Influence of net freshwater supply on salinity in Florida Bay

An annual water budget for Florida Bay, the large, seasonally hypersaline e stuary in the Everglades National Park, was constructed using physically ba sed models and long-term (31 years) data on salinity, hydrology, and climat e. Effects of seasonal and interannual variations of the net freshwater sup ply (runoff plus rainfall minus evaporation) on salinity variation within t he bay were also examined. Particular attention was paid to the effects of runoff, which are the focus of ambitious plans to restore and conserve the Florida Bay ecosystem. From 1965 to 1995 the annual runoff from the Evergla des into the bay was less than one tenth of the annual direct rainfall onto the bay, while estimated annual evaporation slightly exceeded annual rainf all. The average net freshwater supply to the bay over a year was thus appr oximately zero, and interannual variations in salinity appeared to be affec ted primarily by interannual fluctuations in rainfall. At the annual scale, runoff apparently had little effect on the bay as a whole during this peri od. On a seasonal basis, variations in rainfall, evaporation, and runoff we re not in phase, and the net freshwater supply to the bay varied between po sitive and negative values, contributing to a strong seasonal pattern in sa linity, especially in regions of the bay relatively isolated from exchanges with the Gulf of Mexico and Atlantic Ocean. Changes in runoff could have a greater effect on salinity in the bay if the seasonal patterns of rainfall and evaporation and the timing of the runoff are considered. One model was also used to simulate spatial and temporal patterns of salinity responses expected to result from changes in net freshwater supply. Simulations in wh ich runoff was increased by a factor of 2 (but with no change in spatial pa ttern) indicated that increased runoff will lower salinity values in easter n Florida Bay, increase the variability of salinity in the South Region, bu t have little effect on salinity in the Central and West Regions.