SPATIAL VARIABILITY OF AGRICULTURAL NONPOINT SOURCE POLLUTION CONTROL COSTS

Public concern for controlling agricultural nonpoint source (NPS) pollution has expanded the development of computer-aided watershed assessment modeling for determining least cost policy alternatives for improving water quality. The Watershed Assessment Integration Toolbox (WAIT) is a spatial decision support system being developed to evaluate NPS pollution control policies in terms of both environmental and economic impacts. The spatial variability of phosphorus (P) delivery and control costs associated with a P-based nutrient management standard was compared with a baseline no nutrient standard scenario in a livestock-intensive sub-watershed of Muddy Creek in Rockingham County, Virginia. A modified version of WAIT comprised of a farm optimization programming model, a NPS/water quality model, and a GIS was used. Phosphorus delivery was reduced by 57% under the P-based standard at an average cost of 8.61 per lb of P reduced. The P-based standard adversely impacted the farms with poultry because of the high P content in litter and reduced revenues from selling poultry litter. Targeting the P-based standard on farms having fields adjacent to the blue line stream reduced P delivery by 51% at approximately one-half the aggregate farm cost of a uniform P-based standard. Distance to water significantly influences pollution potential associated with a specific field. Resource managers may be able to use WAIT to assess and/or target NPS pollution control policy alternatives more effectively.