Technical note

Isotopic composition of river water across a continent

B.P. Singh n

Amity School of Engineering and Technology, Bijwasan, New Delhi 110061, India

H I G H L I G H T S

� The plot of slopes versus intercept from the plot of δ18O and δ2H of various locations are done giving new pattern.� This new pattern is analyzed to arrive at a isotopic composition of precipitation to be on GMWL.� The continent is divided on the basis of original isotopic composition to be taken as injected tracer (δ18O and δ2H).

a r t i c l e i n f o

Article history:Received 17 May 2013Accepted 18 November 2013Available online 6 December 2013

Keywords:IsotopesRiver sampleHydrological cycle

a b s t r a c t

Isotopic composition of water across United States is available and also baseline data prepared for morethan 4800 samples (with depth and width-integrated stream samples) from 391 selected sites withinUSGS National Stream Quality Accounting Network (NASQAN). Data had been analyzed with respect toarrival at National Meteoric Water Line (NMWL). Large number of NMWL water samples has much lowerslopes than 8 and intercepts ranging from þ10 to �39. These lower slopes and intercepts need a re-lookto ascertain coherent δ2H and δ18O across USA in precipitation. A method is worked out by plottingslopes versus intercepts on δ2H axis to arrive at the isotopic composition of water on GMWL and also tolook the regional pattern that reflects the origin of vapour mass.

& 2013 Elsevier Ltd. All rights reserved.

1. Introduction

Stable isotopes of water molecules are powerful tracers inhydrosphere and water cycle especially 2H and 18O. Stable isotopesratio 2H/1H and 18O/16O are expressed as δ2H and δ18O, where δsample¼(Rsample/RSMOW�1)1000 where R¼2H/1H or 18O/16O astaking standard of sea mean ocean water (SMOW). Lot of mea-surements are available for δ2H and δ18O on global basis. One ofthe important investigations was made by Craig (1961) as co-relation of δ18O and δ2H in the fresh precipitation on global scaleknown as Craig's Global Meteoric Water Line (GMWL) in ‰ to beδ2H¼8δ18Oþ10‰. Plot between δ2H and δ18O and the slopes andintercepts are being studied globally through a network known asGlobal Network for Isotope in Precipitation (GNIP) established bycollaboration between International Atomic Energy Agency (IAEA)and World Metrological Organization (WMO).

Isotopic composition of water in different environmental con-ditions had been studied and has established the natural spatialdistribution of δ18O and δ2H over continental area. These wereprimilarily a function of fraction of water remaining in the air massas it moves inland over topographic features. Sub-continentstudies had been carried out by Kendall and Coplen (2001) for

distribution of 18O and 2H (deuterium) in river water in the UnitedStates of America. The experimental results of plot of δ2H and δ18Ohad been both theoretically and experimentally discussed byvarious investigators (Friedman, 1953; Craig, 1961; Dansgaard,1964; Singh and Kumar, 2005; Yurtsever, 1975). All these studiesreflect the variation of slope and intercept on δ2H axis on plotof δ2H and δ18O water in various stages of hydrological cycle. Onewould like to know the original isotopic composition of meteoricwater source prior to evaporation (temperature and humidity) andother hydrological process at a place or in a region as suggested bySingh (2013) now to extend to continent studies so as to take δ2Hand δ18O as injected tracer. This is the important aspect for thepresent interpretation of the data and to further find the pattern ofisotopic composition of precipitation/river water across USA.

2. Experimental data

More than 4800 samples from 391 selected sites were collectedwith depth and width-integrated stream using USGS NationalStream Quality Accounting Network (NASQAN). The data thusobtained was analyzed for δ18O and δ2H (http://water.usgs.gov/pubs/ofr/ofr00-160/pdf/ofr00-160.pdf). Each site was sampledbi-monthly or quarterly for 2.5 to 3 years. This data set for thewater composition of modern precipitation is supported byexcellent agreement between the river data set and the isotopic

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Applied Radiation and Isotopes 85 (2014) 14–18

composition of adjacent precipitation of monitoring sites. Kendalland Coplen (2001) were able to generate a National MeteoricWater Line (NMWL) for 48 contiguous States and compared withthe Global Network Isotopic precipitation of International AtomicAgency and World Meteorological Organization (WMO). It is foundthat a water sample gives a diverse local condition where the localmeteoric water lines usually have much lower slopes and theslopes of the regional MWL, do reflect the environmental condi-tion i.e. humidity and temperature.

