UC San Diego

Hydrothermal systems are important for a myriad of reasons. Life itself may have begun in hydrothermal ecosystems, and in more modern times these environments are serving as refugia for many unique and vulnerable species. In the Great Basin region of North America, regional aquifer hydrothermal springs support a disproportionate number of endemic species, some of which live in only one hydrothermal spring. Many of these organisms appear to be relict species that may have had far wider distributions in the past when climatic conditions were wetter and large pluvial lakes covered vast areas within the Great Basin. Today, regional aquifer hydrothermal springs provide important information regarding regional biogeography, paleohydrological connectivity, and climate change. However, these unique ecological hotspots also face many anthropogenic threats including groundwater depletion and pollution, flow diversions, and the introduction of exotic species. The unique physical and geochemical characteristics of hydrothermal systems may also protect some vulnerable amphibian species from pathogens. In Arizona and Nevada, several species of frogs and toads inhabit hydrothermal ecosystems, and the elevated temperatures in these environments appear to be protecting them from the amphibian chytrid fungus Batrachochytrium dendrobatidis, which causes the potentially fatal disease chytridiomycosis. The Dixie Valley toad, a yet undescribed species currently restricted to four thermal spring-fed wetlands within Dixie Valley NV, appears to be a relict member of the western toad (Anaxyrus boreas) species group. We surveyed populations of Dixie Valley toads between 2009-2012, and also tested individuals for Bd in 2011-12. While none of the toads tested positive for Bd, the prevalence of Bd infections among nearby populations of introduced American bullfrogs increased significantly. This unique and vulnerable species also faces threats from increased exploitation of nearby geothermal energy resources. In Napa and Sonoma Counties, California we used multivariate statistical analyses and mixing models to elucidate the occurrence and extent of contamination of local groundwater used for drinking water by hydrothermal fluids. We found that several public supply wells used for drinking water and irrigation have concentrations of As, F and B that exceed drinking-water standards or notification levels due to contamination by hydrothermal fluids