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At least 1,027 records · Page 57Linked to original sources
USGS1991

Seasonal variations of carbon dioxide concentrations in stony, coarse-textured desert soils of southern Nevada, USA

Knowledge of carbon dioxide concentration in desert soils is required in theoretical models of the development of pedogenic and ground-water calcium carbonate. Most studies have concentrated on medium- to fine-textured soils in temperate to humid environments. Very little data exist for CO 2 concentrations in stony, coarse-textured deposits such as those making up alluvial fans and fluvial terraces. The purpose of this study was to obtain CO 2 concentration data in stony, coarse-textured, uncultivated soils in a desert environment. Soil gas samples were collected from two sites—Yucca Wash and Rock Valley—at the Nevada Test Site in southern Nevada between June 1985 and June 1986 to determine soil CO 2 concentrations and their seasonal and depth variations in the soil profile. Soil CO 2 concentrations ranged from 0.03 volume percent in winter and summer to 0.25 volume percent in spring. During the summer, fall, and winter, CO 2 concentrations were close to atmospheric levels and varied randomly with depth. In spring, CO 2 varied with root density, highest concentrations occurring between 40 and 80 cm of depth. Maximum CO 2 values decrease and occur at progressively deeper levels toward the end of spring. Biological activity appears to be limited throughout the year because of the arid climate. During the winter and spring, soil CO 2 appears to be more dependent on temperature than moisture, whereas in the summer and fall it appears to be dependent on moisture. Soil gas samples were also collected during the spring from three sites in the Kyle Canyon area in southern Nevada to determine the variation of soil CO 2 levels with changes in elevation and vegetation. Soil CO 2 values increased from 0.04 to 0.24 volume percent with increasing elevation.

Nevada↗
USGS2015

A simplified, data-constrained approach to estimate the permafrost carbon–climate feedback

We present an approach to estimate the feedback from large-scale thawing of permafrost soils using a simplified, data-constrained model that combines three elements: soil carbon (C) maps and profiles to identify the distribution and type of C in permafrost soils; incubation experiments to quantify the rates of C lost after thaw; and models of soil thermal dynamics in response to climate warming. We call the approach the Permafrost Carbon Network Incubation–Panarctic Thermal scaling approach (PInc-PanTher). The approach assumes that C stocks do not decompose at all when frozen, but once thawed follow set decomposition trajectories as a function of soil temperature. The trajectories are determined according to a three-pool decomposition model fitted to incubation data using parameters specific to soil horizon types. We calculate litterfall C inputs required to maintain steady-state C balance for the current climate, and hold those inputs constant. Soil temperatures are taken from the soil thermal modules of ecosystem model simulations forced by a common set of future climate change anomalies under two warming scenarios over the period 2010 to 2100. Under a medium warming scenario (RCP4.5), the approach projects permafrost soil C losses of 12.2–33.4 Pg C; under a high warming scenario (RCP8.5), the approach projects C losses of 27.9–112.6 Pg C. Projected C losses are roughly linearly proportional to global temperature changes across the two scenarios. These results indicate a global sensitivity of frozen soil C to climate change ( γ sensitivity) of −14 to −19 Pg C °C −1 on a 100 year time scale. For CH 4 emissions, our approach assumes a fixed saturated area and that increases in CH 4 emissions are related to increased heterotrophic respiration in anoxic soil, yielding CH 4 emission increases of 7% and 35% for the RCP4.5 and RCP8.5 scenarios, respectively, which add an additional greenhouse gas forcing of approximately 10–18%. The simplified approach presented here neglects many important processes that may amplify or mitigate C release from permafrost soils, but serves as a data-constrained estimate on the forced, large-scale permafrost C response to warming.

