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At least 523 records · Page 29Linked to original sources
USGS2020

Climate and local environment structure asynchrony and the stability of primary production in grasslands

Aim Climate variability threatens to destabilize production in many ecosystems. Asynchronous species dynamics may buffer against such variability when a decrease in performance by some species is offset by an increase in performance of others. However, high climatic variability can eliminate species through stochastic extinctions or cause similar stress responses among species that reduce buffering. Local conditions, such as soil nutrients, can also alter production stability directly or by influencing asynchrony. We test these hypotheses using a globally distributed sampling experiment. Location Grasslands in North America, Europe and Australia. Time period Annual surveys over 5 year intervals occurring between 2007 and 2014. Major taxa studied Herbaceous plants. Methods We sampled annually the per species cover and aboveground community biomass [net primary productivity (NPP)], plus soil chemical properties, in 29 grasslands. We tested how soil conditions, combined with variability in precipitation and temperature, affect species richness, asynchrony and temporal stability of primary productivity. We used bivariate relationships and structural equation modelling to examine proximate and ultimate relationships. Results Climate variability strongly predicted asynchrony, whereas NPP stability was more related to soil conditions. Species richness was structured by both climate variability and soils and, in turn, increased asynchrony. Variability in temperature and precipitation caused a unimodal asynchrony response, with asynchrony being lowest at low and high climate variability. Climate impacted stability indirectly, through its effect on asynchrony, with stability increasing at higher asynchrony owing to lower inter‐annual variability in NPP. Soil conditions had no detectable effect on asynchrony but increased stability by increasing the mean NPP, especially when soil organic matter was high. Main conclusions We found globally consistent evidence that climate modulates species asynchrony but that the direct effect on stability is low relative to local soil conditions. Nonetheless, our observed unimodal responses to variability in temperature and precipitation suggest asynchrony thresholds, beyond which there are detectable destabilizing impacts of climate on primary productivity.

Global Ecology and Biogeography↗
USGS2004

Use of a latitudinal gradient in bald cypress (Taxodium distichum) production to examine physiological controls of biotic boundaries and potential responses to environment change

Aim: Predictions of vegetation change with global warming require models that accurately reflect physiological processes underlying growth limitations and species distributions. However, information about environmental controls on physiology and consequent effects on species boundaries and ecosystem functions such as production is limited, especially for forested wetlands that are potentially important carbon sinks. Location: The bald cypress (Taxodium distichum) region of the south-eastern United States was studied to examine how production of an important forested wetland varies with latitude and temperature as well as local hydrology. Methods: We used published data to analyse litter production across a latitudinal gradient from 26.2 to 37.8?? N to determine how bald cypress swamps might respond to alternate climate conditions and what changes might occur throughout the distributional range. Results: Litterfall rates followed a bell shaped curve, indicating that production was more limited at the distributional boundaries (c. 225 g/m2 year-1) compared to the mid-range (795-1126 g/m2 year-1). This pattern suggests that conditions are sub-optimal near both boundaries and that the absence of populations outside this latitudinal range may be largely due to physiological constraints on the carbon balance of dominant species. While dispersal limitations cannot be totally discounted, competition with other wetland types at the extremes of the range does not seem likely to be important because the relative basal area of bald cypress does not decrease near the edges of the range. Impaired hydrology depressed production across the entire range, but more in the south than the north. Main conclusions: Our findings suggest that (1) physiological limitations constrain biotic boundaries of bald cypress swamps; (2) future changes in global temperature would affect litter production in a nonlinear manner across the distributional range; (3) local changes in hydrology may interact with climate to further reduce litter production, particularly at lower latitudes; and (4) southernmost forests could be extirpated if environmental conditions compromise carbon balance and water-use efficiency of trees. ?? 2004 Blackwell Publishing Ltd.

