| Data on hydrogeology, soils and vegetation collected on the wetland-to-upland transition zone of the Great Dismal Swamp were used to characterize this zone, to analyze changes along the moisture/elevation gradient, and to select tentative wetland-upland boundaries based on these three parameters. Recharge-discharge relationships on the transects, hydraulic connection of the Tabb aquifer underlying the swamp with aquifers in formations further west, evapotranspiration, and precipitation were responsible for high water tables and water-table fluctuations encountered on all transects during the growing season. Transition zone vegetation was dominated by three facultative hydrophytes, Acer rubrum, Liquidambar styraciflua, and Nyssa sylvatica. On the basis of DECORANA ordination performed on consecutive 25-m increments, the increments were divided into three types: wetland (subdominants primarily obligate hydrophytes, facultative wetland or facultative species occurring at the wetter end of the moisture/elevation gradient); transitional wetland (subdominants primarily a mixture of facultative wetland, facultative and facultative upland species); and upland (subdominants primarily facultative, facultative upland or upland species). Water was within the root zone (0-30 centimeters below the ground surface) an average of 50-100 percent of the growing season for well sites classified wetland, 25-100 percent for most well sites classified transitional wetland and {dollar}<{dollar}25 percent for well sites classified upland. Soils were classified as hydric along almost the entire length of transects A, B, and C; more than half of transect D had nonhydric soils. Except on transect B, wetland boundaries determined on the basis of each parameter were different, but fairly close considering the length of the transects and certain assumptions made during the analysis. Elevation of the individual wetland-upland boundaries decreases from north-to-south along the 48-kilometer transition zone except at transect B. A method developed to determine wetland boundaries based on the 3 parameters has 3 alternatives for delineating boundaries and should result in greater precision in placement. |
