Collaborative Research: Suspended Sediment Transport in Karst

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0125551WhiteAlthough it seems intuitively obvious that karst aquifers will carry more sediment than porous media aquifers, because of the large conduits and faster velocities, relatively few studies have tried to quantify sediment transport in karst. Understanding sediment transport is important for a number of reasons. First, sediment may enhance transport of contaminants that are mobilized by attaching to sediment. Second, the mobility of sediment also reflects the potential mobility of bacteria and viruses, which are of concern in evaluating groundwater quality. And third, the mobility of sediment is a measure of velocities and transport pathways in karst, a complex issue involving mixing from different reservoirs, which is difficult to quantify. This research will address how sediment transport varies with seasons and different storm events by measuring sediment transport in a set of karst aquifers over the course of a year and during several different types of storm events. Storm events will include small and large storms, plus storms with wet and dry antecedent conditions. Three distinct karst aquifers have been selected that include a high, medium, and low discharge system. At each site, continuous loggers will be installed to monitor conductance, discharge, and turbidity to record seasonal variation and antecedent conditions for storms. In additional, stormwater samplers will automatically trigger to sample during the selected storm events. Samples collected monthly and during storms will be analyzed for detailed water chemistry, sediment composition, and sediment size distribution. Efforts will be made to model the transport processes for sediment movement within karst aquifers. The combination of fieldwork and modeling to assess the controls on sediment transport will be used to classify the different karst systems using the mixing ratios implied by sediment transport. Unraveling mixing from different reservoirs is important in both karst and non-karst systems, and this study will help show how temporal heterogeneity (changes between storm events, not just within storm events) can provide clues to the internal structure of a system. This work will demonstrate the importance of temporal heterogeneity in hydrologic systems by studying an end-member system (karst) and quantifying the types of measurements needed to understand system response.