Characterization of seasonal groundwater origin and evolution processes in a geologically heterogeneous catchment using geophysical, isotopic and hydro‐chemical techniques (Lough Gur, Ireland)

Lough Gur is a shallow groundwater fed eutrophic lake situated within small agricultural catchment containing volcanic and karst rock features in mid-west Ireland. Seasonally active conduits linking two spring discharge locations from the under high flow conditions were revealed using dye tracing terrestrial geophysical survey, highlighting architecture of conduit path to its spring. A radon survey combined with identified in-lake springs thickness lakebed sediments. Falling head hydraulic characterization experiments illustrated heterogenous nature sediments hydrograph analysis coupled stable isotopes water (δ18O δ2H) significant surface - interaction during periods. Significantly, δ18O δ2H signatures plot above global meteoric line local indicating hydration silicate minerals direct isotope exchange between minerals. Groundwater low periods indicate that recharge sources are influenced by enriched waters precipitation while wider range indicates greater variation sources. D-excess illustrate rapid rainfall infiltration conditions, thereby demonstrating vulnerability groundwater, confirm widespread water-groundwater interaction/mixing. Hydrochemical analyses both weathering carbonate dissolution as primary geochemical processes Mg/Ca ratios suggesting residence time Correlations δ13CDIC dissolved organic carbon suggest seasonal switch source DIC groundwaters oxidation matter summer winter. The SI saturation index for calcite (SIC) illustrates calcium along CO2 evasion be perennial processes. Finally, spatial nitrate isotopic (δ18ONO3- δ15NNO3-) suggests number including soil nitrogen, manure and/or domestic effluent indications denitrification conditions.