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At least 451 records · Page 25Linked to original sources

USGS2014

The case for a modern multiwavelength, polarization-sensitive LIDAR in orbit around Mars

We present the scientific case to build a multiple-wavelength, active, near-infrared (NIR) instrument to measure the reflected intensity and polarization characteristics of backscattered radiation from planetary surfaces and atmospheres. We focus on the ability of such an instrument to enhance, perhaps revolutionize, our understanding of climate, volatiles and astrobiological potential of modern-day Mars.

Journal of Quantitative Spectroscopy and Radiative↗

USGS2002

A 1500-year record of climatic and environmental change in Elk Lake, Clearwater County, Minnesota II: Geochemistry, mineralogy, and stable isotopes

Most of the sediment components that have accumulated in Elk Lake, Clearwater County, northwestern Minnesota, over the past 1500 years are authigenic or biogenic (CaCO3, biogenic SiO2, organic matter, iron and manganese oxyhydroxides, and iron phosphate) and are delivered to the sediment-water interface on a seasonal schedule where they are preserved as distinct annual laminae (varves). The annual biogeochemical cycles of these components are causally linked through the 'carbon pump', and are recapitulated in longer-term cycles, most prominently with a periodicity of about 400 years. Organic carbon is fixed in the epilimnion by photosynthetic removal of CO2, which also increases the pH, triggering the precipitation of CaCO3. The respiration and degradation of fixed organic carbon in the hypolimnion consumes dissolved oxygen, produces CO2, and lowers the pH so that the hypolimnion becomes anoxic and undersaturated with respect to CaCO3 during the summer. Some of the CaCO3 produced in the epilimnion is dissolved in the anoxic, lower pH hypolimnion and sediments. The amount of CaCO3 that is ultimately incorporated into the sediments is a function of how much is produced in the epilimnion and how much is consumed in the hypolimnion and the sediments. Iron, manganese, and phosphate accumulate in the anoxic hypolimnion throughout the summer. Sediment-trap studies show that at fall overturn, when iron-, manganese-, and phosphate-rich bottom waters mix with carbonate- and oxygen-rich surface waters, precipitation of iron and manganese oxyhydroxides, iron phosphate, and manganese carbonate begins and continues into the winter months. Detrital clastic material in the sediments of Elk Lake deposited over the last 1500 years is a minor component (<10% by weight) that is mostly wind-borne (eolian). Detailed analyses of the last 1500 years of the Elk Lake sediment record show distinct cycles in eolian clastic variables (e.g. aluminum, sodium, potassium, titanium, and quartz), with a periodicity of about 400 years. The 400-yr cycle in eolian clastic material does not correspond to the 400-yr cycles in redox-sensitive authigenic components, suggesting that the clastic component is responding to external forcing (wind) whereas the authigenic components are responding to internal forcing (productivity), although both may ultimately be forced by climate change. Variations in the oxygen and carbon isotopic composition of CaCO3 are small but appear to reflect small variations in ground water influx that are also driven by external forcing.

Journal of Paleolimnology↗

USGS2019

Heterogeneity in hyporheic flow, pore water chemistry, and microbial community composition in an alpine streambed

The hyporheic zone, where surface water and groundwater mix, is an important microbial habitat where biogeochemical reactions influence water quality. We show that spatial variability in hyporheic flow in the East River near Crested Butte, Colorado, drives heterogeneity in streambed geochemical conditions and microbial community assemblages, but the diversity of assemblages remains nearly constant throughout the reach. In July 2018, we collected approximately 100 pore water samples at 20 cm depth and analyzed them for anions, cations, dissolved organic carbon, dissolved organic matter (DOM) quality, and basic water quality parameters. Vertical hydraulic head gradients were also measured to assess the potential for upward or downward flow, and heat tracing was used to quantify vertical flux rates at a subset of locations. We found that regions of the streambed that are more groundwater-dominated contain less dissolved oxygen, higher concentrations of reduced metals, and more microbially-processed, recalcitrant DOM, while more surface water-dominated locations contain higher dissolved oxygen concentrations and terrestrially-derived, labile DOM. 16S rRNA gene sequencing of extracted DNA revealed that microbial community composition varies with geochemical gradients related to hyporheic flow. These findings provide a better understanding of hyporheic controls on streambed biogeochemistry during the baseflow season, which is expected to lengthen with climate change in alpine watersheds due to earlier snowmelt onset and reduced snowpack.

