Water Quality in the

Eastern Iowa Basins

Iowa and Minnesota, 1996–98

U.S. Department of the Interior

U.S. Geological Survey

Circular 1210
POINTS OF CONTACT AND ADDITIONAL INFORMATION

Front cover: Aerial view of the Old Mans Creek basin showing pattern of wooded riparian buffers and cropland 

typical of the Southern Iowa Drift Plain landform in Iowa. (Photograph by Doug Schnoebelen, USGS.)

Back cover: Left, study unit biologist measuring water transparency (photograph by Stephen Porter, USGS); 

center, study unit staff collecting aquatic organisms from woody debris (photograph by Stephen Porter); right, 

scientists measuring water temperature and dissolved oxygen in Old Mans Creek in preparation for sample 

collection (photograph by Debra Sneck-Fahrer, USGS). 

The companion Web site for NAWQA summary reports:

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

Eastern Iowa Basins contact and Web site:

USGS State Representative

U.S. Geological Survey

Water Resources Division

PO Box 1230

400 South Clinton St., Rm 269

Iowa City, IA 52244

e-mail: dc_ia@usgs.gov

http://iowa.usgs.gov/nawqa/index.html

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)

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)

Mississippi Embayment (Circular 1208)

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 Eastern Iowa Basins, 

Iowa and Minnesota, 1996–98

1210

By Stephen J. Kalkhoff, Kimberlee K. Barnes, Kent D. Becher, 

Mark E. Savoca, Douglas J. Schnoebelen, Eric M. Sadorf, Stephen D. Porter, 

and Daniel J. Sullivan
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

GALE A. NORTON, SECRETARY

U.S. GEOLOGICAL SURVEY

Charles G. Groat, Director

2000

Water quality in the eastern Iowa basins, Iowa and Minnesota, 1996–98 / by Stephen J. Kalkhoff...[et al.].

p. cm. -- (U.S. Geological Survey Circular ; 1210)

Includes bibliographical references.

ISBN 0-607-95415-9 (alk. paper)

1. Water quality--Iowa. 2. Water quality--Minnesota. 3. Watersheds--Iowa. 4. Watersheds--

Minnesota. I. Kalkhoff, Stephen J. II. Geological Survey (U.S.) III. Series.

TD224.I8 W274 2000

363.739’42’097776--dc21

00-049465
CONTENTS

Contents III

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

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

Stream and River Highlights ......................................................................................................... 1

Ground-Water Highlights .............................................................................................................. 2

INTRODUCTION TO THE EASTERN IOWA BASINS........................................................................ 3

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

Nutrients in Ground Water and Streams....................................................................................... 7

NATIONAL PERSPECTIVE—Nutrient concentrations in streams were among the 

highest in the Nation ............................................................................................................... 8

Animal Feeding Operations contribute additional nutrients to streams......................................... 13

Pesticides in Ground Water and Streams ..................................................................................... 14

NATIONAL PERSPECTIVE—Pesticide concentrations rank higher in ground water 

than in streams and rivers...................................................................................................... 15

What is a Pesticide Degradate?.................................................................................................... 17

Multiple pesticide compounds occur more frequently in streams than in 

ground water .............................................................................................................................. 20

Other Organic Compounds .......................................................................................................... 21

NATIONAL PERSPECTIVE—MTBE detection rates are similar to the average detection rate

in the Nation............................................................................................................................... 21

NATIONAL PERSPECTIVE—Biological communities in streams consist of organisms 

that are moderately to highly tolerant of environmental degradation ............................... 22

Riparian buffer zones influence the quality of Midwestern streams and rivers ............................. 25

STUDY UNIT DESIGN........................................................................................................................ 26

GLOSSARY........................................................................................................................................ 28

REFERENCES ................................................................................................................................... 30

APPENDIX—WATER-QUALITY DATA FROM THE EASTERN IOWA BASINS IN A 

NATIONAL CONTEXT ..................................................................................................................... 32
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

Eastern Iowa Basins

THIS REPORT summarizes major findings about water quality in the Eastern Iowa Basins that emerged from 

an assessment conducted between 1996 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 also are 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 Eastern Iowa Basins 

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 management, 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 Eastern Iowa Basins 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 one-half 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 

EXPLANATION

LAND COVER

Row crops

Urban

Forest

Water and wetlands

0 20 40 60 MILES

0 20 40 60 KILOMETERS

Ames

Cedar Rapids

Waterloo

Iowa

City

Mason

City

MINNESOTA

IOWA

LOCATION

OF STUDY

AREA

Stream And River Highlights

Nitrogen and phosphorus concentrations in streams in the 

Eastern Iowa Basins Study Unit rank as some of the highest 

in the Corn Belt (see map, p. 8) as well as the Nation and 

were higher than the drinking-water standard in many samples. These conditions reflect intensive use of the land for 

growing crops and dense populations of livestock in some 

basins.

• Nitrate concentrations in 22 percent of the stream samples 

exceeded the U.S. Environmental Protection Agency 

(USEPA) drinking-water standard of 10 mg/L (milligrams per 

liter). The standard was most frequently exceeded during 

June, soon after spring fertilizer application. Although many 

of the streams sampled are not currently used for drinking-water 

supplies, the Cedar and Iowa Rivers are the direct or indirect 

source for Cedar Rapids and Iowa City—two of the largest cities 

in the study area.

• The highest nitrate concentrations occurred in medium-sized 

streams draining basins with the most intensive row-crop agriculture and in a stream draining a basin with both intensive rowcrop agriculture and dense concentrations of large-scale animal 

feeding operations. Nitrate concentrations in these streams 

exceeded 10 mg/L in almost 50 percent of the samples. Conversely, nitrate concentrations were lowest in basins that had 

greater percentages of pasture, grassland, and forest.

• Total phosphorus concentrations frequently (75 percent of the 

samples) exceeded the 0.1-mg/L USEPA-recommended goal to 

minimize algal growth in rivers. Total phosphorus concentrations 

were greatest in streams and rivers that drain basins with more 

highly erodible soils and in large river basins that contain the 

largest cities and towns in the Study Unit.

• The large amounts of nitrogen and phosphorus that are transported to the Mississippi River from the Study Unit represent an 

economic loss to farmers and a potential environmental threat to 

downstream waters. The estimated annual loss of 17 to 41 lb/acre 

(pounds per acre) of nitrogen and 1.2 to 1.5 lb/acre of phosphorus represents a potential loss in crop yield or the cost of additional fertilizer needed to compensate for that flushed from the 

fields. Nutrients transported to the Mississippi River likely reach 

the Gulf of Mexico where they contribute to eutrophication and 

hypoxia.

• Although the use of herbicides and insecticides in the Study Unit 

is among the most intense nationwide, herbicide concentrations 

in streams were not among the highest 25 percent nationally, and 

insecticide concentrations were in the lowest 25 percent nationally. Breakdown compounds (degradates), whose widespread 

occurrence has only recently been discovered and about which 

little is known of the human and environmental effects, generally 

accounted for the majority of the pesticide compounds present in 

rivers and streams.

• The most commonly used herbicides were the most frequently 

detected and were generally present in the greatest concentrations. Atrazine and metolachlor were detected in all stream samples. Concentrations generally ranged from 0.1 to 1.0 μg/L 

(microgram per liter). Atrazine concentrations exceeded the 

USEPA 3.0-μg/L drinking-water standard in about 10 percent of 

the samples; exceedances occurred mainly during late-spring 

runoff. 

• Acetochlor, a conditionally registered herbicide that is intended 

to replace several other commonly used herbicides, was frequently detected, but concentrations were less than 0.1 μg/L in 

75 percent of the samples. Mean annual acetochlor concentrations did not exceed the 2.0-μg/L USEPA registration requirement at any site, but concentrations did exceed that level in about 

3 percent of the individual samples. The maximum concentration 

measured during the study (10.6 μg/L) exceeded the level that 

would require biweekly sampling by water-supply systems. 

• Alachlor, metolachlor, and acetochlor degradates are present in 

relatively high concentrations throughout the year, indicating 

that they are more persistent than their parent compounds. 

• Carbofuran and chlorpyrifos, insecticides that have been identified as posing a high risk to aquatic insects and mussels, were 

present in as much as 60 percent of the monthly samples during 

the summer when these insecticides are normally applied. 

• Riparian buffer zones influence the quality of water in streams 

and rivers. Biological communities respond to tree density in 

riparian buffer zones. Invertebrate taxa indicative of good stream 

quality increased with increased numbers of trees. In contrast, 

streams that were not shaded by trees contained large algal 

growths considered indicative of eutrophication.

The Eastern Iowa Basins Study Unit encompasses the Wapsipinicon, the 

Cedar, the Iowa, and the Skunk River Basins and covers about 19,500 mi2

in eastern Iowa and southern Minnesota. In 1990, about 40 percent of the 

more than 1 million people in the Study Unit were concentrated in cities 

with populations of greater than 20,000 people. Cedar Rapids is the only 

city with a population greater than 100,000. Ground water is the major 

source for municipal, industrial, and domestic supplies. During the study, 

Iowa City was the largest municipal user of surface water. Over 90 percent 

of the land in the Study Unit is used for agricultural purposes. Forested 

areas account for only 4 percent of the land. Data from Eros Data Center, 

1994. 

SUMMARY OF MAJOR FINDINGS

• •

•

•

•

•

•

•

•

•
 2 Water Quality in the Eastern Iowa Basins

 Major influences on streams and rivers

• Agricultural storm runoff

• Animal feeding operations

• Tile-line drainage

• Urban areas

Ground-Water Highlights

Compared to surface water, ground water in the 

Eastern Iowa Basins had substantially lower nutrient 

concentrations and less frequent detections. Land use, 

however, had a substantial effect on the quality of 

water in alluvial aquifers. Pesticide degradates were 

some of the most commonly detected constituents in 

these aquifers. Nitrate and methyl tert-butyl ether 

(MTBE) exceeded the USEPA standard or advisory in 

some of the samples. In contrast, bedrock aquifers, 

which are generally protected by clay and shale layers, 

typically had low nitrate concentrations and low frequency of pesticide detections.

• Nitrate concentrations generally decreased with depth in the 

alluvial aquifers. Biological denitrification may result in 

decreased nitrate concentration with depth, but it is also possible that the deeper water infiltrated during past years when 

less fertilizer was used for crops. 

Small Streams Major Rivers

Agricultural Urban 

Selected Indicators of Stream-Water Quality

Mixed

Land Uses

—

Nitrate1

Pesticides

Trace

elements2

Semivolatile

organics5

Organochlorines3

Percentage of samples with concentrations greater 

than or equal to health-related national guidelines for 

drinking water, protection of aquatic life, or contact 

recreation

Percentage of samples with detected concentrations 

less than health-related national guidelines for drinking 

water, protection of aquatic life, or contact recreation

Percentage of samples with no detection

Not assessed

Pesticide

degradates

—

—

—

Total

phosphorus1 —

Selected Indicators of Ground-Water Quality

* **

Shallow Ground Water Supply Wells

Urban Domestic Agricultural Public

Nitrate

Pesticides

Radon

Volatile

organics4

—

Percentage of samples with concentrations greater 

than or equal to health-related national guidelines for 

drinking water, protection of aquatic life, or contact 

recreation (**Detected in 1 percent or less of samples)

Percentage of samples with concentrations less than

health-related national guidelines for drinking water, 

protection of aquatic life, or contact recreation

Percentage of samples with no detection (*Not 

detected in 1 percent or less of samples)

Not assessed

• Nutrients move from ground water to streams by natural drainage and tile lines. Nitrate concentrations in 24 of 25 mediumsized streams exceeded 10 mg/L during the sampling period in 

May 1998 when streamflow originated primarily from groundwater discharge. Nitrate concentrations consistently exceeded 10 

mg/L in water from a selected tile line draining to the Iowa 

River. 

• Pesticides were detected in alluvial aquifers underlying both 

agricultural and urban areas, but shallow ground water in agricultural areas contained greater concentrations than urban areas. 

A greater variety of pesticide compounds was detected in urban 

areas than agricultural areas, reflecting a more diverse usage.

• Pesticides most commonly detected in the alluvial aquifers 

underlying urban areas were atrazine, prometon, and metolachlor. Pesticide concentrations did not exceed established 

drinking-water standards. 

• With the exception of atrazine and metolachlor and prometon in 

urban areas, pesticides were infrequently detected in alluvial 

aquifers. Pesticide degradates generally were more commonly 

detected in the alluvial aquifers than their parent compounds. 

The greater presence of degradates indicates that many pesticides 

break down in the soil and that the resulting pesticide degradates 

are transported to the shallow aquifers. 

• MTBE, a common gasoline additive used to increase the octane 

content or ensure cleaner burning, was detected in 23 percent of 

samples from alluvial aquifers in urban areas. Concentrations 

exceeded the USEPA drinking-water advisory in samples from 

6 percent of the wells.

 Major influences on ground water

• Lawn, garden, and agricultural fertilizers

• Agricultural and urban pesticides

• Leaking underground fuel-storage tanks

1 Phosphorus and nitrogen, sampled in water.

2 Arsenic, mercury, and metals, sampled in sediment, fish tissue, and water.

3 DDT and PCBs, sampled in sediment and fish tissue.

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

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

sediment and fish tissue.

•

•

•

•

•

•
 Introduction to the Eastern Iowa Basins 3

INTRODUCTION TO THE EASTERN IOWA BASINS

The Des Moines Lobe is characterized by flat topography and fertile

soils; conditions ideal for growing

corn and soybeans.

The more steeply rolling terrain of

the Southern Iowa Drift Plain is

extensively farmed but has relatively

more forests, pastures, and

grassland than the other landform

regions.

Gently rolling topography with

long, gentle slopes characterize

the Iowan Surface. Wooded

buffers are present along many

streams.

The Eastern Iowa Basins Study 

Unit encompasses the Wapsipinicon, the Cedar, the Iowa, and the 

Skunk River Basins and encompasses about 19,500 mi2 (square 

miles) in eastern Iowa and southern 

Minnesota (fig. 1). The four major 

rivers in the Study Unit generally 

flow in a southeasterly direction 

and empty into the Mississippi 

River. The basins of these four 

major rivers are relatively long and 

narrow. The Wapsipinicon River 

originates in southeastern Minnesota and extends about 225 mi 

(miles) to its confluence with the 

Mississippi River. The Wapsipinicon River Basin has a drainage area 

of 2,540 mi2. The Cedar River 

originates in southern Minnesota 

and joins the Iowa River about 

30 mi upstream from the mouth of 

the Iowa River. The Iowa River 

originates in north-central Iowa. 

The Iowa and the Cedar River 

Basins cover 12,640 mi2

, more 

than 90 percent of which is in 

Iowa. The Skunk River originates 

in central Iowa and drains about 

4,350 mi2

.

Geology

Glaciers created a land surface 

with three distinct regions in the 

Eastern Iowa Basins Study Unit: 

the Des Moines Lobe, the Iowan 

Surface, and the Southern Iowa 

Drift Plain (fig. 1). The Des 

Moines Lobe is characterized by 

low relief with some distinct ridges 

near the eastern boundary and 

occasional depressions that form 

lakes, ponds, and swamps. Glacial 

till is the dominant surficial material, and alluvium is present along 

the streams. Poorly drained soils 

have developed on the tills. The 

Iowan Surface has gently rolling 

topography with long slopes, low 

relief, and a mature drainage pattern. The surficial material is primarily glacial drift with thin layers 

of windblown loess on the ridges 

and alluvium near the streams. A 

subregion of the Iowan Surface 

(Iowan Karst) was defined for this 

study in an area where bedrock is 

close to the land surface. In the 

Southern Iowa Drift Plain, streams 

have eroded deeply into the glacial 

drift and loess mantle to produce a 

steeply rolling terrain with broad, 

flat drainage divides. Moderately 

well-drained soils have developed 

on the loess. 

Figure 1. Glacial deposits formed three major landforms with characteristic soils and topography in the Eastern Iowa 

Basins.
4 Water Quality in the Eastern Iowa Basins

Loess

Bedrock Alluvial aquifer

Water table

Till

Tile line

0

150

50

100

ESTIMATED 1990 WATER USE,

IN MILLION GALLONS PER DAY

Ground water

Surface water

Public supply

Domestic

Industrial

Irrigation

Climate

Water originates as rainfall in 

late spring through late fall and as 

snow during winter and early 

spring. Average annual precipitation in the basins ranges from 

about 30 inches in the northwestern 

part of the Study Unit to about 

36 inches in the southeast. The 

greatest rainfall typically occurs 

during the growing season in 

spring and summer. The mean 

April-to-October precipitation is 

about 25 inches. The most intense 

24-hour rainfall (5-year recurrence 

interval) can be more than 4 inches. 

Snowfall has been recorded from 

September to May. The greatest 

24-hour snowfall seldom (less than 

25 percent of the years) exceeds 

10 inches. Yearly rainfall during 

the study period ranged from below 

average in 1996 to about average in 

1997 and above average in 1998. 

Land Use

Because water flows over the 

land surface or infiltrates the soil, 

human activities may have a substantial effect on the quality of 

ground and surface water. The production of row crops, such as corn, 

and cover crops, such as alfalfa and 

small grains, constitutes the major 

land use in the Study Unit. Land 

near the streams and rivers has a 

combination of crops and forests. 

About 40 percent of the more than 

1 million people in the Study Unit 

are concentrated in cities with populations greater than 20,000. 

