Conclusions

The findings of this study demonstrate the vulnerability of the unconfined sections of the Floridan aquifer to rapid contamination from surface streams. The 222Rn and d18O data and water clarity observations presented in this paper clearly demonstrate the occurrence of rapid river water intrusion to the unconfined Floridan aquifer. The two component mixing model used in this investigation revealed that as much as 62% of the discharge at Devil’s Ear spring can be river water that has recently intruded into the Devil’s Ear cave system. Observations of water clarity reductions in the cave system during and after flood events that originated in the Northern Highlands physiographic province reveal that wholesale contamination of the major karstic conduits underlying the Santa Fe river can occur in as little as one day.

Given the prevalence of karst in Florida, the hydrologic character of the part of the western Santa Fe river basin investigated in this study can be considered typical of other regions in Florida where rivers or streams dissect the unconfined Floridan aquifer. Currently, environmental regulations in Florida segregate ground water from surface water in these regions and permit high nitrate sewage from dairies, and fertilizers and pesticides from agricultural lands to be discharged to rivers and streams. However, the results of this investigation demonstrate that there can be no clear distinction between ground and surface waters in these regions. Instead, water is actively exchanged between the aquifer and rivers and streams at scales that are imperceptible to standard hydraulic analyses. Contaminants that enter the river will be carried into the aquifer by the exchange process and potentially degrade water quality.