.67 Medium sand

0.7 99.3 0.0 0.7

Mean 1.70 1.5 98.5 0.1 1.9 2.9 0.5 Standard deviation 0.04 1.5 1.5 0.1 1.2 0.1 *: not included in the mean value

Total organic matter (TOM)

The contents of TOM in the sediments are very low, and only small variations are found at the ordinary stations. The concentrations vary from 0.36 % at YMEB9, 240°/250m to 0.42 % at YMEB4, 150°/250m. The results are similar to the previous surveys. At the Installation Centre, 0°/0m the TOM content is 2.45 %, compared to 1.56 % found in the 2002 survey. At the 100m

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stations the concentrations range from 0.39 % to 0.59 %. The contents of TOM are similar to the 2002 survey.

Compared to the Yme Gamma Installation Centre the contents of TOM are considerably lower at Yme Beta. The results correspond to the grain size distribution, and are shown in Table 4.16.2. Table 4.16.2. Yme Beta 2005, total organic matter (% of dry sediment). Station 2005, 0-5 cm Mean 2002 SD

2002 Mean 1999 Mean

1996 YMEB1 60°/250m 0.38 0.44 0.47 YMEB4 150°/250m 0.42 0.53 0.51 0.42 0.41 YMEB9 240°/250m 0.36 0.40 0.56 0.87 YMEB12 330°/250m 0.39 0.42 0.63 0.41 YMEB Cent. 0°/0m 2.45 1.56 0.72 YMEB-I 60°/100m 0.42 0.53 0.55 YMEB-II 150°/100m 0.59 0.54 0.63 YMEB-III 240°/100m 0.39 1.02 0.79 YMEB-IV 330°/100m 0.39 0.40 0.03

4.16.2 Chemical analyses

Parameters analysed in the sediments at Yme Beta:

• THC • Olefins • NPD, PAH, decalins • Metals (Ba, Cd, Cr, Cu, Hg, Pb, Zn)

Three replicate samples at each station are analysed. The samples are taken from the top 0-1 cm sediment layer. In addition, the 1-3 cm and 3-6 cm sediment layers are sampled at one station. YMEB Central is analysed for additionally five layers; 1-3 cm, 3-6 cm, 6-9 cm, 9-12 cm and 12-15 cm.

Based on the results from 2002 the sampling programme has focussed on the stations close to the centre. The removal of the template made it possible to conduct an additional study, including stations close to the centre in 2002. These stations have also been sampled in 2005, including centre positions.

THC and olefins

The THC results including olefins are shown in Table 4.16.2 and olefins separately in Table 4.16.3. The corresponding data from the previous surveys in 2002, 1999 and 1996 are also included for comparison. Bar diagrams of the THC content in the sediments are shown in Figure 4.16.1 and Figure 4.16.2.

In 1999 the mean THC concentrations ranged from 0.5 mg/kg to 1.6 mg/kg. The THC content at Yme Beta was very low, and no elevated levels were found. Olefins were not analysed. In 2002 the mean THC concentrations in the field ranged from 0.3 mg/kg to 4.1 mg/kg. Elevated levels were not found. The contents of olefins were very low.

In the present survey the THC concentrations at the regular monitoring stations vary from 0.3 mg/kg at YMEB9, 240°/250m to 5.8 mg/kg at YMEB4, 150°/250m. Elevated levels are not found. The concentrations are mainly at the same level as in the 2002 survey.

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Olefins are only found in one grab sample at YMEB4, 150°/250m (0.4 mg/kg) and in one grab sample at the 3-6 cm layer (3.5 mg/kg). The olefin level is the same as in the 2002 survey.

At the Installation Centre (YMEB Centtral, 0°/0m) the THC concentration is high, 354 mg/kg. A distinct difference between the replicate samples is observed. Elevated THC levels are found in the deeper sections and range from 9 mg/kg to 99 mg/kg. The mean THC concentrations at the 100m stations vary from 2.5 mg/kg at YMEB-IV to 63 mg/kg at YMEB-II. Elevated concentrations are found at the YMEB-I (40 mg/kg) and YMEB-II. The sediments contain olefins, however these are not quantified.

Compared to the 2002 survey it is emphasized that the THC contents have decreased distinctly for all the deeper layers at YMEB central. For the 100m stations the THC contents have decreased at YMEB-III. The other stations have THC contents similar to the 2002 survey.

The olefins found at Yme Beta consist mainly of C14 and C16 olefins. This is in agreement with the reported discharges of 290 m3 of synthetic drilling fluids in 1999.

Representative gas chromatograms are given in Appendix C. These include YMEB4, 150°/250m, (all three layers), YMEB Centre 0°/0m, YMEB-II, 150°/100m, YMEB-IV, 330°/100m and, YMEG18 Ref., 300°/10000m.

Yme Beta, THC 2005

0

1

2

3

4

5

6

7

8

9

10

YMEB1 YMEB4 YMEB9 YMEB12 YMEG18 Ref

station

mg/kg

1999

2002

2005

LSC A

Figure 4.16.1. Bar diagram of the THC content in the sediments at Yme Beta 1999-2005.

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Yme Beta, THC 2005

0

20

40

60

80

100

120

140

160

180

200

YMEB Cent. YMEB-I YMEB-II YMEB-III YMEB-IV

station

mg/kg

1999

2002

2005

LSC A

5000±4060

Figure 4.16.2. Bar diagram of the THC content in the sediments at Yme Beta Central 1999-2005. Table 4.16.3. Yme Beta 2005, total hydrocarbon content (mg/kg dry sediment). Station Grab

#1 Grab

#2 Grab

#3 Mean SD Mean Mean Mean

2005 2005 2002 1999 1996 YMEB1 60°/250m 0.3 1.4 3.0 1.6 1.3 0.9 17.1 YMEB4 150°/250m 4.9 3.8 8.7 5.8 2.6 4.1 1.6 4.5 1-3 cm 3.4 2.5 1.1 <1.2 3-6 cm 21 2.5 1.5 <1.2 YMEB9 240°/250m 0.5 0.3 0.2 0.3 0.2 0.4 YMEB12 330°/250m 0.8 0.8 1.2 0.9 0.2 0.3 YMEB Cent. 0°/0m 354 107 62 174 157 5000 1-3 cm 79 406 3-6 cm 91 756 6-9 cm 99 400 9-12 cm 14.9 12-15 cm 9.0 *1400 YMEB-I 60°/100m 40 6.0 11.1 19 18.3 15.1 YMEB-II 150°/100m 58 70 62 63 6.3 30 YMEB-III 240°/100m 2.3 3.2 1.9 2.5 0.7 69 YMEB-IV 330°/100m 9.1 5.4 2.6 5.7 3.3 1.2 LSC Region B 4.6 5.1 *: 6-15 cm

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Table 4.16.4. Yme Beta 2005, olefins (mg/kg dry sediment). Station Grab

#1 Grab

#2 Grab

#3 Mean SD Mean SD

2005 2005 2002 2002 YMEB4 150°/250m <0.3 <0.3 0.4 <0.3 0.3 0.1 1-3 cm <0.3 0.28 3-6 cm 3.5 <0.2 Detection limit: 0.3 mg/kg

NPD, PAH and decalins One station in the 150° direction and the Installation Centre are analysed. In addition, station YMEB-II, 150°/100m, with THC content >50 mg/kg, was included for analyses. The results are shown in Table 4.16.5.

In 1999 and 2002 elevated levels of NPD, PAH and decalins were not found at YMEB4, 150°/250m. In the present survey also, the content of NPD, PAH and decalins are low at YMEB4 and for NPD and PAH it is below the limit of contamination.

At the installation Centre the NPD and decalin concentrations are relatively high, 2.22 mg/kg of NPD and 7.4 mg/kg of decalins. The concentration of NPD in the top 0-1 cm layer is at the same level as in 2002, while the concentration of decalins has decreased. However, the concentrations of NPD and decalins in the vertical layers 1-3 cm, 3-6 cm and 6-9 cm have increased significantly since the previous survey. NPD varies from 1.3 to 8 mg/kg and decalins from 3.3 to 30 mg/kg. A similar trend is seen for PAH. An enhanced level of PAH was found in the section 1-9 cm, as the level of PAH in the top layer is unchanged. Deeper in the sediment the concentrations of NPD, PAH and decalins were relatively low.

The distribution seen for NPD, PAH and decalins is consistent with the distribution observed for THC at the same station. A relatively high content of decalins is found for YMEB-II, 150°/100m (~2 mg/kg), in agreement with the high content of THC found for this station. Table 4.16.5. Yme Beta 2005, sum NPD, PAH and decalins (mg/kg dry sediment).

Station Grab #1

Grab #2

Grab #3

Mean SD Mean SD Mean SD Mean

2005 2005 2002 2002 1999 1999 1996 NPD YMEB4 150°/250m 0.018 0.012 0.003 0.011 0.007 0.020 0.013 0.003 0.001 0.012 1-3 cm nd 0.010 0.004 0.008 3-6 cm nd 0.013 0.005 0.008YMEB Cent. 0°/0m 3.22 2.97 0.46 2.22 1.53 2.44 1.88 1-3 cm 7.56 0.20 3-6 cm 8.04 0.33 6-9 cm 1.29 0.18 9-12 cm 0.088 12-15 cm 0.038 *3.68 YMEB-II 150°/100m 0.43 0.36 0.26 0.35 0.09 LSC Subregion B 0.012 0.024 0.040 Cont.

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Table 4.16.5. cont. Station Grab

#1 Grab

#2 Grab

#3 Mean SD Mean SD Mean SD Mean

2005 2005 2002 2002 1999 1999 1996 PAH YMEB4 150°/250m 0.019 0.009 0.004 0.010 0.008 0.009 0.004 0.006 0.001 0.013 1-3 cm nd 0.005 0.004 0.028 3-6 cm nd 0.005 0.006 0.032YMEB Cent. 0°/0m 0.58 0.48 0.051 0.37 0.28 0.36 0.28 1-3 cm 1.29 0.031 3-6 cm 1.39 0.041 6-9 cm 0.23 0.032 9-12 cm 0.023 12-15 cm 0.010 *0.58 YMEB-II 150°/100m 0.056 0.047 0.043 0.048 0.007 LSC Subregion B 0.024 0.048 0.090 Decalins YMEB4 150°/250m 0.053 0.056 0.004 nd 0.10 nd 0.28 1-3 cm nd nd nd 0.019 3-6 cm nd nd nd 0.042YMEB Cent. 0°/0m 10.5 4.9 6.8 7.4 2.8 52.1 38.5 1-3 cm 20.9 5.4 3-6 cm 30.1 7.9 6-9 cm 3.31 5.2 9-12 cm 0.76 12-15 cm 1.48 *13.4 YMEB-II 150°/100m 2.04 2.00 1.88 1.97 0.08 *: 6-15 cm nd: not detected Limit of detection for NPD is 0.01 mg/kg, for PAH 0.005 mg/kg and for decalins 0.1mg/kg

Metals

The results are shown in Table 4.16.6. For comparison, data from the present survey and previous surveys in 2002, 1999 and 1996 are included in Table 4.16.7. Bar diagrams of the Ba contents in the sediments are shown in Figure 4.16.3 and Figure 4.16.4.

In 1999 the mean Ba concentrations ranged from 7 mg/kg to 103 mg/kg (YMEB4, 150°/250m). In 2002 the mean Ba concentrations ranged from 7 mg/kg to 404 mg/kg (YMEB4, 150°/250m). In the present survey the mean Ba concentrations at the regular monitoring stations vary from 11 mg/kg at YMEB12, 330°/250m to 520 mg/kg at YMEB4, 150°/250m. The limit of contamination is 12.1 mg/kg. Thus, elevated Ba concentrations are observed at the 250m stations in the 60°, 150° and 240° directions. The level of Ba is similar or slightly higher compared to the level found in the 2002 survey. Compared to Yme Gamma the content of Ba at Yme Beta is low.

The concentrations of the heavy metals are low, and elevated concentrations are not found.

At the Installation Centre, 0°/0m the Ba concentration is relatively high, 3038 mg/kg. However, the Ba content is halved since the 2002 survey. This trend is also observed in the deeper layers. The Ba content has decreased from 3030 mg/kg to 460 mg/kg and from 3280 mg/kg to 755 mg/kg for the layers 1-3 cm and 3-6 cm respectively.

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Elevated concentrations are found at the 100m stations in all four directions, ranging from 89 mg/kg in the 330° direction to 1339 mg/kg in the 150° direction.

Elevated levels of the metals are found at YMEB Central in all layers investigated. For the other 100 m stations the content of heavy metals are low.

Yme Beta, Ba 2005

0

50

100

150

200

250

300

350

400

450

500

550

YMEB1 YMEB4 YMEB9 YMEB12 YMEG18 Ref

station

mg/kg

1999

2002

2005

LSC A

Figure 4.16.3. Bar diagram of the Ba content in the sediments at Yme Beta 1999-2005.

Yme Beta, Ba 2005

0

500

1000

1500

2000

2500

3000

3500

4000

4500

5000

5500

6000

6500

7000

YMEB Cent. YMEB-I YMEB-II YMEB-III YMEB-IV

station

mg/kg

1999

2002

2005

LSC A

6060±1800

Figure 4.16.4. Bar diagram of the Ba content in the sediments at Yme Beta Central 1999-2005.

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The following variations were found at Yme Beta in the top 0-1 cm layer, at the Installation Centre and 100m distance in mg/kg: Yme Beta: YMEB1 – YMEB12 YMEB0 – YMEB-IV YMEG18 Reference station Ba: 11 – 520 89 – 3038 10 Cr: 7.6 – 9.1 7.0 – 14.7 7.3 Cu: <0.5 <1 <0.5 Pb: 6.6 – 7.3 5.0 – 25 7.7 Zn: 4.9 -6.4 4.4 – 17.7 7.0 Cd: <0.01 <0.01 – 0.04 <0.01 Hg: <0.01 <0.01 – 0.02 <0.01

Table 4.16.6. Yme Beta 2005, metals (mg/kg dry sediment). Station Sample Ba Cd Cr Cu Hg Pb Zn 2005 2005 2005 2005 2005 2005 2005 YMEB1 60°/250m 1 79 <0.01 7.4 <0.5 7.4 5.9 2 132 <0.01 8.0 <0.5 6.5 5.5 3 105 <0.01 7.3 <0.5 7.1 5.0 mean 105 <0.01 7.6 <0.5 7.0 5.5 SD 26 0.3 0.4 0.5 YMEB4 150°/250m 1 628 <0.01 9.5 <0.5 <0.01 7.8 6.3 2 614 <0.01 8.9 <0.5 <0.01 6.8 6.3 3 317 <0.01 9.0 <0.5 <0.01 6.8 6.6 mean 520 <0.01 9.1 <0.5 <0.01 7.1 6.4 SD 176 0.3 0.6 0.1 1-3 cm 1 300 <0.01 9.3 <0.5 <0.01 7.2 5.7 3-6 cm 1 996 <0.01 9.4 <0.5 <0.01 7.2 6.7 YMEB9 240°/250m 1 16 <0.01 8.2 <0.5 6.0 5.2 2 35 <0.01 8.0 <0.5 6.4 4.6 3 7 <0.01 8.0 <0.5 7.6 5.0 mean 19 <0.01 8.1 <0.5 6.6 4.9 SD 14 0.1 0.8 0.3 YMEB12 330°/250m 1 9 <0.01 8.3 <0.5 7.9 5.0 2 13 <0.01 7.4 <0.5 7.5 5.1 3 9 <0.01 7.8 <0.5 6.4 4.9 mean 11 <0.01 7.8 <0.5 7.3 5.0 SD 2 0.5 0.8 0.1 YMEB Central 0°/0m 1 873 0.06 26 36 0.03 51.5 33 2 5071 0.04 12.5 7 0.01 16.2 15.2 3 3170 <0.01 5.8 1.5 <0.01 7.4 5.2 mean 3038 0.04 14.7 15 0.02 25 17.7 SD 2102 0.03 10.2 19 0.01 23 13.9 1-3 cm 1 460 0.09 41 61 0.04 74 55 3-6 cm 1 755 0.12 47 35 0.04 47 63 YMEB-I 60°/100m 1 384 <0.01 8.2 <0.5 5.0 5.0 2 1114 <0.01 8.9 <0.5 5.6 5.6 3 792 <0.01 8.1 <0.5 5.3 6.2 mean 763 <0.01 8.4 <0.5 5.3 5.6 SD 366 0.5 0.3 0.6 cont.