Water Use

Water used for household, 

municipal, commercial, industrial, 

and agriculture purposes originates 

primarily from ground water. Surface water, although an important 

supply for several larger cities 

including Cedar Rapids and Iowa 

City, is used primarily for cooling 

water in the generation of electric 

power. 

Water that infiltrates through the 

soil into underlying sand and 

gravel deposits and ultimately into 

the underlying bedrock formations 

is used as a water supply for about 

94 percent of the population in the 

Eastern Iowa Basins Study Unit. 

Rivers and streams are the source 

of public-water supplies for about 6 

percent of the population (fig. 2). 

Figure 3. In the Eastern Iowa Basins, water originating from precipitation flows overland or through loess, till, and 

alluvial deposits to nearby streams. Areas with high water tables and poor natural drainage have commonly been 

artificially drained with tile lines. (Graphic created by Suzanne Roberts, U.S. Geological Survey.)

Figure 2. An abundant ground-water 

resource provides water to municipalities, homes, and industry. Ground 

water is used by more than 90 percent 

of the population in the Study Unit. 
Introduction to the Eastern Iowa Basins 5 

1996 1997 1998

1,000

100,000

2,000

5,000

10,000

20,000

50,000

DISCHARGE,

IN CUBIC FEET PER SECOND

EXPLANATION

Long-term

discharge

75th percentile

25th percentile

Mean daily

discharge

Iowa River at Wapello, Iowa (11)

Surface Water

Excess precipitation that does 

not infiltrate into the soil or evaporate runs off to the streams (fig. 3). 

Generally, poorly permeable till 

soils typical of the Des Moines 

Lobe and steeper slopes typical of 

the Southern Iowa Drift Plain generate greater overland flow than the 

moderately well drained loess soils 

and gentle slopes typical of the 

Iowa Surface. Overland flow to 

streams is slowed or reduced by 

grass, perennials, shrubs, and trees 

(riparian buffers) where present 

near streambanks. Runoff to 

streams averages about 25 percent 

of the annual precipitation and 

ranges from less than 7 inches per 

year in the northern part of the 

Study Unit to about 9 inches per 

year in the southeastern part. Overland flow and ground-water discharge are the major sources of 

streamflow. However, tile lines 

may be an important source to 

streams during base flow in areas 

where they have been installed to 

remove standing water from surface depressions and to lower the 

water table.

Long-term yearly discharge from 

the Eastern Iowa Basins Study Unit 

averages about 9.2 million acrefeet. The overall increase in rainfall 

from 1996 to 1998 was reflected in 

the substantial increase in yearly 

stream discharge (fig. 4). Yearly 

discharge from the Eastern Iowa 

Basins increased from about 

8.6 million acre-feet in 1996 to 

almost 13.8 million acre-feet in 

1998. Yearly discharge was not 

uniform in the major basins. Discharge from the Wapsipinicon and 

Iowa River Basins increased in 

1997 and 1998, and the discharge 

from the Skunk River Basin 

decreased from 1996 to 1998. 

Ground Water

 Water from rainfall infiltrates 

through the soil and, depending on 

whether permeable sand, gravel, 

and fractured bedrock are present, 

may continue to move to the deeper 

aquifers (fig. 3). If low-permeability clay or shale lies below the 

unconsolidated surficial materials, 

water may move laterally to a 

nearby stream. 

Alluvial material that has been 

deposited by rivers and streams 

commonly consists of sand and 

gravel layers that store and transmit 

water readily. The alluvial aquifers 

(fig. 5) are the most frequently 

used source of ground water in the 

Eastern Iowa Basins because they 

are near land surface and can supply large amounts of water. The 

same properties (shallow depth and 

permeable material) that make alluvial aquifers excellent sources of 

water also make the alluvial aquifers susceptible to contamination 

from surface activities.

Two additional surficial deposits, not assessed during this study, 

provide water for domestic and 

municipal supplies. Sand and 

gravel deposits in low-permeability 

glacial till generally yield small 

quantities of water that are used 

mostly for rural domestic and stock 

supplies. Also, deep sand and 

Figure 4. Stream discharge in the 

Eastern Iowa Basins ranged from 

below normal in 1996 to near normal 

in 1997 and above normal in 1998 

(site number in parentheses; see site 

map in “Study Unit Design” section). 
6 Water Quality in the Eastern Iowa Basins

EXPLANATION

UNCONSOLIDATED AQUIFER

BEDROCK AQUIFER

Alluvial aquifer

Silurian-Devonian aquifer 

Cambrian-Ordovician

aquifer system

Mississippian aquifer

Upper Carbonate aquifer

Bedrock surface

Approximate boundary

between the

Silurian-Devonian and

Upper Carbonate

aquifers (Olcott, 1992)

gravel deposited in bedrock valleys 

before the last glacial advance is an 

important source of water in parts 

of the Eastern Iowa Basins. 

Rock formations (bedrock) generally underlie the clay, silt, sand, 

and gravel surficial materials and 

can provide water for use. Bedrock 

aquifers are generally deep and are 

protected from surficial contamination. However, in areas such as the 

Iowan Karst, bedrock is exposed or 

is covered by very thin unconsolidated deposits and is susceptible to 

contamination from urban and agricultural land uses. 

 The most extensively used 

bedrock aquifers are the SilurianDevonian and Upper Carbonate 

aquifers. The Silurian-Devonian 

and Upper Carbonate aquifers 

consist mainly of limestone and 

dolomite with locally interbedded 

shale and evaporite beds. Bedrock 

aquifers that are used as a source of 

water in the Study Unit but were 

not evaluated during this study are 

the Mississippian aquifer and the 

Cambrian-Ordovician aquifer 

system.

Figure 5. Several major bedrock and 

unconsolidated aquifers are used as 

sources of water for domestic, 

municipal, and industrial supplies. 

Only the most heavily used aquifers, 

the Silurian-Devonian and Upper 

Carbonate aquifers and the alluvial 

aquifers, were sampled.
Major Findings 7 

Agricultural

land use

Urban

land use

Alluvial

aquifer

SilurianDevonian

and

Upper Carbonate

aquifers

0.01

10

0.02

0.05

0.1

0.2

0.5

1

2

5

MEDIAN NITRATE CONCENTRATION,

IN MILLIGRAMS PER LITER

0

300

100

200

MEDIAN WELL DEPTH,

IN FEET BELOW LAND SURFACE

EXPLANATION

Nitrate concentration Well depth

Monitoring

wells (alluvial)

Domestic

wells

Detection limit

Nutrients in Ground Water 

and Streams

Two naturally occurring nutrients, nitrogen and phosphorus, 

commonly are applied in the form 

of fertilizers and manure in agricultural areas to increase the yield of 

crops and as fertilizer in cities and 

towns to enhance the appearance of 

residential lawns, city parks, and 

golf courses. Nitrogen and phosphorus also are commonly discharged from wastewater-treatment 

facilities. Nutrients that are not 

used by plants or attached to soil 

particles can move to shallow 

ground water or can be washed into 

nearby streams during intense 

rains. Runoff from rainfall and 

ground-water inflow can transport 

excess nutrients to streams, causing 

algal blooms that deplete oxygen 

for fish and other aquatic organisms. High concentrations of nitrogen in the form of nitrate may 

make untreated water unsuitable 

for human consumption. The 

USEPA has established a Maximum Contaminant Level (MCL) of 

10 mg/L (milligrams per liter) for 

nitrate as nitrogen in drinking 

water (U.S. Environmental Protection Agency, 1996). High concentrations of nitrogen in the form of 

ammonia may kill fish and other 

aquatic organisms. To minimize 

algal growth in streams and reservoirs, a total phosphorus concentration of 0.10 mg/L or less has 

been recommended by the USEPA 

(1986).

Nutrients in Ground Water

Nitrogen and phosphorus are 

prevalent in ground water. Nitrogen readily moves from the land 

surface to ground water in the shallow alluvial aquifers but not as 

readily to most parts of the deeper 

Silurian-Devonian and Upper Carbonate bedrock aquifers in the 

Eastern Iowa Basins. Nitrogen, in 

the form of nitrate and ammonia, 

and dissolved phosphorus were 

detected in more than 65 percent of 

124 ground-water samples. Nitrate 

concentrations were significantly 

higher in the shallow alluvial aquifers, which have been identified as 

being susceptible to contamination 

(Hoyer and Hallberg, 1991), than 

in the Silurian-Devonian and 

Upper Carbonate bedrock aquifers 

(fig. 6). Nitrate concentrations in 

water samples from monitoring 

wells screened near the water table 

in urban areas were higher than 

concentrations in samples from 

domestic wells, which generally 

are screened deeper in the aquifers.

Human and natural factors 

affect movement of nutrients to 

ground water. Downward movement of water containing nitrogen 

and phosphorus is slowed by finegrained materials overlying the 

aquifers. The presence of clay in 

the soil and in the shallow subsurface and low-permeability rocks, 

such as shale, can slow groundwater infiltration rates and limit the 

amount of nutrients at depth. Surficial contamination most affects 

water near the top of the alluvial 

aquifers where the clay layer above 

the water table is thin or nonexistent (see fig. 8, p. 8). 

In the Silurian-Devonian and 

Upper Carbonate aquifers, groundwater ages (determined by analysis 

of tritium concentrations) were significantly younger and nitrate concentrations were significantly 

higher in samples from areas where 

an overlying low-permeability 

shale layer was absent or where 

less than 100 feet of unconsolidated deposits overlies the aquifer 

(Savoca and others, 1999). These 

two results indicate that longer 

flow paths (deeper sample depth 

and thicker clay layer) increase 

opportunities for sorption, degradation, and dispersion and may contribute to decreases in nutrient 

concentrations with depth. Alternatively, water deeper in the aquifer 

may have infiltrated in years when 

fertilizer use was not as prevalent.

MAJOR FINDINGS

Figure 6. The shallowest ground water is most heavily affected by current landuse practices. Agricultural practices result in higher levels of nitrate in ground 

water than urban activities.
8 Water Quality in the Eastern Iowa Basins

NUTRIENT CONCENTRATIONS IN STREAMS WERE

AMONG THE HIGHEST IN THE NATION

Concentrations of nitrate and total phosphorus in streams in Eastern Iowa 

Basins rank among the highest in the Nation (fig. 7). The median dischargeweighted nitrate concentrations also were significantly greater in Eastern 

Iowa Basins streams than in streams sampled elsewhere in the Corn Belt and 

Northern Great Plains ecoregion (Omernik, 2000)—an area of similar climate, topography, regional geology and soils, and broad land-use patterns. 

Overall, total nitrogen concentrations were similar to the streams sampled in 

Illinois and to an agricultural stream sampled in southern Minnesota. Nitrate 

concentrations were in the upper 25th percentile nationally for 9 of 11 Basic 

Fixed Sites. The defined reference site (Wapsipinicon River near Tripoli) and the site on the stream draining 

the Iowan Karst landform (Flood Creek near Powersville) were within the middle 50 percent nationally. Concentrations of total phosphorus ranged from moderate to high in relation to other streams sampled in the United 

States. Average discharge-weighted total phosphorus concentrations at two sites (Old Mans Creek near Iowa 

City and Skunk River at Augusta) in the southern part of the Eastern Iowa Basins, where highly erodible loess 

soils cover most of the basins, were in the upper fifth percentile nationally. 

Although substantially lower than in 

surface water, nitrate concentrations in the 

alluvial aquifers in agricultural areas in 

Eastern Iowa Basins are greater than those 

in ground water sampled elsewhere in the 

Corn Belt and the Nation. The alluvial 

aquifer is a relatively susceptible aquifer in 

contrast to aquifers within glacial till sampled in Illinois; therefore, the ranking of 

concentrations may not be directly comparable. However, nitrate concentrations in 

urban areas and in aquifers that serve as a 

source of water supply for municipal and 

domestic use in the Eastern Iowa Basins 

are comparable to those from the rest of 

the Nation. Dissolved phosphorus concentration in the alluvial aquifers in agricultural areas of Eastern Iowa Basins was 

greater than in ground water in the rest of 

the Nation. Increased susceptibility and 

greater fertilizer use may account for the 

higher phosphorus concentrations.

Natural processes may remove 

nitrogen from alluvial aquifers. 

The relation between nitrogen, dissolved oxygen, and organic carbon 

concentrations suggests that nitrogen is being biologically transformed and removed from the 

alluvial aquifers. Nitrate remaining after water moves through or 

around clay layers may be converted to nitrogen gas in a lowoxygen or oxygen-free environment in the presence of organic 

carbon. This process is called 

denitrification. Nitrate concentrations were significantly higher in 

alluvial ground water having dissolved oxygen concentrations 

Figure 7. Nitrate and phosphorus concentrations in Eastern Iowa Basins 

streams and ground water are higher when compared with a wide variety 

of land uses across the Nation and when compared to similar land use in 

other parts of the Corn Belt. (Phosphorus in ground water as dissolved 

orthophosphorus and phosphorus in streams as total phosphorus)

Corn Belt

Agricutural

Urban

Mixed

Iowa

Eastern

Belt

Corn

States

United

Agricutural

Urban

Mixed

0

15

5

10

Iowa

Eastern

Belt

Corn

States

United

0

0.4

0.2

MEDIAN CONCENTRATION, 

IN MILLIGRAMS PER LITER

GROUND WATER RIVERS AND STREAMS

NITRATE PHOSPHORUS
Major Findings 9 

0

6

2

4

0

0.04

0.02

0

0.04

0.02

MEDIAN CONCENTRATION, IN MILLIGRAMS PER LITER

0

4

2

0

2

1

Agricultural Urban

LAND USE

0

6

2

4

ORGANIC CARBON,

 IN MICROGRAMS PER 

KILOGRAM

Nitrate

Ammonia

Phosphorus

Oxygen

Organic carbon

Soil carbon

aquifers in agricultural areas than 

in urban areas. Nitrate was detected 

in 77 percent of samples at a 

median concentration of 1.8 mg/L 

from urban areas (fig. 6). Nitrate 

exceeded the USEPA MCL 

(10 mg/L as N) in 39 percent of 

samples from agricultural areas and 

in none of the samples from urban 

areas. Dissolved phosphorus concentrations tended to be higher in 

samples from agricultural areas 

(median of 0.03 mg/L) than urban 

areas (median of 0.01 mg/L); however, the difference was not statistically significant. The higher 

reliance on fertilizers in agricultural areas than in urban areas most 

likely contributed to the higher 

nitrate and phosphorus concentrations.

Ammonia is prevalent in shallow urban ground water. Dissolved ammonia concentrations 

were significantly higher in samples from urban areas than in 

samples from agricultural areas 

(fig. 9). The median dissolved 

ammonia concentration in samples 

from shallow urban ground 

water (0.025 mg/L) was more than 

twice the median concentration in 

samples from agricultural areas 

(0.010 mg/L). Anhydrous ammonia 

is used frequently as a nitrogen fertilizer for corn, but soil microbes 

quickly convert ammonia to 

nitrate. 

Conditions in the alluvial aquifers (fig. 9) indicate that ammonia 

in shallow urban ground water 

originates, at least partly, from degradation of organic matter most 

likely derived from human activities. Substantial amounts of organic 

matter are available in the soil, silt, 

and clay above the aquifer and dissolved in water within the aquifer. 

Dissolved oxygen concentrations 

were significantly lower in urban 

greater than 0.5 mg/L and were significantly lower in ground-water 

samples having increased dissolved 

organic carbon concentrations 

(Savoca and others, 2000). Denitrification may be an important natural process that reduces nitrate 

concentrations before water moves 

to ground-water supplies or is discharged to streams.

The type of land use affects 

shallow ground-water quality. 

Different uses, whether the land is 

used for agriculture, homes, business, or industry, are reflected in 

the nutrient concentrations in the 

ground water. Animal feeding 

operations can further affect water 

quality in areas with intensive rowcrop agriculture (fig. 9). Nitrate 

was detected more frequently 

(94 percent of samples) and in 

greater concentrations (median of 

5.1 mg/L) in shallow alluvial 

areas than in agricultural areas. 

Microbial degradation of abundant 

organic matter would result in the 

decrease in dissolved oxygen concentrations and in the increase of 

dissolved ammonia concentrations 

in shallow ground water.

Nutrients move from ground 

water to streams by natural 

drainage and tile lines. At times, 

ground water contributes a substantial amount of nitrogen to streams 

in the Eastern Iowa Basins Study 

Unit. In most parts of the Study 

Less than

 1 foot

Greater than

or equal to

 1 foot

Less than

 100 feet

Greater than

or equal to

 100 feet

CLAY THICKNESS,

IN FEET

0

6

2

4

UNCONSOLIDATED MATERIAL 

THICKNESS, IN FEET

0

0.6

0.1

0.2

0.3

0.4

0.5

0.6

MEDIAN NITRATE CONCENTRATION, IN MILLIGRAMS PER LITER

Alluvial aquifer

Silurian-Devonian and

Upper Carbonate aquifer

Detection limit

Figure 8. Overlying clay and other lowpermeability material hinder movement 

of nitrate to ground water.

Figure 9. Agricultural and urban land 

uses contribute nitrogen to shallow 

alluvial aquifers. Conditions are 

suitable in urban areas for the 

formation of ammonia in the organicenriched aquifers. 
10 Water Quality in the Eastern Iowa Basins

Unit, water naturally flows from 

alluvial aquifers to streams through 

the streambanks and streambeds. 

