Geology topics

Research about Nevada

Source-linked reports with geographic coverage including Nevada.

At least 181 records · Page 10Linked to original sources

USGS2017

Steady state fractionation of heavy noble gas isotopes in a deep unsaturated zone

To explore steady state fractionation processes in the unsaturated zone (UZ), we measured argon, krypton, and xenon isotope ratios throughout a ∼110 m deep UZ at the United States Geological Survey (USGS) Amargosa Desert Research Site (ADRS) in Nevada, USA. Prior work has suggested that gravitational settling should create a nearly linear increase in heavy-to-light isotope ratios toward the bottom of stagnant air columns in porous media. Our high-precision measurements revealed a binary mixture between (1) expected steady state isotopic compositions and (2) unfractionated atmospheric air. We hypothesize that the presence of an unsealed pipe connecting the surface to the water table allowed for direct inflow of surface air in response to extensive UZ gas sampling prior to our first (2015) measurements. Observed isotopic resettling in deep UZ samples collected a year later, after sealing the pipe, supports this interpretation. Data and modeling each suggest that the strong influence of gravitational settling and weaker influences of thermal diffusion and fluxes of CO 2 and water vapor accurately describe steady state isotopic fractionation of argon, krypton, and xenon within the UZ. The data confirm that heavy noble gas isotopes are sensitive indicators of UZ depth. Based on this finding, we outline a potential inverse approach to quantify past water table depths from noble gas isotope measurements in paleogroundwater, after accounting for fractionation during dissolution of UZ air and bubbles.

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USGS2017

The 2008 Wells, Nevada earthquake sequence: Source constraints using calibrated multiple event relocation and InSAR

The 2008 Wells, NV earthquake represents the largest domestic event in the conterminous U.S. outside of California since the October 1983 Borah Peak earthquake in southern Idaho. We present an improved catalog, magnitude complete to 1.6, of the foreshock-aftershock sequence, supplementing the current U.S. Geological Survey (USGS) Preliminary Determination of Epicenters (PDE) catalog with 1,928 well-located events. In order to create this catalog, both subspace and kurtosis detectors are used to obtain an initial set of earthquakes and associated locations. The latter are then calibrated through the implementation of the hypocentroidal decomposition method and relocated using the BayesLoc relocation technique. We additionally perform a finite fault slip analysis of the mainshock using InSAR observations. By combining the relocated sequence with the finite fault analysis, we show that the aftershocks occur primarily updip and along the southwestern edge of the zone of maximum slip. The aftershock locations illuminate areas of post-mainshock strain increase; aftershock depths, ranging from 5 to 16 km, are consistent with InSAR imaging, which shows that the Wells earthquake was a buried source with no observable near-surface offset.

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USGS2017

Vertebrate paleontology, stratigraphy, and paleohydrology of Tule Springs Fossil Beds National Monument, Nevada (USA)

Tule Springs Fossil Beds National Monument (TUSK) preserves 22,650 acres of the upper Las Vegas Wash in the northern Las Vegas Valley (Nevada, USA). TUSK is home to extensive and stratigraphically complex groundwater discharge (GWD) deposits, called the Las Vegas Formation, which represent springs and desert wetlands that covered much of the valley during the late Quaternary. The GWD deposits record hydrologic changes that occurred here in a dynamic and temporally congruent response to abrupt climatic oscillations over the last ~300 ka (thousands of years). The deposits also entomb the Tule Springs Local Fauna (TSLF), one of the most significant late Pleistocene (Rancholabrean) vertebrate assemblages in the American Southwest. The TSLF is both prolific and diverse, and includes a large mammal assemblage dominated by Mammuthus columbi and Camelops hesternus. Two (and possibly three) distinct species of Equus, two species of Bison, Panthera atrox, Smilodon fatalis, Canis dirus, Megalonyx jeffersonii, and Nothrotheriops shastensis are also present, and newly recognized faunal components include micromammals, amphibians, snakes, and birds. Invertebrates, plant macrofossils, and pollen also occur in the deposits and provide important and complementary paleoenvironmental information. This field compendium highlights the faunal assemblage in the classic stratigraphic sequences of the Las Vegas Formation within TUSK, emphasizes the significant hydrologic changes that occurred in the area during the recent geologic past, and examines the subsequent and repeated effect of rapid climate change on the local desert wetland ecosystem.

