ABSTRACT TITLE: INVESTIGATION OF GROUNDWATER-SURFACE WATER INTERACTION IN A SOUTH FLORIDA ESTUARY: SHARK RIVER SLOUGH

South Florida’s freshwater wetlands are susceptible to stress due to saltwater intrusion as more saline water pushes further inland with sea level rise. Shark River Slough is the largest waterway draining the freshwater portion of the Everglades into the Gulf of Mexico. Near the Gulf of Mexico, Shark River Slough is tidally influenced with saltwater intrusion occurring in the underlying limestone bedrock. The objective of this investigation was to determine how the surface water in the river interacts with the underlying brackish groundwater. The specific site investigated, SH2, is located in the mangrove ecotone and contains shallow wells drilled by the USGS in the peat (~.7m deep) and limestone bedrock (~2.5 m deep). Within these wells are pressure transducers placed by the Florida Coastal Everglades-Long Term Ecological Research project. Those transducers, along with data from the USGS EDEN network, were used to establish long term water level and salinity trends(Aug 2016-Jun 2018). Short term data collected from June 5-19, 2018 included water quality measurements from YSI exo2 sondes. Data analysis proved that all three water sources (river, peat groundwater, bedrock groundwater) are affected primarily by tides and rainfall in the short term. Long term changes are due to seasonal variations in temperature and cumulative rainfall. Water interactions occur on a seasonal basis with density inversion driving the interaction. Water quality measurements were only taken in the river and bedrock well, with salinity in the peat well influenced by saltwater upconing caused by rapid pumping of the well prior to sonde deployment. In conclusion, relative isolation amongst the various water types investigated (river, peat groundwater, bedrock groundwater) was observed in the short term data, but during dryer, colder parts of the year, density differences caused greater variability in salinity and temperature conditions in both the peat and bedrock groundwater.