Publication Date

8-1-1998

Degree Program

Department of Geography and Geology

Degree Type

Master of Science

Abstract

The following research describes the collection and evaluation of geochemical data from the Logsdon River, an open-flow conduit that drains a portion of the Turnhole Spring drainage basin within the Mammoth Cave karst aquifer of south-central Kentucky. This spatial survey of nearly 10 km of continuous base-level conduit included seasonal sampling of carbon dioxide partial pressures (Pco2)> dissolved ions, and saturation indices for calcite (SIcal). The highest PC02 values are found at the upstream site, closest to the Sinkhole Plain recharge area, which creates under-saturated conditions. Rapid outgassing of C02 into the cave atmosphere creates oversaturated conditions for several thousand meters. This change in chemistry results in the accumulation of rimstone in these areas. A boost in PC02 roughly half-way through the flow path returns the water to slightly under-saturated conditions. The most likely source for additional C02 is in-cave organic decay, as the boost also occurs during winter, when microbial activity in the soil is at a minimum. A general decline in Ca2+ , Mg2+, and HC03 concentrations occurred over the distance through the Logsdon River conduit. This decline may reflect a diluting of water by localized inputs from the plateau and precipitation of travertine along the flow path. Although values for all parameters are greater in summer than winter, the trend in evolution is similar for both seasonal extremes. The nature of the transition from summer to winter conditions in the aquifer was investigated by way of an intensive study of the geochemistry at the Logsdon River monitoring well. The relationship between conductivity (spC) and pH was evaluated during both seasons in an attempt to predict the activity of hydrogen for any given water sample based on continuous spC measurements at the well. Data collected during the 1997-98 seasonal transition supported a single, nonlinear regression equation that may represent two distinct seasonal regimes.

Disciplines

Geography | Hydrology

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