Nevada↗

USGS2017

Eruptive history, geochronology, and post-eruption structural evolution of the late Eocene Hall Creek Caldera, Toiyabe Range, Nevada

The magmatic, tectonic, and topographic evolution of what is now the northern Great Basin remains controversial, notably the temporal and spatial relation between magmatism and extensional faulting. This controversy is exemplified in the northern Toiyabe Range of central Nevada, where previous geologic mapping suggested the presence of a caldera that sourced the late Eocene (34.0 mega-annum [Ma]) tuff of Hall Creek. This region was also inferred to be the locus of large-magnitude middle Tertiary extension (more than 100 percent strain) localized along the Bernd Canyon detachment fault, and to be the approximate location of a middle Tertiary paleodivide that separated east and west-draining paleovalleys. Geologic mapping, 40 Ar/ 39 Ar dating, and geochemical analyses document the geologic history and extent of the Hall Creek caldera, define the regional paleotopography at the time it formed, and clarify the timing and kinematics of post-caldera extensional faulting. During and after late Eocene volcanism, the northern Toiyabe Range was characterized by an east-west trending ridge in the area of present-day Mount Callaghan, probably localized along a Mesozoic anticline. Andesite lava flows erupted around 35–34 Ma ponded hundreds of meters thick in the erosional low areas surrounding this structural high, particularly in the Simpson Park Mountains. The Hall Creek caldera formed ca. 34.0 Ma during eruption of the approximately 400 cubic kilometers (km 3 ) tuff of Hall Creek, a moderately crystal-rich rhyolite (71–77 percent SiO 2 ) ash-flow tuff. Caldera collapse was piston-like with an intact floor block, and the caldera filled with thick (approximately 2,600 meters) intracaldera tuff and interbedded breccia lenses shed from the caldera walls. The most extensive exposed megabreccia deposits are concentrated on or close to the caldera floor in the southwestern part of the caldera. Both silicic and intermediate post-caldera lavas were locally erupted within 400 thousand years of the main eruption, and for the next approximately 10 million years sedimentary rocks and distal tuffs sourced from calderas farther west ponded in the caldera basin surrounding low areas nearby. Patterns of tuff deposition indicate that the area was characterized by east-west trending paleovalleys and ridges in the late Eocene and Oligocene, which permitted tuffs to disperse east-west but limited their north-south extent. Although a low-angle fault contact of limited extent separates Cambrian and Ordovician strata in the southwestern part of the study area, there is no evidence that this fault cuts overlying Tertiary rocks. Total extensional strain across the caldera is on the order of 15 percent, and there is no evidence for progressive tilting of 34–25 Ma rocks that would indicate protracted Eocene–Oligocene extension. The caldera appears to have been tilted as an intact block after 25 Ma, probably during the middle Miocene extensional faulting well documented to the north and south of the study area.

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USGS2017

The role of salinity tolerance and competition in the distribution of an endangered desert salt marsh endemic

