An isotopic study of groundwater seepage in the central Kentucky Karst

Ratios of 18O/16O were determined for meteoric precipitation and vadose seepage at Great Onyx Cave in Mammoth Cave National Park from March through July 1973. Results of this study indicate that (1) the δ18O/dT for precipitation at this site is 0.38‰/°C, (2) short-term fluctuations in the 18O/16O ratio of seepage water in the vadose zone above the cave do not affect the oxygen isotopic composition of the speleothem calcite precipitated in the cave, and (3) the residence time of seepage water in the vadose zone is about 2 weeks. From spot sampling of base level springs in November 1972 the isotopic composition of the karst groundwater body is estimated to be about δ18O = −5.6‰ and δD = −40‰.

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