A CONCEPTUAL MODEL OF THE FLOW AND DISTRIBUTION OF ORGANIC CARBON IN CAVES
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We present a conceptual model for the movement of organic carbon in karst. We argue that the drainage basin is the most appropriate unit for analyzing energy flux in karst. There are two main inputs in karst basins: 1) localized flow of particulate organic carbon (POC) and dissolved organic carbon (DOC) through sinks and shafts and 2) diffuse flow of POC and DOC from soils and epikarst. After entry, this organic matter is processed and transported before eventual loss through respiration or export from the basin. To begin parameterizing our conceptual model, we estimated carbon fluxes for the first two inputs for two karst basins (Organ Cave in West Virginia and Postojna-Planina Cave System (PPCS) in Slovenia) that have sinking streams and many active epikarst drips. We made a series of measurements of organic carbon, especially DOC in epikarst drip water, cave streams, surface streams sinking into the cave, and at resurgences, which we combined with other published data. In both caves, most of the organic carbon entering through the epikarst was DOC, at concentrations averaging around 1 mg C L21. In both basins, sinking streams accounted for the large majority of DOC input. It is likely that considerable processing of organic carbon occurs within both caves, but more detailed measurements of organic carbon flux at both the basin and stream scale are needed.