National Capital Parks-East - Springs and Seeps

Seeps occur in most of the parks of National Capital Parks-East (NACE). In Piscataway and Fort Washington Parks, clay lenses layered between the geologic formations along the base and face of the Tertiary Slopelands influence the surface water patterns and account for seasonal seeps. These seeps spring from exposed clay banks in meadows or shallow soil in woods and seasonally discharge because of the changing water table depths. The substrates associated with these seeps, especially in meadows, are often dry and hard by mid-summer but are wet from increased rainfall and resultant groundwater rise by late summer. Plant species characteristic of these seeps include Common Horsetail (Equisetum arvense), Netted Chainfern (Woodwardia areolata), Slender Spikerush (Eleocharis tenuis var. tenuis), and Clearweed (Pilea fontana). Seeps also feed the acidic gravel bog at Oxon Run Parkway, the only site in NACE known to support species such as Southern Clubmoss (Lycopodiella appressa) and Bog Fern (Thelypteris simulata). Forested seeps are also the habitat of the Gray Petaltail Dragonfly, a state rare species present at NACE. As recently as 1988 a new species of invertebrate animal, the copepod, Acanthocyclops columbiensis, was found at a seep in a Fort Circle Park and at Oxon Cove Park.