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Table 4.16.6. cont. Station Sample Ba Cd Cr Cu Hg Pb Zn 2005 2005 2005 2005 2005 2005 2005 YMEB-II 150°/100m 1 1224 <0.01 8.3 <0.5 4.9 6.3 2 1614 <0.01 8.7 1.2 5.0 7.7 3 1180 <0.01 8.5 0.6 5.1 6.0 mean 1339 <0.01 8.5 5.0 6.7 SD 239 0.2 0.1 0.9 YMEB-III 240°/100m 1 176 <0.01 8.4 <0.5 6.5 6.5 2 260 <0.01 8.0 <0.5 6.2 5.0 3 409 <0.01 8.8 <0.5 6.0 5.7 mean 282 <0.01 8.4 <0.5 6.2 5.8 SD 118 0.4 0.2 0.8 YMEB-IV 330°/100m 1 94 <0.01 7.0 <0.5 4.7 4.4 2 59 <0.01 7.0 <0.5 5.3 4.6 3 114 <0.01 6.9 2 5.1 4.3 mean 89 <0.01 7.0 5.0 4.4 SD 28 0.1 0.3 0.2 YMEG18 Ref. 300°/10000m 1 18 <0.01 6.9 <0.5 <0.01 7.2 6.2 2 7 <0.01 7.6 <0.5 <0.01 8.2 6.6 3 7 <0.01 6.9 <0.5 <0.01 7.4 5.6 4 13 <0.01 7.8 <0.5 <0.01 8.7 10.8 5 5 <0.01 7.2 <0.5 <0.01 7.2 5.9 mean 10 <0.01 7.3 <0.5 <0.01 7.7 7.0 SD 5 0.4 <0.5 0.7 2.1 1-3 cm 5 5 <0.01 7.1 <0.5 <0.01 6.8 5.8 3-6 cm 5 13 <0.01 7.3 <0.5 <0.01 6.9 6.5 LSC Subregion B 12.1 11.1 1.4 9.0 8.8 Table 4.16.7. Yme Beta 1996, 1999, 2002 and 2005, Metals (mg/kg dry sediment), comparing mean values with previous surveys. Station Ba Ba Ba Ba Cd Cd Cd Cr Cr Cr

2005 2002 1999 1996 2005 2002 1999 2005 2002 1999 YMEB1 60°/250m 105 93 1840 <0.01 <0.01 7.6 6.5 YMEB4 150°/250m 520 404 103 87 <0.01 <0.01 <0.02 9.1 8.0 8.2 1-3 cm 300 183 81 <0.01 <0.01 <0.02 9.3 8.1 8.6 3-6 cm 996 359 91 <0.01 <0.01 <0.02 9.4 8.0 8.8 YMEB9 240°/250m 19 20 1320 <0.01 <0.01 8.1 7.5 YMEB12 330°/250m 11 29 691 <0.01 <0.01 7.8 6.9 YMEB Cent 0°/0m 3038 6060 0.04 0.10 14.7 10.5 1-3 cm 460 3050 0.09 0.02 41 4.4 3-6 cm 755 3280 0.12 0.02 47 3.4 YMEB-I 60°/100m 763 631 <0.01 <0.01 8.4 7.3 YMEB-II 150°/100m 1339 951 <0.01 <0.01 8.5 8.0 YMEB-III 240°/100m 282 2540 <0.01 <0.01 8.4 11.5 YMEB-IV 330°/100m 89 209 <0.01 <0.01 7.0 7.1 YMEB18 Ref. 300°/10000m 10 6 6 6 <0.01 <0.01 <0.2 7.3 6.9 9.8 1-3 cm 5 6 9 <0.01 <0.01 <0.02 7.1 6.9 9.7 Cont. 3-6 cm 13 9 14 <0.01 0.01 <0.02 7.3 6.8 9.2

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Table 4.16.7. cont. Station Cu Cu Cu Hg Hg Hg Pb Pb Pb Zn Zn Zn 2005 2002 1999 2005 2002 1999 2005 2002 1999 2005 2002 1999YMEB1 60°/250m <1 0.5 7.0 5.6 5.5 4.9 YMEB4 150°/250m <1 0.8 <0.3 <0.01 0.01 <0.01 7.1 6.5 7.1 6.4 5.1 4.5 1-3 cm <1 0.4 <0.3 <0.01 0.01 <0.01 7.2 6.0 6.9 5.7 5.2 4.0 3-6 cm <1 0.5 <0.3 <0.01 0.01 <0.01 7.2 6.4 6.9 6.7 6.4 4.2 YMEB9 240°/250m <1 0.4 6.6 5.6 4.9 4.0 YMEB12 330°/250m <1 0.4 7.3 5.7 5.0 6.8 YMEB Cent 0°/0m 15 8.0 0.02 0.03 25 9.8 17.7 27

1-3 cm 61 3.0 0.04 0.01 74 2.7 55 4.7 3-6 cm 35 1.6 0.04 0.01 47 6.7 63 3.3 YMEB-I 60°/100m <1 0.8 5.3 5.2 5.6 5.4 YMEB-II 150°/100m <1 1.0 5.0 6.1 6.7 6.3 YMEB-III 240°/100m <1 5.1 6.2 9.6 5.8 14 YMEB-IV 330°/100m <1 0.5 5.0 5.4 4.4 4.0 YMEG18 Ref 300°/10000m <0.5 0.8 0.3 <0.01 <0.01 0.05 7.7 7.5 9.9 7.0 5.4 7.4

1-3 cm <0.5 0.8 0.4 <0.01 <0.01 0.03 6.8 7.2 10.1 5.8 5.1 7.6 3-6 cm <0.5 1.4 0.7 <0.01 0.01 0.03 6.9 7.7 9.2 6.5 5.7 7.8

4.16.3 Biological analyses

A total of 184 species and 4855 individuals were sampled at 9 stations. Greatest abundance (49.8 %) was found among the polychaetes, of which the species Paramphinome jeffreysii constitutes about 7.9 % of the total number of Polychaeta (Table 4.16.8). Table 4.16.8. Number of species and individuals distributed between the main groups, Yme Beta 2005.

Individuals Species Main animal groups Number % Number % Varia 925 19.1 16 8.7Polychaeta 2419 49.8 82 44.6- Paramphinome jeffreysii 192 7.9 - Myriochele oculata 34 1.4 Crustacea 243 5.0 35 19.0Mollusca 364 7.5 42 22.8Echinodermata 904 18.6 9 4.9- Amphiura filiformis 38 4.2 Total 4855 100.0 184 100.0

Figure 4.16.5 shows the numbers of species and individuals sampled at each station and variations between grab samples.

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020

406080

100YMEB-C

entral

YMEB-01YMEB-04YMEB-09YMEB-12

YMEB-I

YMEB-IIYMEB-II

IYMEB-IV

Stations

No.

of s

peci

es (S

)

Station º/m

YMEB-Central 0/0 YMEB-01 60/250 YMEB-04 150/250 YMEB-09 240/250 YMEB-12 330/250 YMEB-I 60/100 YMEB-II 150/100 YMEB-III 240/100

YMEB-IV 330/100

0

200

400

600

800

YMEB-Cent

ralYMEB-01YMEB-04YMEB-09YMEB-12

YMEB-IYMEB-II

YMEB-III

YMEB-IV

Stations

No.

of i

ndiv

idua

ls (N

)

Ex. P. jeffreysii and M. oculata

0

200

400

600

800

YMEB-Cen

tral

YMEB-01YMEB-04YMEB-09YMEB-12

YMEB-IYMEB-II

YMEB-III

YMEB-IV

Stations

No.

of i

ndiv

idua

ls (N

)

Figure 4.16.5. Numbers of species (S) and individuals (N) per 0.5 m2 (incl./excl. P. jeffreysii and M. oculata), mean values per grab sample and standard deviation, Yme Beta 2005.

Diversity and dominant species

The dominant species at each station varied from 12.9 % at YMEB-01 (60°/250m) to 37.8 % at YMEB-Central (0°/0m). The 10 most abundant species made up from 55.6 % at YMEB-01 to 73.7 % at YMEB-Central, see Table 4.16.9. The most dominant species throughout the stations at the Yme Beta field was the Echinoidea juveniles, followed by the bristle worms Exogone verugera, Aricidea cerrutii, the ribbon worm Nemertea spp. and the hydroid Corymorpha nutans. The ribbon worm is a deposit feeder and E. verugera is mainly a carnivore species. The other mentioned species are either suspension- or both suspension- and deposit feeders. The structure in the fauna community indicates a healthy environment in general. Table 4.16.9. The 10 most abundant species at each station, Yme Beta 2005. 10 most dominating species YMEB-Central No. % Cum. % YMEB-01 No. % Cum. % Echinoidea spp.juv. 141 37.8 37.8 Echinoidea spp.juv. 71 12.9 12.9 Paramphinome jeffreysii 20 5.4 43.2 Exogone verugera 52 9.4 22.3 Cerianthus lloydii 18 4.8 48.0 Edwardsia sp. 46 8.3 30.6 Glycera alba 16 4.3 52.3 Aricidea cerrutii 25 4.5 35.1 Chaetozone setosa 16 4.3 56.6 Nephtys longosetosa 21 3.8 39.0 Nemertea spp. 14 3.8 60.3 Corymorpha nutans 20 3.6 42.6 Ampharete falcata 14 3.8 64.1 Aricidea simonae 20 3.6 46.2 Phyllodoce groenlandica 13 3.5 67.6 Acaulis primarius 19 3.4 49.6 Heteromastus filiformis 12 3.2 70.8 Spiophanes bombyx 19 3.4 53.1 Harmothoe spp. 11 3.0 73.7 Aricidea suecica 14 2.5 55.6 Cont. Table 4.16.9. cont.

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YMEB-04 No. % Cum. % YMEB-09 No. % Cum. % Echinoidea spp.juv. 87 17.4 17.4 Echinoidea spp.juv. 162 21.8 21.8 Exogone verugera 39 7.8 25.2 Exogone verugera 63 8.5 30.2 Aricidea cerrutii 28 5.6 30.7 Edwardsia sp. 40 5.4 35.6 Paramphinome jeffreysii 26 5.2 35.9 Spiophanes bombyx 34 4.6 40.2 Edwardsia sp. 25 5.0 40.9 Aricidea cerrutii 32 4.3 44.5 Spiophanes bombyx 23 4.6 45.5 Corymorpha nutans 27 3.6 48.1 Myriochele oculata 22 4.4 49.9 Polycirrus norvegicus 25 3.4 51.5 Corymorpha nutans 19 3.8 53.7 Paramphinome jeffreysii 21 2.8 54.3 Aricidea simonae 15 3.0 56.7 Aonides paucibranchiata 20 2.7 57.0 Nephtys longosetosa 12 2.4 59.1 Acaulis primarius 17 2.3 59.3 YMEB-12 No. % Cum. % YMEB-I No. % Cum. % Echinoidea spp.juv. 150 22.6 22.6 Exogone verugera 93 20.5 20.5 Aricidea cerrutii 59 8.9 31.4 Nemertea spp. 60 13.3 33.8 Exogone verugera 48 7.2 38.7 Paramphinome jeffreysii 39 8.6 42.4 Polycirrus norvegicus 43 6.5 45.1 Spiophanes bombyx 23 5.1 47.5 Spiophanes bombyx 30 4.5 49.6 Aricidea cerrutii 14 3.1 50.6 Corymorpha nutans 18 2.7 52.3 Edwardsia sp. 13 2.9 53.4 Paramphinome jeffreysii 16 2.4 54.7 Chaetozone setosa 13 2.9 56.3 Edwardsia sp. 15 2.3 57.0 Nephtys longosetosa 13 2.9 59.2 Notomastus sp. 14 2.1 59.1 Corymorpha nutans 11 2.4 61.6 Aricidea simonae 13 2.0 61.1 Ampharete falcata 9 2.0 63.6 YMEB-II No. % Cum. % YMEB-III No. % Cum. % Nemertea spp. 83 23.9 23.9 Exogone verugera 72 13.5 13.5 Corymorpha nutans 32 9.2 33.1 Nemertea spp. 43 8.1 21.5 Acaulis primarius 28 8.1 41.2 Echinoidea spp.juv. 38 7.1 28.7 Chaetozone setosa 23 6.6 47.8 Edwardsia sp. 33 6.2 34.8 Cerianthus lloydii 21 6.1 53.9 Spiophanes bombyx 32 6.0 40.8 Paramphinome jeffreysii 20 5.8 59.7 Corymorpha nutans 30 5.6 46.4 Spiophanes bombyx 15 4.3 64.0 Aricidea cerrutii 29 5.4 51.9 Lucinoma borealis 9 2.6 66.6 Paramphinome jeffreysii 24 4.5 56.4 Paguridae sp. 6 1.7 68.3 Ampharete falcata 15 2.8 59.2 Tunicata spp. 6 1.7 70.0 Nephtys longosetosa 15 2.8 62.0 YMEB-IV No. % Cum. % Echinoidea spp.juv. 100 14.6 14.6 Exogone verugera 52 7.6 22.2 Edwardsia sp. 51 7.4 29.6 Aricidea cerrutii 40 5.8 35.4 Corymorpha nutans 33 4.8 40.2 Spiophanes bombyx 26 3.8 44.0 Travisia forbesii 22 3.2 47.2 Polycirrus norvegicus 21 3.1 50.3 Nephtys longosetosa 20 2.9 53.2 Acaulis primarius 18 2.6 55.8

The number of species varied from 48 at YMEB-Central (0°/0m) to 91 at YMEB-IV (330°/100m). The number of individuals varied from 232 at YMEB-Central to 581 at YMEB-IV. The Shannon Wiener diversity index varied from 4.5 at YMEB-II (150°/100m) to 5.5 at YMEB-01 (60°/250m) and YMEB-IV. The Hurlberts index varied from 33 at station YMEB-Central to 44 at station YMEB-01 (60°/250). The indices characterize a healthy fauna community, see Table 4.16.10.

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Table 4.16.10. Numbers of individuals (N) and species (S), depth, Shannon-Wiener diversity index (H’), Pielou’s evenness index (J), and expected number of species per 100 individuals (ES100) for each station at Yme Beta 2005, (excl. juv.). Station Direction ° Distance m Depth S N H' J ES100 YMEB-Central 0 0 74 48 232 4.8 0.9 33 YMEB-01 60 250 80 85 478 5.5 0.9 44 YMEB-04 150 250 74 84 414 5.4 0.9 42 YMEB-09 240 250 74 88 578 5.4 0.8 42 YMEB-12 330 250 74 81 514 5.3 0.8 42 YMEB-I 60 100 79 77 443 4.8 0.8 37 YMEB-II 150 100 74 57 343 4.5 0.8 32 YMEB-III 240 100 79 75 496 5.0 0.8 35 YMEB-IV 330 100 74 91 581 5.5 0.8 42

During sampling there were observed large amounts of yellow granules in the sediment samples from the Installation Centre and the 100m stations. Similar granules were observed at Valhall (Photo 1). Analyses of the granules (Photo 3) showed that they contain 33-34% Al, 34-35% Si, 27-29% O, ca.1,4 % Ti and 1,3-1,7% Fe.

Classification and ordination

The dendrogram from the cluster analysis and the MDS plot from the ordination analysis at station level are presented in Figure 4.16.6 and Figure 4.16.7. YMEB-Central (0°/0m) separates from the other stations at the Yme Beta field, having higher abundances of typical indicator species such as the bristle worms Heteromastus filiformis, Phyllodoce groenlandica and Glycera alba. These species are mainly deposit feeders. The other stations contained higher numbers of the suspension feeding hydrozoans Corymorpha nutans and Acaulis primarius. The stations YMEB-I (150°/100m), -II (150°/100m) and –III (240°/100m) are not included in groups like the rest of the stations that cluster at about 70 % similarity:

Group 1: YMEB-1 (60°/250m), -4 (150°/500m), -9 (240°/250m), -12 (330°/100m) and –IV (330°/100m)

The difference between group 1 and the other stations (located 100m from the centre) is mainly due to higher numbers of the bristle worm C. setosa and the ribbon worm (Nemertea) at the 100m stations. Another factor is higher numbers of the suspension feeding bristle worm Polycirrus norvegicus and the brittle star Amphiura filiformis in group 1. The similarity analyses indicate a slight distrubance in the fauna at the Central station and at most of the 100m stations.

