Water: Nonpoint Source Success Stories
District of Columbia
Reviving the Anacostia -
Freshwater Tidal Marsh Restoration
The decline of the Anacostia River, one of the nation's most threatened rivers, is a familiar tale. To make way for urban growth, its freshwater tidal marshes were filled, its meanders straightened, and its banks diked and walled. Eventually the watershed was paved and piped, leaving the river vulnerable to high nutrient inputs from combined sewer outfalls and excessive sedimentation from eroding streambanks.
Historically, expansive tidal freshwater marshes had helped buffer the river from the urban environment, but population pressures soon overcame the wetlands' natural ability to process and trap excessive nutrients and sediments. Dredging operations to deepen the river channel and the threat of illness from sewage in the marshes led to the diking and filling of most of the Anacostia's unique wetlands.
The Kenilworth Marsh, which is connected to the Anacostia River in northeast Washington, D.C., is one of the last unfilled marshes in an area that once was dominated by tidal wetlands. This marsh, and the surrounding Kenilworth Aquatic Gardens, is managed by the U.S. National Park Service, which is now in the process of restoring it. The goal is to restore a portion of the emergent tidal wetlands that once characterized the Anacostia River.
The National Park Service sees the Kenilworth's restoration as one in a series of steps to save the Anacostia from high nutrient and sediment loadings, while simultaneously expanding the habitat of native species a function of the marshes that all but disappeared during the last century.
Opportunity to begin the Kenilworth Marsh restoration coincided with the U.S. Army Corps of Engineers' mandated dredging of the Anacostia River. A lack of suitable upland disposal sites and the National Park Service's longstanding intention to restore the marsh lead to a proposal for an innovative use of the dredge material. The subsequent filling of the marsh mud flats with the dredged river material created favorable conditions for emergent macrophyte growth. The project had begun.
Preliminary tests were conducted with cells of different macrophyte species grown under varying degrees of tidal inundation. These tests determined that substrate elevation and resulting tidal inundation were the limiting factors in emergent vegetative growth.
A partnership of many agencies
The Kenilworth project involved several federal and local agencies. The Army Corps of Engineers did the primary construction work with the National Park Service as the lead agency for planning and coordination. The District of Columbia's Water Resource Management Division, the Metropolitan Washington Council of Governments, and the Interstate Commission on the Potomac River Basin were among the local agencies consulted. The Army Corps of Engineers provided the funds to construct the marsh. The reconstruction and revegetation of Kenilworth was completed in July 1993. The Kenilworth Marsh Monitoring Committee, a workgroup and advisory committee, then planned and initiated a detailed physical, chemical, and biological monitoring program to track the development of the new marsh.
The District of Columbia uses a 319 grant to monitor the restored marsh. Its findings contribute to the compilation of an overall database on the evolving, essentially new, wetland ecosystem. The aquatic biological monitoring design used by the District can also be used to gather baseline data on areas targeted for future wetlands restoration. The first season after the replanting saw a dense greening of the major areas. The seed bank in the fill sediments contributed greatly to this rapid growth, and even eliminated the planted species in some areas. Growth in the remaining barren areas occurred in the second year of the project.
Studies of the surface sediment found the sediments clean after the filling and planting operations. Nutrient studies and surveys of birds and various aquatic communities, for example, fish, plankton, benthic, and macroinvertebrate communities, are ongoing, multiyear efforts. Monitoring the restored Kenilworth Marsh is expected to be a five-year process that will afford valuable insights into the early successional stages of large-scale wetland reconstructions.
Findings from the Kenilworth Marsh will help other partnerships develop successful wetland restoration projects on the Anacostia River. At this time, several such projects are in the planning and implementation stages. These new restoration projects have already benefited from the Kenilworth data, and it is believed that the Kenilworth experience will lead to more accurate and less costly restorations.
|CONTACT: Sheila A. Besse
District of Columbia Department of Consumer and Regulatory Affairs