Colorado↗

USGS2016

Variability and trends in runoff efficiency in the conterminous United States

Variability and trends in water-year runoff efficiency (RE) — computed as the ratio of water-year runoff (streamflow per unit area) to water-year precipitation — in the conterminous United States (CONUS) are examined for the 1951 through 2012 period. Changes in RE are analyzed using runoff and precipitation data aggregated to United States Geological Survey 8-digit hydrologic cataloging units (HUs). Results indicate increases in RE for some regions in the north-central CONUS and large decreases in RE for the south-central CONUS. The increases in RE in the north-central CONUS are explained by trends in climate, whereas the large decreases in RE in the south-central CONUS likely are related to groundwater withdrawals from the Ogallala aquifer to support irrigated agriculture.

Journal of the American Water Resources Associatio↗

USGS2007

Analysis and modeling of long‐term stream temperatures on the Steamboat Creek Basin, Oregon: Implications for land use and fish habitat

Steamboat Creek basin is an important source of timber and provides crucial spawning and rearing habitat for anadromous steelhead trout ( Oncorhynchus mykiss ). Because stream temperatures are near the upper limit of tolerance for the survival of juvenile steelhead, the possible long‐term effect of clear‐cut logging on stream temperatures was assessed. Twenty‐year (1969–1989) records of summer stream temperature and flow from four tributaries and two reaches of Steamboat Creek and Boulder Creek (a nearby unlogged watershed) were analyzed. Logging records for the Steamboat Creek basin and air temperature records also were used in the analysis. A time‐series model of the components of stream temperature (seasonal cycle of solar radiation, air temperature, streamflow, an autoregressive term of order 1, and a linear trend variable) was fitted to the water‐temperature data. The linear trend variable was significant in all the fitted models except Bend Creek (a tributary fed by cool ground‐water discharge) and Boulder Creek. Because no trends in either climate (i.e., air temperature) or streamflow were found in the data, the trend variable was associated with the pre‐1969 loss and subsequent regrowth of riparian vegetation and shading canopies.

Oregon↗

USGS2014

Population viability of Pediocactus brady (Cactaceae) in a changing climate

• Premise of the study: A key question concerns the vulnerability of desert species adapted to harsh, variable climates to future climate change. Evaluating this requires coupling long-term demographic models with information on past and projected future climates. We investigated climatic drivers of population growth using a 22-yr demographic model for Pediocactus bradyi , an endangered cactus in northern Arizona. • Methods: We used a matrix model to calculate stochastic population growth rates (λ s ) and the relative influences of life-cycle transitions on population growth. Regression models linked population growth with climatic variability, while stochastic simulations were used to (1) understand how predicted increases in drought frequency and extreme precipitation would affect λ s , and (2) quantify variability in λ s based on temporal replication of data. • Key results: Overall λ s was below unity (0.961). Population growth was equally influenced by fecundity and survival and significantly correlated with increased annual precipitation and higher winter temperatures. Stochastic simulations increasing the probability of drought and extreme precipitation reduced λ s , but less than simulations increasing the probability of drought alone. Simulations varying the temporal replication of data suggested 14 yr were required for accurate λ s estimates. • Conclusions: Pediocactus bradyi may be vulnerable to increases in the frequency and intensity of extreme climatic events, particularly drought. Biotic interactions resulting in low survival during drought years outweighed increased seedling establishment following heavy precipitation. Climatic extremes beyond historical ranges of variability may threaten rare desert species with low population growth rates and therefore high susceptibility to stochastic events.

