Cost effectiveness of agricultural BMPs for sediment reduction in the mississippi delta

ABSTRACT:

Sediment has been identified as the pollutant most limiting to fishery health in oxbow lakes in the Mississippi Delta. The Mississippi Delta Management System Evaluation Area (MDMSEA) project seeks to reduce the adverse agricultural impacts on water resources and ecological processes through the development and adoption of alternative best management practices (BMPs). However, resource limitations dictate that only a few combinations of BMPs can actually be physically tested over a few years at a limited number of locations. To extend results and better evaluate the effectiveness of alternative BMP combinations on sediment reduction, the Annualized Agricultural Nonpoint Source pollutant loading model (AnnAGNPS 2.1) was applied to a 12 ha (30 ac) MDMSEA subwatershed. BMPs considered included cover crops, filter strips, grade control pipes, and impoundments. Each BMP was considered in combination with three tillage systems: conventional tillage, reduced tillage, and no-till. Costs of BMPs were estimated using 2001 state average prices for Mississippi. Amortized fixed costs, using a 25 yr planning horizon and interest rates of both 5% and 10%, were combined with direct annual costs into total annual cost estimates. AnnAGNPS predicted that no-till alone, reduced tillage with winter cover and an edge-of-field pipe, or conventional tillage with a small permanent impoundment (covering less than 3% of the watershed) would all reduce sediment yield by at least 50%. The most cost-effective BMPs were management of volunteer winter weeds as cover crops and various types of edge-of-field grade-control pipes. The average marginal cost using BMPs for sediment yield reduction was about $8 MT⁻¹ ($7.3 t⁻¹) for conventional and reduced tillage. The cost was higher, about $10.7 MT⁻¹, ($9.7 t⁻¹) for no-till because the practice of no-till alone reduced sediment yield by half, and further marginal reductions were more expensive.