EPIKARST CONTROL ON QUANTITY AND QUALITY OF RECHARGE TO KARST AQUIFERS: CURRENT RESULTS FROM LONG-TERM MONITORING WITHIN JAMES CAVE, VIRGINIA

Since 2007, we have collected continuous hydrologic and geochemical data from a cave in Virginia (James Cave) to examine relationships between recharge, precipitation, drip response, drip quality, and epikarst properties. At the site, we have five monitoring stations, one each at the surface and cave stream, and three in-cave drip sites. At each station, we are continuously monitoring hydrologic response (precipitation/drip rate/discharge) and basic geochemical parameters (i.e., pH, temperature, specific conductance). We also collect monthly grab samples of soil, drip and stream water for major and minor elements and DIC/DOC as well as O/H and DIC/DOC isotopes.

Our four years of data show that cave drips respond to precipitation events only after sufficient rainfall during late winter and early spring, with rapid responses for quickflow, and corresponding increases in baseflow. Baseflow recession analyses indicate that epikarst contributions support stream baseflow during the summer months, which depends on sufficient fall and winter precipitation. Drip geochemistry is complex, reflecting different surface sources of major and minor elements and storage time in the epikarst, as well as biogeochemical processes.

Overall, our results thus far support a complex conceptual model of flow and storage in the epikarst where physical and hydrologic properties, in combination with climatic conditions, determine how the epikarst regulates the quantity and quality of recharge to the underlying aquifer. In addition to providing specific information about the site, our continuous and high-frequency records of flow and geochemistry can be used as benchmarks for developing predictive models of recharge and solute transport through the epikarst that can be used at other sites where epikarst exerts strong control on karst aquifer recharge.