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At least 487 records · Page 27Linked to original sources

USGS2002

Effect of dissolved organic carbon quality on microbial decomposition and nitrification rates in stream sediments

1. Microbial decomposition of dissolved organic carbon (DOC) contributes to overall stream metabolism and can influence many processes in the nitrogen cycle, including nitrification. Little is known, however, about the relative decomposition rates of different DOC sources and their subsequent effect on nitrification. 2. In this study, labile fraction and overall microbial decomposition of DOC were measured for leaf leachates from 18 temperate forest tree species. Between 61 and 82% (mean, 75%) of the DOC was metabolized in 24 days. Significant differences among leachates were found for labile fraction rates (P < 0.0001) but not for overall rates (P = 0.088). 3. Nitrification rates in stream sediments were determined after addition of 10 mg C L-1 of each leachate. Nitrification rates ranged from below detection to 0.49 ??g N mL sediment-1 day-1 and were significantly correlated with two independent measures of leachate DOC quality, overall microbial decomposition rate (r = -0.594, P = 0.0093) and specific ultraviolet absorbance (r = 0.469, P = 0.0497). Both correlations suggest that nitrification rates were lower in the presence of higher quality carbon. 4. Nitrification rates in sediments also were measured after additions of four leachates and glucose at three carbon concentrations (10, 30, and 50 mg C L-1). For all carbon sources, nitrification rates decreased as carbon concentration increased. Glucose and white pine leachate most strongly depressed nitrification. Glucose likely increased the metabolism of heterotrophic bacteria, which then out-competed nitrifying bacteria for NH4+. White pine leachate probably increased heterotrophic metabolism and directly inhibited nitrification by allelopathy.

Freshwater Biology↗

USGS1999

Characterization of fly ash from low-sulfur and high-sulfur coal sources: Partitioning of carbon and trace elements with particle size

Fly ash samples were collected in November and December of 1994, from generating units at a Kentucky power station using high- and low-sulfur feed coals. The samples are part of a two-year study of the coal and coal combustion byproducts from the power station. The ashes were wet screened at 100, 200, 325, and 500 mesh (150, 75, 42, and 25 mu m, respectively). The size fractions were then dried, weighed, split for petrographic and chemical analysis, and analyzed for ash yield and carbon content. The low-sulfur ''heavy side'' and ''light side'' ashes each have a similar size distribution in the November samples. In contrast, the December fly ashes showed the trend observed in later months, the light-side ash being finer (over 20 % more ash in the 500 mesh [25 mu m] fraction) than the heavy-side ash. Carbon tended to be concentrated in the coarse fractions in the December samples. The dominance of the 325 mesh (42 mum) fractions in the overall size analysis implies, though, that carbon in the fine sizes may be an important consideration in the utilization of the fly ash. Element partitioning follows several patterns. Volatile elements, such as Zn and As, are enriched in the finer sizes, particularly in fly ashes collected at cooler, light-side electrostatic precipitator (ESP) temperatures. The latter trend is a function of precipitation at the cooler-ESP temperatures and of increasing concentration with the increased surface area of the finest fraction. Mercury concentrations are higher in high-carbon fly ashes, suggesting Hg adsorption on the fly ash carbon. Ni and Cr are associated, in part, with the spinel minerals in the fly ash.

Energy Sources↗

USGS2004

Flood-related, organic-carbon anomalies as possible temporal markers in reservoir bottom sediments

Results of a study of sediment cores from four reservoirs in the upper Mississippi River Basin, USA, indicated that anomalous organic carbon concentrations associated with flood deposits may provide detectable temporal markers in reservoir bottom sediments. Temporal markers are needed for reservoir sediment studies to date sediment layers deposited between the 1963–64 cesium-137 peak and the present. For two of four reservoirs studied, anomalously low organic carbon concentrations were measured for a sample interval in the upper part of a sediment core. The anomalous interval was interpreted to have been deposited during the July 1993 flood that affected a large area of the upper Mississippi River Basin. Potentially, the July 1993 flood deposit may be used as a temporal marker in reservoir bottom sediments in parts of the basin affected by the flood. Several uncertainties remain regarding the viability of organic carbon as a temporal marker including the combination of flood, basin, and reservoir characteristics required to produce a recognizable organic carbon marker in the bottom sediment and the optimal sampling strategy needed to detect the marker in a sediment core. It is proposed that flood duration and basin size may be important factors as to whether or not an anomalous and detectable organic carbon layer is deposited in a reservoir.

