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Quantification of karst aquifer discharge components during storm events through end-member mixing analysis using natural chemistry and stable isotopes as tracers |
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| Authors: | Daniel H Doctor E Calvin Alexander Jr Metka Petri? Janja Kogov?ek Janko Urbanc Sonja Lojen Willibald Stichler |
| Institution: | 1. Department of Geology and Geophysics, University of Minnesota, 310 Pillsbury Dr. SE, Minneapolis, MN, 55455, USA 6. US Geological Survey, 345 Middlefield Rd., Menlo Park, CA, 94025, USA 2. Karst Research Institute, Titov trg 2, Postojna, Slovenia 3. Geological Survey of Slovenia, Dimi?eva, 14, Ljubljana, Slovenia 4. Jo?ef Stefan Research Institute, 39 Jamova Cesta, Ljubljana, Slovenia 5. GSF Institute of Hydrology, Ingolst?dter Landstr. 1, Neuherberg, Germany |
| Abstract: | Karst aquifer components that contribute to the discharge of a water supply well in the Classical Karst (Kras) region (Italy/Slovenia) were quantitatively estimated during storm events. Results show that water released from storage within the epikarst may comprise as much as two-thirds of conduit flow in a karst aquifer following rainfall. Principal components analysis (PCA) and end-member mixing analysis (EMMA) were performed using major ion chemistry and the stable isotopes of water (δ18O, δ2H) and of dissolved inorganic carbon (δ13CDIC) to estimate mixing proportions among three sources: (1) allogenic river recharge, (2) autogenic recharge, and (3) an anthropogenic component stored within the epikarst. The sinking river most influences the chemical composition of the water-supply well under low-flow conditions; however, this proportion changes rapidly during recharge events. Autogenic recharge water, released from shallow storage in the epikarst, displaces the river water and is observed at the well within hours after the onset of precipitation. The autogenic recharge end member is the second largest component of the well chemistry, and its contribution increases with higher flow. An anthropogenic component derived from epikarstic storage also impacts the well under conditions of elevated hydraulic head, accounting for the majority of the chemical response at the well during the wettest conditions. |
| Keywords: | Karst Hydrochemistry Stable isotopes Statistical modeling Groundwater/surface-water relations |
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