Water Quality in the

Mississippi Embayment

Mississippi, Louisiana, Arkansas, Missouri, Tennessee, and Kentucky

1995–98

U.S. Department of the Interior

U.S. Geological Survey

Circular 1208
POINTS OF CONTACT AND ADDITIONAL INFORMATION

Front cover: Photograph of the Black Swamp, Cache River Basin, near Gregory, Arkansas.

Back cover: Left, cotton grows on the banks of bayous in the Yazoo Basin; center, many of the rivers in the 

bootheel of Missouri have been channelized; right, soybeans are a major crop in the Mississippi Embayment Study 

Unit.

Photographs in this report were all taken by members of the MISE NAWQA Study Unit, U.S. Geological Survey.

The companion Web site for NAWQA summary reports:

http://water.usgs.gov/nawqa/

MISE contact and Web site:

USGS State Representative

U.S. Geological Survey

Water Resources Division

308 South Airport Road

Pearl, MS 39208–6649

e-mail: dc ms@usgs.gov

http://ms.water.usgs.gov/misenawqa/

National NAWQA Program:

Chief, NAWQA Program

U.S. Geological Survey

Water Resources Division

12201 Sunrise Valley Drive, M.S. 413

Reston, VA 20192 

http://water.usgs.gov/nawqa/

River Basin Assessments

Albemarle–Pamlico Drainage Basin (Circular 1157)

Allegheny and Monongahela River Basins (Circular 1202)

Apalachicola–Chattahoochee–Flint River Basin (Circular 1164)

Central Arizona Basins (Circular 1213)

Central Columbia Plateau (Circular 1144)

Central Nebraska Basins (Circular 1163)

Connecticut, Housatonic, and Thames River Basins (Circular 1155)

Eastern Iowa Basins (Circular 1210)

Georgia-Florida Coastal Plain (Circular 1151)

Hudson River Basin (Circular 1165)

Kanawha–New River Basins (Circular 1204)

Lake Erie–Lake Saint Clair Drainages (Circular 1203)

Las Vegas Valley Area and the Carson and Truckee River Basins

(Circular 1170)

Lower Illinois River Basin (Circular 1209)

Long Island–New Jersey Coastal Drainages (Circular 1201)

Lower Susquehanna River Basin (Circular 1168)

Ozark Plateaus (Circular 1158)

Potomac River Basin (Circular 1166)

Puget Sound Basin (Circular 1216)

Red River of the North Basin (Circular 1169)

Other NAWQA summary reports

Rio Grande Valley (Circular 1162)

Sacramento River Basin (Circular 1215)

San Joaquin–Tulare Basins (Circular 1159)

Santee River Basin and Coastal Drainages (Circular 1206)

South-Central Texas (Circular 1212) 

South Platte River Basin (Circular 1167)

Southern Florida (Circular 1207)

Trinity River Basin (Circular 1171)

Upper Colorado River Basin (Circular 1214) 

Upper Mississippi River Basin (Circular 1211)

Upper Snake River Basin (Circular 1160)

Upper Tennessee River Basin (Circular 1205)

Western Lake Michigan Drainages (Circular 1156)

White River Basin (Circular 1150)

Willamette Basin (Circular 1161)

National Assessments

The Quality of Our Nation‘s Waters—Nutrients and Pesticides (Circular 1225)
U.S. GEOLOGICAL SURVEY CIRCULAR

Water Quality in the Mississippi Embayment, 

Mississippi, Louisiana, Arkansas, Missouri, 

Tennessee, and Kentucky,1995–98

1208

By Barbara A. Kleiss, Richard H. Coupe, Gerard J. Gonthier, and Billy G. Justus
Library of Congress Cataloging-in-Publications Data

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. Government.

Free on application to the

U.S. Geological Survey

Information Services

Box 25286 Federal Center

Denver, CO 80225

Or call: 1-888-ASK-USGS

U.S. DEPARTMENT OF THE INTERIOR

BRUCE BABBITT, Secretary

U.S. GEOLOGICAL SURVEY

Charles G. Groat, Director

2000

Water quality in the Mississippi Embayment, Mississippi, Louisiana, Arkansas, Missouri, Tennessee, and Kentucky, 1995–98 / by Barbara A. Kleiss...[et al.].

p. cm. -- (U.S. Geological Survey Circular ; 1208)

Includes bibliographical references.

ISBN 0-607-95414-0 (alk. paper)

1. Water quality--Mississippi Embayment. I. Kleiss, Barbara A., 1958- II. Geological Survey (U.S.)

III. Series.

TD225.M64 W375 2000

363.739’42’09633--dc21

00-049462
CONTENTS

Contents III

NATIONAL WATER-QUALITY ASSESSMENT PROGRAM ............................................................... IV

SUMMARY OF MAJOR FINDINGS.................................................................................................... 1

INTRODUCTION TO THE MISSISSIPPI EMBAYMENT .................................................................... 3

MAJOR FINDINGS ............................................................................................................................. 7

Nutrient Contributions to the Mississippi River System ................................................................ 7

NATIONAL PERSPECTIVE—National Comparison of Total Nitrogen in Streams........................ 8

Pesticides Commonly Found in Mississippi Embayment Surface Water ...................................... 10

NATIONAL PERSPECTIVE—Pesticides in Streams Across the United States............................ 11

Tertiary Aquifers Have High-Quality Drinking Water ..................................................................... 12

Few Pesticides Detected in Memphis Shallow Aquifers................................................................ 12

Water-Quality Differences in Geological Subunits of the Alluvial Aquifer...................................... 13

NATIONAL PERSPECTIVE—Radon Levels in Ground Water Low in Mississippi Embayment 

Study Unit .................................................................................................................................. 14

 Aquatic Communities Show Environmental Stress...................................................................... 15

NATIONAL PERSPECTIVE—Comparison of Mississippi Embayment Aquatic Communities to 

National Results......................................................................................................................... 17

Organochlorine Pesticides Persist in Fish Tissue ......................................................................... 18

Pesticides in Air and Rain Samples from Agricultural and Urban Sites ........................................ 20

Integration of Biological, Geological, and Chemical Data Improves Understanding of Aquatic 

Systems ..................................................................................................................................... 22

STUDY UNIT DESIGN........................................................................................................................ 24

GLOSSARY........................................................................................................................................ 26

REFERENCES ................................................................................................................................... 28

APPENDIX —WATER-QUALITY DATA FROM THE MISSISSIPPI EMBAYMENT 

IN A NATIONAL CONTEXT .......................................................................................................... 30
NATIONAL WATER-QUALITY ASSESSMENT PROGRAM

IV National Water-Quality Assessment Program 

1991 95

1994 98

1997 2001

Not yet scheduled

High Plains Regional

Ground Water Study,

1999-2004

NAWQA Study Units

Assessment schedule

Mississippi

Embayment

THIS REPORT summarizes major findings about water quality in the Mississippi Embayment that emerged from 

an assessment conducted between 1995 and 1998 by the U.S. Geological Survey (USGS) National Water-Quality 

Assessment (NAWQA) Program. Water quality is discussed in terms of local and regional issues and compared to 

conditions found in all 36 NAWQA study areas, called Study Units, assessed to date. Findings are also explained in 

the context of selected national benchmarks, such as those for drinking-water quality and the protection of aquatic 

organisms. The NAWQA Program was not intended to assess the quality of the Nation’s drinking water, such as by 

monitoring water from household taps. Rather, the assessments focus on the quality of the resource itself, thereby 

complementing many ongoing Federal, State, and local drinking-water monitoring programs. The comparisons 

made in this report to drinking-water standards and guidelines are only in the context of the available untreated 

resource. Finally, this report includes information about the status of aquatic communities and the condition of instream habitats as elements of a complete water-quality assessment.

Many topics covered in this report reflect the concerns of officials of State and Federal agencies, water-resource 

managers, and members of stakeholder groups who provided advice and input during the Mississippi Embayment 

assessment. Basin residents who wish to know more about water quality in the areas where they live will find this 

report informative as well. 

THE NAWQA PROGRAM seeks to improve scientific and public understanding of water quality in the Nation’s 

major river basins and ground-water systems. Better understanding facilitates effective resource managment, 

accurate identification of water-quality priorities, and successful development of strategies that protect and restore 

water quality. Guided by a nationally consistent study design and shaped by ongoing communication with local, 

State, and Federal agencies, NAWQA assessments support the investigation of local issues and trends while 

providing a firm foundation for understanding water quality at regional and national scales. The ability to integrate 

local and national scales of data collection and analysis is a unique feature of the USGS NAWQA Program.

The Mississippi Embayment is one of 51 water-quality assessments initiated since 1991, when the U.S. Congress 

appropriated funds for the USGS to begin the NAWQA Program. As indicated on the map, 36 assessments have 

been completed, and 15 more assessments will conclude in 2001. Collectively, these assessments cover about onehalf of the land area of the United States and include water resources that are available to more than 60 percent of 

the U.S. population.
Summary of Major Findings 1

SUMMARY OF MAJOR FINDINGS

communities in most of the streams were dominated by 

fish tolerant of poor water quality conditions. The aquatic 

insects and algal communities generally were tolerant of 

turbid, silty conditions.

 • Methyl parathion, a metabolite of DDT, and several other 

pesticides were detected in air and rain samples collected 

in an agricultural area and in the urban area of Jackson, 

Mississippi.

Major Influences on Streams and Rivers

• Runoff from agricultural and urban areas

• Drainage modifications and channelization of 

streams 

• Modification or elimination of riparian habitat

Stream and River Highlights

The climate, rainfall, soil type, and surficial geology 

of the Mississippi Embayment (MISE) Study Unit 

strongly influence land use in the basin and subsequently influence water quality. About 62 percent of 

the Study Unit is used for agriculture. In areas of 

intensive row-crop production, as much as 90 percent 

of the land is used for agriculture. This influence from 

agricultural land use, with additional contributions 

from urban areas, has resulted in streams that often 

have high turbidities, mixtures of pesticides, and 

degraded riparian habitat. Biological communities in 

the streams commonly are stressed. However, human 

activities on the Earth’s surface seem to have a limited 

effect on the ground-water resources, which supply the 

vast majority of the region’s drinking water.

• Herbicides frequently were detected in streams draining 

agricultural or mixed land-use basins; insecticides were 

detected less often. Pesticides in over 60 percent of samples collected from these streams exceeded aquatic-life 

guidelines. Insecticides frequently were detected in samples from the urban stream; diazinon and chlorpyrifos 

were detected in every sample, usually in concentrations 

above aquatic-life guidelines.

• Nitrogen concentrations in the MISE generally were in 

the middle range of the national data, whereas total phosphorus concentrations were in the 67th to 93d percentile. 

The phosphorus concentrations in the Study Unit probably 

were related to many factors, such as rainfall amounts, 

soils, and artificial drainage of agricultural fields. No sample exceeded the guidelines and standards for nitrate or 

ammonia, but most exceeded the U.S. Environmental Protection Agency’s (USEPA) goal of 0.1 mg/L (milligram 

per liter) of phosphorus for the prevention of plant nuisances in streams. 

• Although the sale of the organochlorine insecticide DDT 

was discontinued in 1972, DDT and metabolites (chemicals resulting from the breakdown of DDT) were widespread within the MISE. DDT, or one of its metabolites, 

was found in every fish tissue sample collected and was 

found in 67 percent of the streambed-sediment samples. 

Detectable levels of a metabolite of DDT were measured 

in 14 percent of surface-water samples.

• Although volatile and semivolatile organic compounds 

often were detected in urban stream water and in bed sediment, they were rarely at levels of concern.

• Aquatic organisms present in the MISE streams were typical of those found in impacted or degraded streams. Fish 

The Mississippi Embayment (MISE) Study Unit is an 

approximately 49,800-square-mile area in the six States of 

Arkansas, Kentucky, Louisiana, Mississippi, Missouri, and 

Tennessee. Land use in the MISE is principally agricultural. 

Approximately 62 percent of the study area is agricultural, 33 

percent is forested, and 5 percent represents other land uses. The 

land use in some of the smaller drainage basins sampled is 

greater than 90 percent agricultural. 

MO

MS

AL

LA

AR

TN

KY

IL

Memphis Mississippi River

EXPLANATION

Land use

Surface water

Urban

Forest

Agricultural

MISE boundary

0 30

30 60 KILOMETERS

60 MILES

0
2 Water Quality in the Mississippi Embayment 

Selected Ground-Water Quality Indicators

Shallow Ground Water Supply Wells

Urban Agricultural Domestic Public

Pesticides1

Percentage of samples with concentrations

a health-related national guideline for drinking water,

aquatic life, or water-contact recreation; or above a national

goal for preventing excess algal growth

equal to or greater

than

Percentage of samples with concentrations a

health-related national guideline for drinking water, aquatic

life or water-contact recreation; or above a national goal

for preventing excess algal growth

less than

Percentage of samples with no detection

Not assessed

Nitrate2

Radon

Volatile

organics3

Bentazon, molinate, and fluometuron were the pesticides 

most frequently detected in the alluvial aquifer. Atrazine 

and dieldrin were detected one time each in shallow 

urban wells at levels above the drinking-water standards 

and guidelines.

• Nutrient concentrations in the ground water in the MISE 

generally were low. All nitrate concentrations were 

below the USEPA drinking-water standard of 10 mg/L.

• Radon is naturally occurring and was detected in almost 

every well sampled. Concentrations above the USEPAproposed drinking water standard of 300 picocuries per 

liter were found in water from only 16 of 109 wells. 

These levels are low, relative to levels detected in other 

NAWQA Study Units.

• Volatile organic compounds (VOCs) were detected in 

ground water throughout the Study Unit; however, concentrations were well within drinking-water standards. 

The most frequently detected VOCs were 1,2,4-trimethylbenzene and carbon disulfide.

Major Influences on Ground Water

• Ground water is commonly protected from surface 

activities by thick, regional clay layers.

Ground-Water Highlights

Ground-water quality in the Mississippi Embayment 

Study Unit generally is very good. Ground water in the 

deep Tertiary aquifers, which supply most of the 

region’s drinking water, generally is isolated from surface activities by thick “confining layers” of clays. Surface activities influence ground water where shallow 

deposits cover the hills in the eastern part of the Study 

Unit and in the Memphis shallow aquifers more than in 

the deeper aquifers. The abundant ground water in the 

alluvial aquifer of the Mississippi River valley is near 

the land surface but is covered by dense clays.

• Pesticides, such as atrazine, simazine, and metolachlor, 

were detected most frequently in the ground water in the 

shallow deposits that cover the hills in the eastern part of 

the Study Unit and in ground water underlying urban areas. 

Selected Stream-Quality Indicators

Small Streams Major Rivers

Urban

Agricultural Undeveloped

Mixed

Land Uses

Pesticides1

Percentage of samples with concentrations

a health-related national guideline for drinking

water, aquatic life, or water-contact recreation; or above a

national goal for preventing excess algal growth

equal to or

greater than

Percentage of samples with concentrations a

health-related national guideline for drinking water, aquatic

life or water-contact recreation; or below a national goal

for preventing excess algal growth

less than

Not assessed

Total

phosphorus2

Trace

elements4

Organochlorines5

Volatile

organics6

Semivolatile

organics7

Nitrate3

1 Insecticides, herbicides, and pesticide metabolites, sampled in water.

2 Total phosphorus, sampled in water.

3 Nitrate (as nitrogen), sampled in water.

4 Arsenic, mercury, and metals sampled in sediment.

5 DDT and PCBs sampled in fish tissue.

6 Solvents, refrigerants, fumigants, and gasoline compounds sampled in water.

7 By-products of fossil-fuel combustion; components of coal and crude oil sampled in 

 sediment.

1 Insecticides, herbicides, and pesticide metabolites, sampled in water.

2 Nitrate (as nitrogen), sampled in water.

3 Solvents, refrigerants, fumigants, and gasoline compounds sampled in water.
Introduction to the Mississippi Embayment 3

INTRODUCTION TO THE MISSISSIPPI EMBAYMENT

the related ecoregions defined by 

Omernik in 1987 (fig. 1). 

 About 57 percent of the MISE 

Study Unit lies within the Mississippi Alluvial Plain physiographic 

province and ecoregion. This area 

has been dominated by the flow 

and flooding of the Mississippi 

River during the past 2 million 

years or more. The Mississippi 

Alluvial Plain is an area of little 

topographic relief with an average 

slope of about 0.5 foot per mile 

toward the Gulf of Mexico. One of 

the distinct features of the alluvial 

plain is the formation of natural 

levees along the banks of the rivers, and the associated backswamp 

deposits that are dominated by 

dense alluvial clays and historically 

have supported extensive wetland 

areas. These clays have created low 

permeability soils, which limit the 

ability of rainwater to infiltrate the 

ground surface and may cause runoff from agricultural fields to rapidly enter rivers and streams. These 

clays also seem to limit the susceptibility of the ground water to surface activities in intense agricultural areas.

Thirty-five percent of the 

remainder of the Study Unit lies in 

In 1821, while painting a peregrine falcon, John James Audubon 

described the Yazoo River, the 

largest river wholly contained 

within the Mississippi Embayment 

Study Unit, as “a beautiful stream 

of transparent water, covered by 

thousands of geese and ducks and 

filled with fish” (Smith, 1954). 