Rare plants are often associated with distinctive soil types, and understanding why endemic species occur in unique environments is fundamental for their management. At Ash Meadows National Wildlife Refuge in southern Nevada, USA, we evaluated whether the limited distribution of endangered Amargosa niterwort (Nitrophila mohavensis) is explained by this species’ tolerance of saline soils on salt-encrusted mud flats compared with the broadly distributed desert saltgrass (Distichlis spicata var. stricta). We simultaneously explored whether niterwort distribution is restricted from expanding due to interspecific competition with saltgrass. Surface soils collected throughout niterwort’s range were unexpectedly less saline with lower extractable Na, seasonal electroconductivity, and Na absorption ratio, and higher soil moisture than in adjacent saltgrass or mixed shrub habitats. Comparison of niterwort and saltgrass growth along an experimental salinity gradient in a greenhouse demonstrated lower growth of niterwort at all but the highest NaCl concentrations. Although growth of niterwort ramets was similar when transplanted into both habitats at the refuge below Crystal Reservoir, niterwort reproductive effort was considerably higher in saltgrass compared to its own habitat, implying reallocation of resources to sexual reproduction to maximize fitness when the probability of ramet mortality increases with greater salinity stress. Saltgrass was not a demonstrated direct competitor of niterwort; however, this species is known to increase soil salinity by exuding salt ions and through litterfall. Niterwort conservation will benefit from protecting hydrological processes that reduce salinity stress and preventing saltgrass colonization into niterwort habitat.

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USGS2017

Short-term vegetation response following mechanical control of saltcedar ( Tamarix spp.) on the Virgin River, Nevada, USA

Tamarisk (a.k.a. saltcedar, Tamarix spp.) is an invasive plant species that occurs throughout western riparian and wetland ecosystems. It is implicated in alterations of ecosystem structure and function and is the subject of many local control projects, including removal using heavy equipment. We evaluated short-term vegetation responses to mechanical Tamarix spp. removal at sites ranging from 2 to 5 yr post-treatment along the Virgin River in Nevada, USA. Treatments resulted in lower density and cover (but not eradication) of Tamarix spp., increased cover of the native shrub Pluchea sericia (arrow weed), decreased density and cover of all woody species combined, increased density of both native annual forbs and the nonnative annual Salsola tragus (prickly Russian-thistle), and lower density of nonnative annual grasses. The treated plots had lower mean woody species richness, but greater herbaceous species richness and diversity. Among herbaceous species, native taxa increased in richness whereas nonnative species increased in both species richness and diversity. Thus, efforts to remove Tamarix,/i> spp. at the Virgin River reduced vegetative cover contributing to fuel loads and probability of fire, and resulted in positive effects for native plant diversity, with mixed effects on other nonnative species. However, absolute abundances of native species and species diversity were very low, suggesting that targets of restoring vegetation to pre-invasion conditions were not met. Longer evaluation periods are needed to adequately evaluate how short-term post-treatment patterns translate to long-term patterns of plant community dynamics.

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USGS2017

X-ray diffraction analysis of pictograph pigments from Toquima Cave, central Nevada

X-ray diffraction analysis of red, yellow, white, and black pigments from pictographs in Toquima Cave in central Nevada reveals that gypsum was used as a binder in all colors; ocher (hematite and goethite) and carbon (charcoal) formed the coloring agents. Gypsum and ocher are not found in or near the cave, so the paint mixtures were made from ingredients found elsewhere and then transported to the site of the paintings.

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USGS2017

Hydraulic characterization of volcanic rocks in Pahute Mesa using an integrated analysis of 16 multiple-well aquifer tests, Nevada National Security Site, 2009–14

