Analysis of Hydrologic and Geochemical Time Series Data at James Cave, Virginia: Implications for Epikarst Influence on Recharge

Abstract

Karst aquifers are productive groundwater systems around the world, supplying approximately 25% of the world's drinking water. However, they are highly vulnerable to contamination due to rapid groundwater transit in the transmission zone (KWI 2006). The epikarst, also known as the subcutaneous zone, is an interface between the soil overburden and the transmission zone. The epikarst is considered a critical zone as it can control hydrologic and geochemical characteristics of recharge to the underlying karst aquifer. The overall goal of this thesis is to utilize time series hydrologic and geochemical data collected at James Cave, Virginia, to examine the influence of epikarst on the quantity, quality, and rates of recharge to aquifers in Appalachian karst.

Results of this study indicate a strong seasonality of both the hydrology and geochemistry of recharge. The conceptual model of the epikarst developed in this study identifies three hydrologic seasons: recharge, recession, and baseflow. Seasonality of recharge geochemistry coincides with these three hydrologic seasons. These results have implications for management of karst aquifers. First, recharge to Appalachian karst aquifers is seasonal, reaching a maximum during the winter-early spring; the onset of recharge depends on antecedent climatic conditions. Second, water that infiltrates into the epikarst will have seasonally variable residence times due to changes in hydrologic storage; these variations in attenuation affect geochemical reactions in the epikarst, which can influence recharge quality. Overall, these results point to the complex influence of epikarst on karst recharge, which necessitates collection of long-term and high resolution datasets.