UNSATURATED ZONE HYDROLOGY OF THE EDNA'S DOME SHAFT COMPLEX OF THE MAMMOTH CAVE SYSTEM, KENTUCKY

A long-term hydrochemical monitoring program is underway in the vicinity of the Edna's Dome Shaft Complex in Mammoth Cave National Park to study karst aquifer development, atmospheric carbon fluxes, and groundwater flow within the unsaturated zone above the shafts. The complex drains a small, forested surface catchment protected by the park and thus offers relatively pristine conditions to study the background geochemistry of the aquifer. As part of this work we are mapping out the conduit flow system feeding the shafts using fluorescent dyes. Understanding this flow system is a prerequisite to detailed geochemical studies, and offers an interesting challenge: the known conduits are all too small for human exploration, and so the traditional methods of cave survey used so extensively elsewhere in the cave are of little use.

Five dye injections were conducted during wet conditions in spring 2000. After testing for the absence of background contamination, 25 mL each of Rhodamine WT and fluorescein dyes were injected into two sinking surface streams (the “Eastern” and “Western” branches of an unnamed ephemeral stream) above the shaft area in February. The waters of six separate shafts (Hawkins's Spring, the "Water Clock", and Edna's, Nelson's, Einbigler's, and Cathedral Domes) were monitored with charcoal dye receptors, which were replaced and analyzed by elution and spectrofluorophotometry over the next 67 days. The five shafts closest to Edna's Dome were all positive for fluorescein within nine days, and no dye was detected at Cathedral Domes. No Rhodamine was detected, so larger amounts of were injected into the Eastern Branch in early and late March and were detected at three of the shafts, including the most distant at Cathedral Domes. A third dye, eosine, was injected in late March at different sinkpoint nearby and was detected within a week at a different trio of shafts with some overlap between the other traces.

Results show that the flow paths consist of steep, vertically bifurcating conduits between a single surface input and multiple shafts within the cave. These are also overlapping networks, in that a single shaft can receive flow from more than one surface input. While shafts are known to occur commonly in groups (complexes), the bifurcating flow identified here may provide an explanation for this clustering.