Arizona↗

USGS2017

Associations among habitat characteristics and meningeal worm prevalence in eastern South Dakota, USA

Few studies have evaluated how wetland and forest characteristics influence the prevalence of meningeal worm ( Parelaphostrongylus tenuis ) infection of deer throughout the grassland biome of central North America. We used previously collected, county-level prevalence data to evaluate associations between habitat characteristics and probability of meningeal worm infection in white-tailed deer ( Odocoileus virginianus ) across eastern South Dakota, US. The highest-ranked binomial regression model for detecting probability of meningeal worm infection was spring temperature + summer precipitation + percent wetland; weight of evidence ( w i =0.71) favored this model over alternative models, though predictive capability was low (Receiver operating characteristic=0.62). Probability of meningeal worm infection increased by 1.3- and 1.6-fold for each 1-cm and 1-C increase in summer precipitation and spring temperature, respectively. Similarly, probability of infection increased 1.2-fold for each 1% increase in wetland habitat. Our findings highlight the importance of wetland habitat in predicting meningeal worm infection across eastern South Dakota. Future research is warranted to evaluate the relationships between climatic conditions (e.g., drought, wet cycles) and deer habitat selection in maintaining P. tenuis along the western boundary of the parasite.

Journal of Wildlife Diseases↗

USGS2016

Interactions among vegetation, climate, and herbivory control greenhouse gas fluxes in a subarctic coastal wetland

High-latitude ecosystems are experiencing the most rapid climate changes globally, and in many areas these changes are concurrent with shifts in patterns of herbivory. Individually, climate and herbivory are known to influence biosphere-atmosphere greenhouse gas (GHG) exchange; however, the interactive effects of climate and herbivory in driving GHG fluxes have been poorly quantified, especially in coastal systems that support large populations of migratory waterfowl. We investigated the magnitude and the climatic and physical controls of GHG exchange within the Yukon-Kuskokwim Delta in western Alaska across four distinct vegetation communities formed by herbivory and local microtopography. Net CO 2 flux was greatest in the ungrazed Carex meadow community (3.97 ± 0.58 [SE] µmol CO 2 m −2 s −1 ), but CH 4 flux was greatest in the grazed community (14.00 ± 6.56 nmol CH 4 m −2 s −1 ). The grazed community is also the only vegetation type where CH 4 was a larger contributor than CO 2 to overall GHG forcing. We found that vegetation community was an important predictor of CO 2 and CH 4 exchange, demonstrating that variation in regional gas exchange is best explained when the effect of grazing, determined by the difference between grazed and ungrazed communities, is included. Further, we identified an interaction between temperature and vegetation community, indicating that grazed regions could experience the greatest increases in CH 4 emissions with warming. These results suggest that future GHG fluxes could be influenced by both climate and by changes in herbivore population dynamics that expand or contract the vegetation community most responsive to future temperature change.

Alaska↗

USGS1993

Geologic and geomorphic controls of coal development in some Tertiary Rocky Mountain basins, USA

Previous investigations have not well defined the controls on the development of minable coals in fluvial environments. This study was undertaken to provide a clearer understanding of these controls, particularly in of the lower Tertiary coal-bearing deposits of the Raton and Powder River basins in the Rocky Mountain region of the United States. In this region, large amounts of coals accumulated in swamps formed in the flow-through fluvial systems that infilled these intermontane basins. Extrabasinal and intrabasinal tectonism partly controlled the stratigraphic and facies distributions of minable coal deposits. The regional accumulation of coals was favored by the rapid basin subsidence coupled with minimal uplift of the source area. During these events, coals developed in swamps associated with anastomosed and meandering fluvial systems and alluvial fans. The extensive and high rate of sediment input from these fluvial systems promoted the formation of ombrotrophic, raised swamps, which produced low ash and anomalously thick coals. The petrology and palynology of these coals, and the paleobotany of the associated sediments, suggest that ombrotrophic, raised swamps were common in the Powder River Basin, where the climate during the early Tertiary was paratropical. The paleoecology of these swamps is identical to that of the modern ombrotrophic, raised swamps of the Baram and Mahakam Rivers of Borneo.

