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AGNPS Tracks Pollutants to Their Source

When someone turns on a faucet in one part of a watershed, someone else 20 miles away at another end of the area may be affected.

"It's all interrelated," says Robert A. Young, an ARS engineer in Morris, Minnesota. A watershed includes all the land that drains into a main river, lake, or reservoir.

That's why Young developed a watershed-scale computer prediction model called AGNPS, for Agricultural Non-Point-Source pollution. It is used by planning agencies to simulate the effects of various management practices on pollution in the watershed. It can tell where runoff from rain or snowmelt or irrigation may carry pesticides, fertilizers, or sediment throughout a watershed.

Fred D. Theurer, technology model development leader for USDA's Natural Resources Conservation Service in Washington, D.C., says that NRCS planners use AGNPS for watersheds as large as 500 square miles.

"What AGNPS does that no other model can do is allow us to track pollutants back to their source," Theurer says.

Theurer says NRCS has linked the model to an automated mapping computer program that allows for easy use.

With AGNPS, Young explains, he can divide a watershed into grids of any size. "For each grid, we tell the computer the soil type, topography, and land use. If crops are planted, we tell it the chemicals applied, tillage method, and whether contour farming or other conservation practices are being used. We also put in weather data for an area. From all of this, the computer estimates the pollution potential of each grid."

"If we're not happy with the results from any particular grid, we can simulate a different scenario to see which changes would be most cost-effective," Young says.

That's the biggest advantage of AGNPS, he says—being able to evaluate practices on a computer. "We can then find the best combinations of practices for each part of a watershed, keeping soil and chemical losses to a minimum without putting farmers out of business."

By pinpointing the major pollution sources, or "hot spots," the computer helps planners focus corrective actions at those locations. A little money spent on fixing these limited areas can do more good than a lot of money spent on general practices throughout the watershed, Young says.

The model is also used by other government and private agencies and organizations interested in keeping chemicals out of water, such as lake property owners' associations, throughout the world. — By Don Comis, ARS.

Robert A. Young, recently retired, is now a research collaborator at the USDA-ARS North Central Soil Conservation Research Laboratory, 803 Iowa Avenue, Morris, MN 56267; phone (320) 589-3411, fax (320) 589-3787.

 

"AGNPS Tracks Pollutants to Their Source" was published in the February 1995 issue of Agricultural Research magazine.

 

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