Abstract
A distinct change in coastal geomorphology exists in Southwest Florida between the Ten Thousand Islands (TTl) and the Everglades Estuarine Tract (EET). It has been documented that the geomorphology of the TTl is the result of vermetiform gastropods and the American oyster, Crassostrea virginica, producing loci of increased sedimentation to form intertidal reef structures that provide substrate for red mangrove settlement. This succession produces mangrove islands typical of the TTl, with a morphology that mimics that of the relict oyster reefs upon which they formed. These reefs define the extent of a network of inner bays from the Gulf of Mexico, which together compose the TTl geomorphology. South of Lopez River this geomorphology is replaced by a series of large landmasses separated by river channels connecting a similar interior bay complex to the Gulf of Mexico. Because the geomorphology of the TTl has been successfully tied to Holocene coastal processes and the presence of reef-building mollusks. the shift in coastal geomorphology to that of the EET is likely to be indicative of a coastal response to Holocene sea- level rise and distribution to reef-building mollusks unique to the EET. To quantify the distribution of extant reef-building organisms within the study area, oyster reefs within seven estuaries were mapped and a spatial analysis was preformed. Furthermore, the presence of oysters encrusting fringing mangrove prop roots was mapped to determine whether apparent trends in oyster reef distribution were the result of water quality or substrate limitation. The spatial analysis was conducted by calculating the total area of oyster reefs within five quadrants located along the estuarine axis within the Chatham, Lostmans, and Broad Rivers. These data were then compared to the results of Savarese et al. (2004) which used similar techniques to quantify the distribution of oyster reefs within Blackwater Bay. Pumpkin Bay, raka Union Bay, and Fakahatchee Bay of the TTI. Results from the comparison show that oyster reefs are relatively well distributed throughout the TTl, while the distribution of oyster reefs within the estuaries composing the EET are restricted to the mouths of these rivers. This is likely the result of regional differences in watersheds producing distinct water quality in the EET and TTl. In order to document historic coastal processes and predict future responses of coastal processes to accelerated sea-level rise (SLR) associated with global warming, a three fronted approach was taken. To document the regional stratigraphy live sediment core transects. each containing 4-6 cores, were completed from the Fakahatchee estuary (TTl), Chatham River (transition region). Lostmans River (EET). Broad River (EET). and the inner bays of the EET. The stratigraphy of these estuaries depicts a transition from an environmental succession typical of the TTl containing a transgressive stratigraphy capped by a regressive sequence to that of the EET. The EET stratigraphy is exclusively transgressive in the inner bays depicting a transition from fresh and intertidal wetlands to the extant inner bays. with any regressive sequence limited to the mouths of Chatham. Lostmans. and Broad Rivers. To identify a possible mechanism tor the formation of the EET inner bays aerial imagery from 1940 and 2006 was compared to calculate changes in the area of tidal ponds in five quadrants surrounding the inner bay complex of both the EET and TTl using ArcGIS software. These data suggest that increased rates of SLR are accompanied by the expansion of tidal ponds causing the degradation of coastal wetlands. These results, coupled with the stratigraphy of the EET, suggest the regional geomorphology is the result of Holocene SLR promoting the expansion and coalescence of tidal ponds within a coastal wetland ecotone leading to the EET inner bay complex.