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Florida manatees (Trichechus manatus latirostris) overwintering in the Ten Thousand Islands and western Everglades have no access to power plants or major artesian springs that provide warm-water refugia in other parts of Florida. Instead, hundreds of manatees aggregate at artificial canals, basins, and natural deep water sites that act as passive thermal refugia (PTR). Monitoring at two canal sites revealed temperature inverted haloclines, which provided warm salty bottom layers that generally remained above temperatures considered adverse for manatees. At the largest PTR, the warmer bottom layer disappeared unless significant salt stratification was maintained by upstream freshwater inflow over a persistent tidal wedge. A detailed threedimensional hydrology model showed that salinity stratification inhibited vertical convection induced by atmospheric cooling. Management or creation of temperature inverted haloclines may be a feasible and desirable option for resource managers to provide passive thermal refugia for manatees and other temperature sensitive aquatic species.

The SWIFT2D surface-water flow and transport code, which solves the St. Venant equations in two dimensions, was coupled with the SEAWAT variable-density groundwater code to represent hydrologic processes in coastal wetlands and adjacent estuaries. The integrated code was applied to the southern Everglades of Florida to quantify flow and salinity patterns and to evaluate effects of hydrologic processes. Results indicate that most surface water within Taylor Slough flows through Joe Bay and into Florida Bay through Trout Creek. Overtopping of the Buttonwood Embankment, a narrow but continuous ridge that separates the coastal wetlands from Florida Bay, does occur in response to tropical storms, but the net overflow is only 1.5 percent of creek discharge. The net leakage rate for the coastal wetland is about zero with nearly equal upward (17.1 cm/yr) and downward (17.4 cm/yr) rates. During the dry season, the coastal wetland increases in salinity to 30-35 practical salinity units but is flushed each year with the onset of the wet season. Model results demonstrate that surface-water/ground-water interactions, density-dependent flow, and wind affect flow and salinity patterns.

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A production well, called the south well, is located behind the white trailer in the middle of the photograph. This well and two other production wells pump groundwater from the sand and gravel aquifer to elevated storage tanks, such as the two shown in the background. In 1985, contaminants were detected in samples collected from the south well. To help understand groundwater flow in the underlying sand and gravel aquifer, the U.S. Geological Survey completed borehole geophysical logging at multiple locations, including the deepest monitoring well, WHF-05-OW-1D, shown here under the blue awning.