The sample collection over the years has the potential forsignificant seasonal bias. The size of the drainage area ranges from6 to almost 3�106 km2. The medium drainage area is approxi-mately 8000 km2 which corresponds to drainage basin 90 km onthe site and about 90% of the sites has the basin area, which is lessthan 133,000 km2. Entire data set has been reported by Coplen andKendall (2000). The analysis has been given between the plot ofδ2H and δ18O and all the data set is around GMWL in the form of aflatter ellipse around it.

d-Excess (deuterium excess) is defined by Dansgaard (1964) asd¼δ2H�8δ18O for 391 sites ranges from �8 to þ17‰. About 8%of 4800 river samples have d-excess value less than 0. The specialdistributions of d-excess values for 317 sites within 48 states arealso plotted. It was suggested that in d-excess the slopes are moredependent on small scale local processes or conditions. In most ofthe states, the slopes range from 6 to 8 even lesser than 6 exceptfor the four states having slopes greater than 8 found in isolatedpatches. The slopes and intercepts of the LMWL are listed for allthe 48 states. This list is given in Table 1 and slopes and interceptsare plotted as shown in Fig. 1(a). This is a very interesting plotshowing some sort of pattern between slopes and intercepts.

3. Analysis of the pattern as given in Fig. 1(a)

In order to analyze certain pattern of the plot as given in Fig. 1(a),the data has been grouped together in such a manner that states areadjacent to each other so as to get the best fit line between slopesand intercepts and this has been given in Fig. 1(b)–(f). The data havebeen fitted in five groups of states as given in Fig. 2 in different colourcodes. Care has been taken to find the best fit line with better R2. Thecorrelation between slopes and intercepts are given in figures alongwith the best fit line with R2. These are given below

Fig: 1 ðbÞ y¼ 14:82x–110:1 or �110:1¼ �14:82xþy ð1ÞTherefore, δ18O¼�14.82; δ2H¼�110.1 to be on GMWL

Fig: 1 ðcÞ y¼ 16:71x–129:01 or �129:01¼ �16:71xþy ð2ÞTherefore, δ18O¼�16.71; δ2H¼�129.01 to be on GMWL

Fig: 1 ðdÞ y¼ 6:02x–38:92 or �38:92¼ �6:02xþy ð3ÞTherefore, δ18O¼�6.02; δ2H¼�38.92 to be on GMWL

Fig: 1 ðeÞ y¼ 3:65x–19:12 or �19:12¼ �3:65xþy ð4ÞTherefore, δ18O¼�3.65; δ2H¼�19.12 to be on GMWL

Fig: 1 ðf Þ y¼ 5:37x–34:46 or –34:46¼ –5:37xþy ð5ÞTherefore, δ18O¼�5.37; δ2H¼�34.46 to be on GMWL

x and y are experimental slopes and intercepts as given in dataset in Table 1. It is interesting to note that slope versus interceptare straight line for all the five groups of states.

4. How to interpret these straight lines between slopes andintercepts

In search of a method to interpret these data we may considerthe GWML for meteoric water as suggested by Craig (1961) andfinally adopted international as given by Rozanski et al. (1993) tobe δ2H¼8.13δ18Oþ10.8.

Now if we take water having δ18O¼�5‰, �7‰, �10‰, �15‰and �20‰ on GMWL, as given by Rozanski et al. (1993), thencorresponding values for δ2H shall be δ2H¼�29.85‰, �46.1‰,�70.5‰, �111.16‰, �146.34‰ and �151.8‰ respectively.

Let us take the water of these composition and take differentslopes similar to those of LMWL for example 7.4–8.1 and calculatethe intercept by the equation

δ2H ¼ slope δ18O ðx�axisÞþ intercept ðy�axisÞ:These slopes thus calculated with intercept for different iso-

topic compositions of water, are plotted as shown in Fig. 3. All the6 lines plots are straight lines similar to the experimental plots i.e.slopes and intercepts are on x and y axes respectively. Thereforeδ18O and δ2H are isotopic composition on GMWL as suggested bySingh (2013).

Table 1(a) Slope and intercept on δ2H at different states.

