U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2004–3098

September 2004 Printed on recycled paper

The U.S. Geological Survey’s National 

Water-Quality Assessment (NAWQA) 

Program is assessing the sources, transport, and fate of chemicals applied to 

crops in agricultural basins across the 

Nation (referred to as “study units,” see 

map, p. 3). Chemicals selected for study 

include nutrients (nitrogen and phosphorus) and about 50 commonly used pesticides and their transformation products, 

including triazine and acetanilide herbicides such as atrazine and metolachlor, 

and organophosphorus insecticides such 

as chlorpyrifos and diazinon.

The basins in the studies represent a 

range of agricultural settings—with varying crop types and agricultural practices 

related to tillage, irrigation, artificial 

drainage, and chemical use—as well 

as a range of landscapes with different 

geology, soils, topography, climate, and 

hydrology. Consistent methodology and 

analysis allow comparisons among the 

different basins. This study design leads 

to an improved understanding of the 

many factors that can affect the movement of water and chemicals in different 

agricultural settings (see “Complex factors,” next page).

Information from these studies will 

help with decision-making related to 

chemical use, conservation, and other 

farming practices that are used to reduce 

runoff of agricultural chemicals and 

sediment from fields. This information 

also will benefit the U.S. Environmental 

Protection Agency, the Department of 

Agriculture, local and regional water 

managers, and agricultural chemical manufacturers who are involved in managing 

chemical use and pesticide registration. 

Studies by the U.S. Geological Survey on Sources, Transport, 

and Fate of Agricultural Chemicals

Objectives of the agricultural 

chemicals study

1. Quantify the amount of water and 

selected agricultural chemicals 

entering, leaving, and accumulating 

within the watershed (referred to as 

an annual “mass budget”).

2. Determine rates of transport and 

residence times of water and chemicals in ground water, the soil zone, 

and in streams.

3. Assess transport and transformation 

of selected chemicals in different 

parts of the hydrologic system, 

as affected by natural processes, 

chemical properties, and agricultural 

management practices.

4. Develop tools and quantitative 

methods, such as models, to characterize the transport and fate of 

chemicals within the watershed, and 

extrapolate the findings to similar, 

unmonitored agricultural and environmental settings.

Agricultural chemicals in 

water resources

• About a half million tons of pesticides, 12 million tons of nitrogen, 

and 4 million tons of phosphorus 

fertilizer are applied annually to 

crops in the continental United 

States (Heimlich, 2003; Gianessi 

and Silvers, 2000).

• A small amount of these chemicals 

may move upward into the atmosphere, downward through the soil 

into ground water, or across the 

land into streams.

• Although progress has been made 

in reducing pollution from point 

sources and nonpoint sources 

(including agriculture), agriculture 

is the “leading source of remaining 

impairments in the Nation’s rivers 

and lakes” (Heimlich, 2003).

• Concentrations of pesticides and 

their breakdown products are widespread in surface water and ground 

water across the United States. 

For example, at least one pesticide 

was found in about 97 percent of 

water samples and in more than 90 

percent of fish samples from agricultural streams, and in nearly 60 

percent of shallow wells sampled 

in agricultural areas (Hamilton and 

others, 2004). 

Almond orchard in the Mustang Creek watershed of the San Joaquin Valley of California. Microsprinklers deliver a gentle spray of water around the orange-colored outlets, helping to conserve 

water and reduce runoff of pesticides and other agricultural chemicals.

Photo by Joseph Domagalski, USGS
Complex factors control the 

transport and fate of agricultural 

chemicals

These USGS studies address the complex processes controlling the transport, 

and fate of agricultural chemicals in 

streams and ground water, as well as how 

these processes are affected by natural 

factors, agricultural practices, and chemical properties. 

Not all of the agricultural chemicals 

remain in the soil or are taken up by 

plants; a small amount can move upward 

into the atmosphere, downward through 

the soil into shallow ground water and 

underlying aquifers, or across the land 

into streams. This movement is controlled, in part, by natural factors such as 

hydrogeology, climate, topography, and 

soils, making water resources in some 

basins more vulnerable to contamination 

than others. 