During the sampling and sample processing, there were made observations of oil, black spots and scents of oil at the 100m stations and YMEB-Central. The observations support the results from the analysis.

The Bioenv analysis reveals a correlation of 0.9 between the fauna and the combination of the complex of chemical parameters THC, Ba1, TOM and grain size, indicating that these factors varies across the field in the same manner as the fauna composition.

1 Ba and the other metals are not degradable and will not disappear from the sediments. These metals may

presumable not have any effect on the fauna in itself, but could be regarded as trace elements for other degradable substances.

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YB-0

0

YB-II

YB-I

YB-II

I

YB-0

9

Y B-1

2

YB-0

4

YB-0

1

YB-IV

100

80

60

40

20Si

mila

rity

240/250m 330/250m 150/250m 60/250m 330/100m150/100m 60/100m 240/100m0/0mGroup 1

Figure 4.16.6. Dendrogram of the stations from Yme Beta 2005 (excl. juv.). YB-00 = YMEB Central.

YB-01YB-04

YB-09YB-12

YB-00

YB-I

YB-II

YB-III

YB-IV

Stress: 0,02

240/250m, 330/250m, 150/250m, 60/250m, 330/100m

240/100m

60/100m

150/100m

Figure 4.16.7. MDS plot of the stations from Yme Beta 2005 (excl. juv.). YB-00 = YMEB Central.

Comparison with 1996, 1999, 2002 and 2005

In Figure 4.16.8 the results from the present survey are compared to the results from previous surveys. Since the last survey the numbers of species have slightly increased at all comparable stations except for YMEB-01 (60°/250m) and YMEB-04 (150°/250m) where the numbers have decreased slightly. The numbers of individuals have decreased at all comparable stations except at YMEB-12 and –IV, where the numbers have increased slightly. The changes are not significant compared to most other fields in the region, mainly because M. oculata occurs in considerably smaller numbers at Yme Beta. The Shannon-Wiener diversity indices (H’) in general reflect small increases from the previous years’ surveys.

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020406080

100

YMEB-Cent

ral

YMEB-01

YMEB-04

YMEB-09

YMEB-12

YMEB-I

YMEB-II

YMEB-III

YMEB-IV

Stations

No.

of s

peci

es (S

)1996 1999 2002 2005

Station º/m YMEB-Central 0/0

YMEB-01 60/250

YMEB-04 150/250

YMEB-09 240/250

YMEB-12 330/250

YMEB-I 60/100

YMEB-II 150/100

YMEB-III 240/100

YMEB-IV 330/100

0200400600800

1000

YMEB-Cent

ral

YMEB-01

YMEB-04

YMEB-09

YMEB-12

YMEB-I

YMEB-II

YMEB-III

YMEB-IV

Stations

No.

of i

ndiv

idua

ls (N

)

1996 1999 2002 2005

0123456

YMEB-Cent

ral

YMEB-01

YMEB-04

YMEB-09

YMEB-12

YMEB-I

YMEB-II

YMEB-III

YMEB-IV

Stations

H'

1996 1999 2002 2005

Figure 4.16.8. Numbers of species (S) and individuals (N) per 0.5 m2 and diversity (H’). incl.P. jeffreysii and M. oculata, excl. juv., Yme Beta 1996, 1999, 2002 and 2005.

Classification and ordination analyses

The stations from all years have been analysed at family level∗, except the Central station sampled in 2005 which has been removed from the data set. The dendrogram from the cluster analyses reveals that two of the 100m stations from 2005 cluster together with the 100m stations from 2002 at a similarity of about 55 %. The rest of the stations divide into two main groups at a similarity of about 60 %. The 1996 stations cluster together and the other stations sampled in 1999 – 2005 forms a separate group. The 1999 – 2005 stations could further be divided into subgroups based on year at a similarity of about 75 %.

Group 1: 1996 stations Group 2: 1999 - 2005 stations including the 100 m stations YMEB-III (240°/100m)

and –IV (330°/100m) sampled in 2005 Group 3: YMEB-I (60°/100m) and –II (150°/100m) from 2005, and YMEB-I

(60°/100m), -II (150°/100m), -III (240°/100m) and –IV (330°/100m) from 2002

The 1996 stations have significantly higher numbers of sea squirts and of the bristle worms within the family Spionidae than the other groups. In group 2 and 3 there were found higher abundances of species within the bristle worm family Syllidae (mainly Exogone verugera which are known as carnivore, scavengers and deposit feeders) and the suspension feeding hydrozoans and Anthozoa species.

∗ Necessary when comparing between years, to avoid significant source of error due to both different years and different

taxonomists.

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Group 3 (some of the 100m stations) separates from group 2 (1999-2005) mostly because of higher numbers of hydrozoans and Anthozoan species together with smaller numbers of suspension feeding bristle worms from the family Terebellidae (mainly Terebellida stroemi). The movement of the 100m stations YMEB-III and –IV from group 3 to group 2 in 2005 indicates some improvement in the fauna at these stations since 2002.

The Bioenv analysis gave a correlation of 0.7 between the fauna community and the combination of the complex of the chemical parameters THC, Cd, Cu and pelite, indicating that this chemical complex has had some impact on the fauna community over the years.

YB-0

5-96

Y B-0

6-96

YB-0

4 -96

YB- 0

1-96

YB-0

2-9 6

YB-0

3 -96

YB-II

I-05

YB-0

4-05

YB-0

1-05

YB-IV

-05

YB- 0

9-05

YB-1

2-05

YB-0

2-99

YB-1

3-99

Y B-0

4-99

YB-1

0-99

Y B-0

3-99

YB-0

7-9 9

YB-0

2-0 2

YB-0

1-0 2

Y B-0

7-02

YB-1

0 -02

YB-1

3-02

YB-0

3-02

Y B-0

5-02

YB-1

2-02

YB-I-

05Y B

-II-0

5

YB-II

- 02

YB- I-

02

YB-II

I-02

YB-IV

-02

100

90

80

70

60

50

Sim

ilarit

y

2005 1999 2002

Group 1 (1996) Group 2 (1999-2005) Group 3 Figure 4.16.9. Dendrogram showing similarity between Yme Beta stations 1996, 1999, 2002 and 2005. Family level, incl. M. oculata, excl. juv., sq. root transformation.

4.16.4 Conclusion

The sediments at the Yme Beta field consist of medium sand, and the sand content varies from 97.7 % at YMEB1, 60°/250m to 99.8 % at YMEB12, 330°/250m. The gravel content is low. The silt and clay content is similar to the previous surveys.

Samples from the Installation Centre and from stations at 100m distance are included in the investigation. At the centre, 0°/0m, the sediments consist of 70 % sand and 30 % silt and clay. The medium diameter for YMEB Central is 2.52φ, thus this sediment is characterized as fine sand. At the 100m stations, the silt and clay content is similar to the regular Yme Beta monitoring stations, and the sand content varies from 95.2 % at YMEB-II, 150°/100m to 99.3 % at YMEB-IV, 330°/100m. The sediments are characterized as medium sand.

The contents of total organic matter in the sediments are very low, and only small variations are found at the regular monitoring stations. The concentrations vary from 0.36 % at YMEB9, 240°/250m to 0.42 % at YMEB4, 150°/250m. The results are similar to the previous surveys. At the Installation Centre the TOM content is 2.45 %, compared to 1.56 % found in the 2002 survey. At the 100m stations the concentrations vary from 0.39 % to 0.59 %. The contents of TOM are similar to the 2002 survey and are considerably lower than at Yme Gamma.

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The mean THC concentrations at the regular monitoring stations vary from 0.3 mg/kg at YMEB9, 240°/250m to 5.8 mg/kg at YMEB4, 150°/250m. Elevated levels are not found. The concentrations are mainly at the same level as in the 2002 survey.

Olefins are only found in one grab sample at YMEB4, 150°/250m (0.4 mg/kg) and in one grab sample in the 3-6 cm layer (3.5 mg/kg). The levels of olefins are the same as in the 2002 survey.

At the Installation Centre the THC concentration is high, 354 mg/kg. Distinct differences between the replicate samples are observed. Elevated THC levels are found in the deeper sections and range from 9 mg/kg to 99 mg/kg. The mean THC concentrations at the 100m stations vary from 2.5 mg/kg at YMEB-IV to 63 mg/kg at YMEB-II. Elevated concentrations are found at the YMEB-I (40 mg/kg) and YMEB-II. The sediments contain olefins, however these are not quantified.

Compared to the 2002 survey it is emphasized that the THC contents have decreased considerably at the Installation Centre for all the deeper layers. At the 100m stations the THC content has decreased at YMEB-III. The other stations have THC contents similar to the 2002 survey.

Elevated levels of NPD, PAH and decalins are not found at YMEB4, 150°/250m. At the installation Centre the NPD and decalin concentrations are relatively high, 2.22 mg/kg of NPD and 7.4 mg/kg of decalins. The concentration of NPD in the top 0-1 cm layer is at the same level as in 2002, but the concentration of decalins has decreased. However, the concentrations of NPD and decalins in the deeper layers 1-3 cm, 3-6 cm and 6-9 cm have increased significantly since the previous survey. A similar trend is seen for PAH. An enhanced level of PAH is found in the 1-9 cm section, but the level of PAH in the top layer is unchanged. Deeper in the sediment the concentrations of NPD, PAH and decalins are relatively low. The distributions seen for NPD, PAH and decalins are consistent with the distribution observed for THC at the same station. Relatively high contents of decalins are found at YMEB-II, 150°/100m, in agreement with the high content of THC found at this station.

The mean Ba concentrations at the regular monitoring stations vary from 11 mg/kg at YMEB12, 330°/250m to 520 mg/kg at YMEB4, 150°/250m. Elevated Ba concentrations are found at the stations at 250m in the 60°, 150° and 240° directions. The levels of Ba are similar or slightly higher compared to the levels found in the 2002 survey. Compared to Yme Gamma the Ba levels at Yme Beta are low. The concentrations of the heavy metals are low, and elevated concentrations are not found.

At the Installation Centre the Ba concentration is relatively high, 3038 mg/kg. However, the Ba content is halved since the 2002 survey. The same trend is also observed in the deeper layers. The Ba contents have decreased from 3030 mg/kg to 460 mg/kg and from 3280 mg/kg to 755 mg/kg respectively for the layers 1-3 cm and 3-6 cm. Elevated concentrations of Ba are found at the 100m stations in all four directions, ranging from 89 mg/kg in the 330° direction to 1339 mg/kg in the 150° direction. Elevated levels of the metals are found at the Installation Centre in all layers investigated. For the other 100m stations the content of heavy metals are low.

Generally the results agree with the drilling history at Yme Beta.

The structure in the fauna community and the biodiversity indices characterize a healthy fauna community at Yme Beta. However, the similarity analyses indicate a slight disturbance in the fauna at the Installation Centre and at most of the 100m stations. This is in accordance with the observations made in the field and during sample processing (oily substances). Station YMEB-IV (330°/100m) seems to have improved the most since 2002. Station YMEB-III is also believed to have improved slightly. However, all of the 100m stations are still slightly disturbed.

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In general the numbers of species and the biodiversity indices have increased slightly since the last survey, indicating general improvements in the fauna communities.

During sampling there were observed large amounts of yellow granules in the sediment samples from the Installation Centre and the 100m stations.

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4.17 Kogge

4.17.1 Sediment characterization

Grain size distribution

The grain size distribution from the present survey is given in Table 4.17.1.

The sediments consist mainly of medium sand, and the sand content varies from 94.5 % to 97.7 %. The mean median diameter is 1.69φ. The gravel content is low, 3.4 % and 0.4 % for KOG1 and KOG2 respectively. The results from the complete grain size distribution are given in Appendix C. Table 4.17.1. Kogge 2005, grain size distribution. Station Median

diameter Classification Grain size distrib. 2005

(%) Mdφ Silt and

clay Sand Gravel

KOG1 45°/1000m 1.69 Medium sand 2.1 94.5 3.4 KOG2 45°/2000m 1.69 Medium sand 1.9 97.7 0.4 Mean 1.69 2.0 96.1 1.9 Standard deviation 0 0.14 2.3 2.1

Total organic matter (TOM)

The sediments at Kogge consist mainly of sand and the content of TOM in the sediments is therefore low. The average TOM is 0.44 %. The results are shown in Table 4.15.2. Table 4.17.2. Kogge 2005, total organic matter (% of dry sediment). Station 2005

0-5cm, 1 sample KOG1 45°/1000m 0.45 KOG2 45°/2000m 0.42 Mean 0.44 Standard deviation 0.02

4.17.2 Chemical analyses

In the sediment samples from Kogge the following parameters are analysed:

• THC • Metals (Ba, Cd, Cr, Cu, Hg, Pb, Zn).

Three replicate samples from the top layer, 0-1 cm, at each station are analysed.

THC

The THC results are given in Table 4.17.3. Bar diagram of the THC content in the sediments is given in Figure 4.17.1.

In the present survey the mean THC concentration is 0.5 mg/kg in average.

The level of THC can be characterized as the natural background level for the area.

Gas chromatograms from the two stations are given in Appendix C.

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Kogge, THC 2005

0

1

2

3

4

5

6

7

8

9

10

KOG1 KOG2

station

mg/kg

2005

LSC B

LSC A

LSC B

LSC A

Figure 4.17.1. Bar diagram of the THC content in the sediments at Kogge 2005. Table 4.17.3. Kogge 2005, total hydrocarbon content (mg/kg dry sediment).

Station Grab #1 Grab #2 Grab #3 Mean 2005 SD 2005

KOG1 45°/1000m 0.6 0.5 0.5 0.5 0.1 KOG2 45°/2000m 0.4 0.5 0.6 0.5 0.1 LSC Subregion A 6.6 LSC Subregion B 4.6

Metals

The results are given in Table 4.17.4.

The concentrations of Ba, in the present survey, are low and uniform. The concentrations are 3.5 mg/kg in average. The concentrations of the other heavy metals are also low. The concentrations of Ba, Cr, Cu, Pb, Zn and Cd are considered as the natural background level for the area. A bar diagram of the Ba content in the sediments is shown in Figure 4.17.2.

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Kogge, Ba 2005

0

10

20

30

40

50

60

70

80

90

100

KOG1 KOG2

station

mg/kg

2005

LSC B

LSC A

LSC A

LSC B

Figure 4.17.2. Bar diagram of the Ba content in the sediments at Kogge 2005. The variations at the Kogge stations in mg/kg: Ba: 3 – 4 Cr: 8.6 – 9.3 Cu: <0.5 Pb: 5.2 – 5.6 Zn: 5.0 – 5.6 Cd: <0.01

Table 4.17.4. Kogge 2005, metals (mg/kg dry sediment). Station Sample Ba Cd Cr Cu Pb Zn 2005 2005 2005 2005 2005 2005 KOG1 45°/1000m 1 3 <0.01 8.7 <0.5 5.3 5.1 2 3 <0.01 8.4 <0.5 6.2 5.0 3 3 <0.01 8.8 <0.5 5.3 4.9 Mean 3 <0.01 8.6 <0.5 5.6 5.0 SD 0 - 0.2 - 0.5 0.1 KOG2 45°/2000m 1 3 <0.01 9.3 <0.5 5.5 6.3 2 3 <0.01 9.3 <0.5 4.6 4.9 3 7 <0.01 9.3 <0.5 5.4 5.6 Mean 4 <0.01 9.3 <0.5 5.2 5.6 SD 2 - 0.0 - 0.5 0.7 LSC Subregion A 76.2 8.0 1.3 7.4 6.9 LSC Subregion B 12.1 11.1 1.4 9.0 8.8

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4.17.3 Biological analyses

A total of 114 species and 1588 individuals were sampled at 2 stations. Greatest abundance (47.5 %) was found among the polychaetes, of which the species Myriochele oculata constitutes 2.4 % and Paramphinome jeffreysii constitutes about 18.4 % of the total number of Polychaeta, see Table 4.17.5. Table 4.17.5. Number of species and individuals distributed between the main groups, Kogge 2005.

