The Ecohydrology of Devils Hole, Death Valley National Park
AuthorHausner, Mark B.
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Devils Hole, a water-filled fracture in the carbonate aquifer underlying the Mojave Desert, is home to the only extant population of Devils Hole pupfish (<italic>Cyprinodon diabolis</italic>). In the mid to late 1990s, the population of <italic>C. diabolis</italic> began an unexplained decline. A number of different hypotheses have been advanced to explain this decline, including the impacts of climate change. This study combines field observations and computational fluid dynamic (CFD) modeling to address the effects of climate on the physical processes in Devils Hole, relating those physical processes to the conservation of Devils Hole pupfish. Fiber-optic distributed temperature sensors (DTS) were deployed in Devils Hole to observe temperatures at high spatial and temporal resolution, and the DTS data were used in conjunction with previously recorded temperatures to calibrate and validate FLUENT-based CFD models of convection in Devils Hole. Seasonal convection cycles in the deep pool of Devils Hole are controlled by surface temperatures and the geothermal gradient in the area, and occur primarily during the food-limited winter. Diurnal convection cells controlled by daily meteorological variation occur on the ecologically critical shallow shelf throughout the year, limiting the temporal window during which <italic>C. diabolis</italic> can successfully spawn. Simulations of the shallow shelf under past climate conditions and future projections show that climate change has likely already impacted the population of <italic>C. diabolis</italic>, contributing to their recent decline. Future simulations indicate that the window of annual recruitment is likely to occur earlier and earlier in the year, resulting in a shift of more than two weeks in the timing of annual recruitment cycle. This shift drives a considerable reduction of the food available to larval pupfish, reducing the likelihood of successful recruitment and exacerbating the conditions that led to the recent decline of the <italic>C. diabolis</italic> population. Finally, potential mitigation strategy of raising the water level in Devils Hole is examined, and future research into this strategy is recommended.