U.S. GEOLOGICAL SURVEY

Water-Resources Investigations Report 

Isotopic and Chemical Composition of 

Inorganic and Organic Water-Quality 

Samples from the Mississippi River 

Basin, 1997–98

By William A. Battaglin, Carol Kendall, Cecily C.Y.Chang, 

Steve R. Silva, and Donald H. Campbell

Denver, Colorado

2001

01-4095

Prepared in cooperation with the

U.S. ENVIRONMENTAL PROTECTION AGENCY

GULF OF MEXICO PROGRAM
U.S. DEPARTMENT OF THE INTERIOR

GALE A. NORTON, Secretary

U.S. GEOLOGICAL SURVEY

Charles G. Groat, Director

The use of firm, trade, and brand names in this report is for identification purposes only and does

not constitute endorsement by the U.S. Geological Survey.

For additional information write to: Copies of this report can be purchased

U.S. Geological Survey

Information Services

Box 25286

Federal Center

Denver, CO 80225

from:

District Chief

U.S. Geological Survey

Box 25046, Mail Stop 415

Denver Federal Center

Denver, CO 80225-0046
CONTENTS III

CONTENTS

Abstract.................................................................................................................................................................................. 1 

Introduction............................................................................................................................................................................ 1 

Problem........................................................................................................................................................................ 1 

Objectives and Hypotheses.......................................................................................................................................... 2

Background.................................................................................................................................................................. 2

Gulf of Mexico Hypoxia and Mississippi River Discharge............................................................................... 2

Nitrogen Sources ............................................................................................................................................... 3

Previous Isotope Investigations ......................................................................................................................... 5

Nitrogen Transformations.................................................................................................................................. 6

Acknowledgments ....................................................................................................................................................... 7

Methods ................................................................................................................................................................................. 7

Plan of Study................................................................................................................................................................ 7

Sampling Stations ........................................................................................................................................................ 7

Large River Stations .......................................................................................................................................... 7

Small Stream Stations........................................................................................................................................ 7

Sampling Schedule and Procedure .............................................................................................................................. 7

Lagrangian Samples........................................................................................................................................... 10

Analytical Methods...................................................................................................................................................... 11

Analysis of δ15N and δ18O of NO3 in Water ..................................................................................................... 11

Analysis of δ15N, δ13C, and δ34S of Suspended POM in Water........................................................................ 15

Nutrients and Major Ions ................................................................................................................................... 15

Discharge and Physical Properties..................................................................................................................... 15

GIS Data and Analysis................................................................................................................................................. 15

Quality Assurance........................................................................................................................................................ 16

Sample Collection.............................................................................................................................................. 16

NO3 in Water Isotope Analysis.......................................................................................................................... 16

Particulate Organic Material Isotope Analysis .................................................................................................. 16

Results.................................................................................................................................................................................... 18

δ15N and δ18O of NO3 Isotope Ratio Values ............................................................................................................... 18

Large Rivers ...................................................................................................................................................... 18

Small Streams ................................................................................................................................................... 24

δ15N and δ13C of POM Isotope Ratio Values ............................................................................................................. 30

Large Rivers ...................................................................................................................................................... 30

Small Streams ................................................................................................................................................... 30

Concentrations of Nutrients and Major Ions ............................................................................................................... 34

Large Rivers ...................................................................................................................................................... 34

Small Streams ................................................................................................................................................... 44

Physical Properties and Field Chemistry..................................................................................................................... 46

Relations Between Isotopic Ratios and Basin Characteristics .................................................................................... 46

Evidence for Sources of Nitrogen in the Mississippi River......................................................................................... 46

Evidence for Transformation of Nitrogen in the Mississippi River............................................................................. 51

Conclusions............................................................................................................................................................................ 53

Suggestions for Future Research ................................................................................................................................. 54

References Cited.................................................................................................................................................................... 54
IV CONTENTS

FIGURES

1. Graph showing estimated annual nitrogen inputs in the 20 States that comprise most of the agricultural land 

in the Mississippi River basin, 1951 to 1999 ............................................................................................................. 4

2–4. Maps showing:

2. Locations of sampling stations and associated drainage basins for: (a) large rivers, and (b) small streams ..... 5

3. Land cover in the Mississippi River basin ......................................................................................................... 9

4. Land cover in the Sugar Creek at New Providence, IN basin............................................................................ 17

5–15. Graphs showing:

5. Differences between: (a) NO2 plus NO3 concentrations (in mg/L), and δ15N and δ18O of NO3

values (in per mil) in 18 pairs of concurrent duplicate water samples; and (b) δ15N and δ13C of POM 

values (in per mil) in 8 pairs of field collected concurrent duplicate sediment samples. ................................. 18

6. Time series of 1997 data for large river stations; (a) discharge, (b) δ15N, (c) δ18O, and 

(d) NO2 plus NO3. ............................................................................................................................................. 20

7. Time series of 1998 data for large river stations; (a) discharge, (b) δ15N, (c) δ18O, and 

(d) NO2 plus NO3. ............................................................................................................................................. 22

8. δ15N and δ18O of NO3 values and NO2 plus NO3 concentrations from small streams by 

dominant basin land cover type, 1997–1998. ................................................................................................... 25

9. Time series of 1997 data for small stream stations; (a) discharge, (b) δ15N, (c) δ18O, and 

(d) NO2 plus NO3. ............................................................................................................................................. 26

10. Time series of 1998 data for small stream stations; (a) discharge, (b) δ15N, (c) δ18O, and 

(d) NO2 plus NO3. ............................................................................................................................................. 28

11. δ15N and δ13C of POM values by basin type, 1997–1998. ............................................................................... 36

12. Typical ranges of δ15N and δ18O of NO3 for various N sources and measured values from 

large river stations, 1997–1998.......................................................................................................................... 52

13. Typical ranges of δ15N and δ18O of NO3 for various N sources and measured values from 

small stream stations, 1997–1998...................................................................................................................... 52

14. δ15N and δ18O of NO3 values and NO2 plus NO3 concentrations from large river stations. ........................... 53

15. Particulate organic material data time series for the Yazoo river in 1997 (open circles are all 

data and filled circles are data collected for this study); (a) δ15N, and (b) δ13C. .............................................. 54

TABLES

1. Selected characteristics of sampling stations in the Mississippi River basin. ........................................................ 8

2. Generalized land cover and estimated annual manure nitrogen production in the large river and small 

stream drainage basins (land cover derived from reclassified Advanced Very High Resolution 

Radiometer data with a 1000 meter cell size). ........................................................................................................ 10

3. Land cover in the small stream drainage basins (derived from National Land Cover data with a 

30 meter cell size). .................................................................................................................................................. 11

4. Nitrite plus Nitrate concentration, daily mean discharge and δ15N and δ18O of nitrate values in 

water samples collected in 1997–1998. .................................................................................................................. 12

5. Statistical summary of δ15N and δ18O of nitrate values, nitrite plus nitrate concentrations, and 

daily mean discharges in water samples collected in 1997–1998. ......................................................................... 19

6. The δ15N and δ13C of particulate organic material in suspended sediment samples collected 

in 1997–1998........................................................................................................................................................... 31

7. Statistical summary of δ15N and δ13C of particulate organic material in suspended sediment samples 

collected in 1997–1998. .......................................................................................................................................... 35

8. Nutrient concentrations in water samples collected in 1997–1998......................................................................... 37

9. Statistical summary of nutrient concentrations in water samples collected in 1997–1998..................................... 41

10. Major ion concentrations in water samples collected in 1997–1998. ..................................................................... 42

11. Statistical summary of major ion concentrations in water samples collected in 1997–1998.................................. 45

12. Physical properties and field chemistry in water samples collected in 1997–1998. ............................................... 47

13. Statistical summary of physical properties and field chemistry data in water samples collected 

in 1997–1998. ......................................................................................................................................................... 50
CONTENTS V

CONVERSION FACTORS AND ABBREVIATIONS

Multiply By To obtain

cubic meters per second 3.531 x101 cubic foot per second

metric ton 2.205 x 103 pound

kilogram 2.2046 pound

square kilometer 3.861 x 10-1 square mile

hectare 2.471 acre

micron 2.0 x 10-6 meters

liter 2.642 x 10-1 gallon

____________________________________________________________________________________________

Abbreviations

NASQAN - National Stream Quality Accounting Network

NAWQA - National Water Quality Assessment

microgram per liter (μg/L)

microsiemens per centimeter at 25 degrees Celsius (μS/cm)

milligram per liter (mg/L)

milliliter (ml)

degrees, minutes, second (ddmmss)

cubic meters per second (m3

/s)

square kilometer (km2)
Abstract 1

Isotopic and Chemical Composition of Inorganic

and Organic Water-Quality Samples from the 

Mississippi River Basin, 1997–98

By William A. Battaglin, Carol Kendall, Cecily C.Y. Chang, Steve R. Silva, and

Donald H. Campbell

Abstract

Nitrate (NO3) and other nutrients 

discharged by the Mississippi River combined 

with seasonal stratification of the water column 

are known to cause a zone of depleted dissolved 

oxygen (hypoxic zone) in the Gulf of Mexico 

each summer. About 120 water and suspended 

sediment samples collected in 1997 and 1998 

from 24 locations in the Mississippi River Basin 

were analyzed for the isotope ratios δ15N and 

δ18O of dissolved NO3, and δ15N and δ13C of 

suspended particulate organic material (POM). 

Sampling stations include both large rivers 

(drainage areas more than 30,000 square kilometers) that integrate the effects of many land uses, 

and smaller streams (drainage areas less than 

2,500 square kilometers) that have relatively 

uniform land use within their drainage areas. The 

data are used to determine sources and transformations of NO3 in the Mississippi River. 

Results of this study demonstrate that much 

of the NO3 in the Mississippi River originates in 

the agriculturally dominated basins of the upper 

midwestern United States and is transported 

without significant transformation or other loss to 

the Gulf of Mexico. Results from major tributaries 

that drain into the Mississippi River suggest that 

NO3 is not significantly altered by denitrification 

in its journey, ultimately, to the Gulf of Mexico. 

The spatial variability of isotope ratios among the 

smaller streams appears to be related to the dominant nitrogen source in the basins. There are some 

distinct isotope differences among land-use types. 

For example, for both NO3 and POM, the 

majority of δ15N isotope ratio values from basins 

dominated by urban and undeveloped land are 

less than +5 per mil, whereas the majority of 

values from basins dominated by row crops and 

row crops and/or livestock production are greater 

than +5 per mil. Also, the median δ18O of NO3

isotope ratio value (+14.0 per mil) from undeveloped basins is more than 6 per mil higher than the 

median value (+7.3 per mil) from the row crop 

dominated basins and 5 per mil higher than the 

median value (+9.0 per mil) from the row crop 

and/or livestock production dominated basins. 

The median δ18O of NO3 isotope ratio value 

(+21.5 per mil) from urban basins is 6.5 per mil 

higher than the median value (+14.0 per mil) from 

the undeveloped basins. The majority of NO3

concentrations are greater than 3 milligrams per 

liter (mg/L) in basins dominated by row crops and 

row crops and/or livestock production, whereas 

all NO3 concentrations are less than 2 mg/L in 

basins dominated by urban and undeveloped land. 

INTRODUCTION

Problem

Nitrate (NO3) and other nutrients discharged 

from the Mississippi River basin along with seasonal 

stratification of the water column are known to cause a 

zone of depleted dissolved oxygen (hypoxic zone) in 

the Gulf of Mexico (Turner and Rabalais, 1991; 

Rabalais and others, 1996; 1999). The magnitude of 
2 Isotopic and Chemical Composition of Inorganic and Organic Water-Quality Samples from the Mississippi River Basin, 1997–98

nitrogen (N) inputs contributed from various sources 

in the Mississippi basin can be estimated (Battaglin 

and others, 1997; Burkart and James, 1999; Goolsby 

and others, 1999), but N from each source is affected 

differently by physical, chemical, and biological 

processes that control N transport and cycling in 

terrestrial and aquatic systems (Kendall, 1998). Hence, 

the relative contributions from the various N sources 

may not be in proportion to their inputs in the Mississippi River basin. It may be possible to determine the 

major sources of NO3 in river water and gauge the 

importance of in-stream transformations of NO3 using 

the stable isotopic ratios δ15N and δ18O of NO3 in 

water and δ15N and δ13C of suspended particulate 

organic material.

Objectives and Hypotheses

The objective of this project is to determine if 

the δ15N and δ18O isotope ratio values of dissolved 

NO3 in water (δ15N and δ18O of NO3 values) and 

δ15N and δ13C isotope ratio values of suspended 

particulate organic material (δ15N and δ13C values of 

POM) can be used to help identify the sources of inorganic and organic N to the main-stem Mississippi 

River. Specific objectives include: determination of 

geographic sources of N; the proportion of contributions from various land uses within large and small 

tributary basins; and the effects and types of N transformation and cycling processes that affect the eventual transport of NO3 to the Gulf of Mexico. The 

following hypotheses are tested (Battaglin and others, 

1997):

1. There are significant temporal and spatial variations 

in δ15N and δ18O of NO3 values in water from 

the Mississippi River and its major tributaries.

2. The NO3 in small streams draining areas of 

distinctly different land use (corn and soybean 

production, livestock production, urban land, or 

undeveloped land) will have distinctly different 

δ15N and δ18O of NO3 values.

3. The δ15N and δ18O of NO3 values in Mississippi 

River water can be used to determine the principal sources of the NO3 that enters the Gulf of 

Mexico.

4. The δ15N and δ18O of NO3 values in Mississippi 

River water provide information about NO3

transformations in the river. 

5. There are significant temporal and spatial variations 

in δ15N and δ13C of POM values in suspended 

organic material from the Mississippi River and 

its major tributaries.

6. The suspended organic material in small streams 

draining areas of distinctly different land use will 

have distinctly different δ15N and δ13C of POM 

values.

7. Results from selected samples collected as 

Lagrangian sets can be used in simple mixing 

models to determine how conservatively NO3

behaves in the Lower Mississippi River. 

Background

Gulf of Mexico Hypoxia and Mississippi River 

Discharge

When the concentration of dissolved oxygen in 

seawater drops below 2 mg/L for prolonged periods, 

benthic communities can be disrupted and mass 

mortalities of aquatic life can occur (Diaz and Rosenberg, 1995; Council for Agricultural Science and 

Technology, 1999). This condition, called hypoxia, 

currently occurs in many parts of the world and probably has occurred in some locations periodically 

throughout geologic time (Rabalais and others, 1999). 

The hypoxic zone in the bottom waters of the northern 

Gulf of Mexico along the Louisiana and Texas coast is 

the largest such area in the coastal waters of the United 

States. Hypoxia here occurs during late spring and 

summer following inputs of freshwater and nutrients. 

Evidence from analysis of benthic foraminifera 

species in sediment cores from the northern Gulf of 

Mexico suggest that (1) there was little or no hypoxia 

prior to 1900, (2) there was a change in the offshore 

ecosystem with regard to hypoxia at the turn of the 

last century, and (3) that hypoxia severity has worsened since the 1950s (Rabalais and others, 1999). 

From 1985 to 1992, the area of the hypoxic zone averaged about 10,000 square kilometers (km2); following 

the 1993 flood, the zone nearly doubled in size to 

17,000 km2

. Subsequently, the hypoxic zone area has 

been reported to be 15,500 km2

 or more in 1994–97, 
INTRODUCTION 3

and 1999 (Council for Agricultural Science and Technology, 1999; N. Rabalais,, Louisiana Universities 

Marine Consortium, written commun., 1999). 

The Mississippi and Atchafalaya Rivers (fig. 1) 

are the primary riverine sources of freshwater and 

nutrients discharged to the Gulf of Mexico. The 

combined annual mean discharge, 21,800 cubic meters 

per second (m3

/s), for the Mississippi and Atchafalaya 

Rivers represents about 80 percent of the freshwater 

discharge to the Gulf of Mexico (Dunn, 1996). This 

river system drains approximately 3.2 million km2

 of 

the midwestern USA, making it the third-largest 

drainage basin in the world after the Amazon and 

Congo River basins (Van der Leeden and others, 

1990). 

The Atchafalaya River currently functions as a 

distributary of the Mississippi River. About 225 km 

downstream from Vicksburg, Miss, approximately 

25 percent of the Mississippi River discharge is 

diverted into the Old River outflow channel (Goolsby 

and others, 1999). The diverted flow joins the Red 

River to form the Atchafalaya River, which flows 

almost directly south about 200 km to the Gulf of 

Mexico. Historically, the lower Mississippi River 

meandered in a 300-kilometer wide arc and the location of the outlet to the Gulf of Mexico shifted dramatically about every millennium (McPhee, 1989; Meade, 

1995). It is likely that the Mississippi River would no 

longer flow past New Orleans, were it not for the 

control structures built by the U.S. Army Corps of 

Engineers (McPhee, 1989). These structures keep the 

lower Mississippi River in its current channel and 

prevented the Atchafalaya River from capturing the 

entire flow of the Mississippi River. 

Currently, the Mississippi and Atchafalaya 

Rivers account for an estimated 90% of the total N 

load and 87 percent of the total phosphorus (P) load 

discharged annually by rivers and streams to the Gulf 

of Mexico (Dunn, 1996). Analysis of historical data 

(Palmer, ca. 1903; Leighton, 1907; Dole, 1909) 

suggests that at the beginning of the twentieth century 

(1905–06) the average concentration of NO3 (as N) in 

the lower Mississippi River was about 0.55 milligram 

per liter (mg/L) (Goolsby and Battaglin, 2001). The 

concentration of NO3 in the lower Mississippi River 

has increased since that time to an average of 

1.45 mg/L during 1980–98. The resulting flux of NO3

to the Gulf of Mexico from the Mississippi and Atchafalaya Rivers has also increased substantially. During 

the 1950s and 1960s, the NO3 flux to the Gulf of 

Mexico never exceeded 0.5 million metric tons per 

year (Mton/y), but during the 1980s and 1990s the 

NO3 flux to the Gulf of Mexico averaged 1.0 Mton/y, 

and exceeded 1.5 Mton/y during the 1993 flood 

(Goolsby and others, 1999; Goolsby and Battaglin, 

2001). The NO3 flux generally peaks during the spring 

and early summer months and can exceed 6,000 metric 

tons per day (Battaglin and others, 1997; Goolsby and 

others, 1999). 

Nitrogen Sources

Major sources of N in the Mississippi River 

basin are mineralization of organic N in soils, application of nitrogen based fertilizer, fixation of atmospheric N by legumes, application of N in animal 

manure, deposition of atmospheric N in precipitation, 

and discharge of N in municipal and industrial waste. 

The magnitudes of these sources in large subbasins of 

the Mississippi basin have been estimated in previous 

investigations (Battaglin and others, 1997; Burkart and 

James, 1999; Goolsby and others, 1999). Estimates of 

annual N inputs from various sources during 1951–99 

were compiled for 20 states that account for most of 

the agricultural land in the Mississippi River Basin 

(fig. 1). The 20 States are: Arkansas, Colorado, Illinois, Indiana, Iowa, Kansas, Kentucky, Louisiana, 

Minnesota, Mississippi, Missouri, Montana, Nebraska, 

Ohio, Oklahoma, South Dakota, Tennessee, West 

Virginia, Wisconsin, and Wyoming.

The relative magnitudes and the temporal trends 

of estimated N inputs from the 20 States in the Mississippi River basin are shown in figure 2. The state-level 

fertilizer N inputs shown (fig. 2) include both agricultural and nonagricultural (home and garden) fertilizer 

use (Alexander and Smith; 1990; Battaglin and 

Goolsby, 1995; National Agricultural Statistics 

Service, 1999). Estimates of non-agricultural fertilizer 

use range between 5 and 20 percent of the total usage 

(H. Taylor, U.S. Department of Agriculture, written 

commun., 1998). Other N inputs were estimated using 

the best available data or the most current estimation 

technique (Goolsby and others, 1999). Fertilizer N 

inputs have increased substantially, from less than 1 to 

about 7 million Mton/y between the 1950s and 1990s 

(fig. 2); other N inputs have not changed very much 

during that time.

During the 1800s, increases in food production 

in the USA resulted from an expanding cropland base, 

the addition of nutrients in animal manure, and the 
4 Isotopic and Chemical Composition of Inorganic and Organic Water-Quality Samples from the Mississippi River Basin, 1997–98 Urban land Predominantly agricultural land Predominantly woodland Predominantly range or barren land Wetlands Water EXPLANATION

00

500 KILOMETERS

300 MILES

Gulf ofMexico

Figure 1. Land cover in the Mississippi River Basin.
INTRODUCTION 5

crop residue/

soil mineralization

fertilizer

legume and pasture

all manure

atmospheric nitrate

atmospheric ammonia

municipal and industrial

1950 1960 1970 1980 1990 2000

YEAR

9.0

8.0

7.0

6.0

5.0

4.0

3.0

2.0

1.0

0.0

ANNUAL NITROGEN INPUTS IN THE

MISSISSIPPI BASIN, IN MILLIONS OF METRIC TONS

utilization of soil nutrients. In the early 1900s, soil 

fertility and crop yields were maintained by the addition of N- and P-containing natural waste materials 

like animal manure, seaweed, bone meal, and guano. 

Beginning in the 1940s, manufactured fertilizers like 

super-phosphates, urea, and anhydrous ammonia 

replaced most natural fertilizers (U.S. Department of 

Agriculture, 1997). Since the 1930s, yields per acre for 

major crops like corn and wheat have doubled or 

tripled (Mannion, 1995). Some of this increase can be 

attributed to better plant hybrids and some can be 

attributed to increased application of crop nutrients.

As indicated in the problem statement, the N 

from each source is affected differently by physical, 

chemical, and biological processes that control N 

cycling in terrestrial and aquatic systems. Hence, the 

relative contributions from the various N sources to 

NO3 loads in the Mississippi River may not be proportional to their inputs in the basin. 

Previous Isotope Investigations

Stable isotopes of NO3 have been used in N 

source and cycling investigations for over 30 years 

(Kreitler, 1975; Hubner, 1986; Heaton, 1986; Clark 

and Fritz, 1997; Kendall, 1998). One of the first 

studies (Kohl and others, 1971) used δ15N of NO3 to 

investigate the sources NO3 in an agricultural watershed. They estimated that 55% of N found as NO3 in 

the Sangamon River originated as fertilizer N. Several 

recent studies have utilized isotopic techniques to 

identify the sources and transformations of NO3 in 

rivers with varying degrees of success. Showers and 

others (1990) used NO3 δ15N values in the Neuse 

River, NC, to determine that the relative contributions 

from point and nonpoint sources varied seasonally and 

by water discharge rate. They also determined that 

nitrate’s isotopic composition was exponentially 

related to river discharge, and they concluded that the 

mixing of point and nonpoint source N reservoirs was 

Figure 2. Estimated annual nitrogen inputs in the 20 States that account for most of the agricultural land 

in the Mississippi River basin, 1951 to 1999 (modified from Goolsby and others, 1999). 
6 Isotopic and Chemical Composition of Inorganic and Organic Water-Quality Samples from the Mississippi River Basin, 1997–98

not entirely controlled by surface water runoff of agricultural fertilizer and excess soil NO3, but that nonpoint source NO3 passing through a reservoir (either 

groundwater or wetlands) modulated the mixing. 