Group State Slope Intercept Intercept

1 Washington 8.50 15.50Oregon 8.70 17.50Nevada 5.00 �37.70California 7.80 5.40Idaho 7.90 6.60Utah 6.70 �12.60Arizona 7.00 �5.10Colorado 6.30 �18.00New Mexico 6.70 �5.50

2 Montana 5.00 �46.50Wyoming 5.30 �39.20North Dakota 6.80 �15.40South Dakota 7.10 �10.50Minnesota 5.70 �16.90

3 Kansas 8.40 10.90Oklahoma 6.20 0.20Texas 7.50 2.30Wisconsin 7.40 4.70Illinois 7.80 6.60Missouri 8.80 14.00Arkansas 6.30 1.10Iowa 9.30 18.80Nebraska 9.20 18.20

4 Albama 5.30 �0.80Missisipi 7.30 7.80Verginia 6.30 4.30Tansese 7.00 6.20North Carolina 6.30 2.90South Carolina 7.10 7.50Georgia 5.50 0.50Florida 5.40 1.30Lousiana 4.10 �3.60Maryland 7.30 7.00New Jersey 6.90 6.60

5 Ohio 5.20 �8.20Kentucky 6.40 1.20Pennsylvania 6.70 2.00West Virginia 6.40 0.40Michigan 7.10 1.60Indiana 5.90 �1.60New Hampshire 7.30 5.30Maine 7.10 3.60Massachusetts 5.50 �5.60Connecticut 6.50 0.70Rhode Island 5.50 �3.60New York 6.50 �3.00Vermont 6.50 �5.00

B.P. Singh / Applied Radiation and Isotopes 85 (2014) 14–18 15

We are now in a position to compare the results as shown inFig. 1(b)–(f) and calculation as shown in Fig. 4 to understand linesobserved in different groups of states as given by Eqs. (1)–(5), torewrite these equations, also shown in Eqs. (1)–(5), say forexample, y¼14.82x–110.1 or –110.1¼�14.82xþy. x and y corre-spond to slopes and intercepts respectively and therefore,δ2H¼�110.1 and δ18O¼�14.82, the water composition of meteo-ric water to be on GMWL.

The plots as given in Fig. 1(a)–(f) are the straight lines for eachgroup of states with good experimental fit. Therefore, values ofδ18O and δ2H are obtained in each five groups of states. These aregiven above along with the best fit of line in the Fig. 1(b)–(f) to bemeteoric water by the method as suggested above.

(i) δ18O¼�14.82‰; δ2H¼�110.1‰(ii) δ18O¼�16.71‰; δ2H¼�129.0‰(iii) δ18O¼�6.02‰; δ2H¼�38.92‰(iv) δ18O¼�3.65‰; δ2H¼�19.12‰(v) δ18O¼�5.37‰; δ2H¼�34.46‰

These isotopic compositions in precipitation for each group ofthe states are different due to environmental condition duringprecipitation and also due to latitude, longitude and altitudeeffects etc. All the observations fall on the straight line in eachgroup of states. As per our consideration in the analysis as outlinedabove that each line of each group of states give δ18O and δ2H to bemeteoric precipitation of each group of states. If this is so we canshow the water composition of all the groups of states on GMWLwhich is given in Fig. 4. All the experimental values of watercomposition fall in GMWL. This method of interpretation for fivegroups of states is simple but authentic without any flaw.

5. Discussion

The results as given above are for meteoric water in differentregions can be compared to the stable hydrogen and oxygenisotope ratios from selected sites of the U.S. Geological Survey'sNASQAN and Benchmark Surface-water Networks as given by

Fig. 1. (a) Plot of slope versus intercept for all the states together. (b)–(f) gives the plot slope versus intercept for each group of the State as given in Table 1.

B.P. Singh / Applied Radiation and Isotopes 85 (2014) 14–1816

Coplen and Kendall (2000) of almost all the rivers. GeologicalSurvey's National Stream Quality Accounting Network (NASQAN)and Benchmark surface water networks collected during the years.This report can be accessed at the web site: http://pubs.water.usgs.gov/ofr-00-160. The sites were selected from the National SteamQuality Accounting Network (NASQAN) and the Benchmark waterquality monitoring networks established and maintained by the

USGS. All the plots were made between δ2H and δ18O for eachsite. δ18O had certain range of value for each site on GMWL eitheron the GMWL or around it. The deviation from GMWL is due toenvironmental conditions mainly temperature and humidity.However, in the present calculated values in each region, we findinvariably in one of the observed values to be on GMWL.