Global Ecology and Biogeography↗
USGS2005

Chemical and isotopic methods for quantifying ground-water recharge in a regional, semiarid environment

The High Plains aquifer underlying the semiarid Southern High Plains of Texas and New Mexico, USA was used to illustrate solute and isotopic methods for evaluating recharge fluxes, runoff, and spatial and temporal distribution of recharge. The chloride mass-balance method can provide, under certain conditions, a time-integrated technique for evaluation of recharge flux to regional aquifers that is independent of physical parameters. Applying this method to the High Plains aquifer of the Southern High Plains suggests that recharge flux is approximately 2% of precipitation, or approximately 11 ± 2 mm/y, consistent with previous estimates based on a variety of physically based measurements. The method is useful because long-term average precipitation and chloride concentrations in rain and ground water have less uncertainty and are generally less expensive to acquire than physically based parameters commonly used in analyzing recharge. Spatial and temporal distribution of recharge was evaluated by use of δ 2 H, δ 18 O, and tritium concentrations in both ground water and the unsaturated zone. Analyses suggest that nearly half of the recharge to the Southern High Plains occurs as piston flow through playa basin floors that occupy approximately 6% of the area, and that macropore recharge may be important in the remaining recharge. Tritium and chloride concentrations in the unsaturated zone were used in a new equation developed to quantify runoff. Using this equation and data from a representative basin, runoff was found to be 24 ± 3 mm/y; that is in close agreement with values obtained from water-balance measurements on experimental watersheds in the area. Such geochemical estimates are possible because tritium is used to calculate a recharge flux that is independent of precipitation and runoff, whereas recharge flux based on chloride concentration in the unsaturated zone is dependent upon the amount of runoff. The difference between these two estimates yields the amount of runoff to the basin.

Groundwater↗
USGS2007

Use of stage data to characterize hydrologic conditions in an urbanizing environment

This paper presents the results of a study on the use of continuous stage data to describe the relation between urban development and three aspects of hydrologic condition that are thought to influence stream ecosystems - overall stage variability, stream flashiness, and the duration of extreme- stage conditions . This relation is examined using data from more than 70 watersheds in three contrasting environmental settings - the humid Northeast (the metropolitan Boston, Massachusetts, area); the very humid Southeast (the metropolitan Birmingham, Alabama, area); and the semiarid West (the metropolitan Salt Lake City, Utah, area). Results from the Birmingham and Boston studies provide evidence linking increased urbanization with stream flashiness. Fragmentation of developed land cover patches appears to ameliorate the effects of urbanization on overall variability and flashiness. There was less success in relating urbanization and streamflow conditions in the Salt Lake City study. A related investigation of six North Carolina sites with long term discharge and stage data indicated that hydrologic condition metrics developed using continuous stage data are comparable to flow based metrics, particularly for stream flashiness measures.

Journal of the American Water Resources Associatio↗
USGS2024

Biological soil crusts are more prevalent in warmer and drier environments within the Great Basin ecoregion: Implications for managing annual grass invasion

Biological soil crusts (biocrusts) can thrive under environmental conditions that are stressful for vascular plants such as high temperatures and/or extremely low moisture availability. In these settings, and in the absence of disturbance, cover of biocrusts commonly exceeds cover of vascular plants. Arid landscapes are also typically slow to recover from disturbance and prone to altered vegetation and invasion by exotic species. In the sagebrush ecosystems, cover of annual, exotic, invasive grasses are lower where cover of biocrusts and vascular plants are greater, suggesting that biocrusts play a role in helping arid sites avoid conversion to dominance by invasive grasses. The conceptual framework for assessing ecological resistance and resilience (R&R) is used across the region to estimate the risk of invasion by annual grasses and the likelihood of recovery of native plants following disturbance. However, this framework does not currently account for biocrusts. We used data collected by the Bureau of Land Management Assessment, Inventory, and Monitoring program to relate biocrusts, specifically the presence of lichens and mosses, to the R&R framework. Lichens frequently occur on warm, dry sites, classified as lower R&R. Mosses frequently occur on sites classified as moderate or moderately low R&R. Without management practices that favor biocrusts in low-moderate R&R, these areas may be more vulnerable to transitioning from being dominated by shrubs to annual grasses. Under climate change scenarios, the area occupied by lower R&R sites is likely to increase, suggesting that the role of biocrusts in maintaining site resistance to invasion may also increase.

