Subterranean Fishes of the World

4471

2019

Journal of Cave and Karst Studies

174-187

81

River Styx and Echo River are two, closely-associated underground rivers located in the Mammoth Cave System. Both rivers are home to a variety of aquatic cave life, including the endangered Kentucky cave shrimp (Palaemonias ganteri). Typically, both underground rivers emerge at their respective springs and flow into the Green River. During flooding conditions, the Green River can back up into its subterranean tributaries, including the River Styx and Echo River. In addition, the hydraulic gradient in the River Styx can reverse under non-flood conditions of the Green River and create a stable, reverse-flow pattern. This phenomenon was identified at least as early as the 1920s, when a dye trace study noted that, after a rain event, Green River water was flowing into River Styx Spring and coming out at Echo River Spring. However, detailed studies on the River Styx's stable, reverse-flow patterns were not conducted until the 1950s, and little additional research has been conducted. Water temperature data were collected between October 2009 and October 2012 on the River Styx, Echo River, and Green River. During the study period, the Green River had a mean water temperature of 15.5 ± 7.2 °C, while River Styx and Echo River had cooler and more stable mean water temperatures of 13.5 ± 2.7 °C and 13.4 ± 0.6 °C, respectively. Water temperature was used as a proxy for determining whether the River Styx was flowing forward (out of the cave) or backward (into the cave). Periods of time when the River Styx was flowing into the cave were classified as being due to back-flooding or a stable reverse-flow. During the times when data were available for all three rivers, the River Styx flowed out of the cave 77 % of the time, was in a stable reverse-flow 17 % of the time, and it was back-flooding 3 % of the time. These results differ from the original studies' results that identified the River Styx's stable, reverse-flow pattern. The different results could be due to anthropogenic influences on the Green River and/or due to differences in precipitation patterns, possibly as a result of climate change.

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