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Modeling Atrazine in Seven Texas Watersheds

Water quality and quantity is a major concern in the United States. The U.S. Environmental Protection Agency (EPA) 1996 water quality inventory report indicated that 40% of the surface waters that were surveyed were not meeting their designated uses (EPA, 1998).

Mathematical models are one of the best tools for analyzing water quality issues. Models can replicate the flow of pollutants throughout the watersheds and can be utilized to evaluate the consequences of management practices, control measures, and planning decisions. Using a modeling approach for evaluating conservation practices is cost-effective and timesaving, compared to field monitoring.

Atrazine, a systemic herbicide that blocks photosynthesis, is currently one of the two most widely used agricultural pesticides in the U.S. It is also the most commonly detected pesticide in ground and surface water. Atrazine's frequent detection in streams, rivers, groundwater, and reservoirs is related directly to both its volume of usage and its tendency to persist in soils and move with water.

Since 1999, the Texas State Soil and Water Conservation Board (TSSWCB) has been working through the (EPA) 319(h) grants program to reduce nonpoint source pollution from agricultural activities in the seven watersheds in this project. Technical and financial assistance was provided through the local Soil and Water Conservation Districts (SWCDs) for development and implementation of water quality management plans.

The goal of this project was to use computer models and geographic information systems (GIS) to simulate the effects of applying best management practices on atrazine loadings in seven Texas watersheds. These were:

Click on map for larger view.
Lake Lavon (PDF; 10 MB) Lake Bardwell (PDF; 2 MB)
Lake Tawakoni (PDF; 10 MB) Lake Waxahachie (PDF; 2 MB)
Richland-Chambers Reservoir (PDF; 6 MB) Lake Aquilla (PDF; 4 MB)
Little River Watershed (PDF; 10 MB) - from the release points of lakes Belton and Stillhouse-Hollow to the junction with the Brazos River.

The Soil and Water Assessment Tool (SWAT) was used to quantify the effects of applying conservation practices on atrazine loadings to streams, rivers, and lakes in each watershed. The Natural Resources Conservation Service (NRCS) Water Resources Assessment Team (WRAT) located at the Blackland Research and Extension Center (BREC) conducted the model simulations.