ARS | Publication request: Seasonal Variations in Background Hydrochemistry of Epikarst Waters in Kentucky’s Pennyroyal Plateau

Submitted to: National Speleological Society Annual Meeting
Publication Type: Abstract Only
Publication Acceptance Date: July 1, 2010
Publication Date: August 3, 2010
Citation: Nguyet, V., Groves, C., Bolster, C.H. 2010. Seasonal Variations in Background Hydrochemistry of Epikarst Waters in Kentucky’s Pennyroyal Plateau. National Speleological Society Annual Meeting.

Technical Abstract: Detailed knowledge of background hydrogeochemical conditions within epikarst systems is useful for understanding not only the geomorphic evolution karst landscapes, but of the fate and transport of contaminants introduced into karst aquifers. Kentucky’s Pennyroyal Plateau in particular is subject to contamination by agricultural land use. Weekly sampling of epikarst water over one year in Crumps Cave near Smiths Grove has been interpreted to further understand CaCO3-H2O-CO2 interactions that control the hydrochemistry in the epikarst system there, including ionic concentrations, CO2 partial pressure, and water/rock interactions. Results show a clear difference in hydrochemistry between the warm and cold seasons, with higher CO2 pressures and ionic strength, and lower pH in the warm season (May to September) in contrast to opposite conditions in the cold season. The seasonal changes can be explained by higher soil temperature in the warm season influencing production of soil CO2, with a significant flux of CO2 into the epikarst storage water. As a result, calcite saturation index values are negative during the warm period and calcite is actively dissolving causing higher calcium and bicarbonate concentrations. During this period at the sampling site CO2 pressures are relatively high and pH low, even after substantial buffering from calcite dissolution has already taken place. As outside temperatures cool, and the CO2 flux into the epikarst storage diminishes, water in the cave becomes oversaturated with respect to calcite for several months, with the associated changes in the influence of water/rock interactions on hydrochemistry. No obvious mineral precipitation occurs at the site.