Contact:
Michael Palace
U.S. EPA Chesapeake Bay Program
410 Severn Ave., Suite 109
Annapolis, MD 21403
palace.michael@epamail.epa.gov
The Chesapeake Bay Program is applying an integrated set of air and water models to track nutrients in the entire Chesapeake watershed and airshed. Three models have been developed and linked together to get an overall simulation of the Chesapeake watershed, airshed and estuary. The integrated models have been used to quantify the nutrients contributing to eutrophication. Most importantly, the models have been used to quantify nutrient reductions necessary to restore Chesapeake Bay resources. The Patuxent River and watershed are a portion of the entire modeling effort. It is of interest to maintain consistent modeling methodology throughout the Chesapeake Bay, be it the northern Susquehanna River to the York River.
The Bay Program nutrient reduction goal is to reduce by the year 2000 40% of the nutrients entering the Bay. The integrated models have demonstrated that this goal will significantly decrease the "dead waters" of the Chesapeake. Further, the models provide guidance to environmental managers and citizens on where the most cost effective nutrient reductions can be made. The integrated models have been used to establish broadly supported nutrient reductions that are achievable, equitable, economically efficient, and protective of the Chesapeake Bay resource.
The Airshed Model (Regional Atmospheric Deposition Model -RADM) tracks nutrient emissions from all sources in the airshed. This three dimensional model simulates movement both vertically and horizontally across a region. The Airshed Model covers the eastern United States from Texas and North Dakota eastward to Maine and Florida with 22,000 cells. Each cell measures eighty square kilometers, with a nested small scale grid of twenty square kilometers over the Chesapeake Bay region. Stacked up the cells make fifteen vertical layers reaching about fifteen kilometers high. The air borne nutrient loads are transported by the Airshed Model and linked to the Watershed Model through deposition to land surfaces and to the Estuary Model through deposition to the water surfaces of the tidal Bay.
The Watershed model divides the 64,000 square mile drainage basin into 86 model segments. The Hydrological Simulation Program-FORTRAN (HSPF) is used to model the watershed. Each segment contains information generated by a hydrolic submodel, a nonpoint source submodel, and a river submodel. The hydrolic submodel uses rainfall, evaporation, and meteorological data to calculate runoff and subsurface flow for all the basin land uses including forest, agricultural lands, and urban lands. The surface and sub surface flow ultimately drive the nonpoint source submodel which simulates soil erosion and the nutrient loads from the land to the rivers. The river submodel routes flow and associated nutrient loads from the land through the lakes, rivers, and reservoirs to the Bay. The estuarine model examines the effects of these loads on water quality.
The Estuary Model examines the effects of the loads generated by the Watershed Model on Bay water quality. In the Estuary Model, the Bay is represented by 4,073 computational cells which average six miles long, two miles wide and five feet deep. The cells are stacked up to 15 layers in the deepest areas of the Bay. The Estuary Model is built on two submodels: the hydrodynamic submodel and the water quality submodel. The hydrodynamic submodel simulates the flow rates into the Bay, the mixing of the Chesapeake with coastal ocean waters, and the mixing of water within the Chesapeake. The water quality submodel calculates the chemical and physical dynamics of the Chesapeake.
These integrated models provide basic information on the loads from all sources, the amount of the load that can be controlled from each source, and the improvements that can be expected from reducing nutrient inputs provided the impetus to act in the Bay Program. With information from the models, cost analyses of nutrient reduction from the sources were completed. The basic understanding of where the nutrient reductions will come from, what the controls will cost, and the benefits expectedmade the Bay Agreement on nutrient reduction possible.
The integrated models will be used to track nutrient reductions each year to provide information of the progress being made toward the nutrient reduction caps. The models provide a continual check on the work of restoration in the Chesapeake Bay Program.
The integrated models, by examining controls applied to all sources, is an example of a successful application of multimedia analysis. A multimedia analysis looks at an environmental problem not as piecemeal solutions of a single media of only air or only water, but in a holistic manner incorporating solutions from all media. This approach allows solutions that are the most cost effective, equitable, and protective of the environment.