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South Fork Iowa River Watershed Selected for a National Water-Quality Study

The South Fork Iowa River 

watershed in central Iowa 

is one of seven watersheds 

selected by the USGS 

National Water-Quality 

Assessment (NAWQA) 

Program for a special 

study of agricultural 

chemicals and water 

quality.

Why study the South Fork Iowa River watershed?

The South Fork Iowa River and the other watersheds represent 

nationally important agricultural settings (chemical use, crops, 

and AMPs) and natural settings (climate, soils, topography, and 

geology). South Fork Iowa River, which is part of the Iowa River 

watershed, is representative of corn and soybean row cropping in 

the Midwest. 

Other features of the watershed that are relevant to this study: 

• Use of agricultural chemicals: Commonly used chemicals 

include herbicides such as atrazine, acetochlor, metolachlor, 

and glyphosate; and fertilizers, both manure and chemical.

• Distinct natural setting: Low relief topography with common 

depressions that formerly formed ponds and wetlands and that 

are now drained by an extensive network of drainage tiles and 

ditches.

• Variety of agricultural management practices: AMPs include 

both tillage and no-tillage of fields used for corn and soybean 

production; production of large numbers of hogs in concentrated animal feeding facilities; small grassy riparian buffer 

zones commonly used to reduce overland runoff. 

• Water-quality issues: Herbicides and nutrients have been frequently detected in Iowa surface and ground water, including 

in drinking-water wells (findings of USGS studies since the 

1990s).

The U.S. Geological Survey (USGS) is studying seven watersheds across the Nation to better understand how natural factors 

and agricultural management practices (AMPs) affect the transport of water and chemicals. Natural factors include climate and 

landscape (soil type, topography, geology), and AMPs include 

practices related to tillage, irrigation, and chemical application. 

The study approach is similar in each watershed so that we can 

compare and contrast the results and more accurately predict 

conditions in other agricultural settings. 

Study objectives

• Understand the links between the sources of water and 

agricultural chemicals (nutrients and pesticides) and their 

behavior and transport through the environment 

• Predict the behavior and transport of water and agricultural 

chemicals in other agricultural areas not being studied

• Evaluate what the study results mean for management of 

water and water quality in a variety of agricultural settings

We appreciate your help

We are working with local growers and land owners to gain 

access to study sites. We also need information about the watershed and about current as well as historical agricultural management practices—past practices also affect concentrations of 

agricultural chemicals in ground and surface water. 

We will report the findings of the study in public meetings 

and in publications. These findings will provide information that 

will be useful for improving agricultural management locally 

and nationally, and will guide future studies in other watersheds.

Fact Sheet 2005-3064

June 2005

U.S. Department of the Interior

U.S. Geological Survey Printed on recycled paper
Data Collection in the South Fork Iowa River Watershed, 2007–2008

What kind of data Why the data are collected How often

Meteorological data, including rainfall, 

wind speed, solar radiation, and air temperature. Soil temperature and moisture

To determine amount of precipitation, how much 

water from land surface reaches the water table, 

and how much is lost to evapotranspiration

Continuously for 2 years

Amount of streamflow at South Fork Iowa 

River near New Providence, IA, gaging 

station

To interpret water-quality data correctly (the 

amount of water in streams affects chemical concentrations) 

Continuously since 1996 at South 

Fork Iowa River (real-time data 

available at http://waterdata.usgs.

gov/ia/nwis/uv?05451210).

Quality of stream water, runoff water, and 

rain water1

To quantify the transport and behavior of natural 

and agricultural chemicals

Several times a year (>14 

samples) for 2 years, with intensive sampling during application 

seasons

Ground-water levels in wells To determine direction of ground-water flow, 

which affects transport of chemicals

At least quarterly in some wells, 

continuously in others for at least 

1 year

Quality of ground water, soil water, and 

shallow water in and around streambed/

riparian zone1

To quantify the transport and behavior of natural 

and agricultural chemicals

At least quarterly for 1 year

Quality of sediment in streambed and soils 

in agricultural fields1

To quantify the storage, behavior, and transport of 

water and chemicals in the soils and sediment

At least once during study

1

In this study, water-quality and sediment-quality data include concentrations of nutrients (nitrogen and phosphorous), pesticides and pesticide breakdown 

products, and natural constituents and properties, including major ions (calcium, magnesium, chloride, etc.), organic carbon, dissolved oxygen, and temperature.

We would like to thank

U.S. Department of Agriculture

Agricultural Research Service

Natural Resources Conservation 

Service

Iowa Department of Natural Resources 

Iowa Geological Survey

Iowa State University

South Fork Watershed Alliance

Publication

Kalkhoff, S.J., Barnes, K.K., Becher, 

K.D., Savoca, M.E., Schnoebelen, 

D.J., Sadorf, E.M., Porter, S.D., and 

Sullivan, D.J., 2000, Water Quality 

in the Eastern Iowa Basins, Iowa 

and Minnesota, 1996-98, U.S. 

Geological Survey Circular 1210, 37 

p. Available online at http://water.

usgs.gov/pubs/circ/circ1210/

For more information

Stephen Kalkhoff, Lead Scientist, South Fork 

Iowa River study

(319) 358-3611, sjkalkho@usgs.gov

Paul Capel, Team Leader, National study

(612) 625-3082, capel@usgs.gov

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

The USGS provides reliable scientific information to describe and understand the Earth; minimize loss of life and property 

from natural disasters; manage water, biological, energy and mineral resources; and enhance and protect our quality of life.

At a typical study site, several methods 

are used to collect water and chemical 

samples from the air, soil, surface 

water, and ground water.

After being applied to the land 

surface, agricultural chemicals can 

move upward into the atmosphere, 

downward through the soil to shallow 

ground water and underlying aquifers, 

eventually discharge to streams or 

run off across the land into streams, 

and move downstream to reservoirs 

and coastal waters. This process can 

take days, weeks, or even decades if 

water moves underground through the 

ground-water system. 

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