WATER ROUTING THROUGH THE CRITICAL ZONE: A HYDROMETRIC, HYDROCHEMICAL, AND ISOTOPIC INVESTIGATION IN NORTHERN NM

Mountain environments contribute substantially to basin aquifers and surface waters in the American Southwest and are an important component of water resources for large population centers downgradient. Many of those mountainous environments are composed of complex geology and intricate hydrologic flow paths. One such mountainous system, the Valles Caldera National Preserve in northern NM is the location of the Jemez River Basin Critical Zone Observatory (JRB-CZO). There, analysis of hydrometric, hydrochemical, and isotopic data are used to decipher water routing through the JRB-CZO and investigate groundwater contribution to streamflow, focusing on the role that subsurface structure, particularly fracture density and heterogeneous lithology, plays at different scales. Specific attention to groundwater from two hillslopes with contrasting lithology and subsurface structure informs our understanding of hydrologic response to different hydrologic flow regimes. Tritium and 14-carbon age tracers indicate that each groundwater store has a component of modern recharge despite mixing with much older water. Furthermore, distinctions in major ion chemistry and U-series isotope signatures indicate that groundwater in unweathered fractured bedrock dominantly contributes to streamflow, which highlights the need to better characterize the deep subsurface of high-elevation mountain systems.