Ash Meadows Research Articles

Disappearance of a dominant bosque species: screwbean mesquite (Prosopis pubescens)

Historic surveys record screwbean mesquite (Prosopis pubescens) as widespread and dominant within upland riparian communities of the U.S. Southwest. I compared herbarium records and published surveys with surveys I conducted throughout the former range of P. pubescens. I found that this species has disappeared from 53% of its former range and has declined in density at eight of nine sites compared. Of 112 sites surveyed, only Ash Meadows National Wildlife Refuge has dense groves of P. pubescens over a large area. Prosopis pubescens remains in protected areas but not in urbanized areas. Declines of southwestern riparian species such as cottonwood and willow are well documented, but this is the first example of a declining species that is typically considered drought tolerant and is often found farther away from the stream course. Human alteration of rivers is therefore likely to be influencing plant communities as far away as a kilometer from the river itself.

Condensation-corrosion speleogenesis above a carbonate-saturated aquifer: Devils Hole Ridge, Nevada

The Devils Hole Ridge, a small block of Paleozoic carbonate rocks surrounded by the Amargosa Desert in southern Nevada, is located at the discharge end of the Ash Meadows regional carbonate groundwater flow system. The massif hosts the famous Devils Hole, a near-vertical extensional fracture which intersects slightly thermal groundwater (33.6°C) and whose walls are coated below the water table by thick mammillary calcite. The latter was deposited continuously over the last ca. 600kyr, indicating that the water underneath Devils Hole Ridge was supersaturated with respect to calcite during this time span. Rocks, located more than 9m above the present-day water table, remained in the unsaturated (vadose) zone. Continuous, long-term presence of thermal water and the extensional tectonic setting, creating underground thermal lakes in open fractures, is associated with intense dissolution above the water table. Condensation corrosion is responsible for modifications of the morphology of the subaerial parts of the tectonic caves. We also describe, for the first time, the Devils Hole Prospect Cave, which was created almost entirely by condensation corrosion. Caves and cavities in the Devils Hole Ridge are an interesting example of hypogene speleogenesis, by condensation corrosion, operating above an aquifer which was demonstrably supersaturated with respect to calcite for hundreds of thousands of years.

Noteworthy record of Crawford's desert shrew (Notiosorex crawfordi) from southern Nevada

Abstract We review the known records of desert shrews from Nevada and report the results of genetic analyses of a specimen from Ash Meadows National Wildlife Refuge, Nye County, Nevada, which help clarify the evolutionary relationships of the genus Notiosorex from southwestern United States.

Discerning invasion history in an ephemerally connected system: landscape genetics of Procambarus clarkii in Ash Meadows, Nevada

The delimitation of dispersal routes used by individuals moving between populations has the potential to direct management efforts aimed at limiting the spread of invasive species. Red swamp crayfish (Procambarus clarkii) have successfully invaded aquatic ecosystems across much of the globe, causing loss of biodiversity and habitat destruction. Our research focuses on a Mojave Desert spring system in Ash Meadows National Wildlife Refuge, where a combination of anthropogenic habitat degradation and the establishment of invasive species have caused extinctions, extirpations, and severe population declines of endangered fishes. To infer the invasion history of hydrologically isolated springs, we tested alternative hypotheses of P. clarkii dispersal routes and colonization events throughout Ash Meadows using a landscape genetics approach that combined analysis of microsatellite and mitochondrial DNA genotypes with geographic information system (GIS) mapping. Modeled historic outflows, in conjunction with waterway mapping based on aerial imagery and LiDAR data, show variable drainage routes across the flat topography of Ash Meadows. Estimates of gene flow between P. clarkii populations revealed the drainages utilized by crayfish to move from central to peripheral springs. Additionally, analyses of mtDNA haplotype diversity and distribution suggest isolated springs were colonized by few individuals, and subsequent emigration has been rare. These results will inform ecological restoration in Ash Meadows by directing the placement of barriers to prevent reinvasion of distal springs after eradication of P. clarkii populations. Finally, this research provides a case study for elucidating the functional connectivity of ephemerally connected landscapes, using the integration of genetic and GIS techniques.