During high base flow in May 

1998, nitrate concentrations in 

samples from 24 of 25 streams in 

the Eastern Iowa Basins were 

higher than 10 mg/L. In contrast, 

nitrate concentrations in these 

streams ranged from less than 0.05 

to 8.3 mg/L during low base flow 

in August 1997. The high concentrations detected during the spring 

may be due to the increased 

ground-water inflow after fertilizer 

was applied and was readily available for transport. 

 Shallow tile lines have been 

installed to remove excess water 

from the land and to lower the 

water table in many parts of the 

Study Unit. These tile lines typically drain water from the upper 

part of the water table, which generally contains the highest nitrate 

concentrations to nearby streams. 

During the summer, the water table 

may decline below the tile lines 

due to decreased rainfall and 

increased evapotranspiration. Tileline flow and nutrient transport 

then cease. For example, nitrate 

concentrations were consistently 

higher than 10 mg/L in tile-line discharge from April until the end of 

August when flow in this and other 

local tile lines ceased (fig. 10). 

After tile flow ceased, nitrate concentrations in the Iowa River 

decreased. 

When tile flow ceases, streamflow originates from natural 

ground-water inflow, which 

traverses deeper and longer flow 

paths. Water that originates from 

deep in the alluvial aquifers contains low nitrate concentrations 

(see previous discussion) due to 

transformation in the aquifer or 

streambed and plant uptake as it 

passes beneath riparian buffers. 

These results are similar to those of 

previous studies (Cambardella and 

others, 1999; Soenksen, 1996) that 

documented the importance of tileline discharge on stream-water 

quality. 

Increased algal growth in late 

summer and early fall also can contribute to decreased nitrate concentrations in streams (Porter, 2000). 

Tile-line drainage is an important 

hydrologic factor that may serve to 

protect shallow ground water by 

removing contaminants before they 

move down into the aquifers; however, tile lines also may enhance 

the contamination of streams by 

short circuiting natural processes 

that remove nitrogen from ground 

water.

Nutrients in Streams

The concentrations of nutrients 

in a stream or river are the result of 

the interaction of human activities 

and natural factors in the basin. 

Human activities, agricultural and 

urban, generally increase the input 

of nitrogen and phosphorus into the 

basin, alter the land surface and 

drainage patterns (which may 

affect the amount and timing of 

rainfall runoff), and alter vegetation on the land and habitat in 

streams and rivers, resulting in a 

more rapid flushing of nutrients 

from the land and downstream in 

streams and rivers. Natural factors 

including the amount and timing of 

rainfall, soil types, and land-surface slope affect the amount of 

nitrogen and phosphorus washed 

off fields into nearby streams. 

Nitrogen and phosphorus are 

almost always present in streams 

and rivers. Nitrate, the most common form of nitrogen in streams 

and rivers in the Eastern Iowa 

Basins, was present in more than 

98 percent of the samples at concentrations of 0.05 mg/L or greater 

and was most frequently (80 percent of the samples) present in the 

range of 1 to 10 mg/L (fig. 11). 

Nitrate concentrations less than 

about 0.5 mg/L were generally 

associated with low streamflow in 

late summer when nitrogen inputs 

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

1997

0

20

10

NITRATE CONCENTRATION,

IN MILLIGRAMS PER LITER

0

3,000

1,000

2,000

STREAM DISCHARGE, 

IN CUBIC FEET PER SECOND

EXPLANATION

Stream discharge Tile-line nitrate concentration

Tile-line flow Iowa River nitrate concentration

Figure 10. Tile lines can contribute substantial amounts of nitrate to streams 

and rivers. Nitrate concentrations in the Iowa River near Rowan decreased as 

tile-line discharge ceased.
Major Findings 11 

were low and algal uptake was 

high. About 22 percent of the 

samples (fig. 12) contained nitrate 

concentrations at or above the 

USEPA's drinking-water standard 

of 10 mg/L (U.S. Environmental 

Protection Agency, 1996). 

Phosphorus, dissolved in the 

stream water and attached to 

sediment particles or organic 

compounds transported in the 

stream, was present in all samples. 

Total phosphorus concentrations 

exceeded the USEPA goal of 

0.1 mg/L (U.S. Environmental 

Protection Agency, 1986) or less to 

minimize plant and algal growth 

about 75 percent of the time. 

Streams with large total phosphorus concentrations generally contained large suspended-sediment 

concentrations. 

Landform and land use affect 

nitrogen and phosphorus concentrations. Nitrogen and phosphorus 

concentrations in streams differed 

the nonchannelized river may 

decrease streambank erosion and 

enhance biological habitat.

among landform areas and with 

land use (fig. 12). Basins of the size 

investigated during this study 

where human activities are minimal (background) are not present in 

eastern Iowa and southern Minnesota. The Wapsipinicon River near 

Tripoli was identified as a reference site, however, because 

although agricultural land use constitutes more than 90 percent of the 

basin, substantial areas of riparian 

forests and wetlands remain. Samples from the reference site generally had the lowest median nutrient 

concentrations of any stream site 

studied. Median suspended-sediment concentrations also were the 

lowest. Biological indicators of 

water quality at the reference site 

were better than all other sites in 

the Study Unit. Extensive floodplain vegetation may decrease 

direct transport of nutrients from 

fields to the Wapsipinicon River, 

and extensively wooded banks on 

0.001 100 0.01 0.1 1 10

CONCENTRATION, IN MILLIGRAMS PER LITER

0

100

20

40

60

80

PERCENTAGE OF SAMPLES

WITH CONCENTRATION

EQUAL TO OR GREATER THAN

INDICATED CONCENTRATION

EXPLANATION

Total phosphorus

recommended goal

Nitrate Maximum 

Contaminant Level

Nitrate

Total

phosphorus 

Figure 11. Nitrate concentrations in streams were most often in the 

range of 1 to 10 mg/L and equaled or exceeded the Maximum 

Contaminant Level in 22 percent of the samples. In contrast, total 

phosphorus concentrations equaled or exceeded the 0.1-mg/L goal for 

minimization of algal growth in 75 percent of the samples.

0

15

5

10

Smaller streams

draining basins with

one predominant

landform or land use 

Large rivers

draining basin with

mixed landforms

and land use 

0

0.4

0.2

MEDIAN CONCENTRATION, IN MILLIGRAMS PER LITER

Total phosphorus

Nitrate

Iowa River near Rowan (3)

S.F. Iowa R. near New Providence - AFO (4)

Old Mans Creek near Iowa City (6)

Flood Creek near Powersville (7)

Wolf Creek near Dysart (9)

Wapsipinicon River near DeWitt (2)

Reference (1)

Iowa River at Marengo (5)

Cedar River near Conesville (10)

Iowa River at Wapello (11)

Skunk River at Augusta (12)

0

300

100

200

Sediment

Maximum

Contaminant

Level

Recommended

goal

Figure 12. Nitrate concentrations 

generally were lower in large rivers than 

in smaller streams. In contrast, total 

phosphorus concentrations were greater 

in large rivers than in streams. (Site 

number in parentheses; see site map in 

Study Unit Design section. AFO is 

animal feeding operation.)
12 Water Quality in the Eastern Iowa Basins

0

15

5

10

Nitrate

0

0.4

0.2

MEDIAN CONCENTRATION, IN MILLIGRAMS PER LITER

Total phosphorus

0

400

200

Sediment

Maximum

Contaminant

Level

Recommended

goal 

Jan

Feb

Mar

Apr

May

June

July

Aug

Sept

Oct

Nov

Dec

influence dissolved-oxygen conditions during base-flow conditions 

(Porter, 2000).

Intensive row-crop agriculture contributes to greater 

nitrate concentration. The intensity of row-crop agriculture is 

partly responsible for the variability of nitrate concentrations in 

streams. Typically, streams in 

basins that have a higher percentage of corn and soybeans and less 

pasture, forest, and CRP (Conservation Reserve Program) acres had 

higher total nitrogen concentrations 

(fig. 13). However, large rivers in 

basins that had a slightly lower percentage of row crops and a slightly 

larger proportion of urban areas 

typically had higher total phosphorus concentrations. Large rivers 

generally contained higher suspended-sediment concentrations 

than streams, and most large potential point-source phosphorus contributors (large cites) are located on 

the large rivers. 

Increased availability results 

in greater nutrient concentrations during the spring and early 

summer. Concentrations of nitrogen and phosphorus varied seasonally in streams in eastern Iowa 

(fig. 14). Median total dissolved 

Median nitrate concentrations 

were highest in samples from Wolf 

Creek, a stream draining an Iowan 

Surface basin that has more than 

80-percent row-crop agriculture, 

and in samples from the South Fork 

Iowa River, a stream draining a 

Des Moines Lobe basin that has 

concentrated animal-feeding operations (AFO). The median nitrate 

concentration in samples from 

Wolf Creek (10.2 mg/L) exceeded 

the 10-mg/L USEPA MCL. Algal 

status and biomass in Wolf Creek 

indicated degraded conditions 

(from a national perspective), and 

fish and invertebrate communities 

were dominated by species tolerant 

to nutrient and organic enrichment. 

Wolf Creek flows into the upper 

end of a reach of the Cedar River 

that has been listed on the 1998 

USEPA Section 303(d) list (Iowa 

Department of Natural Resources, 

2000) as an impaired water body. 

Wolf Creek may provide substantial amounts of nitrogen that contribute to the degradation of the 

Cedar River between Waterloo and 

Cedar Rapids. 

Landform features affect phosphorus concentrations. Phosphorus and suspended-sediment 

concentrations were typically 

larger in streams that drain the 

Southern Iowa Drift Plain and the 

Des Moines Lobe than in other 

streams. The Southern Iowa Drift 

Plain typically has steeper slopes 

than the rest of the Study Unit and 

contains loess deposits that are easily eroded (Schwarz and Alexander, 1995). Many Des Moines 

Lobe streams have been extensively channelized; to a great 

extent, the streambanks and flood 

plains contain little riparian vegetation, resulting in a greater dominance of phytoplankton than 

benthic algae and relatively higher 

rates of stream metabolism that can 

nitrogen concentrations were highest in June (11.5 mg/L) when 

nitrogen is transported to streams 

and rivers by spring and early summer runoff from rainfall. Nitrogen 

probably originates from that 

accumulated in the soil following 

application of chemical fertilizers 

and manure during the spring and 

previous fall. Nitrate was the 

predominant form of nitrogen 

detected during this period. Total 

dissolved nitrogen concentrations 

in streams decreased through the 

summer as nitrogen was removed 

from the soil by plant uptake, runoff, and leaching to shallow ground 

Figure 14. Nitrate concentrations that 

commonly increase to levels that 

exceed the Maximum Contaminant 

Level in June can decrease to levels 

below detection in October. Total 

phosphorus concentrations were 

rarely below the recommended goal 

for reduction of algal growth. 

40 60 80 100

PERCENTAGE OF BASIN IN

ROW-CROP AGRICULTURE

5

15

10

MEDIAN TOTAL NITROGEN

CONCENTRATION, IN

MILLIGRAMS PER LITER 

Trend line

Basin

Figure 13. Streams draining basins that 

have higher percentages of pasture, 

grassland, and forests and less land 

planted in row crops tended to have 

lower nitrogen concentrations.
Major Findings 13 

water. Algal and plant growth in 

the streams during low streamflow 

in late summer and early fall can 

result in increased uptake of dissolved nutrients (Porter, 2000). The 

combination of reduced source 

loading and instream processing 

results in lowest nitrate concentrations in October. Fall rains, in 

combination with fertilizer and 

manure applications, were associated with another rise in nitrogen 

concentrations beginning in 

November and peaking in January. 

Although nitrate remained the primary form of nitrogen, ammonia 

and organic nitrogen were more 

prevalent during the winter.

Runoff from agricultural and 

urban areas transports substantial 

amounts of phosphorus to streams, 

but the timing of peak phosphorus 

concentrations does not always 

correspond to peak nitrate concentrations. Phosphorus concentrations 

peak during periods of high runoff 

in early spring when substantial 

amounts of soil are eroded into 

the streams. The highest median 

total phosphorus concentrations 

occurred in February (0.33 mg/L) 

and March (0.36 mg/L) with a secondary peak in June (0.29 mg/L) 

(fig. 14). Maximum concentrations 

corresponded with early seasonal 

runoff from snowmelt or rainfall. 

Early summer rains produced runoff that accounted for a secondary 

peak in total phosphorus concentrations during June. 

Transport of nutrients represent an economic loss and a 

potential environmental threat.

The large amounts of nitrogen and 

phosphorus that are transported 

from the Study Unit by the Wapsipinicon, Cedar, Iowa, and Skunk 

Rivers represent an economic loss 

to farmers and an environmental 

concern for downstream water. 

Nitrogen and phosphorus transported to the Mississippi River 

increased yearly from 1996 

through 1998 (fig. 16). Increased 

streamflow was a major factor in 

the increased loads. The estimated 

mass of nitrogen (load) increased 

from about 106,000 tons in 1996 to 

more than 257,000 tons in 1998, 

and the estimated total phosphorus 

load increased from 7,500 tons in 

1996 to 9,700 tons in 1998. 

ANIMAL FEEDING OPERATIONS CONTRIBUTE 

ADDITIONAL NUTRIENTS TO STREAMS

The median nitrate concentration in samples from the South Fork of 

the Iowa River (9.5 mg/L) were significantly higher than those in samples from the Iowa River near Rowan 

(median of 6.3 mg/L), though both 

streams drain the same landform (Des 

Moines Lobe) and have similar crop 

patterns (greater then 80 percent row 

crops). In addition to row-crop agriculture, the basin of the South Fork 

Iowa River contains substantially 

more permitted animal feeding operations (AFO) (29) than the Iowa River 

Basin upstream from Rowan (8). The 

density of hogs (fig. 15) in the South 

Fork basin is more than twice that in 

the Iowa River Basin (Sorenson and 

others, 1999). The manure generated 

from AFOs is commonly applied on 

fields in substitution for chemical fertilizer. However, in areas where there 

is dense concentration of AFOs, sufficient land may not always be available to economically dispose of 

animal wastes, and the potential for 

overapplication exists. Excess 

nutrients seep into the ground 

water and are washed into nearby 

streams. About 1.8 times more 

nitrogen and about 2.5 times more 

phosphorus were transported by 

the South Fork Iowa River than by 

the Iowa River (fig. 15). The 

higher nitrate concentrations and the greater nitrogen and phosphorus 

yields from the South Fork Iowa River compared to the Iowa River near 

Rowan may indicate that a reduction in chemical fertilizer application 

equivalent to the increased manure application has not occurred in the 

South Fork Basin. 

Rowan

near

River

Iowa

River

Iowa

Fork

South

0

4

1

2

3

PHOSPHORUS YIELD,

IN POUNDS

PER ACRE

0

40

10

20

30

NITROGEN YIELD,

IN POUNDS

PER ACRE

0

300

100

200

HOG DENSITY,

IN POUNDS OF

HOGS PER ACRE

Figure 15. Large-scale hog production 

adds to the nitrogen and phosphorus in 

streams draining basins in the Des 

Moines Lobe landform. [Hog density 

data calculated from Iowa Department 

of Natural Resources (1999) wastecontrol facility permits.]
14 Water Quality in the Eastern Iowa Basins

Transport of nutrients from the 

Eastern Iowa Basins represents a 

potential loss in crop yield or the 

cost of additional fertilizer needed 

to compensate for that flushed from 

the fields. Nutrient loads transported from the Eastern Iowa 

Basins represent an average loss 

of 17 lb/acre/year of nitrogen and 

1.2 lb/acre/year of phosphorus in 

1996 and 42 lb/acre/year of nitrogen and 1.6 lb/acre/year of phosphorus in 1998. 

 Iowa, including the Eastern 

Iowa Basins, has been identified as 

a major source of nutrients 

(Goolsby and others, 1999) that 

contribute to eutrophication and 

hypoxia in the Gulf of Mexico 

(Rabalais, 1996). Alexander and 

others (2000) estimated that more 

than 90 percent of the nitrogen 

reaching the Mississippi River 

from the Eastern Iowa Basins is 

transported to the Gulf of Mexico.

Pesticides in Ground Water 

and Streams

Pesticides (herbicides and insecticides) are used extensively in 

agricultural and urban settings in 

the Eastern Iowa Basins to control 

unwanted vegetation and insects. 

Triazine (atrazine and cyanazine) 

and chloroacetanilide (alachlor and 

metolachlor) herbicides were the 

most extensively used pesticides 

during 1996–98. However, in 1994, 

acetochlor, a herbicide conditionally registered by the USEPA, 

began to replace alachlor. In 1998, 

acetochlor use exceeded all other 

herbicides in Iowa (U.S. Department of Agriculture, 1999). Other 

classes of low-use herbicides (for 

example, sufonylurea and imidozolinone herbicides) also had become 

more popular. Genetically altered 

corn and soybeans that are resistant 

to glyphosate and genetically 

altered “Bt corn" that contains the 

genes allowing corn to produce 

compounds toxic to damaging 

insects also were beginning to 

change pesticide-use patterns. 

Although urban pesticide-use data 

were not available, herbicides commonly are used on lawns, golf 

courses, and road rights-of-way for 

weed control, and a wide range of 

insecticides are used for insect control. 

Transport of pesticides from the 

site of application is dependent on 

the persistence of the compound, 

its solubility in water, and its tendency to adsorb to soil particles. 