Cravotta (1995) attempted to use the stable isotopes of 

carbon, N, and sulfur to identify sources of N in the 

Susquehanna River, and found that variations in source 

isotopic compositions, transformation, and fractionation during natural cycling of N prevented accurate 

estimation of relative contributions of multiple N 

sources to N loads in streams. 

BÖhlke and Denver (1995) used isotope, water 

chemistry, chlorofluorocarbons (for determining water 

recharge date), and nitrogen gas measurements in two 

adjacent but geologically and hydrologically different 

basins to show that water age and aquifer composition 

can influence the amount of N delivered from a 

groundwater system to a stream. Kendall and others 

(1995) used δ18O and δ15N of NO3 values to determine NO3 sources in snowmelt runoff from three 

small mountainous watersheds in the United States. 

They determined that most of the NO3 in early runoff 

was derived from the soil, and not from atmospheric 

NO3 released from the current year’s snowpack. 

Campbell and others (U.S. Geological Survey, written 

commun., 2001) used δ18O and δ15N of NO3 values to 

show that most NO3 in streams and ground water of 

N-saturated alpine watersheds was affected by microbial processes, even in landscapes with little vegetation or soil. Burns and Kendall (U.S. Geological 

Survey, written commun., 2001) used δ18O and δ15N 

on NO3 values to show that NO3 in stream water was 

similar to soil water, and that microbial cycling of NO3

from atmospheric deposition was rapid. Kellman and 

Hillaire-Marcel (1998) used δ15N values to determine 

the importance of in-stream denitrification on the 

N-budget of a small watershed. The isotopes showed 

that denitrification was significant during dry conditions in late summer. 

Nitrogen Transformations

The isotopic composition of NO3 sources can be 

altered by reactions that fractionate the stable isotopes. 

Nitrogen can be transformed in vegetation, the soil, the 

unsaturated zone, the saturated zone, or in-stream. 

Assimilation and denitrification are the most likely 

transformation processes that may have an in-stream 

effect on NO3 and total N concentrations and loads in 

rivers. Use of both δ15N and δ18O enhances identification of N transformations and identification of NO3

sources (Böttcher and others, 1990; Kendall, 1998). 

Nitrogen assimilation, the use of N-bearing 

compounds by plants or organisms, slightly favors the 

14N isotope over 15N isotope. A large range of isotope 

fractionations [–27 to 0 per mil (‰)] have been 

measured in field and laboratory experiments for 

assimilation of NO3 and ammonium by algae (Fogel 

and Cifuentes, 1993). However, the average apparent 

fractionations caused by assimilation by microorganisms in soils is about –0.5‰ (Hubner, 1986). The 

larger fractionation of NO3 in aquatic versus soil environments reflects the interplay of several kinetic and 

equilibrium isotope effects. In general, smaller fractionations are observed for higher growth rates and for 

lower NO3 and ammonium concentrations. Assimilation would likely favor the 16O isotope relative to the 

18O isotope in the same way the 14N isotope is utilized 

in preference to 15N isotope (Kendall, 1998); hence it 

would increase the δ18O and δ15N isotope ratio of the 

residual NO3 pool. 

Denitrification, the biologically mediated reduction of NO3 to N2, causes the δ15N and δ18O of the 

residual NO3 pool to increase exponentially as NO3

concentration decreases (Böttcher and others, 1990; 

Kendall, 1998). The ratio of enrichment of O to N 

tends to be close to 1:2 (Böttcher and others, 1990; 

Voerkelius and Schmidt, 1990). In-stream loss of N 

coupled with significant positive shifts in isotope 

ratios can indicate that denitrification is consuming 

NO3 (Kellman and Hillaire-Marcel, 1998). 

Volatilization, the loss of N usually as ammonia 

(NH3), involves several steps that can cause fractionation. The remaining dissolved NH3 tends to be 

enriched in the 15N isotope relative to the NH3 that is 

volatilized. The enriched NH3 in solution is rapidly 

nitrified to produce 15N-enriched NO3 in most natural 

conditions (Feigin and others, 1974; Kendall, 1998). 

The loss of N in streams, whether by assimilation, denitrification, or volatilization, tends to cause a 

decrease in N concentration, a loss of N mass (to the 

atmosphere or plants), and a shift towards higher δ15N 

and δ18O of NO3 isotope ratio values between 

upstream and downstream measuring points. In larger 

rivers, the magnitude and mechanism of N loss can be 

difficult to identify because small errors in discharge 

measurements and small differences in concentrations 

or isotope ratios can significantly affect data interpretation. 
METHODS 7

Acknowledgments

The authors would like to acknowledge the 

many USGS personnel who helped collect and process 

these samples. Without their efforts, this work could 

not have been accomplished. This research was 

supported by a grant from the U.S. Environmental 

Protection Agency, Gulf of Mexico Program and 

directly and indirectly by the USGS National Stream 

Quality Accounting Network (NASQAN) and 

National Water-Quality Assessment (NAWQA) 

programs. The manuscript benefited from reviews by 

Steve Komor and Gerhard Kuhn at the U.S. Geological 

Survey, Nancy Rabalais at the Louisiana Universities 

Marine Consortium, and Kenneth Teague at the U.S. 

Environmental Protection Agency. 

METHODS

Plan of Study

The study plan (Battaglin and others, 1997) 

provides details about sample station selection and 

sampling procedures. In 1997, about 150 water and 

particulate organic material (POM) samples were 

collected from 24 stations on rivers in the Mississippi 

River basin, and in 1998, about 100 water and POM 

samples were collected from 23 stations on rivers in 

the Mississippi River basin. Some of the 1997 samples 

and most 1998 samples have complete (both δ15N and 

δ18O of NO3 values in water, and δ15N and δ13C of 

POM values) isotope analyses. Several water samples 

did not contain sufficient NO3 to analyze, and a few 

were ruined during sample processing.

Sampling Stations

All sampling stations are in the Mississippi and 

Atchafalaya River basin. Some stations were sampled 

in association with ongoing U.S. Geological Survey 

(USGS) National Stream Quality Accounting Network 

(NASQAN) and National Water-Quality Assessment 

(NAWQA) programs.

Large River Stations

Samples were collected from eight stations on 

the Mississippi River or its major tributaries (table 1; 

fig. 3a). mostly in conjunction with NASQAN 

(NASQAN, 2001) sample collection activities. These 

stations are on large rivers that drain more than 

200,000 km2

 (except the Yazoo River, that drains only 

34,590 km2

). Land use in these basins is mixed 

(table 2); hence, water samples from these stations 

contain NO3 from several sources. Drainage basins for 

the Mississippi River at Clinton, Iowa (MSR1) and 

Thebes, Ill. (MSR2), and the Yazoo River at Long 

Lake, Miss. (YZR1) are more than 50 percent cropland. The Ohio River at Grand Chain, Ill. (OHR1) 

basin is more than 50 percent forested land. Estimated 

N input from manure production (Goolsby and others, 

1999) exceeded 1,000 kg/km2

/yr only in the drainage 

basin of the MSR1 station. 

Small Stream Stations

Samples were collected from 16 stations on 

smaller streams in the Mississippi River basin. Many 

of these stations are within NAWQA (NAWQA, 2001) 

study units. The small stream stations all drain areas 

less than 2,500 km2

. These stations were selected to 

represent four distinct land-use categories: land in row 

crop agriculture (corn, soybean and sorghum); land in 

hog, cattle, or poultry (livestock) production; urban 

land; or undeveloped land (fig. 3b; tables 2 and 3). 

Land use was not always solely composed of 

one of the four categories, but making more categories 

would leave too few samples in each category to 

perform data analysis. For this report, four categories 

were used, but the original livestock category was 

redefined to include basins with both high-density 

livestock production and row-crop agriculture. The 

four stations in this category all had estimated manure 

production of greater than 3,200 kg N/km2 per year 

(table 2). Two of these stations also had land use dominated by row crop agriculture (table 3). The basin type 

for each station on table 1 and shown in figure 3.

Sampling Schedule and Procedure

Six samples were collected at each station 

during the winter, spring, and summer of 1996–97 

(Battaglin and others, 1997). Most of these samples 

were not analyzed for δ15N and δ18O of NO3 in water 

due to a problem with sample preparation. The δ15N 

and δ13C of POM isotope ratio values are available for 

some of these samples.
8 Isotopic and Chemical Composition of Inorganic and Organic Water-Quality Samples from the Mississippi River Basin, 1997–98

Most stations sampled in 1997 were sampled 

again four times during 1998. The first sample set was 

collected in April or May, 1998, prior to crop emergence. The second and third sample sets were 

collected in June and July 1998 after fertilizer application to fields when stream flows were elevated due to 

storm runoff. The fourth sample set was collected in 

August and September 1998 after harvest, when 

streams were generally dominated by baseflow.

Samples were collected with a depth integrating 

sampler (where conditions were appropriate for this 

collection method) from three or more vertical profiles 

using USGS protocols (Shelton, 1994). Before 

samples were collected, all sampling equipment was 

precleaned with non-phosphate detergent, rinsed thoroughly with tap water, and then rinsed with distilled or 

deionized water. Samples from vertical profiles were 

composited into a glass, polyethylene, or Teflon 

Table 1. Selected characteristics of sampling stations in the Mississippi River basin

(square kilometers, km2)

Map 

no. 

(fig. 3)

Sampling station name Station 

number

Latitude 

(ddmmss)

Longitude 

(ddmmss)

 Drainage 

area

(km2)

Basin type

Large rivers

1 Mississippi River at Clinton, IA 05420500 414650 901507 221,700 mixed agricultural land/forest 

2 Missouri River at Hermann, MO 06934500 384236 912621 1,357,700 mixed rangeland/agricultural land

3 Mississippi River at Thebes, IL 07022000 371300 892750 1,847,200 mixed agricultural land/rangeland 

4 Ohio River at Grand Chain, IL 03612500 371211 890230 526,000 mixed forest/agricultural land 

5 Yazoo River below Steele Bayou near 

Long Lake, MS 07288955 322637 905400 34,590 mixed agricultural land/forest

6a Mississippi River at St. Francisville, 

LA 07373420 304530 912345 2,914,500 mixed agricultural land/forest/

rangeland

6b Mississippi River at Vicksburg, MS 07289000 321845 905425 ~2,900,000 mixed agricultural land/forest/

rangeland

6c Mississippi River at Belle Chasse, LA 07374525 295125 895840 2,916,200 mixed agricultural land/forest/

rangeland/wetland

Small streams

7 S. Fork Iowa River northeast of New 

Providence, IA 05451210 421855 930907 596 row crop agriculture and/or 

livestock production

8 Fourmile Creek near Traer, IA 05464137 421207 923344 50.5 row crop agriculture

9 Walnut Creek near Vandalia, IA 05487550 413213 931532 52.6 row crop agriculture

10 Panther Creek near El Paso, IL 05567000 404605 890430 243 row crop agriculture

11 Indian Creek near Wyoming, IL 05568800 410106 895007 162 row crop agriculture

12 Sugar Creek at Co Rd 400 S at New 

Palstine, IN 03361650 394251 855308 243 row crop agriculture

13 Little Buck Creek near Indianapolis, 

IN 03353637 394000 861148 44 urban land

14 North Dry Creek near Kearney, NE 06770195 403828 990656 201 row crop agriculture and/or 

livestock production

15 Dismal River near Thedford, NE 06775900 414645 1003130 2,500 undeveloped land

16 South Fabius River near Taylor, MO 05500000 395340 913449 1,606 row crop agriculture

17 Elk River near Tiff City, MO 07189000 363753 943512 2,260 row crop agriculture and/or 

livestock production

18 Shingle Creek at Queen Ave. N., MN 05288705 450300 931836 73 urban land

19 Little Cobb River near Beauford, MN 05320270 435948 935430 336.7 row crop agriculture

20 Namekagon River at Leonards, WI 05331833 461017 911945 326 undeveloped land

21 Rattlesnake Creek near North Andover, 

WI 05413449 424649 905632 110 row crop agriculture and/or 

livestock production

22 Bogue Phalia near Leland, MS 07288650 332347 905047 1,254 row crop agriculture
METHODS 9

500 KILOMETERS

300 MILES

0

0

A

B

1 Mississippi River at Clinton, 

IA—(MSR1)

2 Missouri River at Hermann, 

MO—(MOR1)

3 Mississippi River at Thebes, 

IL—(MSR2)

4 Ohio River at Grand Chain, 

IL—(OHR1)

5 Yazoo River near Long Lake, 

MS—(YZR1)

6a Mississippi River at St. Francisville, 

LA—(MSR4)

6b Mississippi River at Vicksburg, 

MS—(MSR3)

6c Mississippi River at Belle Chasse, 

LA—(MSR5)

Sampling Site

LARGE RIVER SITES

South Fork Iowa River, New Prov., IA

Fourmile Creek near Traer, IA

Walnut Creek near Vandalia, IA

Panther Creek near El Paso, IL

Indian Creek near Wyoming, IL

Sugar Creek at New Palistine, IN

Little Buck Creek Indianapolis, IN

North Dry Creek near Kearney, NE

Dismal River near Thedford, NE

South Fabius River, Taylor, MO

Elk River near Tiff City, MO

Shingle Creek, Minneapolis, MN

Little Cobb River, Beauford, MN

Namekagon River at Leonards, WI

Rattlesnake Creek North Andover, WI

Bogue Phalia near Leland, MS

SAMPLING SITE BASIN TYPE

Undeveloped land

Row crop agriculture

Urban land

Row crop agriculture and/or livestock production

SMALL STREAM SITES

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

7 8

9 10

11

12 13

14

15

16

17

18

19

20

21

22

1

2

3

4

5

6a

6b

6c

0

0

500 KILOMETERS

300 MILES

Figure 3. Locations of sampling stations and associated drainage basins for (A) large rivers and (B) small streams.
10 Isotopic and Chemical Composition of Inorganic and Organic Water-Quality Samples from the Mississippi River Basin, 1997–98

container. Isotope samples for NO3 analysis were 

filtered through a 0.45-micron cartridge filter into 

1-liter or 1-gallon pre-cleaned polyethylene bottles, 

chilled without preservative, and shipped to USGS 

district water-quality laboratories in Missouri (prior to 

January 1, 1998) or Colorado (after January 1, 1998) 

for extraction onto anion exchange columns. Samples 

for other analytes including nutrients, major ions, and 

dissolved organic carbon were collected concurrently, 

processed according to standard protocols, and 

analyzed by the USGS National Water Quality Laboratory (NWQL) in Denver, Colo.. 

Lagrangian Samples

Lagrangian sampling (Meade and Stevens, 

1990; Moody, 1993) is a sampling method in which a 

mass of water is sampled repeatedly as it moves down 

a river. The timing of sample collection is determined 

by the velocity (converted to travel time) of the water 

in the river. Major tributaries also are sampled when 

the water mass is near their mouth. Because 

Lagrangian sample sets provide data on the changes in 

water-quality characteristics as a water mass moves 

downstream, these sample sets can be more useful 

than traditional Eulerian sample sets for constructing 

transport models of dissolved chemicals and 

suspended sediment, and for identifying the chemical, 

physical, and hydrologic processes that affect stream 

chemistry (Meade and Stevens, 1990). 

In this study, the collection of a Lagrangian 

sample set for the lower Mississippi River involved 

sampling the Mississippi River at Thebes (MSR2) and 

the Ohio River at Grand Chain (OHR1) (fig. 3a) at 

about the same time. During average spring flow 

Table 2. Generalized land cover and estimated annual manure nitrogen production in the large river and small stream drainage 

basins (land cover derived from reclassified Advanced Very High Resolution Radiometer data with a 1,000 meter-cell size)

Station 

number

Percentage of basin Estimated manure nitrogen

production in kg/km2

Urban Agricultural

Rangeland Forest Water Wetland Barren or 

Tundra Cattle Hogs Poultry Total1

Large rivers

05420500 1.1 61.4 0.3 35.7 1.5 0 0 1,004 292 48.4 1,368

06934500 0.4 42.6 45.3 10.6 0.4 0 0.7 742 92.9 6.7 866

07022000 0.8 51.3 33.0 13.8 0.6 0 0 767 179 13.1 984

03612500 2.2 30.1 0.1 67.0 0.6 0 0 704 110 83.7 933

07288955 0.5 55.1 1.4 41.8 1.1 0.1 0 213 5.3 < 0.05 228

073734202 1.1 45.5 26.2 26.3 0.6 0.01 0.3 780 139 49.4 993

Small streams

05451210 0 100 0 0 0 0 0 422 2,710 74.7 3,232

05464137 0 98.4 0 1.6 0 0 0 814 544 0.6 1,388

05487550 0 100 0 0 0 0 0 1,055 944 0.1 2,031

05567000 0.8 99.2 0 0 0 0 0 247 561 2.0 827

05568800 0 98.8 0 1.2 0 0 0 413 662 0.1 1,099

03361650 0.7 99.3 0 0 0 0 0 229 575 0.2 842

03353637 42.5 57.5 0 0 0 0 0 40.8 7.0 < 0.05 71.6

06770195 0 100 0 0 0 0 0 4,157 169 0.1 4,351

06775900 0 54.6 45.3 0.1 0 0 0 590 0.2 < 0.05 599

05500000 0 86.8 0.3 12.9 0 0 0 1,030 152 0.2 1,203

07189000 1.0 2.8 0 96.1 0.1 0 0 1,949 76.6 2,822 4,887

05288705 89.7 10.3 0 0 0 0 0 298 15.7 0.2 372

05320270 0 97.9 0 2.1 0 0 0 505 1,395 17.5 1,945

05331833 0 5.2 0 93.0 1.8 0 0 132 2.1 0.1 141

05413449 0 98.9 0 1.1 0 0 0 2,874 377 8.9 3,287

07288650 0.2 84.9 8.9 4.8 0.8 0.4 0 61.0 0.6 < 0.05 63.3

1 Total includes cattle, hogs, poultry, horses, and sheep.

2 Estimates of land cover in the drainage basins associated with stations 6b and 6c (table 1) are the same as for station 07373420.
METHODS 11

conditions, it takes water about 8 days to travel from 

the MSR2 or OHR1 stations to the St. Francisville 

(MSR4) station and 2 or 3 more days to travel to the 

Belle Chasse (MSR5) station (Broshears and others, 

2001). Water (and solutes) diverted from the Mississippi River into the Atchafalaya River via the Old 

River outflow (about 25% of Mississippi discharge on 

average) are included in discharge and flux values 

reported for the MSR4 and MSR5 stations.

Samples from the MSR2 on June 11, 1997, the 

OHR1 on June 12, 1997, YZR1 on June 19, 1997, the 

MSR4 on June 19, 1997, and the MSR5 on June 20, 

1997 (table 4) are referred to as the first Lagrangian 

set. While not specifically collected as such, samples 

from the MSR2 on April 16, 1998, the OHR1 on April 

23, 1998, and the MSR4 on April 30, 1998 constitute a 

nearly Lagrangian sample set, and are referred to as 

the second Lagrangian set. 

Analytical Methods

Analysis of δ15N and δ18O of NO3 in Water

Details of the water sample collection protocol 

used are given in Battaglin and others (1997) and 

Chang and others (1999). In early 1997, water samples 

for isotope analysis were passed through 2 ml of anion 

exchange resin to isolate the NO3 from the samples 

(Silva and others, 2000). In most of the previous 

studies, and in many samples collected in this study, 

large volumes of water (up to 20 liters) were passed 

through exchange columns in order to obtain sufficient 

NO3 for isotope analysis. However, when the anion 

capacity of the columns is exceeded because of the 

high concentrations of other anions, the competition 

for exchange sites may result in isotopic fractionation 

(Silva and others, 2000). The highly variable chemistry of samples collected within the Mississippi River 

basin posed a significant challenge to the single 

column method used, especially when concentrations 

of SO4, Cl, and HCO3 were high relative to NO3. After 

analyzing the water-quality data collected concurrently with each isotope sample, it was determined that 

many samples collected and processed in 1997 

exceeded the anion exchange capacity of the columns. 

These samples were not analyze for the isotope ratios 

of NO3. 

Later in 1997 and in 1998, this problem was 

alleviated by using larger anion columns with 5 ml of 

resin and a cation column in front of the anion column 

to reduce concentrations of adsorbed organic constituents and neutralize HCO3 (Chang and others, 1999). 