Pollination Biology ofAstragalus phoenix(Fabaceae) with Notes on the Natural History of its Pollinator,Anthophora porterae(Hymenoptera: Apidae)

Astragalus (Fabaceae) is a broadly distributed, diverse, and economically important group of plants. Given the number of species and its distribution, it is not surprising that there are many species that are highly restricted and endangered. Among these is the Ash Meadows milkvetch, Astragalus phoenix. Here we investigate the breeding biology of As. phoenix. Our data show that As. phoenix is xenogamous and that Anthophora porterae (Hymenoptera: Apidae) is the most likely pollinator. We also noticed Apis mellifera visiting As. phoenix, though it appears unlikely that Ap. rnellifera contributes significantly to the reproductive success of As. phoenix. We located a nesting aggregation of An. porterae and offer a description of its nest architecture.

Systematics of a widely distributed western North American springsnail, Pyrgulopsis micrococcus (Caenogastropoda, Hydrobiidae), with descriptions of three new congeners

We describe three new species of springsnails (genus Pyrgulopsis) from the Amargosa River basin, California and Nevada (P. licina sp. n., P. perforata sp. n., P. sanchezi sp. n.), each of which was previously considered to be part of P. micrococcus. We also restrict P. micrococcus to its type locality area (Oasis Valley) and redefine a regional congener, P. turbatrix, to include populations from the central Death Valley region and San Bernardino Mountains that had been previously identified as P. micrococcus. The five species treated herein form genetically distinct lineages that differ from each other by 4.2–12.6% for mtCOI and 5.2–13.6% for mtNDI (based on previously published and newly obtained data), and are diagnosable by shell and/or penial characters. The new molecular data presented herein confirm sympatry of P. licina and P. sanchezi in Ash Meadows (consistent with morphological evidence) and delineate an additional lineage of P. micrococcus (in the broad sense) that we do not treat taxonomically owing to the paucity of morphological material. Conservation measures are needed to ensure the long term persistence of populations of P. micrococcus and a genetically differentiated lineage of P. sanchezi which live in disturbed habitats on private lands.

Geographically disjunct populations and widespread genets in an endangered halophilic plant, the Amargosa niterwort (Nitrophila mohavensis)

Nitrophila mohavensis, commonly known as Amargosa niterwort, is a perennial forb classified in the family Chenopodiaceae. The species is restricted to moist alkaline soils of the Ash Meadows National Wildlife Refuge and nearby localities within the Amargosa River basin and is currently listed as endangered. We isolated several polymorphic microsatellite loci and characterized genotypes from individuals spanning the range of the species as a means of inferring reproductive mode and population structure for the species. Out of 178 plants sampled from 35 different sample sites, there were 78 different multilocus genotypes. Most individuals had unique genotypes; however, there were many genotypes that were found in more than one individual and the most common genotype was sampled from 13 individuals. In addition, three genotypes were sampled from individuals across the range of the species, a maximum distance of more than 50 km. The results suggest that N. mohavensis reproduces clonally and by outcrossing. The relative frequency of the two reproductive strategies appears to vary among localities. There is not strong genetic differentiation among geographically separated clusters of plants. While the species is locally abundant and does not appear to suffer from inbreeding due to a small number of genets, continued local groundwater extraction coupled with forecasts of increasing regional desiccation due to accelerated climate change may combine to cause future population declines of N. mohavensis across its range.

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

Lay AbstractDevils Hole is an open, water‐filled fault in Ash Meadows National Wildlife Refuge that is home to the world's only population of endangered Devils Hole pupfish (Cyprinodon diabolis). In 1995, the population of Devils Hole pupfish began to decline, and to date no single cause for this decline has been identified. This article examines the influence of water temperature on the Devils Hole pupfish population by considering a part of the habitat that is critical to the pupfish's reproductive cycle: the shallow shelf at the south end of the pool. A mathematical model of the shallow shelf is used to examine the daily patterns of water flow and temperature change that result from the daily cycles of air temperature and solar radiation. The model matches well the data collected during this and other studies and shows that the shallow shelf of Devils Hole will respond to small changes in air temperature. Over the past 30 years, the southwestern United States has experienced an increase of up to 2 °C in average air temperature, and this increase has the potential to negatively affect the population of Devils Hole pupfish. The changes in local climate over this time period may have contributed to the decline of the Devils Hole pupfish population.

