HYDROLOGICAL BALANCE IN THE BEAR LAKE WATERSHED, UTAH AND IDAHO USING MAJOR-ION AND STABLE ISOTOPE ANALYSIS

Geochemical signals from water and carbonate samples derived from lacustrine environments provide insights into past and modern hydrological regimes. Bear Lake, situated on the border of Utah and Idaho within the northeastern Great Basin, is sensitive to regional precipitation and temperature changes in the western United States. Hence, geochemical records from the lake are valuable in characterizing hydrological regimes in the region. Reported measurements in the literature have inferred underfilled to balance-filled conditions of the lake during interglacial periods and overfilled conditions during glacial periods. The present study seeks to disentangle controls on the past and modern hydrological balance of Bear Lake. Preliminary assessments of the geochemistry of lake carbonates sampled from cores deposited in the Continental Scientific Drilling (CSD) Facility at the University of Minnesota demonstrated significant variations in mineralogy, stable isotopes, and trace elements (Mg/Ca and Sr/Ca) over glacial-interglacial cycles. We report new major cation, anion, and stable isotope data of stream, river, and lake waters based on a sampling campaign within the Bear Lake catchment in May 2022, a period of near-peak discharge. Na-normalized Mg and Ca ratios in the water samples show mixing trends between carbonate and silicate end-members. Additionally, stable isotope data suggest weak correlations with elevation. This study aims to utilize these new analyses and, supplemented by previously published datasets, characterize an updated hydrological balance model for the lake system using both empirical concentration-discharge patterns in solute chemistry and observed relationships between stable isotopes in water and elevation.