The cation column protonates and/or adsorbs 

Table 3. Land cover in the small stream drainage basins (derived from National Land Cover data with a 30-meter cell size)

Station 

number

Percentage of basin

Low or 

high 

intensity 

residential and 

urban 

grasses

Commercial/

industrial/

transportation

Deciduous,

evergreen 

or mixed 

forest

Open 

water/

perennial 

snow

Barren 

land

Shrubland or 

grassland

Wetlands Row 

crops

Small 

grains

Pasture 

or fallow

05451210 0.1 1.4 2.6 0.1 <0.1 3.3 0.7 87.5 0.1 4.2

05464137 0.1 1.3 1.6 <0.1 <0.1 4.5 0.1 85.7 <0.1 6.6

05487550 0.1 1.2 3.0 1.1 <0.1 5.4 0.1 75.3 0.4 13.4

05567000 0.7 0.1 0.4 0.1 <0.1 0.1 0.2 94.6 <0.1 3.8

05568800 1.7 0.3 3.0 <0.1 <0.1 <0.1 0.3 82.6 <0.1 12.0

03361650 1.8 0.3 4.9 0.3 <0.1 <0.1 0.7 75.9 <0.1 16.1

03353637 43.4 5.7 3.9 0.1 <0.1 <0.1 0.3 26.1 <0.1 20.4

06770195 <0.1 <0.1 0.4 0.4 <0.1 16.3 0.8 74.0 0.8 7.3

06775900 <0.1 <0.1 0.4 0.8 0.5 93.2 4.6 0.1 <0.1 0.4

05500000 0.4 1.1 19.9 0.6 <0.1 4.1 5.9 24.0 5.6 38.4

07189000 1.5 0.3 49.7 0.4 0.3 2.2 0.4 2.6 2.1 40.5

05288705 62.0 8.7 6.2 5.2 4.6 <0.1 11.0 0.6 <0.1 1.7

05320270 0.2 0.4 2.4 0.8 <0.1 <0.1 3.8 87.2 <0.1 5.2

05331833 0.1 0.1 71.6 7.1 0.2 0.4 16.2 2.2 <0.1 2.1

05413449 <0.1 0.6 3.7 <0.1 <0.1 <0.1 0.1 46.0 <0.1 49.6

07288650 0.7 0.2 1.3 1.3 <0.1 <0.1 10.5 71.2 9.3 5.5
12 Isotopic and Chemical Composition of Inorganic and Organic Water-Quality Samples from the Mississippi River Basin, 1997–98

Table 4. Nitrite plus nitrate concentration, daily mean discharge and δ15N and δ18O of NO3 values in water samples collected in 

1997–98 (*, results not available)

Sampling station name and station number Sample 

ID

Sample 

collection 

date

Daily 

mean 

discharge 

in cubic 

feet per 

second

Nitrite plus 

nitrate as N 

in mg/L1

Average

δ15N in 

per mil

Average δ18O 

in per mil

Large river stations

Mississippi River at Clinton, IA - 05420500 IS-119 6/2/97 60,900 0.449 12.1 15.5

IS-112 9/2/97 53,300 0.914 9.4 10.0

IS-33 5/13/98 58,500 1.82 10.4 11.0

IS-34 5/13/98 58,500 1.85 10.4 9.5

IS-42 5/27/98 56,600 1.22 10.3 10.5

IS-56 6/10/98 48,600 2.00 9.9 15.0

IS-60 7/1/98 101,000 3.00 11.0 9.0

IS-76 7/28/98 41,400 1.51 10.5 11.0

IS-83 8/25/98 38,000 0.620 9.2 17.5

IS-84 8/25/98 38,000 0.624 lost during preparation

IS-97 9/23/98 23,000 0.850 8.5 15.0

Missouri River at Hermann, MO - 06934500 IS-26 4/20/98 159,000 1.90 8.1 9.5

IS-45 6/1/98 87,400 2.12 8.4 14.0

IS-64 7/7/98 159,000 1.20 8.3 14.0

IS-86 8/31/98 86,700 1.27 8.8 13.0

Mississippi River at Thebes, IL - 07022000 IS-101 6/11/97 247,000 2.55 6.9 7.5

IS-25 4/16/98 574,000 3.60 7.0 6.5

IS-50 6/10/98 284,000 3.20 7.8 7.0

IS-51 6/10/98 284,000 3.63 7.7 3.0

IS-74 7/22/98 272,000 3.43 8.5 12.0

IS-91 9/9/98 130,000 1.27 12.4 21.0

Ohio River at Grand Chain, IL - 03612500 IS-102 6/12/97 653,000 2.47 3.1 7.0

IS-27 4/23/98 734,000 1.10 5.7 10.5

IS-44 6/5/98 366,000 1.73 6.3 9.5

IS-77 7/22/98 260,000 1.38 6.0 11.0

IS-78 7/22/98 260,000 1.38 lost during preparation

IS-85 8/12/98 185,000 0.73 4.8 too little N

Yazoo River below Steele Bayou near Long Lake, 

MS - 07288955

IS-103 6/19/97 24,800 0.743 3.8 9.0

IS-19 4/13/98 11,900 0.380 2.8 11.0

IS-57 6/17/98 6,840 0.890 4.8 6.5

IS-66 7/16/98 25,600 0.480 9.1 24.0

IS-96 9/17/98 9,310 0.206 3.6 18.0

Mississippi River, St. Francisville, LA - 

07373420

IS-117 5/6/97 1,006,000 1.43 6.3 7.5

IS-106 6/19/97 1,079,000 2.01 4.0 7.5

IS-10 4/2/98 1,213,000 1.50 ruined in the field

IS-11 4/2/98 1,213,000 1.50 ruined in the field

IS-31 4/30/98 1,266,000 1.97 6.5 8.5

IS-32 4/30/98 1,266,000 1.98 6.3 7.5

IS-49 6/9/98 739,000 2.06 7.1 7.5

IS-63 7/9/98 1,053,000 2.70 7.8 7.0

IS-99 9/28/98 309,000 0.81 9.4 14.0

Mississippi River at Vicksburg, MS - 07289000 IS-2A 1/13/98 933,000 0.87 ruined lab 11.0

IS-2B 1/13/98 933,000 0.87 8.0 12.5

IS-2C 1/13/98 933,000 0.87 7.7 17.5
METHODS 13

Large river stations—Continued

Mississippi River at Belle Chasse, LA - 07374525 IS-118 5/7/97 823,0001 1.23 6.4 8.5

IS-105 6/20/97 937,0001 1.81 3.4 7.5

Small stream stations

S. Fork Iowa River northeast of New Providence, 

IA - 05451210

IS-3A 1/30/98 23 4.30 12.9 10.5

IS-3B 1/30/98 23 4.30 12.9 9.5

IS-3C 1/30/98 23 4.30 12.9 10.5

IS-5 3/30/98 329 13.0 8.2 5.5

IS-8 3/30/98 329 12.0 7.6 5.0

IS-41 5/29/98 833 15.4 5.3 6.0

IS-79 8/3/98 33 7.79 10.9 10.5

Fourmile Creek near Traer, IA - 05464137 IS-107 6/30/97 * 14.9 3.1 5.5

IS-20 4/15/98 54.1 18.0 4.1 3.5

IS-67 7/16/98 23.4 16.0 5.5 9.5

IS-80 8/12/98 9.06 12.0 4.8 9.0

Walnut Creek near Vandalia, IA - 05487550 IS-104 6/21/97 21 9.69 4.9 8.0

IS-9 4/3/98 52 11.0 4.7 5.0

IS-28 5/7/98 167 9.72 3.7 4.5

IS-29 5/7/98 167 9.20 3.8 4.0

IS-54 6/11/98 100 5.57 5.4 5.0

Panther Creek near El Paso, IL - 05567000 IS-115 11/13/97 14 11.5 12.3 ruined in the lab

IS-16 4/9/98 151 18.0 5.6 5.5

IS-48 6/9/98 100 16.2 7.2 6.0

IS-61 7/7/98 145 12.0 8.5 8.0

Indian Creek near Wyoming, IL - 05568800 IS-111 8/27/97 36 9.65 7.8 8.0

IS-15 4/9/98 261 12.0 5.1 4.5

IS-39 5/25/98 80 11.7 5.6 6.0

IS-72 7/22/98 97 7.72 6.3 9.5

IS-73 7/22/98 97 7.68 9.7 9.5

Sugar Creek at Co Rd 400 S at New Palistine, IN 

- 03361650

IS-13 4/9/98 439 2.30 6.3 7.5

IS-38 5/24/98 414 8.48 5.5 8.0

Little Buck Creek near Indianapolis, IN - 

03353637

IS-113 9/9/97 4.0 0.862 3.3 31.0

IS-14 4/9/98 305 0.79 2.4 too little N

IS-37 5/24/98 131 1.28 3.5 4.0

IS-71 7/20/98 44 0.57 1.9 25.0

North Dry Creek near Kearney, NE - 06770195 IS-6 4/1/98 31 8.00 8.3 9.0

IS-40 5/22/98 83 5.30 7.7 10.5

IS-43 6/8/98 37 7.70 8.3 8.5

IS-92 9/9/98 10 7.01 9.4 13.5

Dismal River near Thedford, NE - 06775900 IS-17 4/13/98 225 0.460 5.1 11.0

IS-36 5/19/98 225 0.500 3.2 14.5

IS-55 6/16/98 219 0.421 5.0 6.0

IS-95 9/15/98 219 0.498 4.2 8.0

Table 4. Nitrite plus nitrate concentration, daily mean discharge and δ15N and δ18O of NO3 values in water samples collected in 

1997–98 (*, results not available)—Continued

Sampling station name and station number Sample 

ID

Sample 

collection 

date

Daily 

mean 

discharge 

in cubic 

feet per 

second

Nitrite plus 

nitrate as N 

in mg/L1

Average

δ15N in 

per mil

Average δ18O 

in per mil
14 Isotopic and Chemical Composition of Inorganic and Organic Water-Quality Samples from the Mississippi River Basin, 1997–98

Small stream stations—Continued

South Fabius River near Taylor, MO - 05500000 IS-23 4/7/98 685 0.780 7.4 11.5

IS-46 6/2/98 213 0.600 8.1 6.5

IS-75 7/27/98 55 0.284 11.9 18.0

IS-89 9/1/98 15 0.006 too little N

Elk River near Tiff City, MO - 07189000 IS-24 4/14/98 767 1.10 10.3 11.0

IS-52 6/9/98 318 1.73 9.6 6.0

IS-68 7/14/98 240 0.88 13.0 8.5

IS-87 9/2/98 72 0.396 13.4 10.5

IS-88 9/2/98 72 0.398 13.0 8.0

Shingle Creek at Queen Ave. N., MN - 05288705 IS-108 7/7/97 27 0.327 0.9 21.5

IS-12 4/6/98 56 0.510 15.5 too little N

IS-30 5/8/98 45 0.443 -1.2 23.5

IS-53 6/11/98 5.2 0.183 1.6 19.5

IS-62 7/8/98 5.5 0.217 5.9 19.0

Little Cobb River near Beauford, MN - 05320270 IS-109 7/16/97 162 9.71 5.6 7.0

IS-114 10/28/97 19 8.16 9.2 6.5

IS-1A 1/14/98 2.1 8.0 11.7 8.5

IS-1B 1/14/98 2.1 8.0 12.0 9.0

IS-1C 1/14/98 2.1 8.0 12.1 9.0

IS-4 3/30/98 381 14.0 6.3 7.0

IS-7 3/30/98 381 14.0 6.3 4.5

IS-35 5/18/98 166 16.0 6.5 5.0

IS-70 7/15/98 64 7.4 9.3 5.0

IS-90 8/17/98 2.8 <0.002 too little N

Namekagon River at Leonards, WI - 05331833 IS-116 11/11/97 105 0.12 2.8 14.0

IS-21 3/30/98 458 0.140 -1.4 20.0

IS-47 6/2/98 195 0.041 8.1 too little N

IS-69 7/15/98 102 0.015 too little N

IS-94 9/9/98 51 0.053 6.9 20.0

Rattlesnake Creek near North Andover, WI - 

05413449

IS-110 8/1/97 * 5.98 6.3 5.5

IS-22 4/15/98 32 7.4 9.5 5.0

IS-59 6/19/98 70 6.7 10.3 11.5

IS-81 8/21/98 29 7.0 6.4 9.0

IS-82 8/21/98 29 7.0 6.5 8.5

IS-98 9/22/98 26 7.98 9.0 10.0

Bogue Phalia near Leland, MS - 07288650 IS-18 4/14/98 41 0.006 too little N

IS-58 6/18/98 126 0.860 7.5 9.0

IS-65 7/15/98 2,080 1.10 10.3 43.5

IS-93 9/16/98 218 0.187 9.6 21.0 1 Low-level analyses (reporting limit of 0.002 mg/L) were conducted by the USGS Quality of Water Unit in Ocala, Florida.

2

 Calculated as the sum of the instantaneous discharge at the time of sample collection, plus the discharge out the Old River Diversion 2 days earlier.

Table 4. Nitrite plus nitrate concentration, daily mean discharge and δ15N and δ18O of NO3 values in water samples collected in 

1997–98 (*, results not available)—Continued

Sampling station name and station number Sample 

ID

Sample 

collection 

date

Daily 

mean 

discharge 

in cubic 

feet per 

second

Nitrite plus 

nitrate as N 

in mg/L1

Average

δ15N in 

per mil

Average δ18O 

in per mil
METHODS 15

dissolved organic carbon (DOC), thereby making it 

less likely for the DOC to compete with NO3 for 

exchange stations on the anion column (Chang and 

others, 1999). About 200 μmol of NO3 (equivalent to 

about 2.8 mg of N) was required for the dual isotope 

analysis. A special low-level analyses (0.002 mg/L 

reporting limit) for NO2 plus NO3 (table 4) conducted 

at the USGS Quality of Water Unit in Ocala, Florida, 

was used along with estimated concentrations of other 

anions from historic data to determine how much 

water to pass through the exchange column pair and to 

test for NO3 passing through the column pair. Both the 

minimum volume needed to obtain sufficient NO3 and 

the maximum volume that would avoid exceeding the 

anion column exchange capacity were considered to 

determine the sample volume to be processed.

To verify that all of the sample NO3 was 

adsorbed by the anion column, eluent that passed 

through the cation and anion exchange columns was 

saved and a sub-sample analyzed for NO2 plus NO3. If 

95% or more of the NO3 was retained by the anion 

column, the sample was analyzed for δ15N and δ18O 

of NO3 isotope ratios values using methods described 

by Silva and others (2000). If more than 5% of the 

NO3 was not retained by the anion column the sample 

was not analyzed for δ15N and δ18O of NO3 values. 

Dissolved organic carbon (DOC) and other non-nitrate 

oxygen bearing species are eliminated during this 

laboratory preparation procedure. Oxygen-isotope 

analyses were performed on a Finnigan Mat 251 (the 

use of trade names here or elsewhere in this report 

does not constitute an endorsement by the USGS) 

stable isotope mass spectrometer and nitrogen isotope 

analyses were performed on an Optima mass spectrometer. N isotope values (δ15N) are reported in per 

mil (‰) relative to atmospheric N2, which by definition has a δ15N of 0‰. Oxygen isotope values (δ18O) 

are reported in ‰ relative to the standard VSMOW 

(Vienna Standard Mean Ocean Water), also defined as 

0‰. 

Analysis of δ15N, δ13C, and δ34S of Suspended 

POM in Water

Suspended sediment was collected with each 

sample for isotopic analysis of δ15N, δ13C, and δ34S 

of the POM. Details of suspended sediment sample 

collection and analysis are given in Battaglin and 

others (1997) and Kendall and others (2001). Approximately 1 liter of water was filtered through a 

0.7-micrometer heat-cleaned glass-fiber filter 

(142-mm diameter) with a peristaltic pump and an 

aluminum plate filter. After filtration the glass fiber 

filter was sealed in aluminum foil and a plastic bag and 

then frozen. 

In the laboratory, filters were thawed and 

scraped and the resulting material was freeze-dried 

and ground to a fine powder. After acidification 

(Kendall and others, 2001), the POM samples were 

analyzed for carbon and nitrogen isotopic and 

elemental composition on a Carlo Erba 1500 

elemental analyzer attached to a Micromass Optima 

mass spectrometer. Isotopic compositions are reported 

in per mil (‰) relative to atmospheric air for nitrogen 

and VPDB (Vienna Pee Dee Belemnite) for carbon. 

Due to problems with equipment, and in many cases 

an insufficient amount of material, POM samples were 

not analyzed for δ34S.

Nutrients and Major Ions

All samples were analyzed for nutrient concentrations including NO2 plus NO3, NO2, ammonia, 

ammonia plus organic nitrogen, orthophosphate, and 

total phosphorus. The samples were analyzed by automated colorimetric procedures (Fishman and 

Friedman, 1989) at the USGS NWQL. The method 

reporting limit for NO2 plus NO3 as N is 0.05 mg/L. 

Samples also were analyzed for calcium, chloride, 

magnesium, potassium, sodium, and sulfate by standard analytical methods (Fishman and Friedman, 

1989). 

Discharge and Physical Properties

Specific conductance, pH, and water temperature were measured at the time samples were 

collected. Water-discharge normally was measured 

with current meters. These measurements were used to 

confirm or adjust a rating for converting river stage to 

water discharge. At most stations, estimates of daily 

mean discharge for the dates of sample collection were 

calculated, and are available in the USGS Water-Data 

Reports for the states in the study area. 

GIS Data and Analysis

A geographic information system (GIS) was 

used to manage spatial information on station locations and associated drainage basins and to quantify 
16 Isotopic and Chemical Composition of Inorganic and Organic Water-Quality Samples from the Mississippi River Basin, 1997–98

land cover within the drainage basins. Land cover data 

are derived from two sources: (1) Gridded and reclassified Advanced Very High Resolution Radiometer 

(AVHRR) data (D. Wolock, U.S. Geological Survey, 

written commun., 2000), and (2) the National Land 

Cover Data (NLCD) (U.S. Geological Survey, 2000). 

The AVHRR data were used to quantify land cover in 

the large river and small stream basins; the pixels in 

the AVHRR data set are 1000 meters on a side. Estimates of percent land cover in each basin using 

AVHRR are given in tables 2, and the spatial distribution of land cover within the Mississippi River basin is 

shown in figure 1.

The NLCD data also were used to quantify land 

cover in the small stream basins. Landsat Thematic 

Mapper (TM) data and supporting information, 

including topography, census data, agricultural statistics, soil characteristics, other land-cover maps, and 

wetlands data were used to determine and label the 

land-cover type for each 30 meter pixel in the NLCD. 

Estimates of percent land cover for each small stream 

basin are given in table 3. An example of spatial distribution of land cover within one of the small-river 

basins is shown in figure 4 (plots for all 16 smaller 

river basins can be viewed in the web version of this 

report at http://wwwrcolka.cr.usgs.gov/midconherb/on.line.rep.html).

Quality Assurance

Sample Collection

Quality assurance (QA) samples were collected 

at selected stations to assess the variability and bias of 

the measured isotope ratios. Eighteen pairs of fieldcollected QA samples were analyzed for δ15N and 

δ18O of NO3 in water and eight pairs were analyzed 

for δ15N and δ13C of the suspended POM. All QA 

samples were concurrent duplicates, which are two 

samples collected concurrently in the same location 

but processed, handled, and analyzed separately. 

NO3 in Water Isotope Analysis

Details of laboratory QA procedures used for 

isotope analysis are reported in Kendall and Grim 

(1990), Chang and others, (1999), and Silva and 

others, (2000). The standard error (Iman and Conover, 

1983) of analysis of laboratory standards for δ15N of 

NO3 was ±0.05‰ (n=10), and for δ18O of NO3 was 

±0.21‰ (n=19). For simulated field samples (a solution containing KNO3 reagent and DOC in deionized 

water), the standard error (n=12) was ±0.07‰ for 

δ15N and ±0.36‰ for δ18O (Chang and others, 1999). 

Eighteen pairs of concurrent duplicate water samples 

collected during this study are used to identify both 

sampling and laboratory precision (variability) NO3

concentration, and for δ15N and δ18O of NO3 values 

reported in this study. These include duplicate samples 

collected in 1997–98 from stations on both large rivers 

and smaller streams (Battaglin and others, 1997). The 

standard error of the differences between the pairs of 

samples is ±0.11 mg/L for NO3 (n=11), ±0.22‰ for 

δ15N of NO3 (n=16), and ±0.58‰ for δ18O of NO3

(n=18). The distributions of the difference values are 

shown in figure 5(a). The mean of the differences 

between NO3 concentrations is 0.18 mg/L, between 

δ15N values is 0.38‰, and between δ18O values is 

1.6‰. The standard errors for δ15N and δ18O quantified from QA samples are significantly larger than 

those from laboratory standards or simulated field 

samples. This difference suggests either that sample 

handling introduces significant variability, or that 

matrix effects in natural waters from the Mississippi 

basin are more difficult to account for than those of 

snowmelt samples, for which the analytical method 

was originally developed. 

Particulate Organic Material Isotope Analysis

Details of laboratory QA procedures used for 

isotope analysis of POM samples are reported in 

Kendall and others (2001). Analytical precision for 

laboratory standards is ±0.15 ‰ for both δ15N and 

δ13C of POM (Kendall and others, 2001). Eight pairs 

of concurrent duplicate QA samples are used to identify sampling and laboratory precision (variability) for 

δ15N and δ13C of POM values. The standard error of 

the differences between the pairs of samples is 

±0.30‰ for δ15N (n=7) and ±0.31‰ for δ13C (n=8). 

Distributions of the difference values are shown in 

figure 5(b). The mean of the absolute value of differences between δ15N values is 0.60‰ and between 

δ13C values is 0.71‰. The standard errors for δ15N 

and δ13C of POM from QA samples are significantly 

larger than those from laboratory standards. This is 

probably caused by insufficient homogenization of the 

POM samples.
METHODS 17

Sugar Creek at New Providence, IN

Station No. 03361650

Drainage area = 243 square kilometers

0

0 5 KILOMETERS

3 MILES

INDIANA

Map Location

LAND COVER LAND COVER PERCENTAGES

2.1% developed land

92.0% cultivated land

4.9% forest land

0.7% wetlands

0.3% open water

DEVELOPED LAND

Low intensity residential

High intensity residential

Commercial/industrial/

 transportation

PLANTED/CULTIVATED LAND

Pasture/hay

Row crops

Small grains

Fallow

Urban/recreational grasses

Orchards/vineyards/other

NATURAL/SEMI-NATURAL

VEGETATION

Herbaceous grasslands

Shrubland

FORESTED UPLAND

Deciduous forest

Evergreen forest

Mixed forest

WATER

Open water

Perennial ice/snow

WETLAND

Woody wetlands

Herbaceous wetland

BARREN LAND

Bare rock below tree limit

Strip mines, quarries, pits

Transitional land

Figure 4. Land cover in the Sugar Creek at New Providence, Indiana, basin.
18 Isotopic and Chemical Composition of Inorganic and Organic Water-Quality Samples from the Mississippi River Basin, 1997–98

A B

Water 

Samples

Sediment

Samples

ABSOLUTE DIFFERENCES

ABSOLUTE DIFFERENCES,

IN PER MIL

Nitrate plus Nitrite, in

milligrams per liter

δ15N

in per mil

δ18O

in per mil δ15N δ13C

n=11

n=16

n=7 n=8

n=18

5.0

2.5

0.0

-2.5

-5.0

-7.5

5.0

2.5

0.0

-2.5

-5.0

RESULTS

δ15N and δ18O of NO3 Isotope Ratio Values 

The δ15N and δ18O of NO3 isotope ratio values, 

the concentration of NO2 plus NO3 from the lowlevel (Ocala) analysis, and the daily mean discharge 

for samples from 1997 and 1998 are listed in table 4, 

and statistically summarized in table 5. Discharge 

measurements ranged from 2.1 to 1,266,000 cubic feet 

per second (cfs). The concentration of NO2 plus 

NO3 ranged from less than the reporting limit of 

0.002 mg/L to 18.0 mg/L. The δ15N values ranged 

from –1.4‰ to +15.5‰, while the δ18O values ranged 

from +3.0‰ to +43.5‰ (table 5). In the following 

sections, the results are analyzed by drainage basin 

size (large basins verses small basins) and for the 

small basins, by dominant land cover type within the 

drainage basin. 

Large Rivers

The largest discharge values (6,840 to 1,266,000 

ft3

/s) are from the large river stations. The ranges of 

NO2 plus NO3 concentrations and isotope ratio values 

from the large river stations are generally narrow and 

near the middle of their ranges in measurements from 

all stations. The concentration of NO2 plus NO3

ranges from 0.2 to 3.6 mg/L, the δ15N of NO3 values 

range from +2.8‰ to +12.4‰, and the δ18O of NO3

values range from +3.0‰ to +24.0‰ (table 5). The 

fact that the isotope ratio values from the large river 

stations are within the range of values in smaller 

streams supports the theory that N exported from tributaries is not significantly altered by denitrification in 

the Mississippi and its major tributaries (Goolsby and 

others, 1999; Alexander and others, 2000).

Time-series plots of the data should show 

whether there are significant temporal and spatial variations in NO3 δ15N and δ18O of NO3 values in 

Mississippi River water and its major tributaries. 

