Delineating the recharge and discharge areas of Carroll Cave , and examing aspects of hydrologic behavior and water quality

Delineating the recharge and discharge areas of Carroll Cave , and examing aspects of hydrologic behavior and water quality

By Ben Miller

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Carroll Cave , located in the Ozarks regions of Central Missouri , is a dendritic cave system with over 26.9 kilometers, 16.7 miles, of mapped passage. Aside from being the longest cave in the Ozarks the cave system is significant in many other aspects. Biologically, the cave is the site of a meta-population of the Southern Cavefish (Typhlicthys subterraneus), a large population of the Ozark Blind Cave Salamander (Eurycea spaeleus), and with future work may very well be one of the most biologically diverse cave west of the Mississippi River. Hydrologically the cave is significant with two distinct cave streams, Thunder River and Carroll River . Thunder River is the larger of the two cave streams while Carroll River is much smaller since beheading by Lower Thunder River . The discharge point of the Thunder River is Toronto Springs, a multi-outlet spring system approximately 6 kilometers north of the current siphon. This was determined through a dye trace in 1956 and the discharge outlets are unknown. Access to the cave system is through two entrances, the natural entrance where Carroll River discharges and an artificial entrance at the intersection of upper Carroll River passage and Thunder River . Access is controlled through the non-profit organization the Carroll Cave Conservancy.

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What is not known?

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To date the recharge are of Carroll Cave is completely unknown. While much speculation has taken place as to where potential sources may contribute to Thunder River , no dye tracing has yet occurred. Major contributing sources to Thunder River may be Traw Hollow to the south, Davis Hollow to the northwest, Barnett Hollow to the north, and a series of sinkholes to the west of the known cave. Dye tracing work could confirm these speculations and begin to delineate a recharge area of the cave.

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While the discharge point of the cave has been dye traced in the past, we need to get an understanding of all discharge points for the cave. The complex nature of Toronto Springs does not lend itself to a proper understanding of the connection between the cave and the springs. The true outlet of Thunder River is still unknown as the detection was likely downstream of the springs.

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Stream flow measurements of Thunder River have been taken sporadically throughout the history of Carroll Cave . Today a pressure transducer and data logger have been installed in Thunder River and are collecting hydraulic head data. With additional work a rating curve could be established and would allow for continuous stream flow data to be collected using the pressure transducer. This work should also take place at the multiple outlets of Toronto Springs and correlated to the measurements taken inside Carroll Cave .

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Water quality data measurements have also been collected at various times throughout Carroll Cave ‘s history. No deliberate monitoring at regular intervals has ever been initiated. This data is crucial to understanding and studying the biological diversity and health of the cave system. The land use of the surface above the cave is currently a combination of livestock agriculture and residential development. Increasing residential development is and will continue to impact the water quality of the cave system. Base line water quality data would help study and potentially control this impact.

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What is proposed?

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A series of dye traces in the major surrounding drainages and in the sinkhole plain will begin to delineate a recharge area for the cave system. Monitoring points would not only include in-cave sites, but would also include many local springs, downstream points in injection drainages, and a few smaller cave systems. This carefully planned network of injection sites and monitoring locations would provide a larger area understanding of the local movement of groundwater.

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The discharge point(s) of the cave system must also be well understood in order to properly study the hydrology of Carroll Cave . A mapping of the Toronto Springs area with GPS and GIS will allow for a better visualization of the spring series and will assist in establishing monitoring points. A repeat of the dye trace from the Thunder River siphon will better establish the discharge outlet(s). The detection methods would be through the use of charcoal packets and grab samples collected at regular intervals.

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Flow measurements within Carroll Cave will allow for the plotting of stream flow for use in a rating curve. This rating curve when combined with the established pressure transducer will give a nearly real-time plotting of stream flow in Thunder River . The flow measurements will be collected using a wade stick and pygmy meter anemometer. These flow measurements would take place at the collection of charcoal packets from in-cave sites. Though a significantly smaller flow rate, several stream flow measurements may also take place in Carroll River .

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Water quality monitoring will take place in Thunder River and one other site, either Toronto Springs or another in-cave location. This monitoring will utilize a series of YSI Sond data logger probes. The probes/data loggers will be installed at locations suitable and accessible during charcoal packet replacement. The probes will monitor for pH, turbidity, dissolved oxygen, specific conductivity, and chlorophyll (which emits the same wavelength as rhodamin WT). Grab samples will also be collected during these trips and sent to the USDA-ARS water quality lab in Columbia , MO for analysis of dissolved nutrients and bacteria levels.

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The significance of this work

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Carroll Cave is the longest cave in the Ozarks and represents a significant hydrologic as well as biological resource. Understanding the hydrologic behavior and recharge are of the cave will lead to a better management and additional protection of the cave system. As no previous recharge area delineation has taken place this will be a significant scientific contribution. When combined with pinpointing the discharge area, stream flow measurements, and water quality monitoring this will provide the necessary framework for protecting not only the land above the cave but the areas that directly impact the overall health of the cave system.

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