CHEMICAL WEATHERING AND SOLUTE FLUX IN THE CRITICAL ZONE: CATCHMENT-SCALE HYDROLOGY IN THE JEMEZ RIVER BASIN, NEW MEXICO AND SANTA CATALINA MOUNTAINS, ARIZONA

In this study we aim to quantify solute fluxes and thus determine hydrologic factors that affect water fluxes and storage capacity at the catchment scale. Spatial and temporal relationships between chemical weathering and solute fluxes will be examined at the Jemez River Basin – Santa Catalina Mountains (JRB-SCM) Critical Zone Observatory. These sites– in northern New Mexico (JRB) and in southern Arizona (SCM) – span gradients in climate, lithology, and biota representative of the Southwestern US. Previous studies in the JRB show transit times may be related to flow path heterogeneity and aspect, however these alone do not explain hydrologic variability at the catchment scale. Solute sources and mineral weathering fluxes may depend on available water and energy. Precipitation in the JRB and SCM have two seasons of input; winter snowmelt and summer monsoons. SCM has a stronger monsoon input relative to snowmelt, whereas the inverse is true for JRB. Hydrochemically-distinct waters have been used to characterize intra-catchment flushing of shallow surface solutes and vegetation-mediated runoff generation processes. Catchment-specific surface and subsurface materials result in different geochemical reactions based on mineralogy, storage capacity and residence time. Solute flux was quantified using local precipitation and catchment outflow measurements of concentration and flow volume. Solutes in the streamflow originate from atmospheric deposition via local precipitation and mineral weathering within the catchment. The mass generated via mineral weathering equals the input mass was subtracted from the total mass measured. Daily flow data were combined with hydrochemical data collected at flumes at greater time intervals. Mass flux for each solute was calculated for each catchment. Comparisons between catchments at the same site (JRB or SCM) show the influence of physical variables on solute flux under the same climatic conditions. These flux calculations, along with our physical understanding of the system, give insight into the relationship between weathering rates and hydrologic residence time distributions that help explain both short (event-scale) and long-term (annual) fluxes of solutes.