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the soil and epikarst and are habitat specialists with respect to micro - environment. For example, copepod species living in small fissures tend to be morphologically different from species living in larger fractures or soil. Drip waters typically contain specimens that are flushed out of their environment, thus giving clues about the flow -path water may have taken on their way through the epikarst. In this study we will adopt an experimental design which includes copepod analysis similar to that used in the Virginia study. Schwinning has conducted studies on the water relations of live oak (Quercus fusiformis), Ashe juniper (Juniperus ashei) and honey mesquite (Prosopis glandulosa) in the recharge and contributing zones of the Edwards Aquifer. By monitoring plant water potentials, leaf transpiration rates and the stable isotope composition of stem water, Schwinning (in review) demonstrated that the structure of the soil /epikarst system has strong effects on the temporal patterns of water use by trees. For example, on a Glen Rose limestone site with negligible soil cover and exposed dolostone (a "tread" site according to Wilcox et al.'s (2007) model), trees remained well- hydrated even through a 2 -month long summer drought, suggesting that tree roots penetrated through the dolostone and reached a relatively well protected, persistent water source below. By contrast, on an Edwards limestone outcrop, trees became severely water stressed, indicating a comparatively short residence time for water in epikarst formed from Edwards limestone. The study also demonstrated clear differences in rooting depth of the study species, with live oak (Quercus fusiformis) and honey mesquite (Prosopis glandulosa) being deeper rooted than Ashe juniper (Juniperus ashei). One fascinating observation, obtained by monitoring stem water isotope ratios and comparing them to the isotope ratios of rainwater, was that water transport between the soil /epikarst surface and the active root zone of the trees may have been driven by a piston -flow mechanism, rather than by direct infiltration. Though this result is yet to be corroborated by subsequent experiments, we expect that the proposed study, by uniquely combining hydrological and ecological techniques, will resolve some of the uncertainties of plant - epikarst interactions and become a milestone for the study of coupled hydrogeological and ecological dynamics in karst terrain. B) Methodology The key component of our research approach is to simultaneously monitor precipitation (input into the soil /epikarst system), the sap flow rates of trees (a measure of tree transpiration), and the flow rates of drip waters in shallow caves below (a measure of recharge out of the epikarst into the aquifer). Drip and sap flow rates are expected to change dynamically with variation in precipitation, but with characteristic delays that will provide information on the travel time of precipitation pulses through the epikarst, and its storage capacity. Patterns of variation in sap flow rates will reveal if transpiration is coupled more closely with precipitation, which would indicate relatively shallow and transient plant water sources, or more closely with drip flow, which would indicate an ability of trees to utilize water stored throughout the epikarst. Concurrent measurements of rain, soil, stem and drip water stable isotope composition, and the biogeochemistry of drip waters, will allow further clarification on water residence time and flow pathways through the epikarst, and the location of the active root zone of trees. Site selection and characterization We have tentatively identified 10 research sites in the recharge and contributing zones of the Edwards Aquifer along the San Antonio- Austin corridor. All sites have the shallow underlying caves required for this study. Soils range from zero to approximately I in in thickness on epikarst and bedrock consisting of either Glen Rose or Edwards carbonates. Vegetation cover is similar and composed of live oak, Ashe juniper, and in some sites, honey mesquite in an open savanna configuration. All sites provide secure and long -term access to both the surface and underlying caves and are not influenced by urban development and septic systems. The Texas Speleological Society (TSS) has agreed to provide all information in its files which could be useful in this study. Each site will be further characterized using 2 -D Electrical Resistivity Tomography (ERT), available to PI Schwartz through TSU start-up funds. Eventually, we will narrow the sites to six and create detailed topographic maps of the land surface over and around the caves and of the caves themselves, showing the measured or modeled thickness of the soil and epikarst at each