Boston Harbor Islands National Recreation Area - Wetlands

Intertidal / Freshwater Wetland Habitats The US Fish Wildlife Service, through its National Wetlands Inventory Program, last published maps of the wetlands of the Boston Harbor Islands in 1995 (USFWS 1995a, 1995b). This mapping was based upon stereographic analysis of 1:58,000 scale color infra-red photography taken in 1986 and generally classified wetlands of greater than one acre in extent. These wetlands were classified according to the system developed by Cowardin et al. (1979). Table XX provides a summary of the general wetland types mapped by the National Wetlands Inventory for the Boston Harbor Islands national park area (USFWS 1995a, 1995b). Marine Intertidal Wetlands The National Wetlands Inventory maps indicate that marine intertidal wetlands are the predominant coastal wetland type found in both the Outer Harbor Islands (Great Brewster Island, Middle Brewster Island, Outer Brewster Island, Calf Island, Little Calf Island, and Green Island) and along the eastern exposures of Deer Island and Lovell Island. These habitats are exposed to the waves and currents of the open ocean (Massachusetts Bay) with the water regimes being determined primarily by the ebb and flow of the tides. Salinity in these habitats will exceed 30 parts per thousand and generally support typical marine biota (Cowardin et al., 1979).

The distribution of plants and animals within the marine intertidal wetlands primarily reflects differences in four factors: 1) the degree of exposure of the site to waves; 2) the composition and physiochemical nature of the substrate ; 3) the amplitude of the tides; and 4) latitude, which governs water temperature, the intensity and duration of solar radiation, and the presence or absence of ice (Cowardin et al., 1979). Classes of marine intertidal wetlands within the national park area include rocky shore, aquatic bed and unconsolidated marine intertidal wetlands (USFWS 1995a, 1995b). Estuarine Intertidal Wetlands Estuarine intertidal wetlands are the predominant wetland type in the shoreline habitats of the majority of the Inner Harbor, Quincy Bay and Hingham Harbor areas within the Boston Harbor Islands national park area. These include the shorelines of Bumpkin Island, Button Island, Gallops Island, Georges Island, Grape Island, Hangman Island, Long Island, Moon Island, Nut Island, Peddocks Island, Raccoon Island, Ragged Island, Rainsford Island, Sarah Island, Sheep Island, Slate Island, Spectacle Island, Thompson Island, and World's End, as well as the western shores of both Deer Island and Lovell Island (USFWS, 1995a, 1995b). Estuarine wetlands may also be found in low-lying areas adjacent to the shoreline which may be partially or fully enclosed by land, but have regular or sporadic access to tidally influenced harbor water. These habitats include low-lying regions on Thompson Island, Spectacle Island, Deer Island, Long Island, Moon Island, Peddocks Island, Sheep Island, World's End and Calf Island (USFWS, 1995a, 1995b). Salinity in estuarine intertidal wetlands are heavily influenced by freshwater dilution caused by the river systems discharging into Boston Harbor. Salinity in these habitats may fluctuate significantly, being influenced not only by freshwater input but also by winds and tidal factors, and in some cases by evaporation in those estuarine wetlands which are periodically cut off from the tidal cycle. Classes of estuarine intertidal wetlands within the national park area include unconsolidated, emergent, aquatic bed and rocky shore estuarine intertidal wetlands(USFWS 1995a, 1995b). A review of the general geomorphological, physical, and biological characteristics of the estuarine wetland resource habitat types found in the northeastern United States has recently been published by Roman et al., 2000.