Since that time, the bottomland 

hardwood forests that covered the 

Mississippi River Alluvial Plain 

have been cleared for agricultural 

use of the rich alluvial soils for the 

production of cotton, soybeans, 

rice, and corn. This clearing of the 

land has exposed the fine alluvial 

soils to erosion. Over time, the 

clays, along with nutrients and 

agricultural chemicals sorbed to the 

clay surfaces, were washed into the 

rivers and streams, thus greatly 

changing the water quality of the 

area. 

Physiography and 

Ecoregions

 Within the Mississippi Embayment (MISE) Study Unit, the surficial geology is the underlying 

controlling factor for the physiography, land use, biological communities, and water quality of the 

area. Therefore, the areas defined 

as physiographic regions (Fenneman, 1938) strongly correspond to 

the Gulf Coastal Plains physiographic province, which includes 

the area identified as the Mississippi Valley Loess Plains and 

Southeastern Plains ecoregions 

(fig. 1). The Gulf Coastal Plains are 

separated from the eastern edge of 

the Mississippi Alluvial Plain by 

the Loess Hills, which extend most 

of the length of the Study Unit. 

These hills are made of windblown silts, rise a few hundred feet 

above the Mississippi Alluvial 

Plain, and average about 15 miles 

in width. The remaining part of the 

Gulf Coastal Plains uplands and 

Southeastern Plains ecoregion generally is rolling to hilly with low to 

moderate topographic relief. The 

soils are composed, in part, of silts 

and are more permeable than the 

alluvial clays; there are indications 

that this allows for the downward 

infiltration of precipitation. This 

may partly protect the streams and 

rivers from compounds carried in 

runoff but may make the ground 

water slightly more susceptible to 

surface contamination. These 

coarser soils on steeper slopes are 

more erodible than alluvial soils, 

and large amounts of soil from the 

Gulf Coastal Plains uplands have 

Much of the Mississippi Embayment 

Study Unit was bottomland hardwood 

forests and wetlands well into the 20th 

century. 

John James Audubon’s painting of the peregrine falcon that he

worked on while visiting the Yazoo River area in 1821. 

(Reprinted courtesy of the National Audubon Society.)
4 Water Quality in the Mississippi Embayment

Figure 1. Boundaries for Fenneman’s (1938) physiographic regions are very similar to Omernik’s Level III ecoregions (1987), at 

least in part because the surficial geology is a controlling factor in the MISE Study Unit. The only major metropolitan area in the 

Study Unit is Memphis, Tennessee. The area has many rivers, as well as several large river systems, including the Yazoo and 

St. Francis Rivers and parts of the White and Arkansas Rivers. Major crops include soybeans, cotton, rice, and corn. Catfish 

farms are a major component of the landscape as well as a principal user of ground water.

eroded into the Mississippi Alluvial Plain.

In the west, the Study Unit abuts 

small areas of the Ozark Highlands. Limited sampling was done 

in these areas during this project. 

The land surface generally 

slopes toward the Mississippi River 

from both the eastern and western 

sides of the Study Unit and to the 

south toward the Gulf of Mexico. 

Thus, nearly all of the activities in 

this Study Unit that influence water 

quality ultimately influence the 

water quality of the Mississippi 

River and the Gulf of Mexico.

Geology

The Mississippi Alluvial Plain is 

in the northern part of the Mississippi Embayment, a geologic structural trough in which the underlying crust of the Earth forms a 

deep valley. Large rivers, such as 

the Mississippi, Arkansas, and 

Ohio Rivers, have flowed through 

this region, carved the surface, and 

deposited clay, silt, sand, and 

gravel, collectively called alluvium. During the past 2 million 

years, up to 300 feet of alluvium 

has filled this valley. The alluvium 

can be grouped into three major 

units: the Pleistocene Prairie Complex, Pleistocene valley trains, and 

the Holocene alluvium (see fig. 7 

for map; Autin and others, 1991; 

Saucier, 1994). 

The Prairie Complex is older 

than the Pleistocene valley trains 

and the Holocene alluvium. Saucier (1994) suggested that the Prairie 

Complex was deposited between 

about 120,000 years ago and the 

time of the greatest extent of the 

last glacier, about 18,000 years 

ago. The Pleistocene valley trains 

were mostly deposited during two 

time periods, between about 60,000 

and 25,000 years ago and during 

the waning phase of the latest glacial period between 18,000 and 

10,000 years ago. Glacial outwash 

(melting) flowing from north to 

south provided enough energy to 

cause a braided stream depositional 

environment to form in the Lower 

Mississippi River Valley during 

this time. By about 9,000 years 

ago, the rate of glacial outwash in 

the Lower Mississippi River Valley 

declined, and valley train deposiMemphis

Vicksburg

White River Yazoo River

Mississippi Valley

Loess Plains

Ecoregion

Southeastern

Plains Ecoregion

Mississippi Alluvial

Plain Physiographic Province

and Ecoregion

Gulf

Coastal Plains

Physiographic

Province

Ozark

Highlands

Ecoregion

Mississippi River

St. Francis R

Arkansas R

Cotton is still “king” in many areas of 

the Mississippi Embayment. Cotton 

requires extensive use of agricultural 

chemicals for successful cultivation.

Ground water is used to maintain 

more than 100,000 acres of catfish 

ponds in the MISE Study Unit.

During much of the growing season, 

rice crops are flooded with water 

withdrawn from the alluvial aquifer.
Introduction to the Mississippi Embayment 5 

tion ceased. The braided stream 

depositional process of the Pleistocene epoch was replaced by the 

lower energy meander stream depositional process of the Holocene 

epoch near major rivers, such as 

the Mississippi and Arkansas Rivers. (See fig. 2 for more explanation.) Autin and others (1991) 

reported that the depositional transition from Pleistocene valley 

trains (braided streams) to 

Holocene alluvium (meander 

streams) started near Baton Rouge, 

Louisiana, around 12,000 years ago 

and migrated northward to near 

Cairo, Illinois, by 9,000 years ago. 

 The Pleistocene valley train 

deposits generally have a coarser 

grain size than the Holocene alluvium. Also, water well drillers’ 

logs indicate that the clay and silt 

layer near the surface is thicker in 

the Holocene alluvium, whereas 

the underlying sand and gravel 

layer (alluvial aquifer) is thicker in 

the Pleistocene valley train deposits.

Hydrogeology

Two principal aquifer systems 

provide drinking-water supplies in 

the Mississippi Embayment—the 

Tertiary and the alluvial aquifers 

(fig. 3).

Tertiary Aquifers

The geologic groups associated 

with the deep Tertiary aquifers are 

the Midway, Wilcox, Claiborne, 

and the Jackson groups. The deep 

Tertiary aquifers sampled in this 

study are thick sand deposits within 

the Wilcox and Claiborne groups. 

The names of the aquifers, from 

youngest to oldest, include the 

Cockfield, Sparta, WinonaTallahatta, Memphis, Meridianupper Wilcox, and Wilcox. 

The natural regional flow of 

ground water in the Mississippi 

Embayment in the Tertiary aquifers 

is from the outcrop areas in the 

upper Gulf Coastal Plain, laterally 

along the aquifers toward the 

embayment axis, and then upward 

through overlying confining units 

and aquifers to the surface of the 

Mississippi Alluvial Plain (Grubb, 

1986; Ackerman, 1989). Pumping 

in the deep Tertiary aquifers has 

caused recharge rates to increase in 

the outcrop and production areas of 

the aquifer (Williamson and others, 

1990). 

Alluvial Aquifers

The Mississippi River confining 

unit is composed of the upper silt 

and clay of the Quaternary alluFigure 2. Although the photograph on the left was recently taken of a stream in the 

Western United States, its braided condition is representative of what streams in the 

Mississippi Valley may have looked like during the Pleistocene geologic period. 

These high-energy systems allow sand and gravel carried by the stream to be deposited in the flood plain. The photograph on the right depicts a classic meandering 

stream. Streams like this are low-energy systems and primarily deposit clay, silt, and 

fine sand in the flood plains adjacent to the streams. This depositional pattern is 

present today and has been the dominant form of deposition in the Lower Mississippi 

River Valley during the last 9,000 to 12,000 years. These differences in depositional 

environments appear to influence the chemistry of the ground water, the bioaccumulation of pesticides, and biological communities. 

Figure 3. Generalized geohydrologic section of the Mississippi River alluvial aquifer 

and underlying Tertiary aquifers (from Arthur, 1994).
6 Water Quality in the Mississippi Embayment

vium, whereas the Mississippi 

River alluvial aquifer is composed 

of the lower sand and gravel of the 

Quaternary alluvium (Boswell and 

others, 1968; Ackerman, 1989). 

Overlying silt and clay of the confining unit impedes recharge into 

the alluvial aquifer. Confining unit 

thickness generally ranges from 10 

to 50 feet and generally increases 

from north to south within the 

MISE Study Unit. The thickness of 

the alluvial aquifer ranges from 60 

to 140 feet. Wells screened in the 

alluvial aquifer typically yield 

between 1,000 and 2,000 gallons 

per minute (Whitfield, 1975). Prior 

to development, ground-water flow 

is believed to have been generally 

from the older adjacent and underlying aquifers toward the alluvial 

aquifer (Williamson and others, 

1990).

Climate

Climate in the MISE Study Unit 

varies from humid, temperate in 

the northern part to humid, subtropical in the southern part. This 

warm climate results in a long 

growing season and few killing 

frosts, which influences the types 

of crops that can be grown and the 

amount of pesticides that generally 

are applied. Mean annual precipitation ranges from about 48 inches 

per year in the northern part of the 

Study Unit to 56 inches per year in 

the southern part. Precipitation 

generally is greatest in April and 

least in October but is distributed 

fairly evenly throughout the year. 

This causes minor drought conditions to occur frequently during the 

summer, when the evapotranspiration rate is higher than the precipitation rate. These conditions also 

result in streams which flood rapidly, remain at high levels for long 

periods of time, and have low 

flows in the fall (fig. 4).

Water Use

In general, about three times as 

much ground water is used compared to surface water in the MISE 

Study Unit (fig. 5). During the 

summer months, both ground and 

surface water are used for irrigating 

crops. Most (in excess of 7 billion 

gallons per day) of the irrigation 

water is withdrawn from the alluvial aquifer. This aquifer is also 

used for domestic drinking water, 

aquaculture (primarily for catfish 

ponds), power production, and 

other commercial and industrial 

needs. Ground water, primarily 

from the Tertiary aquifers, is used 

for public supply. The principal use 

of surface water is for power production where it is used for cooling 

water for electric power generation. The second largest use of surface water is for irrigation.

Figure 5. Ground-water use in the Mississippi Embayment (MISE) Study Unit is 

dominated by irrigation usage. Surface water is also used for irrigation, but more is 

used for cooling water for electrical power production.

0

5

10

15

20

25

O N D J F M A M J J A S O N D J J F F M M A A M M J J J J A A S S O N D

1995 1996 1997 1998

STAGE, IN FEET

Figure 4. This hydrograph is representative of streams in the Mississippi Alluvial 

Plain. Often streams in this Study Unit flood rapidly, remain at high levels for long 

periods, and have very low streamflows in the fall. During the years of this project, 

1996 was drier than usual, and 1997 and 1998 were wetter than usual.

Aquaculture

Publicsupply/Domestic

Irrigation

Power production*

Commercial/Industrial

Ground-water use in the

MISE Study Unit in 1995

(Values given in millions of gallons per day)

Surface-water use in the

MISE Study Unit in 1995

(Values given in millions of gallons per day)

596.51

5.86*

157.32

6,593.14

445.42 60.7

1,400.78

27.25 85.56 926.2

EXPLANATION
Major Findings 7

MAJOR FINDINGS

Constituent Site Year Maximum Minimum Mean

Total nitrogen Yazoo River 1996–97 3.3 0.57 1.3

Mississippi River 1984–93 3.8 1.1 2.3

Nitrate as N Yazoo River 1996–97 1.2 0.16 0.45

Mississippi River 1984–93 2.7 0.70 1.5

Total phosphorus Yazoo River 1996–97 0.89 0.12 0.26

Mississippi River 1984–93 0.38 0.04 0.16

Orthophosphate as P Yazoo River 1996–97 0.10 0.01 0.043

Mississippi River 1984–93 0.13 0.02 0.058

Nutrient Contributions to the 

Mississippi River System

Although nitrogen and phosphorus, as well as silica and other 

nutrients, are natural and important parts of a healthy ecosystem, 

severe water-quality problems can 

arise if an ecosystem becomes 

enriched, or overloaded, with nutrients. In recent years, scientists have 

become aware of a large area of 

low dissolved oxygen that develops 

off the coast of Louisiana and 

Texas each summer. The extent and 

duration of this area of low dissolved oxygen has been related to 

the amount of nutrients, especially 

nitrogen, and freshwater flowing 

from the Mississippi River into the 

Gulf of Mexico (Goolsby and others, 1999). The proximity of the 

MISE Study Unit to the Gulf and 

the use of nitrogen fertilizer in the 

agricultural areas of the Study 

Unit, especially the Yazoo River 

Basin, have led to speculation that 

the surface waters of the Study 

Unit may be contributing a disproportionate amount of nitrogen and 

phosphorus to the Mississippi 

River and ultimately to the Gulf of 

Mexico.

In the MISE Study Unit investigations have shown that concentrations of nutrients (except total 

phosphorus) are higher in the Mississippi River at Vicksburg, Mississippi than near the mouth of the 

Yazoo River (table 1). The annual 

load of nitrogen and phosphorus 

from the Yazoo River for the 1996–

97 calendar years, while significant, was only a small percentage 

of the load carried by the Mississippi River (Coupe, 1998).

Water-Quality Standards

Concentrations of nitrogen and 

phosphorus were measured from 

weekly to at least monthly at nine 

stream-sampling sites in the MISE 

Study Unit. Nitrate concentrations 

never exceeded the drinking-water 

standard of 10 mg/L in any sample, 

and ammonia concentrations did 

not exceed aquatic-life guidelines. 

However, the USEPA goal of 0.1 

mg/L or less total phosphorus for 

streams not entering reservoirs was 

exceeded in every sample from the 

urban stream and in more than 50 

percent of the samples from five 

streams located in the Mississippi 

Alluvial Plain. Samples from the 

streams located in the Gulf Plains 

exceeded the recommended goal of 

0.1 mg/L or less total phosphorus 

in less than 50 percent of the samples.

Comparison of Nitrogen and 

Phosphorus in Streams in the 

Mississippi River Basin 

The yield of nitrogen (mass per 

unit area), from streams in the 

MISE Study Unit during 1995–96 

was compared to the average yield 

during 1980–96 from streams in 

The Yazoo River, the river with the largest drainage area wholly contained in the 

Mississippi Embayment Study Unit, enters the Mississippi River just north of these 

bridges at Vicksburg, Mississippi. 

Table 1. Concentrations of nutrients near the mouth of the Yazoo River compared to 

the Mississippi River at Vicksburg, Mississippi. 

[Concentrations are in milligrams per liter]
8 Water Quality in the Mississippi Embayment

Mississippi

Embayment

EXPLANATION

Urban Areas

Mixed Land-Use Areas

Agricultural Areas

Nitrogen is a natural and important component of a 

healthy stream; however, too much nitrogen can lead to 

degraded stream-water quality, affecting both the aquatic ecosystem and its use as a recreational or drinkingwater source for humans. The sources of nitrogen in 

surface water are many and include atmospheric deposition, municipal and industrial wastewater, and fixation 

of nitrogen from the atmosphere by plants and some 

species of algae.

By far, the biggest source of nitrogen in an agricultural 

setting, such as the Mississippi Embayment (MISE) 

Study Unit, is from the application of fertilizer to crops. 

For most of the Study Unit, the average annual total nitrogen input from fertilizer, manure, and the atmosphere 

combined is greater than 25 pounds per acre. Most of 

the agriculturally productive Midwest receives the same 

amount. 

 

The average annual concentration of total nitrogen from 

agricultural and mixed land-use streams in the MISE 

Study Unit is in the medium range, whereas nationally, 

most streams that drain areas with greater than 25 

pounds per acre of nitrogen input are in the high range. 

The lower concentrations of total nitrogen in the MISE 

Study Unit may be due to the milder climate that increases microbial activity in the winter and to the increased uptake of nitrogen by vegetation during the 

longer growing season. 

Nationally, the average annual total nitrogen concentrations in urban streams, including the one urban site in 

the Mississippi Embayment Study Unit, tend to fall into 

the “medium” classification.

National Comparison of Total Nitrogen in Streams
Major Findings 9

the Mississippi River Basin. These 

data indicate that the yield of nitrogen from the MISE Study Unit was 

less than the average yield from 

streams in intensive agricultural 

areas of the Midwest, but more 

than from streams in the drier West 

or in the less agricultural Upper 

Mississippi River Basin. The flowweighted mean total nitrogen concentrations for streams in the MISE 

Study Unit were generally in the 

50th to 60th percentile for all data 

collected in the national NAWQA 

Program (372 steam sites). The 

exception was the mean nitrogen 

concentration at the smallest mixed 

land-use site which was near the 

20th percentile, nationally. 

