POTENTIAL SEA LEVEL RISE EFFECTS ON THE ECOHYDROLOGY OF TIDAL FRESHWATER FORESTED WETLANDS

Tidal freshwater forested wetlands (TFFW) have important ecological, cultural, and historic components that stem from their unique hydrological characteristics. TFFW and upstream riparian zones are vulnerable to sea level rise. In this study we investigated the following aspects: (i) how, and to what extent, does the tidal freshwater stream influence the shallow groundwater within the riparian zone, and (ii) if vegetation community structure differs in riparian zones of tidal freshwater streams compared to adjacent non-tidal systems. To address these questions we collected hydrology and vegetation survey data in Huger Creek and its non-tidal tributary, Turkey Creek (USGS gage ID 02172035) in the lower Atlantic coastal plain on the Santee Experimental Forest near Cordesville, South Carolina. This stream forms the headwaters of the East Branch of the Cooper River, which ultimately discharges to the estuary of Charleston Harbor. A network of monitoring gages in Huger and Turkey creeks and water-table wells in the riparian wetlands provided water elevation time series data, and together with vegetation composition surveys in riparian zone plots, data were collected over an eighteen-month period. We will present our main results that (i) the water-table gradient is “upstream” and the tidal pulse affects the shallow ground water table and (ii) the forest community structure showed no significant relationship to tidal vs. non-tidal hydrodynamics in the riparian zones. These results emphasize the need to assess ecology and hydrology characteristics of tidal freshwater stream systems separately from non-tidal systems because of the tidal regulation of the water budget. Considering that rising sea levels may affect large areas of coastal zones with small topographic slope, existing TFFW systems may be inundated and it follows that upstream non-tidal zones would be soon affected by tides.