There are insufficient data from 1997 to identify a 

temporal trend in the results (fig. 6). However, the 

δ15N and δ18O of NO3 values (fig. 6b and 6c) from 

the most up-stream station, the Mississippi River at 

Clinton (fig. 3, map no. 1), are distinct from the values 

at down stream stations such as the Mississippi River 

at St. Francisville (fig. 3, map no. 6a). Looking at the 

samples from the first Lagrangian set (collected in 

June, 1997), one can also see that the δ15N of NO3

Figure 5. Differences between: (A) NO2 plus NO3 concentrations (in mg/L), and δ15N and δ18O of NO3 values (in per 

mil) in 18 pairs of concurrent duplicate water samples; and (B) δ15N and δ13C of POM values (in per mil) in 8 pairs of 

field collected concurrent duplicate sediment samples. 
RESULTS 19

values from the Mississippi River at Thebes (+6.9‰), 

and the Ohio River at Grand Chain (+3.1‰) are 

substantially different and bracket the values from 

St. Francisville (+4.0‰) and Belle Chasse (+3.4‰) 

(fig. 6b). The δ18O of NO3 values from the Mississippi River at Thebes (+7.5‰) and the Ohio River at 

Grand Chain (+7.0‰) are similar, and are approximately equal to the values from the St. Francisville 

(+7.5‰) and Belle Chasse (+7.5‰) stations (fig. 6c). 

These results support the theory that denitrification does not remove much of the NO3 transported by 

the Mississippi River. However, the NO3 concentration 

and resulting flux data conflict. NO3 concentrations in 

samples from the Mississippi River at Thebes and the 

Ohio River at Grand Chain (2.55 mg/L and 2.47 mg/L, 

respectively in samples IS–101 and IS–102; table 4) 

are greater than those in samples from the Mississippi 

River at St. Francisville and Belle Chasse (2.01 mg/L 

and 1.81 mg/L, respectively in samples IS–106 and 

IS–105; figure 6d and table 4). The sum of the NO3

fluxes from samples IS–101, IS–102, and IS–103 

(Yazoo River) is ~4% larger than the flux calculated 

from sample IS–106 from the Mississippi River at St. 

Francisville, even though the sum of the discharges 

from the three samples is smaller (Battaglin and 

others, 2001). This difference suggests a mechanism 

other than denitrification decreases NO3 flux in the 

lower Mississippi River. Battaglin and others (2001) 

provide a more complete analysis of the two sets of 

Lagrangian samples and suggest that assimilation by 

aquatic and riparian plants is a likely mechanism for 

that loss. 

Temporal variability can be observed in the 

1998 data (fig. 7) from the large river stations. In some 

Table 5. Statistical summary of δ15N and δ18O of nitrate values, nitrite plus nitrate concentrations, and daily mean discharges 

in water sampled collected in 1997–98

Parameter Number of 

analyses

Minimum 

value

Maximum 

value Mean value Median value

Standard

deviation

All stations

Nitrite plus nitrate, in mg/L 124 <0.002 18.0 4.3 1.8 4.83

δ15N, in per mil 115 -1.4 15.5 7.3 7.4 3.21

δ18O, in per mil 111 3.0 43.5 10.6 9.0 6.08

Daily mean discharge, in cfs 122 2.1 1,266,000 156,660 232 331,040

Large river stations

Nitrite plus nitrate, in mg/L 46 0.2 3.6 1.6 1.4 0.87

δ15N, in per mil 41 2.8 12.4 7.5 7.8 2.46

δ18O, in per mil 41 3.0 24.0 11.1 10.5 4.31

Daily mean discharge, in cfs 46 6,840 1,266,000 415,220 253,500 430,079

Small stream stations with basins dominated by row crop agriculture and/or livestock production

Nitrite plus nitrate, in mg/L 22 0.4 15.4 6.2 6.9 3.98

δ15N, in per mil 22 5.3 13.4 9.6 9.5 2.54

δ18O, in per mil 22 5.0 13.5 8.8 9.0 2.37

Daily mean discharge, in cfs 21 10 833 162 37 238

Small stream stations with basins dominated by row crop agriculture

Nitrite plus nitrate, in mg/L 38 0.01 18.0 8.4 8.8 5.60

δ15N, in per mil 35 3.1 12.3 7.2 6.3 2.66

δ18O, in per mil 34 3.5 43.5 8.8 7.3 7.11

Daily mean discharge, in cfs 37 2.1 2,080 190 97 354

Small stream stations with basins dominated by urban land

Nitrite plus nitrate, in mg/L 9 0.2 1.3 0.58 0.51 0.35

δ15N, in per mil 9 -1.2 15.5 3.8 2.4 4.81

δ18O, in per mil 7 4.0 31.0 20.5 21.5 8.33

Daily mean discharge, in cfs 9 4.0 305 69 44 97

Small stream stations with basins dominated by undeveloped land

Nitrite plus nitrate, in mg/L 9 0.02 0.50 0.25 0.14 0.21

δ15N, in per mil 8 -1.4 8.1 4.2 4.6 2.88

δ18O, in per mil 7 6.0 20.0 13.4 14.0 5.45

Daily mean discharge, in cfs 9 51 458 200 219 117
20 Isotopic and Chemical Composition of Inorganic and Organic Water-Quality Samples from the Mississippi River Basin, 1997–98

δ15N

δ15N, IN PER MIL

5

15

10

0

4/1/97 7/1/97 10/1/97

DATE

B

0

1.0

1.5

2.0

0.5

4/1/97 7/1/97 10/1/97

DATE

A

Discharge

DISCHARGE, IN MILLION

CUBIC FEET PER SECOND

Figure 6. Time series of 1997 data for large river stations; (A) discharge, (B) δ15N, (C) δ18O, and 

(D) NO2 plus NO3.
RESULTS 21

C

D

25

20

15

10

5

0

4/1/97 7/1/97 10/1/97

DATE

δ15O, IN PER MIL

δ18O

4/1/97 7/1/97 10/1/97

DATE

Nitrite plus nitrate

NITRITE PLUS NITRATE, IN

MILLIGRAMS PER LITER

5.0

4.0

3.0

2.0

1.0

0

Map No.

1 234

5 6a 6b 6c

Figure 6. Time series of 1997 data for large river stations; (A) discharge, (B) δ15N, (C) δ18O, and (D) 

NO2 plus NO3 —Continued.
22 Isotopic and Chemical Composition of Inorganic and Organic Water-Quality Samples from the Mississippi River Basin, 1997–98

0

1.0

1.5

2.0

0.5

4/1/98 7/1/98 10/1/98

DATE

A

Discharge

DISCHARGE, IN MILLION

CUBIC FEET PER SECOND

δ15N

δ15N, IN PER MIL

5

15

10

0

4/1/98 7/1/98 10/1/98

DATE

B

Figure 7. Time series of 1998 data for large river stations; (A) discharge, (B) δ15N, (C) δ18O, and (D) NO2

plus NO3.
RESULTS 23

C

25

20

15

10

5

0

4/1/98 7/1/98 10/1/98

DATE

δ15O, IN PER MIL

δ18O

D

4/1/98 7/1/98 10/1/98

DATE

Nitrite plus nitrate

NITRITE PLUS NITRATE, IN

MILLIGRAMS PER LITER

5.0

4.0

3.0

2.0

1.0

0

Map No.

1 234

5 6a 6b 6c

Figure 7. Time series of 1998 data for large river stations; (A) discharge, (B) δ15N, (C) δ18O, and (D) NO2

plus NO3.—Continued.
24 Isotopic and Chemical Composition of Inorganic and Organic Water-Quality Samples from the Mississippi River Basin, 1997–98

cases, both δ15N and δ18O of NO3 values show a 

slight upward trend from April to September 1998, 

while NO3 concentrations show a slight decreasing 

trend. The minor temporal differences in isotope 

values could be the result of mixing between or 

changing of NO3 sources, or increased transformation 

of NO3. The discharge decreased between April and 

September 1998 at most of the large river stations 

(fig. 7a). The surface-runoff component of stream flow 

is likely more dominant during spring and early 

summer, whereas the ground-water component of 

stream flow is more dominant under low-flow conditions in late summer and fall (Winter and others, 

1998). Surface-runoff would be more likely to 

contribute recently applied fertilizer NO3 or recently 

mineralized NO3, while ground water would be more 

likely to contribute NO3 that was applied to fields or 

mineralized months, years, or decades ago (BÖhlke 

and Denver, 1995).

 Spatial variations in δ15N and δ18O of NO3

values and NO3 concentration in water from the 

Mississippi River and its major tributaries are also 

apparent (fig. 7). Nitrate concentrations are nearly 

always largest in the Mississippi River at Thebes (map 

no. 3) and smallest in the Yazoo River near Long Lake 

(map no. 5). The δ15N and δ18O of NO3 values from 

the Mississippi River at Thebes (map no. 3), and the 

Ohio River at Grand Chain (map no. 4) stations are 

substantially different and again bracket the values 

from the Mississippi River at St. Francisville 

(map no. 6a). 

Small Streams

The δ15N and δ18O of NO3 isotope ratio values, 

the concentration of NO2 plus NO3, and the daily 

mean discharge for samples collected from small 

streams in 1997 and 1998 are given in table 4. A statistical summary of the small stream results, analyzed by 

the predominant land cover type in the drainage 

basins, is given in table 5. Discharge at stations in 

basins dominated by row crop agriculture and undeveloped land tended to be slightly higher than discharge 

at stations in basins dominated by urban land or row 

crops and/or livestock production (table 5; fig. 9a and 

10a). This variability is likely a result of differences in 

basin size and local climatic variability, not directly a 

function of the land cover in the drainage basins. 

We hypothesized that NO3 in small streams 

draining areas dominated by distinctly different land 

use (corn and soybean production, livestock production, urban land, or undeveloped land) would have 

distinctly different δ15N and δ18O of NO3 isotope 

ratio values (Battaglin and others, 1997). In figure 8, 

the ranges of NO2 plus NO3 concentrations and δ15N 

and δ18O of NO3 values for samples from basins 

dominated by the four land cover types are shown in 

boxplots (Helsel and Hirsch, 1992). NO2 plus NO3

concentrations are significantly smaller in basins 

dominated by urban and undeveloped land compared 

to those dominated by row crops or row crops and/or 

livestock production. The maximum NO3 concentration in basins dominated by urban or undeveloped land 

(1.12 mg/L) is exceeded by more than 75% of samples 

from basins dominated by row crops or row crops 

and/or livestock production (table 5, fig. 8). There is a 

difference in δ15N of NO3 values between basins 

dominated by urban or undeveloped land, and basins 

dominated by row crops or row crops and/or livestock 

production. The majority of δ15N of NO3 values from 

basins dominated by urban or undeveloped land are 

less than +5‰, while the majority of values from 

basins dominated by row crops or row crops and/or 

livestock production are greater than +5‰ (fig. 8). 

However, the range of δ15N of NO3 values from just 

the basins dominated by urban land nearly span the 

entire range of the data (table 5). There is also a difference in δ18O of NO3 values between basins dominated 

by urban or undeveloped land, and those dominated by 

row crops or row crops and/or livestock production. 

The majority of the δ18O of NO3 values from basins 

dominated by urban or undeveloped land are greater 

than +10‰, while the majority of values from basins 

dominated by row crops or row crops and/or livestock 

production are less than +10‰ (fig. 8). The range of 

δ18O of NO3 values from basins dominated by rowcrops nearly span the entire range of the data (table 5). 

 Time-series plots should show if there are 

significant temporal and spatial variations in δ15N and 

δ18O of NO3 values in small streams sampled in 1997 

and 1998. There are insufficient data from 1997 to 

identify a temporal trend in the results (fig. 9), but 

some spatial variability is evident. δ15N of NO3 values 

from basins dominated by row crops (open circles) and 

row crop and/or livestock production (filled circles) 

tend to be greater than values from basins dominated 

by urban land (squares) or undeveloped land (triangles) (fig. 9b). The opposite pattern is evident for δ18O 

of NO3; values from basins dominated by urban or 

undeveloped land are greater than values from basins 
RESULTS 25

DOMINANT BASIN LAND COVER

CONCENTRATION IN MILLIGRAMS PER LITER

OR ISOTOPE RATIO IN PER MIL

Nitrite plus nitrate

δ18O

δ15N

dominated by row crops or row crops and/or livestock 

production (fig. 9c). NO2 plus NO3 concentrations in 

samples from basins dominated by row crops and row 

crops and/or livestock production are all greater than 

5 mg/L while values from basins dominated by urban 

or undeveloped land are less than 1.5 mg/L (fig. 9d; 

table 5). 

Some temporal variability is apparent in the 

1998 data from the small stream stations. At some 

stations, δ15N and δ18O of NO3 values decrease from 

January to May, then increase from May through 

September, 1998 (fig. 10b and 10c). NO2 plus NO3

concentrations show the opposite pattern, increasing 

from January to May, then decreasing from May 

Figure 8. δ15N and δ18O of NO3 values and NO2 plus NO3 concentrations from small streams by 

dominant basin land cover type, 1997–1998. {UR, urban land; UN, undeveloped land; RC, row 

crop land; and RL row crop and/or livestock production.}
26 Isotopic and Chemical Composition of Inorganic and Organic Water-Quality Samples from the Mississippi River Basin, 1997–98

δ15N

δ15N, IN PER MIL

5

20

15

10

-5

0

6/1/97 9/1/97 12/1/97

DATE

B

400

300

200

100

0

6/1/97 9/1/97 12/1/97

DATE

A

Discharge

DISCHARGE, IN 

CUBIC FEET PER SECOND

Figure 9. Time series of 1997 data for small stream stations; (A) discharge, (B) δ15N, (C) δ18O, and (D) NO2

plus NO3.
RESULTS 27

C

35

30

25

20

5

10

15

0

6/1/97 9/1/97 12/1/97

DATE

δ18O, IN PER MIL

δ18O

D

6/1/97 9/1/97 12/1/97

DATE

Nitrite plus nitrate

NITRITE PLUS NITRATE, IN

MILLIGRAMS PER LITER

20

15

10

5

0

Figure 9. Time series of 1997 data for small stream stations; (A) discharge, (B) δ15N, (C) δ18O, and 

(D) NO2 plus NO3—Continued.
28 Isotopic and Chemical Composition of Inorganic and Organic Water-Quality Samples from the Mississippi River Basin, 1997–98

δ15N

δ15N, IN PER MIL

5

-5

15

20

10

0

B

0

600

800

1,000

400

200

1/1/98 4/1/98 7/1/98 10/1/98

DATE

1/1/98 4/1/98 7/1/98 10/1/98

DATE

A

Discharge

DISCHARGE, IN 

CUBIC FEET PER SECOND

Figure 10. Time series of 1998 data for small stream stations; (A) discharge, (B) δ15N, (C) δ18O, and 

(D) NO2 plus NO3.
RESULTS 29

C

D

45

40

35

30

10

5

20

15

25

0

1/1/98 4/1/98 7/1/98 10/1/98

DATE

1/1/98 4/1/98 7/1/98 10/1/98

DATE

δ18O, IN PER MIL

δ18O

Nitrite plus nitrate

NITRITE PLUS NITRATE, IN

MILLIGRAMS PER LITER

20

15

10

5

0

Map No.

Figure 10. Time series of 1998 data for small stream stations; (A) discharge, (B) δ15N, (C) δ18O, and 

(D) NO2 plus NO3—Continued.
30 Isotopic and Chemical Composition of Inorganic and Organic Water-Quality Samples from the Mississippi River Basin, 1997–98

through September (fig. 10d). The variability in δ15N 

and δ18O of NO3 values with respect to dominant 

basin type in 1998 is similar to that in 1997. The δ15N 

of NO3 values from drainage basins dominated by row 

crops and row crop and/or livestock production tend to 

be greater than values from drainage basins dominated 

by urban or undeveloped land (fig. 10b). The δ18O of 

NO3 values from basins dominated by urban or undeveloped land tend to be greater than values from basins 

dominated by row crops or row crops and/or livestock 

production (figure 10c). Most of the NO2 plus NO3

concentrations from stations with drainage basins 

dominated by row crops and row crop and/or livestock 

production are higher than 5 mg/L, while values from 

stations with drainage basins dominated by urban or 

undeveloped land are all less than 1.5 mg/L (fig. 10d; 

table 5). 

δ15N and δ13C of POM Isotope Ratio Values

The δ15N and δ13C of POM isotope ratio values 

in suspended sediment for samples from 1997 and 

1998 are listed in table 6, and statistically summarized 

in table 7. In this study, δ15N of POM values ranged 

from –1.2‰ to +12.1‰, while δ13C of POM values 

ranged from –33.2‰ to –17.3‰ (table 7). There was 

considerable and unexpected temporal and spatial 

variation in the δ15N and δ13C of POM values from 

the Mississippi basin. Below the POM isotope data are 

analyzed by drainage basin size (large basins 

compared to small basins), and for the small basins, by 

dominant land cover type within the drainage basin. 

Large Rivers

The δ15N of POM values range from +2.5‰

to +12.1‰, and δ13C of POM values range from 

–31.3‰ to –19.3‰ (table 7; fig. 11). Isotope values 

measured in the large rivers are near the high end of all 

measurements for δ15N of POM and near the middle 

range of all measurements for δ13C of POM. The 

distribution of δ15N POM values from large river 

stations appears to match the values from basins dominated by row crops or row crops and/or livestock 

production (fig. 11), suggesting that the bulk of particulate organic nitrogen in large rivers originates in agricultural watersheds. δ13C of POM values from large 

river stations are more intermediate being generally 

between values from basins dominated by urban or 

undeveloped land and those from basins dominated by 

row crops or row crops and/or livestock production. 

The δ13C of POM values for the stations on the Lower 

Mississippi River (map numbers 6a and 6c in fig. 3) 

ranged from –31.3‰ to –22.7‰, with an average of 

–25.9‰ in 10 samples (table 6). Previous studies 

(Goni and others, 1998; Onstad and others, 2000) had 

insufficiently sampled POM and sediment in the 

Mississippi Basin, and had estimated that the δ13C of 

POM value for Mississippi River was about –20‰. 

They had concluded that terrestrial soil and C4 plant 

debris were the dominant sources of carbon to the gulf. 

The data reported here indicate that the dominant 

source of carbon is more biologically labile aquatic 

plants (algae, macrophyte debris, and heterotrophic 

bacteria). The difference between these results could 

effect models of sedimentation in the gulf and global 

carbon models. 

Small Streams

We hypothesized that POM in small streams 

draining areas of distinctly different land use would 

have distinctly different δ15N and δ13C of POM 

values (Battaglin and others, 1997). Boxplots of δ15N 

and δ13C of POM values (fig. 11) from stations with 

basins dominated by the four land cover types (and the 

large river stations), show a clear difference in POM 

isotope ratio values between basins dominated by 

urban or undeveloped land and basins dominated row 

crops or row crops and/or livestock production. As 

with δ15N of NO3, the majority of δ15N of POM 

values from basins dominated by urban or undeveloped land are less than +5‰, while the majority of 

values from basins dominated by row crops or row 

crops and/or livestock production are greater than 

+5‰ (fig. 11). The difference in δ13C of POM values 

between basins dominated by urban or undeveloped 

land and basins dominated by row crops or row crops 

and/or livestock production is less distinct. The 

majority of δ13C of POM values from basins dominated by urban or undeveloped land are less than 

–25‰, while the majority of values from basins dominated by row crops or row crops and/or livestock 

production are greater than –25‰ (fig. 11). The δ13C 

of POM values from basins dominated by row-crops 

nearly span the entire data set (table 7). 
RESULTS 31

Table 6. The δ15N and δ13C of particulate organic material in suspended-sediment samples (*, sample not

collected; #, analysis not completed; $, insufficient sample material; sample ID’s that begin with XX-, matching 

NO3 isotope analysis is not available) collected in 1997–98

Sampling station name

and station number

Sample 

ID

Sample

collection

date

Average

δ15N

Average

δ13C

Large river stations

Mississippi River at Clinton, IA - 05420500 XX-29 2/19/97 4.6 -23.3

XX-44 3/19/97 4.4 -26.4

IS-119 6/2/97 7.6 -25.6

XX-99 6/27/97 6.2 -23.6

IS-112 9/2/97 * *

IS-33 5/13/98 6.2 -26.8

IS-34 5/13/98 6.1 -26.5

IS-42 5/27/98 5.8 -27.9

IS-56 6/10/98 * *

IS-60 7/1/98 6.0 -23.8

IS-76 7/28/98 12.1 -27.9

IS-83 8/25/98 7.0 -26.2

IS-84 8/25/98 7.5 -27.0

IS-97 9/23/98 * *

Missouri River at Hermann, MO - 06934500 XX-138 10/15/97 6.7 -24.3

IS-26 4/20/98 * *

IS-45 6/1/98 5.5 -19.3

IS-64 7/7/98 * *

IS-86 8/31/98 5.4 -21.6

Mississippi River at Thebes, IL - 07022000 IS-101 6/11/97 7.3 -25.1

XX-116 8/13/97 7.3 -26.5

XX-151 11/24/97 3.6 -24.9

IS-25 4/16/98 * *

IS-50 6/10/98 5.5 -21.6

IS-51 6/10/98 # #

IS-74 7/22/98 * *

IS-91 9/9/98 8.8 -25.0

Ohio River at Grand Chain, IL - 03612500 XX-22 1/22/97 4.8 -26.6

XX-24 2/11/97 3.7 -24.8

XX-64 5/14/97 4.9 -25.1

IS-102 6/12/97 5.9 -26.7

XX-124 9/4/97 7.9 -28.0

XX-142 11/6/97 7.8 -27.5

IS-27 4/23/98 4.7 -26.4

IS-44 6/5/98 5.9 -27.4

IS-77 7/22/98 8.3 -28.4

IS-78 7/22/98 $, combined with IS-77

IS-85 8/12/98 7.7 -29.5
32 Isotopic and Chemical Composition of Inorganic and Organic Water-Quality Samples from the Mississippi River Basin, 1997–98

Large river stations—Continued

Yazoo River below Steele Bayou near Long Lake, MS - 07288955 XX-14 12/17/96 4.1 -26.0