Using Water Chemistry, Isotopes and Microbiology to Evaluate Groundwater Sources, Flow Paths and Geochemical Reactions in the Death Valley Flow System, USA

Springs of Ash Meadows and Furnace Creek (near or in Death Valley, CA) have nearly constant flow, temperature, chemistry, and similar δ2H and δ18O signatures. These factors indicate shared water sources and/or analogous geochemical reactions along similar flow paths. DNA-based (16S rRNA gene) microbial diversity assessments further illuminate these relationships. Whereas, all Ash Meadows springs share related archaeal populations, variations in carbon-14 (Crystal Spring) and strontium isotopes, Na+, SO2-, and methane concentrations (Big Spring), correspond with microbial differences within and between the two discharge areas. Similar geochemical signatures linking Ash Meadows and Furnace Creek springs appear to support a distinct end member at Big Spring in Ash Meadows, which is also supported by coincident enrichment in microbial methanogens and methanotrophs. Conversely, DNA libraries from a deep carbonate well (878 m) located between Ash Meadows and Furnace Creek (BLM-1), indicate no shared microbial diversity between Ash Meadows or Furnace Creek springs.

Faunal study of velvet ants (Hymenoptera: Mutillidae) and their activity patterns and habitat preference at Ash Meadows National Wildlife Refuge, Nye County, Nevada, USA

Faunal study of velvet ants (Hymenoptera: Mutillidae) and their activity patterns and habitat preference at Ash Meadows National Wildlife Refuge, Nye County, Nevada, USA

Faunal study of velvet ants (Hymenoptera: Mutillidae) and their activity pat-terns and habitat preference at Ash Meadows National Wildlife Refuge, Nye County, Nevada, USA

The diversity of velvet ants at Ash Meadows National Wildlife Refuge (AMNWR) is investigated along with seasonal flight time and habitat preference for each species. Of the 45 (SD ± 2) species expected to occur at AMNWR via first order jackknife estimator, 42 species were found to occur based on 8843 specimens. Variation in flight times between specieswere minor and revealed a unique pattern of niche partitioning in only one species, Dasymutilla arenivaga Mickel. Habitat preferences were observed for seven species at AMNWR. Dasymutilla arenivaga, Odontophotopsis melicausa (Blake), and Sphaeropthalma orestes (Fox) were found to be more abundant in sand dune habitats than in non-sand dune habitats. While four other species, Odontophotopsis mamata Schuster, O. microdonta Ferguson, O. serca Viereck, and Sphaeropthalma mendica (Blake), were found to be more abundant in non-sand dune habitats. The diversity of velvet ants found at AMNWR was compared to the diversity of velvet ants found at the Nevada Test Site (NTS) located approximately 25 mile northeast of Ash Meadows. This comparison identified six velvet ant species that occurred at the NTS, but were not found at AMNWR. The status of Photopsis nana Ashmead 1896 is reinstanted. New synonymy is proposed for Photopsis nana Ashmead 1896 (=Mutilla acontius Fox, 1899, syn. nov.). Diagnoses and a key are provided for the velvet ants of AMNWR. The hitherto unknown female of Sphaeropthalma megagnathos Schuster is described, and an updated key to the females is provided for S. imperialis species-group. Lectotypes are designated for twelve species.

Holocene dune formation at Ash Meadows National Wildlife Area, Nevada, USA

Small isolated dune fields in the northern Mojave Desert are important centers of biodiversity and archaeological occupation sites. Currently dunes at Ash Meadows, Nevada, are stabilized by vegetation and are experiencing erosion of their upwind margins, indicating a negative sediment budget. New OSL ages from dunes at Ash Meadows indicate continuous eolian accumulation from 1.5 to 0.8ka, with further accumulation around 0.2ka. Prior studies (e.g., Mehringer and Warren, 1976) indicate periods of dune accumulation prior to 3.3ka; 1.9–1ka; and after 0.9ka. These periods of eolian accumulation are largely synchronous with those identified elsewhere in the Mojave Desert. The composition of the Ash Meadows dunes indicates their derivation from regional fluvial sources, most likely during periods when axial washes were active as a result of enhanced winter precipitation.