The yields of total phosphorus 

generally were higher in the MISE 

Study Unit than from most other 

areas in the Mississippi River 

Basin, and the percentile ranking of 

the flow-weighted mean total phosphorus concentration generally was 

quite high (67th to 93d). Again, the 

exception was the smallest mixed 

land-use site, where the mean total 

phosphorus concentration was near 

the 40th percentile. These high 

phosphorus yields were somewhat 

unexpected, as the soils in the 

MISE Study Unit, while fertile, do 

not contain excessive amounts of 

phosphorus. Also, phosphorus is 

used less as a fertilizer in the MISE 

Study Unit than in many parts of 

the Midwest (Battaglin and 

Goolsby, 1995), and due to the 

rural nature of the MISE, there are 

few significant point sources. One 

hypothesis for the high yields and 

concentrations of phosphorus in the 

MISE involves a combination of 

factors, such as soils, rainfall, and 

agricultural drainage. The sediment 

in the rivers of the MISE Study 

Unit is composed of fine, claysized particles to which phosphorus 

can sorb. Heavy rainfalls in the 

Study Unit increase the potential 

for erosion and the movement of 

these fine clay-sized particles from 

agricultural fields into the streams. 

Additionally, because of the large 

amount of rain, the tight clays that 

decrease infiltration of water, and 

the relatively flat terrain, much of 

the Study Unit has artificial drainage to expedite the movement of 

water. Most of this artificial drainage is surface drainage, which has 

been shown to decrease nitrate concentrations but to increase total 

phosphorus concentrations. 

The Effects of Land Use and 

Geology on Nutrient 

Concen3rations and Yields

Generally, total nitrogen and 

phosphorus concentrations and 

yields were higher in streams with 

predominantly agricultural land use 

in the Mississippi Alluvial Plain, 

but the highest nutrient concentrations and yields were from the 

urban stream. However, one stream 

located in the Gulf Plains in an area 

with no urban land use and only a 

moderate amount of agricultural 

land use had comparatively high 

total nitrogen and phosphorus 

yields. The high yields in this 

stream are reflective of the steep 

topography of the area and channelization of the stream for floodcontrol purposes.

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

Missouri

Lower Mississippi

Upper Mississippi

Mississippi Embayment

Ohio

Mid Mississippi

Basins

TOTAL PHOSPHORUS,

IN TONS PER SQUARE MILE

WATERSHEDS WITHIN MISSISSIPPI RIVER VALLEY BASINS

Phosphorus yields from watersheds within the MISE Study Unit were the highest in 

the Mississippi River Basin (represented by the dark green bars). These high 

phosphorus yields probably are related to several factors such as soils, amounts of 

rainfall, and artificial drainage of agricultural fields. In contrast, total nitrogen yields 

in streams in the Mississippi Embayment were less than those from the 

agriculturally productive Midwest, but more than those in the drier western part of 

the basin or the cooler Upper Mississippi River Basin, and about the same as 

streams in the Ohio River Basin. (Data from Goolsby and others, 1999.)

Nutrient Yields from MISE Watersheds

More details on nutrients in the Yazoo 

River can be found in the report:

Coupe, R.H., 1998, Concentrations and 

loads of nitrogen and phosphorus in the 

Yazoo River, northwestern Mississippi, 

1996–97: U.S. Geological Survey WaterResources Investigations Report 98–4219, 

17 p.

The report also can be downloaded at:

http://ms.water.usgs.gov/misenawqa//
10 Water Quality in the Mississippi Embayment

JFMAMJ J

MONTH

ASON D

Agricultural Stream

MEAN MONTHLY CONCENTRATION,

IN MICROGRAMS PER LITER

FEB. 1996 - JAN. 1998

Pesticide

EXPLANATION

MONTH

Urban Stream

JFMAMJ JA SON D

60 60

50 50

40 40

30 30

20 20

10 10

0 0

Other

Simazine

Norflurazon

Molinate

Metolachlor

Fluometuron

Cyanazine

Atrazine

2,4-D

Pesticides Commonly Found 

in Mississippi Embayment 

Surface Water

The occurrence and temporal 

distribution of more than 80 pesticides and pesticide metabolites 

were determined at five streamsampling sites from 1996 to 1998 

in the MISE Study Unit. More than 

230 stream samples were collected 

and analyzed. The five rivers sampled included three rivers with 

small, primarily agricultural watersheds; one river with a small, urban 

watershed; and one large river (the 

Yazoo River) with mixed land use 

(row-crop agriculture, forest, pasture, and a small amount of urban). 

Pesticides, usually herbicides, frequently were detected in water 

samples from all five rivers sampled. Aquatic-life guidelines were 

frequently exceeded in the urban 

stream and occasionally exceeded 

in all of the rivers sampled in the 

MISE Study Unit. 

Agricultural Streams

The pesticides detected in the 

rivers that drain the agricultural 

watersheds in the MISE Study Unit 

showed distinct seasonal patterns 

that corresponded to the type of 

crops grown in the basin and the 

use of pesticides on those crops. 

For instance, the highest concentration of the pre-emergent herbicide 

atrazine frequently was found early 

in the growing season (April-May) 

corresponding to its application 

prior to the planting of corn and 

grain sorghum (fig. 6). The highest 

concentrations of herbicides that 

are used on other crops (cotton and

rice) with later planting dates, or 

herbicides that are used after the 

crop has emerged from the ground, 

such as fluometuron and molinate, 

were detected later in the growing 

season (June–July). The concentrations of most of these herbicides 

were well below any acute toxicity; 

however, the long-term effects of 

chronic exposure to low levels of 

multiple herbicides are not well 

known. 

Water samples are filtered and processed in a mobile laboratory 

immediately after sample collection.

Figure 6. Herbicides in agricultural streams in the Mississippi Embayment Study Unit had higher concentrations, showed clear 

seasonal patterns, and contained different compounds than herbicides in urban streams. The urban stream samples were dominated by simazine, a turf grass herbicide. Concentrations of herbicides in the urban stream remained fairly constant throughout 

the year, whereas agricultural sites had concentrations that peaked in the spring shortly after application. Agricultural sites also 

were dominated by different herbicides (in this case atrazine). 
Major Findings 11 

0

20

40

60

80

100 Agricultural Land Use

National Data

MISE Data

0

20

40

60

80

100 Urban Land Use

0

20

40

60

80

100

Atrazine

Deethylatrazine

Cyanazine

Alachlor

EPTC

Molinate

Fluometuron

Metolachlor

Simazine

Prometon

2, 4-D

Diuron

Tebuthiuron

Diazinon

Carbaryl

Malathion

Chlorpyrifos

Methyl Parathion

AGRICULTURAL

HERBICIDES

URBAN

HERBICIDES INSECTICIDES

Mixed Land Use

Pesticides in Streams Across the United States

This diagram shows the top 15 pesticides most frequently detected in surface 

water at NAWQA Study Units throughout the United States and detections in 

surface water of the Mississippi Embayment (MISE Study Unit). Three pesticides used heavily in the Study Unit—fluometuron, methyl parathion, and molinate—but not used extensively throughout the United States, also are 

included for comparison. Few areas of the United States are as suited to agriculture as the Mississippi River Alluvial Plain in the MISE Study Unit. The 

combination of rich alluvial soils; a long, hot, growing season; flat terrain; and 

plentiful rainfall make agriculture the dominant economic force in the Study 

Unit. These same conditions also increase the weed and insect pressure and 

subsequently lead to an intensive use of pesticides to encourage profitable 

farming. In general, the frequency of detection of pesticides in surface waters 

of the MISE Study Unit exceed the national average. FREQUENCY OF DETECTION

Urban Stream

The type, amounts, and timing of 

the occurrence of pesticides in the 

stream draining an urban watershed 

are much different from those in 

the agricultural streams (fig. 6). 

The herbicides most frequently 

occurring in the urban stream such 

as atrazine, 2,4–D, simazine, and 

prometon, are those used in lawn 

care and in the maintenance of 

rights-of-way. The urban stream 

was also the only stream with frequent occurrences of insecticides: 

chlorpyrifos and diazinon were 

detected in every urban stream 

sample collected and exceeded the 

aquatic-life guidelines in 12 of 25 

and 24 of 25 samples, respectively.

 DDT Metabolites in Surface Water

Although DDT strongly sorbs to 

sediments rather than readily dissolving in water, detectable levels 

of DDE, a metabolite of DDT, were 

found in 14 percent of the filtered 

stream-water samples analyzed. 

More details on pesticides in streams 

in the MISE can be found in the report:

Coupe, R.H., 2000, Occurrence of 

pesticides in five rivers of the Mississippi 

Embayment Study Unit, 1996–98: U.S. 

Geological Survey Water-Resources 

Investigations Report 99–4159, 69 p. 

The report also can be downloaded at:

http://ms.water.usgs.gov/misenawqa/

Many pesticides are applied by aircraft 

in the Study Unit.
12 Water Quality in the Mississippi Embayment

Tertiary Aquifers Have HighQuality Drinking Water 

During the spring of 1996, water 

samples were collected from 30 

public-supply wells in the deep 

Tertiary aquifers in the MISE 

Study Unit. The most significant 

finding from this part of the study 

is that all of the samples analyzed 

from these public-supply wells met 

all existing drinking-water standards and guidelines. Concentrations of most of the constituents 

measured that could adversely 

affect water quality, including 

nutrients, pesticides, radon, and 

volatile organic compounds, were 

below drinking-water standards 

and guidelines.

The Deep Tertiary Aquifers

The deep Tertiary aquifers 

underlie about 80 percent of the 

MISE Study Unit. Much of the 

population in this part of the country depends on these aquifers for 

drinking water. Wells sampled 

range in depth from 208 to 1,460 

feet below the ground surface.

Sample Results

Water from wells in the deep 

Tertiary aquifers had low nutrient 

concentrations. The highest nutrient concentration measured in a 

sample was 3.8 mg/L of nitrite plus 

nitrate nitrogen, which is less than 

half the drinking-water guideline of 

10 mg/L. Pesticides were detected 

in water from only one of the wells. 

Water from the shallowest well 

sampled had a 0.16-μg/L (microgram per liter) concentration of the 

herbicide bromacil and a 0.004- 

μg/L concentration of deethylatrazine, a metabolite of the herbicide 

atrazine. Volatile organic compounds (VOCs) are compounds 

that have a high vapor pressure relative to their water solubility and 

include such things as components 

of gasoline and organic solvents. 

VOCs were detected frequently in 

the MISE, but concentrations were 

far below drinking-water guidelines. Samples from 26 of the 30 

public-supply wells had at least one 

VOC detection. The VOCs most 

commonly detected were methylethylketone and 1,2,4-trimethylbenzene, detected in 23 and 7 

percent of the wells, respectively. 

Nutrients, pesticides, and VOCs 

generally enter the ground water 

from surface contamination; however, public-supply wells were generally deep enough to avoid 

elevated levels of these compounds.

 Radon in water from the publicsupply wells ranged from 54 to 270 

picocuries per liter; none exceeded 

guidelines. Radon levels found in 

the ground water in the MISE were 

the second lowest of the 16 Study 

Units sampled during 1996–98.

Few Pesticides Detected in 

Memphis Shallow Aquifers 

In addition to the Tertiary aquifers, 32 shallow monitoring wells 

(not public-supply, drinking-water 

wells) were sampled in the shallow 

aquifers near Memphis, Tennessee. Results were similar to those 

from the deep Tertiary aquifer 

study except that pesticides were 

more frequently detected and radon 

concentrations were higher. An 

atrazine concentration of 3.14 μg/L 

was measured in one well, which 

narrowly exceeded the drinkingwater guideline of 3.0 μg/L, and 

dieldrin was measured above the 

drinking-water guideline of 0.02 

μg/L in another well.

Ground-water samples commonly were 

collected from municipal drinking-water 

facilities, such as the one pictured 

above. 

More details on ground-water quality 

in the deep Tertiary aquifers can be 

found in the report:

Gonthier, G.J., 2000, Water quality in the 

deep Tertiary aquifers of the Mississippi 

Embayment, 1996: U.S. Geological Survey 

Water-Resources Investigations Report 

99–4131, 91 p. 

The report also can be downloaded at:

http://ms.water.usgs.gov/misenawqa/

Ground-water sample preparation 

occurred inside plastic enclosures in 

order to minimize sample 

contamination from chemicals in the 

atmosphere.
Major Findings 13 

EXPLANATION

Prairie complex

Pleistocene valley trains

Wells

Holocene alluvium

Mississippi Embayment

Study Unit Boundary

Mississippi River

MISSISSIPPI

LOUISIANA

ARKANSAS

TENNESSEE

KENTUCKY

MISSOURI

Base modified from U.S. Geological Survey digital data 1:2,000,000

Albers Equal-Area projection

Standard parallels 29 30 ́ and 45 30 ́; central meridian 96

Water-Quality Differences in 

Geological Subunits of the 

Alluvial Aquifer

Previous researchers have studied the alluvial aquifer as a single 

Quaternary feature (Grubb, 1986; 

Ackerman, 1989). However, during 

this NAWQA investigation, the 

results of the water-chemistry studies were examined by dividing the 

area into different major geologic 

units, two of which are the Pleistocene valley trains and the 

Holocene alluvium (Saucier, 1994). 

The data collected suggest that the 

differences in the geology influence the chemical makeup of the 

ground water in the alluvial aquifer.

The Alluvial Aquifer

The alluvial aquifer is a large, 

underground, water-bearing layer 

of sand and gravel in the Lower 

Mississippi River Valley (fig. 7). 

Water use from the alluvial aquifer 

is enormous; pumpage from the 

aquifer is about 7 billion gallons 

per day (Mesko and others, 1990). 

Most of the water pumped from the 

alluvial aquifer is used to irrigate 

crops or to maintain aquaculture, 

but the ground water also is used 

for public supply and industry. Water-Chemistry Analysis Results

Twenty-nine wells in the Pleistocene valley trains and 25 wells in 

the Holocene alluvium were sampled during the summer of 1998. 

At least one pesticide was detected 

in water from 19 of the 54 wells, 

but none of the concentrations were 

above drinking-water standards or 

guidelines. The most frequently 

detected pesticide was bentazon, an 

herbicide used to control weeds in 

soybean fields. Other pesticides 

detected in the alluvial aquifer in 

very low concentrations were molinate, fluometuron, 2,4–D, fenuron, 

atrazine, deethylatrazine, metolachlor, propanil, and p,p ́ DDE. At 

least one VOC was detected in 

water from 25 of 46 wells; 1,2,4-

trimethylbenzene was detected 

most frequently. However, all of 

the VOC concentrations were well 

below drinking-water standards or 

guidelines. 

Pleistocene Valley Trains and the 

Holocene Alluvium

The two subunits of the alluvial 

aquifer, the Pleistocene valley 

trains and the Holocene alluvium, 

have different lithological characFigure 7. The colored part of this map depicts the areal extent of the three main 

geologic subunits of the alluvial aquifer and the location of the 54 wells that were 

sampled as part of this study. Statistically significant differences exist in the nutrient, 

carbon, and metal chemistry of the water sampled in wells located in the 

Pleistocene valley trains as compared to the Holocene alluvium, demonstrating the 

effect of geology on other components of the environment.

Many of the water samples collected 

from the alluvial aquifer were taken from 

irrigation wells in agricultural areas.
14 Water Quality in the Mississippi Embayment

teristics. The Pleistocene valley 

trains generally have coarser grain 

sizes than the Holocene alluvium, 

whereas the Holocene alluvium has 

a thicker clay and silt surficial unit. 

These characteristics indicate that 

ground-water flow may be more 

active in the Pleistocene valley 

trains.

Results of the ground-water 

chemistry showed that sulfate, pH, 

tritium, chloride, and radon-222 

were present in higher concentrations in water from wells in the 

Pleistocene valley trains, whereas 

dissolved organic carbon, iron, 

ammonia, fluoride, potassium, 

bicarbonate, magnesium, radium226, barium, calcium, chromium, 

and dissolved solids were present 

in higher concentrations in water 

from wells in the Holocene alluvium. Examples of some of these 

differences are shown in figure 8. 

Water in the Holocene alluvium 

tends to be older than water in the 

Pleistocene valley trains; that is, it 

has been underground longer. This 

increases possible contact with buried organics, resulting in less dissolved oxygen, which could 

influence concentrations of other 

chemical constituents.

Arsenic Concentrations

Arsenic, a compound that has 

been implicated in causing several 

cancers, was found at concentrations that exceeded current drinking-water guidelines in water from 

only one irrigation well that 

pumped water from the alluvial 

aquifer. However, concentrations at 

several other wells were high 

enough to justify additional testing 

if proposals to lower the standards 

are promulgated. 

 Radon Levels in Ground Water Low in Mississippi 

Mississippi

Embayment

NAWQA Study Units with radon concentrations exceeding:

Radon-222 in ground water

Radon is a colorless, odorless, 

radioactive gas that forms naturally in 

rocks and soils as an intermediate 

product in the radioactive decay of 

uranium-238. According to the U.S. 

