Abstract:
Considerable work has been conducted on the benthic communities of inland
aquatic systems and brackish water estuarine wetlands, but there remains a scarcity of
effort on freshwater tidal wetlands. This study characterized the benthic
macroinvertebrate communities of recently reconstructed urban freshwater tidal wetlands
along the Anacostia River in Washington, D.C. The focus of the study was Kingman
Marsh, which was reconstructed by the U.S. Army Corps of Engineers in 2000 using
Anacostia dredge material. Populations from this “new” marsh were compared to those
of the similar, but earlier reconstructed Kenilworth Marsh (1993) just one half mile
upstream, the relic reference Dueling Creek Marsh in the upper Anacostia estuary and the
outside reference Patuxent freshwater tidal marsh in an adjacent watershed. Benthic
macroinvertebrate organisms were collected using a range of techniques including the
Ekman bottom grab sampler, D-net and Hester-Dendy sampler. Samples were collected
at least seasonally from tidal channels, tidal mudflats, three vegetation/sediment zones
(low, middle and high marsh), and pools over a 3-year period (late 2001-2004). The
macroinvertebrate communities present at the marsh sites reflected levels of disturbance,
stress, and pollution, all of which are effects of urbanization in the watershed. There
were also similarities between older reconstructed wetlands and remnant wetlands
indicating an age factor in comparisons of macroinvertebrate communities.
Macroinvertebrate density was significantly greater at Kingman Marsh than Kenilworth
Marsh due to more numerous chironomids and oligochaetes. This may reflect an increase
in unvegetated sediments at Kingman (even at elevations above natural mudflat) due to
grazing pressure from over-abundant resident Canada geese. Unvegetated sediments
yielded greater macroinvertebrate abundance but lower richness than vegetated marsh
sites. Data collected from this study provides information on the extent to which benthic
macroinvertebrate communities can serve as indicators of a functional reconstructed
freshwater tidal marsh.