Pesticide compounds break down 

at various rates due to biological 

and chemical processes. Pesticides 

can be broken down in the soil by 

bacteria and fungi and nonaffected 

plants and in streams by microorganisms, algae, and aquatic plants. 

The older organochlorine pesticides, most of which have been 

banned (for example, DDT) 

strongly attach to soil particles and 

are transported to streams primarily 

with sediment. In contrast, many 

herbicides commonly used in the 

1990’s (for example, atrazine) are 

relatively soluble and are transported almost exclusively dissolved in water. Water is the 

primary mechanism by which most

pesticides and their breakdown 

products (degradates) are leached 

to ground water. Water transports 

pesticides and their degradates to 

streams by overland flow, tile 

drains, and ground-water inflow.

0

300

200

100

1996 1997 1998

TOTAL LOAD,

IN THOUSANDS OF TONS

5

20

10

15

TOTAL DISCHARGE, IN

MILLIONS OF ACRE-FEET

EXPLANATION

Stream discharge

Total nitrogen

Total phosphorus

Figure 16. Increased streamflow from 1996 to 1998 resulted in larger 

amounts of nitrogen and phosphorus transported from the Study Unit 

to the Mississippi River.
Major Findings 15 

PESTICIDE CONCENTRATIONS RANK HIGHER IN

GROUND WATER THAN IN STREAMS AND RIVERS

Herbicide and insecticide concentrations in streams 

do not rank among the highest 25th percentile nationally (fig. 17) even though use in the Eastern Iowa 

Basins is high. Herbicide concentrations rank in the 

middle 50 percent nationally and in the middle onethird in the Corn Belt. Insecticide concentrations are 

among the lowest in the Corn Belt and Nation. Reasons 

for lower pesticide concentrations in the Eastern Iowa 

Basins compared to other parts of the Nation are not 

entirely clear but may include these: (1) although pesticide use is high in Eastern Iowa Basins it may be higher 

in other corn, cotton, and other crop-growing areas of 

the Nation and (2) soils in Eastern Iowa Basins may be 

relatively conducive to leaching to ground water or 

conditions are favorable for breakdown of the pesticides.

In contrast, herbicide and insecticide concentrations 

in the alluvial aquifers in Eastern Iowa Basins are 

among the highest 25th percentile in the Corn Belt and 

Nation (fig. 17). Water in these aquifers has infiltrated 

within the last 20 years when the use of the analyzed 

pesticides was the greatest. Because water from the 

Silurian-Devonian and Upper Carbonate aquifers is 

generally deeper and has infiltrated before pesticides 

were commonly used, pesticide concentrations from 

these aquifers generally were among the lowest in the 

Nation. 

Pesticides in Ground Water

Herbicides are prevalent in the 

shallow alluvial aquifers. Herbicides are prevalent in the shallow 

alluvial aquifers but are not common in the deeper Silurian-Devonian and Upper Carbonate bedrock 

aquifers in the Eastern Iowa 

Basins. Atrazine and metolachlor 

were the most frequently detected 

herbicides in the alluvial aquifers 

and the Silurian-Devonian and 

Upper Carbonate aquifers. Atrazine 

was detected in more than 50 percent of the alluvial aquifer samples 

and in 18 percent of the SilurianDevonian and Upper Carbonate 

aquifer samples. Metolachlor was 

detected in 20 percent of the alluvial samples and in 12 percent of 

the Silurian-Devonian and Upper 

Carbonate samples. Acetochlor 

was detected in slightly less than 2 

percent of the alluvial aquifer samples but at concentrations less than 

0.2 μg/L, which is the concentration of concern for conditional registration. Acetochlor was not 

detected in samples from the Silurian-Devonian and Upper Carbonate aquifers.

 Pesticide degradates commonly 

constitute the majority of the pesticide mass analyzed. Many of the 

detected pesticides and pesticide 

degradates have no established 

drinking-water standard or aquaticlife criteria, and the potential for 

these compounds to affect humans 

or aquatic organisms is unknown. 

Alachlor ethanesulfonic acid 

(ESA), atrazine, and metolachlor 

ESA were detected in more than 30 

percent of samples from shallow 

alluvial (fig. 18) and deep bedrock 

aquifers. 

Figure 17. Although pesticides are heavily used, concentrations in the Eastern Iowa Basins streams are not among 

the highest in the Nation or the Corn Belt. The vulnerability of 

the alluvial aquifers to contamination is seen in pesticide 

concentrations in ground-water samples that are among the 

highest in the Nation.

Iowa

Eastern

Belt

Corn

States

United

SITE RANK

Median rank

Lowest 25 percent

Middle 50 percent

Highest 25 percent

EXPLANATION

Iowa

Eastern

Belt

Corn

States

United

STUDY RANK

GROUND WATER STREAMS AND RIVERS

Site or study

HERBICIDES INSECTICIDES
16 Water Quality in the Eastern Iowa Basins

Carbaryl

p,p'-DDE

Lindane

Malathion

Dieldrin

Diazinon

Fonofos

Chlorpyrifos

Carbofuran

2,6-Diethylaniline

Alachlor OA

Cyanazine Amide

Acetochlor OA

Hydroxy-Atrazine

Deisopropylatrazine

Acetochlor ESA

Deethylatrazine

Metolachlor OA

Alachlor ESA

Metolachlor ESA

Triclopyr

Tebuthiuron

Prometon

Napropamide

Propyzamide

Molinate

Bromoxynil

Butylate

Dacthal

Acifluorfen

Pendimethalin

Diuron

Dicamba

Metribuzin

Trifluralin

EPTC

2,4-D

Simazine

Bentazon

Alachlor

Cyanazine

Acetochlor

Metolachlor

Atrazine

0 100 20 40 60 80 0 100 20 40 60 80

DETECTION RATE, IN PERCENT

Rivers and streams Alluvial aquifer

Agricutural herbicides Nonagricultural

herbicides

Herbicide

degradates

Insecticides

Agricultural and urban applications have resulted in sporadic low 

levels of insecticide contamination 

in the alluvial aquifers. Chlorpyrifos, an insecticide that was recently 

reevaluated by the USEPA for 

safety as part of the Food Quality 

Protection Act (U.S. Environmental Protection Agency, 2000b), was 

detected in about 7 percent of the 

urban land-use samples and about 

13 percent of the agricultural 

land-use samples. The maximum 

concentration in urban areas (0.005 

μg/L) was about four times lower 

than the maximum concentration in 

agricultural areas (0.021 μg/L). 

Malathion, an insecticide also currently (2000) under USEPA review, 

was detected in one sample from an 

urban land-use well.

Pesticides do not occur everywhere in the Study Unit, and when 

they do occur, concentrations can 

be highly variable. This variability 

in occurrence and concentration of 

various pesticide compounds in 

ground water is probably associated with several factors including 

the presence of overlying protective layers and land-use practices. 

Clay and shale materials 

hinder movement of pesticides to 

aquifers. Clay and shale materials 

hinder movement of pesticides by 

slowing the movement of water 

containing pesticides to underlying 

aquifers. In some instances, water 

that has infiltrated the ground during the last 40 years when many of 

the studied compounds were used 

has not yet reached the deeper parts 

of the alluvial and bedrock aquifers. The age of the ground water 

was significantly younger and pesticide concentrations were significantly higher in samples from areas 

where an overlying bedrock confining unit was absent or where less 

than 100 feet of unconsolidated 

deposits overlies the SilurianDevonian and Upper Carbonate 

aquifers. Water is most affected by 

surficial contamination near the top 

of alluvial aquifers where an overlying clay layer is thin or absent. 

Triazine pesticides and degradate 

concentrations were significantly 

higher in samples from wells in 

areas with a thin clay layer above 

the screened interval than those 

from wells in areas with thick overlying clay layers. Concentrations 

decreased with increasing depth in 

the alluvial aquifers. As with 

nitrate, these two results indicate 

that longer and slower flow paths 

(deeper sample and thicker clay 

layer) increase opportunities for 

sorption, degradation, and dispersion of pesticides and may contribute to decreases in pesticide 

concentrations with depth. 

Figure 18. The pesticide compounds present in streams and rivers and the alluvial 

aquifers, which are hydraulically connected, were similar but were detected less 

frequently in ground water. Agricultural herbicides and their degradates were most 

frequently detected.
Major Findings 17 

Pesticides are present in alluvial aquifers both in urban and 

agricultural areas. Pesticides 

were prevalent in the shallow alluvial aquifers both in agricultural 

and urban areas (fig. 20). Pesticides 

were detected in 84 percent of the 

samples from agricultural areas and 

in 70 percent of the samples from 

urban areas. Atrazine and metolachlor were the most frequently 

detected pesticides in samples from 

agricultural areas; atrazine and 

prometon were the most frequently 

detected pesticides in samples from 

urban areas. None of the concentrations exceeded USEPA MCLs, but 

many pesticides do not have 

MCLs. 

Samples from alluvial aquifers 

in agricultural areas contained an 

average total pesticide concentration (1.3 μg/L) that was more 

than seven times the concentration 

in samples from urban wells 

(0.17 μg/L). Although total pesticide concentrations were higher in 

samples from agricultural areas, 

more compounds were detected in 

samples from urban areas. Seventeen compounds were detected in 

samples from urban areas compared to 12 compounds detected in 

samples from agricultural areas. 

Herbicide degradates were detected 

in 94 percent of samples from agricultural areas and 53 percent of the 

samples from urban areas. Alachlor 

ESA, metolachlor ESA, and metolachlor oxanilic acid (OA) were the 

most frequently detected degradates in samples from both agricultural and urban areas; deethylatrazine and deisoproplyatrazine 

were detected frequently in agricultural areas.

 WHAT IS A PESTICIDE DEGRADATE?

Pesticides released into the environment break down into intermediate 

compounds and, over time, into their constituent molecules (fig. 19). The 

intermediate compounds are pesticide degradates that may be short-lived 

or persist for years. The occurrence of atrazine degradates in ground water 

and surface water is relatively well known, but the occurrence of alachlor, 

acetochlor, and metolachlor degradates in Iowa have only recently been 

investigated (Kalkhoff 

and others, 1998; Kolpin 

and others, 1997). Little 

is known about their 

possible effects on 

human health and 

aquatic life (Heydens 

and others, 2000; 

Stamper and Tuovinen, 

1998). The occurrence 

and distribution of several common degradates 

of atrazine, alachlor, acetochlor, cyanazine, and 

metolachlor were documented in the Eastern 

Iowa Basins to develop a 

better understanding of 

the fate and transport of 

these compounds and 

their possible effect on 

the environment. These 

compounds generally are 

the products of the first 

step in the breakdown of 

the most commonly used 

herbicides. Breakdown 

occurs in the soil but 

also can take place in 

plants and in ground 

water and streams. 

Modification of a side 

carbon chain (atrazine 

degradation) or the 

replacement of the halogen (chlorine) with a sulfonic acid or carboxilic 

acid (acetochlor, alachlor, metolachlor degradation) is commonly the first 

step in the breakdown of these herbicides. This first step represents a small 

molecular change that may affect the toxicity, solubility, and persistence of 

the resulting degradate.

Figure 19. Small molecular changes (shown in red) 

occur during the initial breakdown of atrazine and 

metolachlor.

CH3

N

CH2CH3

CH3

CHCH2OCH3

CCH2Cl

O

CH3

N

CH2CH3

CH3

CHCH2OCH3

CCH2SO3

O

CH3

N

CH2CH3

CHCH2OCH2

CH3

C COOH

O

Metolachlor

Metolachlor ESA Metolachlor OA

-

N N

N HN NH2

Cl

H5C2

Deisopropylatrazine

N N

N NH

CH(CH3)

2

H2N

Cl

Deethylatrazine

N N

HN N NH

Cl

CH(CH3) H 2 5C2

Atrazine
18 Water Quality in the Eastern Iowa Basins

Atrazine

Prometon

Metolachlor

Chlorpyrifos

Bentazon

Tebuthiuron

Acetochlor

2,6-Diethylaniline

Simazine

Alachlor

Butylate

Cyanazine

Bromocil

Malathion

Trifluralin

Picloram

0

80

20

40

60

PERCENTAGE OF DETECTION

Agricultural

Urban

0.001 100 0.01 0.1 1 10

CONCENTRATION,

IN MICROGRAMS PER LITER 

0

100

20

40

60

80

PERCENTAGE OF SAMPLES

WITH CONCENTRATION

EQUAL TO OR GREATER THAN

INDICATED CONCENTRATION

EXPLANATION

Atrazine

Metolachlor

Acetochlor

Pesticides in Streams

The most commonly used herbicides were the most frequently 

detected. Atrazine and metolachlor, the two most commonly 

used herbicides in Iowa for rowcrop agriculture during 1996–98, 

were detected in all stream samples 

(fig. 18). Acetochlor, alachlor, and 

cyanazine were detected in more 

than 70 percent of the samples. 

Most atrazine concentrations 

(76 percent) exceeded 0.1 μg/L 

with almost 60 percent of the samples in the 0.1 to 1.0 μg/L range 

(fig. 21). About 10 percent of the 

samples exceeded the atrazine 

MCL level of 3.0 μg/L. Almost 

half of the samples had metolachlor 

concentrations in the range from 

0.1 to 1.0 μg/L (fig. 21). Other less 

frequently detected pesticides were 

carbofuran, 2,4-D, dicamba, EPTC, 

metribuzin, and trifluralin; these 

were applied in Iowa at a rate of 

only 0.6 to 30 percent of the 

amount applied for atrazine (Sands 

and Holden, 1996).

Acetochlor, a conditionally registered herbicide that is intended to 

replace a number of other commonly used herbicides, was frequently detected but most times (75 

percent) at concentrations 

less than 0.1 μg/L. Acetochlor concentrations did not exceed the 

2.0-μg/L annual mean concentration registration requirement at any 

site but did exceed this level in 

about 3 percent of the individual 

samples. The maximum concentration (10.6 μg/L) measured during 

the study exceeded the level that 

would trigger requirements for 

biweekly sampling for watersupply systems (U.S. Environmental Protection Agency, 1994). 

Few nonagricultural herbicide 

compounds were detected. Many 

pesticides are used both in agricultural and urban settings, but only 

three herbicides used almost exclusively in non-row-crop agriculture 

and urban settings (prometon, 

tebuthiuron, and triclopyr) were 

present in streams in eastern Iowa 

and southern Minnesota from 1996 

through 1998 (fig. 18). Prometon, a 

herbicide used for weed control 

around buildings, fence rows, and 

under asphalt, was present at very 

low concentrations (less than 

0.1 μg/L) in more than 80 percent 

of the samples. Prometon is 

extremely persistent (half-life of 

hundreds to thousands of days), 

which may explain the relatively 

high detection rate relative to its 

low use. Tebuthiuron, used on road 

rights-of-way and industrial sites, 

was detected in 7 percent of the 

samples. Triclopyr, used on road 

rights-of-way, industrial sites, and 

turf grass, was detected in 1 percent of the samples.

Insecticides were detected 

mainly during the summer. A 

number of insecticides that have 

been identified as posing a high 

risk to aquatic invertebrates were 

detected in streams from May 

through September, the months 

when most application normally 

occurs (fig. 22). Carbofuran was 

the most frequently detected insecticide (16 percent of all samples). 

Although detected in less than 

20 percent of all samples, carbofuFigure 20. Pesticides were frequently 

detected in the alluvial aquifers in both 

agricultural and urban areas. Although 

the total concentrations of pesticides 

were higher in agricultural areas than in 

urban areas, more compounds were 

detected in urban than in agricultural 

areas.

Figure 21. Atrazine and metolachlor were present in more than 50 percent of the 

samples from rivers and streams at concentrations between 0.1 and 1.0 μg/L. In 

contrast, acetochlor was present in 76 percent of the samples at concentrations 

less than 0.1 μg/L.
Major Findings 19 

Jan

Feb

Mar

Apr

May

June

July

Aug

Sept

Oct

Nov

Dec

0

80

20

40

60

DETECTION RATE, IN PERCENT

Carbofuran

Chlorpyrifos

Fonofos

Diazinon

EXPLANATION

0

5

1

2

3

4

MEDIAN CONCENTRATION,

IN MICROGRAMS PER LITER 

Metolachlor Metolachlor 

ethanesulfonic

acid (ESA)

0

5

1

2

3

4

EXPLANATION

Atrazine Deethylatrazine

Jan

Feb

Mar

Apr

May

June

July

Aug

Sept

Oct

Nov

Dec

ran was detected in 68 percent of 

the samples collected in June. 

When present, carbofuran concentrations generally were less than 

0.80 μg/L. Chlorpyrifos was 

detected in about 7 percent of the 

samples. As with the other insecticides, chlorpyrifos was detected 

most frequently in June (about 30 

percent of the samples). The highest concentration was 0.06 μg/L. 

Malathion was detected in only 

three samples in spring and early 

summer at concentrations that 

ranged from 0.023 to 0.078 μg/L. 

Insecticides were detected more 

frequently in streams than in shallow ground water in the alluvial 

aquifers. Lower use relative to the 

herbicides, short half-life, and 

application during periods of 

reduced runoff may account for the 

overall low detection rate and low 

concentrations of insecticides in 

rivers and streams.

Pesticide degradates constitute the majority of the pesticide 

compounds in streams. The pesticide degradate compounds were 

some of the most frequently 

detected pesticide compounds in 

streams (fig. 18) and on average 

constituted the majority of the pesticide mass in water samples. Acetochlor ESA, alachlor ESA, 

metolachlor ESA, and metolachlor 

OA were detected in more than 

75 percent of the samples. The degradates were detected much more 

frequently than their parent compounds with the exception of atrazine and two of its degradates—

deethylatrazine and deisopropylatrazine (fig. 18).