Environmental Protection Agency, 

breathing radon in indoor air is the 

second leading cause of lung cancer in 

the United States. Radon can enter 

homes from soil or bedrock through 

cracks in basements or foundations, or 

it can be released from water during 

bathing, cooking, or showering.

 

Radon is highest in areas where there 

are uranium-rich metamorphic and 

igneous rocks. Because the MISE 

Study Unit is located in an area of thick 

alluvial soils that have few rocks, the 

radon levels in the ground water are 

some of the lowest reported by the 

NAWQA Program. 

0

2

4

6

8

10

Ammonia Dissolved

organic carbon

Iron

Pleistocene valley trains

Holocene alluvium

MEDIAN CONCENTRATION,

IN MILLIGRAMS PER LITER

Figure 8. This graph shows some of 

the differences in chemistry in water 

from the Pleistocene valley trains and 

from the Holocene alluvium for a few 

selected constituents. Water from the 

wells in the Holocene deposits tended 

to be older and had lower oxygen levels. Low dissolved-oxygen concentrations in ground water may be 

associated with the presence of ammonia, dissolved organic carbon, and iron.

 Embayment Study Unit
Major Findings 15 

Streams in the 

Mississippi Embayment 

Study Unit have small 

changes in elevation 

from their headwaters to 

the mouth of the stream. 

This makes them very 

slow moving and 

generally contributes to 

low oxygen concentrations in the streams. 

The natural streams 

commonly have swamps 

adjacent to them, 

resulting in water 

stained with organics, ample habitat, and difficult sampling conditions, as shown 

above. The many channelized streams in the area (see upper left photograph) have 

commonly lost all of their riparian vegetation, and the streams have little habitat for 

aquatic organisms.

Aquatic Communities Show 

Environmental Stress

A combination of natural and 

anthropogenic (human-related) factors results in stream conditions 

that stress aquatic communities in 

the Mississippi Embayment Study 

Unit. The streams have naturally 

low gradients that result in sluggish 

flows and slow rates of reaeration 

(the ability of oxygen to enter the 

water). Also, the streams, in their 

natural conditions, have an abundance of streamside vegetation and 

swamps, resulting in an abundance 

of organic material in the water. 

This organic material is a good 

source of food for invertebrates 

(aquatic insects, crayfish, and 

freshwater shrimp) that inhabit the 

streams, but decay of the organic 

material and seasonally high water 

temperatures contribute to low dissolved-oxygen concentrations. The 

combination of low flow, high 

organic concentrations, and high 

temperatures results in a natural 

environment in which the organisms are often stressed by low dissolved-oxygen concentrations. 

These natural conditions are 

coupled with many anthropogenic 

conditions in the area. These 

include stream channelization, 

which can eliminate riparian vegetation and degrade stream habitat; 

agricultural runoff into streams, 

which adds sediments, pesticides, 

and fertilizers to the aquatic environment; and the decline in the 

base flow of the streams due to 

ground-water withdrawal, which 

reduces the quantity of water available for organisms. This combination of natural and anthropogenic 

conditions affects each of the major 

biotic communities differently.

Algae

As a result of the dominant agricultural land use, fine alluvial soils, 

and limited vegetation in streamside or riparian areas, most of the 

streams in the MISE Study Unit are 

very turbid. Turbidity refers to the 

reduced clarity of surface water 

due to particles (usually sediment) 

suspended in the water. Many of 

the streams within the MISE also 

have moderately high phosphorus 

levels, which encourage algal 

growth. However, the algal growth 

in the streams is often more limited 

by the inability of light to penetrate 

the turbid waters, than by lack of 

nutrients. One indication of this 

can be seen in the Algal Siltation 

Index on page 17. This index uses 

the relative abundance of diatom 

species, which are able to move 

and avoid being buried under large 

amounts of sediment, as an indication of stream-water quality. Levels 

of this index are high in agricultural areas of the MISE and moderate in mixed land-use areas.

Aquatic Invertebrates

Aquatic invertebrates in the 

MISE are influenced by habitat 

quantity and quality as well as by 

water chemistry. Often, the loss of 

stream and riparian habitat in the 

MISE is associated with stream 

channelization, where streams have 

been cleared, ditched, and straightened to facilitate the movement of 

floodwaters. These activities also 

result in the loss of microhabitats 

that are essential to aquatic invertebrates for food sources and refuge. 

Lower numbers of invertebrate 

taxa were found at sites that had 
16 Water Quality in the Mississippi Embayment

0

10

20

30

40

50

60

Low Medium High

INVERTEBRATE HABITAT QUALITY

NUMBER OF INVERTEBRATE

TAXA

0

4

8

12

16

20

Low Medium High

TURBIDITY (NTU) AT SAMPLING SITE

NUMBER OF BASS COLLECTED

lower habitat quality (fig. 9). Other 

factors, including turbidity, low 

dissolved-oxygen concentrations, 

and the introduction of contaminants to the water, also affect invertebrate communities.

 When compared to samples collected in other NAWQA Study 

Units across the United States 

(p. 17), invertebrate communities 

in MISE agricultural areas have 

low numbers of species and high 

proportions of tolerant organisms.

Fish

The condition of the fish communities in the MISE Study Unit 

was related to both water quality 

and land-use activities. The best 

quality fish communities occurred 

where instream variables such as 

turbidity, total ammonia, the average number of herbicides detected, 

and total DDT in fish tissue were 

lowest. As shown in figure 10, the 

number of bass, an important game 

fish in the MISE, was highest at the 

sites where the turbidity was lowest. The condition of the fish communities also was correlated to 

landscape-level variables such as 

insecticide application rates and 

soil permeability. 

When compared to fish communities collected at NAWQA Study 

Units across the Nation (p. 17), the 

MISE had more fish that are omnivores (that is, fish that eat whatever 

is available and therefore are more 

tolerant than fish that have more 

restrictive diets) and more fish that 

are considered tolerant of poor 

water-quality conditions. However, there were fewer anomolies 

(sores, parasites and other abnormalities on the fish) and non-native 

fish found in the MISE than in 

other locations. This resulted in an 

overall national fish ranking of 

MISE agricultural streams slightly 

below the midpoint between the 

most degraded and least degraded 

streams in the NAWQA Program, 

whereas mixed land-use streams 

ranged from good to less than 

average. 

Figure 9. The number of invertebrate 

taxa increased as the quality of the 

invertebrate habitat increased in MISE 

streams.

A prime habitat for invertebrates in the Mississippi Embayment Study Unit is 

this “undercut bank” where insects and other organisms hide in the roots and 

sticks. This habitat is removed or disturbed by channelization of streams and 

rivers or other habitat alterations.

Figure 10. The number of bass 

collected at a stream site was highest 

in those streams where the turbidity 

was the lowest.

Some of the samples for both algae 

and invertebrates were collected by 

scraping organisms off submerged 

sticks in the streams. These sticks are 

commonly some of the best remaining 

habitats in many streams and rivers in 

the Mississippi Embayment Study Unit. 
Major Findings 17 

Algal Siltation Index

Mixed

Agriculture

0 10 30 20 40 50 60 70 80 90 100

National Range

MISE Study Unit Value

75th Percentile

25th Percentile

 Mississippi Embayment Aquatic Communities 

in a National Context

Algal Siltation Index

Algae collected at the 8 MISE basic fixed ecology sites were compared to algae at 140 other NAWQA sites by use of the Siltation Index 

(Bahls and others, 1992). This index is the relative abundance of motile 

diatoms, the species Navicula, Nitzschia, Cylindrotheca, and Surirella in 

a diatom count. These diatoms are able to move through silt particles and 

are associated with fine sediments. Because they are able to avoid being 

buried, they are considered more tolerant of sedimentation than other 

diatoms. Generally, this index tends to be higher for streams in agricultural basins. Relative to this index, all of the MISE agricultural sites fall 

into the most-degraded category for streams along with one of the mixed 

land-use sites, whereas the other two sites fall into the middle 50 percent.

Fish Community Index

Similar in concept to the invertebrates, a multimetric fish index was 

developed to facilitate the comparison of fish communities across the 

United States. This index included four metrics: the percentage of tolerant individuals, the percentage of omnivorous individuals, the percentage 

of non-native individuals, and the percentage of individuals with anomalies. In all four metrics, a high percentage of individuals with the characteristic is typical of degraded sites. Agricultural sites in the MISE Study 

Unit generally fell at the boundary between the most-degraded category 

and the middle 50 percent (four sites are represented by the symbol at the 

60-percent point). The mixed land-use sites ranged from the leastdegraded category to the highly degraded category. 

FOR POSITION ONLY

Highest 25 percent* Middle 50 percent

Lowest 25 percent

* Higher values suggest a more degraded stream site

A National Ranking of in Streams ALGAL STATUS

ALGAL SILTATION

INDEX

Highest 25 percent* Middle 50 percent

Lowest 25 percent

* Higher values suggest a more degraded stream site

A National Ranking of in Streams FISH STATUS

FISH INDEX

Highest 25 percent* Middle 50 percent

Lowest 25 percent

* Higher values suggest a more degraded stream site

A National Ranking of in Streams INVERTEBRATE STATUS

INVERTEBRATE

STATUS INDEX

Invertebrate Community Status Index

To compare the invertebrate communities at MISE ecological basic 

fixed sites to national sites, a multimetric index called the Invertebrate 

Community Status Index was developed. The index combines 11 metrics, 

including ones that address taxa richness and diversity, richness of mayflies, stoneflies, and caddisflies, and tolerance metrics. Relative to this 

index, MISE agricultural streams are all ranked within the 25-percent 

most-degraded category for streams, whereas the mixed land-use streams 

have one site that falls into each category. Across the United States, both 

agricultural and urban sites tend to fall into the more degraded category.

 

Invertebrate Community Status Index

Mixed

Agriculture

0 10 30 20 40 50 60 70 80 90 100

National Range

MISE Study Unit Value

75th Percentile

25th Percentile

Mississippi

Embayment

Fish Index

Mixed

Agriculture

0 10 30 20 40 50 60 70 80 90 100

National Range

MISE Study Unit Value

75th Percentile

25th Percentile

4

Comparison of Mississippi Embayment Aquatic 

 Communities to National Results
18 Water Quality in the Mississippi Embayment

Organochlorine Pesticides 

Persist in Fish Tissue

During the 1950s and 1960s, 

organochlorine pesticides were 

heavily used in the MISE Study 

Unit to control insects, particularly 

those associated with the cultivation of cotton. One of the most 

widely used organochlorine insecticides was DDT. In 1972, the sale 

of DDT was discontinued, and the 

use of most of the persistent organochlorine pesticides was discontinued during the 1970s. Nearly 30 

years later, however, DDT or its 

metabolites were detected in fish 

tissue from all 41 sites sampled in 

the Study Unit. Thirty of these sites 

have total DDT levels in excess of 

the 0.2-mg/kg (milligram per kilogram) or 200 μg/kg (micrograms 

per kilogram) criterion set by the 

State of New York for the protection of fish-eating wildlife (Newell 

and others, 1987).

Although somewhat less prevalent and at lower concentrations, 

other organochlorine compounds 

also were detected in fish, including chlordane (at 33 percent of the 

sites), dieldrin (79 percent), heptachlor (7 percent), mirex (29 percent), and toxaphene (56 percent). 

Of the 506 sites sampled thus far 

in the National Water-Quality 

Assessment Program, the highest 

concentrations of total DDT and 

toxaphene were found in fish collected in the Mississippi Embayment Study Unit (see pages 33 and 

34 in Appendix A).

Distribution of Concentrations of 

DDT Within the Mississippi 

Embayment Study Unit

Although DDT was detected in 

fish tissue at every sampling site, 

tissue samples from sites in the 

southern part of the Study Unit 

(fig. 11) had much higher concentrations of total DDT. On a national 

scale, Nowell and others, (1999) 

presented a positive correlation 

between median total DDT concentrations in whole fish and agricultural use of DDT in 1966. In the 

MISE, however, there seem to be 

additional factors influencing the 

persistence of DDT in fish tissue. 

Fish tissue data were compared to 

dozens of land-use and waterchemistry variables. Good correlaFigure 11. The concentrations of organochlorine pesticides were measured 

in fish tissue collected at 41 sites in the MISE Study Unit. Total DDT, an 

insecticide that has not been sold in the United States since 1972, was 

detected at all sites and occurs in concentrations that are of possible human 

health concern at some sites.

Most of the rivers in the MISE Study 

Unit were too deep to wade, so boatmounted electroshocking equipment 

was used to collect fish (usually 

common carp) for tissue analysis. 

Mississippi River

ILLINOIS

MISSOURI

KENTUCKY

TENNESSEE

ARKANSAS

LOUISIANA

MISSISSIPPI

33°

35°

37°

89°

91°

92°

EXPLANATION

MISE Boundary

40 - 1,000

1,001 - 5,000

Greater than 5,000

Concentration of total DDT,

in micrograms per kilogram
Major Findings 19 

tions can be made between total 

DDT concentrations and dissolved 

ammonia, nitrate, total phosphorus, 

and turbidity. The correlations with 

land-use variables, such as the percentage of the basin in agricultural 

production or the percentage of the 

basin in which cotton is grown, are 

much weaker, suggesting that factors in addition to land use and pesticide use are contributing to the 

distribution of DDT.

A relation exists between the 

concentrations of DDT in fish tissue and the geology of the area. 

Total DDT concentrations are 

much higher at sites in the 

Holocene alluvium than in the 

Pleistocene valley trains (fig. 12). 

The soils and geologic deposits in 

the Holocene alluvium are largely 

composed of dense clays that may 

cause agricultural runoff from 

these areas to enter the streams 

directly rather than infiltrate 

through the soils. Also, DDT tends 

to sorb onto clay particles and may 

be carried into streams attached to 

these particles. Once in the stream, 

the cohesive nature of clay tends to 

prevent the material from moving 

downstream. These combined 

mechanisms may cause greater 

amounts of DDT to be in streams 

and available to organisms in 

Holocene areas than in streams in 

the Pleistocene valley trains.

Total DDT concentrations were 

detected in streambed sediments at 

all 15 sites measured. However, the 

concentrations in the sediments 

were many times lower than those 

in fish tissue.

Human Health Considerations

Because the NAWQA sampling 

was designed to measure the occurrence and distribution of compounds in the environment rather 

than address human health issues, 

whole fish (usually common carp) 

rather than fish fillets or other edible fish parts were analyzed for 

organochlorine compounds. However, the high concentrations of 

organochlorines that were detected 

at some of the sites in the MISE 

Study Unit suggest the need for 

further investigation. In the years 

since the sale of DDT and toxaphene has been discontinued, concerns have been raised about not 

only the toxicity of the pesticides 

but also the carcinogenic nature of 

organochlorine compounds. 

Less than 150

Greater than or equal to 150 - 1,000

Greater than or equal to 1,000 - 5,000

Greater than 5,000

EXPLANATION

Concentrations, in

micrograms per kilogram

wet weight

Fish collected in 1995 during an interdisciplinary USGS study found that the 

highest total DDT levels in the Mississippi River Valley were measured in the 

MISE Study Unit. Information about study methods can be found in Schmitt 

and Dethloff (2000).

0

1,000

2,000

3,000

4,000

5,000

6,000

7,000

8,000

TOTAL DDT CONCENTRATIONS,

IN MICROGRAMS PER KILOGRAM

HOLOCENE ALLUVIUM PLEISTOCENE

VALLEY TRAINS

Figure 12. The concentration of total DDT in fish tissue is higher at Holocene 

alluvium sampling sites than at sites in the Pleistocene valley trains. The mean 

concentration for the Holocene sites is 2,895 micrograms per kilogram, while the 

mean concentration for the Pleistocene sites is 522 micrograms per kilogram.

DDT in Fish Tissue in the Mississippi River Valley
20 Water Quality in the Mississippi Embayment

Pesticides in Air and Rain 

Samples from Agricultural 

and Urban Sites

 During the 1995 growing season, weekly air and rain samples 

were collected from two sites in 

Mississippi and analyzed for 49 

pesticides and pesticide metabolites. The two sites represented an 

agricultural area and an urban area. 

Every air and rain sample had 

detectable levels of multiple pesticides; the pesticides detected and 

the frequency of detection varied 

between the two sites and were 

related to the types of pesticides 

used nearby. However, long-range 

transport appears to have an effect, 

as some pesticides that are not registered for use in an urban setting 

were found in air and rain samples 

at the urban site. These findings 

demonstrate that small amounts of 

pesticides can be transported 

through the atmosphere and deposited into aquatic and terrestrial ecosystems at a substantial distance 

from their point of use.

Pesticides in the Air

Pesticides can enter the atmosphere through volatilization, wind 

erosion of soil particles to which 

pesticides are attached, and direct 

spraying into the atmosphere during pesticide application.

