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At least 1,153 records · Page 64Linked to original sources

USGS2021

Extreme events trigger terrestrial and marine ecosystem collapses: A tale of two regions

We outline the multiple, cross-scale, and complex consequences of terrestrial and marine ecosystem heatwaves in two regions on opposite sides of the planet: the southwestern USA and southwestern Australia, both encompassing Global Biodiversity Hotspots, and where ecosystem collapses or features of it have occurred in the past two decades. We highlight ecosystem shifts that have clearly demonstrated a substantial change from a baseline state over time, although not necessarily across their entire distribution, with evidence of collapse at local scales. Responses to temperature extremes, such as heatwaves, encompass processes at all scales, including population level (e.g. altered demography such as survival, recruitment, and fecundity, together resulting in structural changes), community level (e.g. species compositional shifts), and ecosystem level (e.g. carbon loss), as well as physical properties altered by vegetation loss (e.g. microclimate, fire behaviour on land). These changes impact all trophic levels with foundational species losses (such as seagrasses, kelp, and trees), flowing through to vertebrates (such as sea turtles, penguins, and cockatoos). Where extensive collapse has occurred, shifts in microclimate could affect important biosphere-to-atmosphere feedbacks including fluxes of energy, carbon, and water. Such extensive changes usually do not occur in isolation and frequently interact with other disturbance processes such as fire, storms, pathogen and pest outbreaks, and anthropogenic stressors. Interactions may alter the likelihood, extent, or severity of subsequent disturbances (linked disturbances) as well as condition the ecological response and recovery (compound disturbances). In addition, if ecosystem collapse is extensive enough (e.g. tree die-off), those changes also can impact climate and ecosystems elsewhere via ecoclimate teleconnections. Increasing rates of climatic extremes will drive a host of direct and indirect feedbacks certain to produce large-scale shifts in ecological functioning at unprecedented rates. Understanding how, why, and where these shifts will occur will be critical for effective ecosystem management and climate change mitigation.

Book chapter↗

USGS2014

Changing climate and the altitudinal range of avian malaria in the Hawaiian Islands: an ongoing conservation crisis on the island of Kaua'i

Transmission of avian malaria in the Hawaiian Islands varies across altitudinal gradients and is greatest at elevations below 1500 m where both temperature and moisture are favorable for the sole mosquito vector, Culex quinquefasciatus, and extrinsic sporogonic development of the parasite, Plasmodium relictum. Potential consequences of global warming on this system have been recognized for over a decade with concerns that increases in mean temperatures could lead to expansion of malaria into habitats where cool temperatures currently limit transmission to highly susceptible endemic forest birds. Recent declines in two endangered species on the island of Kaua'i, the ‘Akikiki (Oreomystis bairdi) and ‘Akeke'e (Loxops caeruleirostris), and retreat of more common native honeycreepers to the last remaining high elevation habitat on the Alaka'i Plateau suggest that predicted changes in disease transmission may be occurring. We compared prevalence of malarial infections in forest birds that were sampled at three locations on the Plateau during 1994–1997 and again during 2007–2013, and also evaluated changes in the occurrence of mosquito larvae in available aquatic habitats during the same time periods. Prevalence of infection increased significantly at the lower (1100 m, 10.3% to 28.2%), middle (1250 m, 8.4% to 12.2%), and upper ends of the Plateau (1350 m, 2.0% to 19.3%). A concurrent increase in detections of Culex larvae in aquatic habitats associated with stream margins indicates that populations of the vector are also increasing. These increases are at least in part due to local transmission because overall prevalence in Kaua'i ‘Elepaio (Chasiempis sclateri), a sedentary native species, has increased from 17.2% to 27.0%. Increasing mean air temperatures, declining precipitation, and changes in streamflow that have taken place over the past 20 years are creating environmental conditions throughout major portions of the Alaka'i Plateau that support increased transmission of avian malaria.

Hawai'i↗

USGS2019

Are polar bear habitat resource selection functions developed from 1985-1996 data still useful?

