Dyke Marsh Restoration

Hog Island Gut in Dyke Marsh Preserve.Dyke Marsh is an important, large tract of freshwater tidal marsh along the Potomac River in the Washington, D.C. area. Located just south of the city of Alexandria, VA, Dyke Marsh is viewed as a national treasure because of its proximity to the nation's capital and a large urban/suburban population, its history, and its current potential for provision of ecological services, recreational values, and educational opportunities. In addition, its location along a major travel corridor (George Washington Memorial Parkway) to one of the most popular tourist destinations in the D.C. area (Mount Vernon) provides Dyke Marsh Preserve with opportunities to enhance the economic productivity and environmental education in the region.

Downloading data from the tide gage at Dyke Marsh.Since 1973 the National Park Service (NPS) has managed the Dyke Marsh Preserve (DMP). Previous to NPS supervision, portions of the emergent marsh at DMP were dredged for sand and gravel with resultant loss of approximately half the emergent wetlands (see aerial photograph series below). Restoration of emergent marsh to the dredged areas would enhance the ecosystem and economic services provided by the marsh, expand the extent and quality of a relatively rare wildlife habitat, and extend the aesthetic appeal of this urban/suburban wetland. However, ecological feasibility and logistical problems of such a restoration effort cannot be taken lightly. Towards this goal, we reviewed the available data on both the physical and biological components of the marsh and supplemented that information with new data on standing vegetation and seed banks, hydrochory, marsh elevation, water and soil chemistry, and tidal fluxes to describe current conditions and evaluate the potential for success and sustainability of a marsh restoration effort.

Starting in 2003, we determined the feasibility of restoring those portions of Dyke Marsh Preserve that were dredged, while maintaining the integrity and health of the existing marsh. If feasible, restoration could return much of the Preserve to historical conditions, enhancing wildlife habitat, recreation opportunities, and ecosystem services.

Aerial views of Dyke Marsh in 1937, 1954, and 1994. By 1940, the marsh was being dredged for sand and gravel. As a result, almost 200 acres of marshland were lost.

Samples were collected along the driftline and returned to AL for germination to help identify which seeds are washing up on shore.Current Work:

Funded under NSF grant DEB 0841394, our current research seeks to forecast the impact of global environmental change on freshwater marsh diversity, sediment deposition and erosion, and, hence, the maintenance of complex marsh surfaces. Our project integrates remote sensing of marsh surface elevations; extensive field observations on the interactions between elevation, sediment dynamics and marsh vegetation; and spatially explicit modeling to address three integrative questions: 1. What are the dominant environmental drivers that lead to localized sediment accretion and erosion events in freshwater marshes? 2. Are spatially aggregated species associations a historical imprint of past sediment accretion and erosion events, or are they simply a reflection of underlying environmental gradients? 3. How will water level change (sea level rise or groundwater withdrawal) coupled with changing sediment supply affect biodiversity and marsh surface evolution within freshwater marshes? This project advances biodiversity theory by highlighting the integral importance of spatial processes in stabilizing biodiversity. The research also advances the development of coupled geomorphic – ecological models of marsh surface evolution, which are still uncommon and do not explicitly consider marsh biocomplexity. The simultaneous consideration of biodiversity theory and geomorphology is a unique integration of two traditionally separate disciplines that should offer tremendous advances in both fields.

Results of the project are used to inform ongoing efforts to restore the study site and freshwater marshes. In addition, the project engages teachers and provides educational opportunities for high school, undergraduate and graduate students.

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Project PI:

Dr. Katia Engelhardt