Author
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Gburek, William |
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Pionke, Harry |
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Submitted to: Animal Waste And The Land Water Interface Conference
Publication Type: Book / Chapter Publication Acceptance Date: 7/19/1995 Publication Date: N/A Citation: N/A Interpretive Summary: In parts of the U.S., nutrients from animal wastes exceed the amounts needed to grow crops. Land-based disposal of the excess animal wastes in these areas requires we first be able to determine those source-areas controlling nutrient export from watersheds. Water movement defines the source-areas, but the emphasis on controlling phosphorus (P) and nitrogen (N) loss are different. Surface runoff controls P loss, while subsurface flow controls N loss. Animal waste disposal strategies can be developed by combining these facts with variable-source-area (VSA) hydrology. The VSA concept says the watershed can be subdivided in preferential runoff, preferential ground water recharge and relatively inert areas depending on their position in the hydrologic system. Where runoff and recharge zones are also the primary areas of waste disposal, the potentially largest export of P and N occurs here. This hydrologic approach to source-area identification implies that different management strategies applied to different parts of the watershed may minimize contamination of ground water and/or surface runoff. It suggests that no single strategy exists for land-based disposal of animal wastes, since optimum disposal zones on the landscape are different for N and P. P loss can be minimized if the animal wastes are disposed of at a distance from the stream where P transport mechanisms do not dominate. However, in these same locations, the N content of disposed wastes may need to be minimized. Using this approach, strategies for environmentally sound land-based disposal of animal wastes can be developed. Technical Abstract: Development of management strategies for land-based disposal of animal wastes requires definition of source-areas controlling nutrient export from watersheds. Water movement is the major control on source-area definition, however, flow components controlling phosphorus (P) and nitrogen (N) nutrient transpost are different. For P, surface runoff is the flow component of concern, while for N, subsurface flow source-areas are important. Land-based disposal strategies for animal wastes can be derived by combining these conditions with variable-source-area (VSA) hydrology. The VSA concept suggests that a dynamic "subwatershed" produces surface runoff within the topographically defined watershed as a function of precipitation, topography, soils, and moisture status. The remainder of the watershed area is dominated by infiltration and ground water recharge processes. The intersection of runoff and recharge zones with areas of waste disposal creates the source-areas controlling export of P and N from the watershed. This hydrologic approach to source-area identification implies that different levels of management applied to different parts of the watershed may most efficiently minimize contamination of ground water and/or surface runoff. It suggests that there is no single strategy for land-based disposal of animal wastes which minimizes impact of both N and P, since optimum disposal zones on the landscape are different for each. The opportunity exists to isolate loss of P from animal wastes, since they can be disposed of at distance from the stream where P transport mechanisms are not available. However, in these same positions, the N component of disposed wastes must be carefully controlled and portions of the subsurface potentially affected by its loss must be considered. |
