Sulfur isotopes and hydrochemical variations in spring waters of southern Indiana, U.S.A.


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February 1983


Water chemistry and δ34 S(SO4) studies suggest two flow systems in the karst terrane of southern Indiana: (1) a shallow flow system exists, which is dominated by surface water entering the ground through fractures; and (2) a deeper regional groundwater flow system recharged by diffuse flow. The chemistry of the water in the regional system may be dominated by the solution of gypsum in the Lower St. Louis Limestone. Sulfur-isotope studies suggest two flow systems and show that the high SO2 −4 concentrations in local waters result from solution of gypsum. Reported δ34 S(SO4) for Upper Mississippian evaporites and fresh water range from +14 to +19 to +8 to +12‰, respectively. Isotope analysis of gypsum cores from the Lower St. Louis Limestone evaporite unit shows δ34 S-values between + 14.10 and + 15.13‰ in the study area. Groundwater chemistry studies show a direct linear relationship between SO2 −4 concentrations and δ34 S-values. Groundwater varies in SO2 −4 concentrations between 20 and 1970 mg l−1. The δ34 S-values range from + 10.61‰ for a conduit spring to + 18.57‰ for a diffuse spring. The waters with high SO2 −4 concentrations have δ34 S(SO4)-values higher than the local gypsum deposits analysed and contain H2S, suggesting a deeper flow system in which fractionation by bacterial reduction of SO2 −4 is occurring. Waters with low SO2 −4 concentrations have δ34 S(SO4)-values in the range of local fresh water, indicating a shallow flow system.


Water Chemisty, Δ34 S(So4), Sulfur Isotopes, Hydrochemical Variations, Spring Waters, Southern Indiana, U.S.A.

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Journal of Hydrology, Vol. 61, no. 1-3 (1983-02).