On average, approximately 83 

percent of the total pesticide mass 

(parent compounds and degradates) 

can be accounted for by 10 common degradates of acetochlor, 

alachlor, atrazine, cyanazine, and 

metolachlor. Concentrations of 

acetochlor ESA, alachlor ESA, and 

metolachlor ESA commonly were 

more than 10 times higher than 

their parent compounds. Although 

herbicide degradates frequently 

occur in substantial concentrations 

in streams, only limited research 

has been conducted on the acute 

and chronic human and environmental effects of these compounds 

(Heydens and others, 2000).

The occurrence of degradates 

and the ratio of degradate to parent 

compound were substantially 

different for the triazine (atrazine 

and cyanazine) than the chloroacetanilide (acetochlor, alachlor, and 

metolachlor) compounds. Concentrations of the triazine degradates 

tended to follow the pattern of the 

parent compounds—highest concentrations during the early summer followed by decreasing 

concentrations during the late summer and fall (fig. 23). However, 

concentrations of the triazine 

degradates were lower than their 

parent compounds except in the fall 

and winter when they were slightly 

higher. In contrast, the ESA and 

OA degradates of alachlor, acetochlor, and metolachlor were 

present in higher concentrations 

than their parent compounds 

throughout the year.

Occurrence of pesticides are 

related to landform type. The triazine herbicides—atrazine and 

cyanazine—and their degradates 

were present in significantly higher 

concentrations in streams draining 

soils dominated by windblown 

Figure 22. Insecticides were prevalent in streams only during the late spring and 

summer. Carbofuran and chlorpyrifos were the most frequently detected 

insecticides.

Figure 23. Pesticides and their 

degradates are readily available for 

transport to streams and rivers in late 

spring and early summer after 

application. A common metolachlor 

degradate persists at higher 

concentrations than a common atrazine 

degradate throughout the year. 
20 Water Quality in the Eastern Iowa Basins

0

30

10

20

AVERAGE MONTHLY

PESTICIDE LOAD, IN TONS

Degradates

Parent

pesticides

Jan

Feb

Mar

Apr

May

June

July

Aug

Sept

Oct

Nov

Dec

loess (Southern Iowa Drift Plains) 

than in streams draining till soils 

(Des Moines Lobe or the Iowan 

Surface). Because of differences in 

soil properties, triazine pesticideuse rates are apparently less in 

areas dominated by till soils such 

as the Des Moines Lobe and Iowan 

Surface landforms (Stoltenberg and 

Pope, 1990). The high pH of the till 

soils (increased calcium carbonate 

content) results in more triazine 

herbicides available for plants and 

greater persistence. Less triazine 

herbicides have been applied to till 

soils (particularly in the Des 

Moines Lobe) because the effects 

of triazine herbicides can “carry 

over” to soybeans planted after 

corn. Results from a regional lowflow synoptic study (Sorenson and 

others, 1999) indicate that the percentage of blue-green algae in 

stream periphyton communities 

increases with total (parent compounds plus degradates) triazine 

herbicide concentrations (Porter 

and others, 2001).

Runoff from rains soon after 

application washes large quantities of pesticides into streams.

Concentrations of pesticides and 

their degradates were highest in the 

late spring and early summer when 

intense rains occurred soon after 

application (fig. 23). Pesticides and 

their degradates are transported 

from the Eastern Iowa Basins in 

largest quantities during the late 

spring and early summer. Pesticide 

degradates make up the largest part 

of the pesticide load transported to 

the Mississippi River. Pesticide 

data from the Iowa River at 

Wapello, Iowa, illustrate that the 

monthly degradate load was higher 

than the loads of the parent 

compounds throughout the year 

(fig. 25) but were particularly dominant during the spring and early 

summer and late fall and winter 

periods. Typically, the loads for all 

compounds were largest during the 

spring and early summer (March 

through June) when significant 

runoff events transported pesticide 

compounds to streams. In the fall 

Multiple Pesticide Compounds Occur More Frequently in 

Streams Than in Ground Water

The use of a 

wide variety of 

pesticides in 

the Eastern 

Iowa Basins is 

reflected by the 

presence of 

multiple compounds in 

streams and 

ground water. 

Two or more 

compounds 

were detected 

in every sample, and five or 

more compounds were 

detected in 

more than 80 percent of the stream samples (fig. 24). As many as 16 pesticide compounds were detected in a single stream sample. In contrast, 2 or 

more compounds were detected in only 17 percent and 5 or more pesticides 

in less than 2 percent of the ground-water samples.

 Multiple degradates were much more frequently detected than multiple 

parent compounds in ground water. Many pesticide compounds attach to 

soil particles and are not readily leached to the ground water. However, the 

pesticide degradates sampled are generally more water soluble and once 

formed in the soil may move readily to the shallow ground water. Also, 

several degradates may form from each pesticide, accounting for additional 

degradate compounds.

The importance of multiple pesticide compounds for human and environmental health is currently unclear. Most toxicity assessments are based 

on results from a single contaminant.

Figure 24. More than one pesticide compound was always 

present and more than five compounds were detected in 

about 80 percent of the stream samples. Multiple 

degradates were more common than multiple parent 

compounds in ground water.

0 11 1 2 3 4 5 6 7 8 9 10

NUMBER OF DETECTED COMPOUNDS

0

100

20

40

60

80

FREQUENCY OF SAMPLES EXCEEDING 

INDICATED NUMBER OF DETECTED

COMPOUNDS, IN PERCENT

Parent pesticide

Degradate

Streams

Ground water

Figure 25. The most frequently used 

pesticides begin breaking down before 

being transported from the Study Unit to 

the Mississippi River. More than 80 

percent of the yearly pesticide load in 

the Iowa River at Wapello is pesticide 

degradates. Of the yearly load, about 57 

percent was transported from the Study 

Unit during May, June, and July. 
Major Findings 21 

MTBE DETECTION RATES ARE SIMILAR TO THE

AVERAGE DETECTION RATE IN THE NATION

Methyl tert-butyl ether (MTBE), a compound added to gasoline to 

enhance the octane content or to ensure cleaner burning with reduced carbon monoxide emissions, was detected in the alluvial aquifers underlying 

towns and cities in the Eastern Iowa Basins at a rate similar to the average 

detection rate in the United States (Squillace and others, 1999). However, 

detection rates (fig. 26) were not as great as in shallow, vulnerable aquifers in Denver, Colorado (Bruce and McMahon, 1996), and other areas 

where MTBE has been used extensively to reduce carbon monoxide emissions. MTBE also has been detected in areas where MTBE is used only to 

enhance the octane content (Zorgorski and others, 1997). Although ethanol is commonly added to gasoline in Iowa, MTBE has also been added to 

increase the octane level. Legislatively mandated sampling of soil and 

ground water from leaking underground storage tank (LUST) sites in 

Iowa verified that MTBE is prevalent in gasoline-contaminated areas 

(Iowa Department of Natural Resources, 2000b). MTBE was present in 

ground water at about 59 percent of the 523 LUST sites in 248 Iowa 

towns and cities.

The effects of MTBE on human health are not fully understood, but 

MTBE has been linked to headaches, nausea, dizziness, and breathing difficulties (Melnick and others, 1997). Experimental studies indicate that 

MTBE is carcinogenic in rats and mice (Melnick and others, 1997).

Basins

Iowa

Eastern United

States

1985-95

Denver,

Colorado

sites

LUST

Iowa

0

100

20

40

60

80

DETECTION RATE, IN PERCENT

Figure 26. The presence of the 

gasoline additive MTBE in alluvial 

aquifers in urban areas reflects the 

common occurrence of MTBE at 

gasoline-contaminated sites in Iowa.

and winter months, however, the 

pesticide degradates accounted for 

nearly all of the pesticide loads 

(fig. 25). Parent compounds 

accounted for only 3 percent 

(December) to 27 percent (May) of 

the total pesticide compounds 

transported from the Iowa River. 

Much of the water and dissolved 

pesticide compounds originated 

from ground-water inflow during 

the relatively dry late fall and winter months. The presence of relatively high concentrations of 

alachlor and metolachlor degradates in the fall and winter, several 

months after pesticide application 

when parent compounds have all 

but disappeared, indicates that 

these compounds are relatively 

stable. 

Other Organic Compounds

 The gasoline additive MTBE 

was the most commonly detected 

volatile organic compound in 

ground water. Shallow alluvial 

ground water in urban areas is susceptible to contamination from 

organic compounds resulting from 

activities such as transportation, 

manufacturing, and service industries. Volatile organic compounds 

(VOCs) were detected in 40 percent of alluvial samples from urban 

areas and 10 percent of the samples 

from agricultural areas. Methyl 

tert-butyl ether was the most frequently detected VOC and was 

present in 23 percent of samples 

from urban areas (fig. 26). 

Although most detected concentrations were low, MTBE concentrations from two urban monitoring 

wells were at levels of potential 

concern for human health (USEPA 

drinking-water advisory of 20 to 

40 μg/L). MTBE was commonly 

found with other gasoline compounds (benzene, ethylbenzene, 

toluene, and xylene), indicating 

that contamination likely originated from leaking fuel storage 

tanks and possibly from surface 

spills. MTBE was not detected in 

agricultural areas. Solvents were 

detected in less than 15 percent of 

the samples, and other VOCs were 

detected in less than 10 percent of 

the samples. 

Water from deeper in the alluvial 

aquifers and in the deeper SilurianDevonian and Upper Carbonate 
22 Water Quality in the Eastern Iowa Basins

BIOLOGICAL COMMUNITIES IN STREAMS CONSIST

OF ORGANISMS THAT ARE MODERATELY TO HIGHLY

TOLERANT OF ENVIRONMENTAL DEGRADATION

Figure 27. Status of biological communities—comparison of Eastern Iowa 

Basins sites to selected national network sites.

Biological communities (algae, fish, and invertebrates) in streams in the Eastern Iowa Basins generally rank in the 

middle 50th to highest 25th percentile most tolerant of environmental degradation nationally (fig. 27). Commonly, 

biological communities in streams change in response to environmental changes (degradation). Degradation can result 

from a variety of factors that modify habitat or other environmental features such as land use, water chemistry, streamflow, and others. The biological community may change from few individuals of 

many species to a community of many 

individuals of a few tolerant species. 

 Algal status focuses on the changes in 

the percentage of certain algae in 

response to increasing siltation and seems 

to correlate relatively well with higher 

nutrient concentrations in many regions. 

Invertebrate status is the average of 

11 invertebrate (primarily insects, 

worms, crayfish, and clams) metrics that 

summarize changes in richness, tolerance, trophic conditions, and dominance 

associated with water-quality degradation. Fish status is the sum of scores of 

four fish metrics (percent tolerant, 

omnivorous, non-native individuals, and 

percent individuals with external anomalies) that change (increase) in association 

with water-quality degradation. For all 

indicators, higher values indicate a more 

degraded stream site.

Community differences occur among 

streams in the Eastern Iowa Basins, but 

these differences are small in relation to 

differences across the Nation. From a 

national perspective, algal status was 

moderate to high in all Study Unit 

streams and rivers and corresponds with 

high concentrations of dissolved and total 

nutrients. With one exception (Wapsipinicon River near DeWitt), invertebrate status tended to rank in the middle to lowest 

25th percentile, indicating a moderate 

degree of degradation in relation to the 

rest of the Nation. Because of nutrient 

enrichment and subsequent abundance of 

algae and organic material, an abundant 

food supply is present to support a diverse 

invertebrate community. From a local and 

regional perspective, invertebrate status indicated greater degradation in large rivers than small streams. However, 

lower status in the Skunk River may be associated more with better habitat at that site than any quantitative differences 

in water chemistry among other large rivers. Fish communities tended to be ranked highest (most degraded) to moderate when compared nationally. Based on the presence of more species sensitive to environmental stress, the fish population at Wapsipinicon River near DeWitt was minimally affected by environmental degradation in relation to other 

sites nationally.











	



 

 
 

  











 !





 "

"	# 

$ 
 


$ 



 %!&

#
#

 '


! 
%

$	 (


% )


% 	#

*#
 " 

+



% "  "
%


! 
, 
% "

 -% (
#

'  ., 


% ./

 

 ., 

(
%

*
	 .,  $/

*#
 " 

$*


% "  


. "  .



% "  *


,, "  

0! 1 # /

 12 # /


% 1 # /

- %
,  342   ! -*5  # 	

%
, ! ! 6  / #6 %
6 #/	!6

#6  	! 
Major Findings 23 

Reference site (1)

Des Moines Lobe (3)

Iowan Surface (9)

Iowan Karst (7)

Animal Feeding 0perations (4)

Southern Iowa Drift Plain (6)

20

50

30

40

INDEX OF BIOTIC INTEGRITY 

bedrock aquifers used for rural 

domestic supply rarely contained 

detectable concentrations of VOCs, 

even though gasoline is commonly 

stored and solvents are at times 

used in the vicinity of these wells.

Pesticides banned or restricted 

in the 1970s and 1980s are still 

present in fish tissue. Although no 

longer in use, residue from organochlorine insecticides (chlordane, 

DDT, dieldrin, and heptachlor 

epoxide) is still found in fish-tissue 

samples collected from eastern 

Iowa streams (Roberts, 1997) but 

not at levels of concern for human 

health. Concentrations were relatively higher in agricultural than 

urban streams, and fish from the 

Wapsipinicon River Basin contained lower concentrations of contaminants than fish from the Cedar 

or Iowa River Basins. Although 

aldrin, an organochlorine pesticide, has been banned since the 

1970s, its degradate, dieldrin, was 

present in five stream samples during or immediately following 

spring runoff. Dieldrin was present 

in tissue samples collected from 

carp at 15 of 16 sites in eastern 

Iowa, and concentrations in fish 

seem to be associated with agricultural settings (Roberts, 1997). Concentrations that peaked in sediment 

deposited in Coralville Reservoir 

during the 1993 flood indicate that 

dieldrin is still transported in rivers 

during high flow (Kalkhoff and 

Van Metre, 1997). In contrast to the 

apparent agricultural source of 

dieldrin, the occurrence and concentration of PCBs (polychlorinated biphenyls) in fish tissue 

indicate an urban source for this 

contaminant (Roberts, 1997).

Biological Communities and 

Stream Habitat 

The quality of water entering 

from runoff and ground water 

inflow is an important factor that 

influences the community structure 

of fish, invertebrates, and algae that 

live in the rivers and streams of the 

Eastern Iowa Basins. Stream habitat, the physical conditions in and 

along streams and rivers, also 

influences the occurrence and distribution of aquatic organisms. 

Water-quality degradation and 

habitat alteration resulting from 

agricultural and urban activities 

can adversely affect aquatic communities. 

In general, degradation results in 

the replacement of native species 

with those that are more tolerant of 

nutrient and organic enrichment. 

There also tends to be a reduction 

in numbers of sensitive species, 

increases in abundance and dominance of tolerant species, and 

decreases in the diversity and evenness of biological communities that 

are typically considered an indicator of environmental stress. 

Biological metrics that contain 

measures of the composition, abundance, function, and tolerance of 

species to environmental stress are 

commonly used to evaluate aquatic 

communities in relation to water 

quality and habitat conditions. 

Fish populations are related to 

stream size and water-quality 

conditions. During 1996–98, 

67 fish species representing 

15 families were collected in six 

streams and six rivers in the Eastern Iowa Basins (Sullivan, 2000). 

The species and trophic composition, as well as the abundance and 

condition of fish communities, varied between the smaller streams 

and large river sites in the Eastern 

Iowa Basins. Measures of fishcommunity status, tolerance, structure, and index of biotic integrity 

(IBI) indicated that fish communities also differed among land uses 

and landforms in the basin 

(fig. 28). Habitat and water-quality 

data indicate that differences in 

species composition between rivers 

and streams are probably due to 

more than just stream size. 

Although differences in stream size 

and associated habitat differences 

favor the occurrence of different 

species, relatively higher concentrations of suspended sediment and 

phosphorus in large rivers may 

contribute to habitat degradation 

and eutrophication that may 

explain the relatively lower IBI 

scores at large river sites (Sullivan, 

2000). 

The two highest IBI-rated river 

sites were the Wapsipinicon River 

near DeWitt and the Cedar River at 

Gilbertville, an integrator site for 

Figure 28. Healthy fish populations 

were present in one of the least affected 

(reference) and one of the most affected 

(animal feeding operations) streams in 

the study area. Factors other than water 

quality (stream habitat) also have an 

important effect on fish populations. 

(Site number in parentheses; see site 

map in “Study Unit Design” Section.)
24 Water Quality in the Eastern Iowa Basins

the upper Cedar River watershed. 

River sites with the lowest IBI 

scores include the Skunk River at 

Augusta and three sites in the Iowa 

River Basin: Iowa River at 

Marengo, Old Mans Creek near 

Iowa City, and the most downstream integrator site (Iowa River 

at Wapello).

Agriculture and subsequent 

organic enrichment of the streams 

have likely reduced habitat, cover, 

and water-quality requirements for 

the maintenance of diverse fish 

populations and communities. 

However, the small number of fish 

species in Flood Creek (fig. 27) 

may be reflective of the karst 

hydrology in the basin; extended 

reaches of Flood Creek may be dry 

during low-flow conditions or 

periods of drought, limiting fish 

communities to juvenile fish or 

those with rapid recolonization 

rates.