Arizona, California, Idaho, Nevada, Utah↗
USGS2016

Environment, host, and fungal traits predict continental-scale white-nose syndrome in bats

White-nose syndrome is a fungal disease killing bats in eastern North America, but disease is not seen in European bats and is less severe in some North American species. We show that how bats use energy during hibernation and fungal growth rates under different environmental conditions can explain how some bats are able to survive winter with infection and others are not. Our study shows how simple but nonlinear interactions between fungal growth and bat energetics result in decreased survival times at more humid hibernation sites; however, differences between species such as body size and metabolic rates determine the impact of fungal infection on bat survival, allowing European bat species to survive, whereas North American species can experience dramatic decline.

Science Advances↗
USGS2004

In situ evidence for an ancient aqueous environment at Meridiani Planum, Mars

Sedimentary rocks at Eagle crater in Meridiani Planum are composed of fine-grained siliciclastic materials derived from weathering of basaltic rocks, sulfate minerals (including magnesium sulfate and jarosite) that constitute several tens of percent of the rock by weight, and hematite. Cross-stratification observed in rock outcrops indicates eolian and aqueous transport. Diagenetic features include hematite-rich concretions and crystal-mold vugs. We interpret the rocks to be a mixture of chemical and siliciclastic sediments with a complex diagenetic history. The environmental conditions that they record include episodic inundation by shallow surface water, evaporation, and desiccation. The geologic record at Meridiani Planum suggests that conditions were suitable for biological activity for a period of time in martian history.

Science↗
USGS2016

Genome sequence of the photoarsenotrophic bacterium Ectothiorhodospira sp. strain BSL-9, isolated from a hypersaline alkaline arsenic-rich extreme environment

The full genome sequence of Ectothiorhodospira sp. strain BSL-9 is reported here. This purple sulfur bacterium encodes an arxA -type arsenite oxidase within the arxB2AB1CD gene island and is capable of carrying out “photoarsenotrophy” anoxygenic photosynthetic arsenite oxidation. Its genome is composed of 3.5 Mb and has approximately 63% G+C content.

Genome Announcements↗
USGS2025

CaDAVEr: A metagenome-assembled genome catalog of microbial decomposers across vertebrate environments

Microbial degradation of organic matter is a fundamental Earth process, yet a mechanistic understanding of microbial metabolisms and successional ecology involved in decomposition remains poorly understood. Here, we announce the recovery of 277 cadaver-associated soil metagenome-assembled genomes to enhance our understanding of vertebrate decomposition microbial processes.

Microbiology Resource Announcements↗
USGS1973

Oil shale formed in desert environment: Green River Formation, Wyoming

The oil shale beds of the Wilkins Peak Member of the Green River Formation differ from most of the Green River oil shale of Colorado and Utah because very few of them have varves; they have numerous mud cracks and, locally, desiccation breccias. Many have a copropelic microstructure and contain labial plates and skin fragments of chironomid larvae. Microfossils of some of these oil shale beds include such normally perishable things as first instar midge larvae, a single spiral chloroplast of a green alga, and sporangia of aquatic fungi. Taken together, these features indicate that the oil shale originated from algal ooze that formed on the bottom of very shallow, spring-fed lakes. The algae (dominantly blue-greens) were not planktonic but grew on, and in, the flocculent ooze. At intervals, perhaps tens to hundreds of years, the lake levels fell enough to expose the algal ooze to the air and partial drying. In the resulting rubbery organic gel, the most delicate microorganisms were heat-fixed and thereby preserved as “mummified” tissue.