Iowa, Kansas↗

USGS2013

Land use and carbon dynamics in the southeastern United States from 1992 to 2050

Land use and land cover change (LUCC) plays an important role in determining the spatial distribution, magnitude, and temporal change of terrestrial carbon sources and sinks. However, the impacts of LUCC are not well understood and quantified over large areas. The goal of this study was to quantify the spatial and temporal patterns of carbon dynamics in various terrestrial ecosystems in the southeastern United States from 1992 to 2050 using a process-based modeling system and then to investigate the impacts of LUCC. Spatial LUCC information was reconstructed and projected using the FOREcasting SCEnarios of future land cover (FORE-SCE) model according to information derived from Landsat observations and other sources. Results indicated that urban expansion (from 3.7% in 1992 to 9.2% in 2050) was expected to be the primary driver for other land cover changes in the region, leading to various declines in forest, cropland, and hay/pasture. The region was projected to be a carbon sink of 60.4 gC m −2 yr −1 on average during the study period, primarily due to the legacy impacts of large-scale conversion of cropland to forest that happened since the 1950s. Nevertheless, the regional carbon sequestration rate was expected to decline because of the slowing down of carbon accumulation in aging forests and the decline of forest area.

Environmental Research Letters↗

USGS2021

Carbon and ecohydrological priorities in managing woody encroachment: UAV perspective 63 years after a control treatment

Woody encroachment, including both woody species expansion and density increase, is a globally observed phenomenon that deteriorates arid and semi-arid rangeland health, biodiversity, and ecosystem services. Mechanical and chemical control treatments are commonly performed to reduce woody cover and restore ecohydrologic function. While the immediate impacts of woody control treatments are well documented in short-term studies, treatment impacts at decadal scales are not commonly studied. Using a controlled herbicide treatment from 1954 in the Sierra Ancha Experimental Forest in central Arizona, USA, we quantify woody encroachment and associated aboveground carbon accumulation in treated and untreated watersheds. Woody encroachment and aboveground carbon are estimated using high resolution multispectral images and photogrammetric data from a fixed-wing unmanned aerial vehicle (UAV). We then combine the contemporary UAV image-derived estimates with historical records from immediately before and after the treatment to consider long-term trends in woody vegetation cover, aboveground carbon, water yield, and sedimentation. Our results indicate that the treatment has had a lasting impact. More than six decades later, woody cover in two treated watersheds are still significantly lower compared to two control watersheds, even though woody cover increased in all four drainages. Aboveground woody carbon in the treated watersheds is approximately one half that accumulated in the control watersheds. The historical records indicate that herbicide treatment also increased water yield and reduced annual sedimentation. Given the sustained reduction in woody cover and aboveground woody biomass in treated watersheds, we infer that the herbicide treatment has had similarly long lasting impacts on ecohydrological function. Land managers can consider legacy impacts from control treatments to better balance carbon and ecohydrological consequences of woody encroachment and treatment activities.

Environmental Research Letters↗

USGS2007

An innovative carbonate coprecipitation process for the removal of zinc and manganese from mining impacted waters

Although mine drainage is usually thought of as acidic, there are many cases where the water is of neutral pH, but still contains metal species that can be harmful to human or aquatic animal health, such as manganese (Mn) and zinc (Zn). Typical treatment of mine drainage waters involves pH adjustment, but this often results in excessive sludge formation and removal of nontoxic species such as magnesium and calcium. Theoretical consideration of the stability of metal carbonate species suggests that the target metals could be removed from solution by coprecipitation with calcium carbonate. The U.S. Geological Survey has developed a limestone-based process for remediation of acid mine drainage that increases calcium carbonate saturation. This treatment could then be coupled with carbonate coprecipitation as an innovative method for removal of toxic metals from circumneutral mine drainage waters. The new process was termed the carbonate coprecipitation (CCP) process. The CCP process was tested at the laboratory scale using a synthetic mine water containing 50 mg/L each of Mn and Zn. Best results showed over 95% removal of both Mn and Zn in less than 2 h of contact in a limestone channel. The process was then tested on a sample of water from the Palmerton zinc superfund site, near Palmerton, Pennsylvania, containing over 300 mg/L Zn and 60 mg/L Mn. Treatment of this water resulted in removal of over 95% of the Zn and 40% of the Mn in the limestone channel configuration. Because of the potential economic advantages of the CCP process, further research is recommended for refinement of the process for the Palmerton water and for application to other mining impacted waters as well. ?? Mary Ann Liebert, Inc.