Individuals Species Main animal groups Number % Number %

Varia 109 6.9 13 11.4Polychaeta 755 47.5 55 48.2- Paramphinome jeffreysii 139 18.4 - Myriochele oculata 18 2.4 Crustacea 34 2.1 13 11.4Mollusca 115 7.2 25 21.9Echinodermata 575 36.2 8 7.0- Amphiura filiformis 22 3.8 Total 1588 100.0 114 100.0

The numbers of the bristle worms, in particular M. oculata, but also P. jeffreysii are moderate at Kogge compared to other fields in the Ekofisk regions. This is mainly due to another structure of the sediment consisting of more silt and clay in this area.

Figure 4.17.3 shows the numbers of species and individuals sampled at each station and variations between grab samples.

020406080

100

KOGGE-01

KOGGE-02

Stations

No.

of s

peci

es (S

)

Station º/m KOGGE-01 1000/45 KOGGE-02 2000/45

Figure 4.17.3. Numbers of species (S) and individuals (N) per 0.5 m2 (incl./excl. P. jeffreysii and M. oculata), mean values per grab sample and standard deviation, Kogge 2005.

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0200

400600800

1000

KOGGE-01

KOGGE-02

Stations

No.

of i

ndiv

idua

ls (N

) Ex. P. jeffreysii and M. oculata

0

200

400

600

800

1000

KOGGE-01

KOGGE-02

Stations

No.

of i

ndiv

idua

ls (N

)

Figure 4.17.3. cont.

Diversity and dominant species

The dominant species at Kogge varied from 32.6 % at KOGGE-01 (1000°/45m) to 33.9 % at KOGGE-02 (2000°/45m). The 10 most abundant species made up from 69.5 % at KOGGE-01 to 72.3 % at KOGGE-02, see Table 4.17.6. The juvenile Echinoidea was the dominating species at the Kogge field. Other frequently found species were the bristle worms P. jeffreysii, Spiophanes bombyx and Exogone verugera. S. bombyx is a suspension- and deposit feeder, while the other two are mainly carnivore species. The top ten lists consist of species which are either suspension feeders or could make use of both suspension- and deposit feeding. The composition of the fauna community (excl. juveniles) reflects a healthy environment. Table 4.17.6. The 10 most abundant species at each station, Kogge 2005. 10 most dominating species KOGGE-01 No. % Cum. % KOGGE-02 No. % Cum. % Echinoidea spp.juv. 296 32.6 32.6 Echinoidea spp.juv. 230 33.9 33.9 Paramphinome jeffreysii 84 9.2 41.8 Spiophanes bombyx 67 9.9 43.7 Spiophanes bombyx 45 5.0 46.8 Paramphinome jeffreysii 55 8.1 51.8 Exogone verugera 44 4.8 51.6 Exogone verugera 40 5.9 57.7 Edwardsia sp. 42 4.6 56.2 Aricidea cerrutii 26 3.8 61.6 Mysella bidentata 37 4.1 60.3 Ampharete falcata 17 2.5 64.1 Ampharete falcata 26 2.9 63.2 Nephtys longosetosa 16 2.4 66.4 Ophelia borealis 20 2.2 65.4 Aonides paucibranchiata 16 2.4 68.8 Amphiura filiformis 19 2.1 67.4 Edwardsia sp. 15 2.2 71.0 Exogone hebes 19 2.1 69.5 Ophiura affinis 9 1.3 72.3

The numbers of species and individuals per station are shown in Table 4.17.7. The Shannon Wiener diversity and Hurlberts indices (ES100) show a healthy fauna community in the area. Table 4.17.7. Numbers of individuals (N) and species (S), depth, Shannon-Wiener diversity index (H’), Pielou’s evenness index (J), and expected number of species per 100 individuals (ES100) for each station at Kogge 2005 (excl. juv.).

Station Direction ° Distance m Depth S N H' J ES100

KOGGE-01 1000 45 76 88 609 5.2 0.8 39 KOGGE-02 2000 45 78 78 448 5.1 0.8 39

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Classification and ordination

The dendrogram from the cluster analysis and the MDS plot from the ordination analysis based on grab level are presented in Figure 4.17.4 and Figure 4.17.5. The grabs divide at a similarity of about 45 %, independent of station, meaning that the differences among sampled grabs within one station were greater than the differences between stations.

KO

GG

E-0 2

-5

KO

GG

E-02

-1

KO

GG

E-01

-4

KO

GG

E-0 1

-1

KO

GG

E-01

-2

KO

GG

E-02

-2

KO

GG

E-02

-3

KO

GG

E-01

-3

KO

GG

E-01

-5

KO

GG

E -02

-4

100

80

60

40

Sim

ilarit

y

Figure 4.17.4. Dendrogram of grab samples from Kogge 2005 (excl. juv.).

KOGGE-01-1KOGGE-01-2

KOGGE-01-3

KOGGE-01-4

KOGGE-01-5

KOGGE-02-1

KOGGE-02-2

KOGGE-02-3KOGGE-02-4

KOGGE-02-5

Stress: 0,14

Figure 4.17.5. MDS plot of grab samples from Kogge 2005 (excl. juv.).

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4.17.4 Conclusion

A baseline survey of sediments from two stations has been performed at Kogge 2005. The intention of the survey was to estimate the background levels of the chemical components and the status of the benthic fauna.

The sediments at Kogge consist mainly of medium sand, and the sand content ranges from 94.5 to 97.7 %. The content of silt and clay is low and ranges from 1.9 to 2.1 %. The content of gravel is also low and varies from 0.4 to 3.4 %.The content of total organic matter is low and the average value is 0.44 %. This low content of organic matter is in consistency with the high sand content of the sediments.

The sediments are not contaminated by THC. The THC concentration is 0.5 mg/kg for both stations surveyed. The concentration of Ba is 3.5 mg/kg as an average. The concentration of hydrocarbons, barium and heavy metals are low and within the limits of what can be characterized as the natural background level for the area.

The study has shown that the Kogge field is polluted by neither hydrocarbons nor metals, and the fauna at the two Kogge stations are characterised as diverse and healthy.

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4.18 Trym

4.18.1 Sediment characterization

Grain size distribution

The grain size distribution from the present baseline survey is given in Table 4.18.1.

The sediments consist mainly of fine sand, and the sand content varies from 91.6 % to 97.5 %. The average median diameter is 2.65φ and the average sand content is 94.8 %. Sediment at Trym shows a uniform grain size distribution. Gravel is found only at two stations, with 3.3 % at TRY5 and 0.1 % at TRY8. The results from the complete grain size distribution are given in Appendix C. Table 4.18.1. Trym 2005, grain size distribution. Station Median

diameter Classification Grain size distribution 2005 (%)

Mdφ Silt and clay Sand Gravel TRY1 70°/250m 2.67 Fine sand 7.4 92.6 0,0 TRY2 70°/500m 2.66 Fine sand 5.5 94.5 0,0 TRY3 70°/1000m 2.63 Fine sand 4.2 95.8 0,0 TRY4 160°/250m 2.66 Fine sand 6.1 93.9 0,0 TRY5 160°/500m 2.60 Fine sand 0.0 96.7 3,3 TRY6 250°/250m 2.68 Fine sand 8.4 91.6 0,0 TRY7 250°/500m 2.68 Fine sand 5.3 94.7 0,0 TRY8 340°/250m 2.64 Fine sand 3.7 96.2 0,1 TRY9 340°/500m 2.60 Fine sand 2.5 97.5 0,0 Mean 2.65 4.8 94.8 0.4 Standard deviation 0.03 2.6 1.9 1.1

Total organic matter (TOM)

The sediments at Trym consist mainly of fine sand and the content of TOM in the sediments is therefore low. The TOM content ranges from 0.65 % to 0.89 % and the average content is 0.70 %. The results are shown in Table 4.18.2. Table 4.18.2. Trym 2005, total organic matter (% of dry sediment). Station 2005

0-5cm, 1 sample TRY1 70°/250m 0.70 TRY2 70°/500m 0.76 TRY3 70°/1000m 0.89 TRY4 160°/250m 0.65 TRY5 160°/500m 0.67 TRY6 250°/250m 0.70 TRY7 250°/500m 0.72 TRY8 340°/250m 0.71 TRY9 340°/500m 0.69 Mean 0.72 Standard deviation 0.07

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4.18.2 Chemical analyses

In the sediment samples from Trym the following parameters are analysed:

• THC • NPD, PAH, decalins • Metals (Ba, Cd, Cr, Cu, Hg, Pb, Zn).

Three replicate samples from the top layer, 0-1 cm, at each station are analysed. In addition, samples of the 1-3 cm and 3-6 cm layer are analysed from two stations.

THC

The THC results are shown in Table 4.18.3. Bar diagram of the THC content in the sediments is shown in Figure 4.18.1.

In the present survey the mean THC concentrations vary from 1.7 mg/kg at TRY8, 340°/250m to 3.8 mg/kg at TRY2, 70°/500m. No significant differences in the hydrocarbon content are found between the upper 0-1 cm layer and the 1-3 and 3-6 cm layers. However, there seems to be a slight increase in the THC content downwards in the sediment.

The level of THC can be characterized as the natural background level for the area. Gas-chromatograms from each station are given in Appendix C.

Trym, THC 2005

0

1

2

3

4

5

6

7

8

9

10

TRY1 TRY2 TRY3 TRY4 TRY5 TRY6 TRY7 TRY8 TRY9

station

mg/kg

2005

LSC B

LSC A

LSC A

LSC B

Figure 4.18.1. Bar diagram of the THC content in the sediments at Trym 2005.

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Table 4.18.3. Trym 2005, total hydrocarbon content (mg/kg dry sediment). Station Grab #1 Grab #2 Grab #3 Mean 2005 SD 2005 TRY1 70°/250m 3.6 2.9 3.3 3.2 0.3 TRY2 70°/500m 3.3 2.7 5.3 3.8 1.4 TRY3 70°/1000m 2.2 2.9 5.0 3.4 1.5 TRY4 160°/250m 1.6 2.9 2.4 2.3 0.6 1-3 cm 2.9 3-6 cm 3.3 TRY5 160°/500m 2.1 3.1 3.1 2.8 0.6 1-3 cm 3.8 3-6 cm 5.3 TRY6 250°/250m 2.9 2.2 1.9 2.3 0.5 TRY7 250°/500m 1.2 2.4 3.3 2.3 1.0 TRY8 340°/250m 1.7 1.0 2.3 1.7 0.6 TRY9 340°/500m 1.6 2.0 2.1 1.9 0.2 LSC Subregion A 6.6 LSC Subregion B 4.6

NPD, PAH and decalins

The concentrations of NPD are low for both the stations investigated, respectively 0.014 mg/kg at TRY4, 160°/250m and 0.010 mg/kg at TRY5, 160°/500m. The NPD content is very slightly increasing downwards in the sediment, to ~0.025 mg/kg in the 3-6 cm layer.

The mean PAH concentrations are low, about 0.030 mg/kg at both TRY4 and TRY5. The PAH content is also slightly increasing downwards in the sediment, to 0.07 mg/kg (TRY4) and 0.1 mg/kg (TRY5) in the 3-6 cm layer.

Decalines are not detected in the area investigated.

The levels of NPD, PAH and decalins are considered to be the natural level in the area.

The results are shown in Table 4.18.4. Table 4.18.4. Trym 2005, sum NPD, PAH and decalins (mg/kg dry sediment). Station Grab #1 Grab #2 Grab #3 Mean SD 2005 2005 NPD TRY4 160°/250m 0.010 0.021 0.010 0.014 0.006 1-3 cm 0.014 3-6 cm 0.023 TRY5 160°/500m 0.010 0.010 0.010 0.010 0.001 1-3 cm 0.010 3-6 cm 0.027 LSC Subregion A 0.030 LSC Subregion B 0.012 Cont

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Table 4.18.3. cont. PAH TRY4 160°/250m 0.023 0.047 0.027 0.032 0.013 1-3 cm 0.043 3-6 cm 0.073 TRY5 160°/500m 0.032 0.034 0.035 0.033 0.002 1-3 cm 0.041 3-6 cm 0.095 LSC Subregion A 0.061 LSC Subregion B 0.024 Decalins were not detected; (<0.1 mg/kg). Limit of detection for NPD is 0.01 mg/kg and 0.005 mg/kg for PAH. nd: not detected.

Metals

The results are shown in Table 4.18.5. The Hg contents are only analysed at two stations. Bar diagram of the Ba content in the sediments is shown in Figure 4.18.2.

The concentrations of Ba, in the present survey, are uniform. The mean concentrations vary from 14 mg/kg at TRY8, 340°/250m to 42 mg/kg at TRY3, 70°/1000m. The concentrations of the other heavy metals are low. The Hg concentrations are <0.01 mg/kg.

The sediment layers 1-3 cm and 3-6 cm are analysed at two stations. At these stations the contents of Ba distinctly increase downwards in the sediments. At TRY4, the Ba content increases from 22 mg/kg in the top layer to 167 mg/kg in the 3-6 cm layer. At TRY5 the Ba contents increase from 21 mg/kg in the top layer to 99 mg/kg in the 3-6 cm layer. Also for the heavy metals Cr, Cu, Pb and Zn there seem to be a trend for slightly higher contents deeper in the sediments. The concentrations of Ba, Cr, Cu, Pb, Zn, Cd and Hg must be considered as the natural background level for the area.

Trym, Ba 2005

0

10

20

30

40

50

60

70

80

90

100

TRY1 TRY2 TRY3 TRY4 TRY5 TRY6 TRY7 TRY8 TRY9

station

mg/kg

2005

LSC B

LSC A

LSC A

LSC B

Figure 4.18.2. Bar diagram of the Ba content in the sediments at Trym 2005.

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The variation at the different Trym stations (the top layer) in mg/kg: Ba: 14 – 42 Cr: 6.2 – 6.8 Cu: <0.5 Pb: 6.6 – 7.2 Zn: 4.9 – 7.2 Cd: <0.01 Hg: <0.01

Table 4.18.5. Trym 2005, Metals (mg/kg dry sediment). Station Sample Ba Cd Cr Cu Hg Pb Zn 2005 2005 2005 2005 2005 2005 2005TRY1 70°/250m 1 20 <0.01 6.2 <0.5 6.3 5.8 2 25 <0.01 7.4 <0.5 6.0 5.3 3 27 <0.01 6.4 <0.5 7.7 5.7 Mean 24 <0.01 6.7 <0.5 6.7 5.6 SD 4 0.7 0.9 0.3 TRY2 70°/500m 1 22 <0.01 6.3 <0.5 6.7 4.9 2 37 <0.01 6.6 <0.5 7.2 9.5 3 47 <0.01 6.9 0.5 6.6 7.2 Mean 35 <0.01 6.6 <0.5 6.9 7.2 SD 13 0.3 0.3 2.3 TRY3 70°/1000m 1 20 <0.01 6.5 <0.5 6.6 4.8 2 44 <0.01 6.6 <0.5 7.1 5.5 3 63 <0.01 7.1 0.6 7.6 8.2 Mean 42 <0.01 6.8 <0.5 7.1 6.2 SD 21 0.3 0.5 1.8 TRY4 160°/250m 1 21 <0.01 6.3 <0.5 <0.01 6.2 5.2 2 24 <0.01 6.2 <0.5 <0.01 6.7 5.4 3 20 <0.01 6.2 <0.5 <0.01 7.1 5.1 Mean 22 <0.01 6.2 <0.5 <0.01 6.7 5.2 SD 2 0.1 0.5 0.2 1-3cm 30 <0.01 6.1 <0.5 <0.01 7.2 5.2 3-6cm 167 0.01 7.5 1.4 <0.01 8.3 7.6 TRY5 160°/500m 1 14 <0.01 6.1 <0.5 <0.01 6.8 4.7 2 20 <0.01 6.0 <0.5 <0.01 6.4 4.8 3 27 <0.01 6.2 <0.5 <0.01 6.7 5.2 Mean 21 <0.01 6.1 <0.5 <0.01 6.6 4.9 SD 6 0.1 0.2 0.3 1-3cm 33 <0.01 6.5 <0.5 <0.01 7.7 5.3 3-6cm 99 <0.01 7.4 0.9 <0.01 8.2 6.9 TRY6 250°/250m 1 44 <0.01 6.5 <0.5 8.6 5.9 2 32 <0.01 6.1 <0.5 6.3 5.2 3 14 <0.01 5.7 <0.5 6.7 4.6 Mean 30 <0.01 6.1 <0.5 7.2 5.2 SD 15 0.4 1.2 0.6 Cont.