1. Greenhouse gas-induced warming in the Arctic has caused declines in sea ice extent and changed its composition, raising concerns by all circumpolar nations for polar bear conservation. 2. Negative impacts have been observed in three well-studied polar bear subpopulations. Most subpopulations, however, receive little or no direct monitoring, hence, resource selection functions (RSF) may provide a useful proxy of polar bear distributions. However, the efficacy of RSFs constructed from past data, i.e., reference RSFs, may be degraded under contemporary conditions, especially in a rapidly changing environment. 3. We assessed published Arctic-wide reference RSFs using tracking data from adult female polar bears captured in the Beaufort Sea. We compared telemetry-derived seasonal distributions of polar bears to RSF-defined optimal sea ice habitat during the period of RSF model development, 1985–1995, and two subsequent periods with diminished sea ice: 1996–2006 and 2007–2016. From these comparisons, we assessed the applicability of the reference RSFs for contemporary polar bear conservation. 4. In the two decades following the 1985–1995 reference period, use and availability of optimal habitat by polar bears declined during the ice melt, ice minimum and ice growth seasons. During the ice maximum season (i.e., winter), polar bears used the best habitat available, which changed relatively little across the three decades of study. During the ice melt, ice minimum and ice growth seasons, optimal habitat in areas used by polar bears decreased and was displaced north and east of the Alaska Beaufort Sea coast. As optimal habitat diminished in these seasons, polar bears expanded their range and occupied greater areas of sub-optimal habitat. 5. Synthesis and applications: Sea ice declines due to climate change continue to challenge polar bears and their conservation. The distribution of Southern Beaufort Sea polar bears remained similar during the ice maximum season, so the reference RSFs developed from data collected >20 years ago continue to accurately model their winter distribution. In contrast, reference RSFs for the ice transitional and minimum seasons showed diminished predictive efficacy but were useful in revealing that contemporary polar bears have been increasingly forced to use sub-optimal habitats during those seasons.

Ecology and Evolution↗

USGS2025

The conundrum of taxonomic uniformitarianism in planktic foraminifera

Planktic foraminiferal species distributions in the modern ocean track environmental features like sea surface temperature (SST). Species shift their distributions as the marine environment changes, providing an analogue for past behaviour. Stationarity of species' ecological tolerances is therefore a first-order assumption of all palaeoenvironmental reconstructions based upon modern analogue methods. In this paper we test the hypothesis that planktic foraminifer species temperature preferences did not change between the Late Pliocene and present, using a dataset which contains faunal abundance data and alkenone palaeotemperature data from the same samples. Our dataset includes 463 samples from 29 localities. Pliocene relative abundances of four taxa ( Globigerina bulloides , Globigerinita glutinata , Neogloboquadrina pachyderma and Neogloboquadrina incompta ) are compared to SST estimates of the same age derived using the alkenone unsaturation ratio ( U K ' 37 ) palaeothermometer. Core-top abundances of the same taxa were compared to pre-industrial SST. Our Pliocene data are generally concordant with previous work. Pliocene SST responses and those of the pre-industrial are similar, supporting the hypothesis that temperature preferences of planktic foraminifera have been relatively stable since the Late Pliocene. This documentation of stationarity of planktic foraminiferal species' temperature tolerances is helpful in identifying situations where environmental variables other than temperature (e.g. salinity or productivity) exhibit a first-order control on faunal diversity. Our results support the notion of taxonomic uniformitarianism and therefore provide additional confidence in using planktic foraminifera to evaluate both regional and global climate change.

Palaeontology↗

USGS2001

Metal loading assessment of a small mountainous sub-basin characterized by acid drainage -- Prospect Gulch, upper Animas River watershed, Colorado

strongly affected by natural acidity from pyrite weathering. Metal content in the water column is a composite of multiple sources affected by hydrologic, geologic, climatic, and anthropogenic conditions. Identifying sources of metals from various drainage areas was determined using a tracer injection approach and synoptic sampling during low flow conditions on September 29, 1999 to determine loads. The tracer data was interpreted in conjunction with detailed geologic mapping, topographic profiling, geochemical characterization, and the occurrence and distribution of trace metals to identify sources of ground-water inflows. For this highly mineralized sub-basin, we demonstrate that SO4, Al, and Fe load contributions from drainage areas that have experienced historical mining?although substantial?are relatively insignificant in comparison with SO4, Al, and Fe loads from areas experiencing natural weathering of highlyaltered, pyritic rocks. Regional weathering of acid-sulfate mineral assemblages produces moderately low pH waters elevated in SO4, Al, and Fe; but generally lacking in Cu, Cd, Ni, and Pb. Samples impacted by mining are also characterized by low pH and large concentrations of SO4, Al, and Fe; but contained elevated dissolved metals from ore-bearing vein minerals such as Cu, Zn, Cd, Ni, and Pb. Occurrences of dissolved trace metals were helpful in identifying ground-water sources and flow paths. For example, cadmium was greatest in inflows associated with drainage from inactive mine sites and absent in inflows that were unaffected by past mining activities and thus served as an important indicator of mining contamination for this environmental setting. The most heavily mine-impacted reach (PG153 to PG800), contributed 8% of the discharge, and 11%, 9%, and 12% of the total SO4, Al, and Fe loads in Prospect Gulch. The same reach yielded 59% and 37% of the total Cu and Zn loads for the subbasin. In contrast, the naturally acidic inflows from the Red Chemotroph iron spring yielded 39% of the discharge and 54%, 73%, and 87% of the SO4, Al, and Fe loads; but only 4% of the total Cu and 30% of the total Zn loads in Prospect Gulch. Base flow from the Prospect Gulch sub-basin contributes about 4.8 percent of the total discharge at the mouth of Cement Creek; compared with sampled instream loads of 1.8%, 8.8%, 15.9%, 28%, and 8.6% for SO4, Al, Fe, Cu and Zn, respectively. Water-shed scale remediation efforts targeted at reducing loads of SO4, Al, and Fe at inactive mine sites are likely to fail because the major sources of these constituents in Prospect Gulch are predominantly discharged from natural sources. Remediation goals aimed at reducing acidity and loads of Cu and other base metals, may succeed, however, because changes in pH and loads are disproportionately greater than increases in discharge over the same reach, and a substantial fraction of the metal loading is from mining-impacted reaches. Whether remediation of abandoned mines in Prospect Gulch can be successful depends on how goals are defined?that is, whether the objective is to reduce loads of SO4, Al, and Fe; or whether loads of Cu and other base metals and pH are targeted.

