Geochemical insights into groundwater movement in alpine karst, Bear River Range, Utah, USA

Alpine karst aquifers control the availability and longevity of some water resources, but are not well understood. A conceptual model of the alpine karst aquifer system in the Bear River Range of northern Utah (USA) has been developed by geochemical analysis (major ions, δ¹⁸O, δ²H and δ¹³C values) of seasonal water samples from seven perennial springs, and residence-time assessment (³H and CFCs) of two low- and two high-discharge springs. All spring data can be explained by reaction paths dominated by the dissolution of calcian dolomite. The δ¹³C values align well with reaction paths for open-system dissolution. Saturation indices and low Ca:Mg molar ratios indicate that incongruent dissolution exerts a strong control on water–rock interactions, complicating interpretation of natural solute tracers. Values of δ¹⁸O and δ²H in springs follow the Utah meteoric water line. Snow δ¹⁸O values correlate with elevation, but not with increasing rainout distance, providing qualitative estimates of recharge elevation that generally align with previous dye-traces to five of the seven springs. Concentrations of ³H and CFCs likely are best described by binary mixing of subannual recharge with 60–65-year-old groundwater, suggesting that the alpine karst aquifer system in the Bear River Range is best represented by a double-porosity model. Subannual recharge documented by dye traces implies that caverns are the primary flowpaths to the springs, but the presence of decadal-age water may indicate that lower permeability flowpaths dominate during baseflow. No evidence was found for a longer-residing flow component, suggesting high sensitivity to future climate variability.