DESERT SPRING CHARACTERIZATION FROM HYDROCHEMICAL DATA ANALYSIS

Springs in the water-stressed southern Great Basin of the U.S. are the primary source of perennial surface water. The hydrological response of springs to climate change, which will likely range from resilience to desiccation, will impact fragile ecosystems and human communities. Increasing climate change-related aridity is contributing to reduced alpine snowpacks, which are the most critical source of groundwater recharge in the western U.S. Some conceptual models for the Death Valley Regional Groundwater Flow System (DVRGFS) suggest that the Spring Mountains and Sheep Range serve as major recharge areas for the regional carbonate aquifer, yet groundwater flowpaths through and exiting these areas are poorly constrained. Extensive regional deformation related to the Sevier Orogeny and late Cenozoic extension has created a landscape with an amalgamation of rock types exhibiting widespread faulting and structural controls on groundwater flow, complicating the delineation of flowpaths.

One goal of our recently initiated research between the Spring Mountains, NV and Owens Valley, CA is to provide metrics linking tectonics to hydrologic connectivity and the evolution of groundwater flowpaths in order to assess spring resilience. To achieve this goal, we need to characterize spring source waters, local- to regional-scale groundwater flowpaths, and the impact of geologically complex terrane on groundwater flow. We assessed 46 recently sampled springs and defined which are suitable for long-term monitoring within the regional hydrochemical framework using a systematic approach. NWIS and USGS historical water quality data from wells, surface waters, and spring waters are combined with data from recently sampled springs to create a hydrochemical database. Using Q-mode HCA, we classify 259 water samples into hydrofacies and then extract statistically significant groupings for inverse geochemical modeling in PHREEQC. Initial results indicate that water recharging in the Spring Mountains geochemically evolves rapidly following carbonate dissolution reactions, even at local-scale springs. Regionally, as water moves west and south, shallower flowpaths interact with basinal evaporite deposits while deeper flowpaths inherit a volcanic aquifer signature, presumably from northern Amargosa Valley.