SULFUR, OXYGEN AND HYDROGEN ISOTOPE STUDIES OF CONDUIT FRESHWATER SPRING AND MINERAL SPRING FLOW ON THE KARST MITCHELL PLAIN AND THE CRAWFORD UPLAND OF SOUTHERN INDIANA

Water chemistry and d³⁴ (SO₄) studies suggest that two flow systems exist in the karst terrain of Southern Indiana: (1) a shallow flow system, which is dominated by surface water that infiltrates through the soil profile to the epikarst then flows laterally to major vertical joints and fractures to the springs; and (2) a deeper flow system driven by topographic cells forcing water downward where it flows through and dissolve evaporate minerals from the St. Louis limestone. The water then flows upward and discharges at topographic lows.

Sulfur isotopic values d³⁴S (SO₄) for springs in the study area range from +1.1 to +22.1 ‰ d³⁴S of HS^- range from –0.2 to –38.4. The fresh water springs have lighter d³⁴S (SO₄) values approximately 10 ‰. The mineral springs are approximately 14 ‰similar to values of the local St. Louis gypsum (14 to 16 ‰). Heavier d³⁴S (SO₄) values (18 to 19 ‰) in water such as Pluto spring are due to bacterial fractionation. Orangeville rise a major fresh water spring has a low flow d³⁴S (SO₄) of approximately +16 ‰ and a sulfate concentration of 160 mg/l. The d³⁴S (SO₄) and sulfate concentration decreases to +9 ‰ and 40 mg/l respectively at high flow. This suggests the mixing of shallow epikarst water and deeper mineral waters.

The ranges of d¹⁸O and ²H in the spring waters are -7.0 to -8.0 ‰ and –42 and –49 ‰ respectively. Except for slight deviations they follow the local meteoric water line. Tritium data previously collected on four of the springs indicate that one is pre-bomb water and the others are a mixture of pre-bomb and recent water.