Open-File Report↗

USGS2023

Volcanic aquifers of Hawaiʻi—Contributions to assessing groundwater availability on Kauaʻi, Oʻahu, and Maui

The volcanic aquifers of the Hawaiian Islands supply water to 1.46 million residents, diverse industries, and a large component of the U.S. military in the Pacific. Groundwater also supplies fresh water that supports ecosystems in streams and near the coast. Hawaii’s aquifers are remarkably productive given their small size, but the capacity of the islands to store fresh groundwater is limited because each island is surrounded by seawater, and salt water underlies much of the fresh groundwater. The amount of fresh groundwater available for human use from Hawai‘i’s volcanic aquifers is constrained by the consequences of groundwater withdrawal. Restrictions placed on these consequences can translate to limitations on groundwater availability. Changes in recharge resulting from changes in land cover or climate can alter the effect of withdrawals. This study uses numerical models of the volcanic aquifers of the islands of Kaua‘i, O‘ahu, and Maui to quantify the consequences of historical and plausible future withdrawals and changes in recharge. The study compares the results of model simulations of multiple scenarios of historical and projected future withdrawal and recharge. Results of the simulations using the groundwater models of the islands of Kaua‘i, O‘ahu, and Maui have implications for other islands in Hawai‘i. Since the first modern water well was drilled in Hawai‘i in 1879, total groundwater withdrawals on Kaua‘i, O‘ahu, and Maui have risen to nearly 400 million gallons per day. Model simulations indicate that these withdrawals have caused reductions in groundwater discharge to streams and springs, reductions in groundwater discharge to the ocean, changes in subsurface flow between sectors within an island, lowering of groundwater levels, and rise of the interface between fresh water and salt water in the aquifers. Future increases in withdrawals will increase the severity of the consequences. Changes in recharge can alter the effect of withdrawals—increases in recharge can offset the consequences of withdrawals, whereas decreases in recharge can exacerbate the effects of withdrawals. This study quantifies the consequences of withdrawals for past and plausible future circumstances. The models can be used to test other circumstances. Limits placed on the consequences of withdrawals—such as restrictions to protect stream or coastal ecosystems that rely on groundwater discharge and limitations on water-level decline and rise of the freshwater-saltwater interface to protect the productivity of existing wells—can translate to limits on groundwater availability from Hawai‘i’s volcanic aquifers. Setting acceptable limits to the consequences of groundwater withdrawal is also a critical part of assessing groundwater availability. Once these limits are set, numerical models can be used to quantify the amount of water that can be withdrawn within those limits and thereby inform management decisions that seek to balance the need to limit the consequences of groundwater withdrawals with the need to develop water for human use.