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Table 4.18.5 cont. Station Sample Ba Cd Cr Cu Hg Pb Zn 2005 2005 2005 2005 2005 2005 2005TRY7 250°/500m 1 17 <0.01 6.2 <0.5 7.1 4.8 2 29 <0.01 6.3 <0.5 6.6 5.3 3 44 <0.01 6.2 <0.5 7.4 5.6 Mean 30 <0.01 6.2 <0.5 7.0 5.3 SD 14 0.1 0.4 0.4 TRY8 340°/250m 1 12 <0.01 5.6 <0.5 7.5 4.6 2 19 <0.01 5.8 <0.5 6.9 5.2 3 13 <0.01 5.6 <0.5 7.1 5.7 Mean 14 <0.01 5.7 <0.5 7.2 5.2 SD 4 0.1 0.3 0.5 TRY9 340°/500m 1 21 <0.01 6.0 <0.5 7.0 8.9 2 31 <0.01 6.5 <0.5 7.2 5.8 3 23 <0.01 6.1 <0.5 8.0 5.2 Mean 25 <0.01 6.2 <0.5 7.4 6.6 SD 5 0.2 0.6 2.0 LSC Subregion A 76.2 8.0 1.3 7.4 6.9 LSC Subregion B 12.1 11.1 1.4 9.0 8.8

4.18.3 Biological analyses

A total of 150 species and 12603 individuals were sampled at 9 stations. Greatest abundance (69.0 %) was found among the polychaetes, of which the species Myriochele oculata constituted 55.6 % and Paramphinome jeffreysii constituted about 11.7 % of the total number of Polychaeta, see Table 4.18.6. Table 4.18.6. Number of species and individuals distributed between the main groups, Trym 2005.

Individuals Species Main animal groups Number % Number %

Varia 1409 11.2 15 10.0Polychaeta 8697 69.0 66 44.0- Paramphinome jeffreysii 1019 11.7 - Myriochele oculata 4835 55.6 Crustacea 166 1.3 23 15.3Mollusca 1091 8.7 37 24.7Echinodermata 1240 9.8 9 6.0- Amphiura filiformis 1068 86.1 Total 12603 100.0 150 100.0

Figure 4.18.3 shows the numbers of species and individuals sampled at each station and variations between grab samples.

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020406080

100TRYM-01TRYM-02TRYM-03TRYM-04TRYM-05TRYM-06TRYM-07TRYM-08TRYM-09

Stations

No.

of s

peci

es (S

)

Station º/m TRYM-01 70/250 TRYM-02 70/500 TRYM-03 70/1000 TRYM-04 160/250 TRYM-05 160/500 TRYM-06 250/250 TRYM-07 250/500 TRYM-08 340/250 TRYM-09 340/500

0300600900

1200150018002100

TRYM-01TRYM-02TRYM-03TRYM-04TRYM-05TRYM-06TRYM-07TRYM-08TRYM-09

Stations

No.

of i

ndiv

idua

ls (N

) Ex. P. jeffreysii and M. oculata

0300600900

1200150018002100

TRYM-01TRYM-02TRYM-03TRYM-04TRYM-05TRYM-06TRYM-07TRYM-08TRYM-09

Stations

No.

of i

ndiv

idua

ls (N

)

Figure 4.18.3. Numbers of species (S) and individuals (N) per 0.5 m2 (incl./excl. P. jeffreysii and M. oculata), mean values per grab sample and standard deviation, Trym 2005.

The standard deviation was in general dramatically reduced when the two species P. jeffreysii and M. oculata were removed. This is evident since the two species constitute 46.5 % of the total number of individuals. At TRYM-05 (160º/500m), -08 (340º/250m) and -09 (340º/500m), the standard deviation was only slightly reduced due to the large differences between the grabs sampled at each station.

Diversity and dominant species

The dominant species at each station varied from 19.7 % at TRYM-05 (160°/500m) to 50.9 % at TRYM-03 (70°/1000m). The 10 most abundant species made up from 68.4 % at TRYM-05 to 83.5 % at TRYM-02 (70°/500m), see Table 4.18.7. The bristle worms M. oculata and P. jeffreysii together with the brittle star Amphiura filiformis dominated the fauna, but also the hydroid Corymorpha nutans was relatively abundant at the Trym field. Other frequently found species were the bristle worms Scoloplos armiger, Scalibregma inflatum and Chaetozone setosa. P. jeffreysii is mainly a carnivore species. The other species are either suspension or both suspension- and deposit feeders. The structure of the fauna community reflects a relatively healthy environment.

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Table 4.18.7. The 10 most abundant species at each station, Trym 2005. 10 most dominating species TRYM-01 No. % Cum. % TRYM-02 No. % Cum. % Myriochele oculata 230 21.1 21.1 Myriochele oculata 1020 49.8 49.8 Amphiura filiformis 127 11.7 32.8 Amphiura filiformis 176 8.6 58.3 Paramphinome jeffreysii 110 10.1 42.9 Paramphinome jeffreysii 165 8.1 66.4 Corymorpha nutans 98 9.0 51.9 Corymorpha nutans 91 4.4 70.8 Scoloplos armiger 50 4.6 56.5 Scoloplos armiger 72 3.5 74.3 Phoronis muelleri 35 3.2 59.7 Scalibregma inflatum 42 2.1 76.4 Scalibregma inflatum 29 2.7 62.4 Mysella bidentata 41 2.0 78.4 Nemertea spp. 29 2.7 65.1 Chaetozone setosa 41 2.0 80.4 Magelona filiformis 29 2.7 67.7 Goniada maculata 35 1.7 82.1 Mysella bidentata 28 2.6 70.3 Nemertea spp. 29 1.4 83.5 TRYM-03 No. % Cum. % TRYM-04 No. % Cum. % Myriochele oculata 890 50.9 50.9 Myriochele oculata 225 23.9 23.9 Paramphinome jeffreysii 142 8.1 59.0 Amphiura filiformis 130 13.8 37.8 Amphiura filiformis 91 5.2 64.2 Paramphinome jeffreysii 84 8.9 46.7 Corymorpha nutans 82 4.7 68.9 Scalibregma inflatum 48 5.1 51.8 Scalibregma inflatum 58 3.3 72.3 Corymorpha nutans 48 5.1 56.9 Scoloplos armiger 49 2.8 75.1 Chaetozone setosa 44 4.7 61.6 Chaetozone setosa 48 2.8 77.8 Scoloplos armiger 39 4.2 65.7 Abra prismatica 29 1.7 79.5 Nemertea spp. 39 4.2 69.9 Nemertea spp. 29 1.7 81.1 Mysella bidentata 23 2.5 72.3 Mysella bidentata 28 1.6 82.7 Goniada maculata 22 2.3 74.7 TRYM-05 No. % Cum. % TRYM-06 No. % Cum. % Myriochele oculata 230 19.7 19.7 Myriochele oculata 805 50.8 50.8 Paramphinome jeffreysii 134 11.5 31.2 Corymorpha nutans 112 7.1 57.9 Amphiura filiformis 113 9.7 40.9 Amphiura filiformis 106 6.7 64.5 Corymorpha nutans 79 6.8 47.7 Paramphinome jeffreysii 94 5.9 70.5 Scoloplos armiger 64 5.5 53.2 Scoloplos armiger 52 3.3 73.8 Scalibregma inflatum 55 4.7 57.9 Chaetozone setosa 38 2.4 76.2 Chaetozone setosa 33 2.8 60.7 Nemertea spp. 25 1.6 77.7 Abra prismatica 32 2.7 63.5 Goniada maculata 24 1.5 79.2 Mysella bidentata 30 2.6 66.0 Scalibregma inflatum 23 1.5 80.7 Ennucula tenuis 28 2.4 68.4 Abra prismatica 21 1.3 82.0 TRYM-07 No. % Cum. % TRYM-08 No. % Cum. % Myriochele oculata 500 35.3 35.3 Myriochele oculata 485 40.3 40.3 Amphiura filiformis 108 7.6 42.9 Corymorpha nutans 114 9.5 49.7 Paramphinome jeffreysii 99 7.0 49.9 Amphiura filiformis 92 7.6 57.3 Corymorpha nutans 85 6.0 55.9 Paramphinome jeffreysii 63 5.2 62.6 Scoloplos armiger 62 4.4 60.3 Scoloplos armiger 42 3.5 66.1 Chaetozone setosa 44 3.1 63.4 Nemertea spp. 41 3.4 69.5 Mysella bidentata 40 2.8 66.2 Aonides paucibranchiata 35 2.9 72.4 Scalibregma inflatum 38 2.7 68.9 Chaetozone setosa 32 2.7 75.0 Nemertea spp. 35 2.5 71.4 Scalibregma inflatum 24 2.0 77.0 Goniada maculata 28 2.0 73.3 Tharyx sp. 23 1.9 78.9 Cont.

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Table 4.18.7. cont. 10 most dominating species TRYM-09 No. % Cum. % Myriochele oculata 450 32.1 32.1 Paramphinome jeffreysii 128 9.1 41.2 Amphiura filiformis 125 8.9 50.1 Corymorpha nutans 81 5.8 55.8 Mysella bidentata 60 4.3 60.1 Scoloplos armiger 48 3.4 63.5 Echinoidea spp.juv. 41 2.9 66.5 Nemertea spp. 41 2.9 69.4 Scalibregma inflatum 37 2.6 72.0 Chaetozone setosa 31 2.2 74.2

The number of species varied from 63 at station TRYM-04 (160°/250m) to 83 at TRYM-02 (70°/500m). The number of individuals varied from 937 at TRYM-04 to 2040 at TRYM-02. The Shannon Wiener diversity index varied from 3.3 at TRYM-02, -03 (70°/1000m) and -06 (250°/250m) to 4.5 at TRYM-05 (160°/500m). The Hurlberts index (ES100) varied from 22 at TRYM-02, -03 and -06 to 30 at TRYM-05 including M.oculata. Removing M.oculata from the data1 results in minor changes in the biodiversity indices, even though the field is located in the central parts of the North Sea. Diversity indices above 4 indicate a relatively undisturbed fauna. Indices between 3 and 4 indicate a slight disturbance, while indices between 2 and 3 indicate a distinct disturbance in the fauna. In general ES100 indices above 20 characterize a relatively normal fauna community, see Table 4.18.8. Table 4.18.8. Numbers of individuals (N) and species (S), depth, Shannon-Wiener diversity index (H’), Pielou’s evenness index (J), and expected number of species per 100 individuals (ES100) for each station at Trym 2005 (excl. juv.).

H' ES100 Station Direction ° Distance m Depth S N Incl.

M. o. Excl. M. o.

J Incl. M. o.

Excl. M. o.

TRYM-01 70 250 65 72 1077 4.4 4.5 0.7 28 29TRYM-02 70 500 65 83 2040 3.3 3.3 0.5 22 23TRYM-03 70 1000 65 77 1736 3.3 3.3 0.5 22 23TRYM-04 160 250 65 64 937 4.2 4.2 0.7 26 27TRYM-05 160 500 65 79 1153 4.5 4.6 0.7 30 30TRYM-06 250 250 66 68 1567 3.3 3.3 0.5 22 23TRYM-07 250 500 66 75 1390 4.1 4.1 0.7 27 28TRYM-08 340 250 66 68 1195 3.7 3.8 0.6 25 26TRYM-09 340 500 69 72 1359 4.1 4.2 0.7 27 28M. o.= M. oculata

Classification and ordination

The dendrogram from the cluster analysis and the MDS plot from the ordination analysis based on station level are presented in Figure 4.18.4 and Figure 4.18.5. The stations have a similarity of about 75 % and the analysis show the same overall pattern inclusive and exclusive M. oculata. Due to the high similarity between stations there is no need to further subdivide the stations into groups.

The Bioenv-analysis gives a rather poor correlation (0.4) between the fauna and the abiotic parameters.

1 The role of Myriochele oculata in the Ekofisk Region is discussed on a general basis in X.X.

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T RYM

-04

TRYM

-08

TRYM

-01

TRYM

-05

TRYM

- 06

TRYM

-07

TRYM

-09

TRYM

- 02

TRYM

-03

100

95

90

85

80

75

70Si

mila

rity

Figure 4.18.4. Dendrogram of stations from Trym 2005 (excl. juv.).

TRYM-01

TRYM-02

TRYM-03

TRYM-04

TRYM-05

TRYM-06TRYM-07

TRYM-08

TRYM-09

Stress: 0,09

Figure 4.18.5. MDS plot of stations from Trym 2005 (excl. juv.).

4.18.4 Conclusion

A baseline survey of sediments from 9 stations has been performed at Trym 2005. The intention of the survey was to estimate the background levels of the chemical components in the sediments.

The sediments at Trym consist mainly of fine sand, and the sand content varies from 91.6 to 97.5 %. The grain size distribution is uniform. The content of silt and clay varies from 0 to 8.4 %. Gravel is only found in small amounts at two stations. The content of total organic matter varies from 0.65 to 0.89 %. This low content of organic matter is consistent with the high sand content of the sediments.

The sediments are not contaminated by THC. The THC concentrations in the top layer range from 1.7 to 3.8 mg/kg. In the deeper layers, the THC concentrations vary from 2.9 to 5.3 mg/kg.

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The mean concentrations of NPD are low (0.010 – 0.015 mg/kg) for both stations investigated. The mean PAH concentrations are also low, about 0.030 mg/kg. Both NPD and PAH contents are slightly increasing downwards in the sediments. Decalines were not detected in the present survey. The concentration of Ba in the top layer ranges from 14 to 42 mg/kg and in the deeper layers from 21 to 167 mg/kg. The concentrations of hydrocarbons, barium and heavy metals are within what can be characterized as the natural background level for the area. The survey has shown that the Trym field is not polluted by hydrocarbons and metals.

The survey at Trym in 2005 was a baseline study and the fauna community at Trym is in general characterized as relatively healthy, not influenced by any field activities. However, the fauna community seems to be slightly disturbed, which is probably due to the high energy environment together with a general diffuse organic enrichment in the central parts of the Ekofisk region, see chapter 5 – Regional trends and Conclusions for details.

