DEVILS HOLE: THE INTERSECTION OF GROUNDWATER AND SURFACE WATERS AS AN INDICATOR OF CLIMATE CHANGE

Devils Hole, a water-filled fracture in the carbonate aquifer of the Death Valley Regional Flow System, comprises an entire ecosystem at the intersection of groundwater and surface waters. This 50 m² pool of unknown depth is home to the only extant population of the endangered Devils Hole pupfish (Cyprinodon diabolis), and has been at the center of conflicts between economic development and ecological protection for forty years. A shallow shelf in the system provides the most suitable habitat for spawning, and the pupfish population counts have been correlated to the water level in the system. Recently, however, population declines unrelated to water level have been observed. The 33° C waters of Devils Hole are near the upper threshold for most Cyprinodon species. A hydrodynamic model of the shallow shelf demonstrates the strong influence of climate drivers (temperature, solar radiation, and relative humidity) on the water temperatures where adult fish spawn, eggs hatch, and larvae develop. The thermal convection patterns caused by these drivers also influence the oxygen dynamics, nutrient cycling, and food web within Devils Hole. Although increased peak temperatures are unlikely to have an acute impact on the system, longer summers may result in a shortened reproductive season and reduced recruitment in the pupfish population. The limited habitat and very small population (there were approximately 100 individuals in spring, 2011) of Devils Hole pupfish combine to make this ecosystem extremely susceptible to climate change, and the modeling and management efforts currently undertaken in this system may be considered a pilot project for larger scale climate monitoring efforts.