An improved understanding of groundwater flow and radionuclide migration downgradient from underground nuclear-testing areas at Pahute Mesa, Nevada National Security Site, requires accurate subsurface hydraulic characterization. To improve conceptual models of flow and transport in the complex hydrogeologic system beneath Pahute Mesa, the U.S. Geological Survey characterized bulk hydraulic properties of volcanic rocks using an integrated analysis of 16 multiple-well aquifer tests. Single-well aquifer-test analyses provided transmissivity estimates at pumped wells. Transmissivity estimates ranged from less than 1 to about 100,000 square feet per day in Pahute Mesa and the vicinity. Drawdown from multiple-well aquifer testing was estimated and distinguished from natural fluctuations in more than 200 pumping and observation wells using analytical water-level models. Drawdown was detected at distances greater than 3 miles from pumping wells and propagated across hydrostratigraphic units and major structures, indicating that neither faults nor structural blocks noticeably impede or divert groundwater flow in the study area. Consistent hydraulic properties were estimated by simultaneously interpreting drawdown from the 16 multiple-well aquifer tests with an integrated groundwater-flow model composed of 11 well-site models—1 for each aquifer test site. Hydraulic properties were distributed across volcanic rocks with the Phase II Pahute Mesa-Oasis Valley Hydrostratigraphic Framework Model. Estimated hydraulic-conductivity distributions spanned more than two orders of magnitude in hydrostratigraphic units. Overlapping hydraulic conductivity ranges among units indicated that most Phase II Hydrostratigraphic Framework Model units were not hydraulically distinct. Simulated total transmissivity ranged from 1,600 to 68,000 square feet per day for all pumping wells analyzed. High-transmissivity zones exceeding 10,000 square feet per day exist near caldera margins and extend along the northern and eastern Pahute Mesa study area and near the southwestern edge of the study area. The estimated hydraulic-property distributions and observed hydraulic connections among geologic structures improved the characterization and representation of groundwater flow at Pahute Mesa.

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USGS2017

Mercury and drought along the lower Carson River, Nevada: IV. Snowy egret post-fledging dispersal, timing of migration and survival, 2002–2004

This telemetry study is an extension of our 1997–2006 research on historical mercury contamination on snowy egrets ( Egretta thula ) up to ~ 20 days of age. Findings from initial studies at the mercury-contaminated Carson River colony at Lahontan Reservoir (LR) and a similar-sized reference (REF) colony on the Humboldt River included mercury-related physiological, biochemical, histopathological and reproductive effects up to ~20 days of age; with poor water years (2000–04), i.e., reduced prey availability, exacerbating effects. Herein, we compare timing of dispersal and migration at LR vs. REF, but the primary question now addressed is “whether survival of young mercury-exposed snowy egrets from LR would be further compromised beyond ~20 days of age? ” Based upon telemetry signals until 90–110 days of age (including dead bird counts and survival rate estimates), we conclude that mercury did not further compromise survival. Dead bird counts and survival rate estimates included time in the colony when fed by adults, plus the critical period when young dispersed from the colony to forage independently. The extended drought during this 3-year study was most critical in 2002 when production of ~20 d old egrets at LR was only 0.24 young/nest. In 2002, survival rates were low at both colonies and we documented the highest counts of dead egrets for both colonies. We suggest the losses in 2002 beyond 20 days of age were more a function of prey availability influenced by drought than exposure to mercury, especially at LR, because higher mercury concentrations, higher survival rates and fewer dead birds were documented at LR in 2003 when water conditions improved. Furthermore, total mercury (THg) in blood in 2003 was more than double 2002 (geometric mean, 3.39 vs 1.47 µg/g wet weight (ww). This higher THg exposure at LR in 2003 was associated with a redistribution of parent and post-dispersal feeding activities upstream (where there was higher mercury from historic mining) related to slightly improved water levels. When comparing the 3-year telemetry findings based upon ~20 d old young at LR (blood THg, geo. means 1.47, 3.39 and 1.89 µg/g ww), we found no evidence that age at dispersal, Julian date at dispersal, timing of migration, or pre-migration survival (~20 to ~100 days post-hatch) were adversely affected by elevated mercury.

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USGS2017

Long-term trends of surface-water mercury and methylmercury concentrations downstream of historic mining within the Carson River watershed

