Groundwater Management of an Atlantic Coastal Plain Forested Peatland:  The Great Dismal Swamp

Speiran, Gary

Groundwater Management of an Atlantic Coastal Plain Forested Peatland: The Great Dismal Swamp

Monday, June 6, 2016: 4:20 p.m.

Gary Speiran , U.S. Geological Survey, Henrico, VA

Frederic Wurster , The Great Dismal Swamp National Wildlife Refuge, U.S. Fish and Wildlife Service, Suffolk, VA

Classification of wetlands as surface water or groundwater-dominated ecosystems can affect their management, leading to mismanagement if misclassified. Wetlands commonly are misclassified as surface water–dominated ecosystems because of the abundance of standing and flowing surface water; however, groundwater commonly is the dominant water source.

The Great Dismal Swamp National Wildlife Refuge (a forested peatland in the Atlantic Coastal Plain of Virginia and North Carolina) could be classified as a surface water–dominated ecosystem because of a 144-mile ditch network and small streams that flow across the Suffolk Scarp into the swamp; however, the swamp actually is a groundwater-dominated ecosystem. Groundwater is derived from upland flow from west of the scarp that discharges into the swamp at the base of the scarp and recharge to the surficial aquifer by direct precipitation across the swamp. The surficial aquifer consists primarily of peat that can have a thickness as great as 15 feet. Porosity and permeability of the peat, however, decrease abruptly below a depth of 1.5 to 2 feet so that storage and transport of most groundwater typically is limited to the upper peat. Because the water-table depth typically is less than 3 feet and the upper peat is permeable, recharge is rapid. Groundwater flows and discharges along two pathways: (1) discharge to the atmosphere as evapotranspiration by the forest vegetation, and (2) lateral flow and discharge to the ditches. Discharge to ditches historically has created drier than natural conditions across the swamp, altering forest-species composition, increasing the risk of wildfire, and causing decomposition of peat to release carbon dioxide. To manage the swamp as a groundwater-dominated ecosystem, the U.S. Fish and Wildlife Service is installing and managing water-control structures on the ditches to maintain groundwater levels.

Gary Speiran, U.S. Geological Survey, Henrico, VA

Gary Speiran has conducted studies of the hydrology and chemistry of a variety of hydrologic systems including streams, lakes, shallow and deep groundwater, and wetlands. Recently, he studied the groundwater chemistry of riparian forest buffers. His current studies include the effects of hydrology and water-chemistry on wetland forest ecosystems and carbon budgets in the Great Dismal Swamp and the effects of sea-level rise on groundwater levels and chemistry as they affect ecosystems and archaeological and cultural resources of Jamestown Island, Virginia.

Frederic Wurster, The Great Dismal Swamp National Wildlife Refuge, U.S. Fish and Wildlife Service, Suffolk, VA

Frederic Wurster since 2010 has served as the staff hydrologist for the Great Dismal Swamp National Wildlife Refuge and the U.S. Fish and Wildlife Service Northeast Region. He has studied the hydrology of the refuge and coupled knowledge from this effort with the knowledge from other research to manage the water across the refuge. Wurster helps other refuges across the region address hydrologic issues.