Philosophical Transactions of the Royal Society A:↗
USGS2019

Earlier plant growth helps compensate for reduced carbon fixation after 13 years of warming

1. Drylands play a dominant role in global carbon cycling and are particularly vulnerable to increasing temperatures, but our understanding of how dryland ecosystems will respond to climatic change remains notably poor. Considering that the area of drylands is projected to increase 11–23% by 2100, understanding the impacts of warming on the functions and services furnished by these arid and semiarid ecosystems has numerous implications. 2.In a unique 13‐year ecosystem warming experiment in a southwestern U.S. dryland, we investigated the consequences of rising temperature on Achnatherum hymenoides , a widespread, keystone grass species on the Colorado Plateau. We tracked individual‐ and population‐level responses to identify optimal strategies that may have been masked if considering only one level of plant response. 3.We found several factors combined to affect the timing and magnitude of plant responses during the 13 th year of warming. These included large warming‐induced biomass increases for individual plants, an 8.5‐day advancement in the growing season, and strong reductions in photosynthetic rates and population cover. 4.Importantly, we observed a lack of photosynthetic acclimation and, thus, a warming‐induced down regulation of photosynthetic rates. However, these physiological responses were concurrent with warmed‐plant increases in growing season length and investment in photosynthetic surfaces, demonstrating the species' ability to balance carbon fixation limitations with warming. 5.These results, which bring together ecophysiological, phenological, reproductive, and morphological assessments of plant responses to warming, suggest that the extent of change in A. hymenoides populations will be based upon numerous adaptive responses that vary in their direction and magnitude. Plant population responses to climatic warming remain poorly resolved, particularly for Earth's drylands, and our in situ experiment assessing multiple strategies offers a novel look into a warmer world.

Utah↗
USGS2021

Forest thinning in the seaward fringe speeds up surface elevation increment and carbon accumulation in managed mangrove forests

Mangroves are significant carbon (C) sinks and ecological engineers as they accumulate sediments and increase soil surface elevation. Thus, the forest management practice of thinning may not only alter forest structure, but also facilitate new biogeomorphological processes that affect soil development. Thinning may create additional opportunity for understorey species, such as the light-demanding Acanthus ilicifolius , to become a more prominent vegetation component of mangroves, which may further alter soil surface elevation trajectories. Forest structure and soil surface elevation change (SEC) were monitored along transects from the landward edge (upper intertidal) to seaward fringe before and after thinning of non-native Sonneratia apetala plantations along the seaward edge of a mangrove site in China. Soil C accumulation was also evaluated. Acanthus individuals colonized the forest gaps created by Sonneratia thinning in the seaward forest edge of the intertidal zones. In the absence of other pioneer species or other mangrove propagules/seeds, Acanthus pioneers occupied the areas rapidly (from 33.6 to 72.6 stems/m 2 ), and were successful opportunists. Newly colonizing Acanthus vegetation significantly increased SEC from 25.1 mm/year before Sonneratia was thinned to 46.5 mm/year after thinning-induced Acanthus occupation. Furthermore, Acanthus occupation enhanced soil C accumulation at the seaward edge to 49.9 MgC ha −1 year −1 ; a rate twofold higher than in the Sonneratia plantation before thinning. Synthesis and applications . Prolific Acanthus growth formed small elevation mounds on the seaward forest edge, which was suspected as a positive effect induced by thinning Sonneratia plantations that further facilitated colonization of Acanthus clones. Thinning non-native Sonneratia disturbed the established zonation, altered SEC, and is facilitating further succession of these mangrove forests into un-occupied aquatic areas. Higher elevations created by Acanthus expansion (vertically and horizontally) may further promote a greater percentage of landward edge mangrove species to colonize at these more favourable intertidal elevations yielding at least short-term gains in soil carbon accumulation by altering ecosystem function. Silvicultural activity should consider unintended influences on sedimentation patterns both in situ and in adjacent habitats in tidal forests, where small elevation changes affect mangrove species habitat preferences.

Journal of Applied Ecology↗
USGS2022

The effects of cheatgrass invasion on US Great Basin carbon storage depend on interactions between plant community composition, precipitation seasonality, and soil climate regime