XX-33 3/11/97 3.0 -25.8

IS-103 6/19/97 6.6 -27.1

XX-107 7/21/97 # #

XX-108 7/21/97 6.9 -28.5

IS-19 4/13/98 # #

IS-57 6/17/98 # #

IS-66 7/16/98 9.6 -29.3

IS-96 9/17/98 3.9 -27.4

Mississippi River, St. Francisville, LA - 07373420 XX-23 1/15/97 2.5 -26.5

XX-45 3/14/97 6.4 -26.5

IS-117 5/6/97 6.7 -31.3

IS-106 6/19/97 7.1 -24.8

IS-10 4/2/98 6.1 -23.8

IS-11 4/2/98 4.8 -24.7

IS-31 4/30/98 * *

IS-32 4/30/98 * *

IS-49 6/9/98 7.1 -24.9

IS-63 7/9/98 6.3 -22.7

IS-99 9/28/98 8.0 -25.7

Mississippi River at Vicksburg, MS - 07289000 IS-2A 1/13/98 * *

IS-2B 1/13/98 * *

IS-2C 1/13/98 * *

Mississippi River at Belle Chasse, LA - 07374525 IS-118 5/7/97 5.9 -27.6

IS-105 6/20/97 * *

Small stream stations

S. Fork Iowa River northeast of New Providence, IA - 05451210 IS-3a 1/30/98 * *

IS-5 3/30/98 7.6 -22.2

IS-8 3/30/98 $, combined with IS-5

IS-41 5/29/98 * *

IS-79 8/3/98 4.7 -26.0

Fourmile Creek near Traer, IA - 05464137 IS-107 6/30/97 * *

IS-20 4/15/98 4.8 -22.2

IS-67 7/16/98 4.3 -22.0

IS-80 8/12/98 4.5 -21.9

Walnut Creek near Vandalia, IA - 05487550 IS-104 6/21/97 * *

IS-9 4/3/98 4.5 -21.0

IS-28 5/7/98 4.6 -21.8

IS-29 5/7/98 3.8 -20.7

IS-54 6/11/98 5.1 -19.8

Table 6. The δ15N and δ13C of particulate organic material in suspended-sediment samples (*, sample not

collected; #, analysis not completed; $, insufficient sample material; sample ID’s that begin with XX-, matching 

NO3 isotope analysis is not available) collected in 1997–98—Continued

Sampling station name

and station number

Sample 

ID

Sample

collection

date

Average

δ15N

Average

δ13C
RESULTS 33

Small stream stations—Continued

Panther Creek near El Paso, IL - 05567000 IS-115 11/13/97 * *

IS-16 4/9/98 6.5 -23.8

IS-48 6/9/98 7.0 -24.0

IS-61 7/7/98 7.8 -23.5

Indian Creek near Wyoming, IL - 05568800 IS-111 8/27/97 * *

IS-15 4/9/98 5.3 -21.6

IS-39 5/25/98 5.8 -20.3

IS-72 7/22/98 4.9 -24.8

IS-73 7/22/98 $, combined with IS-72

Sugar Creek at Co Rd 400 S at New Palistine, IN - 03361650 IS-13 4/9/98 5.5 -26.1

IS-38 5/24/98 5.9 -25.4

Little Buck Creek near Indianapolis, IN - 03353637 IS-113 9/9/97 2.2 -26.8

IS-14 4/9/98 4.6 -26.7

IS-37 5/24/98 4.6 -26.8

IS-71 7/20/98 4.1 -28.8

North Dry Creek near Kearney, NE - 06770195 XX-70 5/27/97 6.5 -20.3

XX-71 5/27/97 6.7 -20.3

XX-106 7/17/97 8.2 -20.5

XX-114 8/11/97 9.2 -19.1

XX-147 11/19/97 6.4 -21.9

IS-6 4/1/98 5.6 -17.3

IS-40 5/22/98 5.0 -20.2

IS-43 6/8/98 6.3 -21.7

IS-92 9/9/98 6.4 -22.8

Dismal River near Thedford, NE - 06775900 IS-17 4/13/98 # #

IS-36 5/19/98 # #

IS-55 6/16/98 2.3 -25.5

IS-95 9/15/98 1.5 -26.0

South Fabius River near Taylor, MO - 05500000 IS-23 4/7/98 * *

IS-46 6/2/98 5.6 -31.1

IS-75 7/27/98 * *

IS-89 9/1/98 6.7 -31.2

Elk River near Tiff City, MO - 07189000 IS-24 4/14/98 * *

IS-52 6/9/98 $ -26.2

IS-68 7/14/98 * *

IS-87 9/2/98 $ -26.1

IS-88 9/2/98 $ -25.1

Table 6. The δ15N and δ13C of particulate organic material in suspended-sediment samples (*, sample not

collected; #, analysis not completed; $, insufficient sample material; sample ID’s that begin with XX-, matching 

NO3 isotope analysis is not available) collected in 1997–98—Continued

Sampling station name

and station number

Sample 

ID

Sample

collection

date

Average

δ15N

Average

δ13C
34 Isotopic and Chemical Composition of Inorganic and Organic Water-Quality Samples from the Mississippi River Basin, 1997–98

Small stream stations—Continued

Shingle Creek at Queen Ave. N., MN - 05288705 IS-108 7/7/97 * *

IS-12 4/6/98 2.2 -30.1

IS-30 5/8/98 1.2 -28.9

IS-53 6/11/98 1.6 -31.0

IS-62 7/8/98 0.3 -30.5

Little Cobb River near Beauford, MN - 05320270 IS-109 7/16/97 * *

IS-114 10/28/97 * *

IS-1A 1/14/98 * *

IS-4 3/30/98 5.1 -23.6

IS-7 3/30/98 6.0 -24.6

IS-35 5/18/98 6.3 -25.4

IS-70 7/15/98 6.8 -25.4

IS-90 8/17/98 * *

Namekagon River at Leonards, WI - 05331833 IS-116 11/11/97 * *

IS-21 3/30/98 -1.2 -27.5

IS-47 6/2/98 # #

IS-69 7/15/98 8.6 -27.0

IS-94 9/9/98 $ -26.7

Rattlesnake Creek near North Andover, WI - 05413449 IS-110 8/1/97 * *

IS-22 4/15/98 1.1 -26.4

IS-59 6/19/98 6.5 -23.5

IS-81 8/21/98 # - ruined in analysis

IS-82 8/21/98 $, combined with IS-81

IS-98 9/22/98 # #

Bogue Phalia near Leland, MS - 07288650 XX-25 2/6/97 4.9 -25.0

XX-53 4/28/97 5.7 -25.5

XX-68 5/21/97 5.9 -25.1

XX-89 6/18/97 5.4 -24.0

XX-103 7/9/97 9.2 -29.7

XX-131 7/9/97 9.4 -29.3

IS-18 4/14/98 7.26 -33.2

IS-58 6/18/98 7.0 -28.2

IS-65 7/15/98 4.2 -26.9

IS-93 9/16/98 7.1 -30.4

Table 6. The δ15N and δ13C of particulate organic material in suspended-sediment samples (*, sample not

collected; #, analysis not completed; $, insufficient sample material; sample ID’s that begin with XX-, matching 

NO3 isotope analysis is not available) collected in 1997–98—Continued

Sampling station name

and station number

Sample 

ID

Sample

collection

date

Average

δ15N

Average

δ13C
RESULTS 35

Concentrations of Nutrients and Major 

Ions

Nutrient concentrations for samples from 1997 

and 1998 are listed in table 8, and statistically summarized in table 9. NO2 plus NO3 concentrations ranged 

from less than 0.05 to 18.3 mg/L. Ammonia plus 

organic N concentrations ranged from less than 0.1 to 

3.42 mg/L. Dissolved organic carbon concentrations 

ranged from 0.7 to 14.0 mg/L. Orthophosphate 

concentrations ranged from less than 0.01 to 0.71 

mg/L.

Major ion concentrations for samples from 1997 

and 1998 are listed in table 10, and statistically 

summarized in table 11. Major ions, in particular 

sulfate and chloride, can compete with NO3 for sites 

on the anion exchange column. Overloading the anion 

columns with these ions can result in NO3 being preferentially displaced from the column thus biasing the 

isotope analyses (Silva and others, 2000). In samples 

from 1997 and 1998, chloride concentrations ranged 

from 0.7 to 148.3 mg/L, sulfate concentrations ranged 

from 2.6 to 339 mg/L, and sodium concentrations 

ranged from 1.4 to 69.4 mg/L.

Large Rivers

The NO2 plus NO3 concentrations in samples 

collected in 1997 and 1998 from the large river 

stations are in the middle range (0.21 to 3.78 mg/L) of 

all measurements (<0.05 to 18.3 mg/L). Ammonia 

plus organic N concentration are in the low range 

(<0.10 to 0.59 mg/L) of all measurements (<0.10 to 

3.42 mg/L). Dissolved organic carbon concentrations 

are in the middle range (2.5 to 6.6 mg/L) of all 

measurements (0.7 to 14.0 mg/L). Orthophosphate 

concentration are in the low range (<0.10 to 0.24 

mg/L) of all measurements (<0.10 to 0.71 mg/L).

Major ions concentrations in samples collected 

from the large river stations are in general towards the 

middle range of all measurements. Chloride concentrations range from 2.9 to 22.7.3 mg/L, sulfate concentrations range from 5.0 to 129.5 mg/L, and sodium 

concentrations range from 3.9 to 42.4 mg/L.

Small Streams

The median NO2 plus NO3 concentrations from 

basins dominated by row crops or row crops and/or 

livestock production (9.62 and 7.39 mg/L, respectively) are greater than median concentrations from 

Table 7. Statistical summary of δ15N and δ13C of particulate organic material values in suspended sediment samples collected 

in 1997–98 (all values in per mil) 

Parameter Number of 

analyses

Minimum 

value

Maximum 

value

Mean

value

Median

value

Standard 

deviation

All stations

δ15N in per mil 101 -1.2 12.1 5.7 5.9 2.1

δ13C in per mil 105 -33.2 -17.3 -25.4 -25.6 3.1

Large river stations

d15N in per mil 45 2.5 12.1 5.9 6.2 1.8

δ13C in per mil 45 -31.3 -19.3 -25.9 -26.4 2.2

Small stream stations with basins dominated by row crop agriculture and/or livestock production

δ15N in per mil 13 1.1 9.2 6.2 6.4 2.0

δ13C in per mil 16 -26.4 -17.3 -22.5 -22.0 2.8

Small stream stations with basins dominated by row crop agriculture

δ15N in per mil 31 3.8 9.4 5.9 5.7 1.4

δ13C in per mil 31 -33.2 -19.8 -25.1 -24.8 3.5

Small stream stations with basins dominated by urban land

δ15N in per mil 8 0.3 4.6 2.6 2.2 1.6

δ13C in per mil 8 -31.0 -26.7 -28.7 -28.9 1.8

Small stream stations with basins dominated by undeveloped land

δ15N in per mil 4 -1.2 8.6 2.8 1.9 4.2

δ13C in per mil 5 -27.5 -25.5 -26.5 -26.7 0.8
36 Isotopic and Chemical Composition of Inorganic and Organic Water-Quality Samples from the Mississippi River Basin, 1997–98

DOMINANT BASIN LAND COVER

δ15N

δ15N OR 

δ13C, IN PER MIL

δ13C

Figure 11. δ15N and δ13C of POM values by basin type, 1997–1998. {LR, large river; UR, urban 

land; UN, undeveloped land; RC, row crop land; and RL row crop and/or livestock production.}
RESULTS 37

Table 8. Nutrient concentrations in water samples collected in 1997–1998 (*, results not available; mg/L, milligrams 

per liter)

Sampling station 

name and station 

number

Sample 

ID

Sample 

collection

date

Ammonia 

as N 

(mg/L)

Ammonia 

plus 

organic N 

(mg/L)

Nitrite 

as N 

(mg/L)

Nitrite 

plus 

nitrate 

as N 

(mg/L)

Phosphorus 

(dissolve

d) as P 

(mg/L)

Orthophosphate as 

P (mg/L)

Dissolved 

organic 

carbon 

(mg/L)

Large river stations

Mississippi River at 

Clinton, IA - 

05420500

IS-119 6/2/97 <0.015 0.38 0.012 0.45 <0.010 <0.001 6.3

IS-112 9/2/97 0.049 0.47 0.024 0.91 0.142 0.100 6.1

IS-33 5/13/98 0.066 0.54 0.024 1.89 0.019 0.012 5.9

IS-34 5/13/98 0.061 0.52 0.024 1.84 0.013 0.013 6.0

IS-42 5/27/98 0.033 0.59 0.063 1.17 0.026 0.065 6.5

IS-56 6/10/98 0.138 0.52 0.051 2.00 0.048 0.007 5.2

IS-60 7/1/98 <0.020 0.47 0.146 2.80 0.132 0.141 5.0

IS-76 7/28/98 <0.020 0.46 0.023 1.53 0.090 0.126 6.4

IS-83 8/25/98 0.126 0.49 0.019 0.70 0.118 0.128 5.5

IS-84 8/25/98 . ... .. .

IS-97 9/23/98 0.125 . 0.027 0.87 0.121 0.115 5.2

Missouri River at 

Hermann, MO - 

06934500

IS-26 4/20/98 0.026 0.38 0.036 2.02 0.091 0.092 5.8

IS-45 6/1/98 0.060 0.37 0.018 2.39 0.096 0.115 4.1

IS-64 7/7/98 <0.020 0.37 <0.010 1.84 0.091 0.094 4.9

IS-86 8/31/98 <0.020 0.33 <0.010 1.29 0.135 0.135 4.6

Mississippi River at 

Thebes, IL - 

07022000

IS-101 6/11/97 0.032 0.36 0.030 2.55 0.071 0.083 6.1

IS-25 4/16/98 0.071 0.49 0.044 3.64 0.089 0.080 4.6

IS-50 6/10/98 <0.020 0.47 0.045 3.78 0.135 0.119 4.3

IS-51 6/10/98 . ... .. .

IS-74 7/22/98 <0.020 0.43 0.016 3.23 0.143 0.163 6.6

IS-91 9/9/98 <0.020 0.37 0.014 1.16 0.139 0.144 4.1

Ohio River at Grand 

Chain, IL - 03612500

IS-102 6/12/97 <0.015 0.24 0.020 2.46 0.025 0.042 3.2

IS-27 4/23/98 <0.020 0.22 0.024 1.20 0.042 0.049 3.4

IS-44 6/5/98 0.026 0.23 0.043 1.74 <0.010 0.242 2.5

IS-77 7/22/98 0.020 0.22 0.016 1.27 0.024 0.054 3.2

IS-78 7/22/98 . ... .. .

IS-85 8/12/98 0.039 0.14 0.025 0.75 0.040 0.050 2.9

Yazoo River below 

Steele Bayou near 

Long Lake, MS - 

07288955

IS-103 6/19/97 <0.015 0.33 <0.010 0.74 0.042 0.049 5.4

IS-19 4/13/98 0.059 0.29 0.014 0.37 0.033 0.036 4.4

IS-57 6/17/98 0.054 0.28 <0.010 0.81 0.063 0.060 4.4

IS-66 7/16/98 0.129 0.49 0.107 0.55 0.064 0.070 4.9

IS-96 9/17/98 0.039 0.25 0.013 0.21 0.041 0.045 3.7
38 Isotopic and Chemical Composition of Inorganic and Organic Water-Quality Samples from the Mississippi River Basin, 1997–98

Large river stations—Continued

Mississippi River, St. 

Francisville, LA - 

07373420

IS-117 5/6/97 <0.015 0.24 0.028 1.43 0.045 0.048 4.0

IS-106 6/19/97 0.015 <0.20 <0.010 2.01 0.052 0.061 3.3

IS-10 4/2/98 * *** ** *

IS-11 4/2/98 * *** ** *

IS-31 4/30/98 0.035 0.26 0.019 1.96 0.043 0.056 5.5

IS-32 4/30/98 * *** ** *

IS-49 6/9/98 0.052 0.26 0.011 2.01 0.076 0.080 3.7

IS-63 7/9/98 0.039 0.23 <0.010 2.63 0.091 0.108 3.9

IS-99 9/28/98 <0.020 * <0.010 0.92 0.088 0.079 *

Mississippi River at 

Vicksburg, MS - 

07289000

IS-2A 1/13/98 * *** ** *

IS-2B 1/13/98 * *** ** *

IS-2C 1/13/98 * *** ** *

Mississippi River at 

Belle Chasse, LA - 

07374525

IS-118 5/7/97 <0.015 0.21 0.017 1.23 0.046 0.043 3.8

IS-105 6/20/97 <0.015 <0.20 <0.010 1.81 0.086 0.066 3.6

Small stream stations

S. Fork Iowa River 

northeast of New 

Providence, IA - 

05451210

IS-3A 1/30/98 * *** ** *

IS-3B 1/30/98 * *** ** *

IS-3C 1/30/98 * *** ** *

IS-5 3/30/98 0.089 0.52 0.021 12.97 0.135 0.140 3.4

IS-8 3/30/98 0.106 0.51 0.024 13.74 0.137 0.140 3.4

IS-41 5/29/98 0.259 1.06 0.089 16.92 0.198 0.174 7.0

IS-79 8/3/98 0.047 0.41 0.051 7.58 0.016 0.031 4.0

Fourmile Creek near 

Traer, IA - 05464137

IS-107 6/30/97 0.177 0.50 0.071 14.88 0.200 0.159 2.2

IS-20 4/15/98 0.057 0.20 0.014 17.51 0.020 0.024 2.0

IS-67 7/16/98 0.052 0.17 0.032 16.39 0.013 0.016 1.7

IS-80 8/12/98 0.042 0.22 0.045 11.05 0.032 0.048 2.1

Walnut Creek near 

Vandalia, IA - 

05487550

IS-104 6/21/97 0.097 0.66 0.102 9.69 0.148 0.073 5.2

IS-9 4/3/98 0.058 0.30 0.042 13.08 0.057 0.062 3.9

IS-28 5/7/98 0.125 <0.10 0.037 9.62 0.179 0.101 4.4

IS-29 5/7/98 0.127 <0.10 0.039 9.46 0.146 0.106 4.4

IS-54 6/11/98 0.157 0.84 0.041 5.26 0.241 0.229 9.5

Panther Creek near 

El Paso, IL - 

05567000

IS-115 11/13/97 0.175 0.52 0.144 11.52 0.025 0.049 2.6

IS-16 4/9/98 0.083 0.42 0.050 18.29 0.077 0.077 2.2

IS-48 6/9/98 0.033 0.42 0.086 15.45 0.080 0.078 2.0

IS-61 7/7/98 0.058 0.67 0.059 12.35 0.232 0.226 4.0

Table 8. Nutrient concentrations in water samples collected in 1997–1998 (*, results not available; mg/L, milligrams 

per liter)—Continued

Sampling station 

name and station 

number

Sample 

ID

Sample 

collection

date

Ammonia 

as N 

(mg/L)

Ammonia 

plus 

organic N 

(mg/L)

Nitrite 

as N 

(mg/L)

Nitrite 

plus 

nitrate 

as N 

(mg/L)

Phosphorus 

(dissolve

d) as P 

(mg/L)

Orthophosphate as 

P (mg/L)

Dissolved 

organic 

carbon 

(mg/L)
RESULTS 39

Small stream stations—Continued

Indian Creek near 

Wyoming, IL - 

05568800

IS-111 8/27/97 0.025 0.27 0.042 9.65 0.117 0.085 1.7

IS-15 4/9/98 0.146 0.56 0.035 11.79 0.124 0.125 3.0

IS-39 5/25/98 0.097 0.49 0.078 12.49 0.079 0.084 4.0

IS-72 7/22/98 <0.020 0.51 0.081 7.99 0.154 0.089 3.8

IS-73 7/22/98 * *** ** *

Sugar Creek at Co Rd 

400 S at New Palistine, IN - 03361650

IS-13 4/9/98 0.058 0.62 0.019 2.25 0.075 0.072 5.6

IS-38 5/24/98 0.174 0.74 0.084 8.61 0.079 0.063 6.2

Little Buck Creek 

near Indianapolis, IN 

- 03353637

IS-113 9/9/97 0.041 0.32 0.031 0.86 0.010 0.014 4.6

IS-14 4/9/98 0.071 0.48 0.015 0.68 0.058 0.055 6.0

IS-37 5/24/98 0.129 0.60 0.042 1.12 0.050 0.051 8.8

IS-71 7/20/98 <0.020 0.40 0.044 0.63 <0.01 0.012 5.7

North Dry Creek near 

Kearney, NE - 

06770195

IS-6 4/1/98 1.897 3.42 0.244 8.33 0.806 0.714 12.0

IS-40 5/22/98 0.763 2.04 0.220 5.37 0.627 0.567 9.1

IS-43 6/8/98 0.231 0.91 0.223 7.57 0.539 0.503 6.1

IS-92 9/9/98 <0.020 0.54 0.048 7.32 0.312 0.293 4.8

Dismal River near 

Thedford, NE - 

06775900

IS-17 4/13/98 0.037 <0.10 0.011 0.46 0.137 0.144 1.4

IS-36 5/19/98 0.038 0.11 <0.010 0.48 0.132 0.150 1.3

IS-55 6/16/98 0.034 0.11 <0.010 0.39 0.124 0.011 2.2

IS-95 9/15/98 0.031 <0.10 0.015 0.51 0.127 0.135 1.7

South Fabius River 

near Taylor, MO - 

05500000

IS-23 4/7/98 0.044 0.77 0.017 0.75 0.071 0.053 6.6

IS-46 6/2/98 <0.020 * 0.023 0.62 0.021 <0.010 6.2

IS-75 7/27/98 <0.020 0.44 <0.010 0.28 <0.010 <0.010 5.1

IS-89 9/1/98 0.043 1.26 0.013 <0.05 0.156 0.013 4.7

Elk River near Tiff 

City, MO - 07189000

IS-24 4/14/98 0.029 0.13 <0.010 1.16 0.019 0.014 1.7

IS-52 6/9/98 <0.020 0.13 0.014 1.63 0.098 0.086 0.7

IS-68 7/14/98 0.059 0.13 0.017 0.86 0.111 0.113 1.1

IS-87 9/2/98 0.032 1.24 0.016 0.43 0.208 0.063 1.4

IS-88 9/2/98 * *** ** *

Shingle Creek at 

Queen Ave. N., MN - 

05288705

IS-108 7/7/97 0.206 0.74 0.030 0.24 0.042 0.032 14.0

IS-12 4/6/98 0.061 0.66 0.018 0.40 0.012 0.012 7.0

IS-30 5/8/98 0.063 0.43 0.052 0.41 <0.010 <0.010 6.1

IS-53 6/11/98 0.214 0.64 0.028 0.21 0.029 0.022 6.9

IS-62 7/8/98 0.225 0.82 0.069 0.22 0.021 0.045 7.7

Table 8. Nutrient concentrations in water samples collected in 1997–1998 (*, results not available; mg/L, milligrams 

per liter)—Continued

Sampling station 

name and station 

number

Sample 

ID

Sample 

collection

date

Ammonia 

as N 

(mg/L)

Ammonia 

plus 

organic N 

(mg/L)

Nitrite 

as N 

(mg/L)

Nitrite 

plus 

nitrate 

as N 

(mg/L)

Phosphorus 

(dissolve

d) as P 

(mg/L)

Orthophosphate as 

P (mg/L)

Dissolved 

organic 

carbon 

(mg/L)
40 Isotopic and Chemical Composition of Inorganic and Organic Water-Quality Samples from the Mississippi River Basin, 1997–98

