PALYNOLOGICAL STUDIES REVEAL HOLOCENE CLIMATE CHANGES IN A FORESTED FLOOD PLAIN WETLAND, SAVANNAH RIVER VALLEY, SOUTH CAROLINA (USA)

Forested wetland sediments can record many aspects of Holocene climate variability, for example local and regional hydrology. On the Atlantic Coastal Plain of the southeastern United States, a 15 km long and 0.2 to 3.2 km wide group of vegetated eolian dunes is present within the valley of the Savannah River approximately 60 km inland from the coast. The dunes are parabolic and were active during the last glacial maximum. The dunes now are stabilized by xeric sand community vegetation dominated by Pinus, whereas much of the rest of the valley is stabilized by alluvial wetland community vegetation dominated by Nyssa and Taxodium. Sediment cores collected in the interdune areas document at least 235 cm of post-dune sediment that consists of grayish-black sand, overlain by black silty sand, overlain by brown to gray clay.

Pollen assemblages from a core collected at one of these interdune sites reveal vegetation responses to changes in hydrology and climate during the Holocene. In this core, the basal grayish-black sand (233-204 cm) is dominated by Quercus, Poaceae, Asteraceae, and Artemisia pollen, which is consistent with regionally dry conditions. Nymphaea and Myriophyllum pollen also are present, indicating locally wet conditions with standing water. The silty sand (204-183 cm) and overlying dark gray clay (183-154 cm) are dominated by Nyssa pollen (approximately 30% of the assemblage), which is characteristic of seasonal flowing water. A piece of wood within this clay at 183-180 cm yielded a radiocarbon age of 5035 +/-25 years before present (BP), which is equivalent to 5738-5903 calibrated years BP. From 154-92 cm, the core consists of clay containing pollen assemblages dominated by Pinus and Nyssa. From 92-70 cm, the core consists of clay containing abundant monolete ferns spores and decreased abundances of Pinus and Nyssa pollen. From 70-0 cm, the core consists of clay containing increased abundances of Pinus, Nyssa, Ulmus, and Ambrosia pollen (indicative of post-colonial land clearance).