Hawaii↗

USGS2009

Agroenvironmental transformation in the Sahel: Another kind of "green revolution"

A farmer-managed, agroenvironmental transformation has occurred over the past three decades in the West African Sahel, enabling both land rehabilitation and agricultural intensification to support a dense and growing population. This paper traces the technical and institutional innovations, their impacts, and lessons learned from two successful examples. The first is the story of the improvement and replication of indigenous soil and water conservation practices across the Central Plateau of Burkina Faso. Rehabilitation of at least 200,000 hectares of degraded land enabled farmers to grow cereals on land that had been barren and intensify production through developing agroforestry systems. Additionally, rehabilitation appears to have recharged local wells. The second example is a farmer-managed process of natural regeneration, using improved, local agroforestry practices over an estimated 5 million hectares in southern Niger. This large-scale effort reduced wind erosion and increased the production and marketing of crops, fodder, firewood, fruit, and other products. In both cases, income opportunities were created, reducing incentives for migration. Women benefited from the improved supply of water, fuelwood, and other tree products. Human, social, and political capital was strengthened in a process of farmer-driven change. Fluid coalitions of actors expanded the scale of the transformation. These stories have important lessons for those who seek to create effective agricultural development partnerships and meet the challenges of climate change and food security.

Central Plateau, West African Sahel↗

USGS2005

Summary of significant results from studies of triazine herbicides and their degradation products in surface water, ground water, and precipitation in the midwestern United States during the 1990s

Nonpoint-source contamination of water resources from triazine herbicides has been a major water-quality issue during the 1990s in the United States. To address this issue, studies of surface water, ground water, and precipitation have been carried out by the U.S. Geological Survey in the Midwestern United States. Reconnaissance studies of 147 streams were conducted to determine the geographic and seasonal distribution of atrazine, cyanazine, propazine, and simazine. These studies showed that high concentrations of herbicides were flushed from cropland and transported through the stream system as pulses in response to spring and summer rainfall. The studies also revealed the persistence of herbicides and their degradation products in streams. An investigation of 76 reservoirs showed that the occurrence and temporal distribution of herbicides and their degradation products in reservoir outflow could be related to reservoir and drainage-basin characteristics, water and land use, herbicide use, and climate. Significant findings showed that concentrations of atrazine and its degradation products remained elevated all summer and into the fall and that recently applied atrazine mixed with atrazine applied the previous year as water moved through a reservoir. Reconnaissance studies of 303 ground-water wells were completed to determine hydrogeological and seasonal occurrence, concentration, and distribution of herbicides and their degradation products. Samples collected from across the Midwestern United States consistently revealed that triazine herbicide degradation products commonly were found more frequently than their parent herbicide and that ground-water age could be an important factor in explaining variations in herbicide contamination. A final study investigated precipitation in the Midwestern United States, northeast to the Atlantic Ocean, and northward to the Canadian border. It found that the highest herbicide concentrations in precipitation occurred following herbicide application to cropland. Atrazine was detected most often, followed by deethylatrazine, cyanazine, and deisoproplyatrazine. Mass deposition of herbicides by precipitation was greatest in areas where herbicide use was intense and decreased with distance from the Midwest. Findings of the 1990s studies include an improved understanding of the occurrence, persistence, chemistry, and transport of triazine herbicides and their degradation products in the hydrologic environment. A significant increase in knowledge of triazine herbicides and development and improvement of analytical methods were accomplished in the past decade. The results produced are not only significant for the present (2005) but provide an important data set for future use.

Midwest region↗

USGS1983

Hydrology of area 54, northern Great Plains, and Rocky Mountain coal provinces, Colorado and Wyoming

