DETERMINING GROUNDWATER INPUTS INTO EVERGLADES COASTAL ESTUARINE LAKES USING HYDROLOGICAL AND GEOCHEMICAL BUDGET METHODS

Groundwater discharge can contribute water and constituents to estuarine areas at concentrations equal to or higher than surface water inflow. Estuarine lakes in the Alligator Creek and McCormick Creek watersheds along the coastal region of Everglades National Park have experienced a reduction in freshwater inflow due to a diversion of water from the upstream Greater Everglades watershed. Over the last century, increases in both salinity and phosphorus has been observed in the estuarine lakes coincident with upstream water diversion activities. Saltwater intrusion is known to occur in the aquifer beneath the lakes. The objective of this study is to quantify groundwater discharge to the estuarine lakes of Everglades National Park, which has not been previously determined. Hydrological and chemical water budgets were computed in daily, monthly, annual, and seasonal timesteps for seven years of data (2014-2020). Precipitation and estimated evapotranspiration were obtained from stations near the creek systems. Gage height, salinity, and surface water exchange were obtained from USGS monitoring stations in the creek systems. In-situ multiprobes in surface water monitoring casings and groundwater wells located in four lakes also provided salinity and lake stage data. Gage height data was applied as a change in mean daily gage height to calculate a more accurate lake storage value for daily timesteps. Daily discharge was applied as a daily sum to provide higher resolution data than the monthly sum of discharge. Preliminary estimates indicate that groundwater contributes between 0.65 m yr^-1 to 2.25 m yr^-1 to the estuarine lakes. Higher and fresher groundwater inflows were observed in the estuarine lake closest to active freshwater rehydration efforts. Groundwater recharge volumes will be explored to define how these relate to other water budget parameters, seasonality, and water deliveries into Everglades National Park. Trends and signals will be observed to describe conditions that lead to more significant groundwater recharge in the coastal estuarine lakes. The results of this investigation will provide important information on the effects of Everglades Restoration efforts on water quality in the coastal regions of Everglades National Park.