Small stream stations—Continued

Little Cobb River 

near Beauford, MN - 

05320270

IS-109 7/16/97 <0.015 0.62 0.071 9.71 0.103 0.104 6.4

IS-114 10/28/97 <0.020 0.60 0.041 8.16 <0.010 <0.010 5.9

IS-1A 1/14/98 * * * * * * *

IS-1B 1/14/98 * * * * * * *

IS-1C 1/14/98 * * * * * * *

IS-4 3/30/98 0.074 1.03 0.067 15.03 0.239 0.216 7.7

IS-7 3/30/98 * * * * * * *

IS-35 5/18/98 0.068 0.89 0.127 16.19 0.103 0.103 6.6

IS-70 7/15/98 0.056 0.94 0.059 7.09 0.093 0.086 6.6

IS-90 8/17/98 0.037 0.89 <0.010 <0.05 0.092 0.084 8.5

Namekagon River at 

Leonards, WI - 

05331833

IS-116 11/11/97 <0.020 0.19 0.010 0.12 0.014 0.033 4.0

IS-21 3/30/98 0.057 0.43 <0.010 0.09 0.021 0.011 11.0

IS-47 6/2/98 0.023 0.39 0.017 0.07 0.021 <0.010 8.9

IS-69 7/15/98 <0.020 0.26 <0.010 <0.05 <0.010 <0.010 4.5

IS-94 9/9/98 0.045 0.12 <0.010 0.84 <0.050 <0.010 2.2

Rattlesnake Creek 

near North Andover, 

WI - 05413449

IS-110 8/1/97 0.035 0.29 0.050 5.98 0.183 0.193 3.2

IS-22 4/15/98 <0.020 0.32 0.035 7.39 0.086 0.076 2.9

IS-59 6/19/98 0.334 1.58 0.134 5.37 0.534 0.462 7.5

IS-81 8/21/98 0.116 0.55 0.068 7.57 0.209 0.220 3.0

IS-82 8/21/98 * * * * * * *

IS-98 9/22/98 0.028 0.31 0.030 8.70 0.111 0.119 2.2

Bogue Phalia near 

Leland, MS - 

07288650

IS-18 4/14/98 0.039 0.50 0.012 <0.05 0.023 0.020 5.7

IS-58 6/18/98 0.060 0.92 0.157 0.82 0.019 0.018 6.5

IS-65 7/15/98 0.377 0.91 0.276 1.09 0.093 0.087 5.0

IS-93 9/16/98 0.041 0.63 0.025 0.19 0.140 0.130 7.4

Table 8. Nutrient concentrations in water samples collected in 1997–1998 (*, results not available; mg/L, milligrams 

per liter)—Continued

Sampling station 

name and station 

number

Sample 

ID

Sample 

collection

date

Ammonia 

as N 

(mg/L)

Ammonia 

plus 

organic N 

(mg/L)

Nitrite 

as N 

(mg/L)

Nitrite 

plus 

nitrate 

as N 

(mg/L)

Phosphorus 

(dissolve

d) as P 

(mg/L)

Orthophosphate as 

P (mg/L)

Dissolved 

organic 

carbon 

(mg/L)
RESULTS 41

Table 9. Statistical summary of nutrient concentrations in water samples collected in 1997–198 (all value are in milligrams 

per liter)

Parameter

Analytical 

reporting 

limit

Number 

of

analyses

Minimum 

value

Maximum 

value

Mean 

value

Median 

value

Standard 

deviation

All stations

Ammonia as N 0.02 105 <0.02 1.90 0.09 0.04 0.20

Ammonia plus organic N 0.10 102 <0.10 3.42 0.50 0.43 0.44

Nitrite as N 0.01 105 <0.01 0.28 0.04 0.03 0.05

Nitrite plus nitrate as N 0.05 105 <0.05 18.3 4.42 1.84 5.13

Phosphorus (dissolved) as P 0.01 105 <0.01 0.81 0.10 0.08 0.12

Orthophosphate as P 0.01 105 <0.01 0.71 0.10 0.08 0.11

Dissolved organic carbon as C 0.33 105 0.7 14.0 4.8 4.6 2.4

Large river stations

Ammonia as N 0.02 37 <0.02 0.14 0.03 0.03 0.04

Ammonia plus organic N 0.10 35 <0.10 0.59 0.34 0.36 0.14

Nitrite as N 0.01 37 <0.10 0.15 0.03 0.02 0.03

Nitrite plus nitrate as N 0.05 37 0.21 3.78 1.63 1.53 0.89

Phosphorus (dissolved) as P 0.01 37 <0.01 0.14 0.07 0.06 0.04

Orthophosphate as P 0.01 37 <0.01 0.24 0.08 0.07 0.05

Dissolved organic carbon as C 0.33 36 2.5 6.6 4.7 4.6 1.1

Small stream stations with basins dominated by row crop agriculture and/or livestock production

Ammonia as N 0.02 17 <0.02 1.90 0.24 0.06 0.47

Ammonia plus organic N 0.10 17 0.13 3.42 0.83 0.52 0.86

Nitrite as N 0.01 17 <0.01 0.24 0.08 0.05 0.86

Nitrite plus nitrate as N 0.05 17 0.43 16.92 6.99 7.39 4.58

Phosphorus (dissolved) as P 0.01 17 0.02 0.81 0.25 0.18 0.23

Orthophosphate as P 0.01 17 0.01 0.71 0.23 0.14 0.21

Dissolved organic carbon as C 0.33 18 0.7 12.0 4.1 3.3 3.1

Small stream stations with basins dominated by row crop agriculture

Ammonia as N 0.02 33 <0.02 0.38 0.08 0.06 0.08

Ammonia plus organic N 0.10 32 <0.10 1.26 0.58 0.58 0.30

Nitrite as N 0.01 33 <0.01 0.28 0.06 0.04 0.05

Nitrite plus nitrate as N 0.05 33 <0.05 18.29 8.40 9.62 6.01

Phosphorus (dissolved) as P 0.01 33 <0.01 0.24 0.10 0.09 0.07

Orthophosphate as P 0.01 33 <0.02 0.23 0.08 0.08 0.06

Dissolved organic carbon as C 0.33 33 1.7 9.5 4.8 5.0 2.1

Small stream stations with basins dominated by urban land

Ammonia as N 0.02 9 <0.02 0.23 0.11 0.07 0.08

Ammonia plus organic N 0.10 9 0.32 0.82 0.56 0.60 0.17

Nitrite as N 0.01 9 0.02 0.07 0.04 0.03 0.02

Nitrite plus nitrate as N 0.05 9 0.21 1.12 0.53 0.41 0.32

Phosphorus (dissolved) as P 0.01 9 <0.01 0.06 0.02 0.02 0.02

Orthophosphate as P 0.01 9 <0.01 0.06 0.03 0.02 0.02

Dissolved organic carbon as C 0.33 9 4.6 14.0 7.4 6.9 2.7

Small stream stations with basins dominated by undeveloped land

Ammonia as N 0.02 9 <0.02 0.06 0.03 0.03 0.02

Ammonia plus organic N 0.10 9 <0.10 0.43 0.18 0.12 0.15

Nitrite as N 0.01 9 <0.01 0.02 0.01 <0.01 0.01

Nitrite plus nitrate as N 0.05 9 <0.05 0.84 0.33 0.39 0.28

Phosphorus (dissolved) as P 0.01 9 <0.01 0.14 0.06 0.02 0.06

Orthophosphate as P 0.01 9 <0.01 0.15 0.05 0.01 0.07

Dissolved organic carbon as C 0.33 9 1.3 11.0 4.1 2.2 3.5
42 Isotopic and Chemical Composition of Inorganic and Organic Water-Quality Samples from the Mississippi River Basin, 1997–98

Table 10. Major ion concentrations in water samples collected in 1997–1998 (mg/L, milligrams per liter; *, results 

not available)

Sampling station 

name and station 

number

Sample 

ID

Sample 

collection date

Calcium 

(mg/L)

Chloride 

(mg/L)

Magnesium 

(mg/L)

Potassium 

(mg/L)

Sodium 

(mg/L)

Sulfate 

(mg/L)

Large River Stations

Mississippi River at 

Clinton, IA - 05420500

IS-119 6/2/97 41.2 12.8 19.1 2.50 8.9 48.7

IS-112 9/2/97 42.8 14.1 18.3 2.52 9.4 30.3

IS-33 5/13/98 45.1 14.6 23.0 2.57 9.7 58.6

IS-34 5/13/98 * 14.6 * * * 58.8

IS-42 5/27/98 44.9 15.3 22.0 2.70 9.9 51.3

IS-56 6/10/98 47.8 16.9 21.5 2.54 10.3 43.4

IS-60 7/1/98 45.5 13.7 18.0 2.94 8.4 31.0

IS-76 7/28/98 44.6 13.7 19.1 0.28 7.6 26.3

IS-83 8/25/98 42.3 13.1 19.1 2.29 8.3 21.3

IS-84 8/25/98 * * * * * *

IS-97 9/23/98 43.2 15.1 21.2 2.56 9.5 23.3

Missouri River at Hermann, MO - 06934500IS-26 4/20/98 58.6 17.6 16.7 5.59 26.2 87.4

IS-45 6/1/98 61.9 19.7 20.2 6.13 42.3 129.4

IS-64 7/7/98 47.3 14.1 13.4 5.46 24.9 74.9

IS-86 8/31/98 47.0 17.1 15.8 6.11 37.3 104.2

Mississippi River at 

Thebes, IL - 07022000

IS-101 6/11/97 58.4 19.5 22.5 4.70 30.2 97.3

IS-25 4/16/98 47.1 17.0 15.7 3.73 14.7 44.0

IS-50 6/10/98 49.0 20.8 18.4 4.11 19.1 58.5

IS-51 6/10/98 * * * * * *

IS-74 7/22/98 54.9 18.5 18.8 4.32 18.7 51.6

IS-91 9/9/98 52.0 21.9 19.6 5.57 30.7 84.1

Ohio River at Grand 

Chain, IL - 03612500

IS-102 6/12/97 33.5 10.6 7.7 2.65 7.2 31.5

IS-27 4/23/98 32.8 9.7 7.2 2.30 7.1 29.5

IS-44 6/5/98 36.4 11.2 9.7 2.53 8.5 34.2

IS-77 7/22/98 32.9 11.0 9.0 2.93 7.8 30.0

IS-78 7/22/98 * * * * * *

IS-85 8/12/98 29.3 10.4 7.1 2.65 7.5 23.7

Yazoo River below 

Steele Bayou near 

Long Lake, MS - 

07288955

IS-103 6/19/97 7.9 2.8 2.6 2.94 3.8 4.9

IS-19 4/13/98 7.8 3.9 2.7 2.07 4.9 7.2

IS-57 6/17/98 11.9 4.5 4.0 2.94 6.2 7.6

IS-66 7/16/98 27.8 10.1 9.7 3.82 15.2 16.0

IS-96 9/17/98 16.6 5.7 6.0 2.81 9.0 9.4

Mississippi River, St. 

Francisville, LA - 

07373420

IS-117 5/6/97 33.0 17.1 10.5 3.27 15.7 45.8

IS-106 6/19/97 36.4 16.0 10.6 3.17 14.9 50.5

IS-10 4/2/98 * * * * * *

IS-11 4/2/98 * * * * * *

IS-31 4/30/98 37.4 14.5 10.9 3.36 12.2 35.2

IS-32 4/30/98 * * * * * *

IS-49 6/9/98 40.0 16.4 13.1 3.29 15.0 45.4

IS-63 7/9/98 40.3 13.1 12.2 3.62 11.1 31.8

IS-99 9/28/98 43.1 22.7 14.5 3.69 23.4 58.1

Mississippi River at 

Vicksburg, MS - 

07289000

IS-2A 1/13/98 * * * * * *

IS-2B 1/13/98 * * * * * *

IS-2C 1/13/98 * * * * * *
RESULTS 43

Large river stations—Continued

Mississippi River at 

Belle Chasse, LA - 

07374525

IS-118 5/7/97 * * * * * *

IS-105 6/20/97 * * * * * *

Small stream stations

S. Fork Iowa River 

northeast of New Providence, IA - 05451210

IS-3A 1/30/98 83.3 18.9 29.4 2.14 9.2 28.1

IS-3B 1/30/98 * * * * * *

IS-3C 1/30/98 * * * * * *

IS-5 3/30/98 89.7 24.4 27.1 1.90 7.9 26.4

IS-8 3/30/98 87.8 25.3 26.5 1.88 7.7 26.2

IS-41 5/29/98 69.4 14.8 19.6 3.04 3.7 13.6

IS-79 8/3/98 74.4 16.3 29.6 2.06 7.0 24.2

Fourmile Creek near 

Traer, IA - 05464137

IS-107 6/30/97 68.3 17.7 23.1 1.84 7.0 20.4

IS-20 4/15/98 60.6 17.1 20.4 0.81 6.4 18.6

IS-67 7/16/98 63.8 13.7 21.6 0.55 6.7 16.8

IS-80 8/12/98 68.3 13.2 22.9 0.78 6.9 18.2

Walnut Creek near 

Vandalia, IA - 

05487550

IS-104 6/21/97 47.7 12.1 17.2 2.35 5.3 16.8

IS-9 4/3/98 53.9 12.3 19.2 1.42 6.0 21.0

IS-28 5/7/98 * * * * * *

IS-29 5/7/98 * 9.6 * * * 16.1

IS-54 6/11/98 24.7 5.4 7.9 6.00 3.3 7.9

Panther Creek near El 

Paso, IL - 05567000

IS-115 11/13/97 94.8 58.5 41.6 2.78 23.0 49.1

IS-16 4/9/98 80.9 36.2 35.2 1.32 11.4 40.7

IS-48 6/9/98 79.4 35.2 35.4 1.38 14.5 41.6

IS-61 7/7/98 61.3 23.7 26.8 3.22 9.5 30.9

Indian Creek near 

Wyoming, IL - 

05568800

IS-111 8/27/97 99.4 23.7 36.3 1.15 13.2 38.8

IS-15 4/9/98 67.2 17.4 27.4 1.86 8.3 27.7

IS-39 5/25/98 73.9 18.7 31.2 1.52 9.8 31.5

IS-72 7/22/98 65.3 20.6 27.5 3.29 14.2 29.3

IS-73 7/22/98 * * * * * *

Sugar Creek at Co Rd 

400 S at New Palistine, 

IN - 03361650

IS-13 4/9/98 42.0 24.0 14.3 1.89 10.8 21.9

IS-38 5/24/98 52.5 19.7 18.2 2.39 6.4 22.1

Little Buck Creek near 

Indianapolis, IN - 

03353637

IS-113 9/9/97 39.7 41.5 11.0 2.03 24.2 20.4

IS-14 4/9/98 37.9 25.1 10.2 2.39 16.2 19.8

IS-37 5/24/98 52.5 34.1 14.5 2.92 21.3 24.4

IS-71 7/20/98 34.6 24.2 9.6 2.60 14.7 18.3

North Dry Creek near 

Kearney, NE - 

06770195

IS-6 4/1/98 149.6 33.0 25.5 27.60 49.8 283.2

IS-40 5/22/98 115.4 21.2 21.0 23.80 47.0 255.2

IS-43 6/8/98 117.1 21.5 20.9 19.05 41.5 233.3

IS-92 9/9/98 152.7 32.5 27.4 21.50 69.4 339.1

Dismal River near 

Thedford, NE - 

06775900

IS-17 4/13/98 22.2 0.8 3.4 4.95 6.8 5.8

IS-36 5/19/98 22.3 0.7 3.4 5.08 7.0 5.9

IS-55 6/16/98 23.0 0.8 3.7 5.20 8.1 5.4

IS-95 9/15/98 21.1 1.0 3.2 5.27 10.1 5.8

Table 10. Major ion concentrations in water samples collected in 1997–1998 (mg/L, milligrams per liter; *, results 

not available)—Continued

Sampling station 

name and station 

number

Sample 

ID

Sample 

collection date

Calcium 

(mg/L)

Chloride 

(mg/L)

Magnesium 

(mg/L)

Potassium 

(mg/L)

Sodium 

(mg/L)

Sulfate 

(mg/L)
44 Isotopic and Chemical Composition of Inorganic and Organic Water-Quality Samples from the Mississippi River Basin, 1997–98

Small stream stations—Continued

South Fabius River 

near Taylor, MO - 

05500000

IS-23 4/7/98 * * * * * *

IS-46 6/2/98 50.1 8.0 9.3 3.95 10.1 39.7

IS-75 7/27/98 62.3 9.8 11.2 5.11 12.4 42.9

IS-89 9/1/98 57.8 10.5 11.6 5.04 13.0 40.6

Elk River near Tiff 

City, MO - 07189000

IS-24 4/14/98 45.0 5.3 2.3 1.56 7.1 7.8

IS-52 6/9/98 51.1 6.7 2.6 2.09 4.6 5.7

IS-68 7/14/98 49.4 7.8 2.6 2.42 6.0 5.1

IS-87 9/2/98 48.7 9.6 3.0 3.18 7.2 6.9

IS-88 9/2/98 48.5 10.0 3.0 3.20 7.2 6.9

Shingle Creek at 

Queen Ave. N., MN - 

05288705

IS-108 7/7/97 56.1 79.3 14.2 3.26 43.2 34.1

IS-12 4/6/98 55.0 115.3 15.0 3.98 63.1 34.3

IS-30 5/8/98 61.8 99.8 18.2 2.58 49.0 59.5

IS-53 6/11/98 69.1 148.2 20.6 2.39 52.1 60.8

IS-62 7/8/98 70.3 104.1 19.8 <0.10 51.4 42.8

Little Cobb River near 

Beauford, MN - 

05320270

IS-109 7/16/97 81.3 12.9 27.4 2.20 9.1 18.3

IS-114 10/28/97 73.6 19.9 33.1 2.07 12.9 26.5

IS-1A 1/14/98 * * * * * *

IS-1B 1/14/98 * * * * * *

IS-1C 1/14/98 * * * * * *

IS-4 3/30/98 73.5 14.9 23.3 3.59 6.7 22.8

IS-7 3/30/98 * * * * * *

IS-35 5/18/98 81.3 15.9 28.3 2.22 8.9 21.3

IS-70 7/15/98 53.1 13.8 21.4 1.76 7.2 17.3

IS-90 8/17/98 62.3 21.2 28.3 2.51 14.5 21.7

Namekagon River at 

Leonards, WI - 

05331833

IS-116 11/11/97 16.9 2.8 4.6 0.61 2.3 3.6

IS-21 3/30/98 6.9 1.5 2.0 0.73 1.4 2.6

IS-47 6/2/98 12.2 1.7 3.3 0.43 1.9 2.8

IS-69 7/15/98 16.9 2.5 4.7 0.59 2.4 3.1

IS-94 9/9/98 22.4 2.8 6.1 0.66 2.8 4.5

Rattlesnake Creek near 

North Andover, WI - 

05413449

IS-110 8/1/97 81.4 27.9 43.3 3.32 8.5 25.9

IS-22 4/15/98 80.6 27.2 44.3 2.23 9.1 24.7

IS-59 6/19/98 71.0 22.6 37.6 9.66 7.8 19.1

IS-81 8/21/98 86.9 25.3 47.7 3.20 8.9 22.8

IS-82 8/21/98 * * * * * *

IS-98 9/22/98 84.9 26.4 46.0 2.07 8.4 25.0

Bogue Phalia near 

Leland, MS - 

07288650

IS-18 4/14/98 52.1 6.2 15.4 3.31 11.6 27.5

IS-58 6/18/98 52.5 13.0 21.1 4.32 28.2 89.2

IS-65 7/15/98 37.7 5.0 13.0 3.82 13.4 30.6

IS-93 9/16/98 53.4 * 20.0 8.91 19.0 *

Table 10. Major ion concentrations in water samples collected in 1997–1998 (mg/L, milligrams per liter; *, results 

not available)—Continued

Sampling station 

name and station 

number

Sample 

ID

Sample 

collection date

Calcium 

(mg/L)

Chloride 

(mg/L)

Magnesium 

(mg/L)

Potassium 

(mg/L)

Sodium 

(mg/L)

Sulfate 

(mg/L)
RESULTS 45

Table 11. Statistical summary of major ion concentrations in water sampled collected in 1997–98 (all values are in milligrams 

per liter)

Parameter

Analytical 

reporting 

limit

Number of

analyses

Minimum 

value

Maximum 

value Mean value Median value Standard deviation

All stations

Calcium 0.02 101 6.9 152.7 54.1 51.1 26.6

Chloride 0.29 102 0.7 148.3 20.5 15.3 22.9

Magnesium 0.014 101 2.0 47.7 17.8 18.3 10.9

Potassium 0.24 101 <0.24 27.6 3.8 2.7 4.3

Sodium 0.09 101 1.4 69.4 15.1 9.6 13.9

Sulfate 0.31 102 2.6 339 41.1 26.5 53.9

Large river stations

Calcium 0.02 34 7.8 62.0 39.5 42.6 13.3

Chloride 0.29 35 2.9 22.7 14.0 14.5 4.8

Magnesium 0.014 34 2.7 23.0 14.2 15.2 6.1

Potassium 0.24 34 0.3 6.1 3.4 2.9 1.3

Sodium 0.09 34 3.9 42.4 14.6 10.1 9.5

Sulfate 0.31 35 5.0 129.5 45.3 43.5 28.8

Small stream stations with basins dominated by row crop agriculture and/or livestock production

Calcium 0.02 19 45.0 152.7 83.6 81.4 31.6

Chloride 0.29 19 5.4 33.0 19.9 21.5 8.7

Magnesium 0.014 19 2.4 47.7 24.2 26.6 15.7

Potassium 0.24 19 1.6 27.6 7.2 3.0 8.7

Sodium 0.09 19 3.8 69.4 16.8 7.9 19.4

Sulfate 0.31 19 5.2 339.1 72.6 24.8 110.7

Small stream stations with basins dominated by row crop agriculture

Calcium 0.02 30 24.7 99.4 63.2 62.4 16.2

Chloride 0.29 30 5.1 58.6 17.7 15.4 10.7

Magnesium 0.014 30 8.0 41.7 23.0 22.3 8.6

Potassium 0.24 30 0.6 8.9 2.8 2.3 1.8

Sodium 0.09 30 3.3 28.3 11.0 10.0 5.3

Sulfate 0.31 30 8.0 89.2 29.0 24.7 15.1

Small stream stations with basins dominated by urban land

Calcium 0.02 9 34.6 70.3 53.0 55.1 13.2

Chloride 0.29 9 24.3 148.3 74.7 79.3 45.2

Magnesium 0.014 9 9.7 20.7 14.8 14.5 4.1

Potassium 0.24 9 <0.24 4.0 2.5 2.6 1.1

Sodium 0.09 9 14.7 63.1 37.3 43.2 18.2

Sulfate 0.31 9 18.4 60.8 35.0 34.2 16.5

Small stream stations with basins dominated by undeveloped land

Calcium 0.02 9 6.9 23.0 18.2 21.2 5.6

Chloride 0.29 9 0.7 2.8 1.7 1.5 0.9

Magnesium 0.014 9 2.0 6.1 3.8 3.4 1.2

Potassium 0.24 9 0.4 5.3 2.6 0.7 2.4

Sodium 0.09 9 1.4 10.2 4.8 2.8 3.2

Sulfate 0.31 9 2.6 6.0 4.4 4.6 1.4
46 Isotopic and Chemical Composition of Inorganic and Organic Water-Quality Samples from the Mississippi River Basin, 1997–98

basins dominated by urban or undeveloped land 

(0.41 and 0.39 mg/L, respectively) (table 9). The 

median ammonia plus organic N concentrations from 

basins dominated by row crops, row crops and/or livestock production, or urban land (0.58, 0.52, and 0.60, 

respectively) are greater than the median concentration 

from basins dominated by undeveloped land 

(0.12 mg/L). The median dissolved organic carbon 

concentrations from basins dominated by row crops, 

row crops and/or livestock production, or urban land 

(5.0, 3.3, and 6.9 mg/L, respectively) are greater than 

the median concentration from undeveloped basins 

(2.2 mg/L). The median orthophosphate concentrations from basins dominated by row crops or row 

crops and/or livestock production (0.08 and 

0.14 mg/L, respectively) are greater than median 

concentrations basins dominated by urban or undeveloped land (0.02 and 0.01 mg/L, respectively).

