WEEKI WACHEE GROUND-WATER BASIN REGIONAL STUDY USING δ18O AND δD STABLE ISOTOPE ANALYSIS

Our research applies stable isotope analysis to investigate surface water and groundwater drainage into karst formations in the Weeki Wachee Ground-water Basin in Hernando County, Florida. On the Sandhill Boy Scout Reservation particularly, surface water and groundwater resources are impacted by drainage through karst topography. This could limit residents’ water resources by the desiccation of wells, springs, lakes and sinkholes if excessive well pumping is present. As Floridan Aquifer levels drop, ground water shortages will become increasingly critical. Past studies using a fluorescent dye trace have not revealed connections between regional groundwater flow and surface water sources in the Weeki Wachee Ground-water Basin. This study utilizes rain water, surface water, and ground water concentration of δ¹⁸O and δD as isotopic tracers for isotopic analysis. The samples were analyzed to identify differences in the evaporated isotopic signature and develop a mixing model to illustrate interactions among water sources. Groundwater sampling was performed by Southwest Florida Water Management District (SWFWMD) using the Water Quality Monitoring Program Standard Operating Procedures (SOP). Samples were analyzed at the University of South Florida Stable Isotope Laboratory (USFSI). Data was calculated to create a mixing model and compared the δ¹⁸O and δD averages to Global Meteroic Water Line and Florida Local Meteroic Line. Results suggest that the area’s karst topography causes surface water to rapidly recharge the Floridan aquifer, indicated by the high percentage of surface water in groundwater sources and low percentage of surface water in surface water sources. In addition, the overall similarity of evaporated isotopic signatures of both surface water and groundwater samples exhibits nearly homogenous water sources in the area due to rapid recharge. Data did not reveal direct connections between regional groundwater flow and surface water sources; however, the data did provide some explanation of which areas in the Weeki Wachee Ground-Water Basin experience the most surface water recharge during the dry season.