For example, throughout much of 

the upper Midwest, large amounts of 

chemicals are used on corn and soybean 

fields, but underlying ground water generally has relatively low concentrations 

of agricultural chemicals because the low 

permeability soils and glacial till minimize downward movement. On that part 

of the Delmarva Peninsula in Maryland, 

ground water is more vulnerable because 

of permeable soils underlain by sand and 

gravel, which enable rapid infiltration 

and downward movement of water and 

chemicals. Streams are most vulnerable 

to contamination from agricultural chemicals where poorly drained soils, agricultural practices, and topography encourage 

the rapid movement of water off of fields, 

or where tile drains and ditches quickly 

transport agricultural runoff from fields to 

streams, such as in the White River Basin 

in Indiana. 

Natural transformation processes, such 

as denitrification, and chemical properties play an important role in transport. 

For example, poorly drained and poorly 

oxygenated soils with organic-rich sediments can promote denitrification, which 

can thereby reduce nitrate concentrations 

entering streams. 

Some chemicals, such as atrazine 

and nitrate, readily dissolve and move 

with water in both streams and aquifers, 

whereas many forms of phosphorus and 

some pesticides, such as chlorpyrifos and 

permethrin, attach to soil particles and are 

transported to streams with eroded soil, 

particularly during times of runoff from 

precipitation or irrigation. Ground water 

typically is less vulnerable to contamination by chemicals that strongly attach to 

soils. 

Some chemicals, such as atrazine, are 

slowly transformed by natural processes 

and can persist in soil and water for years 

or even decades. Other pesticides, such as 

diazinon, are relatively unstable in water 

and break down to other compounds 

within days or weeks. Chemicals that persist for a long time are more likely to be 

transported farther than compounds that 

are short lived.

Chemical transport also is influenced 

by agricultural practices, such as methods 

of tillage and drainage, and chemical 

use. For example, farmers may leave the 

soil surface undisturbed from harvest to 

planting (referred to as “no-till”), and 

may plant and maintain buffer strips 

around fields and streams. By decreasing 

runoff and soil erosion, these practices 

also decrease chemical transport. Use of 

drip irrigation in lieu of furrow irrigation 

decreases the amount of water lost to 

ditches or evaporation, and allows better 

control of the amounts of pesticides and 

nutrients added to irrigation water. 

A unique feature of these studies is 

the simultaneous assessment of agricultural chemicals throughout the hydrologic system at many scales. 

In a small sub-basin within each 

study unit, data are collected on precipitation, wind speed, solar radiation, 

and air temperature; on streamflow 

(discharge); on water quality in streams, 

runoff, tile drains and shallow ground 

water; and on sediment quality in the 

streambed and agricultural soils. Streamflow and water quality also are assessed 

in the larger river network of the study 

unit. A network of wells is sampled to 

characterize the age, movement, and 

quality of shallow ground water; in most 

areas, wells along a 1- to 2-mile-long 

flow system are used to characterize 

chemical transport rates and transformation processes in the shallow system 

recharged within about the last 50 years. 

In this study area near Indianapolis, 

Ind., the 2.4-square-mile (mi2) drainage 

area of the Leary-Weber Ditch is nested 

within the Sugar Creek watershed, a 95-

mi2 agricultural basin nested within the 

larger, more heterogeneous White River 

Basin (more than 11,000 mi2).

Multi-scale studies improve understanding of chemical transport

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Leary- W eber Ditch

White River 

at Hazleton, Ind.

White, Great, and Little Miami River Basins Study Unit

Sugar Creek 

watershed

LearyWeber 

Ditch

(downstream 

from heterogeneous land use)

(downstream 

from agricultural land use)

Soil (soil moisture, soil and

water quality)

Atmosphere (precipitation 

quality and meteorological data)

Ground water (water level 

and water quality) Surface water (discharge and 

water quality)

Overland flow 

(discharge and water quality)

Ground-water-surface-water

interaction (water flux

and porewater quality)

Tile drain (discharge

and water quality)

X

+

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TYPE OF STATION AND DATA COLLECTED

Sugar Creek at New 

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1

2

3

4 5

6

7

Agricultural chemicals are studied in basins across the Nation 

Studies were begun in 2001 in five agricultural basins within NAWQA study units. Two more studies (gray-shaded study units in map) are scheduled 

to begin in 2005. As the studies progress, additional basins will likely be added. The study areas represent diverse agricultural settings, as defined by 

crop and animal production activities, management practices (related to chemical use, irrigation, drainage, and tillage), and hydrogeologic settings (a 

combination of surface and subsurface systems with characteristic climate, topography, geology, and soils). 

