Stochastic optimization of non-point source pollution abatement for the Eucha-Spavinaw watershed
Abstract
Scope and Method of Study: This study develops and applies a comprehensive decision-support tool, an integrated biophysical-hydrologic - economic watershed model to determine the least cost mix, location, and magnitude of grazing management practices to meet various phosphorus TMDLs for the Eucha-Spavinaw watershed in Oklahoma within specified margins of safety. The GIS - based Soil Water Assessment Tool (SWAT) was calibrated and used to estimate sediment and nutrient loading under alternative management practices comprising of different combinations of litter application rates, commercial nitrogen, maintaining minimum biomass during grazing, and stocking densities. SWAT -generated site-specific coefficients were used in a Target MOTAD programming model to select a management practice for each site in the watershed. Findings and Conclusions: Results indicate there is no single management practice that dominates in all parts of the watershed and that optimal poultry litter application rates can vary from one soil type to another within the watershed. That is a mix of management practices applied at different locations in the watershed are required to achieve any level of phosphorus abatement from the watershed at least cost. This implies that it may be more cost effective to develop phosphorus reduction programs that target specific soil types within the watershed rather than continue with the current uniform policy of limiting litter application rates strictly by soil test phosphorus. Complete elimination of all fertilizer was found to actually increase total phosphorus loss on some soils because of increased erosion and sediment bound phosphorus. Large increases in the use of commercial nitrogen to replace poultry litter and reduce phosphorus runoff do increase nitrogen loss. As either average annual limit on nutrient loss or the average deviations above the limit are reduced more of the litter is converted to energy or hauled from the watershed. The litter-to-energy plant does not appear profitable on its own merit but becomes a more cost effective method of reducing both the level and the variability of phosphorus runoff as pollution limits are reduced.
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- OSU Dissertations [11222]