Geochemical Trends in Selected Lechuguillla Cave Pools


David B. Levy


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December 2007

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Journal of Cave and Karst Studies

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Lechuguilla Cave is the deepest known limestone cave in the United States with a surveyed length in excess of 185 km, and hosts some of the world’s most exemplary speleogenetic features. Since its discovery in 1986, Lechuguilla Cave has provided researchers with a unique location to study speleogenesis, geology, microbiology, and geochemistry. Although approximately 200 water samples were collected by numerous researchers between 1989 and 1999, subsequently little water quality monitoring has occurred. The primary objective of this study was to collect recent major ion chemical data from pools which either have experienced chemical changes in the past, or which have been designated as drinking-water sources for cavers, and to use those results in conjunction with previous data to evaluate historical trends. The study locations consisted of Lake Lechuguilla, and three pools designated as drinking-water supply (Lake Louise, Pearlsian Gulf Water Supply, and Tower Place Water Supply). In conjunction with sampling for general chemistry, the oxidation-reduction (redox) states of the pools were also assessed by conducting additional measurements for dissolved oxygen, dissolved organic carbon, redox potential (Eh), ferrous iron (Fe 2+), total dissolved iron, manganese, and nitrogen (NH 3 -N and NO 3 -N). Although Lake Lechuguilla experienced unexplained increases in nitrate and sulfate between 1988 and 1990, the major ion chemistry has apparently returned to baseline conditions. Results also show that between 1988 and 2006, the major ion chemistry of Lake Louise, Pearlsian Gulf, and Tower Place has remained relatively constant. Evaluation of redox status in these pools between 2005 and 2006 indicate an oxic (aerobic) environment, with dissolved oxygen levels in equilibrium with the atmosphere, and concentrations of dissolved organic carbon, NH 3 -N, iron, and manganese below detection limits.

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