APPLICATION OF HOLOCENE PALEO-SALINITY ESTIMATES TO EVERGLADES RESTORATION PERFORMANCE MEASURES

Restoration of coastal ecosystems often depends on balancing the supply of freshwater with the influx of marine water – a problem that is being exacerbated by increasing rates of sea-level rise. In South Florida, the Everglades ecosystem restoration effort is focused on restoring more natural hydrologic function to Everglades National Park (ENP), while balancing competing demands for freshwater with inundation of coastal systems as sea level rises over the next century. The goal is to re-establish pre-water-management hydrology (~1910 CE) and restore the system’s natural resilience in the face of predicted changes over the next century. Comparison of living mollusks to assemblages found in radiometrically-dated sediment cores from the estuaries is the first step in developing estimates of past salinity in the estuaries, and flow and stage in the wetlands of ENP. Here we use the cumulative weighted percent method (CWP) to calculate an average salinity value for each sample by multiplying the average salinity, derived from field observations of living species, by the percent abundance of each species in a given sample, then dividing by 100. Near-shore or basin correction factors can be applied, depending on location of a core, to account for wide salinity tolerances of euryhaline species. To test the CWP method, we collected modern samples from locations with near-continuous instrumental records of salinity, applied the CWP method to estimate salinity, and compared it to the observed salinity. Our estimates came within 2 practical salinity units (psu) of estimating the observed salinity. To date, the CWP method has been applied to five cores from different basins in Florida Bay (ENP), and the results indicate that salinity averaged 7 psu less around 1900 CE, prior to alteration of natural flow, compared to observed salinity from ~1990-2009 CE. To apply these results to resource management needs, the circa 1900 CE paleosalinity estimates are used in linear regression equations developed from observed salinity, flow and stage relationships. These equations allow us to estimate past salinity in un-sampled regions of the bay, and flow and stage in the wetlands. The results are being used by resource managers to set salinity targets and performance measures for restoration.