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Hydrological and biological investigations were done during 2005 and 2006 in cooperation with the U.S. National Park Service to investigate the source, discharge, and chemical characteristics of selected springs and the abundance and health of endemic anuran (frog and toad) species at Darwin Falls in Death Valley National Park, Piute Spring in Mojave National Preserve, and Fortynine Palms Oasis in Joshua Tree National Park. Discharge from the springs at these sites sustains isolated riparian habitats in the normally dry Mojave Desert. Data were collected on water quantity (discharge) and quality, air and water temperature, and abundance and health of endemic anuran species. In addition, a single survey of the abundance and health of endemic anuran species was completed at Rattlesnake Canyon in Joshua Tree National Park. Results from this study were compared to limited historical data, where they exist, and can provide a baseline for future hydrological and biological investigations to evaluate the health and sustainability of the resource and its response to changing climate and increasing human use. Radiocarbon dating of the water yielded estimated ages of about 7,000 years at Piute Spring and about 3,000 years at Darwin Spring, and tritium-helium-3 dating indicated an age of less than 2 years at Fortynine Palms Oasis. Stable hydrogen-isotope ratios were used to interpret an average altitude of recharge of 2,348 meters for Darwin Spring (about 1,415 meters higher than the altitude of Darwin Spring), 1,668 meters for Piute Spring (about 766 meters higher than the altitude of Piute Spring), and 1,400 meters for the Upper Pool at Fortynine Palms Oasis (about 543 meters higher than the altitude of the Upper Pool). Water-quality data collected for this study did not appear to be sensitive to trends in precipitation or seasonality in the Darwin Falls and Piute Spring study areas; however, it was sensitive to trends in Fortynine Palms Oasis where salinity increased by more than 10 percent during the 2 years of this study. Such a rapid response is consistent with the comparatively short travel time of less than 2 years from recharge to discharge at Fortynine Palms Oasis. Of the 14 trace elements analyzed, only concentrations of uranium at Fortynine Palms Oasis and arsenic at Darwin Spring were above drinking water standards; both constituents are derived from natural sources in the drainage basin and, therefore, are likely to have accumulated as a result of natural processes. Endemic anuran species were surveyed at Darwin Falls for the western toad (Anaxyrus boreas) and the red-spotted toad (Anaxyrus punctatus), at Piute Spring for the red-spotted toad, and at Fortynine Palms Oasis for the red-spotted toad and California treefrog (Pseudacris cadaverina). Historically, redspotted toads were at the edge of their range at Darwin Falls, but they were not detected during this study and have not been detected since the early 1980s. The 2006 western toad population at Darwin Falls was estimated at 381 adults (95-percent confidence interval [CI] of 314–482). The population of red-spotted toads at Piute Spring was estimated at 1,153 adults (95-percent CI of 935–1,503). However, an elevated rate of abnormalities (approximately 5 percent) was recorded in redspotted toads as well as the presence of the chytrid fungus, Bactrochochytrium dendrobatidis, at Piute Spring. In Joshua Tree National Park, the California treefrog now occupies only three of the seven historically occupied drainages. Populations of California treefrogs at Fortynine Palms Oasis have declined more than 50 percent from 288 in 1969–71 to 109 in 2006. A similar decline was observed in the populations of red-spotted toads at Fortynine Palms Oasis from 300 adults in 1969–71 to 155 adults (95-percent CI of 90–139) in 2006. The red-spotted toads at Fortynine Palms Oasis also exhibited the presence of Bactrochochytrium dendrobatidis. 2 Source, Discharge, and Chemical Characteristics of Selected Springs and Endemic Anuran Species, Mojave Network Parks Chapter A. Introduction By Roy A. Schroeder, Elizabeth Gallegos, Gregory A. Smith, Peter Martin, and Robert N. Fisher The Mojave Desert consists of 152,000 square kilometers (km2) of land that extends across eastern California, southern Nevada, northern Arizona, and western Utah (fig. 1), and is considered one of the most climatically extreme environments within the United States (Bailey, 1995). A substantial amount of the Mojave Desert’s biodiversity is present in isolated riparian habitats that are supported by perennial springs, and these habitats commonly include a few endemic anuran (frogs and toads) species (Greene and Luke, 1996). Anurans, whose skin is susceptible to desiccation, are at the edge of their physiological limits in this arid region and, therefore, rely on spring-supported habitats for breeding and recruitment (Greene and Luke, 1996). Desert springs generally discharge small volumes of water that are derived from either infrequent, short-lived, high-intensity precipitation