|Lerch, Robert - Bob|
Submitted to: Journal of Cave and Karst Studies
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/17/2005
Publication Date: 12/1/2005
Citation: Lerch, R.N., Wicks, C.M., Moss, P.L. 2005. Hydrologic characterization of two karst recharge areas in Boone County, Missouri. Journal of Cave and Karst Studies. 67(3):158-173. Interpretive Summary: A number of major cities in the U. S., including St. Louis, MO, Austin, TX, Chattanooga, TN, and Huntsville, AL, sit on karst topography. Karst topography happens when surface water leaks through limestone or dolomite bedrock layers and forms sinkholes, caves, springs, and losing streams. Any land use change that can dramatically change the hydrology of surface water can then also dramatically impact sub-surface watersheds. Examples include parking lots, rooftops, roads, and other impervious surfaces that increase with increasing urban land use. This study was undertaken to establish non-urban baselines for Hunters Cave and Devils Icebox caves in the Bonne Femme watershed in central Missouri. These baselines included describing stream flow from the two cave streams, finding the sources of water and size of their recharge areas, and assessing basic water quality of the cave streams. The watershed is rapidly urbanizing, and this study was initiated before significant development occurred. The quantity and quality of the water in the cave streams was monitored from April 1999 to March 2002. Both recharge areas were formed in the same limestone bedrock, and they were determined to be of similar size (about 13 square miles). Land uses in both recharge areas were about 80% grasslands and row crops. Despite these similarities, the quantity and quality of the water in the two cave streams differed because of physical differences in their recharge areas. Hunters Cave receives most of its water directly from a losing stream while the Devils Icebox receives water from a losing stream plus through numerous sinkholes. Locally, the public benefits from this research because an EPA 319 Nonpoint Source Pollution Control grant awarded to the Boone County (MO) Commission engages citizens and politicians to lead the development of a land-use plan for the greater Bonne Femme watershed, where these caves are located. These findings also benefit state and local governmental agencies because the pre-urban hydrologic conditions and land uses within each recharge area can be compared to future conditions. Specifically, the hydrologic impact of impervious surfaces and the effectiveness of best management practices implemented as urban growth occurs can be evaluated to assure sustained environmental quality of surface and sub-surface streams in this watershed. In a broader context, this project and the associated 319 grant provided a model for transferring research information to citizens and local politicians to improve urban land management in karst or non-karst areas.
Technical Abstract: The Bonne Femme watershed, located in central Missouri, is a karst watershed in a rapidly urbanizing area. This study was undertaken to characterize the hydrology of two karst aquifers within this watershed before significant increases in impervious surface have occurred. The specific objectives of this study were to: 1) use dye tracing to delineate the recharge area for Hunters Cave (HC); 2) quantify and summarize annual and monthly stream discharge at the resurgence of HC and Devils Icebox (DI) caves; and 3) characterize the chemical and physical status of the cave streams relative to temperature, pH, specific conductance, dissolved oxygen, and turbidity. The quantity and quality of the water at the resurgence of both cave streams was monitored from April 1999 to March 2002. Both recharge areas were determined to be of similar size (33.3 km**2 for HC and 34.0 km**2 for DI) and were formed in the same geologic strata. Average annual discharge was 1,900,000 m**3 at DI and 1,170,000 m**3 at HC. Relative discharge, as a percent of annual precipitation, averaged 6.1% at DI and 3.8% at HC. Average monthly discharge was 97,700 m**3 at HC and 158,000 m**3 at DI, but monthly discharge varied by three orders of magnitude at HC compared to only one order of magnitude at DI. However, median instantaneous discharge over the three years was about 18% higher at HC (74 m**3/h) compared to DI (63 m**3/h). Turbidity and pH showed the largest differences between sites over the three years while the other parameters had similar median values. The greater turbidity and lower pH at DI largely reflected the greater magnitude and duration of runoff events for this system. Although the three-year median water temperatures were very similar between systems, the seasonal variation was nearly twice as much at HC compared to DI. The physical characteristics of the two recharge areas explained the observed differences in discharge. The HC recharge area is characterized by limited sub-surface conduit development, small conduits, short flow paths from surface to resurgence, and predominantly allogenic recharge. The DI recharge area is characterized by extensive sub-surface conduit development, large conduits, long flow paths to the resurgence, and autogenic and allogenic recharge.