A nationwide need for information characterizing hydrologic conditions in mined and potential mine areas has become paramount with the enactment of the Surface Mining Control and Reclamation Act of 1977. This report, one in a series covering the coal provinces nationwide, presents information thematically by describing single hydrologic topics through the use of brief texts and accompanying maps, graphs, or other illustrations. The summation of the topical discussions provides a description of the hydrology of the area. Area 54, in north-central Colorado and south-central Wyoming, is 1 of 20 hydrologic reporting areas of the Northern Great Plains and Rocky Mountain coal provinces. Part of the Southern Rocky Mountains and Wyoming Basin physiographic provinces, the 8,380-square-mile area is one of contrasting geology, topography, and climate. This results in contrasting hydrologic characteristics. The major streams, the North Platte, Laramie, and Medicine Bow Rivers, and their principal tributaries, all head in granitic mountains and flow into and through sedimentary basins between the mountain ranges. Relief averages 2,000 to 3,000 feet. Precipitation in the mountains may exceed 40 inches annually, much of it during the winter, which produces deep snowpacks. Snowmelt in spring and summer provides most streamflow. Precipitation in the basins averages 10 to 16 inches annually, insufficient for sustained streamflow; thus, streams originating in the basins are ephemeral. Streamflow quality is best in the mountains where dissolved-solids concentrations generally are least. These concentrations increase as streams flow through sedimentary basins. The increases are mainly natural, but some may be due to irrigation in and adjacent to the flood plains. In the North Platte River, dissolved-solids concentrations are usually less than 300 milligrams per liter; in the Laramie and the Medicine Bow Rivers, the concentrations may average 500 to 850 milligrams per liter. However, water-quality stations on the Laramie and the Medicine Bow Rivers are farther removed from the mountain sources than the stations in the North Platte drainage. Because of the semiarid climate of the basins, soils are not adequately leached. Consequently, flow in ephemeral streams usually has a larger concentration of dissolved solids than that in perennial streams, averaging 1,000 to 1,600 milligrams per liter. Aquifers containing usable ground water are combined into three groups: (1) consolidated and unconsolidated non-coal-bearing Quaternary and Upper Tertiary deposits, (2) Mesozoic and Paleozoic sedimentary rocks, and (3) Lower Tertiary and Upper Cretaceous sedimentary rocks containing coal. These aquifers are used for municipal, domestic, irrigation, and stock supplies. Well yields range from about 5 to 1,000 gallons per minute, and depend on type of aquifer, saturated thickness, and degree of fracturing. The best quality ground water usually comes from the non-coal-bearing Quaternary and Upper Tertiary rocks or the Mesozoic and Paleozoic rocks; often it is dominated by calcium and bicarbonate ions. The coal-bearing formations have a large variability in water chemistry; dominant ions may be bicarbonate or sulfate and sodium, calcium, or magnesium. Dissolved-solids concentrations are generally larger than in the former two groups. The U.S. Geological Survey operates a network of hydrologic stations to observe the streamflow and groundwater conditions. This network currently includes 31 surface-water stations and 35 observation wells; information is available for many other sites observed in the past. Data available include rate of flow, water levels, and water quality; much of the data are available in published reports or from computer storage through the National Water Data Exchange (NAWDEX) or the National Water Data Storage and Retrieval System (WATSTORE). Five formations of Late Cretaceous and early Tertiary age contain coal.

Colorado, Wyoming↗

USGS1999

Dry Valley streams in Antarctica: Ecosystems waiting for water

An axiom of ecology is: 'Where there is water, there is life.' In dry valley ecosystems of Antarctica, this axiom can be extended to: 'Where there has been and will be water, there is life.' Stream communities in the dry valleys can withstand desiccation on an annual basis and also for longer periods - as much as decades or even centuries. These intact ecosystems, consisting primarily of cyanobacteria and eukaryotic algae, spring back to life with the return of water. Soil organisms in the dry valleys also have remarkable survival capabilities (Virginia and Wall 1999), emerging from dormancy with the arrival of water. Streams in the dry valleys carry meltwater from a glacier or ice-field source to the lakes on the valley floors and generally flow for 4-10 weeks during the summer, depending on climatic conditions. Many of these streams contain abundant algal mats that are perennial in the sense that they are in a freeze-dried state during the winter and begin growing again within minutes of becoming wetted by the first flow of the season. The algal species present in the streams are mainly filamentous cyanobacteria (approximately 20 species of the genera Phormidium, Oscillatoria, and Nostoc), two green algal species of the genus Prasiola, and numerous diatom taxa that are characteristic of soil habitats and polar regions. Algal abundances are greatest in those streams in which periglacial processes, acting over periods of perhaps a century, have produced a stable stone pavement in the streambed. This habitat results in a less turbulent flow regime and limits sediment scour from the streambed. Because dry valley glaciers advance and retreat over periods of centuries and millennia and stream networks in the dry valleys evolve through sediment deposition and transport, some of the currently inactive stream channels may receive flow again in the future. Insights- into the process of algal persistence and reactivation will come from long-term experiments that study the effects of reintroducing water flow to channels in which flow has not occurred for decades or centuries. The present work of the McMurdo Dry Valleys LTER has led us to conclude that the legacy of past conditions constitutes a dominant influence on present-day ecosystem structure and function in the dry valleys (Moorhead et al. 1999). For example, Virginia-and Wall (1999) have found that soil nematodes are partly sustained by relict organic carbon from algae that grew during the high lake stands of 8000-10,000 years ago. Similarly, the growth of current algal populations in the lakes of the dry valleys is supported by diffusion of nutrients from relict nutrient pools in the deep bottom waters (Priscu et al. 1999). For the stream ecosystems, abundant algal mats are present in channels that have stable stone pavements, which formed through freeze-thaw cycles occurring over long periods, possibly hundreds of years. We hypothesize that these stone pavements are an important ecological legacy permitting the successful 'waiting for water' strategy. Similarly, the biodiversity of algal species that can survive the harsh conditions in the streams of the dry valleys may be stable for centuries or more, representing a second important ecological legacy.

BioScience↗

USGS2009

Spatial and temporal variation in distribution of larval lake whitefish in eastern Lake Ontario: signs of recovery?

