Targets Water Pollution
By Don Comis
October 7, 2002
Rivers and lakes throughout the
United States and world are kept cleaner with the aid of a computer model
called SWAT, for Soil and Water Assessment Tool. Whether it's the Great Salt
Plains Lake of Oklahoma--a shallow, briny lake that's an important way station
for migratory birds--the Joanes River watershed in Brazil, or the Rio Grande
watershed that spans eight states and parts of Mexico, water quality managers
rely on SWAT to reduce the flow of silt, fertilizers or toxic chemicals into
Agricultural Research Service
engineers Jeffrey G. Arnold and Kevin W. King and agronomist James R. Kiniry,
all with the Grassland Soil and Water
Research Laboratory in Temple, Texas, developed SWAT by assembling 30 years
of ARS research data into an easy-to-use package. The key is an interactive
color mapping software interface that enables managers to bring large, complex
watersheds to life.
The maps pinpoint hot spots likely to be important sources of water
pollution. The U.S. Environmental Protection
Agency uses the model to set allowable pollution limits for 20,000 streams
it has found to have poor water quality.
The SWAT model helps managers extend the life of reservoirs and cut their
maintenance costs by reducing the amount of soil entering them. It has even
been used in drought-stricken parts of Texas to increase streamflow by showing
where to remove brush that was lowering water levels.
The model helps reduce farming's effects on waterways, whether that impact
comes from pesticides and fertilizers in runoff from wheat fields of Oklahoma
and Kansas washing into tributaries that feed into the Great Salt Plains Lake
reservoir, or from large livestock feedlots polluting rivers that flow into
downstream drinking water reservoirs. Excessive nutrients from fertilizers or
manure cause algal blooms in waterways--or can even deplete the water of
For more on the SWAT model, see the
October issue of
Agricultural Research magazine.
ARS is the U.S. Department of
Agriculture's chief scientific research agency.