Sam Rayburn and Toledo Bend Reservoir Nutrient Modeling

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Modeling Nutrient Loads from Poultry Operations in the Toledo Bend Reservoir and Sam Rayburn Reservoir 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 percent of the surface waters that were surveyed were not meeting their designated uses (EPA, 1998).

Sam Rayburn Reservoir and Toledo Bend Reservoir (Figure 1), created in 1965 and 1966, respectively, were designed to control floods, generate hydroelectric power, and conserve water for municipal, industrial, agricultural, and recreational uses. Both lakes are very popular for fishing and boating.

In 2000, data indicated that parts of both reservoirs were not optimal for aquatic life due to low concentrations of dissolved oxygen, likely from excess algae growth. This excess growth is attributed to an over abundance of nutrients in the lake, primarily phosphorous. Mercury in fish tissue and elevated fecal coliform bacteria are additional concerns in parts of the reservoirs.

Nonpoint pollution sources include agricultural, residential, forestry, etc. Point sources include many permitted wastewater discharges from the towns and cities, paper mills, etc. However, this project was concerned with nonpoint agricultural sources, primarily commercial poultry operations.

Much of the Texas poultry industry is located in the contributing watersheds of these reservoirs. A combined total of approximately 262,615,000 birds are produced annually in the two watersheds along with about 273,600 metric tonnes of manure. Statewide, the economic benefit of the Texas poultry industry is estimated at about $1.6 billion to the state’s economy and employs more than 11,500 people.

The Texas State Soil and Water Conservation Board (TSSWCB) has been working through the Senate Bill 503 program since 1994, and the (EPA) §319(h) grants program since 2001 to reduce nonpoint source pollution from agricultural activities in the watersheds in this project. Technical and financial assistance was provided through the local Soil and Water Conservation Districts (SWCDs) for voluntary development and implementation of water quality management plans. A total of 674 water quality management plans (WQMP) on 35,591 ha (87,947 ac) had been developed at the time the data was gathered for this study in January, 2007.

The goal of this project was to use computer models and geographic information systems (GIS) to simulate the effects of applying conservation practices on nutrient and sediment loadings in these two Texas watersheds. The Soil and Water Assessment Tool (SWAT) was used to quantify the effects of applying BMPs on nutrient and sediment loadings to streams, rivers, and lakes in each watershed. The Natural Resources Conservation Service (NRCS) Water Resources Assessment Team (WRAT) located at the Blackland/Grassland Research and Extension Center conducted the model simulations.

	Modeling Nutrient Loads from Poultry Operations in the Toledo Bend Reservoir and Sam Rayburn Reservoir Watersheds - Map (PDF; 5 MB)
	Modeling Nutrient Loads from Poultry Operations in the Toledo Bend Reservoir and Sam Rayburn Reservoir Watersheds - Final Report (PDF; 9.75MB)