Annual-grass invasions are transforming desert ecosystems in ways that affect ecosystem carbon (C) balance, but previous studies do not agree on the pattern, magnitude and direction of changes. A recent meta-analysis of 41 articles and 386 sites concludes that invasion by annual grasses such as cheatgrass ( Bromus tectorum L) reduces C in biomass across the Great Basin (Nagy et al., 2021). Reanalysis reveals that whether cheatgrass affects biomass C stocks is not generalizable, but rather depends on the considerable variation in climate across the subject sites. Our analysis suggests that accurate Great Basin-scale estimates of cheatgrass effects on C balance are not yet possible. Addition of climate variables to the meta-analysis reveals that cheatgrass invasion (a) reduced C in above-ground biomass in relatively summer-wet sites but not in summer-dry sites, (b) increased surface soil C in sites with intermediate resistance and resilience classifications (R&R) but not in low R&R sites—that is, mesic/aridic soil climates and (c) did not affect deep soil C. Considering that cheatgrass has expanded most in relatively summer-dry sites and mesic/aridic sites, omission of climate factors leads to model overestimates of cheatgrass effects on C when extrapolating to larger areas. Estimates of cheatgrass effects on C would also be improved if the analysis considered that (a) perennial grasslands are a common community state in the Great Basin that have intermediary C relative to annual grasslands and sagebrush stands, that is the omission of perennial grasslands from analysis inflates the baseline C storage of uninvaded Great Basin ecosystems, and( b) cheatgrass does not often exist in stable monocultures and soil carbon can reflect current or recent presence of other species. Synthesis and applications . Invasions often reveal heterogeneity in ecosystem structure and function that is not otherwise evident, and the heterogeneity can influence estimation of the net impacts of the invaders. For cheatgrass and other invaders, we propose that formally accounting for the spatial variability of invasion on ecosystem functions will improve the estimation of their net effect on ecosystem C, and thus improve prospects for adjusting management practices to optimize C sequestration.

western United States↗
USGS2016

Experimental whole-lake increase of dissolved organic carbon concentration produces unexpected increase in crustacean zooplankton density

The observed pattern of lake browning, or increased terrestrial dissolved organic carbon (DOC) concentration, across the northern hemisphere has amplified the importance of understanding how consumer productivity varies with DOC concentration. Results from comparative studies suggest these increased DOC concentrations may reduce crustacean zooplankton productivity due to reductions in resource quality and volume of suitable habitat. Although these spatial comparisons provide an expectation for the response of zooplankton productivity as DOC concentration increases, we still have an incomplete understanding of how zooplankton respond to temporal increases in DOC concentration within a single system. As such, we used a whole-lake manipulation, in which DOC concentration was increased from 8 to 11 mg L−1 in one basin of a manipulated lake, to test the hypothesis that crustacean zooplankton production should subsequently decrease. In contrast to the spatially derived expectation of sharp DOC-mediated decline, we observed a small increase in zooplankton densities in response to our experimental increase in DOC concentration of the treatment basin. This was due to significant increases in gross primary production and resource quality (lower seston carbon-to-phosphorus ratio; C:P). These results demonstrate that temporal changes in lake characteristics due to increased DOC may impact zooplankton in ways that differ from those observed in spatial surveys. We also identified significant interannual variability across our study region, which highlights potential difficulty in detecting temporal responses of organism abundances to gradual environmental change (e.g., browning).

Michigan↗
USGS2015

Geostatistical borehole image-based mapping of karst-carbonate aquifer pores

Quantification of the character and spatial distribution of porosity in carbonate aquifers is important as input into computer models used in the calculation of intrinsic permeability and for next-generation, high-resolution groundwater flow simulations. Digital, optical, borehole-wall image data from three closely spaced boreholes in the karst-carbonate Biscayne aquifer in southeastern Florida are used in geostatistical experiments to assess the capabilities of various methods to create realistic two-dimensional models of vuggy megaporosity and matrix-porosity distribution in the limestone that composes the aquifer. When the borehole image data alone were used as the model training image, multiple-point geostatistics failed to detect the known spatial autocorrelation of vuggy megaporosity and matrix porosity among the three boreholes, which were only 10 m apart. Variogram analysis and subsequent Gaussian simulation produced results that showed a realistic conceptualization of horizontal continuity of strata dominated by vuggy megaporosity and matrix porosity among the three boreholes.

Groundwater↗
USGS2009

On carbon sequestration in desert ecosystems

Recent reports of net ecosysytem production >100 g C m -2 yr -1 in deserts are incompatible with existing measurements of net primary production and carbon pools in deserts. The comparisions suggest that gas exchange measurements should be used with caution and better validation if they are expected to indicate the magnitude of carbon sink in these ecosysytems. ?? 2009 Blackwell Publishing.

