NUMERICAL-MODELS AND NUTRIENT REDUCTION STRATEGIES IN VIRGINIA

Numerical models of Chesapeake Bay, its tributaries, and watershed are being used to simulate eutrophication and anoxia in the Bay. Simulation results from a two-dimensional steady-state model indicate a 40% reduction of nitrogen and phosphorus loadings would be necessary to raise the minimum dissolved oxygen levels to 1.0 mg/l and eliminate anoxic conditions. Based on these model results, a comprehensive nutrient reduction strategy is being implemented in Virginia as part of an interstate plan to reduce nutrient loadings by 40%. Nonpoint sources above the fall line were identified as contributing most of the nitrogen input to the Bay while phosphorus loadings originated primarily from point sources below the fall line. Point source discharges of phosphorus were identified as the most controllable and were the first target for reasons of cost effectiveness. Included in Virginia's plan were a phosphate-based detergent ban, financial assistance programs to municipalities for nutrient removal, and point source nutrient discharge limitations. Preliminary studies indicate that the reduction strategies are beginning to work and Virginia has achieved its initial goal of reducing nutrient loadings by 40%. Current modeling efforts are directed toward a re-evaluation of the 40% nutrient reduction strategy as well as establishmen of work plans for future program development over the next several decades. The status of Virginia's nutrient management strategies based on model simulations are discussed.