International Journal of Coal Geology↗

USGS2010

Cyclic changes in Pennsylvanian paleoclimate and effects on floristic dynamics in tropical Pangaea

Wetland floras narrowly define perceptions of Pennsylvanian tropical ecosystems, the so-called Coal Age. Such wetlands reflect humid to perhumid climate, leading to characterizations of Pennsylvanian tropics as everwet, swampy. These views are biased by the high preservation potential of wetlands. Sedimentation patterns, paleosols, and fossil floras indicate the presence of vegetation tolerant of subhumid to dry-subhumid, perhaps semi-arid climate in basins between peat formation times. Understanding the significance of this seasonally-dry vegetation has suffered from conceptual and terminological confusion. A clearer view has emerged as models for framing the data have improved. Basinal floras typical of seasonally-dry conditions, relatively low soil moisture regimes, are well documented but mainly from isolated deposits. Some of the earliest, dominated by primitive pteridosperms ("Fl??zfern" floras), occur in clastic rocks between European Early Pennsylvanian coal beds. Later Early Pennsylvanian, fern-cordaitalean vegetation, different from coal floras, is preserved in marine goniatite bullions. Conifers are first suggested by late Mississippian Potoniesporites pollen. About the same time, in North America, broadleaf foliage, Lesleya and Megalopteris occur in basin-margin settings, on drought-prone limestone substrates. The best known, xeromorphic floras found between coal beds appear in the Middle through Late Pennsylvanian, containing conifers, cordaitaleans, and pteridosperms. The Middle Pennsylvanian appearances of this flora are mainly allochthonous, though parautochthonous occurrences have been reported. Parautochthonous assemblages are mostly Late Pennsylvanian. The conifer flora became dominant in western and central Pangaean equatorial lowlands in earliest Permian. Location of the humid-perhumid wetland flora during periods of relative dryness, though rarely discussed, is as, or more, perplexing than the spatial location of seasonally-dry floras through time - wetland plants had few migratory options and possibly survived in small refugia, within and outside of basins. Coupled oscillations in climate, sea level, and vegetation were driven most likely by glacial-interglacial fluctuations, perhaps controlled by orbital cyclicity. ?? 2010.

International Journal of Coal Geology↗

USGS2023

Unstructured-grid approach to develop high-fidelity groundwater model to understand groundwater flow and storage responses to excessive groundwater withdrawals in the Southern Hills aquifer system in southeastern Louisiana (USA)

Study region The Southern Hills aquifer system in the Louisiana Capital Area Groundwater Conservation District (CAGCD), USA. Study focus The Southern Hills aquifer system provides abundant groundwater for public and industrial supplies in the CAGCD. Groundwater depletion, saltwater intrusion, and land subsidence are potential concerns due to prolonged excessive groundwater withdrawals. This study develops a high-fidelity groundwater flow model utilizing a complex unstructured grid to investigate groundwater flow and storage responses to excessive groundwater withdrawals for the Southern Hills aquifer system in the CAGCD. The groundwater model incorporates the Mississippi River alluvial aquifer down to the Miocene sands extending to depths around 1 km. New hydrological insights Groundwater modeling results indicate large cones of depression in the Evangeline and Jasper formations in the Baton Rouge area due to prolonged groundwater withdrawals. Low-permeability faults are inferred by significant groundwater level difference across the faults. While local groundwater storage depletion in deeper aquifers is evident, overall estimated groundwater storage changes of the Southern Hills aquifer system in the CAGCD are close to zero in the past two decades, indicating insignificant groundwater storage changes. This is attributed to dominant interactions between the major rivers and the shallower alluvial aquifer. In addition, the simulated groundwater storage changes exhibit patterns similar to those derived by the Gravity Recovery and Climate Experiment (GRACE) model that has been used in evaluation of groundwater depletion in many regional studies.

Louisiana↗

USGS2016

Precipitation regime classification for the Mojave Desert: Implications for fire occurrence

Long periods of drought or above-average precipitation affect Mojave Desert vegetation condition, biomass and susceptibility to fire. Changes in the seasonality of precipitation alter the likelihood of lightning, a key ignition source for fires. The objectives of this study were to characterize the relationship between recent, historic, and future precipitation patterns and fire. Classifying monthly precipitation data from 1971 to 2010 reveals four precipitation regimes: low winter/low summer, moderate winter/moderate summer, high winter/low summer and high winter/high summer. Two regimes with summer monsoonal precipitation covered only 40% of the Mojave Desert ecoregion but contain 88% of the area burned and 95% of the repeat burn area. Classifying historic precipitation for early-century (wet) and mid-century (drought) periods reveals distinct shifts in regime boundaries. Early-century results are similar to current, while the mid-century results show a sizeable reduction in area of regimes with a strong monsoonal component. Such a shift would suggest that fires during the mid-century period would be minimal and anecdotal records confirm this. Predicted precipitation patterns from downscaled global climate models indicate numerous epochs of high winter precipitation, inferring higher fire potential for many multi-decade periods during the next century.