The Carson River is a vital water resource for local municipalities and migratory birds travelling the Pacific Flyway. Historic mining practices that used mercury (Hg) to extract gold from Comstock Lode ore has left much of the river system heavily contaminated with Hg, a practice that continues in many parts of the world today. Between 1998 and 2013, the United States Geological Survey (USGS) collected and analyzed Carson River water for Hg and methylmercury (MeHg) concentrations resulting in a sixteen year record of unfiltered total mercury (uf.THg), filtered (dissolved) Hg (f.THg), total methylmercury (uf.MeHg), filtered MeHg (f.MeHg), and particulate-bound THg (p.THg) and MeHg (p.MeHg) concentrations. This represents one of the longest continuous records of Hg speciation data for any riverine system, thereby providing a unique opportunity to evaluate long-term trends in concentrations and annual loads. During the period of analysis, uf.THg concentration and load trended downward at rates of −0.85% and −1.8% per year, respectively. Conversely, the f.THg concentration increased at a rate of 1.7% per year between 1998 and 2005, and 4.9% per year between 2005 and 2013. Trends in flow-normalized partition coefficients for both Hg and MeHg suggest a statistically significant shift from the particulate to the filtered phase. The upwardly accelerating f.THg concentration and observed shift from the solid phase to the aqueous phase among the pools of Hg and MeHg within the river water column signals an increased risk of deteriorating ecological conditions in the lower basin with respect to Hg contamination. More broadly, the 16-year trend analysis, completed 140 years after the commencement of major Hg releases to the Carson River, provides a poignant example of the ongoing legacy left behind by gold and silver mining techniques that relied on Hg amalgamation, and a cautionary tale for regions still pursuing the practice in other countries.

Nevada↗

USGS2017

Geology and vertebrate paleontology of Tule Springs Fossil Beds National Monument, Nevada, USA

Tule Springs Fossil Beds National Monument (TUSK) preserves 22,650 acres of the upper Las Vegas Wash in the northern Las Vegas Valley, Nevada, USA. TUSK is home to extensive and stratigraphically complex groundwater discharge (GWD) deposits, called the Las Vegas Formation, which represent springs and desert wetlands that covered much of the valley during the late Quaternary. The GWD deposits record hydrologic changes that occurred here in a dynamic and temporally congruent response to abrupt climatic oscillations over the last ~300 ka (thousands of years). The deposits also entomb the Tule Springs Local Fauna (TSLF), one of the most significant late Pleistocene (Rancholabrean) vertebrate assemblages in the American Southwest. The TSLF is both prolific and diverse, and includes a large mammal assemblage dominated by Mammuthus columbi and Camelops hesternus. Two and possibly three distinct species of Equus, two species of Bison, Panthera atrox, Smilodon fatalis, Canis dirus, Megalonyx jeffersonii, and Nothrotheriops shastensis are also present, and newly recognized faunal components include micromammals, amphibians, snakes, and birds. Invertebrates, plant macrofossils, and pollen also occur in the deposits and provide important and complementary paleoenvironmental information. This field compendium highlights some of the classic stratigraphic sequences of the Las Vegas Formation within TUSK, emphasizes the significant hydrologic changes that occurred in the area during the recent geologic past, and examines the subsequent and repeated effect of rapid climate change on the local desert wetland ecosystem.

Nevada↗

USGS2017

Common Raven ( Corvus corax ) kleptoparasitism at a Golden Eagle ( Aquila chyrsaetos ) nest in southern Nevada

The Common Raven ( Corvus corax ) is a ubiquitous species in the Mojave Desert of southern Nevada and California. From 5 to 24 May 2014, using remote trail cameras, we observed ravens repeatedly kleptoparasitizing food resources from the nest of a pair of Golden Eagles ( Aquila chyrsaetos ) in the Spring Mountains of southern Nevada. The ravens fed on nine (30%) of the 30 prey items delivered to the nest during the chick rearing period. Kleptoparasitic behavior by the ravens decreased as the eagle nestling matured to seven weeks of age, suggesting a narrow temporal window in which ravens can successfully engage in kleptoparasitic behavior at eagle nests. The observation of kleptoparasitism by Common Ravens at the nest suggests potential risks to young Golden Eagles from Common Ravens.