Global Change Biology↗
USGS2012

Tropical forest carbon balance in a warmer world: a critical review spanning microbial- to ecosystem-scale processes

Tropical forests play a major role in regulating global carbon (C) fluxes and stocks, and even small changes to C cycling in this productive biome could dramatically affect atmospheric carbon dioxide (CO 2 ) concentrations. Temperature is expected to increase over all land surfaces in the future, yet we have a surprisingly poor understanding of how tropical forests will respond to this significant climatic change. Here we present a contemporary synthesis of the existing data and what they suggest about how tropical forests will respond to increasing temperatures. Our goals were to: (i) determine whether there is enough evidence to support the conclusion that increased temperature will affect tropical forest C balance; (ii) if there is sufficient evidence, determine what direction this effect will take; and, (iii) establish what steps should to be taken to resolve the uncertainties surrounding tropical forest responses to increasing temperatures. We approach these questions from a mass-balance perspective and therefore focus primarily on the effects of temperature on inputs and outputs of C, spanning microbial- to ecosystem-scale responses. We found that, while there is the strong potential for temperature to affect processes related to C cycling and storage in tropical forests, a notable lack of data combined with the physical, biological and chemical diversity of the forests themselves make it difficult to resolve this issue with certainty. We suggest a variety of experimental approaches that could help elucidate how tropical forests will respond to warming, including large-scale in situ manipulation experiments, longer term field experiments, the incorporation of a range of scales in the investigation of warming effects (both spatial and temporal), as well as the inclusion of a diversity of tropical forest sites. Finally, we highlight areas of tropical forest research where notably few data are available, including temperature effects on: nutrient cycling, heterotrophic versus autotrophic respiration, thermal acclimation versus substrate limitation of plant and microbial communities, below-ground C allocation, species composition (plant and microbial), and the hydraulic architecture of roots. Whether or not tropical forests will become a source or a sink of C in a warmer world remains highly uncertain. Given the importance of these ecosystems to the global C budget, resolving this uncertainty is a primary research priority.

Biological Reviews↗
USGS2010

The effect of resource quantity and resource stoichiometry on microbial carbon-use-efficiency

The carbon-use-efficiency (CUE) of microorganisms is an important parameter in determining ecosystem-level carbon (C) cycling; however, little is known about how variance in resources affects microbial CUE. To elucidate how resource quantity and resource stoichiometry affect microbial CUE, we cultured four microorganisms - two fungi (Aspergillus nidulans and Trichoderma harzianum) and two bacteria (Pectobacterium carotovorum and Verrucomicrobium spinosum) - under 12 unique C, nitrogen (N) and phosphorus (P) ratios. Whereas the CUE of A. nidulans was strongly affected by C, bacterial CUE was more strongly affected by mineral nutrients (N and P). Specifically, CUE in P. carotovorum was positively correlated with P, while CUE of V. spinosum primarily depended on N. This resulted in a positive relationship between fungal CUE and resource C : nutrient stoichiometry and a negative relationship between bacterial CUE and resource C : nutrient stoichiometry. The difference in the direction of the relationship between CUE and C : nutrient for fungi vs. bacteria was consistent with differences in biomass stoichiometry and suggested that fungi have a higher C demand than bacteria. These results suggest that the links between biomass stoichiometry, resource demand and CUE may provide a mechanism for commonly observed temporal and spatial patterns in microbial community structure and function in natural habitats.

