Effects of drought on the water-table dynamics of a southern Appalachian mountain floodplain and associated fen

Abstract

Annual and seasonal variations in precipitation have been shown to influence the hydrology of nontidal wetlands, including depth to water table. Water-table depth is assessed in wetlands for a variety of reasons, most notably for wetland delineations or determining the success of restoration projects. Many short-term assessment efforts probably occur during periods of abnormal precipitation and, as such, may not provide a thorough understanding of wetland hydrology. I have been evaluating water-table dynamics of a wetlands complex in western North Carolina for seven years in support of a wetlands restoration project. A series of water-table wells and piezometers were installed to determine the spatial and temporal patterns of the water table and vertical hydraulic gradient (VHG). For over three years, the area was classified as having conditions of moderate to severe drought. The drought lowered the average monthly water table by 26 cm in a mountain fen and 22 cm in the adjacent floodplain. The fen was a constant ground-water recharge area before the drought and a discharge area for three of 12 months during the drought. The drought also impacted a shallow, constant ground-water source to the fen on an adjacent hillslope. The impacts of the drought were greater during the active growing season, presumably due to increased evapotranspiration. The results support the need for long-term hydrologic assessment of wetlands and the need to relate wetland hydrology to annual, seasonal, and monthly precipitation patterns.