GEOCHEMISTRY OF GROUNDWATER WITHIN A KARSTIFIED LIMESTONE HAMMOCK OF EVERGLADES NATIONAL PARK

Macro-porosity in the Biscayne carbonate aquifer commonly occurs as horizons of centimeter-scale-diameter, touching-vug porosity, in some instances, traceable between wells at the regional scale. The ichnofabrics generated by callianassid burrowing can dominate zones within or the entire thickness of the Marine Isotope Stage 5e part of the Miami Limestone and some or most of those of the underlying Quaternary Fort Thompson Formation. Yet, even within these highly permeable zones of the MIS 5e, we find examples of caves, particularly air-filled caves associated with transverse glades that dissect relatively high elevations along the Atlantic Coastal Ridge. A broad-spectrum monitoring program is underway at one of these caves in Everglades National Park, Palma Vista Cave, and the nearby freshwater Taylor Slough, and is providing water-level, meteorological, geochemical, microbiological, petrologic, and isotopic data over the course of one year. The goal is to provide a detailed look at the development of cavernous porosity in coastal, eogenetic carbonates.

Water levels, measured every ten minutes in Taylor Slough and Palma Vista Cave, respond rapidly to individual storms, in one case rising more than 30 centimeters in less than 12 hours. Present geochemical data from the slough, sampled every two weeks, reveal a shift toward lower values of pH, specific conductance, and total alkalinity at the onset of the wet season. The pH of waters from the cave also decreases at the onset of the wet season; however, specific conductance and total alkalinity remain relatively stable. The waters of both the slough and the cave, however, remain saturated with respect to both calcite and aragonite at each sampling period up to the onset of the wet season, and soon after major rain events. These preliminary data suggest rapid saturation of recharge waters (minutes to hours). It appears that the enlargement of Palma Vista Cave does not proceed uniformly unless aided by not yet quantified microbiologic activity.