Potomac River Ecosystem Project (PREP)


Land cover map of the Potomac River watershed.  Classification is based on 1992 National Land Cover Dataset (NLCD) that was aggregated to level-one NLCD cover classes. Percent of watershed in each cover category is provided in the legend.

Click image for a larger, higher quality view of Potomac River watershed land use.


Patterns of growth in the Potomac watershed tend to concentrate in ecologically sensitive areas within close proximity to waterways. Here forested riparian buffers are replaced by residential lawns.

Large river systems, which drain vast areas and transport sediment, nutrients and chemicals over long distances, provide an integrative measure of the impact of social, economic and ecological change at regional scales. Urbanization impacts on streams of the Potomac River basin date back to at least 1790, which, along with early agriculture, have shaped the trajectory of freshwater communities and ecosystem functions.  We are currently investigating the direct and indirect consequences of landscape change on the Potomac River Ecosystem using state of the art methods in remote sensing, biogeochemistry, and GIS.

The 617 kilometer-long Potomac River runs through five geological provinces, draining approximately 37,800 square kilometers of Maryland, Pennsylvania, Virginia, and West Virginia. Over 5.3 million people live within this watershed, with approximately 3.7 million residing within the Washington, D.C. metropolitan area alone and depending on its water (the greater D.C. area now withdraws ~1.8 billion liters of water per day from the river). The Potomac is also one of the main tributaries to the Chesapeake Bay, the largest estuary in the United States, and millions of dollars have been spent on efforts to reduce river pollution and related nitrogen loading to the Chesapeake Bay Watershed.

Our research initiative investigates the following questions:



Land use change does not occur uniformly across the landscape but is a spatially biased process. At least three distinct growth patterns have been proposed: clusters of growth expanding from population centers, growth along major transportation corridors, and less-spatially structured growth disjunct from major urban centers. These different processes are apparent in a map (see left) of current (red) and 2010 projected (black) patterns of urban development in Washington, D.C., central Maryland and northern Virginia. Projections are based on a model of urban expansion provided courtesy of D. Theobald, Colorado State University. Population trends over the last one hundred years in these areas are provided at right.

Click here for a larger view of growth patterns in the Baltimore-Washington Corridor.

Project PI:

Bob Gardner

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Over 5.3 million people live in the Potomac River watershed with most of the growth occurring in Maryland and Virginia since the 1960's.

Streams and river flooplains can be "hot spots" of human activities.  Small amounts of development in these areas can lead to disproportionate ecological effects on receiving waters (Potomac River at Harpers Ferry, West Virginia).