Predictive modelling of burn probability and burn severity in a desert spring ecosystem

Little is known about the fire ecology of desert springs, despite their importance for biodiversity and for provision of ecosystem services. Desert spring ecosystems are characterised by high and continuous fuel loads compared with surrounding uplands, suggesting that fire may play a significant ecological role. For the Ash Meadows spring complex in the south-western USA, we used ecological-niche factor analysis and a Bayesian model averaging regression technique to characterise the environmental conditions associated with spatially explicit burn probability and burn severity over a 24-year period. Burn probability and burn severity were both more strongly associated with fuel availability than with proximity to anthropogenic ignition sources; however, areas with more homogeneous vegetation cover were positively associated with high-severity burns but were negatively associated with burn probability. Burn probability was greater near areas of high anthropogenic influence, whereas areas further from anthropogenic alteration were more likely to experience high-severity fire. Riparian forest and emergent wetland vegetation were most likely to burn although they were among the rarest vegetation types. Human activities may strongly influence fire regimes in desert spring wetlands through groundwater pumping and introductions of exotic plants that alter fuelbed heterogeneity and shift the balance among woody and herbaceous vegetation.

New species and records of springsnails (Caenogastropoda: Cochliopidae: Tryonia) from the Chihuahuan Desert (Mexico and United States), an imperiled bio-diversity hotspot

We describe 13 new, narrowly localized species of the aquatic gastropod genus Tryonia from springs in the Chihuahuan Desert (Chihuahua and Texas): T. allendae n. sp., T. angosturae n. sp., T. chuviscarae n. sp., T. contrerasi n. sp., T. julimesensis n. sp., T. metcalfi n. sp., T. minckleyi n. sp., T. molinae n. sp., T. oasiensis n. sp., T. ovata n. sp., T. peregrina n. sp., T. taylori n. sp. and T. zaragozae n. sp.. These novelties are distinguished by shell and other morphologic characters and are well differentiated genetically from each other and from other congeners (mtCOI sequence divergence >1.9%). We also provide two new records for T. seemani (Frauenfeld, 1863), which is distributed near the southern limit of the Chihuahuan Desert (Durango State) and previously had been thought to be possibly extinct. Bayesian analysis of a mtCOI dataset resolved two clades composed of novelties described herein: one (containing four species) is distributed in several drainages in Chihuahua, the other (containing three species) is a local species flock in the Río Conchos basin (also in Chihuahua) that lives in the warmest waters yet recorded for Tryonia (41–44°C). (The phylogenetic relationships of the other new species were not well supported.) Both of these clades contain sympatric species pairs; co-occurrence of Tryonia congeners previously had been reported only in Ash Meadows (southern Nevada). Some of the species described herein are from previously unsurveyed localities and may help delineate new areas of endemism within the Chihuahuan Desert. One of the new species (T. julimesensis) became extinct between 1991 and 2001 and another (T. oasiensis) disappeared from its single known locality shortly after it was first discovered in 2009 and also may be extinct. The other species treated herein are at risk of extirpation owing to the declining extent and condition of their unprotected habitats.

THE EFFECTS OF GLOBAL CLIMATE CHANGE ON THE ENERGETICS OF AN ENDANGERED DESERT PUPFISH

When Pleistocene waters receded from the Death Valley region, once continuous pupfish populations became stranded in isolated warm springs. One of these springs, Devils Hole, maintains a temperature of 33–34° C year round except on a shallow ledge where temperatures may range from 28 to 39° C on a seasonal basis. Between 1995 and 2006 population estimates declined from a maximum of over 500 to only 38 individuals. Supplemental feeding, beginning in 2007, resulted in recovery to approximately 120 fish. We have estimated energetic requirements from oxygen consumption measurements with hybrids between Devils Hole and Ash Meadows Pupfish (Cyprinodon diabolis x C. nevadensis mionectes) and found the population decline and subsequent recovery to be consistent with the decline in primary production and the energetic value of the supplemental diet. We have also found that oxygen consumption increases as predicted between 28 and 31° C, with Q10 values between 2 and 3 but does not further increase between 31 and 34° C indicating an inability to sustain oxidative metabolism at temperatures normally encountered in Devils Hole. We contend that although these fish inhabit warm springs, they are poorly adapted to thrive at warm temperatures. Modest temperature increases associated with global climate change may be applying an energetic stress that will result in the extirpation of these and other desert pupfish populations.

