GEOMORPHIC INVESTIGATIONS FOR A CAROLINA BAY WETLAND RESTORATION PROJECT

Carolina Bays are elliptical depressions common on the Atlantic Coastal Plain. Most of the larger of these features were wetlands before settlement (some are lakes), and many have been ditched and drained. Given their location low in a landscape with high water tables, with a ditch system that may only be partially successful at removing excess water, there is an interest in restoring some of these former wetlands. The 300 ha Juniper Bay is one of these Carolina Bays, located in Lumberton County, North Carolina (N 34° 30’ 00’, W 79° 01’ 18”). It is being restored for wetland mitigation credits to balance future highway projects in the county. Successful wetland restoration depends on an understanding of the geomorphic and hydrologic factors that determine the potential for achieving project goals. We have collected cores to 7.5 or 15 meters in and outside the bay and our understanding has been improved by other studies, including GPR (ground penetrating radar) and EMI (electromagnetic inductance). Large numbers of Carolina Bays and their shared orientation has inspired many hypotheses for their formation. Our stratigraphic and geophysical investigations support the hypothesis that these features evolved over time, under the influence of a series of natural events, driven by changes in climate and prevailing wind directions. Cores and subsurface features suggest sandy sediment deposition on an incised landscape that had formed on finer textured sediments, with incision possibly driven by changes in sea level. Basins were excavated in the sandy sediments and have filled in over time. Bay shape probably was determined by prevailing wind direction and water depth in the bay during wetter periods. Larger bays increased in size by capturing smaller basins by a process analogous to stream capture. Radiocarbon ages that we obtained point to several periods of surface stability and soil formation (and thus lower water levels) that were followed by influxes of new sediment. The last two events occurred during the Holocene, and other ages are from before 30,000 radiocarbon years before present. The bays may not fill as a simple additive process. Periods of erosion may complicate recreating the entire history of the bay.