Seasonal distribution of pesticides at the agricultural site is 

related to local application times of 

individual compounds. At the start 

of the study in April, the herbicides 

pendimethalin and trifluralin were 

the pesticides found in the highest 

concentrations in the air. In May, 

the two pesticides with the highest 

measured concentrations were the 

herbicides propanil and thiobencarb, which typically are used on 

rice. By August, the insecticide 

methyl parathion was detected in 

the highest concentration of any of 

the pesticides in the air at the agricultural site. 

In contrast, diazinon was 

detected in the highest concentration in the air at the urban site. 

Chlorpyrifos also was detected frequently, and carbaryl, methyl parathion, and trifluralin were found 

less often. Although most of these 

compounds are used commonly in 

residential settings for such purposes as termite control, methyl 

parathion is used only for insect 

control in agricultural settings, thus 

suggesting the long distance atmospheric transport of this compound.

Pesticides in the Rain

Once in the atmosphere, pesticides can be degraded, transported, 

and (or) redeposited. Deposition 

can be either wet, as with rain or 

snow, or dry, as with gaseous sorption and particle fallout. 

The urban atmospheric sampling site on the left is in a residential area in southern Jackson, Mississippi, a metropolitan area of 

about 400,000 people. The site is more than 10 miles from the nearest agricultural field. The agricultural site on the right is

located in the center of a catfish pond complex in Sharkey County, Mississippi. This site was selected to measure pesticides in

the atmosphere in an area with minimal influence of direct application of pesticides to nearby fields. The nearest agricultural

field is about one-half mile away, and the major crops grown in this area are soybeans, cotton, corn, and rice.

The yellow polyurethane foam plug 

was used to collect pesticides distributed into the gas phase of the atmosphere.
Major Findings 21 

The concentrations of selected 

pesticides detected in rainfall samples from the agricultural site are 

shown in figure 13. The pesticides 

detected in the highest concentrations during the early part of the 

growing season were the herbicides 

atrazine, used on corn and grain 

sorghum, and propanil, used 

mainly on rice. Later in the growing season, the pesticide found in 

the highest concentrations was the 

insecticide methyl parathion. 

The pesticides detected in rainfall samples from the urban site— 

atrazine, carbaryl, methyl parathion, and propanil—were similar 

to those found at the agricultural 

site, but the concentrations were 

much lower. Because methyl parathion and propanil do not have 

legal urban uses, it is assumed that 

these pesticides were transported in 

the atmosphere from their application areas. Methyl parathion and 

propanil are the first and sixth most 

heavily used agricultural pesticides in Mississippi.

Metabolites of DDT in the Air

In order to fully understand the 

fate, transport, and environmental 

effects of a pesticide, major metabolites of the pesticide commonly 

are included in the sampling program. One of the major metabolites 

of the organochlorine insecticide 

DDT is p,p ́-DDE. In 1971, Stanley 

and others (1971) detected p,p ́- 

DDE in the air at an agricultural 

site near Stoneville, Miss. (about 

60 miles north of the Sharkey 

County site) in concentrations 

ranging from 2.6 to 7.1 ng/m3 (nanograms per cubic meter). Twentyfour years later, the range of p,p ́- 

DDE in air samples from the agricultural site ranged from 0.13 to 

1.1 ng/m3

, lower than reported by 

Stanley and others (1971) but still 

significant considering that there is 

no current use of DDT in the area. 

These results indicate that a persistent metabolite of p,p ́- DDT was 

still measurable in the air more 

than two decades after the sale of 

DDT was discontinued in the 

United States.

Figure 13. Pesticide concentrations in rainfall samples collected at an agricultural 

site in Mississippi during the 1995 growing season. In the spring, atrazine and 

propanil were detected in higher concentrations, but by summer the dominant 

pesticide measured was methyl parathion.

Agriculture

Urban

100

80

60

40

20

0

Jackson, MS

Sharkey

Co., MS

Iowa

City, IA

Cedar RapIds, IA

Minneapolis, MN

Princeton, MN

DETECTION FREQUENCY, IN PERCENT

The air concentrations of p,p ́-DDE, a 

metabolite of DDT, were determined 

at paired urban and agricultural sites 

in Mississippi, Iowa, and Minnesota 

(Foreman and others, 2000). The agricultural site in Mississippi and the 

urban site in Iowa had detectable levels of p,p ́-DDE in every sample. Approximately 10 to 30 percent of the 

samples collected at the other sites 

had detectable levels of p,p ́-DDE. It 

is likely that these concentrations of 

p,p ́-DDE are from past local use of 

DDT. However, DDT is still being 

used in other parts of the world, and it 

is possible that some proportion of 

this p,p ́-DDE originated elsewhere 

and was transported in the atmosphere.

More details on pesticides in the 

atmosphere can be found in the paper:

Coupe, R.H., Manning, M.A., Foreman, 

W.T., Goolsby, D.A., and Majewski, M.S., 

2000, Occurrence of pesticides in urban 

and agricultural areas of Mississippi, April–

September 1995: Science of the Total 

Environment, v. 248, no. 2–3, p. 227.

The paper also can be downloaded at:

http://ms.water.usgs.gov/misenawqa/

DDT Metabolites in the 

Air Across Mid-America 

4/5/95

4/19/95

4/22/95

4/26/95

5/9/95

5/16/95

5/30/95

6/6/95

6/20/95

6/27/95

7/5/95

7/12/95

7/18/95

7/25/95

8/1/95

8/29/95

Propanil

Molinate

Methyl Parathion

Atrazine

Cyanazine

TOTAL PESTICIDE CONCENTRATIONS,

IN MICROGRAMS PER LITER

0

1

2

3

4

8

9

22

23

24

DATE OF SAMPLE COLLECTION
22 Water Quality in the Mississippi Embayment

ANUMBER OF INSECTIVORE FISH TAXA

0

4

8

12

16

0 0.5 1.0 1.5 2.0 2.5

TOTAL AMMONIA,

IN MILLIGRAMS PER LITER

C

0

5

10

15

20

25

30

35

40

45

0 20 40 60 80 100

TURBIDITY, IN NEPHELOMETRIC

TURBIDITY UNITS

NUMBER OF BLACK BASS

0

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

0 10 20 30 40 50 60 70 80

PERCENTAGE OF STREAM BUFFER

THAT IS FORESTED

CONCENTRATION OF ORTHOPHOSPHATE,

IN MILLIGRAMS PER LITER

B

0

1,000

2,000

3,000

4,000

5,000

6,000

7,000

8,000

0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6

NITRITE PLUS NITRATE,

IN MILLIGRAMS PER LITER AS N

TOTAL DDT IN FISH TISSUE,

IN MICROGRAMS PER KILOGRAM

D

Integration of Biological, 

Geological, and Chemical 

Data Improves 

Understanding of Aquatic 

Systems

One of the most significant 

advances in the aquatic sciences 

during the last century is the growing understanding that aquatic systems, such as lakes and rivers, are 

profoundly influenced by the biological, chemical, and physical 

aspects of the drainage basin in 

which the water body is located 

(Wetzel, 1983). Although the conceptual framework for these ideas 

is decades old, scientists are still 

developing the technologies and 

accumulating the data bases necessary to more fully understand the 

relations between a body of water, 

the biotic components within it, 

and the chemical and physical 

influences of the drainage basin. 

In the NAWQA Program, 

researchers often collect biological, 

geological, and chemical information from the same stream sites and 

analyze land use from the corresponding drainage basins. This 

information presents an opportunity to examine biogeochemical 

relations within the watersheds. 

This interdisciplinary approach has 

yielded at least three broad findings 

in the MISE Study Unit. Three 

findings, which need to be examined in more detail to guide scientific understanding and management in this region, are: (1) DDT 

and its metabolites remain detectable in many parts of the environment; (2) numerous interrelations 

exist between the biological, geological, and chemical components 

of the MISE Study Unit; and (3) 

evidence exists that the geology of 

the Study Unit exerts an influence 

on many aspects of the environment.

DDT and Its Metabolites Are 

Present Throughout the 

Environment

 Nearly 30 years after the sale of 

DDT was discontinued, the pesticide and its metabolites were 

detected in all parts of the MISE 

Study Unit environment. While 

residual total DDT is found 

throughout the world, the concentrations in the MISE are among the 

highest in the United States. (See 

water, fish tissue, and bed sediment 

sections of the national comparison 

tables on pages 31, 33, and 34 for a 

comparison of MISE results to 

other NAWQA Study Units in the 

United States.) A metabolite of 

DDT, DDE persists in various concentrations in many different parts 

of the MISE environment, including the air, water, streambed sediment, and fish tissue, generating 

interesting questions about its 

transport, accumulation, and persistence. 

Biological and Chemical Relations

 The MISE Study Unit has 

numerous complex interrelations 

among stream biology, basin 

geology, stream chemistry and land 

use. Some of these interrelations 

are illustrated by a variety of linear 

relations among biological, 

geological, and chemical components of 36 stream sites and their 

drainage basins in the MISE Study 

Unit (fig. 14). Figures 14A and 

14C illustrate how differences in 

stream chemistry can affect 

biological communities in the 

stream. Figure 14A shows that the 

number of insectivore fish taxa 

decreases as total ammonia 

increases, whereas figure 14C 

Figure 14. There are numerous interrelations among stream biology, basin geology, 

stream chemistry, and land use in the Mississippi Embayment Study Unit. The lines 

in these graphs represent linear relations between some of the variables.
Major Findings 23 

clustered in the Holocene alluvium 

(fig. 15A), whereas similar clusters 

occurred for the number of herbicides detected in the water (fig. 

15B) and the amount of total DDT 

found in fish tissue (fig. 15C). In 

turn, many biological metrics were 

lower at sites located in the 

Holocene alluvium, and differences 

in ground-water chemistry were 

detected (pages 13 and 14). 

This information reaffirms that a 

better understanding of the underlying geology of the Earth itself is 

needed to fully understand the 

effects of human activities on the 

environment. 

EXPLANATION

A. Ammonia B. Herbicide detections C. DDT in fish tissue

Prairie complex

Pleistocene valley trains

Holocene alluvium

Mississippi Embayment

Study Unit Boundary

High concentration

Moderate concentration

Low concentration

shows that the number of black 

bass decreases as turbidity 

increases. Figures 14B and 14D 

show how factors in the drainage 

area, but not in the stream, can 

influence the stream. Figure 14B 

shows that as the percentage of forested stream buffer (the area within 

60 meters of the streams) increases, 

concentrations of orthophosphate 

in the stream decrease, indicating 

the value of vegetated stream buffers in minimizing the amount of 

runoff entering streams and rivers. 

Finally, figure 14D illustrates that 

as the concentration of dissolved 

nitrite plus nitrate increases, the 

amount of total DDT in fish tissue 

increases, suggesting that conditions that facilitate agricultural runoff affect nutrient levels in the 

streams and the long-term bioaccumulation of organochlorine pesticides in fish tissue. 

The sum of these various relations shows the complexity of the 

system, underscores the need for 

multidisciplinary studies in order to 

thoroughly understand the Mississippi Embayment Study Unit, and 

discourages simplistic, one-dimensional management solutions.

Geology Influences Many Variables

Within the Mississippi Embayment Study Unit, the geology of 

the land surface appears to exert an 

overarching influence on many 

components of the environment. 

The dense, tight clays of the 

Holocene alluvium dictate the 

types of crops grown and cause 

high runoff potential in the area. 

These factors help to determine the 

types of agricultural chemicals that 

are applied and the amounts of 

these chemicals that are transported 

into rivers and streams. Once in the 

streams, the clays tend to cause 

chemicals sorbed to sediments to 

remain locally in the bed sediment 

rather than to be washed downstream. Sites where high concentrations of ammonia were found are 

Figure 15. Several variables in the MISE Study Unit vary spatially and correspond generally to the Quaternary geology of the

Mississippi Alluvial Plain. Soils formed from the Holocene alluvium tend to be dense, thick clays, whereas the Pleistocene features tend to have soils that have more silts and sands. These soils influence permeability and runoff, which in turn, appear to

affect the amount and persistence of agricultural chemicals in the streams.

Carp used for tissue analysis.
24 Water Quality in the Mississippi Embayment

STUDY UNIT DESIGN

#

###

#

#

Deep Tertiary Aquifers

Memphis Shallow Aquifer

Alluvial Aquifer

EXPLANATION

Basic and Intensive Fixed Sites

Basic Fixed, Intensive Fixed,

and Synoptic Sites

Basic Fixed and Synoptic Sites

Synoptic Sites

EXPLANATION

Ecological Assessment,

Synoptic, Bed Sediment,

and Tissue Sites

Synoptic, Bed Sediment,

and Tissue Sites

Synoptic and Tissue Sites

Bed Sediment and Tissue Sites

EXPLANATION

Stream Chemistry

The stream-chemistry network was designed to measure the effects of 

land use (primarily cropland) on stream quality and to integrate the effects 

of multiple land uses and hydrogeologic settings on water quality. Data 

from the Basic Fixed Sites were used to examine differences in water quality from one basin to another. Data from Intensive Fixed Sites, which were 

sampled more often, were used to examine seasonal changes in stream 

quality and to calculate fluxes from the basin. Also, detailed data on pesticides dissolved in the water were collected at intensive sites. A synoptic 

study was conducted to measure a selected set of constituents at 38 sites in 

the Study Unit in order to better understand spatial differences among the 

basins and to compare water chemistry to biological and landscape parameters. 

Ground-Water Chemistry

Three surveys examined the effects of land use on ground water in different aquifer settings. The deep Tertiary aquifers are the deepest aquifers 

studied and the ones that provide drinking water to the greatest number of 

people in the Study Unit. The Memphis shallow aquifer survey was 

designed to assess the ground-water quality in commercial and residential 

areas. The alluvial aquifer survey examined ground-water quality from a 

shallow aquifer that is heavily used for agriculture.

Stream Ecology

Ecological assessments were done annually at the basic and intensive 

stream-chemistry sites. The objective of these studies was to investigate 

biological, chemical, and physical data as multiple lines of evidence to 

assess water quality. Some of the assessments examined multiple reaches 

of a stream to determine spatial variations in the community structure of 

the aquatic organisms. Synoptic studies were designed to examine spatial 

variability in biological communities in the Study Unit and to relate this 

variability to stream chemistry and landscape variables. Early in the 

project, bed sediment and fish tissue were sampled at a subset of sites; later 

in the project, fish tissue was sampled for organochlorine concentrations at 

all of the synoptic sites.
Study Unit Design 25 

SUMMARY OF DATA COLLECTION IN THE MISSISSIPPI EMBAYMENT STUDY UNIT, 1995–98

Study

component What data were collected and why Types of sites sampled Number of 

sites

Sampling frequency 

and period

Stream Chemistry

Basic Fixed 

Sites

Continuous streamflow, nutrients, major ions, organic carbon, suspended sediment, and physical parameters were 

measured to describe concentrations and seasonal variations.

Sites were selected to represent the range 

of ecoregions, physiographic regions, 

and land uses present in the Study Unit.

9 Samples were collected 

monthly February 1996 – 

January 1998.

Intensive Fixed 

Sites

In addition to the above list of data collected at the Basic 

Fixed Sites, information on 82 dissolved pesticides was 

collected to determine concentrations, seasonal variations, and loads. Volatile organic compounds also were 

measured at the urban site. 

Three of the sites were located at streams 

that drained intensive agricultural areas 

but were dominated by different crop 

types. One site was a large river site with 

mixed land use. The remaining site was 

located in a rapidly growing urban area.

5 Sampling frequency 

ranged from biweekly during the growing season to 

weekly throughout the 

remainder of the period 

February 1996 – January 

1998.

Synoptic Sites—

Water Chemistry

Nutrients, pesticides, and physical properties were measured to broaden the spatial coverage of water-quality 

information in the Study Unit.

Synoptic sites were selected in an effort to 

sample streams that drained all major 

crop types grown in the Study Unit.

38 Samples were collected 

once during May, July, and 

August 1997.

Stream Ecology

Ecological 

Assessment 

Sites

Fish, macroinvertebrate, algae, and habitat data were collected to examine relations among the biological community and water chemistry, land use, and physical 

components of the landscape and drainage basin.

Sites were selected to represent the range 

of ecoregions, physiographic regions, 

and land uses present in the Study Unit.

8 Samples were collected 

once during low-flow conditions in the summers of 

1996–98; at two sites, 

three reaches were sampled in 1996.

Synoptic Sites—

Ecology

Fish, macroinvertebrate, habitat, and streamflow data were 

collected once at a larger number of sites to develop a 

better understanding of the spatial aspects of aquatic 

communities in the Study Unit.

Synoptic sites were selected in an effort to 

sample streams that drained all major 

crop types grown in the Study Unit.

38 Samples were collected 

July–September 1997 for 

macroinvertebrates; July– 

September 1998 for fish.

Contaminants in 

Bed Sediments

Total PCB’s, organochlorine pesticides, semivolatile 

organic compounds, and trace elements were measured 

in order to determine the occurrence and distribution of 

contaminants in stream sediments.

Sites were selected to represent the range 

of ecoregions, physiographic regions, 

and land uses present in the Study Unit.

15 Samples were collected 

during August and

September 1995.

Contaminants in 

Fish Tissue

Organochlorine pesticides were measured in whole fish, and 

trace elements were measured in fish liver. 

