ON FLORIDA BAY HYPERSALINITY AND WATER EXCHANGE

摘要

Florida Bay is made up of a collection of shallow basins separated by mud banks and mangrove islands situated between the Florida mainland and the Florida Keys. The bay is located downstream of the Everglades discharge that has been altered over the past century due to South Florida land use practices, leading to reduced water delivery to Florida Bay and elevated salinities. The reduced freshwater flow has had the strongest impacts in the north-central region of the bay, in the vicinity of Whipray basin (WB), where extreme hypersalinity can develop along with degradation of water quality and seagrass die-off. We use direct measurement of water exchange between Whipray and surrounding regions for dry and wet seasons of 2001 together with detailed salinity surveys, sea level measurements, and freshwater flux estimates to evaluate water and salt balances, and to estimate basin water renewal rates and residence times. Water renewal of WB is strongly regulated by local wind forcing. Winds toward the east from the passage of cold fronts during the winter/spring dry season resulted in a mean eastward flow through Whipray of 11 m~3 s~(-1), with inflows over the wide western mud banks, and outflows through the eastern and southern channels. Conversely, winds toward the southwest and west typical of the summer/fall wet season produced a mean throughflow of 3 m~3 s~(-1), with inflows through the eastern channels and outflows over the western banks. The time required for complete renewal of WB waters is estimated at 6-12 mo. Water balances are used to estimate a weak seasonal average groundwater input to Whipray of 1.7 m~3s~(-1) during the dry season and a negative groundwater flow or downwelling of -4.7 m~3s~(-1) for the wet season. Hypersalinity development was found to be caused by the combination of reduced freshwater inputs during the dry season combined with weak basin water renewal rates. Hypersalinity development could be greatly reduced by diversion of freshwater to WB via McCor-mick Creek during dry seasons.