Mojave Desert↗

USGS2022

Hydrologic modeling of a perennial firn aquifer in southeast Greenland

A conceptual model, based on field observations and assumed physics of a perennial firn aquifer near Helheim Glacier (southeast Greenland), is evaluated via steady-state 2-D simulation of liquid water flow and energy transport with phase change. The simulation approach allows natural representation of flow and energy advection and conduction that occur in vertical meltwater recharge through the unsaturated zone and in lateral flow within the saturated aquifer. Agreement between measured and simulated aquifer geometry, temperature, and recharge and discharge rates confirms that the conceptual field-data-based description of the aquifer is consistent with the primary physical processes of groundwater flow, energy transport and phase change. Factors that are found to control simulated aquifer configuration include surface temperature, meltwater recharge rate, residual total-water saturation and capillary fringe thickness. Simulation analyses indicate that the size of perennial firn aquifers depends primarily on recharge rates from surface snowmelt. Results also imply that the recent aquifer expansion, likely due to a warming climate, may eventually produce lakes on the ice-sheet surface that would affect the surface energy balance.

Journal of Glaciology↗

USGS2005

Inferring differential evolutionary processes of plant persistence traits in Northern Hemisphere Mediterranean fire-prone ecosystems

1 Resprouting capacity (R) and propagule-persistence (P) are traits that are often considered to have evolved where there are predictable crown fires. Because several indicators suggest a stronger selective pressure for such traits in California than in the Mediterranean Basin, we hypothesize that plant species should have evolved to become R+ and P+ more frequently in California than in the Mediterranean Basin. 2 To test this hypothesis we studied the phylogenetic association between R and P states in both California and the Mediterranean Basin using published molecular phylogenies. 3 The results suggest that R and P evolved differently in the two regions. The occurrence of the states differs significantly between regions for trait P, but not for trait R. The different patterns (towards R+ and P+ in California and towards R+ and P- in the Mediterranean Basin) are reflected in the higher abundance and the wider taxonomic distribution of species with both persistence traits (R+P+ species) in California. 4 The differential acquisition of fire persistence mechanisms at the propagule level (P+) supports the idea that fire selective pressures has been higher in California than in the Mediterranean Basin. 5 Our comparative phylogenetic-informed analysis contributes to an understanding of the differential role of the Quaternary climate in determining fire persistence traits in different Mediterranean-type ecosystems and, thus, to the debate on the evolutionary convergence of traits. ?? 2006 British Ecological Society.

Journal of Ecology↗

USGS2010

Phylogeography of declining relict and lowland leopard frogs in the desert Southwest of North America

We investigated the phylogeography of the closely related relict leopard frog Rana onca (= Lithobates onca ) and lowland leopard frog Rana yavapaiensis (= Lithobates yavapaiensis ) – two declining anurans from the warm‐desert regions of south‐western North America. We used sequence data from mitochondrial DNA (mtDNA) to assess 276 individuals representing 30 sites from across current distributions. Our analysis supports a previously determined phylogenetic break between these taxa, and we found no admixing of R. onca and R. yavapaiensis haplotypes within our extensive sampling of sites. Our phylogeographic assessment, however, further divided R. yavapaiensis into two distinct mtDNA lineages, one representing populations across Arizona and northern Mexico and the other a newly discovered population within the western Grand Canyon, Arizona. Estimates of sequence evolution indicate a possible Early Pleistocene divergence of R. onca and R. yavapaiensis , followed by a Middle Pleistocene separation of the western Grand Canyon population of R. yavapaiensis from the main R. yavapaiensis clade. Phylogeographic and demographic analyses indicate population or range expansion for R. yavapaiensis within its core distribution that appears to predate the latest glacial maximum. Species distribution models under current and latest glacial climatic conditions suggest that R. onca and R. yavapaiensis may not have greatly shifted ranges.

