Evolution of a freshwater barrier-island marsh in coastal Georgia, USA

Beach Pond is a freshwater pond and marsh, located approximately 50-100 m f rom the beach scarp in the mid-southern portion of St. Catherines Island, L iberty County, Georgia (31 degrees 37'N latitude, 81 degrees 09'W longitude ). A 4.5-m sediment core was obtained from the pond in an effort to reconst ruct the paleoecology of the site. The sediments (sand, clay, and peat) are Holocene age (<10,000 years). Gross sedimentological characteristics of th e core suggest cyclic depositional trends. The modern vegetation of Beach P ond is dominated by Pluchea and other composites, Typha, Cyperaceae, and Po aceae. The palynology of the core reveals dynamic changes in depositional e nvironments and plant communities during sediment accumulation. Sediments f rom the lower portion of the core were derived from nearshore marine enviro nments and probably represent accumulation in a shallow lagoon; these are c haracterized by the abundant pollen of Pinus and a large percentage of brok en Pinus pollen grains. A piece of wood recovered from the uppermost lagoon al sediments yielded a radiocarbon date (AMS) of 1210 +/- 40 BP. These sedi ments are overlain by tidal-flat-derived sediments, which are overlain by a thin peat layer derived from an interdunal swale community dominated by My rica. A return to brackish marsh conditions then occurred, as indicated by the presence of Limonium, Cheno-Am type (e.g., Salicornia), and abundant Po aceae pollen. The modern freshwater pond plant community became established as the salinity decreased; this is indicated by the abundance of freshwate r plant taxa (i.e., Azolla, Typha, Cyperaceae). Sea-level fluctuation, eros ion, storm overwash, and anthropogenic factors (i.e., road building, water- well drilling) have all influenced the development of past and modern plant communities by altering the hydrology and salinity of the site.