The lake whitefish ( Coregonus clupeaformis ) is one of the native Lake Ontario fishes that declined severely over the past century. Recent evidence of larval lake whitefish production in a historic spawning area (Chaumont Bay) might signal a recovery of this species in New York waters. We surveyed coastal and open water areas to evaluate densities and estimate total abundance of larval lake whitefish in Chaumont Bay. Other historic spawning areas and embayments with appropriate spawning and nursery habitat were also surveyed, but only a few larvae were found outside of Chaumont Bay. Lake whitefish larvae were found in every embayment sampled within Chaumont Bay, with larval densities of nearly 600/1000 m 2 in some samples. Greatest abundances occurred in the northern sectors and near the mouth of the bay. Open water densities were generally less than half that of nearshore sites. The total bay-wide estimate for 2005 was approximately 644,000 lake whitefish larvae, but dropped to 230,000–400,000 in 2006 and 2007, respectively. Mean larval growth rates (0.36 mm/day) did not differ by year, but were consistently higher in early May than in late April. Lake whitefish production in Chaumont Bay is encouraging for this species, but the cause and persistence of the decline after 2005 can be determined only by continued monitoring. Other possible bottlenecks of survival may exist at juvenile and adult stages and could significantly affect recruitment dynamics. This species is sensitive to normal climatic fluctuations and increased variability associated with global climatic change could make winter nursery conditions unfavorable for this species.

Journal of Great Lakes Research↗

USGS1990

Chronology of expansion and contraction of four great Basin lake systems during the past 35,000 years

During the past 35,000 years, Lake Bonneville, Lake Russell, and Lake Searles underwent a major period of lake-level change. The lakes were at moderate levels or dry at the beginning of the period and seem to have achieved highstands between about 15,000 and 13,500 yr B.P. The rise of Lake Lahontan was gradual but not continuous, in part because of topographic constraints (intrabasin spill). Lake Lahontan also had an oscillation in lake level at 15,500 yr B.P. Radiocarbon-age estimations for materials that were deposited in the lake basins indicate that Lake Bonneville rose more or less gradually from 32,000 yr B.P., and had major oscillations in level between 23,000 and 21,000 yr B.P. and between 15,250 and 14,500 yr B.P. Lake Russell and Lake Searles had several major oscillations in lake level between 35,000 and 14,000 yr B.P. The timing and exact magnitude of the oscillations are difficult to decipher but both lakes may have achieved multiple highstand states. All four lakes may have had nearly synchronous recessions between about 14,000 and 13,500 yr B.P. After the recessions, the lakes seem to have temporarily stabilized or experienced a minor increase in size between about 11,500 and 10,000 yr B.P. These data provide circumstantial evidence that the Younger Dryas Event affected climate on at least a hemispheric scale. During the Holocene, the four lakes remained at low levels, and small oscillations in lake level occurred. An important aspect of the lake-level data is the accompanying expansion of lake-surface area at the time of the last highstand. Lake Bonneville and Lake Lahontan had surface areas about 10 times larger than their mean-historical reconstructed areas whereas Lake Russell and Lake Searles had surface areas about 5 times larger than their mean-historical reconstructed areas. Differences in the records of effective wetness may have been due to the locations of the basins relative to the position of the jetstream, or they may have resulted from lake/atmosphere feedback processes.

California, Idaho, Nevada, Oregon↗

USGS2017

Isotopic characterization of late Neogene travertine deposits at Barrancas Blancas in the eastern Atacama Desert, Chile

Here we explore the potential of spring-related, surface and subsurface carbonates as an archive of paleoenvironmental change at Barrancas Blancas, located in the broadest and driest sector of the Atacama Desert at 24.5°S. From these deposits we present a new stable isotopic record of paleoenvironmental conditions over portions of the past ~ 11.5 Ma. U-Pb dates from the carbonates, both surface and subsurface, demonstrate that springs have discharged at this location over much of the last 11.5 Ma, attesting to the exceptional geomorphic stability of the central Atacama. Many of the sampled vein systems line vertical fissures, and formed within the aquifer before groundwater discharged at the surface. Carbonates in such circumstances should not undergo off-gassing and kinetic fractionation prior to formation, simplifying the interpretation of their isotopic composition. Oxygen isotopic compositions of carbonates are generally high (>− 5‰VPDB), and using paleospring water temperatures of 3–13 °C reconstructed from clumped isotopes, point to strongly (up to 50%) evaporated water isotope values, like those associated with the hyperarid core of the Atacama Desert today. Carbon isotopic compositions are also high (≥+3‰ PDB), reflecting a recharge area essentially devoid of plants and dominated by volcanic CO 2 , as is the case today. Our isotopic results are very similar to those from the Calama Basin to the north, suggesting that the western face of the Andes between 21 and 25°S has been highly evaporative and nearly plantless when these springs discharged over the last 11.5 Ma. The spring carbonates at Barrancas Blancas strongly resemble those found at Devils Hole and Furnace Creek in Death Valley, USA, and as such warrant further exploration as potential archives of climate change.

