The shallow thermal regime of Devils Hole, Death Valley National Park

Devils Hole, a fracture in the carbonate aquifer underlying the Death Valley Regional Groundwater Flow system, is home to the only extant population of Devils Hole pupfish (Cyprinodon diabolis). Since 1995, the population of C. diabolis has shown an unexplained decline, and a number of hypotheses have been advanced to explain this. Here, we examine the thermal regime of Devils Hole and its influence on the pupfish population. We present a computational fluid dynamic (CFD) model of thermal convection on the shallow shelf of Devils Hole, which provides critical habitat for C. diabolis to spawn and forage for food. Driven by meteorological data collected at Devils Hole, the model is calibrated with temperature data recorded in the summer of 2010 and validated against temperatures observed on the shallow shelf between 1999 and 2001.The shallow shelf experiences both seasonal and diel variations in water temperature, and the model results reflect these changes. A sensitivity analysis shows that the water temperatures respond to relatively small changes in the ambient air temperature (on the order of 1 8C), and a review of local climate data shows that average annual air temperatures in the Mojave Desert have increased by up to 2 8C over the past 30 years. The CFD simulations and local climate data show that climate change may be partially responsible for the observed decline in the population of C. diabolis that began in 1995.

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