Sites were selected in an effort to sample 

streams that drained all major crop types 

grown in the Study Unit.

41 (pesticides) 

15 (trace elements) 

Samples were collected 

during late summer lowflow conditions in 1995–

98.

Ground-Water Chemistry

Deep Tertiary 

Aquifers

Nutrients, major ions, pesticides, volatile organic compounds, radioisotopes, stable isotopes, and physical 

parameters were measured to determine overall water 

quality in a deep aquifer used for drinking water.

Public-supply wells screened in the deep 

Tertiary aquifers (Claiborne and Wilcox 

Groups) were sampled.

30 Samples were collected 

once during April and 

May 1996.

Memphis 

Shallow 

Aquifers

Nutrients, major ions, trace elements, pesticides, volatile 

organic compounds, radioisotopes, stable isotopes, and 

physical parameters were measured to determine overall 

water quality in shallow aquifers in a rapidly developing 

urban area.

Twenty-four monitoring wells screened in 

the shallow water-table aquifer and eight 

monitoring wells screened in the upper 

part of the Memphis aquifer were sampled.

32 Samples were collected 

once during April and 

May 1997.

Alluvial Aquifer Nutrients, major ions, trace elements, pesticides, volatile 

organic compounds, radioisotopes, stable isotopes, and 

physical parameters were measured to determine overall 

water quality in an aquifer largely used for agricultural 

irrigation, but also for public supply and industry.

Twenty-five irrigation wells screened in the 

Holocene alluvium and 29 irrigation 

wells screened in the Pleistocene valley 

trains were sampled.

54 Samples were collected 

once during the summer of 

1998.

Special Studies

Pesticides in the 

Atmosphere

Pesticides were measured in the air and in the rain. Two sites were sampled–one in an agricultural area in Sharkey County, Miss., and 

one in an urban area in Jackson, Miss.

2 Samples were collected 

April–September 1995.

Pesticides in 

Fish Tissue in 

the Mississippi 

River

Organochlorine pesticides in whole fish (common carp) 

were measured to determine if pesticides leaving the 

Yazoo River Basin could be detected in fish in the Mississippi River.

Four sites were selected within an area 100 

miles upstream and another four sites 

were selected 100 miles downstream 

from the confluence of the Yazoo River 

and the Mississippi River.

8 Samples were collected 

once during November 

1997.
26 Water Quality in the Mississippi Embayment

GLOSSARY 

Algae - Chlorophyll-bearing nonvascular, primarily aquatic 

species that have no true roots, stems, or leaves; most 

algae are microscopic, but some species can be as large 

as vascular plants.

Alluvial aquifer - A water-bearing deposit of unconsolidated material (sand and gravel) left behind by a river or other flowing 

water. 

Alluvium - Deposits of clay, silt, sand, gravel or other particulate 

rock material left by a river in a streambed, on a flood plain, 

delta, or at the base of a mountain.

Aquatic-life criteria - Water-quality guidelines for protection of 

aquatic life. Often refers to U.S. Environmental Protection 

Agency water-quality criteria for protection of aquatic organisms. See also Water-quality guidelines, Water-quality criteria, 

and Freshwater chronic criteria.

Aquifer - A water-bearing layer of soil, sand, gravel, or rock that 

will yield usable quantities of water to a well.

Atmospheric deposition - The transfer of substances from the air 

to the surface of the Earth, either in wet form (rain, fog, snow, 

dew, frost, hail) or in dry form (gases, aerosols, particles).

Basic Fixed Sites - Sites on streams at which streamflow is measured and samples are collected for temperature, salinity, suspended sediment, major ions and metals, nutrients, and organic 

carbon to assess the broad-scale spatial and temporal character 

and transport of inorganic constituents of streamwater in relation 

to hydrologic conditions and environmental settings.

Bed sediment - The material that temporarily is stationary in the 

bottom of a stream or other watercourse. 

Bioaccumulation - The biological sequestering of a substance at a 

higher concentration than that at which it occurs in the surrounding environment or medium. Also, the process whereby a substance enters organisms through the gills, epithelia tissues, 

dietary, or other sources.

Biota - Living organisms.

Channelization - Modification of a stream, typically by straightening the channel, to provide more uniform flow; often done for 

flood control or for improved agricultural drainage or irrigation.

Community - In ecology, the species that interact in a common 

area.

Concentration - The amount or mass of a substance present in a 

given volume or mass of sample. Usually expressed as microgram per liter (water sample) or microgram per kilogram (sediment or tissue sample).

Criterion - A standard rule or test on which a judgment or decision 

can be based.

Degradation products - Compounds resulting from transformation 

of an organic substance through chemical, photochemical, 

and/or biochemical reactions.

Detection limit - The minimum concentration of a substance that 

can be identified, measured, and reported within 99 percent confidence that the analyte concentration is greater than zero; determined from analysis of a sample in a given matrix containing the 

analyte.

DDT - Dichloro-diphenyl-trichloroethane. An organochlorine 

insecticide no longer registered for use in the United States.

Dissolved solids - Amount of minerals, such as salt, that are dissolved in water; amount of dissolved solids is an indicator of 

salinity or hardness.

Drainage area - The drainage area of a stream at a specified location is that area, measured in a horizontal plane, which is 

enclosed by a drainage divide.

Drinking-water standard or guideline - A threshold concentration in a public drinking-water supply, designed to protect 

human health. As defined here, standards are U.S. Environmental Protection Agency regulations that specify the maximum 

contamination levels for public water systems required to protect 

the public welfare; guidelines have no regulatory status and are 

issued in an advisory capacity.

Ecosystem - The interacting populations of plants, animals, and 

microorganisms occupying an area, plus their physical environment.

Eutrophication - The process by which water becomes enriched 

with plant nutrients, most commonly phosphorus and nitrogen.

Fixed Sites - NAWQA's most comprehensive monitoring sites. See 

also Basic Fixed Sites and Intensive Fixed Sites.

Ground water - In general, any water that exists beneath the land 

surface, but more commonly applied to water in fully saturated 

soils and geologic formations. 

Habitat - The part of the physical environment where plants and 

animals live. 

Herbicide - A chemical or other agent applied for the purpose of 

killing undesirable plants. See also Pesticide.

Holocene - A subdivision of geologic time which began at the end 

of the Pleistocene (approximately 9,000 to 11,000 years ago) and 

extends to the present.

Human health advisory - Guidance provided by U.S. 

Environmental Protection Agency, State agencies or scientific 

organizations, in the absence of regulatory limits, to describe 

acceptable contaminant levels in drinking water or edible fish.

Intensive Fixed Sites - Basic Fixed Sites with increased sampling 

frequency during selected seasonal periods and analysis of dissolved pesticides for 1 year. Most NAWQA Study Units have 

one to two integrator Intensive Fixed Sites and one to four indicator Intensive Fixed Sites.

Load - General term that refers to a material or constituent in solution, in suspension, or in transport; usually expressed in terms of 

mass or volume.

Loess - Homogeneous, fine-grained sediment made up primarily of 

silt and clay, and deposited over a wide area (probably by wind).

Maximum contaminant level (MCL) - Maximum permissible 

level of a contaminant in water that is delivered to any user of a 

public water system. MCLs are enforceable standards established by the U.S. Environmental Protection Agency.

Median - The middle or central value in a distribution of data 

ranked in order of magnitude. The median is also known as the 

50th percentile. 

Metabolite- A compound derived by chemical, biological, or physical action upon a pesticide. The breakdown is a natural process 

which may result in a more toxic or a less toxic compound and a 

more persistent or less persistent compound.

Method detection limit - The minimum concentration of a substance that can be accurately identified and measured with 

present laboratory technologies.
Glossary 27

Micrograms per liter (μg/L) - A unit expressing the concentration 

of constituents in solution as weight (micrograms) of solute per 

unit volume (liter) of water; equivalent to one part per billion in 

most streamwater and ground water. One thousand micrograms 

per liter equals 1 mg/L.

Minimum reporting level (MRL) - The smallest measured concentration of a constituent that may be reliably reported using a 

given analytical method. In many cases, the MRL is used when 

documentation for the method detection limit is not available.

Nitrate - An ion consisting of nitrogen and oxygen (NO3-). Nitrate 

is a plant nutrient and is very mobile in soils.

Nonpoint source - A pollution source that cannot be defined as 

originating from discrete points such as pipe discharge. Areas of 

fertilizer and pesticide applications, atmospheric deposition, 

manure, and natural inputs from plants and trees are types of 

nonpoint source pollution. 

Nutrient - Element or compound essential for animal and plant 

growth. Common nutrients in fertilizer include nitrogen, phosphorus, and potassium.

Organochlorine insecticide - A class of organic insecticides containing a high percentage of chlorine. Includes dichlorodiphenylethanes (such as DDT), chlorinated cyclodienes (such as 

chlordane), and chlorinated benzenes (such as lindane). Most 

organochlorine insecticides were banned because of their carcinogenicity, tendency to bioaccumulate, and toxicity to wildlife.

Periphyton - Organisms that grow on underwater surfaces; periphyton include algae, bacteria, fungi, protozoa, and other organisms.

Phosphorus - A nutrient essential for growth that can play a key 

role in stimulating aquatic growth in lakes and streams.

Physiography - A description of the surface features of the Earth, 

with an emphasis on the origin of landforms. 

Pleistocene - A subdivision of geologic time which began about 2 

million years ago and ended at the beginning of the Holocene 

epoch, approximately 9,000 to 11,000 years ago.

Quaternary - A subdivision of geologic time which began about 2 

million years ago and extends to the present. The Quaternary 

period is further divided into two epochs, the Pleistocene and the 

Holocene.

Recharge - Water that infiltrates the ground and reaches the saturated zone.

Sediment quality guideline - Threshold concentration above 

which there is a high probability of adverse effects on aquatic 

life from sediment contamination, determined using modified 

USEPA (1996) procedures.

Semivolatile organic compound (SVOC) - Operationally defined 

as a group of synthetic organic compounds that are solventextractable and can be determined by gas chromatography/mass 

spectrometry. SVOCs include phenols, phthalates, and polycyclic aromatic hydrocarbons (PAHs).

Species diversity - An ecological concept that incorporates both 

the number of species in a particular sampling area and the evenness with which individuals are distributed among the various 

species. 

Species (taxa) richness - The number of species (taxa) present in a 

defined area or sampling unit. 

Stream reach - A continuous part of a stream between two specified points. 

Study Unit - A major hydrologic system of the United States in 

which NAWQA studies are focused. Study Units are geographically defined by a combination of ground- and surface-water features and generally encompass more than 4,000 square miles of 

land area.

Study-Unit Survey - Broad assessment of the water-quality conditions of the major aquifer systems of each Study Unit. The 

Study-Unit Survey relies primarily on sampling existing wells 

and, wherever possible, on existing data collected by other agencies and programs. Typically, 20 to 30 wells are sampled in each 

of three to five aquifer subunits.

Synoptic sites - Sites sampled during a short-term investigation of 

specific water-quality conditions during selected seasonal or 

hydrologic conditions to provide improved spatial resolution for 

critical water-quality conditions.

Taxon (plural taxa) - Any identifiable group of taxonomically 

related organisms.

Total DDT - The sum of DDT and its metabolites (breakdown 

products), including DDD and DDE.

Trace element - An element found in only minor amounts (concentrations less than 1.0 milligram per liter) in water or sediment; 

includes arsenic, cadmium, chromium, copper, lead, mercury, 

nickel, and zinc.

Triazine herbicide - A class of herbicides containing a 

symmetrical triazine ring (a nitrogen-heterocyclic ring composed of three nitrogens and three carbons in an alternating 

sequence). Examples include atrazine, propazine, and simazine.

Turbidity - Reduced clarity of surface water because of suspended 

particles, usually sediment. 

Volatile organic compounds (VOCs) - Organic chemicals that 

have a high vapor pressure relative to their water solubility. 

VOCs include components of gasoline, fuel oils, and lubricants, 

as well as organic solvents, fumigants, some inert ingredients in 

pesticides, and some by-products of chlorine disinfection.

Water-quality criteria - Specific levels of water quality which, if 

reached, are expected to render a body of water unsuitable for its 

designated use. Commonly refers to water-quality criteria established by the U.S. Environmental Protection Agency. Waterquality criteria are based on specific levels of pollutants that 

would make the water harmful if used for drinking, swimming, 

farming, fish production, or industrial processes.

Water-quality guidelines - Specific levels of water quality which, 

if reached, may adversely affect human health or aquatic life. 

These are nonenforceable guidelines issued by a governmental 

agency or other institution.

Water-quality standards - State-adopted and U.S. Environmental 

Protection Agency-approved ambient standards for water bodies. 

Standards include the use of the water body and the water-quality criteria that must be met to protect the designated use or uses.

Water year - The continuous 12-month period, October 1 through 

September 30, in U.S. Geological Survey reports dealing with 

the surface-water supply. The water year is designated by the 

calendar year in which it ends and which includes 9 of the 12 

months. Thus, the year ending September 30, 1980, is referred to 

as the water year 1980.

Wetlands - Ecosystems whose soil is saturated for long periods 

seasonally or continuously, including marshes, swamps, and 

ephemeral ponds.
28 Water Quality in the Mississippi Embayment

 REFERENCES

Ackerman, D.J., 1989, Hydrology of the Mississippi 

River Valley alluvial aquifer, south-central United 

States—A preliminary assessment of the regional 

flow system: U.S. Geological Survey WaterResources Investigations Report 88–4028, 74 p.

Arthur, J.K., 1994, Thickness of the upper and lower 

confining units of the Mississippi River alluvial 

aquifer in northwestern Mississippi: U.S. Geological Survey Water-Resources Investigations Report 

94–4172, 1 p.

Autin, W.J., Burns, S.F., Miller, B.J., Saucier, R.T., and 

Snead, J.I., 1991, Quaternary geology of the 

Lower Mississippi Valley, in Morrison, R.B., ed., 

Quaternary nonglacial geology—Conterminous 

U.S., in The Geological of North America: Boulder, Colo., Geological Society of America, The 

Geology of North America, v. K–2, p. 547–582.

Bahls, L.R., Burkantis, R., and Tralles, S., 1992, 

Benchmark biology of Montana reference streams: 

Helena, Montana, Department of Health and Environmental Science, Water Quality Bureau, 47 p.

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 

Water-Resources Investigation Reports 94–4176, 

87 p.

Boswell, E.H., Cushing, E.M., and Hosman, R.L., 

1968, Quaternary aquifer in the Mississippi 

Embayment with a discussion of Quality of the 

water, by Jeffery, H.G.: U.S. Geological Survey 

Professional Paper 448–E, 15 p., 2 pls.

Coupe, R.H., 1998, Concentrations and loads of nitrogen and phosphorus in the Yazoo River, northwestern Mississippi, 1996–97: U.S. Geological Survey 

Water-Resources Investigations Report 98–4219, 

17 p.

_____2000, Occurence of pesticides in five rivers of 

the Mississippi Embayment Study Unit, 1996–98: 

U.S. Geological Survey Water-Resources Investigations Report 99–4159, 69 p.

Coupe, R.H., Manning, M.A., Foremen, W.T., Goolsby, 

D.A., and Majewski, M.S., 2000, Occurrence of 

pesticides in urban and agricultural areas of Mississippi, April–September, 1995: Science of the 

Total Environment, v. 248, no. 2–3, p. 227.

Fenneman, N.M., 1938, Physiography of the eastern 

United States: New York, McGraw-Hill, 714 p.

Foreman, W.T., Majewski, M.S., Goolsby, D.A., 

Wiebe, F.W., and Coupe, R.H., 2000, Pesticides in 

the atmosphere of the Mississippi River Valley, 

Part II—Air: Science of the Total Environment, 

v. 248, no. 2–3, p. 213–226.

Gonthier, G.J., 2000, Water quality in the deep Tertiary 

aquifers of the Mississippi Embayment, 1996: 

U.S. Geological Survey Water-Resources Investigations Report 99–4131, 91 p.

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, Fluxes and 

sources of nutrients in the Mississippi-Atchafalaya 

River Basin—Topic 3 Report for the integrated 

assessment on hypoxia in the Gulf of Mexico: Silver Spring, Md., NOAA Coastal Ocean Program 

Decision Analysis Series No. 17, 130 p.

Grubb, H.F., 1986, Gulf Coastal Plain regional aquifersystem study, in Sun, R.J., ed., Regional AquiferSystem Analysis Program of the U.S. Geological 

Survey; summary of projects, 1978–84: U.S. Geological Survey Circular 1002, p. 152–161.

Mesko, T.O., Willliams, T.A., Ackerman, D.J., and 

Williamson, A.K., 1990, Ground-water pumpage 

for the Gulf Coast aquifer systems, 1960–85, 

south-central United States: U.S. Geological Survey Water-Resources Investigations Report 89–

4180, 177 p.

Newell, A.J., Johnson, D.W., and Allen, L.K., 1987, 

Niagara River biota contamination project—Fish 

flesh criteria for piscivorous wildlife: New York 

State Department of Environmental Conservation, 

Division of Fish and Wildlife, Bureau of Environmental Protection Technical Report 87-3, 182 p.
References 29

Nowell, L.H., Capel, P.D., Dileanis, P.D., 1999, Pesticides in stream sediment and aquatic biota—Distribution, trends, and governing factors: Boca 

Raton, Fla., Lewis Publishers, 1001 p.