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USGS2017

Reversible reduction of estrone to 17β-estradiol by Rhizobium, Sphingopyxis, and Pseudomonas isolates from the Las Vegas Wash

Environmental endocrine-disrupting compounds (EDCs) are a growing concern as studies reveal their persistence and detrimental effects on wildlife. Microorganisms are known to affect the transformation of steroid EDCs; however, the diversity of estrogen-degrading microorganisms and the range of transformations they mediate remain relatively little studied. In mesocosms, low concentrations of added estrone (E1) and 17β-estradiol (E2) were removed by indigenous microorganisms from Las Vegas Wash water within 2 wk. Three bacterial isolates, Rhizobium sp. strain LVW-9, Sphingopyxis sp. strain LVW-12, and Pseudomonas sp. strain LVW-PC, were enriched from Las Vegas Wash water on E1 and E2 and used for EDC transformation studies. In the presence of alternative carbon sources, LVW-9 and LVW-12 catalyzed near-stoichiometric reduction of E1 to E2 but subsequently reoxidized E2 back to E1; whereas LVW-PC minimally reduced E1 to E2 but effectively oxidized E2 to E1 after a 20-d lag. In the absence of alternative carbon sources, LVW-12 and LVW-PC oxidized E2 to E1. This report documents the rapid and sometimes reversible microbial transformation of E1 and E2 and the slow degradation of 17α-ethinylestradiol in urban stream water and extends the list of known estrogen-transforming bacteria to the genera Rhizobium and Sphingopyxis . These results suggest that discharge of steroid estrogens via wastewater could be reduced through tighter control of redox conditions and may assist in future risk assessments detailing the environmental fate of estrogens through evidence that microbial estrogen transformations may be affected by environmental conditions or growth status.

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USGS2017

Tolerance to disturbance regulated by attractiveness of resources: A case study of desert bighorn sheep within the River Mountains, Nevada

Human activity may mimic predation risks for wildlife by causing abandonment of foraging sites and increasing expenditure of energy. Animals that can tolerate nonlethal disturbance may minimize these fitness costs. We examine this aspect of the risk—disturbance hypothesis by first analyzing recent habitat use of desert bighorn sheep relative to areas of attraction and disturbance. We then compare and contrast sheep responses to differing levels of anthropogenic disturbance between 2 time periods, 30 years apart. Desert bighorn sheep were tolerant of suburban activity when a consistent forage resource (municipal grass) was provided. Males were more tolerant than females, and females returned to natural, steep areas during the birthing season. Increased recreation activity, specifically mountain bike use, may have resulted in avoidance by sheep of otherwise suitable habitat that had been occupied decades earlier, thereby reducing availability of limited habitat. Tolerance increased only when attractiveness was relatively high and decreased as perceived fitness decreased, supporting risk—disturbance theory.

Nevada↗

USGS2017

Between hot rocks and dry places: The status of the Dixie Valley toad

In Dixie Valley, Nevada, an isolated population of toads has been the subject of proactive conservation measures by the Nevada Department of Wildlife and the U.S. Fish and Wildlife Service since 2008 due to concerns about potential habitat degradation resulting from exploitation of nearby geothermal energy resources. These toads appear to belong within the Anaxyrus boreas species group but are commonly referred to as Dixie Valley toads (DVTs). The DVT is currently confined to an extremely narrow habitat range (370 ha) that is geographically isolated from any other A. boreas population. In this study, genetic variations in mitochondrial genes and 11 microsatellite loci were used to assess the affinities of DVTs in relation to members of the A. boreas species group. We compared results from DVTs with previously published data spanning much of the range of A. boreas in the United States and new data from a nearby toad population within Dixie Valley. Data from both mitochondrial DNA and microsatellites placed DVTs inside the A. boreas species group. In particular, DVTs fell into a cluster of A. boreas from Washington and California, along with other species from the A. boreas species group, namely A. nelsoni, A. canorus, and A. exsul. Genetic differentiation of DVTs was lowest between A. boreas populations in Washington and California. However, allele frequencies were significantly different between DVTs and all other populations, including a nearby locality within Dixie Valley. This genetic differentiation, along with the DVT's geographical isolation and restricted habitat, warrants recognition of the DVT as a distinct management unit.

