References

Discussion

Water is a major constituent of the fluids of living things. Furthermore, the hydrologic cycle

can explain the interactions between the hydrosphere, atmosphere, and lithosphere.

Besides being a major driving force on our planet, water is in constant motion be it through

evaporating or condensing into the atmosphere from oceans, lakes, rivers and streams. Both

oxygen and hydrogen are found in many forms in the earth’s biosphere and geosphere.

Variations of the isotope composition of water can be used for determining precipitation as

well as helping us figure out paleo-climate and paleo-hydrologic information because

isotopic compositions do differ for sea water, ice, atmospheric water vapor and meteoric

water. There are about nine isotopic configurations for water which can be distinguished by

their mass numbers as well as other characteristics. To show these variations, data will be

presented on hydrogen and oxygen isotope values of rain and river water from Southern

Illinois and Missouri. These isotopic values will be correlated with average humidity, and

precipitation amount to show disparities between these regions.

Abstract

Introduction

Results

Analyzing and collecting an extensive data base of precipitation, and river

samples allowed us to determine the various isotopic variations in these

systems. In regards to the Missouri region, we saw that the δ18O values of

precipitation varied throughout the year. In Missouri the Illinois springs and

rivers isotopic base flow can be very variable as well as dependent on the

isotopic values of the previous several months of rainfall. Local Meteoric Water

Lines normally fall below Global Meteoric Water Lines given that local

processes play a major role. For example water that has evaporated or has

mixed with evaporated water typically plots below the Global Meteoric Water

Line. We did see that some LMWLs had generally low slopes, this might entail

that significant post-rain evaporation occurred prior to collection. An alternative

explanation is that the similarity in slopes for adjacent sites reflects some

regional characteristic of mixing of precipitation and groundwater. We believe

that the extent of evaporative fractionation of rain in a specific region is

controlled by the long term average humidity and temperature of the specific

region, this itself is what gives a distinctive Local Meteoric Water Line slope to

each specific area. This also implies that large geographic areas are responding

similarly to some common processes, perhaps evaporation.

Since both hydrogen and oxygen are a part of the water molecule, we can therefore use the

hydrogen and oxygen isotopic values to fingerprint water movement in geological and biological

systems. Oxygen has three stable isotopes, 16O, 17O, and 18O, while hydrogen has two stable

isotopes, 1H and 2H. Both of these are measured using isotope ratio mass spectrometry and are

reported as delta values. Stable isotope ratios of deuterium/hydrogen (2H/1H) and 18O/16O of

water are conventionally expressed as a per mil (‰) deviation from SMOW (Standard Mean

Ocean Water) or VSMOW (Vienna SMOW) (SAHRA). Both d18O and d2H can be used to

determine water evaporation from rivers, reservoirs, and lakes, as well as trace the hydrological

cycle from evaporation in the oceans to local precipitation and groundwater. Temperature is

known to be one of the major factors that play a role in isotopic composition. With increasing

temperature, precipitation becomes enriched in the heavier isotopes,18O and 2H, in a linear

relationship (SAHRA). The δD and δ18O values for precipitation worldwide behave predictably,

falling along the global meteoric water line (GMWL) as defined by Craig (1961b), who expresses

the relationship between18O and 2H in meteoric waters as follows: δ2H = 8 δ18O +10‰ (SAHRA).

Precipitation is liquid or solid water that falls or has fallen from the sky and includes rain, fog,

hail, sleet, and snow. Fresh water resides on Earth principally in glaciers, groundwater systems,

rivers, and lakes. Just like temperature, relative humidity affects the isotopic composition of

water. Water in most rivers has two main components: (1) recent precipitation that has reached

the river either by surface runoff, channel precipitation, or by rapid flow through the shallow

subsurface flow paths; and (2) groundwater. The relative contributions of these sources differ in

each watershed or basin, and depend on the physical setting of the drainage basin (e.g.

topography, soil type, depth to bedrock, vegetation, fractures, etc.), climatic parameters (e.g.

precipitation amount, seasonal variations in precipitation, temperature, potential

evapotranspiration, etc.), and human activities (e.g. dams, reservoirs, irrigation usages, clearing

for agriculture channel restructuring, etc.) (Coplen Kendall 2001). The δ18O and δD of rivers will

reflect how the relative amounts of precipitation and groundwater vary with time, and how the

isotopic compositions of the sources themselves change over time. Seasonal variations will be

larger in streams where recent precipitation is the main source of flow, and smaller in streams

where groundwater is the dominant source. As the basin size increases, the isotopic

compositions of rivers are increasingly affected by subsequent alterations of the precipitation

compositions by selective recharge and runoff, mixing with older groundwater and newer rain

water, and by evaporation. (Gat and Tzur, 1967; Fritz, 1981; Gat, 1996).

