Central Nebraska Basins NAWQA Study Unit

Agricultural Chemical Transport (ACT) in Maple Creek Watershed

The U.S. Geological Survey (USGS) is studying five watersheds across the Nation to better understand how natural factors and agricultural management practices (AMP's) affect the transport of water and chemicals. Natural factors include climate and landscape (soil type, topography, geology), and AMP's 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.

Why study the Maple Creek watershed?

Maple Creek and four other watersheds represent nationally important agricultural settings (chemical use, crops, and AMPSs) and natural settings (climate, geology, topography, and soils). Maple Creek, which is part of the Elkhorn River watershed, is representative of corn and soybean row cropping in the upper Great Plains.

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

• Use of agricultural chemicals: Chemicals used include herbicides such as atrazine, alachlor, acetochlor, metolachlor, and glyphosate; and fertilizers, both organic and inorganic.
• Distinct natural setting: The rolling upland hills and a permeable surficial aquifer overlain by less permeable glacial till allow water and chemicals to move overland to streams and into Maple Creek. The relatively flat valley bottom lands and wooded riparian zones along Maple Creek reduce runoff from fields.
• Variety of agricultural management practices: AMPs include tillage and no-tillage; use of central pivot irrigation; maintenance of grassy waterways and riparian buffer zones; construction of storm retention ponds.
• Water-quality issues: Herbicides and nutrients have been frequently detected in eastern Nebraska surface and ground water, including in drinking-water wells (findings of USGS studies since the 1990's).

We appreciate your help

We thank the local growers and land owners for allowing us access to study sites. We also appreciate the information that has been provided 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.

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 discharging to streams, or run off across the land into streams, eventually moving 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 Maple Creek Watershed, 2003-2004

* In this study, water-quality and data include concentrations of nutrients (nitrogen and phosphorous), pesticides and pesticide break down products, and natural constituents and properties, including major ions (calcium, magnesium, chloride, etc.), organic carbon, dissolved oxygen, and temperature.

Progress as of March 2005

The CNBR ACT team finished sampling for the rainfall, surface water, ground-water/surface-water interaction and ground-water flowpath portions of the study in 2004. Sampling in the vadose zone began in 2004 will continue in 2005. The national ACT team will be working on journal articles to synthesize national results for each of the processes investigated during the study during 2005. Additional publications will also be completed in 2005-2006 to document the environmental setting at each site, surface-water and ground-water modeling parameters at each site, and the mass balance of water and chemicals for each study unit.

We would like to thank the University of Nebraska-Lincoln, Conservation and Survey Division

For more information

Jason Vogel, Lead Scientist, Maple Creek study (402)437-5129, jrvogel@usgs.gov
Paul Capel, Team Leader, National study (612) 625-3082, capel@usgs.gov
National NAWQA Program

Publication

Frenzel, S.A., and others, 1998, Water Quality in the Central Nebraska Basins, 1992-95, U.S. Geological Survey Circular 1163

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