Atacama Desert↗

USGS2005

A comparative analysis of the Global Land Cover 2000 and MODIS land cover data sets

Accurate and up-to-date global land cover data sets are necessary for various global change research studies including climate change, biodiversity conservation, ecosystem assessment, and environmental modeling. In recent years, substantial advancement has been achieved in generating such data products. Yet, we are far from producing geospatially consistent high-quality data at an operational level. We compared the recently available Global Land Cover 2000 (GLC-2000) and MODerate resolution Imaging Spectrometer (MODIS) global land cover data to evaluate the similarities and differences in methodologies and results, and to identify areas of spatial agreement and disagreement. These two global land cover data sets were prepared using different data sources, classification systems, and methodologies, but using the same spatial resolution (i.e., 1 km) satellite data. Our analysis shows a general agreement at the class aggregate level except for savannas/shrublands, and wetlands. The disagreement, however, increases when comparing detailed land cover classes. Similarly, percent agreement between the two data sets was found to be highly variable among biomes. The identified areas of spatial agreement and disagreement will be useful for both data producers and users. Data producers may use the areas of spatial agreement for training area selection and pay special attention to areas of disagreement for further improvement in future land cover characterization and mapping. Users can conveniently use the findings in the areas of agreement, whereas users might need to verify the informaiton in the areas of disagreement with the help of secondary information. Learning from past experience and building on the existing infrastructure (e.g., regional networks), further research is necessary to (1) reduce ambiguity in land cover definitions, (2) increase availability of improved spatial, spectral, radiometric, and geometric resolution satellite data, and (3) develop advanced classification algorithms.

Remote Sensing of Environment↗

USGS2016

Using structure from motion photogrammetry to examine glide snow avalanches

Structure from Motion (SfM), a photogrammetric technique, has been used extensively and successfully in many fields including geosciences over the past few years to create 3D models and high resolution digital elevation models (DEMs) from aerial or oblique photographs. SfM has recently been used in a limited capacity in snow avalanche research and shows promise as a tool for broader applications. In this study, we used SfM to examine glide avalanches along the Going-to-the-Sun Road (GTSR) corridor in Glacier National Park (GNP), Montana. Glide avalanches pose substantial hazard to railroads, highways, and other infrastructure in many avalanche prone regions around the world, and yet basic measurements of crown depth and ground/snow interface can be hard to observe. Along the GTSR, glide avalanches can impact worker and public safety, but accessing glide avalanche crowns or glide cracks is often prohibited by inaccessible terrain or residual avalanche hazard. We used SfM techniques to derive high resolution DEMs for four glide avalanches that occurred in the spring of 2016. This allowed us to estimate selected full depth glide avalanche dimensions without visiting the site. However, our analysis was limited to qualitative assessments of the glide avalanche dimensions as the high resolution coordinates necessary to analyze the vertical dimension of avalanche crowns were not available. Despite this, our results suggest SfM can be a robust tool for examining glide avalanche crowns and of sufficient resolution to accurately characterize glide avalanche dimensions. Under a warming and more variable future climate, glide avalanches could become a more prevalent problem, and using SfM as a tool to help characterize glide avalanches over a larger spatial area will help us to better document and further understand these phenomena.

Conference Paper↗

USGS2026

Seasonal migrations and other movements

In the past 25 years new information has been obtained on the migrations and movements of mountain sheep (bighorn [Ovis canadensis], thinhorn [Ovis dalli]). This chapter provides a comprehensive overview of mountain sheep migration and other movements across their broad distribution in western North America. Across the range of mountain sheep, migrations and other seasonal movements define a complex movement portfolio that relates to and supports all aspects of mountain sheep ecology. Bighorn and thinhorn species have examples of migratory behaviors that span the continuum between annual residents and long-distance migrants. Migratory behaviors can be characterized as low- or high-elevation residents; elevational migrations and other variants; and geographic migrants. Native populations that have been extant on the landscape without notable human intervention have greater migratory propensity and more diverse migratory portfolios due to the maintenance of migration through cultural learning and social transmission. Restored and augmented populations, where the population-level knowledge of migration has been lost or greatly reduced, are largely nonmigratory, although translocations show some ability to restore short-distance elevational migrations. Seasonal spring and fall migrations are less common in desert bighorn sheep (O. canadensis spp.) or bighorn sheep living in canyon or prairie breaks landscapes. Mineral lick visitation is important and common across the range of mountain sheep. Managing for migratory diversity can help to sustain migratory behavior in the face of climate change and other anthropogenic pressures, which can limit landscape connectivity between seasonal ranges or alter the spatiotemporal dynamics of regional phenology with cascading effects to other biotic and abiotic interactions such as the need to balance forage and predation risk or the spatial refugia with increased temperatures.