Environmental Engineering Science↗

USGS2015

Linking carbon and water limitations to drought-induced mortality of Pinus flexilis seedlings

Survival of tree seedlings at high elevations has been shown to be limited by thermal constraints on carbon balance, but it is unknown if carbon relations also limit seedling survival at lower elevations, where water relations may be more important. We measured and modeled carbon fluxes and water relations in first-year Pinus flexilis seedlings in garden plots just beyond the warm edge of their natural range, and compared these with dry-mass gain and survival across two summers. We hypothesized that mortality in these seedlings would be associated with declines in water relations, more so than with carbon-balance limitations. Rather than gradual declines in survivorship across growing seasons, we observed sharp, large-scale mortality episodes that occurred once volumetric soil-moisture content dropped below 10%. By this point, seedling water potentials had decreased below −5 MPa, seedling hydraulic conductivity had decreased by 90% and seedling hydraulic resistance had increased by >900%. Additionally, non-structural carbohydrates accumulated in aboveground tissues at the end of both summers, suggesting impairments in phloem-transport from needles to roots. This resulted in low carbohydrate concentrations in roots, which likely impaired root growth and water uptake at the time of critically low soil moisture. While photosynthesis and respiration on a leaf area basis remained high until critical hydraulic thresholds were exceeded, modeled seedling gross primary productivity declined steadily throughout the summers. At the time of mortality, modeled productivity was insufficient to support seedling biomass-gain rates, metabolism and secondary costs. Thus the large-scale mortality events that we observed near the end of each summer were most directly linked with acute, episodic declines in plant hydraulic function that were linked with important changes in whole-seedling carbon relations.

Tree Physiology↗

USGS2025

Biocrust mosses and cyanobacteria exhibit distinct carbon uptake responses to variations in precipitation amount and frequency

Dryland organisms exhibit varied responses to changes in precipitation, including event size, frequency, and soil moisture duration, influencing carbon uptake and reserve management strategies. This principle, central to the pulse-reserve paradigm, has not been thoroughly evaluated in biological soil crusts (biocrusts), essential primary producers on dryland surfaces. We conducted two experiments to investigate carbon uptake in biocrusts under different precipitation regimes. In the first, we applied a gradient of watering amounts to biocrusts dominated by moss or cyanobacteria, hypothesising distinct pulse-response strategies. The second experiment extended watering treatments over three months, varying pulse size and frequency. Our results revealed distinct carbon uptake patterns: moss crusts exhibited increased CO2 uptake with larger, less frequent watering events, whereas cyanobacteria crusts maintained similar carbon uptake across all event sizes. These findings suggest divergent pulse-response strategies across biocrust types, with implications for modelling dryland carbon dynamics and informing land management under changing precipitation regimes.

Utah↗

USGS2014

Scale criticality in estimating ecosystem carbon dynamics

Scaling is central to ecology and Earth system sciences. However, the importance of scale (i.e. resolution and extent) for understanding carbon dynamics across scales is poorly understood and quantified. We simulated carbon dynamics under a wide range of combinations of resolution (nine spatial resolutions of 250 m, 500 m, 1 km, 2 km, 5 km, 10 km, 20 km, 50 km, and 100 km) and extent (57 geospatial extents ranging from 108 to 1 247 034 km 2 ) in the southeastern United States to explore the existence of scale dependence of the simulated regional carbon balance. Results clearly show the existence of a critical threshold resolution for estimating carbon sequestration within a given extent and an error limit. Furthermore, an invariant power law scaling relationship was found between the critical resolution and the spatial extent as the critical resolution is proportional to A n ( n is a constant, and A is the extent). Scale criticality and the power law relationship might be driven by the power law probability distributions of land surface and ecological quantities including disturbances at landscape to regional scales. The current overwhelming practices without considering scale criticality might have largely contributed to difficulties in balancing carbon budgets at regional and global scales.

