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    Kenilworth Park & Aquatic Gardens

    District of Columbia

Park Case Study

Anacostia Park Case Study- Kenilworth Marsh

In the park, there is a 50 foot wide strip of wetland that has been relatively unchanged since the early 1900s and probably earlier. Total area is about an acre and a half. Water depths range at high tide from about two feet at one end to about six inches at the other. High and low tides differ by approximately one meter. At the deep water end, the marsh is dominated by broadleaf emergent plants. Grasses, hibiscus, cattails, and shrubs dominate the middle ground. At the high ground area and hummocky areas, pawpaw, turtlehead, ferns, alder, spice bush, viburnum species, blueberries, holly, river birch, and ash are common. Throughout the area, rice cut grass, wild rice,several other grasses, sedges, rushes, cattail, and emergent plants such as sagittaria, pickerel, and Tuckahoe are common.

Over 30 native species of plants are in this wetland, used by deer, muskrat, fox, opossum, raccoon, and a variety of resident and migratory song birds and waterfowl including wood duck. Turtlehead, spice bush, and pawpaw in this wetland provide larval food for three food specific butterflies. (Spice bush also grows in another area of the park.) The flowers in this wetland attract other butterflies and moths as well. Film on the water provides evidence of at least two kinds of bacterial activity. There is one significant invasive species (European water iris). Fresh water mussels have been found in the marsh and adjacent ponds. There has never been a study of the benthic community of the remnant marsh.

The man-made marsh is a product of a partnership that took shape in the early 1990s when the park partnered with the Corps of Engineers, DC Government, and other public and private partners on an ambitious program of “restoring” Anacostia wetlands that had been dredged in a 1930’s. Total area reconstructed was about 30 acres in a total wetland area of about 70 acres. There were two reasons for the project. One was to improve water quality flowing from urban areas of Maryland and Washington, DC through the park before it reached the Anacostia River. The other was to improve wildlife habitat.

Of the three constructed tidal marsh areas, one, a low marsh area, has a water depth of nearly three feet at high tide. It remains mostly nuphar.

A high marsh area was made with an initial flooding of about 4 inches. After ten years of vegetation build up, this area frequently floods only along a tidal “gut” or channel. The high marsh area was planted with hibiscus (semi- woody), rice cutgrass, lizard tail (herbaceous), and button bush (woody). An assortment of volunteer plants, some herbaceous, some woody, began growing even before the area was planted. In the first year after planting, the aggressive, non-native purple loosestrife (Lythrum salicaria) and phragmites, along with cattail, wild rice, several broad leaf herbaceous plants, spike rush, sedges, and woody species volunteered in the areas planted. Efforts were made to control the purple loosestrife. In the high marsh, rice cut grass shaded and overwhelmed many of the plantings due to its tendency to form mats. Fourteen species were found in the area after a year. After three years, rice cutgrass, cattails, biddens, and sagittaria (one of several broadleaf herbaceous plants) dominated. After ten years, rice cut grass, cattails, and pickerel weed dominate. The area remains plagued to some extent with loosestrife and phragmites.

A mid marsh area was made to be flooded to a depth of about two feet at high tide. The mid marsh area was planted with an assortment of broad leaf emergent flowering plants, sedges, and blue flag. In this mid marsh area, after a year there was more of a variety (20 species). Of these, about half were planted and half were volunteers. After three years, sedges, blue flag iris and sagittaria dominated. The area still has a good mix of wetland plants, some volunteer, and some planted.

Much of the restored marsh areas are populated by volunteer plants; some like purple loosestrife, phragmites, and cattail are of dubious wildlife value for most wildlife species. Toxicity of the soil was a concern in the restoration and remains a concern, but a study of the sediment done before the restoration showed the levels of pollutants in the soil did not suppress clam reproduction. (Phelps, 1994)

With the exception of mink, groundhogs, and some small species, wildlife roam the entire park and do not limit themselves to either the remnant or restored marsh, and are most often seen (accessibility probably being the reason) in areas that border trails and fields. Long billed marsh wrens, among other birds, beaver, fox, and deer have returned to the park. Some of these species may have been pushed out of developing areas around the park into the park as the last open land in the area.

The benthic or bottom dwelling life in the restored marsh continues to be restricted. Initially, only two species of segmented worms were found. After a year there were five different species found. The bulk of the bacteria activity in the park is still found in the remnant marsh and in pools outside the restoration areas.

After the restoration, aerial photos clearly showed a stream of clear water flowing from the wetland restoration area to the Anacostia River. Water quality varies through the year and depends to some extent on the river flow. Anoxic zones existed in both restored and remnant marsh areas in summer. However fish and other aquatic life continue to live in pools in both areas during low tide and come into the park with high tides. Sediments are building up in the restored and remnant marsh. Beaver are creating channels changing the tidal dynamics and water quality flowing to the Anacostia River in the restored marsh.

 

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