Nevada↗

USGS2017

A serosurvey of Greater Sage-grouse ( Centrocercus urophasianus ) in Nevada, USA

To better understand the potential avian diseases in Greater Sage-grouse ( Centrocercus urophasianus ) in the Great Basin in Nevada, we collected 31 blood samples March–April 2014 and tested for antibodies to eight viruses and two bacteria. Specifically, sera were tested for antibodies to avian leukosis virus type A, B, and J (ALV-A, ALV-B, and ALV-J, respectively), infectious bursal disease virus, infectious bronchitis virus, reticuloendothelial virus, avian influenza virus (AIV), West Nile virus, Pasteurella multocida (PM), and Salmonella enterica serovar Pullorum. Serum antibodies against ALV-A and -B (1/31, 3%), ALV-J (5/31, 16%), PM (1/31, 3%), and AIV (2/31, 6%) were detected by enzyme-linked immunosorbent assay (ELISA). While ELISA tests used have only been validated in domestic poultry, the serologic data should be used as a potential indicator of the range of bacterial and viral infectious agents that can infect the Greater Sage-grouse.

Nevada↗

USGS2017

Crotalus oreganus lutosus (Great Basin Rattlesnake). Defensive behavior/head hiding and tongue display

A variety of snake species employ head hiding as defensive behavior (Greene 1973. J. Herpetol. 7:143–161), but such behavior seems to be rarely observed in rattlesnakes. A recent report (Medica 2009. Herpetol. Rev. 40:95–97) presented observations on Crotalus scutulatus scutulatus and cited cases of similar behavior involving C. atrox , C. ruber , and C. viridis viridis . Here we report an encounter on 28 May 2016 with a C. oreganus lutosus (total length ca. 900 mm) observed 16 km S of Fallon, Churchill County, Nevada, USA. At 0925 h this snake was spotted by AKJ near the edge of the pavement on U.S. Hwy. 95. When approached, the snake presented typical active defensive behavior, with the rattle elevated (although not rattling), striking occasionally, and frequently flicking its conspicuous lavender and black tongue. As AKJ continued to take pictures the snake coiled more tightly (Fig. 1A), maintaining its rattle concealed and finally hiding its head beneath its coils (Fig. 1B). After photographing this pose AKJ made his first physical contact with the snake by scooping it up with a small shovel and placing it off the road. At this point the snake recovered its feisty attitude and would not retreat despite attempts to move it further away from the road. The snake did not rattle during the entire encounter (which lasted less than 5 min). Head hiding as a “last resort” in response to a persistent unavoidable threat may be more widespread within the family Crotalidae than previously documented.

Nevada↗

USGS2016

Evaluating mountain meadow groundwater response to Pinyon-Juniper and temperature in a great basin watershed

This research highlights development and application of an integrated hydrologic model (GSFLOW) to a semiarid, snow-dominated watershed in the Great Basin to evaluate Pinyon-Juniper (PJ) and temperature controls on mountain meadow shallow groundwater. The work used Google Earth Engine Landsat satellite and gridded climate archives for model evaluation. Model simulations across three decades indicated that the watershed operates on a threshold response to precipitation (P) >400 mm/y to produce a positive yield (P-ET; 9%) resulting in stream discharge and a rebound in meadow groundwater levels during these wetter years. Observed and simulated meadow groundwater response to large P correlates with above average predicted soil moisture and with a normalized difference vegetation index threshold value >0.3. A return to assumed pre-expansion PJ conditions or an increase in temperature to mid-21st century shifts yielded by only ±1% during the multi-decade simulation period; but changes of approximately ±4% occurred during wet years. Changes in annual yield were largely dampened by the spatial and temporal redistribution of evapotranspiration across the watershed: Yet the influence of this redistribution and vegetation structural controls on snowmelt altered recharge to control water table depth in the meadow. Even a small-scale removal of PJ (0.5 km 2 ) proximal to the meadow will promote a stable, shallow groundwater system resilient to droughts, while modest increases in temperature will produce a meadow susceptible to declining water levels and a community structure likely to move toward dry and degraded conditions.

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