Macroinvertebrate communities in the Eastern Iowa Basins 

reflect cumulative effects of both 

land use and downstream succession—the natural sequence of communities from headwater streams 

to large rivers (Vannote and others, 

1980). More than 250 benthic 

invertebrate taxa were found in collections from submerged woody 

debris at 12 Basic Fixed Sites (see 

Glossary). Aquatic insects, including mayflies, net-spinning caddisflies, and midges, accounted for 

more than one-half of the organisms collected. The abundance of 

highly tolerant midges (Chironomidae) and worms (Oligochaeta), as 

well as collector-filterers was 

higher in large rivers, whereas the 

abundance of less-tolerant mayflies, stoneflies, and caddisflies 

(EPT taxa; see Glossary) was relatively larger in small tributary 

streams (Brigham and Sadorf, 

2001). However, most invertebrate 

taxa in eastern Iowa streams and 

rivers are considered to be tolerant 

of nutrient and organic enrichment 

(Hilsenhoff, 1987). Stream velocity, rates of stream respiration, minimum dissolved oxygen, woodedriparian zones, and the composition 

and abundance of periphyton were 

the primary factors associated with 

invertebrate community structure 

(M.A. Harris, U.S. Geological Survey, written commun., 2000).

 In general, invertebrate diversity 

was lower in unshaded streams 

with silt, sand, or gravel bottoms 

(for example, Iowa River near 

Rowan and Old Mans Creek) than 

in shaded streams with bedrock or 

large rocks (for example, Flood 

Creek and Wapsipinicon River near 

Tripoli). Despite similarities in 

agricultural land-use intensity in 

the Midwestern Corn Belt, invertebrate communities reveal substantial differences in the quality of 

streams and rivers, corresponding 

to physical (modifications of 

stream channels and riparian 

zones) and hydrologic (rainfallrunoff and ground-water relations) 

differences among basins (M.A. 

Harris, U.S. Geological Survey, 

written commun., 2000).

Algal communities are dominated by nutrient- and sedimenttolerant taxa. More than 330 algal 

species were found in periphyton 

collections from submerged woody 

debris. Algal communities were 

dominated by taxa that are tolerant 

to nutrients and other agricultural 

contaminants such as herbicides 

and sediment. 

Relative differences are seen in 

algal status (an indicator of nutrient 

and sediment enrichment) and biomass among sites from a regional 

and local perspective. For example, 

algal biomass (the amount of 

attached algae) was relatively 

higher in Old Mans Creek, Flood 

Creek, and the Cedar River at Gilbertville than other sites. Within 

the Eastern Iowa Basins, algal status was relatively better in the 

Wapsipinicon River near Tripoli 

(the reference site) and in the Cedar 

River near Gilbertville and Conesville.

During low-flow conditions in 

August 1997, shaded streams that 

drain permeable soils (for example, 

the upper Cedar and Wapsipinicon 

River Basins) were dominated by 

periphyton taxa (diatoms, red 

algae, and green algae) that are a 

good food source for invertebrates 

and fish. In contrast, channelized 

streams and rivers with poor riparian shading, impermeable soils, 

and slow velocity were dominated 

by phytoplankton taxa (notably 

blue-green algae) that are avoided 

as food sources and contribute to 

organic enrichment, higher rates of 

stream respiration, and lower dissolved oxygen concentrations during the night (Sorenson and others, 

1999; Porter, 2000). 
Major Findings 25

RIPARIAN BUFFER ZONES INFLUENCE THE QUALITY OF MIDWESTERN 

STREAMS AND RIVERS

resulting from excessive algal production in some Midwestern streams may 

reduce dissolved oxygen concentrations and be detrimental to other 

requirements of aquatic organisms.

Shading from tree cover in riparian 

buffer zones may influence nutrient 

concentrations indirectly by reducing 

the growth of phytoplankton. In 

streams where phytoplankton were 

abundant (often where buffer zones 

were thin or lacking), dissolved nitrate 

concentrations were significantly 

lower (fig. 30; Porter, 2000). The 

lower nutrient concentrations may 

result from uptake by the abundant 

phytoplankton. Thus, assessments of 

eutrophication would benefit from 

consideration of biological communities and the riparian zone, rather than 

being based solely on nutrient concentrations in the water.

Despite similar land use throughout 

the Corn Belt region of the Midwest, 

streams flowing through cropland 

differ considerably in their ecological 

characteristics, in part because of 

differences in riparian buffer zones 

(see text box). This conclusion is 

based on an investigation of 

70 streams and rivers within three 

NAWQA Study Units in the upper 

Midwest during August 1997 (fig. 29; 

Sorenson and others, 1999; Porter and 

others, 2001). Specifically, increases 

in tree cover in buffer zones were 

associated with aquatic biological 

communities indicative of good 

stream quality, reduced nuisance algal 

growths, and maintenance of sufficient dissolved oxygen concentrations 

to support diverse communities of 

aquatic organisms. For example, the 

number of aquatic insects indicative 

of good stream quality tended to 

increase with increases in percentage 

of tree cover, especially in sites where 

streamflow and dissolved oxygen conditions were favorable. Fish communities, sampled at 24 sites in the UMIS 

Study Unit, also indicated better overall conditions in streams with wooded 

riparian zones than those with more 

open canopy (Stauffer and others, 

2000). 

Streams with less tree cover, and 

thus less shading, contained relatively 

large growths of phytoplankton (algae 

suspended in the water) at levels considered indicative of eutrophication 

(Porter, 2000). Organic enrichment 

Figure 29. The influence of riparian buffer 

zones on the quality of 70 Midwestern streams 

and rivers was evaluated in the Upper Mississippi River (UMIS), Eastern Iowa (EIWA), and 

Lower Illinois River Basins (LIRB).

Digital images derived from USGS topographic maps were used to estimate the 

percentage of trees in a riparian buffer zone (a 100-meter width on each side of the 

stream) for 2- to 3-mile segments upstream from each sampling site, supplemented by 

vegetation surveys at the sampling site (Sorenson and others, 1999).

Resource agencies, including the U.S. 

Department of Agriculture, encourage 

maintenance of strips of trees or grass between cropland and streams as a best management practice. These “riparian buffer 

zones” are thought to intercept runoff of 

sediment and chemicals from fields, promote bank stability, and provide shading 

and habitat for aquatic life (Osborne and 

Kovacic, 1993). Riparian buffer zones 

should be considered along with other important factors that affect chemical and biological indicators of stream quality, such as 

soil drainage properties and stream

hydrology (Porter and others, 2001).

Figure 30. Dissolved nutrient concentrations decreased in eutrophic streams with 

excessive algal productivity. Rates of nutrient uptake by the algae can exceed rates 

at which nutrients are transported by 

streams during low-flow conditions.

15

10

5

0

0 50 100 150 200

Dissolved nitrite + nitrate (mg/L)

Phytoplankton abundance

Chlorophyll-a ( g/L)

UMIS

LIRB

EIWA

Wisconsin

Minnesota

Iowa

Illinois

Mississippi River
26 Water Quality in the Eastern Iowa Basins

STUDY UNIT DESIGN

Alluvial aquifer

Silurian-Devonian and

Upper Cabonate aquifers

EXPLANATION

Well in Silurian-Devonian

or Upper Carbonate aquifers

Well in Iowa River alluvial aquifer

Domestic well in alluvial aquifer

Well in urban land-use setting

Well in agricultural land-use setting

The objective of the Eastern Iowa Basins NAWQA study 

was to assess the water-quality conditions in streams and 

ground water in the Study Unit. The study design is based on 

a nationally consistent structure that incorporates an interdisciplinary approach (Gilliom and others, 1995). Streamwater quality was assessed using three interrelated components: stream chemistry, streambed-sediment chemistry, and 

stream ecology. Ground-water quality of the alluvial aquifers was selected for assessment because these aquifers are 

the major source of water for municipal and domestic supplies and they provide flow to streams. Water quality in the 

Silurian-Devonian and Upper Carbonate aquifers also was 

investigated.

Stream Chemistry

The Basic Fixed Site sampling network was designed to 

characterize the effects of physiographic differences on 

water quality in the primarily agricultural Study Unit. Waterchemistry, bed-sediment, and reservoir-core data were collected. Sites were selected on large rivers and smaller 

streams. Fixed sites on large rivers were located near the 

mouth of the four major rivers to characterize the integrated 

effects of differing land use and environmental setting on 

stream quality. Two additional large river sites were chosen 

to assess the upper part of the Cedar River and the Iowa 

River, before it flows into Coralville Reservoir. Fixed sites 

on streams were selected to characterize each of the physiographic areas. A reference site was selected on a watershed 

that retains a large amount of bottomland wetlands. Another 

site was selected to assess the effects of concentrated animal 

feeding operations on stream quality. A subset of the Basic 

Fixed Site network was intensively sampled (weekly to 

Iowa River

near

Rowan (3)

South Fork

Iowa River

near New

Providence (4)

Skunk River at

Augusta (12)

Iowa River at

Wapello (11)

Cedar River near

Nichols, Iowa

Wapsipinicon River

near DeWitt (2)

Cedar River near

Conesville (10)

Flood Creek

near

Powersville (7)

Iowa River at

Marengo (5)

Old Mans Creek

near Iowa City (6)

Wapsipinicon

River near Tripoli (1)

Cedar River at

Gilbertville, Iowa

Wolf Creek near

Dysart (9)

Des Moines Lobe

Iowan Karst

Iowan Surface

Southern Iowa

Drift Plain

Intensive fixed site

Basic fixed site

Streambed-sediment

and tissue site

Base-flow synoptic

study site

LANDFORM REGIONS

SAMPLING SITES

Minnesota

Iowa

EXPLANATION

biweekly) through the spring and summer of 1997. 

Two synoptic studies were conducted during baseflow conditions (high and low base flow) to improve 

the spatial resolution and to better evaluate the effects 

of soil type and riparian buffers on stream-water quality and biological communities.

Stream Ecology

Ecological data including fish-tissue chemistry and 

fish, macroinvertebrate, and algal community structure were collected to provide better understanding of 

the relations among physical, chemical, and biological 

characteristics of a stream. Data were collected at the 

Basic Fixed Site sampling network plus four additional sites to provide better spatial coverage. 

Ground-Water Chemistry

The ground-water network was designed to characterize water quality in the most heavily used aquifers 

in the Study Unit. A Study Unit survey characterized 

the water quality in the Silurian-Devonian and Upper 

Carbonate bedrock aquifers, the second greatest 

source of municipal and domestic supplies in the 

Study Unit. Another Study Unit survey characterized 

the water quality of the alluvial aquifers using domestic wells. Land-use studies assessed the occurrence 

and distribution of water-quality constituents in 

recently recharged water in the alluvial aquifers. Agricultural and urban land-use effects on quality of shallow ground water was characterized by sampling two 

networks of monitoring wells constructed at randomly 

selected sites.
Study Unit Design 27 

SUMMARY OF DATA COLLECTION IN THE EASTERN IOWA BASINS, 1996–98

Study 

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

Sampling

frequency

and period

Stream chemistry

Basic Fixed 

Sites—large 

rivers

Major ions, organic carbon, suspended sediment, 

nutrients, pesticides, and streamflow were determined to describe concentrations and the amount 

of selected constituents transported from the 

study area

Streams draining basins from about 2,300 to more 

than 12,000 square miles that integrate the 

effects of urban and agricultural land use and 

physiographic regions

6 in 

1996, 

5 in 

1997–

98

Monthly beginning in 

March 1996 

and during 

selected 

flood events

Basic Fixed 

Sites—

streams

Major ions, organic carbon, suspended sediment, 

nutrients, pesticides, and streamflow were determined to evaluate physiographic effects on 

stream-water quality

Streams draining basins from 120 to 418 square 

miles of homogeneous land use and physiography

6 Monthly beginning in 

March 1996 

and during 

selected 

flood events

Intensive Fixed 

Sites

Major ions, organic carbon, suspended sediment, 

nutrients, pesticides, and streamflow were determined to define short-term temporal variability

One large river and two stream Basic Fixed Sites 3 Weekly during 

1997 growing season; 

biweekly for 

remainder of 

the year

Base-flow synoptic studyNutrients, pesticides, organic carbon, and streamflow were determined to refine spatial variability 

during both low and high base-flow conditions

Streams draining basins ranging from 120 to 530 

square miles representing greater than 90 percent agricultural land use

25 August 1997 

and May 

1998

Bed-sediment chemistry

Bed sediment 

and tissue

Trace elements, organochlorine, and semivolatile 

organic compounds in streambed sediment to 

determine presence of these potentially toxic, 

hydrophobic compounds 

Ecological sites—Large river and tributary/headwater fixed sites plus four additional sites for 

better spatial coverage

16 September 

1995

Reservoir core 

study

Trace elements and organochlorine compounds in 

sediment to determine the historical occurrence 

(from filling in 1958 to 1993) 

Site in a deep depositional zone of the Coralville 

Reservoir about 1.5 miles upstream from the 

dam

1 November 

1993

Stream ecology

Bed sediment 

and tissue

Trace elements and organochlorine compounds in 

fish tissue to determine occurrence

Ecological sites 16 September 

1995

Intensive 

assessments

Fish, benthic invertebrates, algae, and aquatic and 

riparian habitat were sampled and described to 

assess community structure and to document 

within stream and annual variation

Ecological sites 12 All fixed sites 

in 1996 and 

intensive 

sites in 

1997–98 

Ecological 

synoptic survey

Benthic invertebrates, algae, and aquatic and riparian habitat were sampled to assess biological 

responses in relation to water quality and hydrologic variability

Streams draining basins ranging from 120 to 530 

square miles representing greater than 90 percent agricultural land use

25 August 1997 

Ground-water chemistry

Bedrock aquifer surveyMajor ions, nutrients, pesticides, pesticide degradates, VOCs, and tritium were determined to 

assess quality in second most-used aquifer in 

Study Unit

Existing domestic wells completed in the

Silurian-Devonian aquifer (32–700 feet deep)

33 June–July 1996

Alluvial aquifer 

survey

The same constituents as in bedrock aquifer survey 

were determined to assess quality in most-used 

aquifer in the Study Unit

Existing domestic wells completed in unconsolidated alluvial deposits 

32 June–July 1998

Land-use 

effects 

study—

agricultural 

and urban

The same constituents as in bedrock aquifer survey 

were determined to assess water-quality differences due to agricultural and urban land use

Newly constructed monitoring wells at sites randomly selected on alluvial deposits and completed at the water table (31 agricultural and 30 

urban wells)

61 June–August 

1997

Ground-water chemistry special study

Changing landuse studyThe same constituents as in bedrock aquifer survey 

were determined to assess changes in waterquality due to conversion of row crops to wetlands and prairie

Existing monitoring wells plus three new monitoring wells completed at various depths in the 

Iowa River alluvial aquifer

28 August 1996 

and 1998
28 Water Quality in the Eastern Iowa Basins

GLOSSARY 

Acre-foot—A volume of water equal to 1 foot in depth 

and covering 1 acre; equivalent to 43,560 cubic feet 

or 325,851 gallons. 

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—A general term for clay, silt, sand, and gravel 

deposited by a river or stream in the bed of the 

stream or on its flood plain.

Ammonia—A compound of nitrogen and hydrogen 

(NH3) that is a common by-product of animal waste. 

Ammonia readily converts to nitrate in soils and 

streams.

Aquatic guidelines—Specific levels of water quality 

which, if reached, may adversely affect aquatic life. 

These are nonenforceable guidelines issued by a 

governmental agency or other institution.

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

rock that will yield usable quantities of water to a 

well.

Base flow—Sustained, low flow in a stream; groundwater discharge is the source of base flow in most 

places. 

Basic Fixed Sites—Sites on streams at which streamflow 

is measured and samples are collected for temperature, salinity, suspended sediment, major ions, 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.

Breakdown product—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 or less persistent compound.

Concentration—The amount or mass of a substance 

present in a given volume or mass of sample. Usually expressed as micrograms per liter (water sample) or micrograms per kilogram (sediment or tissue 

sample).

Constituent—A chemical or biological substance in 

water, sediment, or biota that can be measured by an 

analytical method.

Contamination—Degradation of water quality compared to original or natural conditions due to human 

activity.

Cubic foot per second (ft3

/s, or cfs)—Rate of water discharge representing a volume of 1 cubic foot passing 

a given point during 1 second, equivalent to approximately 7.48 gallons per second or 448.8 gallons per 

minute or 0.02832 cubic meter per second. 

Degradate—See Breakdown product.

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.

Discharge—Rate of fluid flow passing a given point at a 

given moment in time, expressed as volume per unit 

of time.

Drainage basin—The portion of the surface of the Earth 

that contributes water to a stream through overland 

run-off, including tributaries and impoundments.

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. 

Ecoregion—An area of similar climate, landform, soil, 

potential natural vegetation, hydrology, or other ecologically relevant variables.

EPT richness index—An index based on the sum of the 

number of taxa in three insect orders, 

Ephemeroptera (mayflies), Plecoptera (stoneflies), 

and Trichoptera (caddisflies), that are composed primarily of species considered to be relatively intolerant to environmental alterations.

Eutrophication—The process by which water becomes 

enriched with plant nutrients, most commonly phosphorus and nitrogen. 

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. 