The median chloride concentration from basins 

dominated by urban land (79.3 mg/L) is greater than 

median concentrations from basins dominated by row 

crops, row crops and/or livestock production, or undeveloped land (15.4, 21.5, and 1.5 mg/L, respectively) 

(table 11). The median sodium concentration from 

basins dominated by urban land (43.2 mg/L) also is 

greater than median concentrations from basins dominated by row crops, row crops and/or livestock production, or undeveloped land (10.0, 7.9, and 2.8 mg/L, 

respectively). The median sulfate concentrations 

(4.6 mg/L) from basins dominated by undeveloped 

land is less than median concentrations from basins 

dominated by row crops, row crops and/or livestock 

production, or urban land (24.7, 24.8, and 34.2 mg/L, 

respectively) (table 11).

Physical Properties and Field Chemistry

Physical properties and field chemistry data for 

samples from 1997 and 1998 are listed in table 12, and 

statistically summarized by stream (basin) size and 

dominant drainage basin land cover in table 13. 

Relations Between Isotopic Ratios and 

Basin Characteristics

A project objective was to determine if NO3 and 

POM from streams draining areas of distinctly 

different land use and hence N sources have distinct 

isotope values. The intent was to select small stream 

stations that distinctly represented one of four land-use 

classes: land in corn and soybean production; land in 

hog, cattle, or poultry (livestock) production; urban 

land; or undeveloped land. This objective was difficult 

to accomplish because land use relating to N sources 

was mixed in most basins (tables 2 and 3). 

Examples from three stations demonstrate the 

difficulty with assigning a basin type to each station. 

Little Buck Creek near Indianapolis in Indiana (station 

number 03353637) was selected as an urban station, 

but contains only slightly less agricultural (46.5%) 

than urban land (49.1%) in the associated drainage 

basin (table 3). Walnut Creek near Vandalia in Iowa 

(station number 05487550) was selected as an undeveloped station because some of the basin has been 

converted back to native prairie grasslands. However, 

on-site inspection and analysis of land cover data indicate that there is a mix of undeveloped and agricultural 

land in the basin associated with this station. Hence, 

the basin type designation for this station was changed 

to agricultural land (tables 1 and 3). Elk River near Tiff 

City in Missouri (station number 07189000) was 

selected as a row crops and/or livestock production 

station because several confined animal feeding operations (CAFO’s) were known to operate in the basin. 

Land-cover data show that more than 50% of this 

basin is forested or otherwise undeveloped land, which 

qualify it as an undeveloped type basin (table 3). 

However, the estimate rate of N input from manure 

(4,887 kg N/km2) is greater than for any other basin in 

this study (table 2).

 A more detailed analysis of the isotope results 

relative to land cover and N sources that utilizes multivariate statistics is merited but beyond the scope of 

this report. However, figures 8–11 clearly show some 

differences in isotope ratio values among the stations 

on small streams with basins dominated by different 

land cover types.

Evidence for Sources of Nitrogen in the 

Mississippi River

We proposed (Battaglin and others, 1997) that 

δ15N and δ18O of NO3 values from Mississippi River 

water could be used to determine the principal sources 

of the NO3 entering the Gulf of Mexico. Results from 

this study confirm the findings of other investigations 

(Goolsby and others, 1999; Council for Agricultural 
RESULTS 47

Table 12. Physical properties and field chemistry in water samples collected in 1997–98 (mg/L, milligrams per liter; μS/cm, 

microsiemens per centimeter at 25 degrees Celsius; ft3/s, cubic feet per second; *, result not available)

Sampling station 

name and station 

number

Sample 

ID

Sample 

collection

date

Alkalinity 

as CaCO3 

(mg/L)

Bicarbonate as 

HCO3 

(mg/L)

Dissolved 

oxygen 

(mg/L)

pH in 

standard 

units

Specific 

conductance in 

μs/cm

Water 

temperature 

(degrees 

Celsius)

Instantaneous 

discharge 

(ft3/s)

Large river stations

Mississippi River at 

Clinton, IA - 05420500

IS-119 6/2/97 161 197 10.7 8.59 378 16.9 61,000

IS-112 9/2/97 163 199 6.9 7.66 424 21.8 53,400

IS-33 5/13/98 142 167 9.0 8.24 450 19.0 57,700

IS-34 5/13/98 146 166 9.0 8.24 450 19.0 57,700

IS-42 5/27/98 161 197 5.0 7.60 461 20.5 56,500

IS-56 6/10/98 170 207 6.5 7.42 478 18.5 47,500

IS-60 7/1/98 152 185 4.7 7.40 440 25.7 97,000

IS-76 7/28/98 176 193 7.6 8.02 425 25.5 43,500

IS-83 8/25/98 164 188 6.3 8.05 409 25.7 34,700

IS-84 8/25/98 * * * * 324 25.7 34,700

IS-97 9/23/98 206 251 7.3 7.80 442 20.1 22,500

Missouri River at Hermann, MO - 06934500IS-26 4/20/98 152 185 9.3 7.70 501 12.8 160,000

IS-45 6/1/98 168 205 7.8 7.91 658 23.0 86,400

IS-64 7/7/98 115 141 6.3 7.77 456 26.5 159,000

IS-86 8/31/98 139 169 6.6 7.91 570 27.6 86,800

Mississippi River at 

Thebes, IL - 07022000

IS-101 6/11/97 157 191 8.0 7.49 586 21.5 246,000

IS-25 4/16/98 139 169 9.2 7.85 401 12.6 579,000

IS-50 6/10/98 147 179 7.1 7.93 496 20.9 282,000

IS-51 6/10/98 * * * * * * *

IS-74 7/22/98 156 191 5.9 8.02 500 30.0 271,000

IS-91 9/9/98 168 205 7.7 8.09 571 27.2 130,000

Ohio River at Grand 

Chain, IL - 03612500

IS-102 6/12/97 63 77 7.1 7.42 282 19.8 673000

IS-27 4/23/98 78 95 8.2 7.70 256 15.0 734,000

IS-44 6/5/98 90 109 7.3 7.50 307 25.0 366,000

IS-77 7/22/98 84 102 6.4 7.70 296 29.0 260,000

IS-78 7/22/98 * * * * * * *

IS-85 8/12/98 78 96 6.4 7.70 250 28.0 185,000

Yazoo River below 

Steele Bayou near 

Long Lake, MS - 

07288955

IS-103 6/19/97 27 33 4.4 6.07 91 26.7 24,900

IS-19 4/13/98 30 37 8.0 6.50 92 20.0 11,800

IS-57 6/17/98 144 * 7.5 7.10 * 28.5 6,870

IS-66 7/16/98 119 145 2.5 7.00 247 30.5 27,100

IS-96 9/17/98 62 75 6.6 6.80 202 27.0 9,290

Mississippi River, St. 

Francisville, LA - 

07373420

IS-117 5/6/97 101 123 8.1 7.30 361 16.0 812,000

IS-106 6/19/97 97 118 6.7 7.92 353 23.0 763,000

IS-10 4/2/98 86 104 8.9 7.92 349 13.5 959,000

IS-11 4/2/98 * * * * * * *

IS-31 4/30/98 104 127 8.5 8.03 337 17.0 794,000

IS-32 4/30/98 * * * * * * *

IS-49 6/9/98 110 134 5.9 7.94 350 26.0 541,000

IS-63 7/9/98 113 138 6.1 7.98 354 26.0 708,000

IS-99 9/28/98 145 * 7.4 8.27 471 27.5 254,000

Mississippi River at 

Vicksburg, MS - 

07289000

IS-2A 1/13/98 * * 10.6 7.74 361 8.6 933,000

IS-2B 1/13/98 * * * * * * 933,000

IS-2C 1/13/98 * * * * * * 933,000
48 Isotopic and Chemical Composition of Inorganic and Organic Water-Quality Samples from the Mississippi River Basin, 1997–98

Large river stations—Continued

Mississippi River at 

Belle Chasse, LA - 

07374525

IS-118 5/7/97 * * 8.6 7.28 364 16.0 682,000

IS-105 6/20/97 * * 6.4 7.90 357 23.5 676,000

Small stream stations

S. Fork Iowa River 

northeast of New Providence, IA - 05451210

IS-3A 1/30/98 * * 10.7 7.55 659 1.0 *

IS-3B 1/30/98 * * * * * * *

IS-3C 1/30/98 * * * * * * *

IS-5 3/30/98 211 257 11.1 8.39 661 11.5 312

IS-8 3/30/98 225 275 * * * * *

IS-41 5/29/98 110 134 8.6 7.81 507 17.5 872

IS-79 8/3/98 238 290 9.8 8.20 622 20.4 34.4

Fourmile Creek near 

Traer, IA - 05464137

IS-107 6/30/97 * * 8.5 7.51 583 19.3 *

IS-20 4/15/98 127 155 11.1 7.78 504 7.3 54.1

IS-67 7/16/98 169 206 8.8 7.54 537 16.7 23.4

IS-80 8/12/98 194 237 9.2 8.01 537 18.2 9.1

Walnut Creek near 

Vandalia, IA - 

05487550

IS-104 6/21/97 * * 8.0 7.90 421 20.5 21.0

IS-9 4/3/98 146 178 11.4 8.00 467 6.0 54.6

IS-28 5/7/98 117 143 8.0 7.80 382 12.5 135

IS-29 5/7/98 123 150 8.0 7.80 384 12.5 135

IS-54 6/11/98 70 85 6.8 7.40 240 19.0 210

Panther Creek near El 

Paso, IL - 05567000

IS-115 11/13/97 290 354 12.0 7.62 837 2.7 14.0

IS-16 4/9/98 226 276 11.4 7.85 728 8.3 153

IS-48 6/9/98 226 276 9.4 7.43 720 15.2 104

IS-61 7/7/98 180 220 7.4 7.55 572 23.0 168

Indian Creek near 

Wyoming, IL - 

05568800

IS-111 8/27/97 302 368 8.6 8.02 720 20.8 36.0

IS-15 4/9/98 204 249 10.8 7.60 576 8.1 272

IS-39 5/25/98 230 281 9.4 7.55 641 16.1 104

IS-72 7/22/98 208 254 7.6 7.76 437 24.3 102

IS-73 7/22/98 * * * * * * *

Sugar Creek at Co Rd 

400 S at New Palistine, 

IN - 03361650

IS-13 4/9/98 130 159 8.9 7.82 391 11.8 405

IS-38 5/24/98 * * 8.1 7.75 455 16.1 423

Little Buck Creek near 

Indianapolis, IN - 

03353637

IS-113 9/9/97 102 124 7.6 7.90 419 20.0 1.9

IS-14 4/9/98 115 140 9.2 7.78 351 11.6 329

IS-37 5/24/98 * * 8.2 7.87 485 17.1 137

IS-71 7/20/98 105 128 6.6 7.66 316 23.9 51.0

North Dry Creek near 

Kearney, NE - 

06770195

IS-6 4/1/98 * * 8.7 8.20 1,210 13.0 30.0

IS-40 5/22/98 204 * 6.6 7.98 1,040 16.5 82.0

IS-43 6/8/98 * 230 9.2 7.90 1,040 15.5 40.0

IS-92 9/9/98 * * 9.7 8.70 1,210 26.5 9.8

Table 12. Physical properties and field chemistry in water samples collected in 1997–98 (mg/L, milligrams per liter; μS/cm, 

microsiemens per centimeter at 25 degrees Celsius; ft3/s, cubic feet per second; *, result not available)—Continued

Sampling station 

name and station 

number

Sample 

ID

Sample 

collection

date

Alkalinity 

as CaCO3 

(mg/L)

Bicarbonate as 

HCO3 

(mg/L)

Dissolved 

oxygen 

(mg/L)

pH in 

standard 

units

Specific 

conductance in 

μs/cm

Water 

temperature 

(degrees 

Celsius)

Instantaneous 

discharge 

(ft3/s)
RESULTS 49

Small stream stations—Continued

Dismal River near 

Thedford, NE - 

06775900

IS-17 4/13/98 80 96 9.3 8.20 156 13.5 230

IS-36 5/19/98 73 * 8.4 8.30 186 17.5 227

IS-55 6/16/98 * * 8.8 8.20 185 19.5 223

IS-95 9/15/98 * * 8.7 8.21 173 16.0 217

South Fabius River near 

Taylor, MO - 05500000

IS-23 4/7/98 82 101 10.2 7.77 243 12.0 640

IS-46 6/2/98 135 161 11.3 8.41 377 24.6 213

IS-75 7/27/98 * * 10.3 8.21 455 24.7 56.0

IS-89 9/1/98 168 205 8.4 8.29 439 26.0 15.0

Elk River near Tiff City, 

MO - 07189000

IS-24 4/14/98 119 145 11.7 8.09 259 14.3 858

IS-52 6/9/98 126 154 7.5 7.68 280 20.1 243

IS-68 7/14/98 133 162 9.1 8.07 305 28.0 329

IS-87 9/2/98 133 162 9.1 8.00 336 27.9 12.2

IS-88 9/2/98 * * * * * * *

Shingle Creek at Queen 

Ave. N., MN - 

05288705

IS-108 7/7/97 146 175 5.8 7.29 417 18.0 55.1

IS-12 4/6/98 136 163 8.8 7.34 706 8.7 60.0

IS-30 5/8/98 140 171 7.7 7.59 607 14.4 40.0

IS-53 6/11/98 201 245 5.2 7.75 934 16.7 4.5

IS-62 7/8/98 180 219 3.2 7.44 790 22.4 5.9

Little Cobb River near 

Beauford, MN - 

05320270

IS-109 7/16/97 233 281 6.6 7.98 622 24.0 162

IS-114 10/28/97 274 329 12.8 8.50 629 2.3 19.0

IS-1A 1/14/98 335 433 12.0 7.64 828 0.1 2.1

IS-1B 1/14/98 * * * * * * *

IS-1C 1/14/98 * * * * * * *

IS-4 3/30/98 208 254 8.8 7.76 558 8.6 381

IS-7 3/30/98 * * * * * * *

IS-35 5/18/98 241 294 7.5 7.94 655 19.6 166

IS-70 7/15/98 195 * 7.5 7.67 546 24.8 72.0

IS-90 8/17/98 221 269 6.2 7.97 549 25.8 2.9

Namekagon River at 

Leonards, WI - 

05331833

IS-116 11/11/97 58 70 13.8 7.60 134 2.2 106

IS-21 3/30/98 20 24 12.3 6.80 62 3.5 473

IS-47 6/2/98 37 46 10.0 7.15 108 13.6 195

IS-69 7/15/98 51 62 9.2 8.47 135 23.4 104

IS-94 9/9/98 81 99 10.9 8.30 164 14.9 51.0

Rattlesnake Creek near 

North Andover, WI - 

05413449

IS-110 8/1/97 * * * * * * 17.3

IS-22 4/15/98 * * * * * * 32.0

IS-59 6/19/98 * * 8.0 8.30 604 16.5 70.0

IS-81 8/21/98 * * 8.9 8.00 761 21.0 29.0

IS-82 8/21/98 * * * * * * *

IS-98 9/22/98 * * 13.9 8.30 758 14.4 26.0

Bogue Phalia near 

Leland, MS - 07288650

IS-18 4/14/98 174 212 7.4 7.40 416 19.0 41.0

IS-58 6/18/98 166 203 7.3 7.80 561 31.5 126

IS-65 7/15/98 138 168 3.6 7.20 342 28.0 2,130

IS-93 9/16/98 182 222 5.4 7.80 523 27.0 219

Table 12. Physical properties and field chemistry in water samples collected in 1997–98 (mg/L, milligrams per liter; μS/cm, 

microsiemens per centimeter at 25 degrees Celsius; ft3/s, cubic feet per second; *, result not available)—Continued

Sampling station 

name and station 

number

Sample 

ID

Sample 

collection

date

Alkalinity 

as CaCO3 

(mg/L)

Bicarbonate as 

HCO3 

(mg/L)

Dissolved 

oxygen 

(mg/L)

pH in 

standard 

units

Specific 

conductance in 

μs/cm

Water 

temperature 

(degrees 

Celsius)

Instantaneous 

discharge 

(ft3/s)
50 Isotopic and Chemical Composition of Inorganic and Organic Water-Quality Samples from the Mississippi River Basin, 1997–98

Table 13. Statistical summary of physical properties and field chemistry data in water sampled collected in 1997–98 (mg/L, 

milligrams per liter; μS/cm, microsiemens per centimeter at 25 degrees Celsius; ft3/s, cubic feet per second; C, Celsius)

Parameter

Analytical 

reporting 

limit

Number 

of

analyses

Minimum 

value

Maximum 

value

Mean 

value

Median 

value

Standard 

deviation

All stations

Alkalinity as CaCO3 in mg/L 1.0 76 20 302 147 146 62

Bicarbonate as HCO3 in mg/L 1.0 76 24 368 178 177 75

Dissolved oxygen in mg/L 0.1 104 2.5 13.9 8.2 8.1 2.1

pH in standard units 0.1 104 6.1 8.7 7.8 7.8 0.4

Specific conductance in μs/cm 1.0 102 62 1,210 467 446 223

Water temperature in degrees C 0.1 105 1.0 31.5 19.0 19.5 6.9

Instantaneous discharge in cfs 0.1 112 1.9 959,000 123,794 237 257,513

Large river stations

Alkalinity as CaCO3 in mg/L 1.0 34 27 206 124 139 44

Bicarbonate as HCO3 in mg/L 1.0 34 33 251 150 167 52

Dissolved oxygen in mg/L 0.1 38 2.5 10.7 7.2 7.2 1.5

pH in standard units 0.1 38 6.1 8.6 7.7 7.8 0.5

Specific conductance in μs/cm 1.0 37 90 658 390 401 125

Water temperature in degrees C 0.1 39 12.6 30.5 22.5 23.0 5.1

Instantaneous discharge in cfs 0.1 42 6,870 959,000 329,820 172,500 331,600

Small stream stations with basins dominated by row crop agriculture and/or livestock production

Alkalinity as CaCO3 in mg/L 1.0 4 110 238 196 218 58

Bicarbonate as HCO3 in mg/L 1.0 4 134 290 239 266 71

Dissolved oxygen in mg/L 0.1 15 6.6 13.9 9.5 9.1 1.8

pH in standard units 0.1 15 7.5 8.7 8.1 8.1 0.3

Specific conductance in μs/cm 1.0 15 259 1,210 683 659 324

Water temperature in degrees C 0.1 15 1.0 28.0 17.6 16.5 7.0

Instantaneous discharge in cfs 0.1 16 9.8 872 187 37.2 285

Small stream stations with basins dominated by row crop agriculture

Alkalinity as CaCO3 in mg/L 1.0 25 70 302 191 194 57

Bicarbonate as HCO3 in mg/L 1.0 25 85 368 234 237 69

Dissolved oxygen in mg/L 0.1 33 3.6 12.8 8.7 8.5 2.0

pH in standard units 0.1 33 7.2 8.5 7.8 7.8 0.3

Specific conductance in μs/cm 1.0 32 240 837 521 537 137

Water temperature in degrees C 0.1 33 2.3 31.5 17.5 19.0 7.7

Instantaneous discharge in cfs 0.1 36 2.1 2,130 196 104 363

Small stream stations with basins dominated by urban land

Alkalinity as CaCO3 in mg/L 1.0 8 102 201 141 138 35

Bicarbonate as HCO3 in mg/L 1.0 8 124 245 171 167 43

Dissolved oxygen in mg/L 0.1 9 3.2 9.2 6.9 7.6 1.9

pH in standard units 0.1 9 7.3 7.9 7.6 7.7 0.2

Specific conductance in μs/cm 1.0 9 316 934 558 485 214

Water temperature in degrees C 0.1 9 8.7 23.9 17.0 17.1 4.9

Instantaneous discharge in cfs 0.1 9 1.9 329 76 51 104

Small stream stations with basins dominated by undeveloped land

Alkalinity as CaCO3 in mg/L 1.0 5 20 81 49 51 23

Bicarbonate as HCO3 in mg/L 1.0 5 24 99 60 62 28

Dissolved oxygen in mg/L 0.1 9 8.4 13.8 10.2 9.3 1.8

pH in standard units 0.1 9 6.8 8.5 7.9 8.2 0.6

Specific conductance in μs/cm 1.0 9 62 186 145 156 40

Water temperature in degrees C 0.1 9 2.2 23.4 13.8 14.9 6.9

Instantaneous discharge in cfs 0.1 9 51 473 203 217 121
RESULTS 51

Science and Technology, 1999; Carey and others, 

1999; Alexander and others, 2000); that much of the 

NO3 in the Mississippi River originates in the agriculturally dominated basins of the upper-Midwestern 

United States, and is transported without significant 

transformation or other loss to the Gulf of Mexico. 

Isotope ratio values could not be used to identify 

specific NO3 sources in small streams or large rivers. 

The isotope results did show that in-stream transformations of NO3 do not result in a significant (more 

than 15%) loss in N mass and do not significantly alter 

the isotope signal in large rivers. Hence, basins with 

large annual yields of NO3 are likely to be the most 

significant sources of NO3 to the Gulf of Mexico. 

Clearly, the rivers in the Mississippi basin with the 

highest annual NO3 yields are those in the uppermidwest that are dominated by row crop agriculture 

and/or livestock production (Goolsby and others, 

1999; Goolsby and Battaglin, 2000). 

In figure 12, the δ15N and δ18O of NO3 values 

from large rivers are plotted along with the typical 

ranges of δ15N and δ18O of NO3 values from various 

nitrogen sources. Plots of δ15N versus δ18O of NO3

values have been used to show how NO3 in environmental samples compares to NO3 from various N 

sources and how denitrification can change isotope 

values (Clark and Fritz, 1997; Kendall, 1998). The 

δ15N and δ18O of NO3 values suggest that in large 

rivers NO3 comes from more than one source. All of 

the δ15N of NO3 values from large rivers are within 

the range of values expected from NO3 formed by 

nitrification in soils. Some δ15N of NO3 values are 

within the range of values expected from other sources 

including animal waste and atmospheric nitrate. The 

higher δ18O of NO3 values at some stations suggest 

that atmospheric sources of NO3 are also important. 