Identification of probable groundwater paths in the Amargosa Desert vicinity

In this study, the hydrogeochemical program PHREEQC was used to determine the chemical speciation and mineral saturation indices (SIs) of groundwater in the vicinity of the proposed high-level nuclear waste repository at Yucca Mountain, Nevada (USA). In turn, these data were used to interpret the origin and recharge mode of groundwater, to elucidate the mechanisms of flow and transport, and to determine potential sources of groundwater contamination. PHREEQC was run to determine aqueous dissolved species and minerals that would be in equilibrium with the study area’s groundwater. Selected major ions, associated SI, F− and Ca/Na ion exchange were then examined using the multivariate statistical methods of principal component factor analysis and k-means cluster analysis. Analysis of dissolved ion concentrations, SIs, and Ca/Na ion exchange allows simultaneous consideration of arithmetic (raw concentrations) and logarithmic (SI, ion exchange) variables that describe the hydrochemical system and, therefore, can provide further insight into the system’s behavior. The analysis indicates that the dominant processes and reactions responsible for the hydrochemical evolution in the system are (1) evaporative concentration prior to infiltration, (2) carbonate equilibrium, (3) silicate weathering reactions, (4) limited mixing with saline water, (5) dissolution/precipitation of calcite, dolomite and fluorite, and (6) ion exchange. Principal component factor analysis and k-means cluster analysis of factor scores allow the reduction of dimensions describing the system and the identification of hydrogeochemical facies and the processes that defined and govern their evolution. Statistical analysis results indicate that the northern, west face and southern Yucca Mountain groundwater is fresh water with low concentrations of Ca2+, Mg2+, Cl−, Ca2+/(Na+)2, and CaF2. The Fortymile Wash groundwater is dilute. The carbonate signature is shown in the Ash Meadows and Death Valley waters with high fluorite SI. Finally, the Crater Flat, Stripped Hills, and Skeleton Hills are dominated by Ca/Na ion exchange, Mg and Ca. The hydrochemical and statistical analyses showed three main groundwater signatures or hydrochemical processes indicating groundwater evolution, potential flowpaths, and recharge areas. The flowpaths are the trace of the Amargosa River, the trace of Fortymile Wash, and its convergence with the Amargosa River. This appears to represent not just a groundwater flow path, but traces of surface runoff infiltration as well.

Comparing electromagnetic and seismic geophysical methods: Estimating the depth to water in geologically simple and complex arid environments

An integrated electromagnetic (EM) and seismic geophysical study was performed to evaluate non-invasive approaches to estimate depth to shallow groundwater (i.e., < 5 m) in arid environments with elevated soil salinity, where the installation of piezometers would be limited or prohibited. Both methods were tested in two study areas, one serving as a control site with relatively simple hydrogeology and the other serving as the experimental site with complex hydrogeology. The control site is located near the shore of Utah Lake (Palmyra, Utah, USA) where groundwater is shallow and unconfined in relatively homogeneous lacustrine sediments. The experimental site is in Carson Slough, Nevada, USA near the Ash Meadows National Wildlife Refuge in Amargosa Valley. Carson Slough is underlain by valley fill, with variable shallow depths to water beneath an ephemeral braided stream system. The geophysical methods used include frequency domain electromagnetic induction with multiple antenna–receiver spacings. High-resolution P-wave seismic profiles using a short (0.305 m) geophone spacing for common depth-point reflection stacking and first arrival modeling were also acquired. Both methods were deployed over several profiles where shallow piezometer control was present. EM results at both sites show that water surfaces correspond with a drop in conductivity. This is due to elevated concentrations of evaporative salts in the vadose zone immediately above the water table. EM and seismic profiles at the Palmyra site accurately detected the depth to groundwater in monitoring wells, as well as interpolated depths between them. This demonstrates that an integrated approach is ideal for relatively homogeneous aquifers. On the other hand, interpreting the EM and seismic profiles at Carson Slough was challenging due to the laterally and vertically variable soil types, segmented perched water surfaces, and strong salinity variations. The high-resolution images and models provided by the geophysical profiles confirm the simple soil and hydrological structure at the Palmyra site as well as the laterally complex structure at Carson Slough. The integrated approach worked well for determining depth to water in the geologically simple site, but was less effective in the geologically complex site where multiple water tables appear to be present.