FEMS Microbiology Ecology↗
USGS2007

Hydrologic significance of carbon monoxide concentrations in ground water

Dissolved carbon monoxide (CO) is present in ground water produced from a variety of aquifer systems at concentrations ranging from 0.2 to 20 nanomoles per liter (0.0056 to 0.56 μg/L). In two shallow aquifers, one an unconsolidated coastal plain aquifer in Kings Bay, Georgia, and the other a fractured‐bedrock aquifer in West Trenton, New Jersey, long‐term monitoring showed that CO concentrations varied over time by as much as a factor of 10. Field and laboratory evidence suggests that the delivery of dissolved oxygen to the soil zone and underlying aquifers by periodic recharge events stimulates oxic metabolism and produces transiently high CO concentrations. In between recharge events, the aquifers become anoxic and more substrate limited, CO is consumed as a carbon source, and CO concentrations decrease. According to this model, CO concentrations provide a transient record of oxic metabolism affecting ground water systems after dissolved oxygen has been fully consumed. Because the delivery of oxygen affects the fate and transport of natural and anthropogenic contaminants in ground water, CO concentration changes may be useful for identifying predominantly anoxic ground water systems subject to periodic oxic or microaerophilic conditions.

Ground Water↗
USGS2011

Dissolved oxygen as an indicator of bioavailable dissolved organic carbon in groundwater

Concentrations of dissolved oxygen (DO) plotted vs. dissolved organic carbon (DOC) in groundwater samples taken from a coastal plain aquifer of South Carolina (SC) showed a statistically significant hyperbolic relationship. In contrast, DO-DOC plots of groundwater samples taken from the eastern San Joaquin Valley of California (CA) showed a random scatter. It was hypothesized that differences in the bioavailability of naturally occurring DOC might contribute to these observations. This hypothesis was examined by comparing nine different biochemical indicators of DOC bioavailability in groundwater sampled from these two systems. Concentrations of DOC, total hydrolysable neutral sugars (THNS), total hydrolysable amino acids (THAA), mole% glycine of THAA, initial bacterial cell counts, bacterial growth rates, and carbon dioxide production/consumption were greater in SC samples relative to CA samples. In contrast, the mole% glucose of THNS and the aromaticity (SUVA 254 ) of DOC was greater in CA samples. Each of these indicator parameters were observed to change with depth in the SC system in a manner consistent with active biodegradation. These results are uniformly consistent with the hypothesis that the bioavailability of DOC is greater in SC relative to CA groundwater samples. This, in turn, suggests that the presence/absence of a hyperbolic DO-DOC relationship may be a qualitative indicator of relative DOC bioavailability in groundwater systems.

South Carolina↗
USGS2006

Investigating trophic relationships of pinnipeds in Alaska and Washington using stable isotope ratios of nitrogen and carbon

We measured stable-nitrogen (δ 15 N) and stable-carbon (δ 13 C) isotope ratios in muscle and hair from 7 northern fur seals ( Callorhinus ursinus ) from the Pribilof Islands, Alaska, and 27 Steller sea lions ( Eumetopias jubatus ), and 14 harbor seals ( Phoca vitulina ) from the Gulf of Alaska and coast of Washington State, in order to contrast dietary information derived from isotopic vs. available conventional dietary studies. Stable-nitrogen-isotope analysis of muscle revealed that harbor seals were enriched over sea lions (mean δ 15 N = 18.6‰ vs. 17.5‰) which were in turn enriched over northern fur seals (mean δ 15 N = 16.6‰). Trophic segregation among these species likely results primarily from differential reliance on herring ( Clupea harengus ), Atka mackerel ( Pleurogrammus monopterygius ), and large vs. small walleye pollock ( Theregra chalcogramma ). According to their δ 15 N values, adult male Steller sea lions showed a higher trophic position than adult females (mean δ 15 N: 18.0‰ vs. 17.2‰), whereas adult female northern fur seals were trophically higher than juvenile male fur seals (mean δ 15 N: 16.5‰ vs. 15.0‰). Each of these observed differences likely resulted from differential reliance on squid or differences in the size range of pollock consumed. Three northern fur seal pups showed higher δ 15 N enrichment over adults (mean 17.7‰ vs. 15.8‰) due to their reliance on their mother's milk. Stable-carbon isotope measurements of hair revealed a cline toward more negative values with latitude. Segregation in hair δ 13 C between Steller sea lions and harbor seals off the coast of Washington (mean δ 13 C: -13.6‰ vs. - 15.0‰) reflected the greater association of harbor seals with freshwater input from the Columbia River. Our study demonstrates the utility of the stable isotope approach to augment conventional dietary analyses of pinnipeds and other marine mammals.

