TRACING REVERSING GROUNDWATER FLOWS IN THE COASTAL FLORIDAN AQUIFER

Groundwater tracing done in 2008 and 2009 reveal that Wakulla Spring and Spring Creek Spring Group (vent #1) ( both 1^st magnitude springs) the latter approximately 16 km down-gradient from Wakulla Spring on the coast of the Gulf of Mexico, are connected via one or more conduits. Both Wakulla and Spring Creek springs display a very large range in discharge due to their connection to numerous swallet inputs whose inflows are dependent on rainfall. Prior to 2006, baseflow at both springs was thought to be composed of groundwater flow derived from distant diffuse recharge. Following 2006, the Spring Creek vents reversed flow for extended periods during low stage. This had not previously been documented. During these reversal periods, siphoning water can be observed at the surface of the Spring Creek vents and Wakulla Spring’s discharge increases.

Both tracer tests were performed by injecting C.I. AY73 (uranine) dye into a large swallet (Lost Creek Sink) 8 km SW of Wakulla Spring and 8.5 km NW of Spring Creek. Sampling for both tests was conducted as continuously as possible at three Spring Creek vents (#1, #2, and #10), Wakulla Spring, and at intermediate karst windows known or suspected to connect to conduit. In 2008, the tracer was injected into the swallet prior to the Spring Creek reversal period. The tracer was detected first at Spring Creek until initiation of the reversal and then approximately 45 days later at Revell Sink, a karst window north of the Lost Creek Sink, and then at Wakulla Spring. In 2009, the tracer was injected after Spring Creek began reversing. This time, the tracer again migrated to Revell Sink presumably on the same path toward Wakulla Spring as it did in 2008, but only until Spring Creek began flowing, when the tracer reversed direction to the south and quickly flowed to the Spring Creek vents. These results document the extent to which groundwater flow patterns in the Floridan aquifer are impacted by conduits and also demonstrate the rapidity of and inland extent to which the coastal region of the aquifer can be impacted by saltwater intrusion.