Fact Sheet 2005-3064

June 2005

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

The PDF for the report is 1,202 kb

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

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.

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:


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.


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.

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
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

1In 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 and Natural Resources Conservation Service

Iowa Department of Natural Resources Iowa Geological Survey

Iowa State University

South Fork Watershed Alliance

For more information

Stephen Kalkhoff, Lead Scientist, South Fork Iowa River study
(319) 358-3611,

Paul Capel, Team Leader, National study
(612) 625-3082,

NAWQA Program


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

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.

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