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5.0 Regional Trends and Conclusions

5.1 Chemical analyses and grain size distribution A summary of the sediment characterizations and the chemical analyses of the sediments at Region I is shown in Table 5.1.1. The mean values of the three replicates are given. The TOM values are based on one sample. The results summarized are for the top 0-1 cm layer. Table 5.1.1. Results at Region I 2005 Parameter Regional

stations Valhall Valhall

nordflanke Valhall

sørflanke Hod Ula

(10 stations) (12 stations) (13 stations) (13 stations) (8 stations) (9 stations) Sand % 95 – 99 85 - 98 93 - 100 93 – 97 91 - 97 95 – 97 TOM % 0.7 - 1.1 0.8 - 1.5 0.8 – 0.9 0.6 - 0.8 0.8 - 1.3 0.8 - 1.1 THC mg/kg 1.3 - 5.8 4.3 - 130 4.3 – 8.4 3.6 - 5.3 4.3 - 36 3.9 – 58 Olefins mg/kg na na na na 0.7 - 7.1 na Esters mg/kg na na na na na na NPD mg/kg nd – 0.020 0.04 – 1.24 0.014 nd 0.025 – 0.085 0.043 – 0.16PAH mg/kg 0.018 – 0.062 0.062 – 0.21 0.043 0.020 0.065 – 0.077 0.073 – 0.12Decalins mg/kg nd – 0.24 nd – 2.7 nd nd nd – 0.91 0.19 – 2.4 Ba mg/kg 4.1 - 72 28 - 5587 28 - 468 28 – 194 32 - 900 35 – 4170 Cr mg/kg 5.8 - 9.1 7.7 - 10.5 7.6 – 9.4 6.3 - 7.7 6.9 - 8.9 6.2 - 8.0 Cu mg/kg nd - 0.5 nd - 9.6 nd nd nd - 1.0 nd - 5.5 Pb mg/kg 4.0 - 7.2 6.5 - 19.1 6.5 – 8.5 5.9 - 7.4 5.8 - 10.5 6.2 - 16.4 Zn mg/kg 3.1 - 6.8 5.6 - 33 5.6 – 7.7 4.9 - 5.8 5.9 - 8.6 5.4 – 43 Cd mg/kg nd - 0.2 nd - 0.03 nd nd nd nd Hg mg/kg nd nd - 0.02 nd nd nd nd na: not analysed nd: not detected Detection limits: olefins 0.3 – 0.5 mg/kg (varies with the field), esters: 0.2 mg/kg, decalins: 100 µg/kg Cu: 0.5mg/kg, Cd 0.01 mg/kg, Hg 0.01mg/kg Table 5.1.1. cont. Parameter Gyda Tambar Ekofisk Centre

og 2/4 B&K Ekofisk 2/4 A Eldfisk 2/7

A/FTP Eldfisk 2/7 B

(8 stations) (8 stations) (20 stations) (27 stations) (9 stations) (8 stations) Sand % 94 – 100 93 - 98 65 - 97 83 – 95 92 – 97 95 - 97 TOM % 0.6 - 0.8 0.8 - 1.0 0.9 – 1.3 0.76 – 1.50 0.9 - 1.0 0.9 - 1.0 THC mg/kg 4 – 43 3.3 - 15.2 5.8 - 188 8 – 106 4.3 - 120 5.8 - 30 Olefins mg/kg na na 1.1 - 86 2 – 61 0.5 - 0.6 0.5 - 0.9 Esters mg/kg na na na nd – 3 na na NPD mg/kg 0.018 – 0.70 0.015 – 0.030 0.08 – 0.20 0.03 – 0.94 0.10 – 0.20 0.03 – 0.12 PAH mg/kg nd - 0.056 0.039 – 0.046 0.073 – 0.10 0.029 – 0.248 0.024 – 0.22 0.03 – 0.07 Decalins mg/kg nd – 1.0 nd – 1.4 0.12 – 7.7 nd – 0.9 0.6 – 33* 0.07 – 1.80 Ba mg/kg 36 – 1566 106 - 563 46 - 3860 887 – 5110 590 - 1700 644 - 1706 Cr mg/kg 6.5 – 24 6.8 - 7.4 5.6 - 11.7 4.7 – 14.2 6.7 - 7.6 4.8 - 7.2 Cu mg/kg nd – 21 0.5 - 0.7 Nd - 5.3 1.4 – 17.5 0.7 - 1.4 0.7 - 1.2 Pb mg/kg 5.8 – 24 5.3 - 6.8 6.1 - 22.2 9.0 – 51.7 9.7 - 13.5 7.0 - 14.4 Zn mg/kg 4.9 – 88 5.7 - 6.5 5.4 - 48 11.5 – 154 7.6 - 11.7 5.8 - 10.4 Cd mg/kg nd nd nd - 0.09 0.02 – 0.40 nd nd Hg mg/kg nd nd nd - 0.07 0.01 – 0.12 ~0.03 nd na: not analysed nd: not detected *: only in one grab sample. Detection limits: olefins 0.3 - 0.5 mg/kg (varies with the field), esters: 0.2 mg/kg, 100 µg/kg,Cu: 0.5mg/kg, Cd 0.01 mg/kg, Hg 0.01mg/kg Table 5.1.1. cont. Parameter Embla

2/7 D Tor 2/4 E Yme Gamma* Yme Beta* Kogge Trym

(4 stations) (5 stations) (5 stations) (4 stations) (2 stations) (9 stations)

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Sand % na 97 – 98 94 – 98 98 - 100 95 – 98 92 – 98 TOM % na 0.8 - 0.9 0.5 - 0.7 0.4 0.4 0.7 - 0.9 THC mg/kg 3.9 - 18.2 6.6 – 20 2.4 – 32 0.3 – 5.8 0.5 1.7 - 3.8 Olefins mg/kg na na nd - 2.5 nd na na Ether mg/kg na 1.3 – 28 na na na na Esters mg/kg na na 0.5 – 0.66 na na na NPD mg/kg na 0.04 – 0.07 0.05 – 8.7 0.011 na 0.010 – 0.014PAH mg/kg na 0.05 – 1.6** 0.035 – 0.44 0.010 na 0.032 – 0.033Decalins mg/kg na nd nd – 0.17 nd na nd Ba mg/kg na 341 – 1505 10 – 4490 10 - 520 3 – 4 14 – 42 Cr mg/kg na 8.4 - 8.5 5.8 - 9.5 7.3 – 9.1 8.6 - 9.3 6.2 - 6.8 Cu mg/kg na 0.7 - 2.3 nd -20 nd nd 0.3 - 0.4 Pb mg/kg na 10.4 - 18.3 5.5 - 11 6.6 – 7.3 5.2 - 5.6 6.6 - 7.2 Zn mg/kg na 10.0 - 19.0 7.0 - 56 4.9 – 7.0 5.0 - 5.6 4.9 - 7.2 Cd mg/kg na nd - 0.03 nd - 0.02 nd nd nd Hg mg/kg nd - 0.05 nd nd na nd na: not analysed nd: not detected Detection limits: olefins 0.3 – 0.5 mg/kg (varies with the field), esters: 0.2 mg/kg, 100 µg/kg, Cu: 0.5mg/kg, Cd 0.01 mg/kg, Hg 0.01mg/kg * Installation centre excluded ** High concentration in one grab sample. In addition to the results given in Table 5.1.1 the following analyses are performed: - At Ekofisk 2/4 A drill cuttings pile: PCB analyses of the core samples - At Valhall: PFOS analyses for one station (500m) - At Ekofisk Centre og 2/4 B&K: PFOS analyses for one station (500m) - At Yme Gamma: PFOS analyses for one station (100m) - At Yme Gamma: Installation centre 0°/0m and 100m stations - At Yme Beta: Installation centre 0°/0m and 100m stations PFOS: perfluorooctyl sulphonate.

The results from the Drill cuttings pile and the Installations centre are discussed separately.

5.1.1 Grain size distribution

The sediments from most of the fields in Region I consist of fine sand. At Yme Gamma, Yme Beta and Kogge the sediments are coarser and characterized as medium sand. The sand content in the sediment dominates at all stations. At the regional stations the average sand content is 96.8 %, and the average silt and clay content (pelite) is 3.1 %. This mean value is representative for the region.

The sand content varies from 64.8 % (EKO14, 140°/850m) to ~100 % (VAN2, 74°/500m, GYDA reference station 315°/8000m and YMEB12, 330°/250m). The lowest sand content and thus the highest silt and clay contents are found at some stations at Ekofisk Centre and Valhall. Particularly, EKO14 appears to be different compared to the other stations at Ekofisk Centre and has the lowest sand content (64.8 %) and the highest silt and clay content (35.2 %) observed in this survey.

Generally, only slight differences are observed in the silt and clay content compared to the previous surveys.

During sampling there were observed large amounts of yellow granules in the sediments in the Valhall and Ume Beta. Traces of the granules were also observed in samples from other areas like Ekofisk Centre and 2/4 A, Eldfisk A and Tor, possibly originating from other areas. An investigation group has been established by BP to find out more about the granules.

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5.1.2 Total organic matter (TOM)

The total organic matter contents in the sediments are low. The concentrations vary from 0.4 % (Yme Beta and Kogge) to 1.5 % (Valhall). The results are similar to the previous surveys.

5.1.3 Hydrocarbons

The hydrocarbon contents in the sediments, which originate from drilling mud base oil or base liquid, depend on the drilling history. Hence they vary from field to field. Generally a tendency of vertical transport of hydrocarbons is observed with increased concentrations in the 1-3 cm and 3-6 cm sediment layers.

At the Regional stations and the additional reference stations, the THC concentrations are low and vary from 1.6 mg/kg to 5.9 mg/kg. No increases are observed since the last survey.

At Valhall and Hod, 500m stations were included in the 2002 survey. They are also analysed in this survey. Additionally, two new 500m stations, in the 74° and 254° directions, are included at Valhall in the survey. The maximum THC concentrations observed are 130 mg/kg at Valhall and 35.9 mg/kg at Hod, at stations 500m from the platform. Elevated THC concentrations are found out to 1000m distance at Valhall and out to 500m distance at Hod. In general the THC concentrations have decreased distinctly compared to the 2002 survey. Low contents of olefins are found at all stations at Hod, except for at the reference station. However, the concentrations of olefins have decreased compared to previous surveys for all stations investigated. Olefins were not analysed at Valhall.

At Valhall Nordflanke and Valhall Sørflanke the content of THC are below or just above the limit of contamination. The concentrations are at the same level as in the 2001 baseline survey.

At Ula and Gyda 250m and 500m stations were included in the 2002 survey. These stations are also analysed in this survey and additional 250m stations are included.

At Ula the highest THC concentration observed in the top 0-1 cm layer is 58 mg/kg at a station 250m from the platform. Maximum concentration is, however, observed in the vertical layers for the same station, with 416 mg/kg in the 3-6 cm layer. Elevated THC concentrations are observed for Ula out to 500m in the 45° and 135° directions and to 250m in 120° and 225° directions. The general trend is a decrease in the THC concentrations since 2002. The ether drilling fluid Aquamul BII is also found in the sediments, and give a contribution to the THC content.

At Gyda, elevated concentrations of THC are observed out to 250m, for three stations in the 45°, 135 and 225° directions. Maximum THC concentration observed in the top 0-1 cm layer is 43 mg/kg. In general the THC levels for the other stations are low and similar to those found in 2002 and 1999. Only slightly elevated THC concentrations are found at the 500m stations in the 45°, 135° and 225° directions.

Tambar is situated in the area between Gyda and Ula. As for Gyda the THC concentrations are relatively low. The content is similar or lower compared to the 2002 survey. The highest THC concentration is found at one of the 250m stations, 15.2 mg/kg. The other stations have THC contents below the limit of contamination.

In the Ekofisk area high THC concentrations are found at some of the stations at Ekofisk Centre and at Ekofisk 2/4 A. Maximum concentration observed is 188 mg/kg in the top 0-1 cm layer. The THC concentration is generally increasing going down in the sediment. Highest concentration found is 1031 mg/kg at EKOA5 in the 3-6 cm layer. Slightly elevated THC concentrations are found out to 4400m (7.4 mg/kg) and 2500m (8.7 mg/kg), respectively. Generarally the THC content in the 0-1 cm layer has decreased, for most of the stations, since

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the last survey. Thus, the THC content for most of the stations is only slightly above or below the limit of contamination for the region. Olefins/ethers are found at the stations analysed.

At Eldfisk 2/7 A/FTP, and Eldfisk 2/7 B, the maximum concentration of THC found are 120 mg/kg at Eldfisk 2/7 A/FTP and 30 mg/kg at Eldfisk 2/7 B. Elevated THC concentrations are found out to 370m (Eldfisk 2/7 A/FTP) and to 500m (Eldfisk 2/7 B). Only low contents of olefins are found. Both the THC and olefin contents in the Eldfisk area have decreased since the 2002 survey.

At Embla the four 250m stations, analysed in this survey, have not been investigated since 1993. Elevated THC contents are found at 180° (18.2 mg/kg) and 90° (15.0 mg/kg) directions.

At Tor the highest THC concentrations are 20 mg/kg. Ethers were found at all the stations analysed with concentrations up to 28 mg/kg.

Elevated THC concentrations are found for the 250m stations. The level is similar to the 2002 survey.

The Yme fields are located north-east in Region I. The fields are more recently established, with baseline surveys in 1994. At Yme Gamma, elevated THC concentrations are found out to 250m distance in the 120° direction (32 mg/kg). The THC concentrations have decreased for all the stations compared to the 2002 survey. Olefins are found at most of the stations, but the content is reduced or similar to 2002. Olefins and esters probably come from Petrofree. At Yme Beta no elevated THC concentrations are found.

The baseline surveys at Kogge and Trym show low contents of THC. The Trym and Kogge areas are not polluted by THC from oil activity.

The results for the selected hydrocarbons NPD, PAH and C5 - C8 alkyl decalins generally confirm the THC results. Particularly the presence of decalins indicates drilling mud base oil in the sediment. The base oil HDF 200 contains approx. 2 % of C5 - C8 alkyl decalins.

The present survey indicates that ether compounds from the drilling fluids Aquamul BII and Aquamul B are not degrading as fast as previously anticipated. Discharges performed in 1990/1991 and 1993 are still present in the sediments.

5.1.4 Esters

Esters from the drilling mud base liquids Petrofree and Finagreen are only analysed at Ekofisk 2/4 A at Yme Gamma.

At Ekofisk 2/4 A, Finagreen is found in the sediments at 100m in the 67° and 157° directions. The concentrationas are low, approximately 3 mg/kg.

At Yme Gamma, Petrofree is found at the two stations analysed, 0.5 mg/kg and 3.4 mg/kg. The concentrations are similar to the 2002 survey. As in 2002, Finagreen is not detected.

5.1.5 PFOS (perfluorooctyl sulphonate)

Three stations in Region I are analysed for PFOS (PerFluoroOctyl Sulphonate). The highest content is found at Yme Gamma Central. At Valhall the PFOS concentration was considerably lower, and at the station analysed at Ekofisk Centre and 2/4 B&K no PFOS was detected.

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5.1.6 Barium

Ba is found in the sediments due to use of barite during drilling (with water based drilling mud, oil based drilling mud or pseudo-oil based drilling mud). The higher concentrations of Ba in the sediments the greater dispersal area will be found compared to THC.

As for THC, a vertical transport of Ba down in the sediment layers is observed.

At the Regional stations and the additional reference stations, the Ba concentrations are low and vary from 4 mg/kg to 72 mg/kg. No increase is observed since the last survey in 2002.

The Trym and Kogge area have low contents of Ba and is not polluted by Ba from oil activity.

The Ba concentrations vary from background levels to 5590 mg/kg. The maximum concentrations found at each field will depend on the location of the stations and their distance from the platforms, as most of the barite will deposit near the drilling sites.

Generally elevated Ba concentrations are found at most of the stations. At Valhall Nordflanke og Valhall Sørflanke, Tambar and Yme Beta the Ba concentrations are relatively low. Mainly, the Ba concentrations are similar or lower compared to the survey in 2002.

5.1.7 Metals

Generally low concentrations of the heavy metals are found in the sediments. However, some exceptions are observed.

At Gyda, one 250m station shows high metal concentrations, 0.14 mg/kg Cd, 48 mg/kg Cr, 21 mg/kg Cu, 24 mg/kg Pb and 88 mg/kg Zn.

At Ula relatively high Zn concentrations (43 mg/kg) are found in one 250m station. The same station also had high Zn content in 2002.

At Ekofisk Centre three of the stations (at 500m and 850m) show relatively high Pb and Zn concentrations, up to 22 mg/kg Pb and 48 mg/kg Zn.

At Ekofisk 2/4 A elevated metal concentrations are found at most of the stations. The highest concentrations in the 0-1 cm layer are 14.2 mg/kg Cr, 0.40 mg/kg Cd, 17.5 mg/kg Cu, 0.12 mg/kg Hg, 52 mg/kg Pb and 154 mg/kg Zn.

At Yme Gamma one 250m station shows relatively high Cu and Zn concentrations, 20 mg/kg Cu and 56 mg/kg Zn.

5.1.8 Drill cuttings pile at Ekofisk 2/4 A – Core samples VC-2

Two core samples are analysed, VC-2 (I) and VC-2 (II).

Elevated concentrations of all the chemical parameters analysed are found downwards to 130 cm depth in the drill cuttings pile, except for esters and PCB.

The sediment consists mainly of silt and clay. The TOC content vary from 5.3 % to 13.8 %. Lowest TOC content is found in the deepest layers.

The THC concentrations including olefins vary from 998 - 1153 mg/kg in the 45-65 cm layer to 88088 mg/kg in the 0-5 cm layer. The levels of THC in the core samples are generally higher in 2005 than in 2002. A major part of the THC content results from olefins, up to ~70 % in the most contaminated samples. As in correlation with THC also the levels of olefins in the are generally higher in 2005 than in 2002.

In 2005 no ester or PCB was found in the corer samples. The ester content has decreased considerably since the 2002 survey.

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The concentration of NPD ranges from 5.4–13.1 mg/kg in the 40-65 cm layers to 42.5-80.5 in the 0-10 cm layers. The concentration of PAH ranges from 0.4 mg/kg to 22.4 mg/kg. The concentration of decalins ranges from 2.2 mg/kg to 105 mg/kg. The levels of NPD, PAH and decalins in the samples are generally higher in 2005 than in 2002.