The source of atmospheric NO3 in the Mississippi 

basin is likely a mixture of NO3 volatilized from soils, 

the conversion of atmospheric N2 to NO3 by lightning, 

and NO3 from anthropogenic sources such as industrial emissions or automobile exhaust (Kendall, 1998). 

NO3-based fertilizers such as calcium nitrate also have 

higher δ18O of NO3 values than NO3 formed after 

application of more commonly used (Terry and Kirby, 

1999) ammonium-based fertilizers.

In figure 13, δ15N and δ18O the NO3 values 

from small streams are plotted by dominant land-cover 

type with the ranges of values from various N sources. 

δ15N and δ18O of NO3 values show more of a pattern 

of separation than values from large rivers. NO3 from 

basins dominated by urban land has an isotopic signature that resembles atmospheric NO3 or NO3 fertilizer. 

NO3 from basins dominated by undeveloped land also 

resembles atmospheric NO3. NO3 from basins dominated by row crops or row crops and/or livestock 

production are very similar isotopically, and resemble 

the isotopic signature of the large rivers (fig. 12). 

Evidence for Transformation of Nitrogen 

in the Mississippi River

NO3 isotope values from large rivers are within 

the range of value from the small streams. This relationship suggests that denitrification in the main stem 

Mississippi River is not transforming much NO3 and 

not causing a significant shift in NO3 isotope ratio 

values. In figure 14, the distribution of NO2 plus NO3

concentrations and isotope values from large rivers are 

plotted in boxplots. These plots can be compared with 

boxplots of small streams results (fig. 8). All NO2 plus 

NO3 concentrations from large rivers are less than the 

median concentrations from basins dominated by row 

crops or row crops and/or livestock production, but 

most are greater than concentrations from basins 

dominated by urban or undeveloped land. Most δ15N 

of NO3 values from large rivers are between +5‰ and 

+10‰—a similar range to values from basins dominated by row crops or row crops and/or livestock 

production, but generally greater than values from 

basins dominated by urban or undeveloped land. In 

contrast, most δ18O of NO3 values from large rivers 

are greater than +10‰, a similar range to values from 

basins dominated by urban land, but generally greater 

than values from basins dominated by row crops or 

row crops and/or livestock production.

Results of isotope (table 4), and nutrient 

(table 8), and major ion (table 10) analyses from the 

two Lagrangian sample sets were used (Battaglin and 

others, 2001) to determine whether simple mixing 

models can explain how NO3 behaves in the Lower 

Mississippi River, and what transformations affect 

NO3 in the river. The analysis suggests that a small 

fraction of the NO3 present in the Upper Mississippi 

and Ohio Rivers is lost between their confluence and 

the Gulf of Mexico. However, mixing of water from 

the Upper Mississippi and Ohio Rivers can explain the 

measured isotope values in the Lower Mississippi 

River. This result suggests that denitrification or other 
52 Isotopic and Chemical Composition of Inorganic and Organic Water-Quality Samples from the Mississippi River Basin, 1997–98

Figure 12. Typical ranges of δ15N and δ18O of NO3 values for various N sources and measured 

values from large river stations, 1997–1998 (modified from Kendall, 1998, figure 16.9).

Figure 13. Typical ranges of δ15N and δ18O of NO3 for various N sources and measured values 

from small stream stations, 1997–1998 (modified from Kendall, 1998, figure 16.9).
CONCLUSIONS 53

Nitrite plus δ15N δ18O 

nitrate

CONCENTRATION, IN MILLIGRAMS PER LITER

OR ISOTOPE RATIO IN PER MIL

25

20

15

10

5

0

transformations that favor one isotope over the other 

do not occur to a large degree in the ~1,100 kilometers 

of river between the confluence and the Lower Mississippi stations. Assimilation by benthic or suspended 

algae or exchange of river water with ground water 

that has a lighter δ15N of NO3 isotopic signature are 

plausible explanations for this result (Battaglin and 

others, 2001).

CONCLUSIONS

Identification of sources of nitrate (NO3) and 

mechanisms and rates of NO3 removal in the Mississippi River help to understand the effects of upstream 

activities on development of the Gulf of Mexico 

hypoxic zone. Results from isotopic analyses of about 

120 water and suspended sediment samples collected 

in 1997 and 1998 from 24 locations in the Mississippi 

River Basin during this pilot study are tabulated and 

analyzed in this report. This was a pilot study with a 

relatively small number of sampled collected in a very 

large study area. 

Distinct δ15N and δ18O of NO3 isotope ratio 

values were measured in smaller streams that have 

relatively uniform nitrogen (N) sources of in their 

drainage basins (fig. 8). Most δ15N of NO3 values 

from basins dominated by urban or undeveloped land 

are less than +5‰, while most values from basins 

dominated by row crop or row crops and/or livestock 

production are greater than +5‰. δ18O of NO3 values 

are also distinctive. Most values from basins dominated by urban or undeveloped land greater than 

+10‰, while most values from basins dominated by 

row crops or row crops and/or livestock production are 

less than +10‰. The distinctiveness of δ15N and δ18O 

of NO3 values from the small basins is likely limited 

by the lack of uniformity of land-cover within those 

basins. Separating row crop agriculture from livestock 

production and finding uniformly urban or undeveloped basins in the agriculturally dominated 

midwestern States was particularly difficult.

There was considerable temporal and spatial 

variation in δ15N and δ13C of POM values at stations 

across the Mississippi Basin. δ15N of POM values 

from basins dominated by urban or undeveloped land 

also tended to be less than +5‰, while most values 

from basins dominated by row crops or row crops 

and/or livestock production are greater than +5‰. 

 There is some indication of seasonal- or 

discharge-related variability in the isotope results from 

a given station. δ15N and δ18O of NO3 values tend to 

increase from spring to fall as discharge and NO3

concentrations decrease. δ15N of POM values also 

tend to increase from spring to fall. More data is 

needed to determine if these shifts are the result of a 

change in the source of water, NO3, and POM or are 

evidence for transformation of NO3 during latesummer months.

In part because of the small number of samples, 

the isotope data from large rivers could not be used to 

identify the proportions of NO3 that originated from 

various N sources within the basin. However, the data 

do confirm that NO3 from major tributaries accumulates in the Mississippi River and is not significantly 

Figure 14. δ15N and δ18O of NO3 values and NO2 plus 

NO3 concentrations from large river stations.
54 Isotopic and Chemical Composition of Inorganic and Organic Water-Quality Samples from the Mississippi River Basin, 1997–98

A

B

DATE

DATE

δ15N, IN PER MIL

δ15N

δ13C

δ13C, IN PER MIL

altered by transformations such as denitrification as it 

is transported to the Gulf of Mexico. The ranges of 

NO3 and particulate organic material (POM) isotope 

values from large rivers are generally narrower and 

near the middle of the ranges of measurements from 

all stations. 

Suggestions for Future Research

This pilot study, with comparatively large and 

complex basins, showed that source differentiation and 

transformation characterization in small streams and 

larger rivers is possible with a multi-isotope approach. 

However, because of the limited number of samples 

and sampling stations, it was not always possible to 

sort out the difference between seasonal (or flow 

related) changes in NO3 sources and changes in 

isotope values resulting from NO3 transformations. A 

time-series plot of the POM data from the Yazoo River 

station (fig. 15) highlights this point. At this station 

(and several others on large rivers) POM samples were 

collected more frequently as part of a related study 

(Kendall and others, 2001). In figure 15, all isotope 

ratio values from POM samples collected at this 

station are plotted as open circles and those that have 

matching NO3 isotope data (collected for this study) 

are plotted as filled circles. Clearly there is temporal 

pattern to the δ15N and δ13C of POM values that is not 

well represented by the four samples collected and 

analyzed for this study. 

We suggest that more isotope data be collected 

in the Mississippi Basin. This effort should focus on 

building a long-term baseline of data at few locations 

and then detailed temporal data at a few stations. 

Collection of additional Lagrangian data sets is also 

recommended. This should involve sampling of other 

significant rivers in the Mississippi basins (for 

example, the Illinois River and Red River) that were 

not sampled in this study. Cost is always a limiting 

factor in study design. Newly available equipment, and 

resulting simplifications in sample processing and 

analysis will reduce the per sample cost of isotope 

analysis. These will aid our understanding of the 

dynamics of delivery and transformation of NO3 in the 

Mississippi River basin. The data may also show how 

changes in cultural practices, such as use of agricultural best management practices affect delivery of 

NO3 to streams of the midwestern United States.

REFERENCES CITED

Alexander, R.B., and Smith, R.A., 1990, County-level 

estimates of nitrogen and phosphorus fertilizer use in 

the United States, 1945 to 1985: U.S. Geological 

Survey Open-File Report 90–130, 12 p.

Alexander, R.B., Smith, R.A., and Schwarz, G.E., 2000, 

Effect of stream channel size on the delivery of 

nitrogen to the Gulf of Mexico: Nature, v. 403, 

p. 758–761.

Battaglin, W.A., and Goolsby, D.A., 1995, Spatial data in 

geographic information system format on agricultural 

chemical use, land use, and cropping practices in the 

United States: U.S. Geological Survey WaterResources Investigations Report 94–4176, 87 p.

Battaglin, W.A., Kendall, C., Goolsby, D.A., and Boyer, 

L.L., 1997, Plan of study to determine if the isotopic 

ratios δ15N and δ18O can reveal the sources of nitrate 

discharged by the Mississippi River into the Gulf of 

Mexico: U.S. Geological Survey Open-File Report 97–

230, 18 p.

Battaglin, W.A., Kendall, C., Chang, C.C.Y., Silva, S.R., 

and Campbell, D.H., 2001, Chemical and isotopic 

evidence of nitrogen transformation in the Mississippi 

River, 1997–98: Hydrologic Processes, v. 15, no. 7, 

p. 1285–1300.

Figure 15. Particulate organic material data time series for 

the Yazoo River in 1997 (open circles are all data and filled 

circles are data collected for this study); (A) δ15N, and (B) 

δ13C.
REFERENCES CITED 55

Böhlke, J.K. and Denver, J.M., 1995, Combined use of 

groundwater dating, chemical, and isotopic analyses to 

resolve the history and fate of nitrate contamination in 

two agricultural watersheds, Atlantic coastal plain, 

Maryland: Water Resources Research, v. 31, no. 9, 

p. 2319–2339.

Böttcher, J., Strebel, O., Voerkelius, S., and Schmidt, H.L., 

1990, Using isotope fractionation of nitrate-nitrogen 

and nitrate-oxygen for evaluation of microbial denitrification in a sandy aquifer: Journal of Hydrology, 

v. 114, p. 413–424.

Broshears, R.E., Clark, G.M., and Jobson, H.E., 2001, 

Simulation of discharge and transport of nitrate and 

selected herbicides in the Mississippi River Basin: 

Hydrologic Processes v. 15, no. 8, p.???????.

Burkart, M.R., and James, D.E., 1999, Agricultural-nitrogen 

contributions to hypoxia in the Gulf of Mexico: Journal 

of Environmental Quality, v. 28, p. 850–859.

Carey, A.E., Pennock, J.R., Lehrter, J.C., Lyons, W.B., 

Schroeder, W.W., and Bonzongo, J-C., 1999, The role 

of the Mississippi River in Gulf of Mexico hypoxia. 

University of Alabama Environment Institute Report 

No. 70, 100 p.

Chang, C.C.Y., Langston, J., Riggs, M., Campbell, D.H., 

Silva, S.R., and Kendall, C., 1999, A method of nitrate 

collection for δ15N and δ18O analysis from water with 

low nitrate concentrations: Canadian Journal of 

Fishery and Aquatic Science, v. 56, p. 1856–1864. 

Clark, I. and Fritz, P., 1997, Environmental Isotopes in 

Hydrogeology: Boca Raton, Fla., CRC Press LLC, 

328 p.

Council for Agricultural Science and Technology, 1999, 

Gulf of Mexico Hypoxia Land and sea interactions: 

Task Force Report No. 134, 44 p.

Dole, R.B., 1909, The quality of surface waters in the 

United States: Part 1—Analysis of waters east of the 

one hundredth meridian: U.S. Geological Survey 

Water-Supply Paper 236, 123 p.

Cravotta, C.A., 1995, Use of stable isotopes of carbon, 

nitrogen, and sulfur to identify sources of nitrogen in 

surface waters in the Lower Susquehanna River Basin, 

Pennsylvania: U.S. Geological Survey Open-File 

Report 94–510, 103 p.

Diaz, R.J., and Rosenberg, R., 1995, Marine benthic 

hypoxia—A review of its ecological effects and the 

behavioral responses of benthic macrofauna: Oceanography and Marine Biology—An Annual Review, 

v. 33, p. 245–303.

Dole, R.B., 1909, The quality of surface waters in the 

United States. Part I. Analysis of waters east of the one 

hundredth meridian: U.S. Geological Survey WaterSupply Paper 236.

Dunn, D. D., 1996, Trends in nutrient inflows to the Gulf of 

Mexico from streams draining the conterminous 

United States, 1972–93: U.S. Geological Survey 

Water-Resources Investigations Report 96–4113, 60 p.

Feigin, A., Shearer, G., Kohl, D.H., and Commoner, B., 

1974, The amount of nitrogen-15 content of nitrate in 

soil profiles from two central Illinois fields in a cornsoybean rotation: Soil Science Society of America 

Proceedings, v. 38, p. 465–471.

Fishman, M.J., and Friedman, L.C., 1989, Methods for 

determination of inorganic substances in water and 

fluvial sediments: U.S. Geological Survey Techniques 

of Water-Resources Investigations, book 5, chap. A1, 

545 p.

Fogel, M.L., and Cifuentes, L.A., 1993, Isotope fractionation during primary production, in, M. Engel and S. 

Macko, eds., Organic geochemistry: New York, 

Plenum Press, p. 73–98.

Goni, M.A., Ruttenberg, K.C., and Eglinton, T.I., 1998, A 

reassessment of the sources and importance of landderived organic matter in surface sediments from the 

Gulf of Mexico: Geochimica et Cosmochimica Acta, 

v. 62, p. 3055–3057.

Goolsby, D. A., and Battaglin, W. A., 2000, Nitrogen in the 

Mississippi Basin—Estimating sources and predicting 

flux to the Gulf of Mexico: U.S. Geological Survey 

Fact Sheet 135–00, 6 p.

Goolsby, D. A., and Battaglin, W. A., 2001, Long-term 

changes in concentrations and flux of nitrogen in the 

Mississippi River basin, USA: Hydrologic Processes, 

v. 15, no. 7, p. 1209–1226.

Goolsby, D.A., Battaglin, W.A., Lawrence, G.B., Artz, R.S., 

Aulenbach, B.T., Hooper, R.P., Keeney, D.R., and 

Stensland, G.J., 1999, Flux and sources of nutrients in 

the Mississippi-Atchafalaya River Basin—Topic E 

Report for the Integrated Assessment on Hypoxia in 

the Gulf of Mexico: NOAA Coastal Ocean Program 

Decision Analysis Series No. 17. NOAA Coastal 

Ocean Program, Silver Spring, Md., 130 p.

Heaton, T.H.E., 1986, Isotopic studies of nitrogen pollution 

in the hydrosphere and atmosphere: a review: Chemical Geology (Isotope Geoscience Section), v. 59, 

p. 87–102.

Helsel, D.R., and Hirsch, R.M., 1992, Statistical Methods in 

Water Resources: New York, Elsevier, 522 p.

Hubner, H., 1986, Isotope effects of nitrogen in the soil and 

biosphere, in P. Fritz and J. Fontes, eds., Handbook of 

Environmental Isotope Geochemistry, v. 2b, The 

terrestrial environment: Elsevier, p. 361–425.

Iman, R.L., and Conover, W.J., 1983, A modern approach to 

statistics: New York, John Wiley & Sons, 497 p.

Kellman, L., and Hillaire-Marcel, C., 1998, Nitrate cycling 

in streams—Using natural abundances of NO3 – δ15n 

to measure in-situ denitrification: Biogeochemistry, 

v. 43, p. 273–292.
56 Isotopic and Chemical Composition of Inorganic and Organic Water-Quality Samples from the Mississippi River Basin, 1997–98

Kendall, C., and Grimm, E., 1990, Combustion tube method 

for measurements of nitrogen isotope ratios using 

calcium oxide for total removal of carbon dioxide and 

water: Analytical Chemistry, v. 62, p. 526–529.

Kendall, C., Campbell, D.H., Burns, D.A., Shanley, J.B., 

Silva, S.R., and Chang, C.C.Y., 1995, Tracing sources 

of nitrate in snowmelt runoff using the oxygen and 

nitrogen isotopic compositions of nitrate, in

Biogeochemistry of seasonally snow-covered catchments: International Association of Hydrological 

Sciences Publication No. 228, p. 339–347.

Kendall, C., 1998. Tracing nitrogen sources and cycling in 

catchments, in Kendall, C., and McDonnell, J.J., eds, 

Isotope-tracers in catchment hydrology, The Netherlands, Elsevier, p. 534–569.

Kendall, C., Silva, S.R., and Kelly, V.J., 2001, Carbon and 

nitrogen isotopic compositions of particulate organic 

matter in four large river systems across the United 

States, Hydrologic Processes, v. 15, no. 8, p. 

Kohl, D.H., Shearer, G.B., and Commoner, B., 1971, Fertilizer nitrogen—Contribution to nitrate in surface water 

in a corn belt watershed: Science, v. 174, p. 1331–

1334.

Kreitler, C.W., 1975, Determining the sources of nitrate in 

ground water by nitrogen isotope studies: Austin, 

University of Texas, Bureau of Economic Geology, 

Report of Investigations No. 83, 57 p.

Leighton, M.O., 1907, Pollution of Illinois and Mississippi 

Rivers by Chicago sewage—A digest of the testimony 

taken in the case of the State of Missouri v. the State of 

Illinois and the Sanitary District of Chicago: U.S. 

Geological Survey Water-Supply and Irrigation Paper 

no. 194, 369 p.

Mannion, A.M., 1995, Agriculture and Environmental 

change—Temporal and spatial dimensions: Chichester, 

John Wiley & Sons, 405 p.

McPhee, 1989, The control of nature: New York, Farrar, 

Straus and Giroux, 272 p.

Meade, R.H., 1995, Setting—Geology, hydrology, sediments, and engineering of the Mississippi River, in

R.H. Meade, ed., Contaminants in the Mississippi 

River, 1987–92: U.S. Geological Survey Circular 

1133, p. 13–30.

Meade, R.H., and Stevens, H.H., Jr., 1990, Strategies 

and equipment for sampling suspended sediment and 

associated with toxic chemicals in large rivers—with 

emphasis on the Mississippi River: Science of the Total 

Environment, v. 97/98, p. 125–135.

Moody, J.A., 1993, Evaluation of the Lagrangian scheme 

for sampling the Mississippi River during 1987–1990: 

U.S. Geological Survey Water-Resources Investigations Report 93–4042, 31 p.

NASQAN, 2001, National Stream Quality Accounting 

Network home page. Accessed 1/2001 at 

http://water.usgs.gov/nasqan/.

NAWQA, 2001, National Water Quality Assessment 

program. Accessed 1/2001 at 

http://water.usgs.gov/nawqa/.

National Agricultural Statistics Service, 1999, U.S. Department of Agriculture: National Agricultural Statistics 

Service Historical Data. Accessed 7/99 at URL 

http://www.usda.gov/nass/pubs/histdata.htm.

Onstad, G.D., Canfield, D.E., Quay, P.D., and Hedges, J.I., 

2000, Sources of particulate organic matter in rivers 

from the continental USA—Lignin phenol and stable 

carbon isotope compositions: Geochimica et Cosmochimica Acta, v. 64, no. 20, p. 3439–3546.

Palmer, A.W., ca. 1903, Chemical Survey of the Waters of 

Illinois: Report for the years 1897–1902, University of 

Illinois, 254 p.

Rabalais, N. N., Turner, R. E., Justic, D., Dortch, Q., 

Wiseman, W. J., and Gupta, B. K. S., 1996, Nutrient 

changes in the Mississippi River and System responses 

on the adjacent continental shelf: Estuaries, v. 19,

 no. 2b, p. 386–407.

Rabalais, N. N., Turner, R. E., Justic, D., Dortch, Q., and 

Wiseman, W. J., 1999, Characterization of hypoxia: 

topic 1 report for the integrated assessment on hypoxia 

in the Gulf of Mexico: NOAA Coastal Ocean Program, 

NOAA Coastal Ocean Program Decision Analysis, 

Silver Spring, Md., Series no. 15, 167 p.

Shelton, L. R., 1994, Field guide for collecting and 

processing stream-water samples for the National 

Water-Quality Assessment program: U.S. Geological 

Survey Open-File Report 94–539, 57 p.

Showers, W.J., Eisenstein, D.M., Paerl, H., and Rudek, J., 

1990, Stable isotope tracers of nitrogen sources to the 

Neuse River, North Carolina: Raleigh, North Carolina 

Water Resources Research Institute, Completion 

Report no. 253, 28 p.

Silva, S.R., Kendall, C., Wilkison, D.H., Ziegler, A.C., 

Chang, C.C.Y., and Avanzino, R.J., 2000, A new 

method for collection of nitrate from fresh water and 

analysis of its nitrogen and oxygen isotope ratios: 

Journal of Hydrology, v. 228, p. 22–36.

Terry, D.L., and Kirby, B.J., 1999, Commercial fertilizers 

1999—A summary of fertilizer use in the United 

States: Lexington, Ky., Association of American Plant 

Food Control Officials, Inc. and The Fertilizer Institute, 41 p. 

Turner, R. E., and Rabalais, N. N., 1991, Changes in Mississippi River water quality this century—Implications 

for coastal food webs, BioScience, v. 41, p. 140–147.
REFERENCES CITED 57

U.S. Department of Agriculture, 1997, Agricultural 

resources and environmental indicators, 1996–97:

Washington, D.C., U.S Department of Agriculture, 

Economic Research Service, Natural Resources and 

Environment Division, Agricultural Handbook 

no. 712. 

U.S. Geological Survey, 2000, National land cover characterization project home page, accessed 3/2000 at 

http://edcwww.cr.usgs.gov/programs/lccp/

nationallandcover.html.

Van der Leeden, F., Troise, L., and Dodd, D.K., 1990, The 

Water Encyclopedia: Chelsea, Mich., Lewis Publishers 

Inc., 181 p.

Voerkelius, S., and Schmidt, H.L., 1990, Natural oxygen 

and nitrogen isotope abundance of compounds 

involved in denitrification: Mitteilungen der Deut. 

Bodenkundlichen Gesselschaft, v. 60, p. 364–366.

Winter, T.C., Harvey, J.W., Franke, O.L., and Alley, W.M., 

1998, Ground water and surface water—A single 

resource. U.S. Geological Survey Circular 1139, 70 p.