EVAPOTRANSPIRATION EFFECTS ON SPRING FLOW AND SEASONAL RECHARGE DYNAMICS IN KARST GROUNDWATER SYSTEMS

Karst groundwater systems are subject to dynamic recharge conditions based on a variety of factors, including antecedent moisture conditions, precipitation duration and magnitude, temperature, soil thickness, and evapotranspiration (ET). All but the latter have received widespread attention in conducting groundwater fluctuation, spring discharge, and effective recharge studies. The effects of ET in shallow karst groundwater systems seasonally requires high-resolution datasets on both water table and spring discharge dynamics, as well as meteorological conditions that include soil moisture and temperature at matching resolution. ET calculations are then scalable to capture the quantitative effects of seasonal and diurnal variability on effective recharge during different storm events and within hydrologically stable periods. Using multiple large datasets, the measurable effects of ET on karst groundwater systems is likely underestimated in many cases based on multi-year studies conducted within several different systems in south-central Kentucky, which demonstrate the importance of calculating ET when conducting water balance and effective recharge to a karst system. In certain cases, the effective recharge can be reduced by up to 90%, while the water table response even at depths well below the epikarst influence can be affected up to 0.5 meters or more during seasonal transitions and certain dry periods. Several examples are presented of ways to calculate ET in karst systems and the variability within them under different hydrogeologic conditions.