Hypoxia—Seasonally depleted dissolved oxygen concentrations (less than 2 milligrams per liter) in a 

water body

Index of Biotic Integrity (IBI)—An aggregated number, 

or index, based on several attributes or metrics of a 

fish community that provides an assessment of biological conditions.

Indicator sites—Stream sampling sites located at outlets 

of drainage basins with relatively homogeneous land 

use and physiographic conditions; most indicatorsite basins have drainage areas ranging from 100 to 

about 400 square miles.
Glossary 29

Integrator or Mixed-use site—Stream sampling site 

located at an outlet of a drainage basin that contains 

multiple environmental settings. Most integrator 

sites are on major streams with relatively large 

drainage areas. 

Intolerant organisms—Organisms that are not adaptable to human alterations to the environment and 

thus decline in numbers where human alterations 

occur. See also Tolerant species. 

Karst—A type of topography that results from dissolution and collapse of carbonate rocks such as limestone and dolomite, and characterized by closed 

depressions or sinkholes, caves, and underground 

drainage.

Leaching—Refers to movement of pesticides or nutrients from land surface to ground water. 

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.

Monitoring well—A well designed for measuring water 

levels and testing ground-water quality.

Mouth—The place where a stream discharges to a larger 

stream, a lake, or the sea. 

Nutrient—Element or compound essential for animal 

and plant growth. Common nutrients in fertilizer 

include nitrogen, phosphorus, and potassium.

Overland flow—The part of surface runoff flowing over 

land surfaces toward stream channels.

Periphyton—Organisms that grow on underwater 

surfaces; periphyton include algae, bacteria, fungi, 

protozoa, and other organisms.

Pesticide—A chemical applied to crops, rights-of-way, 

lawns, or residences to control weeds, insects, fungi, 

nematodes, rodents or other "pests."

Physiography—A description of the surface features of 

the Earth, with an emphasis on the origin of landforms.

Plankton—Floating or weakly swimming organisms at 

the mercy of the waves and currents. Animals of the 

group are called zooplankton and the plants are 

called phytoplankton. 

Radon—A naturally occurring, colorless, odorless, 

radioactive gas formed by the disintegration of the 

element radium; damaging to human lungs when 

inhaled.

Recharge—Water that infiltrates the ground and reaches 

the saturated zone.

Reference site—A NAWQA sampling site selected for 

its relatively undisturbed conditions. 

Riparian zone—Pertaining to or located on the bank of a 

body of water, especially a stream. 

Runoff—Excess rainwater or snowmelt that is transported to streams by overland flow, tile drains, or 

ground water.

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. 

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. 

Tile drain—A buried perforated pipe designed to 

remove excess water from soils.

Tolerant species—Those species that are adaptable to 

(tolerant of) human alterations to the environment 

and often increase in number when human alterations occur. 

Total concentration— Refers to the concentration of a 

constituent regardless of its form (dissolved or 

bound) in a sample.

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.

Tritium—A radioactive form of hydrogen with atoms of 

three times the mass of ordinary hydrogen; can be 

used to determine the age of water.

Unconsolidated deposit—Deposit of loosely bound sediment that typically fills topographically low areas.

Urban site—A site that has greater than 50 percent 

urbanized and less than 25 percent agricultural area.

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. 
30 Water Quality in the Eastern Iowa Basins

REFERENCES 

Akers, K.K.B, Schnoebelen, D.J., Savoca, M.E., Roberts, 

L.R., and Becher, K.D., 1999, Water-quality assessment 

of the Eastern Iowa Basins—Hydrologic and biologic 

data, September 1995 through September 1996: U.S. 

Geological Survey Open-File Report 99–66, 154 p.

Akers, K.K.B, Montgomery, D.L., Christiansen, D.E., 

Savoca, M.E., Schnoebelen, D.J., Becher, K.D., and 

Sadorf, E.M., 2000, Water-quality assessment of the 

Eastern Iowa Basins—Hydrologic and biologic data, 

October 1996 through September 1998: U.S. Geological Survey Open-File Report 00–67, 300 p.,

Alexander, R.B., Smith, R.A., and Schwarz, G.E., 2000, 

Effect of stream channel size on the delivery of nitrogen 

to the Gulf of Mexico: Nature, v. 403, p. 758–761.

Becher, K.D., Schnoebelen, D.J., and Akers, K.K.B., 2000, 

Nutrient concentrations and yields in surface water in 

Eastern Iowa: Journal of the American Water Resources 

Association, v. 36, no. 1, p. 161–173.

Brigham, A.R., and Sadorf, E.M., 2001, Benthic invertebrate 

assemblages and their relation to physical and chemical 

characteristics of streams in the Eastern Iowa Basins, 

1996–1998: U.S. Geological Survey Water-Resources 

Investigations Report 00–4256, p.

Bruce, B.W., and McMahon, P.B., 1996, Shallow groundwater quality beneath a major urban center—Denver, 

Colorado, USA: Journal of Hydrology, v. 186, 

p. 129–151.

Cambardella, C.A., Moorman, T.B., Jaynes, D.B., Hatfield, 

J.L., Parkin, T.B., Simpkins, W.W., and Karlen, D.L., 

1999, Water quality in Walnut Creek watershed—

Nitrate-nitrogen in soils, subsurface drainage water, and 

shallow groundwater: Journal of Environmental Quality, v. 28, p. 25–34.

Gilliom, R.J., Alley, W.M., and Gurtz, M.E., 1995, Design of 

the National Water-Quality Assessment Program—

Occurrence and distribution of water-quality conditions: U.S. Geological Survey Circular 1112, 33 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, Flux and sources of nutrients in 

the Mississippi—Atchafalaya River Basin Topic 3 

Report for the Integrated Assessment on Hypoxia in the 

Gulf of Mexico: National Oceanic and Atmospheric 

Administration Decision Analysis Series No. 17, 130 p.

Heydens, W.F., Wilson, A.G., Kraus, L.J., Hopkins, W.E., 

and Hotz, K.J., 2000, Ethane sulfonate metabolite of 

alachlor—Assessment of oncogenic potential based on 

metabolic and mechanistic considerations: Toxicological Sciences, v. 55, p. 36–43.

Hilsenhoff, W.L., 1987, An improved index of organic 

stream pollution: The Great Lakes Entomologist, v. 20, 

no. 1, p. 31–39.

Hoyer, B.E., and Hallberg, G.R., 1991, Groundwater vulnerability regions of Iowa: Iowa Department of Natural 

Resources, Geological Survey Bureau Special Map 

Series II, 1 sheet.

Iowa Department of Natural Resources, 1999, Animal waste 

control facilities with operating permits in Iowa, digital 

data, accessed August 1999 at URL 

http://www.igsb.uiowa.edu/nrgis/gishome.htm

_____2000a, Final approved Iowa 1998 303(d) list:

 accessed September 2000 at URL 

http://www.state.ia.us/epd/wtresrce/303dnotc.htm

_____2000b, Methyl tertiary-butyl ether (MTBE) 

occurrence in Iowa: Iowa Department of Natural 

Resources Report for the 2000 Session of the 

Seventy-Eighth General Assembly, 29 p. accessed 

June 2000 at URL http://www.state.ia.us/

government/dnr/organiza/epd/ust/gwprof/021500.htm.

Kalkhoff, S.J., Kolpin, D.W., and Thurman, E.M., 1998, 

Degradation of chloroacetanilide herbicides—The 

prevalence of sulfonic and oxanilic acid metabolites in 

Iowa ground and surface waters: Environmental Science and Technology, v. 32, no. 11, p. 1738–1740.

Kalkhoff, S.J., and Van Metre, P.C., 1997, Organochlorine 

compounds in a sediment core from the Coralville Reservoir, Iowa: U.S. Geological Survey Fact Sheet 

129–97, 4 p. 

Kolpin, D.W., Kalkhoff, S.J., Goolsby, D.A., Sneck-Fahrer, 

D.A., and Thurman, E.M., 1997, Occurrence of selected 

herbicides and herbicide degradation products in Iowa’s 

ground water, 1995: Ground Water, v. 35, no. 4, 

p. 679–688.

Melnick, R.L., and others, 1997, Interagency assessment of 

oxygenated fuels, Chap. 4, Potential health effects of 

oxygenated gasoline: Washington, D.C., Office of Science and Technology Policy, p. 4–1—4–38.

Olcott, P.G., 1992, Ground water atlas of the United States—

Segment 9, Iowa, Michigan, Minnesota, Wisconsin: 

U.S. Geological Survey Hydrologic Investigations 

Atlas 730–J, 31 p.

Omernik, J.A., 2000, Draft aggregations of level III ecoregions for the National Nutrient Strategy: 

 accessed September 2000 at URL 

http://www.epa.gov/ost/standards/ecomap.html.

Osborne, L.L., and Kovacic, D.A., 1993, Riparian vegetated 

buffer strips in water-quality restoration and stream 

management: Freshwater Biology, v. 29, p. 243–258.

Porter, S.D., Harris, M.A., and Kalkhoff, S.J., 2001, Influence of natural factors on the quality of midwestern 

streams and rivers: U.S. Geological Survey WaterResources Investigations Report 00–4288.

Porter, S.D., 2000, Upper Midwest river systems—Algal and 

nutrient conditions in streams and rivers in the upper 

Midwest region during seasonal low-flow conditions, in

Nutrient criteria technical guidance manual, rivers and 

streams: Washington, D.C., U.S. Environmental Protection Agency, Office of Water, Office of Science and 

Technology, EPA–822–B–00–002, 

p. A–25—A–42.

Prior, J.C., 1991, Landforms of Iowa: Iowa City, University 

of Iowa Press, p. 30–75.
References 31

Rabalais, N.N., 1996, Nutrient changes in the Mississippi 

River and system responses on the adjacent continental 

shelf: Estuaries, v. 19, p. 386–407.

Roberts, L.R., 1997, Occurrence of selected organochlorine 

compounds in fish tissue from eastern Iowa streams, 

1995: U.S. Geological Survey Fact Sheet 027–97, 4 p.

Sadorf, E.M. Linhart, S.M., and Savoca, M.E., 2000, Water 

quality of alluvial aquifers in eastern Iowa and southern 

Minnesota, 1998: U.S. Geological Survey WaterResources Investigations Report 00–4106, 46 p.

Sands, J.K., and Holden, H.R., 1996, Iowa agricultural statistics: Des Moines, Iowa, U.S. Department of Agriculture and Iowa State University Extension, 97 p.

Savoca, M.E., Tobias, J.L., Sadorf, E.M., and Birkenholtz, 

T.L., 1997, Herbicides and nitrates in the Iowa River 

alluvial aquifer prior to changing land use, Iowa 

County, Iowa, 1996: U.S. Geological Survey Fact Sheet 

085–97, 4 p. 

Savoca, M.E., Sadorf, E.M., Akers, K.K., 1999, Groundwater quality in the eastern part of the Silurian-Devonian and Upper Carbonate aquifers in the Eastern Iowa 

Basins, Iowa and Minnesota, 1996: U.S. Geological 

Survey Water-Resources Investigations Report 98–

4224, 31 p.

Savoca, M.E., Sadorf, E.M., Linhart, S.M., and Akers, 

K.K.B., 2000, Effects of land use and hydrogeology on 

the water quality of alluvial aquifers in eastern Iowa 

and southern Minnesota, 1997: U.S. Geological Survey 

Water-Resources Investigations Report 99–4246, 38 p.

Schnoebelen, D.J., Becher, K.D., Bobier, M.W., and Wilton, 

T., 1999, Selected nutrients and pesticides in streams 

of the Eastern Iowa Basins, 1970–95: U.S. Geological 

Survey Water-Resources Investigations Report 

99–4028, 65 p.

Schwarz, G.E., and Alexander, R.B., 1995, State soil geographic (STATSGO) data base for the conterminous 

United States: U.S. Geological Survey Open-File 

Report 95–489. 

Soenksen, P.J., 1996, Transport of agricultural chemicals in 

surface flow, tileflow, and streamflow of the Walnut 

Creek watershed near Ames, Iowa, April 1991–

September 1993: U.S. Geological Survey WaterResources Investigations Report 96–4017, 41 p.

Sorenson, S.K., Porter, S.D., Akers, K.K.B., Harris, M.A., 

Kalkhoff, S.J., Lee, K.E., Roberts, L.R., and Terrio, P.J., 

1999, Water quality and habitat conditions in upper 

Midwest streams relative to riparian vegetation and soil 

characteristics, August 1997—Study design, methods, 

and data: U.S. Geological Survey Open-File Report 

99–202, 53 p.

Squillace, P.J., Moran, M.J., Lapham, W.W., Price, C.V., 

Clawges, R.M., and Zogorski, J.S., 1999, Volatile 

organic compounds in untreated ambient groundwater 

of the United States, 1985–1995: Environmental Science and Technology, v. 33, no. 23, p. 4176–4187.

Stamper, D.M., and Tuovinen, O.H., 1998, Biodegradation 

of the acetanilide herbicides alachlor, metolachlor, and 

propachlor: Critical Reviews in microbiology, v. 24, 

no. 1, p. 1–22.

Stauffer, J.C., Goldstein, R.M., and Newman, R.M., 2000, 

Relationship of wooded riparian zones and runoff 

potential to fish community composition in agricultural 

streams: Canadian Journal of Fisheries and Aquatic Sciences, v. 57, p. 307–316.

Stoltenberg, D., and Pope, R., 1990, Atrazine management 

rules for Iowa: Iowa State University Extension Pamphlet Pm–1390, 2 p.

Sullivan, D.J., 2000, Fish communities and their relation to 

environmental factors in the Eastern Iowa Basins in 

Iowa and Minnesota, 1995–96: U.S. Geological Survey 

Water-Resources Investigations Report 00–4195, 20 p.

U.S. Department of Agriculture, 1999, Agricultural chemical 

usage, 1998 field crops summary: National Agricultural 

Statistics Service and Economic Research Service 

accessed August 1999 at URL http://usda.mannlib.

cornell.edu/reports/nassr/other/pcu-bb

U.S. Environmental Protection Agency, 1986, Quality criteria for water 1986: Washington, D.C., report 440/5–86–

001, 453 p.

_____1994, Acetochlor registration agreement and addendums, accessed August, 2000 at URL 

http://www.epa.gov/oppefed1/aceto/regagree.htm 

_____1996, Drinking water regulations and health advisories: Washington D.C., Report 822–R–96–001, 16 p.

_____2000, Chlorpyrifos revised risk assessment and agreement with registrants: U.S. Environmental Protection 

Agency Factsheet, Prevention, pesticides and toxic substances (7506C), 4 p., accessed September 2000 at URL 

http://www.epa.gov/pesticides/

announcement6800.htm

Vannote, R.L., Minshall.G.W., Cummins, K.W., Sedell, J.R., 

and Cushing, C.E., 1980, The river continuum concept: 

Canadian Journal of Fisheries and Aquatic Sciences, 

v. 37, p. 130–137.

Zogorski and others, 1997, Interagency assessment of oxygenated fuels, chap. 2, Fuel oxygenates and water quality: Washington D.C., Office of Science and 

Technology Policy, p. 2–1—2–80.
32 Water Quality in the Eastern Iowa Basins

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

Other herbicides detected

Acifluorfen (Blazer, Tackle 2S) **

Bromacil (Hyvar X, Urox B, Bromax) 

Bromoxynil (Buctril, Brominal) * 

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

DCPA (Dacthal, chlorthal-dimethyl) * **

Dicamba (Banvel, Dianat, Scotts Proturf) 

CHEMICALS IN WATER

Concentrations and detection frequencies, Eastern Iowa Basins, 

1996–98—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 Eastern Iowa 

Basins. 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 Eastern Iowa Basins 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, acetochlor concentrations in Eastern 

Iowa Basins agricultural streams were similar to the 

national distribution, but the detection frequency was much 

higher (79 percent compared to 33 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

Acetochlor (Harness Plus, Surpass) * **

79 33 192 -- 9 0 83 38 151

6 <1 31 0 <1 30 0 <1 65

Alachlor (Lasso, Bronco, Lariat, Bullet) **

74 44 | 192 -- 20 | 0 72 45 | 151

3 3 | 31 3 <1 | 30 0 1 | 65

Atrazine (AAtrex, Atrex, Atred, Gesaprim) 100 88 | | 192 -- 86 | | 0 100 87 | | 151

77 40 | 31 50 30 | 30 28 18 | 65

Bentazon (Basagran, Bentazone) ** 60 17 | 63 -- 1 | 0 55 12 | 31

7 4 | 29 13 3 | 30 9 2 | 32

Cyanazine (Bladex, Fortrol) 

69 44 | | 192 -- 14 | | 0 89 54 | | 151

0 1 | 31 3 1 | 29 0 <1 | 65

2,4-D (Aqua-Kleen, Lawn-Keep, Weed-B-Gone) 

27 15 | | 63 -- 18 | | 0 16 11 | | 31

0 <1 | 31 0 1 | 30 0 <1 | 31

Deethylatrazine (Atrazine breakdown product) * **

100 75 192 -- 62 0 99 75 151

81 39 31 43 28 30 31 19 65

Metolachlor (Dual, Pennant) 100 81 | | 192 -- 64 | | 0 100 83 | | 151

29 18 | 31 23 9 | 30 15 5 | 65

Prometon (Pramitol, Princep) **

76 44 | 192 -- 86 | 0 91 60 | 151

3 12 | 31 43 21 | 30 9 5 | 65

APPENDIX—WATER-QUALITY DATA FROM THE EASTERN IOWA 

BASINS IN A NATIONAL CONTEXT

For a complete view of Eastern Iowa Basins 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 33 