Slopes and intercepts from the correlation of δ2H and δ18O arestraight line for different group of states i.e. kinetic fractionationbut the value of δ18O and δ2H by the plots is to be on GMWL i.e.,Rayleigh fractionation. It is suggestive that the meteoric water isdifferent in each groups of states. Further, δ2H and δ18O results ofeach state i.e. the meteoric isotopic composition without subject toenvironmental condition (temperature and humidity) are on

Fig. 2. Five groups of states in United states in different colours on the basis of plots of slopes versus intercept: Group 1 – red colour, Group 2 – blue colour, Group 3 – greencolour, Group 4 – grey colour, and Group 5 – mustard colour [States as given Table 1]. (For interpretation of the references to color in this figure legend, the reader is referredto the web version of this article.)

-6

-4

-2

0

2

4

6

8

10

12

7.2 7.4 7.6 7.8 8 8.2Slope

Interceprt

Line1

Line3

Line 4

Line6

Line5

Line 2

Line 1

Line 3

Line 2

Line 4

Line6

Line 5

Fig. 3. Intercept on δ2H axis versus the theoretical values of the slope of δ2H versusδ18O for different waters having δ18O from �5 to �20‰ corresponding values ofδ2H as given below for line 1 to 6 :Line 1: δ18O¼�5, δ2H¼�29.85. Line 2:δ18O¼�7, δ2H¼�46.11. Line 3: δ18O¼�10, δ2H¼�70.50. Line 4: δ18O¼�15,δ2H¼�111.16. Line 5: δ18O¼�18, δ2H¼�135.54. Line 6: δ18O¼�20,δ2H¼�151.80.

Fig. 4. showing δ2H and δ18O for the five group of States on GMWL δ2H¼8.13δ18Oþ10.8.

B.P. Singh / Applied Radiation and Isotopes 85 (2014) 14–18 17

GMWL line. As such the river water samples produce coherentδ18O and δ2H pattern across USA either on GMWL line, Rayleighfractionation or slope versus intercept straight line, kinetic frac-tionation. This line is being controlled by humidity and tempera-ture of local air mass which impart distinctive evaporatingisotopes enrichment to rainfall enhance to stream sample withinthe area.

6. Conclusion

In conclusion, it is suggested that the data available on theslope, less than 8 and intercept δ2H axis and their plots to getanother line within the experimental error to be on GMWL forstream water samples if different regions are to be taken, as waterdue to kinetic fractionation is similar to GMWL line to Rayleighfractionation. These two plots between δ2H and δ18O (Rayleighfractionation) and slope versus intercept (kinetic fractionation)and thereby the total data set shall be accountable by these twolines to arrive to the isotopic water composition to be used astracers in the region.

References

Coplen, T.B., Kendall, C., 2000. Stable hydrogen and oxygen isotope ratios forselected sites of the U.S. Geological Survey's NASQAN and Benchmark Surface-water networks. US Geological Survey Open-File Report 00-160; 424. ⟨http://water.usgs.gov/pubs/ofr/ofr00-160/pdf/ofr00-160.pdf⟩. (accessed 03.05.13).

Craig, H., 1961. Isotopic variations in meteoric waters. Science 133, 1702–1703.Dansgaard, W., 1964. Stable isotopes in precipitation. Tellus 16, 436–468.Friedman, I., 1953. Deuterium content of natural waters and other substances.

Geochim. Consmochim. Acta 4, 891–903.Kendall, C., Coplen, T.B., 2001. Distribution of oxygen-18 and deuterium in river

waters across the United States. Hydrol. Process. 15, 1363–1393.Rozanski, K., Araguas-Araguas, L., Gonfiantini, R., 1993. Isotopic patterns in modern

global precipitation. In: Swart, P.K., Lohman, K.L., McKenzie, J.A., Savin, S. (Eds.),Climate Change in Continental Isotopic Record, 78. American GeophysicalUnion, Washington, pp. 1–37. (Geophysical Monograph).

Singh, B.P., Kumar, B., 2005. Isotopes in Hydrology, Hydrogeology and WaterRecourses. Narosa Publishing House, New Delhi.

Singh, B.P., 2013. Isotopic composition of water in precipitation in a region or place.Appl. Rad. Isot. 75, 22–25.

Yurtsever, Y., 1975. Worldwide Survey of Isotopes in Precipitation. IAEA Report,Vienna ⟨www.naweb.iaea.or/napc/ih/%20documents/global_cycle/…/%20cht_ii_%2003.pdf⟩, (accessed 10.05.12).

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