Abstract
The hydrogeochemistry of Florida’s limestone aquifers is complex, dominated by carbonate equilibrium reactions and the influence of seawater.
Florida rainfall contains dilute Na+ and Cl− from marine aerosols. Quartz-rich parts of the surficial aquifer system (SAS) contain Na-Cl water overprinted by human activity, whereas limestone and shell aquifers contain Ca-HCO3 or Ca-Mg-HCO3 water. The Floridan Aquifer System (FAS) also contains Na-Cl-rich residual marine waters from past sea-level fluctuations; Na-Cl-rich connate water; and SO4
2−-rich waters from sulfide oxidation and dissolution of sulfate minerals.
Potential for dissolution of carbonate-rich strata is enhanced by mixing of groundwater such as at freshwater/saline-water interfaces, as well as chemical complexing, ion pairing, common ion effects, and high levels of dissolved organics.
Metastable minerals aragonite and high-magnesium calcite are present in Florida’s youngest carbonate aquifers and sediments. These minerals are likely to be dissolved during early diagenesis and speleogenesis. High surface area relative to particle volume in fine-grained sediments causes water to equilibrate rapidly with carbonate constituents, resulting in preservation of shell and carbonate mud at depth.
There have been at least two episodes of diagenetic alteration of calcite and/or aragonitic sediments in the FAS. Dolomitization has occurred in Florida’s aquifers, but the degree of subsequent involvement of the dolomite in diagenesis is unclear.
Groundwater-quality issues include arsenic released by aquifer storage and recovery, and H2S derived from reduction of SO4
2− and degradation of organics. Water quality is also impacted by evaporation and transpiration, biotic activity in soils and sediments, reduction/oxidation reactions, and generation of humic substances by plant decay. Nitrate from fertilizers and animal and human waste is a major contributor to eutrophication of Florida springs.