Precipitation samples were collected after each precipitation event using a standard rain

gauge installed on top of the Geology building, SIUC. Ancillary data (e.g. temperature,

precipitation amount, etc.) provided by SI Weather Observatory was also included in the

database. To characterize the spatial and temporal pattern of water isotopes in surface

waters, we selected the Ohio and Mississippi rivers and tributaries with sampling sites

situated across major watersheds of Southern Illinois. The water samples were filtered in the

field and stored in glass bottle for further isotope analysis. Precipitation and river water

samples were analyzed for δ18O and δD at the SIUC Mass Spectrometry Facility using a

Thermo DELTA V isotope ratio mass-spectrometer (IRMS) equipped with a Gasbench II and

Costech TC-EA elemental analyzer. All δ18O and δD values are expressed relative to

Vienna-Standard Mean Ocean Water (V-SMOW) in %, such as δ18O or δD = (Rsample-

Rstandard)×1000/Rstandard (‰), where Rsample and Rstandard refer to the 18O/16O or D/H ratios in

sample and standard, respectively. Isotopic results are used to calculate deuterium excess

(d-excess) as an index of how much evaporation has affected the isotopic value of each

surface water sample using the following equation: d-excess = δD – 8* δ18O (Clark and Fritz

1997).

Stable Isotope Composition of Water in Southern Illinois and Missouri

Gabriela Brito1*, Liliana Lefticariu2, Mihai Lefticariu3

1Department of Microbiology, Southern Illinois University, Carbondale, IL 62901 2Department of Geology, Southern Illinois University, Carbondale, IL 62901

3Department of Chemistry & Biochemistry, Southern Illinois University, Carbondale, IL 62901

Funded partially by the SIUC CURCA Program

Environmental Isotopes in Hydrogeology. 1997. I. D. Clark and P. Fritz, CRC Press/Lewis

Publishers, Boca Raton, 328 p., ISBN 1-56670-249-6.

Frederickson, George C. "WU Stable Isotope Laboratory." WU Stable Isotope Laboratory.

N.p., n.d. Web. 31 Mar. 2015.

Global Network of Isotopes in Precipitation. International Atomic Energy Agency. 22 May

2013. Web. 25 Jan. 2015. http://www-naweb.iaea.org/napc/ih/IHS_resources_gnip.html

Kendall, Carol, and Tyler B. Coplen. "Distribution of Oxygen-18 and Deuterium in River

Waters across the United States†." Distribution of Oxygen-18 and Deuterium in River

Waters across the United States. N.p., n.d. Web. 31 Mar. 2015.

Principles of Stable Isotope Geochemistry. Zachary Sharp, Princeton 2006, 344 p

Sustainability of semi-Arid Hydrology and Riparian Areas. 2005. Web. 29 Mar. 2015.

http://web.sahra.arizona.edu/programs/isotopes/oxygen.html

Figure 2. The isotope values of precipitation can be affected by different variables, including temperature, latitude, altitude, and relative humidity.

Figure 1. Global Meteoric Water Line.

