PALEOECOLOGICAL, BIOCHEMICAL, AND GEOCHEMICAL ANALYSES OF ESTUARINE SEDIMENT CORES: PIECES IN THE SOUTH FLORIDA ECOSYSTEM RESTORATION PUZZLE

The primary goal of the South Florida Ecosystem Restoration Task Force is to restore the natural timing, quantity, quality, and distribution of freshwater in the ecosystem. In Biscayne Bay and Florida Bay, this goal translates to restoring freshwater flow and seasonal salinity patterns that existed prior to the construction of canals and water control structures. Accomplishing these management goals requires reconstruction and analysis of salinity patterns over centennial time scales to determine the natural range in variation of salinity for different sections of the bays. Other long-term factors such as sea-level rise and climate change that may affect the ecosystem also need to be considered. Understanding natural cycles of change and long-term natural trends is essential for sustainable and cost-effective restoration.

Detailed multidisciplinary analyses of sediment cores collected in Florida Bay and Biscayne Bay since 1995 are providing information on the history of the ecosystem that is allowing land managers to set performance measures and targets for restoration. Our significant findings in Florida Bay to date include the following. 1) We have determined that salinity is more strongly correlated to rainfall than to water-management practices or any other single factor (in agreement with findings of Swart et al., 1999, Alvarez-Zarikian et al., 2001, and Nelson et al., 2002). 2) Anthropogenic influences play a secondary, although still very important, role in determining salinity for Florida Bay overall, but on a site-specific basis, anthropogenic influences may be the predominant driver. 3) Declines in species diversity and increases in the predominance of salinity tolerant species have occurred since the 1980’s in several benthic invertebrate groups. In Central and Southern Biscayne Bay, we have found the following. 1) The salinity of central Biscayne Bay has become increasingly marine and increasingly stable over the last 100 years. 2) Card Bank in southern Biscayne Bay has experienced relatively large swings in salinity over multidecadal and centennial time scales, compared to central Biscayne Bay, but marine influence at the site has increased over the last century.