LIFE IN THE RAIN SHADOW: UNDERSTANDING SOURCES OF RECHARGE AND GROUNDWATER FLOWPATHS TO GROUNDWATER DEPENDENT ECOSYSTEMS IN THE PANAMINT RANGE, DEATH VALLEY, CALIFORNIA, USA

Despite its location in the rain shadow of the southern Sierra Nevada, the Panamint Range within Death Valley National Park, CA hosts a complex aquifer system that supports numerous springs. These springs, in turn, support unique groundwater-dependent ecological communities. Spring emergences range in elevation from 2434 m above sea level (within the mountain block) to 77 m below sea level (in the adjacent basins). We collected waters from representative Panamint Range springs and analyzed environmental isotopes and geochemical tracers to address the following questions: 1) What is the primary source of recharge for the springs? 2) What groundwater flowpaths and geologic units support springflow generation? and 3) What are the residence times of the springs? The stable isotopic composition (δ¹⁸O and δ²H) of spring water and precipitation indicate that localized high-elevation snowmelt is the dominant source of recharge to these perennial springs, though recharge from rainfall is not wholly insignificant. Geochemical evolution was evaluated using principle component analysis to compare the concentrations of all major spring cations and anions in a multidimensional space and group them according to dominant geochemical signatures. These resulting geochemical groups are controlled by spring emergence types and residence times rather than distinct geologic controls, and indicate a similar aquifer type throughout the majority of the range. The Noonday Dolomite and Beck Spring Formations are the primary water-bearing units in the mountain block based on ⁸⁷Sr/⁸⁶Sr of spring water and rock samples. They offer higher hydraulic conductivities than other formations and are chemically similar. Radiocarbon and ³⁶Cl derived residence times of these spring waters range from modern to approximately 2000 years, with shortest residence time spring waters at higher elevations and increasing residence times with decreasing elevations. This residence time-elevation relationship is likely topography driven. Two springs located just north of the Owlshead Mountains, however, are the exception to this trend and are likely driven by the intersection of groundwater along deep faults as they are slightly warmer and much older than the remaining springs.