Paleolimnological reconstruction of holocene environments in wetland ponds of the upper Atlantic Coastal Plain using siliceous microfossils

The series of climatic and anthropogenic events effectuating environmental change on the Atlantic Coastal Plain of the southeastern United States over the past several thousand years is poorly understood. This research examines the microfossil record in the sediments of depression wetlands of the upper Atlantic Coastal Plain in South Carolina to determine past hydrologic environments that occurred in the region during the Holocene. The study contains two components: (1) the quantification of the modern relationship of fossilizing organisms to environmental parameters, and (2) the use of these relationships to make inferences about past environmental conditions from fossil assemblages. Chapters 1, 2, and 3 are concerned with the former, or calibration, component and Chapter 4 reconstructs past environmental change in two local ponds.; The first chapter provides a taxonomic and ecological description of the diatoms that occur in Carolina bays and other isolated freshwater wetlands and ponds in South Carolina. The composition of the diatom flora is characteristic of other acidic systems and, because the Carolina bay flora is previously unexplored, contains several new taxa. Research presented in Chapter 2 finds diatom assemblages in the surface sediments of 75 basins on the upper Atlantic Coastal Plain to be strongly related to hydroperiod, a measure of pond permanence. Chapter 3 demonstrates that diatom assemblage composition is highly variable among extant microhabitats and attributes part of that variation to the susceptibility of the diatom substrate to drying. Several diatoms are identified as hydroperiod indicator taxa. Chapter 4 reconstructs past hydroperiods from diatom and other microfossil assemblages in two basins in western South Carolina. The record indicates that the basins were flooded during the early Holocene, were prone to frequent drying 1,000-2,000 yr B.P., and have functioned as temporary ponds typical of the modern environment for the past several centuries.; This study promotes the use of diatoms as drought indicators in closed basin wetlands. It provides evidence that conditions were appropriate during the early Holocene for the formation of Carolina bay depressions, and that subsequent climatic, anthropogenic and landscape-level events effectuated hydrologic change in basins of the upper Atlantic Coastal Plain.