IMPLICATIONS FOR RESTORATION

A general trend emerges from the multiproxy analyses of all the cores examined - increasing salinity during the 20th century. Although the timing and onset of increased salinity varies at the different core sites, there are no exceptions to this trend. In the nearshore sites, the increase in average salinity has been accompanied by an increase in variability of salinity. In contrast, the central Biscayne Bay sites have shown increasingly stable salinity over the last century, indicated in part by the influx of increasing numbers of marine species. These trends could be a result of a number of factors, including (1) rising sea level; (2) changes in the flow of freshwater into the bay either through surficial or groundwater processes; (3) changes in average rainfall or rates of evaporation; (4) changes in sedimentation rates; or (5) a combination of factors. The timing of changes at some of the near-shore sites suggests that both anthropogenic and natural factors are involved.

In addition to the general salinity trend for Biscayne Bay, the near-shore sites at Middle Key and north of Black Point have illustrated distinct, but site specific, changes in freshwater influx over time. Our data suggest that some sites we assumed had historic point-source inflow of freshwater did not. The wetlands cores (near Military Canal) also illustrate that sites in very close proximity to each other have historically been affected by very localized hydrologic regimes.

These results have significant implications for restoration planning. First, the recognition that Biscayne Bay appears to be evolving toward a more marine environment due to both natural and anthropogenic factors must be factored into the planning process. Second, generalized performance measures and targets for the near-shore and wetlands areas may not reflect the natural variability seen at these sites. Third, the nearshore environments are dramatically different from the mid-bay mudbanks, and have been for hundreds of years. Influx of freshwater into the bay appears to have a subtle or indirect effect on the benthic fauna of the mudbanks. Changes in flow during restoration may have little effect on the central bay mudbanks.

Examining decadal-centennial trends in a variety of habitats within the Biscayne Bay ecosystem provides a realistic means to set performance measures, predict system response to changes invoked by restoration, and to enlighten the public on what the natural system of the bay looked like.