Hydrologic and Water-Quality Factors Affecting Habitat Restoration and Management of the Great Dismal Swamp

Problem and Implications

The Great Dismal Swamp National Wildlife Refuge was established by Congress in 1974 to preserve 110,200 acres of unique, seasonally-flooded, wetland habitats threatened by urban development in the Hampton Roads area of southeastern Virginia and by agricultural activities in northeastern North Carolina.

The U.S. Fish and Wildlife Service (the Service) manages the refuge to maintain these habitats. The refuge is dissected by an extensive network of access roads and ditches constructed since 1763 to drain the wetlands to facilitate logging them. This network has profoundly altered the hydrology throughout the refuge causing drier conditions and otherwise changing the characteristics of many of these habitats. One of the main changes has been the invasion of plant species not normally present, primarily red maple (Acer rubrum). Water-control structures on the ditches can be used to control the flow of water across the refuge and manage the wetlands to restore, maintain, and preserve the desired habitats. Pocosins are one of the types of habitats and are located southeast of Lake Drummond in “the Blocks.” The U.S. Geological Survey (USGS), Virginia Water Science Center, in cooperation with the U.S. Fish and Wildlife Service and the North Carolina Division of Parks and Recreation are investigating the relations between water levels in the ditches and groundwater levels in the pocosins to help develop strategies for managing these habitats.

Objectives

The objectives of this study are to identify 1) the relations between water levels in the ditches and groundwater levels near the ditches and in the interior of the Blocks, 2) possible relations between groundwater levels and tree growth rates, and 3) current nutrient chemistry and possible nutrient transport pathways in these wetlands.

Relevance and Benefits

This project is a part of USGS efforts to assist other Department of the Interior agencies address management issues on Department lands. By better understanding the relations between hydrology and wetland habitats, the Service can better restore, manage, and preserve habitats critical to various species. 

Approach

Water levels and quality are being measured in ditches surrounding Block C1 and in wells in 17 clusters across the block. Precipitation amounts are being measured at selected sites. Data are being transmitted “Realtime” and posted on the Science Center web page. Cores from trees near selected well clusters will be analyzed to determine variations in growth related to potential stresses. Water samples are being collected from selected wells and wetland sites and analyzed for a combination of field-determined characteristics and concentrations of nutrients, major ions, and isotopes of various constituents.