CONCENTRATION, IN MICROGRAMS PER LITER

 0.0001 0.001 0.01 0.1 1 10 100 1,000 

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

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

Diuron (Crisuron, Karmex, Diurex) **

EPTC (Eptam, Farmarox, Alirox) * **

Metribuzin (Lexone, Sencor) 

Molinate (Ordram) * **

Napropamide (Devrinol) * **

Pendimethalin (Pre-M, Prowl, Stomp) * **

Picloram (Grazon, Tordon) 

Pronamide (Kerb, Propyzamid) **

Propachlor (Ramrod, Satecid) **

Simazine (Princep, Caliber 90) 

Tebuthiuron (Spike, Tebusan) 

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

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

Herbicides not detected

Benfluralin (Balan, Benefin, Bonalan) * **

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

Clopyralid (Stinger, Lontrel, Transline) * **

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

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

Dinoseb (Dinosebe) 

Ethalfluralin (Sonalan, Curbit) * **

Fenuron (Fenulon, Fenidim) * **

Fluometuron (Flo-Met, Cotoran) **

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

MCPA (Rhomene, Rhonox, Chiptox) 

MCPB (Thistrol) * **

Neburon (Neburea, Neburyl, Noruben) * **

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

Oryzalin (Surflan, Dirimal) * **

Pebulate (Tillam, PEBC) * **

Propanil (Stam, Stampede, Wham) * **

Propham (Tuberite) **

2,4,5-T **

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

Terbacil (Sinbar) **

Thiobencarb (Bolero, Saturn, Benthiocarb) * **

Triallate (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

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 

Chlorpyrifos (Brodan, Dursban, Lorsban) 

7 18 | | 192 -- 37 | | 0 6 20 | | 151

16 1 | 31 10 1 | 30 0 <1 | 65

p,p'-DDE 1 8 | | 192 -- 2 | | 0 1 4 | | 151

0 4 | 31 0 2 | 30 0 2 | 65

gamma-HCH (Lindane, gamma-BHC) 1 1 | | 192 -- 1 | | 0 1 4 | | 151

0 <1 | 31

0 <1 | 65

Other insecticides detected 

Carbaryl (Carbamine, Denapon, Sevin) 

Carbofuran (Furadan, Curaterr, Yaltox) 

Diazinon (Basudin, Diazatol, Neocidol, Knox Out) 

Dieldrin (Panoram D-31, Octalox, Compound 497) 

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

3-Hydroxycarbofuran (Carbofuran breakdown product) * **

Malathion (Malathion) 

Insecticides not detected

Aldicarb (Temik, Ambush, Pounce) 

Aldicarb sulfone (Standak, aldoxycarb) 

Aldicarb sulfoxide (Aldicarb breakdown product) 

Azinphos-methyl (Guthion, Gusathion M) * 

Disulfoton (Disyston, Di-Syston) **

Ethoprop (Mocap, Ethoprophos) * **

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

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

Methomyl (Lanox, Lannate, Acinate) **

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

Oxamyl (Vydate L, Pratt) **

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

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

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

Propargite (Comite, Omite, Ornamite) * **

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

Terbufos (Contraven, Counter, Pilarfox) **

Benzene 

6 10 | 31 30 12 | 30 3 5 | 65

Carbon disulfide * 

55 30 31 60 42 30 51 24 65

Chloroethene (Vinyl chloride) 

7 1 | 30 0 <1 | 65

1,2-Dichloroethane (Ethylene dichloride) 

0 1 | 31 10 1 | 30 0 <1 | 65

Dichloromethane (Methylene chloride) 

3 1 | 31 0 3 | 30 8 4 | 65

Methyl tert-butyl ether (MTBE) 

0 4 | 31 27 16 | 30 0 6 | 65

Methylbenzene (Toluene) 

77 36 | 31 87 30 | 30 62 11 | 65
34 Water Quality in the Eastern Iowa Basins

CONCENTRATION, IN MILLIGRAMS PER LITER

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

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

Dissolved solids in water

Study-unit frequency of detection, in percent

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

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 

Tetrachloroethene (Perchloroethene) 

58 18 | 31 80 29 | 30 45 16 | 65

Trichloromethane (Chloroform) 

26 35 | 31 50 51 | 30 9 30 | 65

Other VOCs detected

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

Bromodichloromethane (Dichlorobromomethane) 

Bromomethane (Methyl bromide) 

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

n-Butylbenzene (1-Phenylbutane) * 

sec-Butylbenzene * 

tert-Butylbenzene * 

Chlorobenzene (Monochlorobenzene) 

Chlorodibromomethane (Dibromochloromethane) 

Chloroethane (Ethyl chloride) * 

Chloromethane (Methyl chloride) 

1,3-Dichlorobenzene (m-Dichlorobenzene) 

1,4-Dichlorobenzene (p-Dichlorobenzene) 

Dichlorodifluoromethane (CFC 12, Freon 12) 

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) 

1,2-Dichloropropane (Propylene dichloride) 

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) * 

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

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

Ethylbenzene (Phenylethane) 

Iodomethane (Methyl iodide) * 

Isopropylbenzene (Cumene) * 

p-Isopropyltoluene (p-Cymene) * 

Naphthalene 

2-Propanone (Acetone) * 

n-Propylbenzene (Isocumene) * 

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

Tribromomethane (Bromoform) 

1,2,3-Trichlorobenzene * 

1,1,1-Trichloroethane (Methylchloroform) 

Trichloroethene (TCE) 

1,2,3-Trichloropropane (Allyl trichloride) 

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) * 

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

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

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

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) 

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 * 

Ethenylbenzene (Styrene) 

Ethyl methacrylate * 

Hexachlorobutadiene 

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

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

Methyl acrylonitrile * 

Methyl-2-methacrylate (Methyl methacrylate) * 

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

Methyl-2-propenoate (Methyl acrylate) * 

2-Propenenitrile (Acrylonitrile) 

1,1,2,2-Tetrachloroethane * 

1,1,1,2-Tetrachloroethane 

Tetrachloromethane (Carbon tetrachloride) 

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

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

1,2,4-Trichlorobenzene 

1,1,2-Trichloroethane (Vinyl trichloride) 

Trichlorofluoromethane (CFC 11, Freon 11) 

Ammonia, as N * **

67 84 253 -- 86 0 61 75 191

35 78 31 70 71 30 95 70 65

Dissolved ammonia plus organic nitrogen, as N * ** 91 78 253 -- 74 0 97 62 191

16 28 31 27 30 30 75 24 65

Dissolved nitrite plus nitrate, as N ** 99 95 | 253 -- 97 | 0 98 91 | 191

94 81 | 31 77 74 | 30 48 71 | 65

Orthophosphate, as P * **

94 79 253 -- 72 0 86 74 191

94 59 31 87 52 30 83 61 65

Total phosphorus, as P * ** 100 92 | 253 -- 90 | 0 100 88 | 191

Dissolved solids * ** 100 100 248 -- 100 0 100 100 191

100 100 31 100 100 30 100 100 65
Water-Quality Data in a National Context 35 

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, Eastern Iowa Basins, 

1996–98—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 

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

Study-unit frequency of detection, in percent

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

CONCENTRATION, IN PICOCURIES PER LITER

 0.01 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

Trace elements in ground water

Radon-222 

100 99 | 31 100 100 | 30 100 97 | 64

Total Chlordane (sum of 5 chlordanes) 64 38 | 11 -- 75 | 1 100 56 | 11

0 9 | 10 -- 57 | 1 0 11 | 10

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

55 49 11 -- 69 1 73 50 11

30 27 | 10 -- 50 | 1 10 20 | 10

p,p'-DDE * **

100 90 11 -- 94 1 100 92 11

30 48 10 -- 62 1 10 39 10

o,p'+p,p'-DDE (sum of o,p'-DDE and p,p'-DDE) * 100 90 11 -- 94 1 100 92 11

30 48 | 10 -- 62 | 1 10 39 | 10

Total DDT (sum of 6 DDTs) **

100 90 | 11 -- 94 | 1 100 93 | 11

30 49 10 -- 66 1 10 41 10

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

18 31 11 -- 53 1 9 29 11

20 19 | 10 -- 38 | 1 0 11 | 10

Dieldrin (Panoram D-31, Octalox) * 

82 53 11 -- 42 1 100 38 11

20 13 | 10 -- 30 | 1 0 9 | 10

Dieldrin+aldrin (sum of dieldrin and aldrin) **

82 52 | 11 -- 42 | 1 100 38 | 11

20 13 10 -- 29 1 0 9 10

Heptachlor epoxide (Heptachlor breakdown product) * 45 8 11 -- 9 1 73 14 11

0 1 | 10 -- 3 | 1 0 <1 | 10

Heptachlor+heptachlor epoxide ** 45 9 | 11 -- 9 | 1 73 14 | 11

0 1 10 -- 2 1 0 <1 10
36 Water Quality in the Eastern Iowa Basins

Other SVOCs detected

Acenaphthene 

Acenaphthylene 

Acridine **

Anthracene 

Benz[a]anthracene 

Benzo[a]pyrene 

Benzo[b]fluoranthene **

Benzo[ghi]perylene **

Benzo[k]fluoranthene **

Butylbenzylphthalate **

Chrysene 

p-Cresol **

Di-n-butylphthalate **

Di-n-octylphthalate **

Dibenz[a,h]anthracene 

Diethylphthalate **

1,2-Dimethylnaphthalene **

1,6-Dimethylnaphthalene **

Dimethylphthalate **

2-Ethylnaphthalene **

9H-Fluorene (Fluorene) 

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

Isoquinoline **

1-Methyl-9H-fluorene **

2-Methylanthracene **

4,5-Methylenephenanthrene **

1-Methylphenanthrene **

1-Methylpyrene **

Naphthalene 

Phenanthrene 

Pyrene 

2,3,6-Trimethylnaphthalene **

SVOCs not detected

C8-Alkylphenol **

Azobenzene **

Benzo[c]cinnoline **

2,2-Biquinoline **

4-Bromophenyl-phenylether **

4-Chloro-3-methylphenol **

bis(2-Chloroethoxy)methane **

2-Chloronaphthalene **

2-Chlorophenol **

4-Chlorophenyl-phenylether **

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

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

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

3,5-Dimethylphenol **

2,4-Dinitrotoluene **

Isophorone **

CONCENTRATION, IN MICROGRAMS PER KILOGRAM, DRY WEIGHT Nitrobenzene **

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

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

Study-unit frequency of detection, in percent

National frequency of detection, in percent

Semivolatile organic compounds (SVOCs)

in bed sediment

Study-unit sample size

Study-unit sample size

Other organochlorines detected

DCPA (Dacthal, chlorthal-dimethyl) * **

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

Mirex (Dechlorane) **

Pentachloroanisole (PCA) * **

Organochlorines not detected

Chloroneb (Chloronebe, Demosan) * **

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

Endrin (Endrine) 

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

Hexachlorobenzene (HCB) **

Isodrin (Isodrine, Compound 711) * **

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

o,p'-Methoxychlor * **

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

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

Toxaphene (Camphechlor, Hercules 3956) * **

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

Total PCB 1

36 38 | 11 -- 81 | 1 100 66 | 11

0 2 | 10 -- 21 | 1 0 9 | 10

Anthraquinone **

30 21 10 -- 83 1 10 39 10

9H-Carbazole **

40 19 10 -- 76 1 10 33 10

Dibenzothiophene **

20 12 10 -- 64 1 40 30 10

2,6-Dimethylnaphthalene **

100 65 10 -- 74 1 100 77 10

bis(2-Ethylhexyl)phthalate **

100 91 10 -- 99 1 100 95 10

Fluoranthene 

100 66 | 10 -- 97 | 1 90 78 | 10

Phenol **

100 81 10 -- 82 1 100 80 10
Water-Quality Data in a National Context 37 

Biological indicator value, Eastern Iowa Basins, by land use, 

1996–98

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

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

 0 5 10 15 20

N-Nitrosodi-n-propylamine **

N-Nitrosodiphenylamine **

Pentachloronitrobenzene **

Phenanthridine **

Quinoline **

1,2,4-Trichlorobenzene **

 Algal status indicator

Undeveloped

Agricultural

Urban

Mixed

 Invertebrate status indicator

Undeveloped

Agricultural

Urban

Mixed

 Fish status indicator

Undeveloped

Agricultural

Urban

Mixed

Arsenic * 

70 56 10 -- 38 1 91 76 11

100 99 | 11 -- 98 | 1 100 97 | 10

Cadmium * 

100 77 10 -- 72 1 100 95 11

100 98 | 11 -- 100 | 1 100 98 | 10

Chromium * 40 62 10 -- 72 1 0 54 11

100 100 | 11 -- 99 | 1 100 100 | 10

Copper * 100 100 10 -- 100 1 100 100 11

100 100 | 11 -- 99 | 1 100 100 | 10

Lead * 

10 11 10 -- 41 1 18 41 11

100 100 | 11 -- 100 | 1 100 99 | 10

Mercury * 

70 71 10 -- 59 1 91 80 11

100 82 | 11 -- 97 | 1 100 93 | 10

Nickel * **

20 42 10 -- 44 1 27 50 11

100 100 11 -- 100 1 100 100 10

Selenium * 100 99 10 -- 100 1 100 99 11

100 100 | 11 -- 100 | 1 100 100 | 10

Zinc * 

100 100 10 -- 100 1 100 100 11

100 100 | 11 -- 99 | 1 100 100 | 10
A COORDINATED EFFORT

Coordination with agencies and organizations in the Eastern Iowa Basins was integral to the success of this waterquality assessment. We thank personnel from the following agencies and organizations who served as members of 

our liaison committee and participated in our liaison committee meetings. 

U.S. Department of Agriculture

Natural Resources Conservation Service

Agricultural Research Service

U.S. Environmental Protection Agency, Region VII

U.S. Fish and Wildlife Service

U.S. Geological Survey

Biological Resources Division

Iowa Department of Agriculture and Land Stewardship

Pesticide Bureau

Iowa Department of Natural Resources

Environmental Protection Division

Geological Survey Bureau

Fisheries Bureau

Minnesota Department of Natural Resources

Minnesota Pollution Control Agency

Minnesota Geological Survey

Linn County Iowa REAP

Linn County Iowa Conservation Board

Johnson County Iowa Board of Supervisors

Cedar Rapids Water Department

Iowa City Public Works

Iowa State University

Center for Sustainable Agriculture

Department of Botany

Extension Service

University of Iowa

Hygienics Laboratory

Limnology Section

Environmental Research

Institute of Hydraulic Research

Center for Health Effects on the Environment

University of Northern Iowa

College of Natural Sciences

Wartburg College

Biology Department

Iowa Farm Bureau Federation

Iowa Environmental Council

Iowa Ground Water Association

Izaak Walton League

Sierra Club

Dow AgroSciences

Dupont Agricultural Products

Novartis Crop Protection

Monsanto 

American Cyanamid Company

American Corn Growers Association

Johnson County Farm Bureau

We thank the following individuals for contributing to this effort. 

James Cerveny, Jon Nania, Joel Galloway, Jennifer Tobias, and Matthew Bobier, the primary field personnel, who 

worked in all conditions to obtain a high-quality data set without which this report would not be possible.

Linda Roberts, the Study Unit biologist, who planned and supervised the collection of algae, macroinvertebrate, 

and fish samples.

The many U.S. Geological Survey personnel (too many to list) from the Iowa District and surrounding States that 

assisted in the collection of biological samples and in the construction of equipment shelters.

Scott Yess and Ann Rundstrom of the Fish and Wildlife Service and J. Kent Johnson University of Iowa Hydraulics 

Institute, who assisted in the collection of fish.

Technicians and chemists at the USGS National Water-Quality Laboratory in Denver, Colorado, who provided 

analysis of all water samples. Mike Thurman and Elizabeth Scribner and the staff of the U.S. Geological Survey 

Organic Geochemistry Research laboratory in Lawrence, Kansas, who analyzed all pesticide samples for 

degradates. Researchers and technicians at the USGS Isotope Tracers Laboratory and the USGS National 

Research Program Laboratory, who provided tritium and stable isotope analysis. 

Tom Wilton of the Iowa Department of Natural Resources who provided a wealth of information, data, and advice 

that was invaluable in the completion of the water-chemistry and biological parts of the study.

Reviewers—Michael Burkhart, USDA Soil Tilth Laboratory; Susan Heathcote, Iowa Environmental Council; Jim 

Ellerhoff, Iowa Department of Agriculture and Land Stewardship; Richard Robinson, Iowa Farm Bureau Federation; 

Bernard Hoyer, Iowa Department of Natural Resources; Geological Survey Bureau. The many colleagues in the 

U.S. Geological Survey whose technical suggestions substantially improved this report. The editorial reviewers, 

Lanna Combs and Betty Palcsak. 

Editors and publication preparation: Alene Brogan, Mary Kidd, Robert Olmstead, and Ed Swibas. 
Kalkhoff and others— Water Quality in the Eastern Iowa Basins

U.S. Geological Survey Circular 1210

National Water-Quality Assessment (NAWQA) Program

Eastern Iowa Basins

NAWQA

WISCONSIN MINNESOTA

IOWA

MISSOURI

ILLINOIS

Missis sippi River

Wapsipinicon R

Cedar River

Iow

N

a River

orth South

Skunk R

Ames

Waterloo

Cedar

Rapids

Iowa

City