SHAPING SOUTH FLORIDA'S UNIQUE COASTAL ECOSYSTEMS: NATURAL AND ANTHROPOGENIC INFLUENCES

The coastal ecosystems of South Florida have been shaped by numerous forces throughout the Cenozoic, beginning with the buildup of a carbonate platform during the Paleocene and Eocene that resembled the Bahamas platform of today. This was followed by an influx of terrigenous sediment from the north, beginning in the Oligocene and continuing through the Pliocene. Rapid climatic changes and accompanying sea-level changes during the Pleistocene led to the development of a very complex subsurface stratigraphy, with interfingering facies from two coastlines. During the Holocene, sea-level rise has led to development of the coastal and freshwater wetlands that are typical of south Florida today, including freshwater marshes, cypress swamps, mangrove forests, and the mudflats and mangrove islands of the coastal bays.

Over the last century, south Florida has continued to be affected by natural forces (changing climatic patterns and rising sea-level), but it also has been profoundly altered by human activity. Construction of the Flagler Railroad and an extensive canal system, development of the Everglades Agricultural Area, and urbanization have changed the natural flow of water throughout the freshwater and estuarine systems of south Florida.

Paleoecologic analyses of faunal and floral assemblages from shallow, Pb-210-dated cores are providing data on the pre-1900 ecosystems. These data allow the recognition of natural cycles of change and provide information on the degree to which changes in the system can be attributed to anthropogenic activity. Molluscan data from Florida Bay have indicated: 1) a decline in water quality and/or an increase in the degree of salinity fluctuations over the last 50 years; 2) changes in salinity that do not correspond to changes in rainfall; and 3) fluctuations in seagrass epiphytes on an approximately 16-year cycle. These data, and additional paleoecologic and biochemical analyses, will provide land managers with the necessary data to make cost-effective and sustainable decisions on the restoration of south Florida's coastal ecosystems.