CONSTRAINING GROUNDWATER DISCHARGE TO THE GIBBON RIVER NEAR NORRIS GEYSER BASIN USING DISSOLVED HELIUM, RADON AND CHLORIDE IN STREAM WATER, YELLOWSTONE NATIONAL PARK, USA

We use dissolved concentration of ²²²Rn, ³He, ⁴He and chloride measured in stream water to identify areas of groundwater discharge to Gibbon River along a near Norris Geyser Basin in Yellowstone National Park. Dissolved noble gas, ²²²Rn and chloride concentrations were measured synoptically at ~1km spacing along a ~35 km reach. Distinct zones of groundwater discharge can be detected by elevated ²²²Rn and increases in chloride. Using concentrations of He, Cl and Rn observed in cool and hydrothermal groundwater in the vicinity, constraints can be placed on the volumes of cool local groundwater discharge versus hydrothermal discharge to the Gibbon River. These results have significant implications for monitoring hydrothermal discharge at the watershed scale, and for separating locally derived water from deeper-circulating, regionally derived groundwater in volcanic terrains.