USE OF SURFACE AND TRACER ANALYSIS TO ESTIMATE NUTRIENT AND SEDIMENT LOAD ALLOCATION TO CHESPAEAKE BAY

A combined surface analysis and tracer simulation is applied to analyze the outputs of the Chesapeake Bay Estuarine Model. The water quality and biological resource responses, in the whole Bay and in segments of the estuary to nitrogen, phosphorous, and sediment loads to the Bay are analyzed. The response surface provides information on the interactions among the parameters of dissolved oxygen, chlorophyll, water clarity, and submerged aquatic vegetation and how to most effectively improve the water quality through nutrient and sediment management. From the continuous function of response surface, we are able to predict water quality response under various loading conditions, and to determine the load reduction requirement for the attainment of a specific water quality criterion. The seasonal response surface helps us to understand how water quality indexes respond seasonally, and provides further information on the interactions in the ecosystem and recommendations on the control of nutrient and sediment loads on a seasonal basis. The tracer simulation provides information on the effect of a model segment of the Bay by the loads from its sources distributed among the sub-watersheds. The response surface for water quality index in a segment of the Bay versus loads to the segment further provides information on allocations of load reduction among sources. This paper discusses how the combined surface and tracer analysis can be applied for TMDL assessment. Three options of strategies in nutrient reduction allocation and cost-related concerns in the allocation are discussed.