The Ba concentrations are relatively high and vary for VC-2 (I) from 343 mg/kg in the 35-40 cm layer to 2100 mg/kg in the 15-20 cm layer. In the VC-2 (II) the concentrations vary from 313 mg/kg in the 40-45 cm layer to 1500 mg/kg in the 80-115 cm layer. Compared to 2002 the concentrations are generally lower. Ba seems to be very heterogeneous distributed in the sediment layers.

Elevated levels of heavy metals are found in all layers. Lowest concentrations of the heavy metals are found in the 40-45 cm layer. Highest concentrations of heavy metals are found in the deepest layer investigated (90-130 cm and 80-115 cm).

5.1.9 Installation Centre at Yme fields

Also included in the survey are samples from the Installation Centre, 0°/0m and from stations at 100m distance at Yme Gamma and Yme Beta.

At Yme Gamma the sediments at the Installation Centre consist mainly of silt and clay, while the 100m stations are characterized as medium sand. The total organic matter content at the Centre is high, 5.6 %. The TOM content at the 100m stations vary from 0.7 to 2.8 %. The THC concentration is high at the Centre, 4510 mg/kg. High levels are also found at some of the 100m stations, up to 706 mg/kg. However, the THC content has decreased considerably since 2002. The “central” sediments also contain olefins, however these are not quantified.

The Ba concentration at the Centre is 700 mg/kg and at the 100m stations, from 2250 mg/kg to 5630 mg/kg. The Ba content has decreased markedly since 2002.

Elevated levels of all the metals are found both at the Centre and at the 100m stations.

At Yme Beta Installation Centre, the silt and clay content is less than at Yme Gamma. At the 100m stations the silt and clay content is similar to the ordinary Yme Beta stations. The total organic matter content is lower than at Yme Gamma, 2.5 % at the Centre and 0.4 % to 0.6 % at the 100m stations.

The THC concentrations at the Centre are 350 mg/kg, and lower at the 100m stations, from 2.3 mg/kg to 58 mg/kg. Olefins are found at some stations. The THC content has decreased considerably since 2002.

PFOS (25.8 µg/kg) is found at the one station analysed at Yme Gamma Central, YMEG-II, 120°/100m.

The Ba concentration is also high at the Centre, 3040 mg/kg. Elevated Ba concentrations are found at the 100m stations, from 90 mg/kg to 1340 mg/kg. The Ba content has decreased considerably since 2002. Elevated levels of the metals are found at the Centre.

5.2 Benthic communities

5.2.1 Factors which impact the composition of the benthic communities

The impacts of human activities on the biological diversity extending from gene to ecosystem, are most evident in coastal areas (Simboura & Zenetos, 2002). According to Phillips & Rainbow (1994) direct chemical analyses of water and sediment, which are usually very sensitive and accurate, do not necessarily reflect the actual ecological state. In additon to

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human impacts the central parts of the North Sea area are influenced by a physical disturbance due to high energy water environments. It is well documented that unconsolidated, fine-grained sediments and their contents of organic matter do not settle on the seabed in high energy water environments. Due to frequent wave and/or current induced resuspension such material is repeatedly brought back into the water column and ultimately transported to their final deposition in sheltered or deep-sea areas. According to Eisma & Kalf (1987) accumulation and deposition of suspended matter in the North Sea occur predominantly in a few areas only (the Waddensea, the German Bight, the Skagerrak/Norwegian Channel).

Repeated movement of sediments in the North Sea affect the structure of the benthic community, and the community will seldom or never reach equilibrium. According to Gage & Tyler (1991) these disturbances are biologically important as a source of repeated major perturbation within the lifetimes of benthic fauna thus affecting the structure of the benthic community. Fine sand/coarse silt is normally a part of the mobile sediment fraction in the wave- and current exposed south-eastern North Sea. The roughness of the bottom further contributes to the turbulence of the bottom boundary layer (Leth & Kuijpers, 1996).

5.2.2 Effects of enrichment on benthic communities

Both offshore and land-based activities release organic matter in so vast amounts that they have a significant effect on the North Sea environment. The extent of the situation is that eutrophication is now a major environmental issue (McGlade, 2002). The effects of eutrophication have been investigated intensely and described mainly for coastal regions but also for the central North Sea. A general decrease in long-lived species like bivalves, an increase in opportunistic small, short-lived species as well as a 4 to 20-fold increase in biomass has been described for the North Sea (<57°N). These effects have been caused by increasing food availability for the benthos caused by increasing primary production in the whole North Sea. Oxygen deficiency in the bottom water of the North Sea occurred in the early eighties and was caused primarily by unusual hydrodynamic conditions rather than by eutrophication alone. The effects of diffuse pollution are difficult to describe. Studies on the contamination of benthic animals with inorganic and organic pollutants reflect the levels of these substances in organisms from different regions in the North Sea. It has been revealed that specimens from the open North Sea often contain higher levels than those from coastal regions (Kröncke & Bergfeld, 2001). However, the trend analyses of the fauna communities in the region indicate less availability of organic material and a fauna that seems to be improving, which is discussed further below.

5.2.2.1 The significance of Myriochele oculata and other dominating species

The analyses reveal that the fauna community in the central part of the Ekofisk region is disturbed to varying extents. This seems to be a consequence of physical disturbances, the activities in the area and a diffuse organic load from various sources affecting the North Sea. However, the trend analyses of the fauna communities in the region indicate reduced supplies of available organic material and a fauna that seems to be improving, see below.

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Ecotone point Pearson and Rosenberg (1978) identified a transitional "ecotone point," between the "peak of opportunists" and the communities that inhabit environments with a lower organic carbon concentration. They have described three successive stages: (1) the peak of opportunists where a few characteristic species are found in high abundance, (2) the ecotone point where species diversity declines steeply and the number of individuals increases steeply, and (3) the transition zone where populations flux and progress toward a more stable “normal” community. The ecotone contains species characteristic of both endpoints of the enrichment gradient. According to Pearson & Rosenberg (1978), species like Myriochele oculata and also Thyasira sp. are typical for a transitional fauna community. They provided a list of species that appeared to be "organic enrichment opportunists". At the "peak of opportunists", these species may exceed one

2

In 1973 the benthic fauna was uniform across the survey area (The Ekofisk oil field) and there were not found any hydrocarbons in the sediments. In 1975 the benthic fauna showed reduced densities of several common species close to the central complex, in particular Myriochele sp. and also Amphiura filiformis. Films of oil and oily clots were seen in a number of samples. In addition, there had been an increase in the content of hydrocarbons in the sediment. In 1977 and 1978 reductions were still observed in the densities of several common species, in particular Myriochele sp. In 1980 the decline of the Myriochele species continued across the centre of the field but the densities of the Cirratulid polychaetes increased. At 8 km distance from the field there was no longer observed decreases in the abundance of Myriochele. In 1981 it was concluded that the density of the formerly dominating Myriochele species had declined across the whole survey area, out to 8 km from the field centre. The densities of opportunistic cirratulid polychaetes were similar to those recorded in 1980. In 1983 there were still reductions in the abundance of Myriochele, while there were found elevated numbers of Cirratulid polychaetes (Hartley, 1983). Gray et. al (1990) found that Chaetozone setosa (Cirratulidae) was increasing dramatically towards the more polluted sites around the Ekofisk- and Eldfisk fields, while M. oculata was found at the sites characterized as “unpolluted”.

In 1996, high numbers of the Cirratulid Chaetozone setosa and to some degree ribbon worms (Nemertea) were still found. These species were dominant in the central part of the Ekofisk region and known as strong indicators of organic enrichment and common in the negative end of the transition zone. In 1999 there was observed a shift in the community. Particularly the numbers of C. cetosa were reduced, but the numbers of M. oculata (transition species) increased in the region and a further increase was observed in 2002. However, there was not possible to see any pattern or trend in the distribution and abundance of this species related to the activity in the area neither in 1999 nor in 2002. The species flourished around the fields in various directions and distances, including reference- and regional stations. The increases were, however, less conspicuous at the stations located closest to the field centers (100 – 250 m). This indicates a high but not too high supply of organic matter, which makes the species flourish outside the 100 and 250 m.

The great abundances and lack of a pattern in the distribution of M. oculata made it necessary to remove this species from the analyses in 1999 and 2002. The 2005 results show a general significant decline in the abundance of M. oculata. However, it is still the dominant species in the central part of the region and at most of the regional stations (relatively unaltered at stations REG-02 and -06 and at the nearby fields Ula, Gyda and Tambar. The general pattern (of reduced numbers of M. oculata in the central part of the region) is supported by the fact that the numbers of M. oculata have declined significantly at Valhall Nord- and Sørflanke since the

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baseline survey in 2001, indicating that the general diffuse influence of organic matter in the region has been reduced.

In 2005 it is possible to trace patterns and trends in the distribution of this species in the Ekofisk region and the species are therefore included in the analyses. Further, the indices and the similarity analyses indicate reduced supplies of available organic matter and an improving fauna in the region. This general pattern is further analysed at the 250 m and 500 m stations in the central Ekofisk region (see below).

Trend analyses of the 250 m and 500 m stations in the central Ekofisk region

The fields Valhall Nordflanke, Valhall Sørflanke and Trym are not representative for the long term trend analyses and are therefore excluded.

500 m stations

A similarity analysis for fields such as Ula, Gyda, Tambar, Tor, Hod, Eldfisk A, Eldfisk B, Valhall, Ekofisk Center and Ekofisk A has been performed. The stations divide mainly by years, see Figure 5.2.1, and the following general pattern was revealed:

The average abundance of transition species within the family Oweniidae (mainly M. oculata) at 500 m was relatively similar in 1996 and 1999. Furthermore, the average abundances of strong indicator species within the families Cirratulidae (mainly C. setosa) and Spionidae, both able to live as deposit feeders, have decreased from 1996 to 1999. At the same time the average abundances of suspension feeders within the family Serpulidae are seen to increase. Further decreases in the species within the families Cirratulidae and Spionidae are registered in the 2005 survey. From 1999 to 2002 it was registered a significant increase in the abundance of the family Oweniidae (mainly M. oculata) together with an increase of carnivore species within the family Amphinomidae and suspension feeders within the families Amphiuridae, Tricobranchidae, Apistobranchidae and Cerianthidae. From 2002 to 2005, the abundance of Oweniidae (mainly M. oculata) has decreased significantly (to the 1996 and 1999 levels), allowing a continued increase in the numbers of suspension feeders within the families Amphinomidae, Amphiuridae, Serpulidae and Apistobranchidae. The 2005 results reveal that the 500 m stations do not separate into distinct groups distributed among fields.

The results from the trend analyses indicate an ongoing general improvement in the environment in Region I from 1996 to 2005 until at least 500 m from the field centres.

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ULA

-05-

96U

LA-1

9-9 6

Gyd

a-16

-96

Gyd

a-19

- 96

EKO

-32-

96TO

R-0

6-96

HO

D-0

8 -96

ELD

A-0

6-96

HO

D- 0

2-96

ELD

B- 0

6-96

E KO

-09A

-02

EKO

-15-

0 2U

LA-1

9-99

TOR

-06-

99G

yda-

16-9

9G

yda-

19-9

9EL

DA

-06-

99EL

DB

- 14-

99EL

DB

-03-

9 9EL

DB

-11-

99EL

DB

-06-

99EK

OA

-07 -

99EK

OA

-15-

99EK

OA

-03-

99EK

OA

- 11-

99EK

O-3

2-99

HO

D-0

8-99

E KO

-32-

02EK

OA

-11-

02EK

OA

-03-

02EK

OA

-07 -

02EK

OA

- 15-

02E L

DA

-03-

02E L

DA

-14-

02EL

DB

-11-

02EL

DB

-03-

02EL

DB

-06-

0 2EL

DB

-14-

02VA

L-21

- 02

HO

D-0

2-02

HO

D-0

8-02

ELD

A-0

6 -02

VAL-

08-0

2TO

R-0

6-02

ULA

-05-

02U

LA-1

9 -02

Gyd

a-16

-02

Gyd

a-08

-02

Gyd

a -19

-02

TOR

-06-

05EL

DA

-06-

05EK

O-0

9A-0

5EK

O-1

5-05

ULA

-05-

05U

LA-1

9-05

Gyd

a-19

-05

Gyd

a-0 8

-05

Gy d

a-16

-05

E KO

-32-

05EK

OA

-07-

05EK

OA

-15-

05EK

OA

-03-

05E K

OA

-11-

0 5EL

DA

-11-

05VA

L-21

-05

ELD

B-0

6-05

ELD

B-1

1-05

ELD

B-1

4-05

ELD

A-1

4 -05

ELD

A-0

3-0 5

ELD

B-0

3-05

HO

D-0

2 -05

HO

D-0

8-05

VAL -

15-0

5VA

L-02

-05

VAL-

08-0

5

100

90

80

70

60

50Si

mila

rity

1996 1999 2002 2005 Figure 5.2.1. Dendrogram, 500 m station from the central Ekofisk region.

250 m stations

The fields that were included in the analysis were limited to Ula, Gyda, Tambar, Tor, and Ekofisk A, because these were the only fields that were sampled at stations 250 m from the field centre in 2005. The stations divided mainly by year, similar to the 500 m stations (see Figure 5.2.1), and the following general pattern was revealed:

At the 250 m stations, the abundance of the transition species within the family Oweniidae (mainly M. oculata) has increased over the years to an average of 1700 in 2002 and 2005 from less than 100 individuals in 1996 (few stations). The increases from 1996 to 1999 and 2002 were significant between years. Furthermore, the numbers of individuals in the families Spionidae and Cirratulidae (mainly C. setosa) have decreased over the years from 1996 to 2002. In contrast to the pattern at the 500 m stations between 2002 and 2005, the abundance of the family Oweniidae did not decrease from 2002 to 2005. However, the numbers of Cirratulidae have in fact increased to the 1996 levels, after a decrease in the abundance from 1996 to 1999. Comparison of the 500 m and 250 m stations reveals an ongoing improvement in the fauna at the 500 m stations during recent years. At the 250 m stations the improvement in the fauna community reveals a less obvious trend and there has not been any improvement from 2002 to 2005. However, the ongoing process is possibly somewhat slower at the 250 m stations. The fauna at 250 m in 2005 could be characterised as about the same state as the 500 m fauna in 2002. Further, in-depth analyses of the 2005 results indicate that the fauna at the 250 m stations at Ekofisk A are somewhat healthier than at similar stations at Ula, Gyda, Tor and Tambar.

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High organic load in the sediments usually favors species able to act as deposit feeders. The trend analyses of the fauna communities in the region show, however, an increase in the share of suspension feeders. Suspension feeders are more sensitive to organic load in the sediments and are thriving in environments with relative clean sediments and a good circulation in the water masses, providing available organic matter. Hence the results indicate reduced availability of organic material and that the fauna seems to be improving.

5.3 Contaminated area The accuracy of the calculations of contaminated areas depends on the numbers and locations of the sampled stations in the region. In Table 5.3.1 the elevated/contaminated area of each of the Ekofisk fields is calculated based on the SURFER plots in Figure 5.3.1, using the three concentration limits; 4.6 mg/kg (LSC value 2005), 10 mg/kg and 50 mg/kg (limit related to UKOOA’s Drill Cutting Initiative). For comparison purposes the calculated areas > LSC for each field in 2002 are included. Note that the LSC are smaller in 2005 (4.6 mg/kg) than in 2002 (6.4 mg/kg). Table 5.3.1. Elevated / contaminated area (km²), THC, Ekofisk Region 2005. 2005 2002 Field >4.6 mg/kg* >10 mg/kg >50 mg/kg >6.4 mg/kg** Ekofisk Centre 41.00 8.1 0.86 >15 Ekofisk 2/4A 10.20 2.5 0.1 >5 Valhall 39.00 8.7 0.15 >20 Ula 1.40 1 0.1 1 Tor 0.38 0.27 0 1 Trym/Kogge 0 0.11 0 - Tambar 0.27 0 0 >0.2 Embla 0.2 0.06 0 >2 Hod 1.95 1.3 0 >6 Gyda 0.50 0.44 0 1 Eldfisk 2/7A 1.20 0.7 0.17 >5 Eldfisk B 1.00 0.6 0 >5 TOTALT 102.80 23.78 1.38 >61 *: LSC 2005 **: LSC 2002 The total elevated/contaminated area in 2002 was calculated using various techniques. It was concluded that the total area with elevated THC concentrations (> LSC 2002, 6.4 mg/kg) in the Ekofisk Region (excluding Yme) was somewhere between 61 and 266 km2. The 2005 estimates are considered to be more reliable than in 2002, and the area with elevated THC concentrations (> LSC 2005, 6.6 mg/kg) is calculated to about 100 km2. Corresponding results using 10 mg/kg as contamination limit are 117 km2 in 2002 versus 24 km2 in 2005, and for contamination limit 50 mg/kg the estimated areas are 9 km2 in 2002 versus 1.4 km2 in 2005. The range zone of THC at each field is indicated in Figure 5.3.1.

