Sources, fate, and flux of geothermal solutes in the Yellowstone and Gardner Rivers, Yellowstone National Park, WY

The total discharge and thermal output from the numerous hydrothermal features in Yellowstone National Park (YNP) can be estimated from the chloride (Cl) flux in the Madison, Yellowstone, Falls, and Snake Rivers. Monitoring the Cl flux in these four major rivers provides a holistic view of the hydrothermal output from YNP and changes in the Cl flux may indicate changes in geothermal or magmatic activity. In this study, the source, fate, and flux of geothermal solutes in the Yellowstone River and Gardner Rivers were determined. Beginning in 2012, the fluxes of geothermal solutes, including Cl, were determined at monitoring sites in the Yellowstone and Gardner Rivers downstream of geothermal inputs within YNP. A method was developed using specific conductance as a surrogate measure for solute concentrations at these monitoring sites. Combining continuous (15-min) specific conductance and discharge data, Cl and other geothermal solute fluxes were determined at both sites and approximately 32% of the Cl flux exiting YNP is from the Yellowstone River watershed. Synoptic sampling of river water and discharge measurements were performed during low-flow conditions of September 2014 allowed for the determinations of geothermal solute sources and their downstream fate. Thus, the contribution of geothermal solutes from the various geothermal areas at the downstream monitoring sites was quantified. The thermal features draining into Yellowstone Lake account for 34% of the Cl flux at the Yellowstone River monitoring site which is located approximately 5 km north of YNP. The Gardner River, which captures geothermal water from Mammoth Hot Springs, is responsible for 22% of the Cl at the Yellowstone River monitoring site. Because the Yellowstone River watershed is large and contains numerous thermal areas, knowing the source and fate of geothermal solutes is import baseline information that can be used to identify future changes in thermal activity.