Historical trends in salinity and substrate in central Florida Bay: A paleoecological reconstruction using modern analogue data

Understanding the natural spatial and temporal variability that exists with in an ecosystem is a critical component of efforts to restore systems to th eir natural state. Analysis of benthic foraminifers and molluscs from moder n monitoring sites within Florida Bay allows us to determine what environme ntal parameters control spatial and temporal variability of their assemblag es. Faunal assemblages associated with specific environmental parameters, i ncluding salinity and substrate, serve as proxies for an interpretation of paleoecologic data. The faunal record preserved in two shallow (< 2 m) core s in central Florida Bay (Russell Bank and Bob Alien Bank) provides a recor d of historical trends in environmental parameters for those sites. Analysi s of these two cores has revealed two distinct patterns of salinity change at these sites: 1) a long-term trend of slightly increasing average salinit y; and 2) a relatively rapid change to salinity fluctuations of greater fre quency and amplitude, beginning around the turn of the century and becoming most pronounced after 1940. The degree of variability in substrate types a t each locality limits interpretations of substrate trends to specific site s. A common sequence of change is present in the Russell Bank and Bob Allen Bank cores: from mixed grass and bare-sediment indicators at the bottom of the cores, to bare-sediment dwellers in the center, to a dominance of vege tative-cover indicators at the top of the cores. Changes in interpreted sal inity patterns around the turn of the century are consistent with the timin g of the construction of the Flagler Railroad from 1905 to 1912, and the Ta miami Trail and the canal and levee systems between 1915 and 1928. Beginnin g around 1940, the changes in the frequency and amplitude of salinity fluct uations may be related to changes in water management practices, meteorolog ic events (frequent hurricanes coupled with severe droughts in 1943 and 194 4), or a combination of factors. The correspondence of these changes in Flo rida Bay with changes in the terrestrial Everglades suggests factors affect ing the entire ecosystem are responsible for the salinity and substrate pat terns seen in Florida Bay.