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528200 528400 528600 528800 529000 529200 529400

6225200

6225400

6225600

6225800

6226000

6226200

6226400

245681012141618202224262830323436

HOD

HOD2

HOD3

HOD8

HOD9

HOD13HOD14

HOD19

HOD20

528200 528400 528600 528800 529000 529200 529400

6225200

6225400

6225600

6225800

6226000

6226200

6226400

516000 516200 516400 516600 5168006247200

6247400

6247600

6247800

6248000

6248200

6248400

6248600

061422303846546270788694102110118

Eldfisk 2/7A

A4

A5

A6

A106

A7

A12 A13

A14

516000 516200 516400 516600 5168006247200

6247400

6247600

6247800

6248000

6248200

6248400

6248600

Hod Eldfisk A

504900 505000 505100 505200 505300 505400 5055006306600

6306700

6306800

6306900

6307000

6307100

6307200

6307300

2

5

8

12

16

20

24

28

32

36

40

44

GYDA

5

6

7

8

16

17

18

19504900 505000 505100 505200 505300 505400 505500

6306600

6306700

6306800

6306900

6307000

6307100

6307200

6307300

mg THC/kg 513000 513100 513200 513300 513400 513500 513600 513700 513800 513900

6252500

6252600

6252700

6252800

6252900

6253000

6253100

6253200

6253300

6253400

135791113151719212325272931

Eldfisk B

B3

B4

B5

B6

B11 B12 B13 B14

513000 513100 513200 513300 513400 513500 513600 513700 513800 513900

6252500

6252600

6252700

6252800

6252900

6253000

6253100

6253200

6253300

6253400

Gyda Eldfisk B Figure 5.3.1. Surfer plots of THC levels 2005, indicating range zone.

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490400 490600 490800 491000 4912006329200

6329400

6329600

6329800

6330000

6330200

6330400

6330600

ULA

4

5

7

8

16

117

118

119

20 0

4

6

10

14

18

22

26

30

34

38

42

46

50

54

58

mg THC/kg

519900 520000 520100 520200 520300

6277300

6277400

6277500

6277600

6277700

6277800

6277900

Tor

4

5

6

12 13

1

3

5

7

9

11

13

15

17

19

21

Ula Tor

522000 524000 526000 528000Øst

6232000

6234000

6236000

6238000

6240000

6242000

Nor

d

ValhVAL2VAL3VAL4

VAL8VAL109

VAL110

VAL15VAL16*VAL16

VAL21VAL22

VAL123

VNVAN 1VAN 2VAN 3

VAN 5VAN 106VAN 107

VAN 8

VAN 9VAN 10VAN 11

VAN 13VAN 14

VAN 15

VSVAS 1VAS 2VAS 3

VAS 5VAS 6VAS 7

VAS 9VAS 10VAS 11VAS113VAS 14

VAS 15

05101520253035404550556065707580859095100105110115120125130

mg THC/kg

ValhallTHC > 4,6 mg/kg = 39 km² THC > 10 mg/kg = 8,7 km ²THC > 50 mg/kg = 0,15 km²

497200 497300 497400 497500 497600 497700 497800

6315300

6315400

6315500

6315600

6315700

6315800

6315900

3456789101112131415

mg THC/kg

Valhall Tambar Figure 5.3.1. cont. Surfer plots of THC levels 2005, indicating range zone.

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512000 512500 513000 513500 514000 514500 515000 515500

6262500

6263000

6263500

6264000

6264500

6265000

2/4A11B1C2

3

4

55B5C67

8

-19

99B9C10

11

12

12a

13*13B13C1415

16

17

0102030405060708090100110120130140150160170180

mg THC/kg

510000 511000 512000 513000 514000 515000 516000

6264000

6265000

6266000

6267000

6268000

6269000

6270000

6271000

EC2/4T

EC2/4B7

EC2/4B8EC2/4B9

EC2/4B9a

EC2/4B11

EC2/4B12

EC2/4B13

EC2/4B14EC2/4B15

EC2/4B18

EC2/4B19

EC2/4B21

EC2/4B22EC2/4B23

EC2/4K

EC2/4B28

EC2/4B29

EC2/4B32

EC2/4B33

EC2/4B34 EC2/4B39

2/4G2/4H

2/4K

2/4P2/4Q

2/4R2/4S

2/4X2/4J

1102030405060708090100110120130140150160170180190

mg THC/kg Ekofisk 2/4 A Ekofisk Centre

580500 580550 580600 580650 580700 580750 580800 580850 580900

6402100

6402150

6402200

6402250

6402300

6402350

6402400

6402450

6402500

-100102030405060708090100110120130140150160170

Yme Beta

YB1

YB4

YB Central

YB I

YB II

YB III

YB IV

580500 580550 580600 580650 580700 580750 580800 580850 580900

6402100

6402150

6402200

6402250

6402300

6402350

6402400

6402450

6402500

590200 590300 590400 590500 590600 590700

6409500

6409600

6409700

6409800

6409900

-2002006001000140018002200260030003400380042004600

Yme Gamma

YG1

YG5

YG6YG10

YG14

YG Central

YG I

YG II

YG III

YG IV

590200 590300 590400 590500 590600 590700

6409500

6409600

6409700

6409800

6409900

Yme Beta Yme Gamma Figure 5.3.1. cont. Surfer plots of THC levels 2005.

5.4 Conclusion Region I - The main characteristics of the sediments at Region I are as follows:

- The sediments at Region I consist mainly of fine sand.

- The total organic matter content in the sediments is low and varies from 0.4 % to 1.5 %.

- The chemical results are in agreement with the drilling history.

- The regional stations and the reference stations are still unaffected by the drilling chemicals, no contamination or elevated concentrations are found in these sediments.

- The Kogge and Trym area are not polluted by THC, Ba or metals from oil activity.

- Relatively high THC levels are still found at most of the fields. However, the concentrations are, with a few exceptions, considerably lower compared to 2002.

- Base liquids from pseudo-oil based drilling mud (olefins) are observed at most stations at the fields drilled with these systems.

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- Base liquids from ester based drilling mud are found in low concentrations at Ekofisk 2/4 A (Finagreen) and Yme Gamma (Petrofree).

- At Tor, ethers from ether based drilling mud (Aquamul B and Aquamul BII) were found for all the stations analysed. These ethers are in addition observed at Ula and Ekofisk Centre and 2/4 B&K. Thus, the ether compounds are not degrading as fast as previously anticipated.

- Dispersion of drill cuttings and mud is illustrated by the barium results. Elevated Ba concentrations are found at most of the stations. Generally the Ba concentrations are similar or slightly lower compared to the 2002 survey. For some stations at Valhall Flanke Nord and Sør and at Ula the content of Ba has increased, in agreement with their discharge history.

- The concentrations of the heavy metals are low, and elevated levels are only found at some stations.

- Two core samples from the drill cuttings pile at Ekofisk 2/4 A are analysed. Elevated concentrations of all the chemical parameters analysed, except esters and PCB, are found to 130 cm depth. The levels of THC in the core samples are generally higher in 2005 than in 2002.

- Samples from the Installation Centre at Yme Gamma and at Yme Beta are analysed. High concentrations of THC and Ba are found, but the contents are considerably lower compared to the 2002 survey.

- Generally, the results from the 2005 survey at Region I show that the levels of THC, Ba and metals have decreased compared to the 2002 survey.

- In 2005 an area about 100 km2 have THC concentrations higher than the LSC (4.6 mg/kg). The estimate is considered to be more reliable than the 2002 calculations (somewhere between 61 and 266 km2). For limits of 10 and 50 mg/kg the corresponding estimated areas are 24 and 1.4 respectively. All in all, the statistical analyses show increasing biodiversity indices and increasing numbers of species. Some increase in the numbers of individuals on the expense of M. oculata reveals a general improvement in the fauna community in the Ekofisk region. Species that are numerous all over the region in 2005 are the brittle star Amphiura filiformis and the bristle worms Paramphinome jeffreysii and Apistobranchus tullbergi. In general the fauna communities are dominated by suspension feeders (M. oculata, Ditrupa arietina, A.filiformis, Thyasira species, hydroids and anthozoa species) and carnivore species like P. jeffreysii. The trend analyses reveal a distinct improvement in the fauna until at least 500 m from the field centers. At a radius of 250 m from the field centers the trend is somewhat diffuse and does not reveal any improving trend from the last survey in 2002. An exception is the Ekofisk A field in 2005, where some stations have improved. The analyses indicate that the organic load is highest around the regional stations 2 and 6 and the improvement of the fauna communities is slowest around the fields Ula, Gyda, Tambar and Tor. However, the densities of individuals in the region still indicate a relatively high, though decreasing supply of organic matter to the macrofauna.

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6.0 Recommendations

Recommendation from 2002 considered

Field stations closer to the installations have been sampled in the present survey to better identify the transition zones between contaminated and uncontaminated areas.

At Tor the sediments contained compounds from synthetic based fluids that could be olefins or ethers. In the present survey ether analysis was included for this field. The main compounds are identified as ethers from the base oil Aquamul B.

Limit of Contamination

The limit of contamination was based on a confidence level of 95 %, according to the guidelines.

Recommendation for the 2008 survey

PFOS (perfluorooctyl sulphonate) is considered as a hazardous environmental substance, which has recently come into focus. Among the most important areas of use for PFOS-related substances in Norway appear to be fire fighting in the offshore industry. In 2005, the Pollution Control Authority decided to make a survey of PFOS-related substances in fire fighting foams and emissions from this source. In the 2005 survey three stations at Region I were analysed regarding PFOS. PFOS was found at two of the stations. It is recommended to get insight into the discharge history of PFOS at the various fields and prepare a sampling programme based on this information.

It is recommended for the 2008 survey to further investigate the transition zones from 500m to 250m stations. At most fields, an improvement in the fauna community was seen at the 500m stations, but not yet at the 250m stations. Valhall should be further investigated at the 250 m distance.

Biological analyses were not included at the Embla field in 2005. Considering additional knowledge about the faunal trends, and the fact that elevated THC levels were found in 2005, it is recommended that both sediment and biological samples are included in 2008.

The reference stations at Hod and Valhall were considered to be somewhat unfit with regards to the fauna communities. At Valhall this was due to a slightly coarser type of sediment which to some extent effects the fauna composition. When comparing the chemical parameters the station seems, however, to be suitable. At the reference station at Hod the sediment is considerably coarser than the field stations, making it unsuitable for faunal comparisons with the field stations. Thus when preparing the monitoring program in 2008 the need for finding alternatively reference stations at Valhall and Hod should be considered.

As the discharges have been reduced during the recent years, the sediment surface receives reduced amounts of hydrocarbons. In some cases, however, oily substances and black sediments are observed in the deeper sediment layers. Biological effects measured as disturbed macro fauna are often accompanying these observations. In order to monitor the impact of previous discharges it should be considered to focus on the relationship between biological effects and chemical parameters in the deeper layers. Aside from describing the environmental status the results would be valuable for studying restitution time and predicting the fate of contaminated sediments in general.

BP has established an investigation group to find out more about the granules found at Valhall. It is recommended that this should be considered at the other fields/operators as well.

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It is recommended that the methods for calculating the contaminated areas should be standardized to ease the comparisons between different areas.

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7.0 References Activities Regulation Appendix 1 – Requirements to Environmental Monitoring of the Petroleum Activities on the Norwegian Shelf. (Ptil, SFT, SHdir 2005). Teknisk vedlegg 2: Sedimentovervåking

Guidelines for Data Acquisition and Data Quality Evaluation in Environmental Chemistry, Anal.chem. 52 (1980) p. 2242-2249.

Chemical analyses and Grain size distribution

Buchanan, J.B. (1984), Sediment analysis. In "Methods for the study of marine benthos". Editors: Holme, N.A., and A.D. McIntyre. Blackwell Scientific Publications, Oxford, UK, pp. 41-65.

SFT, 2001. FOR 2001-09-03 nr 1157: Forskrift om utføring av aktiviteter i petroleumsvirksomheten (aktivitetsforskriften). http://www.lovdata.no/for/sf/as/xs-20010903-1157.html (2006-01-18).

Gjøs, N. (2003). Environmental Monitoring Survey Region I 2002. Grain size distribution and Chemical analyses. SINTEF report STF66 F03500.

Gjøs, N. (2000). Environmental Monitoring Survey Region I 1999. Grain size distribution and Chemical analyses. SINTEF report STF66 F00501.

Faksness, L.G. (2002). Environmental monitoring survey, Region I, Ekofisk 1999. Grain size distribution. SINTEF report STF66 F02117.

Faksness, L.G. (1999). Environmental monitoring survey, Region I, Ekofisk 1999. Grain size distribution. SINTEF report STF66 F99142.

Gjøs, N. (2002). Grunnlagsundersøkelse Valhall Nordflanke og Sør 2001. Kjemiske analyser og kornstørrelsesfordeling. SINTEF report STF66 F01512.

Biology

Bray, J.R. & J.T. Curtis 1957: An ordination of the upland forest communities of southern Wisconsin. Ecol. Monogr. 27: 325-349.

Eckert, Ginny L. 2003. Ecological archives E084-009-A1. Effects of the planktonic period on marine population fluctuations. Ecology 84:372–383.

Eisma, D., and Kalf, J. (1987). Dispersal, concentration and deposition of suspended matter in the North Sea. J. Geol. Soc. London, 144, 161-178.

Ernst, A.G. and J.A. Dietrich. 2006. Guide to benthic invertebrates observed from Hudson River Park Sanctuary water. Cornell University, Ithaca, NY.

Gage, J.D. & Tyler, P.A. 1991: Deep Sea Biology. A natural history of organisms at the Deep Sea Floor. Cambridge University Press.

Gray, J.S., Clarke, K.R., Warwick, R.M., Hobbs, G. 1990: Detection of initial effects of pollution on marine benthos: An example from the Ekofisk and Eldfisk oilfields, North Sea.

Hartley, J.P. 1983. Ten years of environmental monitoring at Ekofisk: A review prepared for Phillips Petroleum Company Norway. Oil Pollution Research Studies Council, Orielton Field Centre, Pembroke, Dyfed, U.K. SA71 5EZ

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Kröncke, I & Bergfeld, C. 2001. Synthesis and New Conception of North Sea Research. Working Group 10: Review of the Current Knowledge on North Sea Benthos. Zentrum für Meeres- und Klimaforschung der Universität Hamburg.

Lance, G. N. & W.T. Williams, 1967: A general theory of classificatory sorting strategies. II. Clustering systems. -Computer Jour. 10: 271-277.

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31 March 2006 Environmental Monitoring Region I, 2005, Main Report 2006-0187 (rev 01) BP Norge AS

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Reference to part of this report which may lead to misinterpretation is not permissible Document id.:190470 O:\635upstream\projects\2005\66110757 Ekofisk\Rapportering\Hovedrapport\mmainrep_11046020061311141726.doc

Appendices:

Program for sedimentovervåking Region I – Ekofisk 2005 version 3, January 2005 (enclosed in Appendix E).

Classification and MDS ordination were carried out using the programme-package PRIMER (Plymouth Routines In Multivariate Ecological Research).

Formulas and further explanations are given in Appendix D.

Quality assurance for total organic matter

Together with the samples, calcium carbonate and two in-house standards were heated to 480 °C. The calcium carbonate was used as a control of loss of carbonate from the sediment samples. The in-house standards have known TOM (0.88 and 8.31 %). If the results of one or both in-house standards were outside the accepted range of variation, the samples were reanalysed. The results of the analyses are given in Appendix C.

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