GEOCHEMICAL CHANGES IN GROUNDWATER SEEN FOLLOWING A LAKE-DRAINING SINKHOLE EVENT IN NORTH FLORIDA, USA

The karst environments of Florida experience rapid groundwater-surface water interactions through surface water flow through sinkholes. A particular case highlighting this process is a lake dry-down event, in which a lake periodically drains into a karst aquifer through sinkholes within the lakebed. These events have been recorded throughout Florida, but are particularly common within the lakes surrounding Tallahassee, with 11 dry-downs having occurred in three different lakes over the past five years. With this rapid influx of surface water into the karst aquifer, there are questions concerning the impacts of these events on groundwater geochemistry. This research examines the chemical impacts of multiple dry-downs of Lake Jackson, which is located in Tallahassee, FL., on groundwater collected 10 miles downgradient of the lake. Daily groundwater sampling of the well has shown distinct shifts in groundwater chemistry, leading to changes in the hydrofacies of the groundwater, following the dry-downs. In this research, we explain the chemical changes through two processes of (1) dilution of carbonate rich waters within the karst aquifer and (2) the chemical weathering of the siliciclastic confining unit as the lake water flows through the sinkhole into the aquifer. Chronical impacts of the dry-down events on aquatic ecosystem have not been studied.