Global Change Biology↗

USGS2006

Commissioned Review. Carbon: freshwater plants

δ13C values for freshwater aquatic plant matter varies from −11 to −50‰ and is not a clear indicator of photosynthetic pathway as in terrestrial plants. Several factors affect δ13C of aquatic plant matter. These include: (1) The δ13C signature of the source carbon has been observed to range from +1‰ for HCO3− derived from limestone to −30‰ for CO2 derived from respiration. (2) Some plants assimilate HCO3−, which is –7 to –11‰ less negative than CO2. (3) C3, C4, and CAM photosynthetic pathways are present in aquatic plants. (4) Diffusional resistances are orders of magnitude greater in the aquatic environment than in the aerial environment. The greater viscosity of water acts to reduce mixing of the carbon pool in the boundary layer with that of the bulk solution. In effect, many aquatic plants draw from a finite carbon pool, and as in terrestrial plants growing in a closed system, biochemical discrimination is reduced. In standing water, this factor results in most aquatic plants having a δ13C value similar to the source carbon. Using Farquhar's equation and other physiological data, it is possible to use δ13C values to evaluate various parameters affecting photosynthesis, such as limitations imposed by CO2 diffusion and carbon source.

Plant, Cell & Environment↗

USGS2002

Environmental variation, vegetation distribution, carbon dynamics and water/energy exchange at high latitudes

The responses of high latitude ecosystems to global change involve complex interactions among environmental variables, vegetation distribution, carbon dynamics, and water and energy exchange. These responses may have important consequences for the earth system. In this study, we evaluated how vegetation distribution, carbon stocks and turnover, and water and energy exchange are related to environmental variation spanned by the network of the IGBP high latitude transects. While the most notable feature of the high latitude transects is that they generally span temperature gradients from southern to northern latitudes, there are substantial differences in temperature among the transects. Also, along each transect temperature co-varies with precipitation and photosynthetically active radiation, which are also variable among the transects. Both climate and disturbance interact to influence latitudinal patterns of vegetation and soil carbon storage among the transects, and vegetation distribution appears to interact with climate to determine exchanges of heat and moisture in high latitudes. Despite limitations imposed by the data we assembled, the analyses in this study have taken an important step toward clarifying the complexity of interactions among environmental variables, vegetation distribution, carbon stocks and turnover, and water and energy exchange in high latitude regions. This study reveals the need to conduct coordinated global change studies in high latitudes to further elucidate how interactions among climate, disturbance, and vegetation distribution influence carbon dynamics and water and energy exchange in high latitudes.

Journal of Vegetation Science↗

USGS2009

Biochemical indicators for the bioavailability of organic carbon in ground water

The bioavailability of total organic carbon (TOC) was examined in ground water from two hydrologically distinct aquifers using biochemical indicators widely employed in chemical oceanography. Concentrations of total hydrolyzable neutral sugars (THNS), total hydrolyzable amino acids (THAA), and carbon‐normalized percentages of TOC present as THNS and THAA (referred to as “yields”) were assessed as indicators of bioavailability. A shallow coastal plain aquifer in Kings Bay, Georgia, was characterized by relatively high concentrations (425 to 1492 μM; 5.1 to 17.9 mg/L) of TOC but relatively low THNS and THAA yields (∼0.2%–1.0%). These low yields are consistent with the highly biodegraded nature of TOC mobilized from relatively ancient (Pleistocene) sediments overlying the aquifer. In contrast, a shallow fractured rock aquifer in West Trenton, New Jersey, exhibited lower TOC concentrations (47 to 325 μM; 0.6 to 3.9 mg/L) but higher THNS and THAA yields (∼1% to 4%). These higher yields were consistent with the younger, and thus more bioavailable, TOC being mobilized from modern soils overlying the aquifer. Consistent with these apparent differences in TOC bioavailability, no significant correlation between TOC and dissolved inorganic carbon (DIC), a product of organic carbon mineralization, was observed at Kings Bay, whereas a strong correlation was observed at West Trenton. In contrast to TOC, THNS and THAA concentrations were observed to correlate with DIC at the Kings Bay site. These observations suggest that biochemical indicators such as THNS and THAA may provide information concerning the bioavailability of organic carbon present in ground water that is not available from TOC measurements alone.

