Publication Date

12-1-1998

Degree Program

Department of Geography and Geology

Degree Type

Master of Science in Geography

Abstract

Many active stream conduits within karst aquifers transport and deposit non-carbonate, clastic sediment. However, little is known about how these sediments impact conduit development and enlargement rates. For example, can dissolution take place at the sediment/bedrock interface beneath a flowing stream? If not, cavern enlargement might be dominated by flood conditions when the bare rock of the walls and ceiling are in contact with the dissolving fluids. An approach using limestone tablet weight loss experiments, along with water sampling and geochemical modeling, has been undertaken to understand the nature of fluid movement and chemistry with the sediment beneath an active flowing cave stream within the Kentucky's Mammoth Cave System. Fluid flow and carbonate chemistry were compared between the active stream and within the sediment at 15, 30, 60, and 90 cm below the stream bed. It was found that carbon dioxide pressure within the interstitial fluids was elevated an order of magnitude above that of the stream waters, having levels as much as 31 times that of atmospheric background, presumably from microbial decomposition of organic material. The fluids were all under-saturated with respect to calcite (SI= -0.4 to -0.9), and limestone blocks buried at these levels all dissolved (rates from 0.8 to 21.9 g m -2 yr -1). These results suggest that at some locations the limestone bedrock may be dissolving beneath clastic sediment deposits; which in turn has implications for understanding rates and geometries of conduit evolution within karst aquifers.

Disciplines

Earth Sciences | Geography | Hydrology

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