HYDROLOGIC AND NUTRIENT CONDITIONS OF ESTUARINE LAKES IN THE FLORIDA EVERGLADES

Altered hydrologic conditions throughout the Florida Everglades have changed the relative importance of different nutrient pathways to the coastal estuaries. Brackish coastal groundwater discharge (CGD), driven by sea level rise and reduced freshwater input, has been shown to be enriched in total phosphorus, the limiting nutrient in the coastal Everglades. A major component of the Comprehensive Everglades Restoration Plan is to increase freshwater delivery to Taylor Slough and ultimately northeastern Florida Bay, in an effort to restore a salinity and nutrient regime conducive for the development of submerged aquatic vegetation. This study is being conducted in the estuarine lakes that connect to Florida Bay west of Taylor Slough. The lakes comprise two distinct drainage systems; the Alligator Creek system (ACS) and the McCormick Creek system (MCS). In order to understand the impacts of restoration efforts and natural seasonal dynamics in this region, current hydrologic conditions must be established. A possible hydraulic connectivity between southern Taylor Slough and the mangrove lakes region to the west via overland flow and/or groundwater flow may provide additional unforeseen benefits of current restoration efforts to improve the drastically diminished water quality in this region.

Preliminary data for this study suggests that the MCS to the east receives lower salinity groundwater than the ACS to the west. In addition, total phosphorus concentrations in the surface waters of the MCS (<1 µM) are far lower than those of the ACS (1 – 6 µM), suggesting a possible higher incidence of CGD in ACS. Surface water salinity varies seasonally in each lake, while groundwater salinity remains fairly constant. Groundwater salinity beneath each of the lakes in the ACS is consistently higher than surface water salinity, regardless of season. Further investigations within this project include the use of geochemical tracers to determine the groundwater – surface water interactions that drive the delivery of P to the mangrove lakes. This study will provide an understanding of the extent of which CGD is affecting the region, and how restoration efforts may change these conditions over time.