Mercury Concentrations in Largemouth Bass (Micropterus salmoides) Collected from Ash Meadows National Wildlife Refuge, Nye County, Nevada

Mercury is a known neurotoxin and contaminant of concern worldwide. Mercury may occur at elevated concentrations adjacent to industrial sources, such as coal-fired power plants, or in remote environments and newly filled water bodies. Mercury tissue concentrations were determined for a sample of largemouth bass (Micropterus salmoides) from Crystal Reservoir, Ash Meadows National Wildlife Refuge, Nye County, Nevada. This investigation was triggered by (1) the presence of several conditions in soil and water that facilitate mercury bioaccumulation, (2) previous investigations that detected mercury in source springs, and (3) the presence of game fish and endangered pupfish within the reservoir. Mercury concentrations were significantly correlated with both fish mass and condition, but were lower than national human health and safety standards. It is possible that high pH and salinity inhibited methylation and subsequent bioaccumulation; however, additional studies are needed to determine causation of the low concentration in fish tissue compared with ambient conditions.

Regional groundwater flow in structurally-complex extended terranes: An evaluation of the sources of discharge at Ash Meadows, Nevada

Summary Ash Meadows, Nevada, USA is a site of major groundwater discharge (∼38,000 L/min) in the arid Mojave Desert, and hosts a number of endemic and threatened wetland species. In addition to these resources, Ash Meadows may also represent the future discharge location of radionuclide-laden waters from nuclear weapons testing at the Nevada Test Site. More importantly, however, Ash Meadows provides the opportunity to understand the controls on water transfer between basins through fractured bedrock. 4000+ solute analyses were assembled from the literature into a single database. The data were screened for spatial distribution, completeness, charge balance, and elevated temperatures (⩾20 °C and within regional flow systems), with 246 candidate up-gradient water remaining distributed among six potential source areas in addition to and Ash Meadows itself. These potential sources include both carbonate, volcanic and perhaps valley-fill aquifer systems. These waters were characterized by cluster analysis in order to sort similar waters in an objective fashion into potential flow paths and to establish representative endmember waters for inverse geochemical models and other modes of analysis. Isotopic tracers, both conservative and those reflecting water–rock interaction, all suggest that waters at Ash Meadows are derived by southward flow from volcanic terranes, parallel to the preferred permeability structure induced by active regional east–west extension. Solute balances support this conclusion. However, this runs counter to the prevailing model that waters at Ash Meadows are derived from easterly and northeasterly flows from the Spring Mountains and Pahranagat Valley areas by interbasin flow through a continuous fractured carbonate aquifer. This work suggests that carbonate aquifer systems in extended terranes are more compartmentalized than previously appreciated and that anisotropy in fracture permeability is key to compartmentalization and the control of flow directions.

Spiders of Ash Meadows National Wildlife Refuge, Nevada

Abstract We studied the spider fauna of Ash Meadows National Wildlife Refuge on six collecting expeditions during October 2004–August 2005. Spiders collected during these field trips produced ≥81 species in 60 genera and 26 families. Faunal diversity was dominated by Salticidae (≥13 species in seven genera), followed by Lycosidae (eight species in seven genera), Araneidae (eight species in seven genera), Gnaphosidae (seven species in seven genera), and Philodromidae (four species in four genera), with Thomisidae, Linyphiidae, Dictynidae, Theridiidae, Miturgidae, Pholcidae, and Tetragnathidae represented by two to seven species in one to three genera each. A total of 14 other families was represented by single species in single genera. The family Lycosidae was at more sites than any other family and it was the family with the largest number of individuals collected. We report an overall landscape-based density of species of only 0.96 species/km2 and, although 45.7% of species were represented by single spe...