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United States Department of Agriculture

Agricultural Research Service

Title: Hydrologic Controls on Phosphorus Loss from Upland Agricultural Watersheds

Authors
item Gburek, William
item Sharpley, Andrew

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 7, 1997
Publication Date: N/A

Interpretive Summary: In much of the northeastern U.S., livestock-based farming is concentrated in small areas around feed mills and processing plants. Because of this, more phosphorus (P) is often produced in manure than is needed by the crops grown in these areas. Almost all of this manure is applied to farmland, and as excess application of P continues year after year, more of it is being lost from the farmland in runoff to streams and rivers. When this P gets to freshwater lakes and estuaries, unwanted weeds can grow. The weeds can consume much of the oxygen dissolved in water, causing fish to suffocate and die. To reduce these water quality problems, Chesapeake Bay authorities for example, have mandated a 40% reduction in P coming into the Bay by the year 2000. To accomplish this reduction, "hot spots," or small areas where most of the P is coming from, must be located. Our research on several farmland watersheds in Pennsylvania shows that areas where both soil P levels are high and most runoff occurs are relatively small and identifiable portions of the landscape. These findings are enabling us to develop methods of identifying these areas so that control measures may be more effectively implemented to reduce P export to streams.

Technical Abstract: Development of strategies for controlling phosphorus (P) loss from upland agricultural watersheds requires an ability to identify specific source- area of P at field and farm scales, and to predict their resultant effects at the watershed scale. Key to identification of P source-areas is defining the interaction between P availability over the landscape and its potential for movement to the watershed outlet by runoff and erosion. A current weakness in quantifying this interaction is determination of the specific zones of runoff and erosion within a watershed, i.e., source-areas for the P transport mechanisms. Research results from a series of studies within a small, upland agricultural watershed in east-central Pennsylvania show that the zones of runoff production, and consequently the areas ultimately controlling P transport, are consistently a limited and identifiable portion of the landscape. Quantifying the hydrologic controls son P transport within and from a watershed in this way allows us to focus management options on small and definable portions of the total watershed area that contribute most P export.

Last Modified: 11/28/2014
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