Omernik, J.M., 1987, Ecoregions of the conterminous 

United States: Annals of the Association of American Geographers, v. 77, no. 1, p. 118–125, scale 

1:7,500,000.

Saucier, R.T., 1994, Geomorphology and Quaternary 

geologic history of the Lower Mississippi Valley: 

Vicksburg, Miss., U.S. Army Engineer Waterways 

Experiment Station, v. I, 398 p.

Schmitt, C.J., and Dethloff, G.M., eds., 2000, Biomonitoring of environmental status and trends (BEST) 

program—Selected methods for monitoring chemical contaminants and their effects in aquatic ecosystems: U.S. Geological Survey Information and 

Technology Report USGS/BRD–2000–0005, 81 p.

Smith, F.E., 1954, The Yazoo River: Jackson, Miss., 

University Press of Mississippi, 362 p.

Stanley, C.W., Barney, J.E., II, Helton, M.R., and Yobs, 

A.R., 1971, Measurement of atmospheric levels of 

pesticides: Environmental Science & Technology, 

v. 5, no. 5, p. 430–435.

Wetzel, R.G., 1983, Limnology [2d ed.]: Philadelphia, 

Pa., Saunders College Publishing, 767 p.

Whitfield, M.S., Jr., 1975, Geohydrology and water 

quality of the Mississippi River alluvial aquifer, 

northeastern Louisiana: U.S. Geological Survey 

Water-Resources Technical Report 10, 29 p.

Williamson, A.K., Grubb, H.F., and Weiss, J.S., 1990, 

Ground-water flow in the Gulf Coast aquifer systems, south-central United States—A preliminary 

analysis: U.S. Geological Survey Water-Resources 

Investigations Report 89–4071, 124 p.
30 Water Quality in the Mississippi Embayment

Streams in agricultural areas 

Streams in urban areas

Streams and rivers draining mixed land uses 

Shallow ground water in agricultural areas

Shallow ground water in urban areas 

Major aquifers 

Detected concentration in Study Unit

Frequencies of detection, in percent. Detection frequencies 

were not censored at any common reporting limit. The lefthand column is the study-unit frequency and the right-hand 

column is the national frequency 

Not measured or sample size less than two

Study-unit sample size. For ground water, the number of 

samples is equal to the number of wells sampled

National ranges of detected concentrations, by land use, in 36 

NAWQA Study Units, 1991–98—Ranges include only samples

in which a chemical was detected

Drinking-water quality (applies to ground water and surface water)

Protection of aquatic life (applies to surface water only)

Prevention of eutrophication in streams not flowing directly into 

lakes or impoundments

No benchmark for drinking-water quality

No benchmark for protection of aquatic life

*

**

66 38

CHEMICALS IN WATER

Concentrations and detection frequencies, Mississippi 

Embayment, 1995–98—Detection sensitivity varies among chemicals 

and, thus, frequencies are not directly comparable among chemicals

Lowest

25 percent

Middle

50 percent

Highest

25 percent

National water-quality benchmarks

National benchmarks include standards and guidelines related to 

drinking-water quality, criteria for protecting the health of aquatic life, and 

a goal for preventing stream eutrophication due to phosphorus. Sources 

include the U.S. Environmental Protection Agency and the Canadian 

Council of Ministers of the Environment

|

|

|

--

This appendix is a summary of chemical concentrations 

and biological indicators assessed in the Mississippi 

Embayment. Selected results for this Study Unit are 

graphically compared to results from as many as 36 

NAWQA Study Units investigated from 1991 to 1998 and 

to national water-quality benchmarks for human health, 

aquatic life, or fish-eating wildlife. The chemical and 

biological indicators shown were selected on the basis of 

frequent detection, detection at concentrations above a 

national benchmark, or regulatory or scientific importance. 

The graphs illustrate how conditions associated with each 

land use sampled in the Mississippi Embayment compare 

to results from across the Nation, and how conditions 

compare among the several land uses. Graphs for chemicals show only detected concentrations and, thus, care 

must be taken to evaluate detection frequencies in addition 

to concentrations when comparing study-unit and national 

results. For example, fluometuron concentrations in 

Mississippi Embayment agricultural streams were similar 

to the national distribution, but the detection frequency 

was much higher (63 percent compared to 8 percent). 

CONCENTRATION, IN MICROGRAMS PER LITER

 0.0001 0.001 0.01 0.1 1 10 100 1,000 

Study-unit frequency of detection, in percent

National frequency of detection, in percent

Pesticides in water—Herbicides

Study-unit sample size

12

Alachlor (Lasso, Bronco, Lariat, Bullet) ** 34 44 | 172 20 20 | 25 61 45 | 56

-- 3 | 0 3 <1 | 32 0 1 | 82

Atrazine (AAtrex, Atrex, Atred, Gesaprim) 

98 88 | | 172 100 86 | | 25 100 87 | | 56

-- 40 | 0 38 30 | 32 1 18 | 82

Cyanazine (Bladex, Fortrol) 

83 44 | | 172 12 14 | | 25 98 54 | | 56

-- 1 | 0 3 1 | 32 0 <1 | 82

2,4-D (Aqua-Kleen, Lawn-Keep, Weed-B-Gone) 29 15 | | 161 52 18 | | 25 17 11 | | 48

-- <1 | 0 3 1 | 30 1 <1 | 83

Deethylatrazine (Atrazine breakdown product) * ** 87 75 172 92 62 25 98 75 56

-- 39 0 25 28 32 2 19 82

Diuron (Crisuron, Karmex, Diurex) **

44 13 | 161 48 22 | 25 81 20 | 48

-- 4 | 0 7 3 | 30 0 2 | 83

Fluometuron (Flo-Met, Cotoran) ** 63 8 | 161 0 <1 | 25 92 6 | 48

-- <1 | 0 3 <1 | 30 4 <1 | 83

Metolachlor (Dual, Pennant) 100 81 | | 172 100 64 | | 25 100 83 | | 56

-- 18 | 0 31 9 | 32 1 5 | 82

Metribuzin (Lexone, Sencor) 

47 19 | | 172 32 8 | | 25 45 20 | | 56

-- 3 | 0 12 2 | 32 0 1 | 82

Molinate (Ordram) * **

73 7 172 28 3 25 45 5 56

-- 1 0

5 <1 82

APPENDIX—WATER-QUALITY DATA FROM THE MISSISSIPPI 

EMBAYMENT IN A NATIONAL CONTEXT

For a complete view of Mississippi Embayment data and for additional information about specific benchmarks used, visit our Web site at 

http://water.usgs.gov/nawqa/. Also visit the NAWQA Data Warehouse for access to NAWQA data sets at http://water.usgs.gov/nawqa/data. 
Water-Quality Data in a National Context 31 

CONCENTRATION, IN MICROGRAMS PER LITER

 0.0001 0.001 0.01 0.1 1 10 100 1,000 

Other herbicides detected

Acetochlor (Harness Plus, Surpass) * **

Acifluorfen (Blazer, Tackle 2S) **

Benfluralin (Balan, Benefin, Bonalan) * **

Bentazon (Basagran, Bentazone) **

Bromacil (Hyvar X, Urox B, Bromax) 

Bromoxynil (Buctril, Brominal) * 

2,4-DB (Butyrac, Butoxone, Embutox Plus, Embutone) * **

DCPA (Dacthal, chlorthal-dimethyl) * **

Dacthal mono-acid (Dacthal breakdown product) * **

Dicamba (Banvel, Dianat, Scotts Proturf) 

Dichlorprop (2,4-DP, Seritox 50, Lentemul) * **

Dinoseb (Dinosebe) 

EPTC (Eptam, Farmarox, Alirox) * **

Fenuron (Fenulon, Fenidim) * **

Linuron (Lorox, Linex, Sarclex, Linurex, Afalon) * 

MCPA (Rhomene, Rhonox, Chiptox) 

Napropamide (Devrinol) * **

Neburon (Neburea, Neburyl, Noruben) * **

Norflurazon (Evital, Predict, Solicam, Zorial) * **

Pebulate (Tillam, PEBC) * **

Picloram (Grazon, Tordon) 

Pronamide (Kerb, Propyzamid) **

Propachlor (Ramrod, Satecid) **

Propanil (Stam, Stampede, Wham) * **

Tebuthiuron (Spike, Tebusan) 

Terbacil (Sinbar) **

Thiobencarb (Bolero, Saturn, Benthiocarb) * **

Triclopyr (Garlon, Grandstand, Redeem, Remedy) * **

Trifluralin (Treflan, Gowan, Tri-4, Trific)

Herbicides not detected

Butylate (Sutan +, Genate Plus, Butilate) **

Chloramben (Amiben, Amilon-WP, Vegiben) **

Clopyralid (Stinger, Lontrel, Transline) * **

2,6-Diethylaniline (Alachlor breakdown product) * **

Ethalfluralin (Sonalan, Curbit) * **

MCPB (Thistrol) * **

Oryzalin (Surflan, Dirimal) * **

Propham (Tuberite) **

2,4,5-T **

2,4,5-TP (Silvex, Fenoprop) **

0Triallate (Far-Go, Avadex BW, Tri-allate) * 

Study-unit frequency of detection, in percent

National frequency of detection, in percent

Pesticides in water—Insecticides

Study-unit sample size

Other insecticides detected 

Disulfoton (Disyston, Di-Syston) **

Methomyl (Lanox, Lannate, Acinate) **

Methyl parathion (Penncap-M, Folidol-M) **

Propargite (Comite, Omite, Ornamite) * **

Insecticides not detected

Aldicarb (Temik, Ambush, Pounce) 

Aldicarb sulfone (Standak, aldoxycarb) 

Ethoprop (Mocap, Ethoprophos) * **

Pendimethalin (Pre-M, Prowl, Stomp) * ** 26 12 172 64 16 25 18 8 56

-- <1 0 6 1 32

Prometon (Pramitol, Princep) **

12 44 | 172 60 86 | 25 27 60 | 56

-- 12 | 0 3 21 | 32 0 5 | 82

Simazine (Princep, Caliber 90) 

50 61 | | 172 100 77 | | 25 93 74 | | 56

-- 21 | 0 38 18 | 32 0 5 | 82

CONCENTRATION, IN MICROGRAMS PER LITER

 0.0001 0.001 0.01 0.1 1 10 100 1,000 

Study-unit frequency of detection, in percent

National frequency of detection, in percent Study-unit sample size

Aldicarb sulfoxide (Aldicarb breakdown product) 

1 <1 | | 161

-- <1 | 0

0 <1 | 80

Azinphos-methyl (Guthion, Gusathion M) * 

1 3 | 169 4 1 | 24 4 2 | 54

-- <1 0

Carbaryl (Carbamine, Denapon, Sevin) 5 9 | | 172 72 46 | | 25 2 16 | | 56

-- <1 | 0 0 2 | 32 0 1 | 82

Carbofuran (Furadan, Curaterr, Yaltox) 15 11 | | 172 4 3 | | 25 20 10 | | 56

-- 2 | 0 3 1 | 32 0 1 | 82

Chlorpyrifos (Brodan, Dursban, Lorsban) 

6 18 | | 170 100 37 | | 25 11 20 | | 56

-- 1 | 0 0 1 | 32 0 <1 | 82

p,p'-DDE 

17 8 | | 172 4 2 | | 25 9 4 | | 56

-- 4 | 0 0 2 | 32 1 2 | 82

Diazinon (Basudin, Diazatol, Neocidol, Knox Out) 

4 16 | | 172 96 70 | | 25 7 39 | | 56

-- <1 | 0 0 2 | 32 0 2 | 82

Dieldrin (Panoram D-31, Octalox, Compound 497) 1 6 | | 172 0 2 | | 25 4 2 | | 56

-- 1 | 0 6 6 | 32 0 1 | 82

Malathion (Malathion) 

11 5 | | 172 56 21 | | 25 36 6 | | 56

-- <1 | 0 0 <1 | 32 0 <1 | 82
32 Water Quality in the Mississippi Embayment

CONCENTRATION, IN MILLIGRAMS PER LITER

 0.001 0.01 0.1 1 10 100 1,000 10,000 100,000 

Nutrients in water

Study-unit frequency of detection, in percent

National frequency of detection, in percent Study-unit sample size

Fonofos (Dyfonate, Capfos, Cudgel, Tycap) **

alpha-HCH (alpha-BHC, alpha-lindane) **

gamma-HCH (Lindane, gamma-BHC) 

3-Hydroxycarbofuran (Carbofuran breakdown product) * **

Methiocarb (Slug-Geta, Grandslam, Mesurol) * **

Oxamyl (Vydate L, Pratt) **

Parathion (Roethyl-P, Alkron, Panthion, Phoskil) * 

cis-Permethrin (Ambush, Astro, Pounce) * **

Phorate (Thimet, Granutox, Geomet, Rampart) * **

Propoxur (Baygon, Blattanex, Unden, Proprotox) * **

Terbufos (Contraven, Counter, Pilarfox) **

Volatile organic compounds (VOCs) in ground water

These graphs represent data from 16 Study Units, sampled from 1996 to 1998

Study-unit frequency of detection, in percent

National frequency of detection in percent Study-unit sample size

CONCENTRATION, IN MICROGRAMS PER LITER

 0.001 0.01 0.1 1 10 100 1,000 10,000 

Methyl tert-butyl ether (MTBE) 

-- 4 | 0 3 16 | 32 4 6 | 84

Other VOCs detected

tert-Amylmethylether (tert-amyl methyl ether (TAME)) * 

Benzene 

Bromodichloromethane (Dichlorobromomethane) 

2-Butanone (Methyl ethyl ketone (MEK)) * 

Carbon disulfide * 

Chlorobenzene (Monochlorobenzene) 

Chloroethane (Ethyl chloride) * 

Chloromethane (Methyl chloride) 

1,4-Dichlorobenzene (p-Dichlorobenzene) 

Dichlorodifluoromethane (CFC 12, Freon 12) 

1,2-Dichloroethane (Ethylene dichloride) 

1,1-Dichloroethane (Ethylidene dichloride) * 

1,1-Dichloroethene (Vinylidene chloride) 

trans-1,2-Dichloroethene ((E)-1,2-Dichlorothene) 

cis-1,2-Dichloroethene ((Z)-1,2-Dichloroethene) 

Dichloromethane (Methylene chloride) 

Diethyl ether (Ethyl ether) * 

Diisopropyl ether (Diisopropylether (DIPE)) * 

1,2-Dimethylbenzene (o-Xylene) 

1,3 & 1,4-Dimethylbenzene (m-&p -Xylene) 

1-4-Epoxy butane (Tetrahydrofuran, Diethylene oxide) * 

Ethenylbenzene (Styrene) 

1-Ethyl-2-methylbenzene (2-Ethyltoluene) * 

Ethylbenzene (Phenylethane) 

4-Methyl-2-pentanone (Methyl isobutyl ketone (MIBK)) * 

Methylbenzene (Toluene) 

2-Propanone (Acetone) * 

Tetrachloroethene (Perchloroethene) 

1,1,1-Trichloroethane (Methylchloroform) 

Trichloroethene (TCE) 

Trichlorofluoromethane (CFC 11, Freon 11) 

Trichloromethane (Chloroform) 

1,2,3-Trimethylbenzene (Hemimellitene) * 

1,2,4-Trimethylbenzene (Pseudocumene) * 

1,3,5-Trimethylbenzene (Mesitylene) * 

VOCs not detected

Bromobenzene (Phenyl bromide) * 

Bromochloromethane (Methylene chlorobromide) 

Bromoethene (Vinyl bromide) * 

Bromomethane (Methyl bromide) 

n-Butylbenzene (1-Phenylbutane) * 

sec-Butylbenzene * 

tert-Butylbenzene * 

3-Chloro-1-propene (3-Chloropropene) * 

1-Chloro-2-methylbenzene (o-Chlorotoluene) 

1-Chloro-4-methylbenzene (p-Chlorotoluene) 

Chlorodibromomethane (Dibromochloromethane) 

Chloroethene (Vinyl chloride) 

1,2-Dibromo-3-chloropropane (DBCP, Nemagon) 

1,2-Dibromoethane (Ethylene dibromide, EDB) 

Dibromomethane (Methylene dibromide) * 

trans-1,4-Dichloro-2-butene ((Z)-1,4-Dichloro-2-butene) * 

1,2-Dichlorobenzene (o-Dichlorobenzene) 

1,3-Dichlorobenzene (m-Dichlorobenzene) 

1,2-Dichloropropane (Propylene dichloride) 

2,2-Dichloropropane * 

1,3-Dichloropropane (Trimethylene dichloride) * 

trans-1,3-Dichloropropene ((E)-1,3-Dichloropropene) 

cis-1,3-Dichloropropene ((Z)-1,3-Dichloropropene) 