events; regional interbasin groundwater flow; or a combination of both. Reliance on these processes makes these riparian habitats sensitive to climatic changes (such as in precipitation and air temperature) and anthropogenic effects (such as water consumption, pollution, introduction of invasive species, and recreational use). It is necessary to understand the hydrological processes supporting spring discharge in order to appropriately manage these riparian habitats. First-order insight into these processes can be gained by examining spring discharge, sources of water to the springs, and rates of recharge to the springs. Detailed habitat and anuran community characterizations over time are needed to document changes in habitat and anuran community dynamics that are taking place in response to human and natural disturbances, declining water supply, and natural cyclical patterns. The U.S. Geological Survey (USGS), in cooperation with the U.S. National Park Service (NPS), undertook this study to help determine the hydrological and biologic health of these riparian habitats, and their susceptibility to drought and possible adverse human effects such as groundwater development. The biological data collected for this study are part of the USGS Amphibian Research and Monitoring Initiative (ARMI), which is a national program of amphibian monitoring, research, and conservation. The state of knowledge regarding the health of riparian biota and the hydrology of perennial desert springs within the Mojave Network Parks (including the Death Valley National Park, Mojave National Preserve, and Joshua Tree National Park) was inadequate to properly manage these resources when this study was started in 2005 (fig. 1). Biological surveys have identified the presence of six anuran species, but little data are available on the hydrological properties of their associated springs habitat (Stebbins, 2003). Poff and others (1997), and Baron and others (2002) documented the adverse effect of urbanization-altered flow regimes on amphibians, and Corn (2005) reported that temperature and precipitation fluctuations have also affected anurans; the extent to which changes in amphibian populations are in response to natural fluctuations or to human effects remains unclear. Pohlmann and others (1998) used water-quality, and stableand radiogenicisotope data to infer water source for 36 springs in and near the Lake Mead National Recreation Area (fig. 1), which also lies within the Mojave Network Parks. The Metropolitan Water District of Southern California proposed a water storage project known as the Cadiz Groundwater Storage and Dry-Year Supply Program adjacent to the Mojave National Preserve (fig. 1) in the late 1990s, which planned to recharge and store Colorado River (fig. 1) water in the Fenner, Bristol, and Cadiz drainage basins during wet years, and to withdraw stored Colorado River water and local groundwater during dry years (Metropolitan Water District of Southern California and Bureau of Land Management, 2001). There were concerns that the project might negatively affect the flow of springs in the Mojave National Preserve (fig. 1; Metropolitan Water District and Bureau of Land Management, 2001). Because of these concerns, a groundwater monitoring and management plan was developed in the final environmental impact statement/ environmental impact report for the Cadiz Groundwater Storage and Dry-Year Supply Program to ensure that the project did not cause adverse effects to groundwater-related critical resources (Metropolitan Water District and Bureau of Land Management, 2001). In 2002, the Metropolitan Water District of Southern California decided not to proceed with the Cadiz Groundwater Storage and Dry-Year Supply Program, and as of 2014 the Program has not been constructed. In 1999, the NPS instituted a program to inventory and monitor natural resources in approximately 270 park units across the Nation, referred to as the Inventory and Monitoring Program (National Park Service, 1999). The program is being implemented by forming 32 networks of parks that share common management concerns and geography. The purpose of the monitoring program is to provide park managers with status and trends data on select indicators that represent the health of natural resources in the different park units. These indicators are termed “vital signs,” and they will be monitored under a set of protocols that provide detailed guidance on the methods, schedules, analytical tools, and reporting procedures. In 2004, the Mojave Network Parks Inventory and Monitoring program began a process to identify and rank vital signs for each of the park units within the Mojave Network Parks. Monitoring the vital signs of aquatic and riparian habitats was ranked high by the Mojave Network Parks for the Death Valley National Park, the Mojave National Preserve, and the Joshua Tree National Park (C

scientific investigations report

The source, discharge, and chemical characteristics of selected springs, and the abundance and health of associated endemic anuran species in the Mojave network parks