Uranium and strontium isotopic geochemistry of karst waters, Leon Sinks Geological Area, Leon County, Florida

The Leon Sinks Geological Area (Florida) is a mature karstic area developed on the OligoceneMiocene Upper Floridan aquifer. This hydrological system is extremely vulnerable to pollution because of the very high permeability of the carbonate aquifer. The threat of water pollution in the study area makes the evaluation of the water sources of the sinkholes necessary. Uranium and strontium isotopes are used in this investigation as tracers to determine the water sources of sinkholes. Uranium isotopes in water have been shown to be useful as tracers to distinguish sources of mixed waters. Isotopic ratios of strontium are often used as a natural flow tracer, as well, because the 87Sr/86Sr ratio of natural waters is a function of soils and rocks with which they have been in contact. The sinkhole waters in Fisher Sink, Fisher Rise sink, and Lost Stream sink, which originate from the Water Table aquifer (Pliocene-Pleistocene), have higher 87Sr/86Sr ratios and lower 234U/238U ratios. The waters of Big Dismal and Hammock come from the Upper Floridan aquifer, which has lower 87Sr/86Sr ratios and higher 234U/238U ratios.