ORIGIN AND DYNAMICS OF NEARSHORE WETLANDS: CENTRAL GEORGIA BIGHT, USA

An understanding of the origin and dynamics of wetlands is fundamental to efficient and effective wetland management, conservation and restoration measures. The subject nearshore wetlands on St. Catherines Island, Georgia are located within 100 meters of an actively retreating marine shoreline. The new collection of undisturbed vibracores, geospatial analyses of historical maps and imagery, an evaluation of Late Holocene sea level, and a synthesis of historical hurricane data provide insights regarding the origin and dynamics of the nearshore wetlands. Sea level and radiometric data indicate that small-scale marine regressions provided the framework for the wetlands through the progradation of beach ridges, forming swales that were subsequently flooded during the overall trend of Late Holocene sea level rise. Beach Pond was transformed into a palustrine environment due to the emplacement of a washover fan attributed to the Great Sea Islands Hurricane of 1893, and shoreline retreat resulted in Beach Pond becoming an intertidal sand flat in May 2012. Flag Pond is an intertidal marsh that was formerly a palustrine wetland that underwent a transition to an intertidal wetland as the result of shoreline retreat and the “Storm of the Century” in the Spring of 1993. The long term stability of similar nearshore non-tidal freshwater environments along the Georgia Bight appears to be temporally limited by modern sea level rise and shoreline retreat. Because of their abundance, marginal marine freshwater wetlands like those along the Georgia Bight, play an important role in ecosystem conservation and carbon sequestration. The conversion from palustrine to intertidal conditions infers a change in the role of the wetlands with respect to carbon cycling. Whereas the palustrine wetlands typically serve as a net annual carbon sink, recent studies suggest that tidal wetlands serve as a net source of carbon to adjacent estuaries. However, the stability of these nearshore non-tidal freshwater environments appears to be temporally limited by modern sea level rise and shoreline retreat. Based on the current study, it is suggested that a shoreline model be developed to evaluate the timing of shoreline retreat, prior to investment in management, conservation, and/or restoration measures in similar nearshore wetlands.