Salinity patterns of Florida Bay

The salinity of Florida Bay has undergone dramatic changes over the past century. Salinity values reached their most extreme, up to 70, in the late 1980s, concurrent with ecological changes in Florida Bay including a mass seagrass die-off. In this study, surface salinity was measured at approximately monthly intervals between 1998 and 2004. The 7-year data set was analyzed to quantify the effects of precipitation, runoff, evaporation, and climatic variability on salinity in Florida Bay. Overall mean Bay-wide salinity varied from a low of 24.2 just after the passing of Hurricane Irene in October 1999 to a high of 41.8 near the end of a drought period in July 2001. Bay-wide mean salinity exhibited dramatic decreases, up to −0.5 per day, whereas increases were slower, with a maximum rate of 0.1 per day. The freshwater budget for Florida Bay was slightly negative on an annual basis with significant positive monthly values observed during the peak of the rainy season (August through October) and significant negative monthly values observed during the peak of the dry season (March through May). This resulted in a minimum mean monthly Bay-wide salinity in January and a maximum monthly mean in July. Mean salinity for the overall Bay and for each of its four sub-regions could be predicted with reasonable accuracy utilizing a mass balance box model. There was no monotonic trend in salinity over this 7-year study; however, meteorological phenomena, such as tropical cyclones and El Nino-Southern Oscillation, dramatically altered the salinity patterns of Florida Bay on interannual time scales.