NAWQA study unit and 

agricultural chemicals 

study area

Major crops and 

animal 

production

Primary agricultural 

management practices*

Hydrogeologic setting Major water-quality issues 

1

Central Columbia 

Plateau-Yakima River 

Basin Study Unit 

(Granger Drain sub-basin 

in Washington)

Orchards, 

vineyards, corn, 

hay, mixed row 

crops; intensive 

dairy

Spray, furrow, and drip 

irrigation; water delivery and 

drainage channels; conventional 

tillage and no-till; tile drains, 

ditches; widespread use of 

polyacrylamide (PAM)

Arid; deep loess soils 

underlain by basalt

Pesticides and nutrients in streams, 

drains, and ground water; water 

temperature; sediment and fecal 

bacteria in streams

2

San Joaquin-Tulare 

Basins Study Unit 

(Lower Merced River 

and Mustang Creek 

watershed in California)

Orchards, 

vineyards, mixed 

row crops; 

intensive dairy 

and poultry

Spray, furrow, flood, and drip 

irrigation; conventional tillage 

and no-till

Arid; permeable 

sands with relatively 

shallow water tables 

and poorly drained 

soils with deeper 

water tables

Runoff from winter rains carries 

pesticides to streams, with toxicity 

to aquatic invertebrates; nitrate in 

ground water in localized areas

3

Central Nebraska Basins 

Study Unit (Maple Creek 

watershed in Nebraska)

Corn, soybeans, 

alfalfa, hay, and 

wheat; beef cattle, 

some dairy and 

hogs

Mostly dryland; central pivot 

irrigation; conventional and 

conservation tillage, no-till 

increasing; some tile drains 

Semiarid; permeable 

surface and subsurface

Herbicides and nutrients in streams 

and ground water, including in 

drinking-water wells; sediment in 

streams

4

White, Great, and Little 

Miami River Basins 

Study Unit (Sugar Creek 

watershed in Indiana)

Corn and 

soybeans; few to 

no animals

No irrigation; conventional and 

reduced tillage; tile drains and 

ditches

Humid; poorly 

drained soils; 

relatively 

impermeable glacial 

till and sediment

Herbicides in streams; accelerated 

transport of pesticides and nutrients 

to streams via tile drains

5

Potomac River Basin 

& Delmarva Peninsula 

Study Unit (Morgan 

Creek watershed in 

Maryland)

Corn and 

soybeans; some 

dairy

Some central pivot irrigation; 

conventional tillage and no-till

Humid; moderately 

to well drained soils; 

permeable sand and 

gravel suficial aquifer

Herbicides in streams and ground 

water, including drinking-water 

wells; nitrate greater than drinkingwater standards in some drinkingwater wells

6

Eastern Iowa Basins 

Study Unit (South 

Fork of the Iowa River 

watershed in Iowa)

Corn and 

soybeans; 

extensive hog 

confined feeding 

operations 

No irrigation; conventional and 

conservation tillage; tile drains 

and ditches

Humid; poorly to 

moderately drained 

soils from glacial till

Herbicides and nutrients in 

streams, transported by overland 

flow and tile drains; potential for 

pharmaceuticals in streams and 

ground water from hog operations

7

Mississippi Embayment 

Study Unit (Bogue 

Phalia watershed in 

Mississippi)

Cotton, rice, 

soybeans, corn; 

catfish, few other 

animals

Flood, pivot, spray, and furrow 

irrigation

Subtropical; poorly 

drained alluvial soils

Streams affected by residual 

organochlorines and currently used 

pesticides, fine sediment, and low 

dissolved oxygen

*Pesticide and fertilizer use is heavy in each study area, and cattle or hog manure is applied to fields in some places. 
How study results can be used

The findings of these studies will 

provide a better understanding of the 

transport and fate of selected agricultural 

chemicals in various agricultural and 

environmental settings. This understanding will enable the development of models to extrapolate information from direct 

water-quality measurements to similar, 

yet unmonitored, agricultural areas. 