Arizona, Nevada, Utah, New Mexico↗

USGS2007

Watershed responses to climate change at Glacier National Park

We have developed an approach which examines ecosystem function and the potential effects of climatic shifts. The Lake McDonald watershed of Glacier National Park was the focus for two linked research activities: acquisition of baseline data on hydrologic, chemical and aquatic organism attributes that characterize this pristine northern rocky mountain watershed, and further developing the Regional Hydro-Ecosystem Simulation System (RHESSys), a collection of integrated models which collectively provide spatially explicit, mechanistically-derived outputs of ecosystem processes, including hydrologic outflow, soil moisture, and snowpack water equivalence. In this unique setting field validation of RHESSys, outputs demonstrated that reasonable estimates of SWE and streamflow are being produced. RHESSys was used to predict annual stream discharge and temperature. The predictions, in conjunction with the field data, indicated that aquatic resources of the park may be significantly affected. Utilizing RHESSys to predict potential climate scenarios and response of other key ecosystem components can provide scientific insights as well as proactive guidelines for national park management.

Journal of the American Water Resources Associatio↗

USGS2014

Evidence against a Pleistocene desert refugium in the Lower Colorado River Basin

Aim The absence of Sonoran Desert plants in late Pleistocene-aged packrat middens has led to speculation that they survived glacial episodes either in refugia as intact associations (Clementsian community concept) or in dry microsites within chaparral or woodland according to individualistic species responses (Gleasonian community concept). To test these hypotheses, we developed a midden record from one likely refugium in north-eastern Baja California, Mexico. We also measured stomatal guard cell size in fossil leaves to further evaluate site-level individualistic responses of Larrea tridentata (creosote bush) ploidy races to climatic changes, including monsoonal history, over the late Quaternary. Location Sierra Juárez, Lower Colorado River Basin, north-eastern Baja California, Mexico. Methods Packrat ( Neotoma ) middens were collected from <300 m elevation on the eastern piedmont of the Sierra Juárez. Plant macrofossils and pollen were analysed from 50 dated middens, including determination of Larrea tridentata ploidy races. Results Pleistocene middens dating back to >55,000 cal. yr BP contained a mix of extralocal species characteristic of chaparral and pinyon–juniper–oak woodland, along with some modern desert elements. Many other desert taxa were absent during the Pleistocene, although most had arrived by the beginning of the Holocene 11,700 years ago. Main conclusions The assemblage of chaparral, woodland and select desert elements refutes the hypothesis that the Lower Colorado River Basin served as a late Pleistocene refugium for Sonoran Desert flora. The rapid arrival of most missing desert species by the early Holocene suggests they did not have far to migrate. They probably survived the last glacial period as smaller, disparate populations in dry microsites within chaparral and pinyon–juniper–oak woodlands. Diploid and tetraploid races of Larrea tridentata were present during the Pleistocene, but hexaploids did not appear until the mid-Holocene. This demonstrates that individualistic responses to climate involved genetic variants, in this case cytotypes, and not just species.

Baja California↗

USGS2010

The changing effects of Alaska’s boreal forests on the climate system

In the boreal forests of Alaska, recent changes in climate have influenced the exchange of trace gases, water, and energy between these forests and the atmosphere. These changes in the structure and function of boreal forests can then feed back to impact regional and global climates. In this manuscript, we examine the type and magnitude of the climate feedbacks from boreal forests in Alaska. Research generally suggests that the net effect of a warming climate is a positive regional feedback to warming. Currently, the primary positive climate feedbacks are likely related to decreases in surface albedo due to decreases in snow cover. Fewer negative feedbacks have been identified, and they may not be large enough to counterbalance the large positive feedbacks. These positive feedbacks are most pronounced at the regional scale and reduce the resilience of the boreal vegetation – climate system by amplifying the rate of regional warming. Given the recent warming in this region, the large variety of associated mechanisms that can alter terrestrial ecosystems and influence the climate system, and a reduction in the boreal forest resilience, there is a strong need to continue to quantify and evaluate the feedback pathways.

Alaska↗