THE ROLE OF CHERT ON THE KARST HYDROGEOLOGY AND GEOMORPHOLOGY OF THE SOTHERN OZARKS

Interdisciplinary research at the Savoy Experimental Watershed (SEW) at the University of Arkansas has provided an increasingly complex characterization of what initially to us appeared to be a simple hydrologic site with “typical” Ozark geomorpology. After 16 years of intense studies, each which had a strong field component, we conclude that the hydrology is actually far from simple, and that the role that chert plays is significant. The SEW site is characterized by near-horizontal soil horizons underlain by bedded regolith composed primarily of insoluble chert and clay. These overlie bedrock layers of variably pure limestone, the uppermost units containing both secondary and original chert, the lowermost units nearly pure limestone. Macropores in the nonindurated layers and systematic jointing in the indurated limestone and chert beds allow focused recharge from precipitation and streamflow to move into and out of the subsurface rapidly, providing discrete points of recharge that can have telltale chemical and physical properties. These fast-flow pathways are imbedded within porous media that store and transmit flow at rates orders of magnitude less than preferred pathways. Horizontal zones in the regolith containing continuous chert layers provide vertical barriers to flow, and divert recharge from ephemeral streambeds to springs and seeps much further away than nearby resurgences. Rapid flow zones are surprisingly compartmentalized within nonindurated media, and they are not easily discernible using geomorphology or interpretation of remotely-sensed imagery. Furthermore, recent geochemical research indicates that surface land management and surface flow is closely connected with nutrient transport along subsurface pathways and ecosystems, zones that were previously interpreted as having little impact on water quality. This has led us to become advocates of continuous high-frequency monitoring to understand catchment hydrochemistry. Most of this understanding was unknown until intensive, long-term interdisciplinary field studies under a wide range of hydrologic conditions had been conducted