Farmers will gain a better understanding 

of how their operations affect water quality. The findings also will guide future 

scientific research on processes affecting 

transport and fate of agricultural chemicals and help water policy makers: 

• Optimize selection and timing of 

monitoring on the basis of understanding geographic areas and water 

resources most likely to be affected;

• Evaluate conservation strategies 

such as the protection of riparian 

areas and buffer strips, crop management, and chemical-use management. Stakeholders associated with 

the U.S. Department of Agriculture and local and regional water 

managers will better anticipate the 

effectiveness and timing of these 

strategies for controlling transport of 

chemicals and sediment from fields, 

in streams, and within the groundwater system; and 

• Improve registration and regulation 

of pesticides on the basis of a better 

understanding of their transport 

(including transport of breakdown 

products), as affected by chemical 

properties and natural processes.

by Paul D. Capel, Pixie A. Hamilton, and 

Martha L. Erwin

For additional information and 

questions, contact:

Paul Capel, Team Leader

(612) 625-3082 capel@usgs.gov

Lead Scientists:

Kathy McCarthy, Central Columbia 

Plateau-Yakima River Basin 

(503) 251-3527 mccarthy@usgs.gov

Jason Vogel, Central Nebraska Basins

(402) 437-5129 jrvogel@usgs.gov

Tracy Hancock, Potomac River Basin and 

Delmarva Peninsula (804) 261-2618 

thancock@usgs.gov

Joseph Domagalski, San Joaquin-Tulare 

River Basins (916) 278-3077 

joed@usgs.gov

Nancy Baker, White, Great, and Little 

Miami River Basins (317) 290-3333 

ntbaker@usgs.gov

Stephen Kalkhoff, Eastern Iowa Basins

(319) 358-3611 sjkalkho@usgs.gov

Richard Coupe, Mississippi Embayment

(601) 933-2982 rhcoupe@usgs.gov

USGS fact sheets about individual 

agricultural chemical studies 

http://water.usgs.gov/pubs/fs/fs08003

http://water.usgs.gov/pubs/fs/fs08103

http://water.usgs.gov/pubs/fs/fs08203

http://water.usgs.gov/pubs/fs/fs08303

http://water.usgs.gov/pubs/fs/fs08403

References 

Gianessi, L.P. and Silvers, C.S., 2000, Trends 

in Crop Pesticide Use: Comparing 1992 

and 1997: Washington, D.C., National 

Center for Food and Agricultural Policy, 

http://www.ncfap.org/ncfap/trendsreport.

pdf, accessed June 3, 2004.

The NAWQA Program

The study of agricultural chemicals is 

one of five national priority topics being 

addressed by the National Water-Quality 

Assessment (NAWQA) Program in its 

second decade of studies, which began in 

2001. Other topics include (1) effects of 

urbanization on stream ecosystems (USGS 

Fact Sheet 042-02); (2) ecological effects 

of nutrient enrichment (USGS Fact Sheet 

118-03); (3) mercury in stream ecosystems (USGS Fact Sheet 016-03); and (4) 

transport of contaminants to public-supply 

wells. 

During the Program’s first decade 

(1991-2001), NAWQA scientists assessed 

water chemistry, stream hydrology, 

habitat, and biological communities in 51 

major river basins (referred to as “Study 

Units”; a map is available at 

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

assessments characterize the ambient 

water resource—the source of about 60 

percent of the Nation’s drinking water 

and water for industrial, irrigation, and 

recreational uses. During its first decade, 

NAWQA made baseline assessments of 

pesticides, nutrients, volatile organic compounds, trace elements, dissolved solids, 

and radon, as well as the condition of 

aquatic habitats and fish, insect, and algal 

communities. These findings are described 

in hundreds of reports, which can be 

accessed at the NAWQA Web site above. 

In the second decade of studies, 42 

of the 51 study units are planned to be 

reassessed to determine trends at many of 

the streams and ground-water monitoring 

sites; to fill critical gaps in the characterization of water-quality conditions; and 

to build upon earlier NAWQA findings 

that show how natural features and human 

activities affect water quality and aquatic 

ecosystems.

Heimlich, Ralph, 2003, Agricultural 

Resources and Environmental Indicators, 

2003: Agriculture Handbook No. (AH722): 

U.S. Department of Agriculture Economic 

Research Service http://www.ers.usda.gov/

publications/arei/ah722/, accessed May 25, 

2004. [available online only]

Hamilton, P.A., Miller, T.L., and Myers, D.N., 

2004: Water quality in the Nation’s Streams 

and Aquifers—Overview of Selected Findings, 1991-2001: U. S. Geological Survey 

Circular 1265, 20 p. [available online at 

http://water.usgs.gov/pubs/circ/2004/1265/]

Soybean field on well-drained farmland on the Delmarva Peninsula. 

Photo by David Usher, USGS