1,1-Dichloropropene * 

Ethyl methacrylate * 

Ethyl tert-butyl ether (Ethyl-t-butyl ether (ETBE)) * 

Hexachlorobutadiene 

1,1,1,2,2,2-Hexachloroethane (Hexachloroethane) 

2-Hexanone (Methyl butyl ketone (MBK)) * 

Iodomethane (Methyl iodide) * 

Isopropylbenzene (Cumene) * 

p-Isopropyltoluene (p-Cymene) * 

Methyl acrylonitrile * 

Methyl-2-methacrylate (Methyl methacrylate) * 

Methyl-2-propenoate (Methyl acrylate) * 

Naphthalene 

2-Propenenitrile (Acrylonitrile) 

n-Propylbenzene (Isocumene) * 

1,1,2,2-Tetrachloroethane * 

1,1,1,2-Tetrachloroethane 

Tetrachloromethane (Carbon tetrachloride) 

1,2,3,4-Tetramethylbenzene (Prehnitene) * 

1,2,3,5-Tetramethylbenzene (Isodurene) * 

Tribromomethane (Bromoform) 

1,1,2-Trichloro-1,2,2-trifluoroethane (Freon 113) * 

1,2,4-Trichlorobenzene 

1,2,3-Trichlorobenzene * 

1,1,2-Trichloroethane (Vinyl trichloride) 

1,2,3-Trichloropropane (Allyl trichloride) 

Ammonia, as N * **

73 84 227 85 86 48 69 75 108

-- 78 0 41 71 32 96 70 84

Dissolved ammonia plus organic nitrogen, as N * ** 84 78 227 98 74 48 76 62 108

-- 28 0 16 30 32 68 24 84

Dissolved nitrite plus nitrate, as N ** 85 95 | 226 98 97 | 48 97 91 | 109

-- 81 | 0 59 74 | 32 38 71 | 84

Orthophosphate, as P * **

92 79 227 96 72 48 88 74 108

-- 59 0 41 52 32 90 61 83

Total phosphorus, as P * ** 100 92 | 227 100 90 | 48 98 88 | 108
Water-Quality Data in a National Context 33 

Fish tissue from streams in agricultural areas

Fish tissue from streams in urban areas

Fish tissue from streams draining mixed land uses

Sediment from streams in agricultural areas 

Sediment from streams in urban areas 

Sediment from streams draining mixed land uses

Protection of fish-eating wildlife (applies to fish tissue)

Protection of aquatic life (applies to bed sediment)

No benchmark for protection of fish-eating wildlife

No benchmark for protection of aquatic life

|

|

**

CHEMICALS IN FISH TISSUE

AND BED SEDIMENT

Concentrations and detection frequencies, Mississippi 

Embayment, 1995–98—Detection sensitivity varies among chemicals 

and, thus, frequencies are not directly comparable among chemicals. 

Study-unit frequencies of detection are based on small sample sizes; 

the applicable sample size is specified in each graph

Lowest

25 percent

Middle

50 percent

Highest

25 percent

National benchmarks for fish tissue and bed sediment

National benchmarks include standards and guidelines related to 

criteria for protection of the health of fish-eating wildlife and aquatic 

organisms. Sources include the U.S. Environmental Protection Agency, 

other Federal and State agencies, and the Canadian Council of 

Ministers of the Environment

*

CONCENTRATION, IN MICROGRAMS PER KILOGRAM

(Fish tissue is wet weight; bed sediment is dry weight)

 0.1 1 10 100 1,000 10,000 100,000 

National ranges of concentrations detected, by land use, in 36 

NAWQA Study Units, 1991–98—Ranges include only samples

in which a chemical was detected

Detected concentration in Study Unit

Frequencies of detection, in percent. Detection frequencies 

were not censored at any common reporting limit. The lefthand column is the study-unit frequency and the right-hand 

column is the national frequency

Not measured or sample size less than two

Study-unit sample size

66 38

--

12

Organochlorines in fish tissue (whole body)

and bed sediment

Study-unit frequency of detection, in percent

National frequency of detection, in percent Study-unit sample size

Other trace elements detected

Selenium 

Uranium 

Trace elements not detected

Cadmium 

Lead 

CONCENTRATION, IN MILLIGRAMS PER LITER

 0.001 0.01 0.1 1 10 100 1,000 10,000 100,000 

Dissolved solids in water

Study-unit frequency of detection, in percent

National frequency of detection, in percent Study-unit sample size

CONCENTRATION, IN PICOCURIES PER LITER

Trace elements in ground water

Study-unit frequency of detection, in percent

National frequency of detection, in percent Study-unit sample size

Arsenic 

-- 58 | 0 19 36 | 32 65 37 | 54

Chromium 

-- 85 | 0 97 79 | 32 96 73 | 54

Radon-222 

-- 99 | 0 96 100 | 26 100 97 | 83

Zinc 

-- 28 | 0 47 29 | 32 13 66 | 54

CONCENTRATION, IN MICROGRAMS PER LITER

 0.01 0.1 1 10 100 1,000 10,000 100,000 

 0.01 0.1 1 10 100 1,000 10,000 100,000 

Dissolved solids * ** 100 100 227 100 100 49 100 100 109

-- 100 0 100 100 32 100 100 84

Total Chlordane (sum of 5 chlordanes) 

52 38 | 42 -- 75 | 0 60 56 | 5

0 9 | 12 -- 57 | 0 0 11 | 3

o,p'+p,p'-DDD (sum of o,p'-DDD and p,p'-DDD) * 

90 49 42 -- 69 0 100 50 5

58 27 | 12 -- 50 | 0 67 20 | 3

p,p'-DDE * ** 100 90 42 -- 94 0 100 92 5

67 48 12 -- 62 0 100 39 3
34 Water Quality in the Mississippi Embayment

Other SVOCs detected

Acenaphthene 

Acenaphthylene 

Acridine **

Anthracene 

Benz[a]anthracene 

Benzo[a]pyrene 

Benzo[b]fluoranthene **

Benzo[ghi]perylene **

Benzo[k]fluoranthene **

2,2-Biquinoline **

Butylbenzylphthalate **

Chrysene 

p-Cresol **

Di-n-butylphthalate **

Di-n-octylphthalate **

Diethylphthalate **

1,6-Dimethylnaphthalene **

Dimethylphthalate **

9H-Fluorene (Fluorene) 

Indeno[1,2,3-cd]pyrene **

CONCENTRATION, IN MICROGRAMS PER KILOGRAM, DRY WEIGHT

 0.1 1 10 100 1,000 10,000 100,000 

Study-unit frequency of detection, in percent

National frequency of detection, in percent

Semivolatile organic compounds (SVOCs)

in bed sediment

Study-unit sample size

Other organochlorines detected

Total-HCH (sum of alpha-HCH, beta-HCH, gamma-HCH, and delta-HCH) **

Heptachlor+heptachlor epoxide (sum of heptachlor and heptachlor epoxide) **

Hexachlorobenzene (HCB) **

Mirex (Dechlorane) **

Pentachloroanisole (PCA) * **

Toxaphene (Camphechlor, Hercules 3956) * **

Organochlorines not detected

Chloroneb (Chloronebe, Demosan) * **

DCPA (Dacthal, chlorthal-dimethyl) * **

Endosulfan I (alpha-Endosulfan, Thiodan) * **

Endrin (Endrine) 

gamma-HCH (Lindane, gamma-BHC, Gammexane) * 

Heptachlor epoxide (Heptachlor breakdown product) * 

Isodrin (Isodrine, Compound 711) * **

p,p'-Methoxychlor (Marlate, methoxychlore) * **

o,p'-Methoxychlor * **

cis-Permethrin (Ambush, Astro, Pounce) * **

trans-Permethrin (Ambush, Astro, Pounce) * **

1 The national detection frequencies for total PCB in sediment are biased low because about 

30 percent of samples nationally had elevated detection levels compared to this Study Unit. 

See http://water.usgs.gov/nawqa/ for additional information.

CONCENTRATION, IN MICROGRAMS PER KILOGRAM

(Fish tissue is wet weight; bed sediment is dry weight)

 0.1 1 10 100 1,000 10,000 100,000 

Study-unit frequency of detection, in percent

National frequency of detection, in percent Study-unit sample size

Anthraquinone **

8 21 12 -- 83 0 33 39 3

9H-Carbazole **

25 19 12 -- 76 0 0 32 3

Dibenzothiophene **

17 12 12 -- 64 0 33 30 3

2,6-Dimethylnaphthalene **

83 65 12 -- 73 0 100 77 3

bis(2-Ethylhexyl)phthalate **

100 91 12 -- 99 0 100 95 3

Fluoranthene 

100 66 | 12 -- 97 | 0 100 78 | 3

Phenol **

92 81 12 -- 82 0 100 80 3

o,p'+p,p'-DDE (sum of o,p'-DDE and p,p'-DDE) * 100 90 42 -- 94 0 100 92 5

67 48 | 12 -- 62 | 0 100 39 | 3

Total DDT (sum of 6 DDTs) **

100 90 | 42 -- 94 | 0 100 93 | 5

67 49 12 -- 66 0 100 41 3

o,p'+p,p'-DDT (sum of o,p'-DDT and p,p'-DDT) * 

48 31 42 -- 53 0 80 29 5

50 19 | 12 -- 38 | 0 33 11 | 3

Dieldrin (Panoram D-31, Octalox) * 

71 53 42 -- 42 0 80 38 5

8 13 | 12 -- 30 | 0 0 9 | 3

Dieldrin+aldrin (sum of dieldrin and aldrin) ** 71 52 | 42 -- 42 | 0 80 38 | 5

8 13 12 -- 29 0 0 9 3

Total PCB 1

83 38 | 42 -- 81 | 0 60 66 | 5

0 2 | 12 -- 21 | 0 0 9 | 3

Toxaphene (Camphechlor, Hercules 3956) * **

38 12 42

40 1 5

0 <1 12
Water-Quality Data in a National Context 35 

Study-unit frequency of detection, in percent

National frequency of detection, in percent

CONCENTRATION, IN MICROGRAMS PER GRAM

(Fish tissue is wet weight, bed sediment is dry weight)

 0.01 0.1 1 10 100 10,000 1,000 

CONCENTRATION, IN MICROGRAMS PER GRAM

(Fish tissue is wet weight, bed sediment is dry weight)

 0.01 0.1 1 10 100 10,000 1,000 

Study-unit frequency of detection, in percent

National frequency of detection, in percent

Trace elements in fish tissue (livers) and 

bed sediment

Study-unit sample size

Study-unit sample size

Isoquinoline **

2-Methylanthracene **

4,5-Methylenephenanthrene **

1-Methylphenanthrene **

1-Methylpyrene **

Naphthalene 

Phenanthrene 

Pyrene 

SVOCs not detected

C8-Alkylphenol **

Azobenzene **

Benzo[c]cinnoline **

4-Bromophenyl-phenylether **

4-Chloro-3-methylphenol **

bis(2-Chloroethoxy)methane **

2-Chloronaphthalene **

2-Chlorophenol **

4-Chlorophenyl-phenylether **

Dibenz[a,h]anthracene 

1,2-Dichlorobenzene (o-Dichlorobenzene) **

1,3-Dichlorobenzene (m-Dichlorobenzene) **

1,4-Dichlorobenzene (p-Dichlorobenzene) **

1,2-Dimethylnaphthalene **

3,5-Dimethylphenol **

2,4-Dinitrotoluene **

2-Ethylnaphthalene **

Isophorone **

1-Methyl-9H-fluorene **

Nitrobenzene **

N-Nitrosodi-n-propylamine **

N-Nitrosodiphenylamine **

Pentachloronitrobenzene **

Phenanthridine **

Quinoline **

1,2,4-Trichlorobenzene **

2,3,6-Trimethylnaphthalene **

Arsenic * 

100 56 11 -- 38 0 75 76 4

100 99 | 10 -- 98 | 0 100 97 | 3

Cadmium * 

100 77 11 -- 72 0 100 95 4

100 98 | 10 -- 100 | 0 100 98 | 3

Chromium * 36 62 11 -- 72 0 75 54 4

100 100 | 10 -- 99 | 0 100 100 | 3

Copper * 100 100 11 -- 100 0 100 100 4

100 100 | 10 -- 99 | 0 100 100 | 3

Lead * 

18 11 11 -- 41 0 50 41 4

100 100 | 10 -- 100 | 0 100 99 | 3

Mercury * 

100 71 11 -- 59 0 100 80 4

100 82 | 11 -- 97 | 0 100 93 | 3

Nickel * **

82 42 11 -- 44 0 75 50 4

100 100 10 -- 100 0 100 100 3

Selenium * 100 99 11 -- 100 0 100 99 4

100 100 | 11 -- 100 | 0 100 100 | 3

Zinc * 

100 100 11 -- 100 0 100 100 4

100 100 | 10 -- 99 | 0 100 100 | 3
36 Water Quality in the Mississippi Embayment

 0 10 20 30 40 50 60 70 80 90 100

 0 5 10 15 20

 Invertebrate status indicator

Undeveloped

Agricultural

Urban

Mixed

 Fish status indicator

Undeveloped

Agricultural

Urban

Mixed

Biological indicator value, Mississippi Embayment, by land 

use, 1995–98

Biological status assessed at a site

National ranges of biological indicators, in 16 NAWQA Study 

Units, 1994–98

Streams in undeveloped areas

Streams in agricultural areas

Streams in urban areas

Streams in mixed-land-use areas

75th percentile

25th percentile

BIOLOGICAL INDICATORS

Higher national scores suggest habitat disturbance, water-quality 

degradation, or naturally harsh conditions. The status of algae, 

invertebrates (insects, worms, and clams), and fish provide a 

record of water-quality and stream conditions that waterchemistry indicators may not reveal. Algal status focuses on the 

changes in the percentage of certain algae in response to 

increasing siltation, and it often correlates with higher nutrient 

concentrations in some regions. Invertebrate status averages 11 

metrics that summarize changes in richness, tolerance, trophic 

conditions, and dominance associated with water-quality 

degradation. Fish status sums the scores of four fish metrics 

(percent tolerant, omnivorous, non-native individuals, and percent 

individuals with external anomalies) that increase in association 

with water-quality degradation

 0 10 20 30 40 50 60 70 80 90 100

 Algal status indicator

Undeveloped

Agricultural

Urban

Mixed
A COORDINATED EFFORT

Coordination with agencies and organizations in the Mississippi Embayment was integral to the success of this waterquality assessment. We thank those who served as members of our liaison committee.

Federal Agencies

U.S. Army Corps of Engineers

U.S. Department of Agriculture

U.S. Environmental Protection Agency

U.S. Fish and Wildlife Service

U.S. Forest Service

U.S. Geological Survey, BRD

State Agencies

Mississippi Department of Environmental Quality

Mississippi Department of Wildlife, Fisheries, and Parks

Local Agencies

Delta Council

Yazoo-Mississippi Delta Joint Water Management District

Universities

Arkansas State University

Mississippi State University

University of Arkansas

University of Mississippi

Other public and private organizations

Wolf River Conservancy

We thank the following individuals, agencies, and organizations for contributing to the success of this study.

• Chip Bray, Al Gibson, David Loch, Michael Beiser, and David Singleton (Mississippi Department of Environmental 

Quality), and Charles Knight (Mississippi Department of Wildlife, Fisheries and Parks) for help with biological field 

work

• Michael Mallory for his work as the first Project Chief for this Study Unit

• Memphis Light, Gas and Water Utilities, the Mississippi Department of Transportation, and numerous towns, cities, and individuals who allowed samples to be collected on their property

• Brian Hughes and Larry Slack (USGS), Henry Folmar and Richard Ingram (Mississippi Department of Environmental Quality), and Bruce Reid (The National Audubon Society) for providing technical review of the report and 

Carol Moss, Rebecca Deckard, Sandra Cooper and Mary Kidd (USGS) for editorial input

• Michael Wade and Lance Cooper for graphics and layout for this report

• Todd Slack, Stephen Ross, and Neil Douglas for verifying and vouchering fish specimens

• Michael Thurman (USGS, Kansas District) for contributing analyses of selected pesticides

• USGS employees Michael Manning, Brian Caskey, Robert Joseph, Charles Lee, Darryl Wilson, Susan McIntosh, 

Desmond Funchess, Paul Floyd, John Storm, Kenny Burks, David Massingill, Bobby Richards, Larry Thomas, 

Lisa Zimmerman, Jim Alvis, Allen Roberts, Rachel Pike, Jennifer Mahaney, Shane Stocks, Michelle Wates, Fred 

Morris III, John Ewing, Eric Strom, Wade Bryant, Anuba Dayama, Jan Jones, Tony Schrader, Marsha Gipson, 

Larry Remsing, Terry Holland, Dwight Lasker, Phil Stephens, Aaron Pugh and others for assisting with collection 

and compilation of data
Kleiss and others— Water Quality in the Mississippi Embayment

U.S. Geological Survey Circular 1208

National Water-Quality Assessment (NAWQA) Program

Mississippi Embayment

NAWQA

River

MISSOURI

ARKANSAS

LOUISIANA

MISSISSIPPI

ILLINOIS

TN

W

Memphis hite River

KY

Mississippi

Yazoo R vi er