Potomac Highlands Watershed School


Stream Cleaner Environmental Forum


Selected Graphs of

Chesapeake Bay Watershed Model Simulations

The Chesapeake Bay Program uses mathematical models to simulate changes in the Bay ecosystem due to changes in population, land use, or pollution management.  The Chesapeake Bay Watershed Model (CBWM) simulations are not the same as actual conditions. They are the best scientific estimate of what average loadings are likely to be.  However, not everyone is willing to accept these as reasonable estimates.

Pennsylvania and Virginia contain the largest percentage of the Chesapeake Bay watershed, followed by Maryland, New York, West Virginia, Delaware, and Washington DC. As the watershed areas of each jurisdiction differ greatly, it is not surprising that their relative contributions to the Bay’s sediment and nutrient problems differ as well.
The Chesapeake Bay Watershed Model is used to estimate past and current water quality conditions, and to predict how changes in land management will affect future conditions. For example, the model can be used to estimate the sources of nutrients and sediment to the Bay in any given year. The following graphs present model estimates of the sources of nitrogen, phosphorus and sediment in the entire Bay watershed in 2002.
The next three graphs compare nutrient and sediment loads from the seven political jurisdictions, as estimated by CBWM, for 1985 baseline, 2002 progress, and 2010 Cap Load Allocations. The jurisdictions with the largest land area (Pennsylvania, Virginia and Maryland) also contribute the largest nutrient and sediment loads. Each jurisdiction has a different mix of land uses that produce their nutrient and sediment loads and require a different mix of remedies.  For example, nitrogen from the highly urbanized Washington DC area comes almost entirely from point sources, in particular the mammoth wastewater treatment plant at Blue Plains, while nitrogen from rural Delaware comes mostly from highly concentrated agriculture. Thus far, CBP signatories Maryland, Virginia, and Washington DC have made the most progress in reducing their baseline (1985) nutrient loadings – but all jurisdictions still have a long way to go to meet the Cap Load Allocations.
West Virginia total nitrogen loads as estimated by the CBWM for 2002.
West Virginia total phosphorus loads as estimated by the CBWM for 2002.
West Virginia total sediment loads as estimated by the CBWM for 2002.