THE ROLE OF GROUNDWATER ON THE HYDROLOGY OF FORESTED WETLANDS: A MULTIPLE-SITE COMPARISON, U.S. ATLANTIC COASTAL PLAIN

Calculating the water budget of a wetland involves accurate measurement of net precipitation (P), evapotranspiration (ET), and runoff (R), yet usually the groundwater discharge or recharge component (G) can only be inferred from imbalances (residuals) in the water budget. We will present a comparison of three wetland sites in the Southeast U.S. using hydrogeologic data to determine the relative importance of groundwater on hydroperiod dynamics of forested wetlands in this region. Long-term deficits in the water budgets may reflect the important role of groundwater and also suggest that wetlands may not necessarily be hydraulically isolated as is often assumed.

The hydrology of wetlands (hydroperiod and water budget) is dependent not only on climate but also site-specific parameters such as landscape position, soils, and vegetation parameters. Measuring the hydroperiod (pond stage) to characterize wetland hydrology allows a quick comparison of different systems, yet it offers only a brief description of the complex interactions between surface water and groundwater and does little to explain the role of the hydrogeologic framework on wetland dynamics. Soils are usually well characterized at wetland sites, but information below 2 m depth is rarely collected. Landscape position (specifically, the topography) can be as important as climate in wetland systems. We have compared several years of hydroperiod and water budget data from three research sites of forested wetlands on the Coastal Plain of the Southeast U.S. (eastern North Carolina, south-central South Carolina, and north-central Florida). The long-term average annual P in this region is higher than annual ET, making the sites generally wet. Dynamic process-based hydrologic models were also used to interpret the pond stage and water table elevation data of the three different wetland sites.