FRESHWATER DIATOM ASSEMBLAGES AND ECOLOGY/PALAEOECOLOGY OF THE OKEFENOKEE SWAMP/MARSH COMPLEX, SOUTHERN GEORGIA, U.S.A.

Abstract

Surface and subsurface peats of the Okefenokee Swamp in the southeastern United States contain low diversity diatom assemblages, composed largely of forms typical of peat-forming environments. Multivariate techniques, utilizing the algorithms EXTENDED CABFAC and FUZZY QMODEL (factor/cluster analyses), recognized five major diatom assemblages in the surface peats and the distribution of these correlates with surface flow patterns and hydrological input from the uplands. Streamflow regulates nutrient flux, and so it appears that the major control on diatom communities in the Okefenokee Swamp is local variation in trophic status. Stratigraphical studies reveal a recent history marked by alternating wet and dry conditions, with vegetational and diatom floral succession evident in some regions and relative ecological stability elsewhere. Minor ecological changes associated with increased human activity in the region, beginning late in the nineteenth century, are reflected by changes in the diatom communities. The construction of canals and logging trails provided increased hydrological exchange in previously hydrologically isolated areas, allowing an increase in nutrient input. Certain diatoms, most notably Melosira nygaardii, responded to enhanced flow conditions by colonizing some of these regions. Two new diatom species are proposed: Anomoeoneis paludigena sp. nov. and Pinnularia pogoii sp. nov.