CHARACTERIZING CO2 CONCENTRATION VARIATIONS IN TWO KARST SPRINGS AND TESTING CURRENT NUMERICAL DISSOLUTION MODELS

Numerical models of speleogenesis typically employ boundary conditions that assume constant chemical conditions within the inflowing water and constant hydraulic head gradients or discharges across the system. While an assumption of constant chemistry eases calculation of dissolution rates and system evolution, natural waters are not constant with regards to chemical and physical parameters. The variability of CO₂ is a major factor in determining the saturation index (SI) of karst spring waters with respect to calcite, which quantifies the aggressivity of the water. Here we study two karst springs, Copperhead Spring and Langle Spring, located at the Savoy Experimental Watershed in Savoy, AR. Monitoring at the sites is ongoing and includes high resolution data logging of pH, conductivity, water level, temperature, and dissolved CO₂. CO₂ is measured using CO₂ gas sensors encased in a waterproof breathable membrane. Weirs are present at both sites, and discharge at the sites will be calculated based on stage/discharge relationships. In conjunction with the geochemical time-series data, we are conducting dissolution experiments using weight loss of limestone tablets. Observed dissolution rates will be compared against dissolution rates calculated from the geochemical data. We will also examine relationships between discharge, SI, and CO₂ in order to determine what factors control the saturation state of the water.