Alaska, Washington↗
USGS2013

Evidence for microbial carbon and sulfur cycling in deeply buried ridge flank basalt

Sediment-covered basalt on the flanks of mid-ocean ridges constitutes most of Earth's oceanic crust, but the composition and metabolic function of its microbial ecosystem are largely unknown. By drilling into 3.5-million-year-old subseafloor basalt, we demonstrated the presence of methane- and sulfur-cycling microbes on the eastern flank of the Juan de Fuca Ridge. Depth horizons with functional genes indicative of methane-cycling and sulfate-reducing microorganisms are enriched in solid-phase sulfur and total organic carbon, host δ 13 C- and δ 34 S-isotopic values with a biological imprint, and show clear signs of microbial activity when incubated in the laboratory. Downcore changes in carbon and sulfur cycling show discrete geochemical intervals with chemoautotrophic δ 13 C signatures locally attenuated by heterotrophic metabolism.

Science↗
USGS1974

Water and carbon in rusty lunar rock 66095

Lunar rock 66095 contains a hydrated iron oxide and has an unusual amount of water for a lunar rock (140 to 750 parts per million), 90 percent of which is released below 690°C. The δof water released at these low temperatures varies from -75 to -140 per mil relative to standard mean ocean water (SMOW). The small amount of water released between 690° and 1300°C has a δ of about -175 ±25 per mil SMOW. These δ values are not unusual for terrestrial water. The δ 18 O of water extracted from 110° to 400°C has a value of +5± I per mil SMOW, similar to the value for lunar silicates from rock 66095 and different from the value of -4 to -22 per mil found for samples of terrestrial rust including samples of rusted meteoritic iron. The amount of carbon varies from 11 to 59 parts per million with a δ 13 C from -20 to -30 per mil relative to Pee Dee belemnite. Only very small amounts of reduced species (such as hydrogen, carbon monoxide, and methane) were found, in contrast to the analyses of other lunar rocks. Although it is possible that most of the water in the iron oxide (goethite) may be terrestrial in origin or may have exchanged with terrestrial water during sample return and handling, evidence presented herein suggests that this did not happen and that some lunar water may have a δD that is indistinguishable from that of terrestrial water.

Science↗
USGS1979

Carbon dioxide in the ocean surface: The homogeneous buffer factor

The amount of carbon dioxide that can be dissolved in surface seawater depends at least partially on the homogeneous buffer factor, which is a mathematical function of the chemical equilibrium conditions among the various dissolved inorganic species. Because these equilibria are well known, the homogeneous buffer factor is well known. Natural spatial variations depend very systematically on sea surface temperatures, and do not contribute significantly to uncertainties in the present or future carbon dioxide budget.

Science↗
USGS1979

Submarine seep of carbon dioxide in Norton Sound, Alaska

Earlier workers have described a submarine gas seep in Norton Sound having an unusual mixture of petroleum-like, low-molecular-weight hydrocarbons. Actually, only about 0.04 percent of the seeping gas is hydrocarbons and 98 percent is carbon dioxide. The isotopic compositions of carbon dioxide (δ 13 C PDB = –2.7 per mil) and methane (δ 13 C PDB = –36 per mil) where PDB is the Peedee belemnite standard) indicate that geothermal processes are active here.

Alaska↗
USGS1994

500,000-year stable carbon isotopic record from Devils Hole, Nevada

The record of carbon-13 (δ 13 C) variations in DH-11 vein calcite core from Devils Hole, Nevada, shows four prominent minima near glacial terminations (glacial-interglacial transitions) V to II. The δ 13 C time series is inversely correlated with the DH-11 oxygen isotope ratio time series and leads it by as much as 7000 years. The δ 13 C variations likely record fluctuations in the δ 13 C of dissolved inorganic carbon of water recharging the aquifer. How such variations are transported 80 kilometers to Devils Hole without obliteration by water-rock reaction remains an enigma. The record may reflect (i) global variations in the δ 13 C of atmospheric CO 2 and, hence, the δ 13 C of continental biomass or (ii) variations in extent and density of vegetation in the southern Great Basin. In the latter case, δ 13 C minima at 414, 334, 246, and 133 thousand years ago mark times of maximum vegetation.

Nevada↗