WATER CIRCULATION IN KARST AQUIFERS: COMPARING PHYSICO-CHEMICAL AND ENVIRONMENTAL ISOTOPIC DATA INTERPRETATION

This study uses major ion chemistry, physical water quality, strontium composition, ⁸⁷Sr/⁸⁶Sr ratio, and stable isotope ratios (oxygen and hydrogen) in samples of precipitation (rain and snow), spring water, and stormwater mixed with the spring water to provide supporting evidence for the nature of water circulation in karst aquifer systems. We compare the physico-chemical and isotopic data in evaluating water circulation through karst aquifer systems. These data are collected from a spring (City Lake at Cookeville TN) discharging from Mississippian carbonate aquifer systems. Scatterplot and time series are used for the data analysis and the interpretation of the results indicates diffuse recharge, piston effect, and inter-aquifer mixing in the karst systems in the Eastern Highland Rim province in central Tennessee, USA that the spring drains. There are evidences supporting that depending on the intensity of precipitation, a piston effect can push old water in the soil zone into the epikarst zone and successively drive old epikarst water into the underlying bedrock aquifer. Water stored in soil, epikarst, and bedrock zones contribute water to the spring flow in dynamic proportions, with epikarst storage dominating base flow. Scatter plots of δ²H versus δ¹⁸O, ⁸⁷Sr/⁸⁶Sr versus Sr, total dissolved ions (TDI) versus Sr or ⁸⁷Sr/⁸⁶Sr and the major ions versus TDI support piston flow, insignificant dilution, and inter-aquifer mixing.