Combination of Multiple Investigation Methods to Reveal the Recharge Area of a Karst Aquifer

Karst aquifers are heterogeneous groundwater systems having both diffuse and concentrated recharge mechanisms. Since their complex recharge, storage, and discharge characteristics, the groundwater divide is generally different from the topographical catchment borders. As a result, karst hydrogeologists are using different methods to obtain more certain recharge areas. Tracer tests are very important and preferred tools to obtain the groundwater recharge areas. An ideal tracer must be detectable in very low concentrations, conservative along the pathways, and cost-effective. In this manner, mineralogical analysis of the suspended particles would be a very good alternative to the isotopic, biochemical, and dye tracers due to the easy collection and cost-efficient analysis methods. In the present study, we collected rock samples from approximately 10 locations surrounding the potential recharge area of the karst aquifer covering all lithological units surrounding the study area. Then, we collected sediment samples at the discharge outlet of the karst spring and suspended particles by filtering the water samples. We analyzed both the sediments and rock samples by the petrographic thin-sections, XRD whole rock, and XRD-clay fraction analysis to compare the minerals between the rock and sediment samples. We obtained Eocene-aged Planktonic Foraminiferal fossils in the spring sediments (in the thin sections), which perfectly fit the Eocene-aged limestone formation in the study area. By overlapping the lithological outcrop of the formation with the isotope-derived recharge elevation, we obtained the locations of two major dolines in the study area. As the final step, we validated our results by conducting dye-tracer tests from these points, and we recovered the tracer dye from the karst springs.