Wyoming↗
USGS1991

Controls on the composition of fluvial sands from a tropical weathering environment: Sands of the Orinoco River drainage basin, Venezuela and Colombia

Fluvial sands in the Orinoco River drainage basin fall into three main compositional groupings: (1) sands of subarkose and arkose composition, from high-relief parts of the Guayana Shield, where crystalline rocks are exposed; (2) sands of litharenite and sub-litharenite composition from the active orogenic belt at the western and northwestern margins of the drainage basin, and in those parts of the Llanos (Andean foreland basin) proximal to the mountain belt; and (3) sands of quartz-arenite composition, widespread throughout the remainder of the basin. Multicycle sands of quartz-arenite composition are produced from platform cover on parts of the elevated shield and from uplifted foreland-basin fill in the eastern Llanos. First-cycle sands of quartz-arenite composition are produced from granitic rocks on low-relief regions of the Guayana Shield and from reworked Holocene alluvium in parts of the western Llanos distal to the orogenic terranes. Erosion in the Orinoco River drainage basin may be described in terms of transport-limited and weathering-limited denudation regimes. In active orogenic terranes and in parts of the elevated shield, transport processes can remove weathered material as rapidly as it is produced by chemical weathering. Thin soils and short soil-mineral residence time result in sands that are incompletely chemically weathered and accurately reflect source-rock composition. In the orogenic terranes, subtle variations in source-rock lithology are preserved in sand composition. In contrast, in low-relief parts of the Guayana Shield and on flat erosion surfaces of the upland shield, weathering exceeds the rate at which transport processes can remove weathered material. Thick soils accumulate, soil-mineral residence time is long, and detritus is highly altered chemically. On much of the lowland Guayana Shield, upper soil layers consist of nearly pure quartz sand that erodes to produce first-cycle fluvial sand of quartz-arenite composition. Chemically weathered orogenically derived sand enters the Orinoco River on the left bank, while feldspathic shield-derived sand enters on the right bank. This geometry is responsible for the nearly total lack of longitudinal variation in sand composition along the 1,400-km length of the Orinoco River mainstem. Except in the upper 100 km of the Orinoco River mainstem, cross-channel heterogeneity in sand composition is also modest. Nevertheless, a weighted linear least-squares modeling approach suggests that sand moves down the Orinoco River mainstem in distinct pulses, perhaps corresponding to times of accelerated erosion in headwater regions. Because rivers that head in the orogenic terranes and traverse the Llanos contribute more than 99% of the sand in the lower Orinoco River mainstem, the composition of this sand is dominated by chemically weathered sands from the Llanos. The Orinoco River—the third largest river in the world—delivers first-cycle sands of quartz-arenite composition to its delta.

Geological Society of America Bulletin↗
USGS1999

Importance of mechanical disaggregation in chemical weathering in a cold alpine environment, San Juan Mountains, Colorado

Weathering of welded tuff near the summit of Snowshoe Mountain (3660 m) in southwestern Colorado was studied by analyzing infiltrating waters in the soil and associated solid phases. Infiltrating waters exhibit anomalously high potassium to silica ratios resulting from dissolution of a potassium-rich glass that occurs as a trace phase in the rock. In laboratory experiments using rock from the field site, initial dissolution generated potassium-rich solutions similar to those observed in the field. The anomalous potassium release decreased over time (about 1 month), after which the dominant cation was calcium, with a much lower potassium to silica ratio.

Colorado↗
USGS1999

Late Pleistocene environments of the western Noatak basin, northwestern Alaska

Glacial Lake Noatak formed repeatedly during middle and late Pleistocene time as expanding glaciers from the DeLong Mountains blocked the Noatak River valley. Downcutting by the Noatak River has exposed thick sediment successions in bluffs up to 86 m high. Two river bluffs, Nk-26 and Nk-29A, contain correlative organic-rich flood-plain deposits that were formed during and after deposition of the Old Crow tephra at about the transition between oxygen isotope stage 6 and oxygen isotope stage 5, at the beginning of the last interglaciation. Both bluffs also contain older interglacial or interstadial flood-plain deposits of uncertain age.

Alaska↗
USGS1976

Sclerochronology: a tool for interpreting past environments

X-radiographs of stony coral slabs reveal two types of annual density bands. Detailed studies of these bands in relation to known variations in air temperatures indicate that sclerochronology is a valid tool for documenting time sequences and changing environmental conditions on a coral reef.

Geology↗