The Potomac Initiative

Caption: 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. Developed land in the Potomac river basin has increased from 1.8% in 1975, to 3.4% in 1990, and to 5.6% in 2000.

UMCES researchers have assembled detailed land use, climate and hydrological data for the Potomac basin as the basis for a nested series of spatially explicit models to characterize the response of large watersheds (100-1,000 square km) to the combined effects of climate and land use change.

Large rivers are important

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. The Potomac watershed has a complex mix of land cover types with a dramatic east-west gradient in topography and climate. This basin is experiencing extensive changes in land-use making the Potomac an excellent representative of landscapes being experienced throughout the eastern seaboard of the United States.

Characteristics of the Potomac watershed

The mainstem of the Potomac river is 617 kilometer-long and 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 Washington, D.C. area residetns drawing about 1.8 billion liters of water per day from the river. The Potomac is also a major contributor to waters of the Chesapeake Bay, the largest estuary in the United States.

Caption: We are investigating a variety of landscape changes within the Potomac watershed, including urbanization, forest disturbance, surface mining, and agriculture.

Linking land-use change to watershed effects

The net effect of local, incremental change in land use has important implications for controlling the levels of sediment and nutrient loading to the Potomac. We know that increasing sediment and nutrient concentrations will adversely affect eutrophication, hypoxia, and light availability for biota within the Chesapeake Bay, but prediction of downstream effects in large river systems cannot be obtained by simply summing upstream inputs. We expect that small, cumulative change can lead to sudden declines in water quality and threaten the biotic integrity of these important river systems.

The Potomac provides a model for study because of its setting within a landscape continuum from mountains to the Bay; its geomorphic and land-use diversity; its rapid population growth; and its importance as the primary drinking water supply for the Nation's capital and as habitat for a diverse biota.

We are investigating the impacts of a variety of landscape changes within the Potomac basin, including urbanization, forest disturbance, and surface mining. Documented impacts include acidification of western Maryland streams, increased flooding, altered fish composition and behavior, and increased leakage of nutriends from forests to surface waters. Tools used for these studies include models at multiple spatial scales, paired watershed studies, and remote-sensing landscape analysis.

Climate change and land-use interactions

The effects of climate change on river systems in the eastern United States are difficult to assess because:

  • current climate models do not adequately predict the full spectrum of expected weather conditions - especially large storms and extended droughts;
  • the fine-scale, detailed response of terrestrial and aquatic ecosystems to changing weather conditions (e.g., earlier phenology, increasing evapotranspiration) have not been systematically explored; and
  • the concurrent effects of land-cover and land-use change have not been included within the assessment process.
Caption:  Flow diagram of plan to assess the impacts of changes in storms, droughts, phenology and land use on water shortages, floods and nutrient loading at multiple spatial scales.

We are investigating these interactive effects by combining weather estimation tools with fine-scale models of land use and ecosystem change within spatially explicit hydrological models that span mulitple spatial resolutions, from the mid-size watershed scale (100 - 1,000 square km) to a large river basin, the Potomac River (37,800 square km).

Restoration across the terrestrial-aquatic boundary

Caption: 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.

The Potomac Initiative includes a strong emphasis on understanding the linkages between upland land-use and aquatic systems, including restoration of the terrestrial-aquatic interface. Streams are effective sinks for nutrients and habitat for native species. These features are enhanced wherever flow can rapidly exchange with groundwater within the floodplain. The goal of science is to quantify these linkages under various disturbance regimes (e.g., surface mining, buried streams) and understand the spatial scales under which they are most significant. Likewise the goal of stream restoration is to reconnect stream flow to the floodplain, providing solutions to our most common watershed problems.

Research team

UMCES Collaborators