Physiochemical Environment
- The Great Dismal Swamp lies in the Atlantic Coastal Plain and is made up of 111, 203 acres. Three physiographic zones comprise the Great Dismal Swamp and they are Lake Drummond, the forested wetland, and transition zone. The Great Dismal Swamp National Wildlife Refuge (NWF) is located between both North Carolina and Virginia with gentle slopes from west to east (Figure 3) (FWS, 2006).
Geomorphology
- The Great Dismal Swamp is about 20 by 50 km in size, running from north to south. The swamp slopes east from the base of the Suffolk scarp and north of U.S. Highway 58. The Great Dismal Swamp is governed by the Tabb Formation, a key component of the geologic formations during Pleistocene age. The Great Dismal Swamp is formed from four geologic formations and they include the Yorktown Formation, the Norfolk Formation, the Lincoln Bridge Formation and the Sandbridge Formation.
- The Yorktown Formation, is the oldest formations and is comprised of impermeable clay that hinders water movement into the permeable basal sands of the Tabb Formation, where an artesian head in the Tabb aquifer is produced (Carter et al., 1994). The Norfolk Formation influenced the hydrology of the swamp and played a pivotal role with the Great Dismal Swamp NWF's water budget. The groundwater that would upwell into the swamp was inputted directly by the Norfolk Formation. Majority of the groundwater got into the swamp through this formation (FWS, 2006). Read More
Climate
- Climate in the Great Dismal Swamp is controlled by the Atlantic Ocean, Chesapeake Bay, and Albemarle Sound. The climate of the Great Dismal Swamp is humid-subtropical, with long humid summers and mild winters. The average temperature is 60ﹾ F and rainfall is scattered throughout the year where the average precipitation is 45.74 in Virginia and yearly snowfall is about 8.8in. The Great Dismal Swamp experiences northwesterly winds during the cold seasons and southwesterly winds during the warm seasons (FWS, 2006). Oxygen availability is low and the pH in Lake Drummond is usually between 4-5 (Wilson, 2001).
- The Great Dismal Swamp has both organic soils and mineral soils, but organic soils dominate the area.Overall the organic soils are black fined-grained and vastly composed of muddy peat. They are known to be poor drainers and high in acidity, where permeability depends on the composition of the subsoil (FWS, 2006). Fire and drainage causes organic soil loss within the Great Dismal Swamp, where the soils become granular and will not become wet under flooding conditions. In other areas, the water gets impounded in the swamp and peat can build up. The variation between dry and saturated periods is what creates this varied soil complex in the swamp (FWS, 2006).
- The dominant biogeochemical cycle in the Great Dismal Swamp is the carbon cycle. Logs and stumps get buried and are decomposed into organic matter, which serves a source of carbon dioxide and is held up in the peat. As mentioned before when the Great Dismal Swamp receives water, especially from precipitation, nutrients in the form of ammonium can enter the swamp. Nitrate and orthophosphate can also enter the swamp from uphill agricultural runoff as sheetflow when it rains (FWS, 2006).