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
(202) 645-6601 |
|
