Hydraulics & Waterways
397604 - Application of isotopic and elemental data streams for estimating source and transformation processes in an agricultural karst system
Wednesday, June 6
8:30 AM - 10:00 AM
Location: Greenway CD
James Fox, Lexington, KY – University of Kentucky; Ethan Adams, Lexington, KY – University of Kentucky; William Ford, Lexington, KY – University of Kentucky; Jason Backus, Lexington, KY – Kentucky Geological Survey; Charles Taylor, Lexington, KY – Kentucky Geological Survey; Carmen Agouridis, Lexington, KY – University of Kentucky
The use of dissolved inorganic nitrogen tracers to assess provenance of groundwater contamination provides researchers and watershed managers a robust tool with which to address nutrient concerns. Traditional nutrient source provenance methods, however, are often limited in application to karst studies due to pathway mixing and isotope fractionation processes during temporary fate of nitrogen in karst. Mature karst systems (i) provide high connectivity between surface and subsurface flowpaths; (ii) exhibit pronounced spatial heterogeneity with regards to distribution and porosity of karst pathways (e.g., quick, fracture, and macropore flow); and (iii) harbor subsurface microbial communities which alter surface-derived dissolved and particulate matter. Our objective was to elucidate pathway and fractionation processes that control nutrient export and fate in karst watersheds. The authors applied elemental and isotope tracer sampling of surface stream and subsurface karst conduit waters under multiple flow scenarios, including flood and drought conditions. Event-based sampling highlights the physical transport and turbulent mixing of karst pathways while low-flow sampling isolates in-conduit biochemical processes from surface recharge. Samples were analyzed for nitrate, nitrate isotopes (δ15N & δ18O), water isotopes (δ2H & δ18O), and dissolved inorganic carbon isotope (δ13C). Additionally, the authors advance numerical karst modeling by coupling isotopic and elemental field data streams with physical and biogeochemical modeling of nitrate source, fate, and transport and apply the model to the Cane Run watershed, Kentucky, USA. Results emphasize the role of pathway mixing and karst storage in controlling nitrate flux from the karst watershed. Further results indicate biochemical enrichment of heavier nitrate isotopes within the surficial fine-grained biofilm of the karst conduit. The authors encourage karst watershed modelers to apply hydrologic routing and nutrient fate methods to contamination source apportionment so as to further constrain and improve the accuracy of results.