Collaborative Research: A new classification system for karst springs using storm hysteresis

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Karst aquifers are an important groundwater resource, but they are vulnerable to contamination because of fast and complex flow paths arising from subsurface caves and large fractures. The complexity of karst aquifers has for a long time imposed challenges for researchers to characterize the groundwater flow system. This project will develop a new classification method for karst springs that will guide monitoring and pollution prevention strategies. Based on water chemistry variability in response to storms, this classification will identify different sources of water and improve water capture area delineation. The new classification system will be tested by revisiting a well-known set of karst springs that show variations in flow paths. Educational opportunities for students and for the general public are incorporated into the project. Classification will be based on the shape of hysteresis plots and changes in hysteresis plots from storm to storm. Storm hysteresis, defined as the difference in chemical trends at the beginning versus the end of a storm, offers opportunities to identify changes over time in water movement and storage in karst networks. The project will test two hypotheses. (1) During a storm, hysteresis occurs as the water flows through the matrix and conduits, and (2) from storm to storm, the hysteresis pattern changes as the water capture area and storage zones change. For example, Mg:Ca ratios in spring water increase with diffusive recharge but decrease with more focused recharge through conduits, and hysteresis plots can show the timing of each type of recharge. Automatic samplers and data loggers will be used during storms to provide data for hysteresis plots. In addition to Mg:Ca ratios, Sr:Ca ratios, rare earth elements, stable isotopes, and carbonate equilibria will be examined and potential flow paths will be evaluated using groundwater models. The combination of multiple natural tracers, modeling, and capture area calculations will help quantify behavior of karst springs and karst aquifers. Ultimately, the new classification system will improve understanding of contaminant transport in karst systems.