Book chapter↗

USGS2010

Emerging viral diseases of fish and shrimp

The rise of aquaculture has been one of the most profound changes in global food production of the past 100 years. Driven by population growth, rising demand for seafood and a levelling of production from capture fisheries, the practice of farming aquatic animals has expanded rapidly to become a major global industry. Aquaculture is now integral to the economies of many countries. It has provided employment and been a major driver of socio-economic development in poor rural and coastal communities, particularly in Asia, and has relieved pressure on the sustainability of the natural harvest from our rivers, lakes and oceans. However, the rapid growth of aquaculture has also been the source of anthropogenic change on a massive scale. Aquatic animals have been displaced from their natural environment, cultured in high density, exposed to environmental stress, provided artificial or unnatural feeds, and a prolific global trade has developed in both live aquatic animals and their products. At the same time, over-exploitation of fisheries and anthropogenic stress on aquatic ecosystems has placed pressure on wild fish populations. Not surprisingly, the consequence has been the emergence and spread of an increasing array of new diseases. This review examines the rise and characteristics of aquaculture, the major viral pathogens of fish and shrimp and their impacts, and the particular characteristics of disease emergence in an aquatic, rather than terrestrial, context. It also considers the potential for future disease emergence in aquatic animals as aquaculture continues to expand and faces the challenges presented by climate change.

Veterinary Research↗

USGS1993

Wetland modeling and information needs at Stillwater National Wildlife Refuge

The marshes in and around Stillwater National Wildlife Refuge (the Refuge) are extremely dynamic; expanding and contracting in size both seasonally, due to runoff and subsequent evapotranspiration, and over longer periods, due to climatic variation. The dynamic nature of these marshes results in a diversity of wetland habitats, which support a variety of migratory birds. To maintain this wetland diversity and control the loss of migratory bird habitat in the Lahontan Valley, the Refuge was established and currently manages a complex of marsh units. However, changes in the hydrology, and changes that will occur as a result of the Fallon Paiute-Shoshone and Truckee-Carson-Pyramid Lake Water Rights Settlement Act (Public Law 101-618, 104 Stat. 3389), greatly affect the Refuge's wetland management capability. In light of these changes, and the legal requirements associated with environmental impact assessments, the Refuge convened a workshop to discuss several aspects of wetland management in the Lahontan Valley. The workshop, described in this report, had three primary objectives: 1. discuss the types and relative proportions of primary wetland habitats that should be provided as described in the settlement act; 2. discuss wetland management models that might be developed to help manage these marshes under hydrologic regimes likely in the future; and 3. discuss future information and monitoring needs, including proposals for valley-wide biodiversity surveys, which would be helpful when considering withdrawn Bureau of Reclamation (BR) lands for possible incorporation into the Refuge. Several presentations at the beginning of the workshop provided a common basis for discussing these objectives. Refuge staff provided background on the history and past management. The Nature Conservatory discussed their role in the settlement act, proposals for valley-wide biodiversity surveys, and results of a literature review for Stillwater Marsh and the Lahontan Valley (Nachlinger 1993). Kay Fowler provided an historical context of changes in vegetation and waterbird use of the marshes based on her ethnography of the local Paiute Indians (Fowler 1993). Finally, Bob Elston discussed a model that predicts archaeological sites based on environmental variables (Raven and Elston 1989). The workshop was organized by staff from the Refuge and facilitated by the authors of this report. Participants included Ron Anglin, Bill Henry, Anne Janik, Cliff Creger, Fred Paveglio, and Mary Jo Elpers of the U.S. Fish and Wildlife Service (the Service); Jeff Baumgartner, Jan Nachlinger, Hope Humphries, and Graham Chisholm of The Nature Conservancy; David Yardas of the Environmental Defense Fund; David Robertson of Robertson Software, Inc.; Norm Saake, Terry Retterer, and Larry Neel of the Nevada Department of Wildlife; Lew Oring and Kay Fowler of the University of Nevada; and Robert Elston of Intermountain Research.

Report↗