Macrophytes and Eutrophication in Oyster Pond

Jennifer Culbertson

Erin Kinney

Background

• Different contributions of wastewater in each sub-watersheds as seen from groundwater data

• Land use source of N into pond δ15N signature of macrophytes

• Why Macrophytes?• Long lived• Abundant• Widespread• Store N in tissues

Survey Questions

• What are the inter-annual changes in the dominant species present?

• What is the dominant source of nitrogen for macrophytes?

• Wastewater• Atmosphere• Fertilizer run-off

Macrophyte

Sampling Sites

1

4

9

3

5

2

15

12

711

108

16

13

6

14

Sixteen Sites

N=40

6 macrophytes

4 algae

Potamogeton spp. Najas flexilis

Chara vulgaris

(Pondweed)

(Stonewort)

(Bushy Pondweed)

(Coontail)Ceratophyllum demersum

Myriophyllum tenellum

Zannichellia palustris(Horned Pondweed)

Schneider and Melzer 2003

Ceratophyllum demersum - Coontail

• Tracy et al. 2003 have found coontail is common in nutrient enriched lakes in Michigan

• Coontail is floating – foliar uptake of nutrients from water column

Isotope Signature

• This is important for examining δ15N signatures of macrophytes to determine nitrogen source – particularly wastewater

Source δ15N(0/00) of nitrate in groundwater

Wastewater 10 - 20

Atmospheric Deposition 2 - 8

Fertilizer -3 - 3

(Valiela et al. 2000)

Isotope Signature

• Dried and packaged for isotope analysis:

UC Davis Stable Isotope Facility• Continuous Flow Isotope Ratio Mass Spectrometer

δ 15N for Each Genus in Oyster Pond in 2001, 2002 and 2004 Combined

-4

-2

0

2

4

6

8

10

12

14

0 100 200 300 400 500

N load (kg N yr-1)

CeratophyllumMyriophyllumNajasPotamogetonZannichelliaCharaEliocharisLemnaDerbesiaElatineSargassum

δ 15

N

Genera

Mean (± s.e.) Macrophyte Nitrogen Signaturein 2001, 2002 and 2004 at Each Measured N load

δ1

5N

0

2

4

6

8

10

12

0 100 200 300 400 500

N load (kg N yr-1)

Isotope Signatures for Rooted and Non-rooted Macrophytes in Oyster Pond for years 2001, 2002 and 2004

δ1

5 N

▲ Rooted - - -

■ Non-rooted —

F = 6.26**

F = 4.64*

-4

-2

0

2

4

6

8

10

12

14

0 50 100 150 200 250 300 350 400 450

N load (kg N yr-1)

Oyster Pond

Location δ15N (o/oo)

Oyster Pond 3-9

Childs River 7 - 8.2

Quashnet River 5.9 - 6.6

Sage Lot Pond 4 - 5

Mashpee River 6 - 8

N. Atlantic 4 - 13

Gulf of Mexico 4 – 6 (Cole 2004)

Conclusions

• Macrophyte genera may indicate eutrophication of Oyster Pond

• δ15N values of macrophytes are more sensitive of nutrient source at low N load

• Floating macrophytes are a better indicator of incipient N load

Thank you!

Residents of Oyster Pond

Mr. Weeks

Mr. and Mrs. Sears

Ivan Valiela and Jennifer Bowen

Leanna Heffner