Figure 3. Spatial distribution of discharge-weighted mean (a) δ18O values, and (b) δ2H values

Figure 4. Deuterium Excess Parameter

y = 7.8632x + 13.295

R² = 0.971

-200.00

-150.00

-100.00

-50.00

0.00

50.00

-25.00 -20.00 -15.00 -10.00 -5.00 0.00 5.00

δ2H

(%

, SM

OW

)

δ18O (%, SMOW)

Carbondale Meteoric Water Line (Precipitation)

y = 6.5188x - 0.5172

R² = 0.8504

-55.00

-50.00

-45.00

-40.00

-35.00

-30.00

-25.00

-20.00

-8.00 -7.00 -6.00 -5.00 -4.00 -3.00

δ2H

(%

, SM

OW

)

δ18O (%, SMOW)

Southern Illinois River Water

δ2H = 7.9 * δ18O + 13.3

δ2H= 6.5 * δ18O - 0.5

y = 7.8973x + 11.164

R² = 0.9654

-150

-130

-110

-90

-70

-50

-30

-10

-20 -15 -10 -5 0

δ2H

(%

, SM

OW

)

δ18O (%, SMOW)

Missouri Meteoric Water Line (Precipitation)

δ2H = 7.9 * δ18O + 11.2

y = 7.1301x + 4.5739

R² = 0.8207

-100

-80

-60

-40

-20

0

20

40

60

80

-15 -10 -5 0 5

δ2H

(%

, SM

OW

)

δ18O (%, SMOW)

Missouri River Water

δ2H = 7.13 * δ18O + 4.6

Methods

Figure 5. Southern Illinois sample locations for Summer and

Fall 2014. Dates collected were 10/18/2014, 7/30/2014, and

9/13/2014.

Figure 6. Map of the states of Missouri and Illinois and their

counties. The study areas are outlined and shaded in grey. The

Meramec River Basin is located to the southwest of St. Louis,

Missouri and south of the confluence of the Missouri and

Illinois Rivers with the Mississippi River.

Figure 7. Isotope results for precipitation in Carbondale,

hydrogen (δ2Hp) oxygen (δ18Op) plotted against one another to

find the Carbondale Meteoric Water Line (CMWL).

Figure 8. Isotope results for precipitation in East Central

Missouri, hydrogen (δ2Hp) oxygen (δ18Op) plotted against one

another to find the Missouri Meteoric Water Line.

Figure 9. Isotope results for river water in Carbondale,

hydrogen (δ2Hp) oxygen (δ18Op) plotted against one another to

find the Carbondale Meteoric Water Line (CMWL).

Figure 10. Isotope results for river water in East Central

Missouri, hydrogen (δ2Hp) oxygen (δ18Op) plotted against one

another to find the Missouri Meteoric Water Line.

Conclusion

The Global Meteoric Water Line states that the equation for global precipitation

falls on a line with an equation of δ2H = 8.13*δ18O+10.8. Various samples were

collected in the Southern Illinois area as shown in Figure 5. Most of these

samples were collected in the summer and fall 2014. The other samples were

collected in the area of Eastern Missouri and Illinois as seen in Figure 6. These

areas are compared because not only are they relatively close in region, but

they should allow us to measure if local processes have any effect on the

overall LMWL of each specific region. We see in Figure 7 that the Carbondale

Meteoric Water Line with respect to precipitation values falls at an equation of

δ2H = 7.9 * δ18O + 13.3, while the Missouri Meteoric Water Line figure 8 with

respect to precipitation values falls at an equation of δ2H = 7.9 * δ18O + 11.2.

Both of these LMWLs fall relatively close in regards to slopes. The GMWL

represents a weighted average of LMWLs whose slopes are uniformly lower

than 8 and whose intercepts vary widely, from values as negative as about - 2 to

values as positive as about + 15. Figure 9 shows the Carbondale Meteoric

Water Line in regards to river water values, the equation falls at δ2H = 6.5 *

δ18O - .5, while in figure 10 we see that the Missouri Meteoric Water Line in

regards to river water values falls at an equation of δ2H = 7.13 * δ18O + 4.6. As

expected the slopes generally fall below 8 and we see the intercepts vary

greatly given that these two areas are relatively close. If the environmental

conditions during rainfall and post-rainfall evaporation are similar then the river

LMWL would be similar to the precipitation LMWL because continued

evaporation of rain in the soil or stream would cause further increases in δ

values but perhaps little change in the slope of the LMWL.

Acknowledgements

This work was partially supported by the SIUC CURCA Program and the

SIUC Research Enriched Academic Challenge (REACH) program.

Geology undergraduate student Minka Bentley assisted our team with

field sampling and various tasks during the duration of this study.