Ground Water↗

USGS2022

Surface ocean warming and acidification driven by rapid carbon release precedes Paleocene-Eocene Thermal Maximum

The Paleocene-Eocene Thermal Maximum (PETM) is recognized by a major negative carbon isotope (δ 13 C) excursion (CIE) signifying an injection of isotopically light carbon into exogenic reservoirs, the mass, source, and tempo of which continue to be debated. Evidence of a transient precursor carbon release(s) has been identified in a few localities, although it remains equivocal whether there is a global signal. Here, we present foraminiferal δ 13 C records from a marine continental margin section, which reveal a 1.0 to 1.5‰ negative pre-onset excursion (POE), and concomitant rise in sea surface temperature of at least 2°C and a decline in ocean pH. The recovery of both δ 13 C and pH before the CIE onset and apparent absence of a POE in deep-sea records suggests a rapid (< ocean mixing time scales) carbon release, followed by recovery driven by deep-sea mixing. Carbon released during the POE is therefore likely more similar to ongoing anthropogenic emissions in mass and rate than the main CIE.

Science Advances↗

USGS1989

Uranium-series dated authigenic carbonates and Acheulian sites in southern Egypt

Field investigations in southern Egypt have yielded Acheulian artifacts in situ in authigenic carbonate deposits (CaCO 3 -cemented alluvium) along the edges of now-aggraded paleovalleys (Wadi Arid and Wadi Safsaf). Uranium-series dating of 25 carbonate samples from various localities as far apart as 70 kilometers indicates that widespread carbonate deposition occurred about 45, 141 and 212 ka (thousand years ago). Most of the carbonate appears to have been precipitated from groundwater, which suggests that these three episodes of deposition may be related to late Pleistocene humid climates that facilitated human settlement in this now hyperarid region. Carbonate cements from sediments containing Acheulian artifacts provide a minimum age of 212 ka for early occupation of the paleovalleys.

southern Egypt↗

USGS1992

Dynamics of soil carbon during deglaciation of the Laurentide Ice Sheet

Deglaciation of the Laurentide Ice Sheet in North America was accompanied by sequestration of organic carbon in newly exposed soils. The greatest rate of land exposure occurred around 12,000 to 8,000 years ago, and the greatest increase in the rate of carbon sequestration by soils occurred from 8,000 to 4,000 years ago. Sequestration of carbon in deglaciated peat lands continues today, and a steady state has not been reached. The natural rate of carbon sequestration in soils, however, is small relative to the rate of anthropogenic carbon dioxide production.

Science↗

USGS1985

Carbonate concretions: an ideal sedimentary host for microfossils

Microfossils extracted from carbonate concretions tend to be better preserved, more abundant and diverse, and more likely to retain delicate and fragile structures than those extracted from the surrounding rocks. Enhanced preservation correlates with early diagenetic concretion formation at or near the sediment-water interface and with higher carbonate, organic material, and metallic cation content than in surrounding rocks. Early diagenetic growth is inferred by diverging sedimentary laminations and small-scale sedimentary structures in fossiliferous carbonate concretions. High initial concentrations of microorganisms or fecal pellets may commonly be responsible for incipient carbonate-concretion growth. Excellent preservation is demonstrated by radiolarians and palynomorphs extracted from a carbonate concretion from the Middle Jurassic Shelikof Formation, southern Alaska.

Geology↗

USGS2026

Evidence for organic and igneous carbon sources in the Mesoproterozoic Adirondack Highlands graphite district, New York

This study examined the origin of graphite mineralization in the Mesoproterozoic Adirondack Highlands. Flake graphite was mined from the historic mining district around Ticonderoga, New York, USA, from the 1850s to the 1920s. Most of the production and reserves from the district are disseminated graphite from feldspathic quartz schists (e.g., Dixon-American Graphite Co. mine, Faxon property, Flake Graphite Company). Protolith sediments of the schists were deposited in the Trans-Adirondack backarc basin at ca. 1.25 Ga and were metamorphosed to high grade at 1.18–1.15 Ga during the accretionary Shawinigan orogeny and at 1.09–1.02 Ga during the Ottawan phase of the Grenvillian orogeny. Major elements and carbon isotopes of graphite from schists (δ 13 C = −28.1‰ to −5.4‰ relative to Vienna Peedee belemnite) are consistent with derivation from organic carbon in protolith sandstones that devolatilized during metamorphism. Some small mines and prospects in the district mined graphitic calcite marbles and clinopyroxene ± scapolite skarns associated with a pegmatite suite dated by U-Pb in zircon to 1.04–1.01 Ga (e.g., Lead Hill and Crown Point deposits), and rare graphite veins are observed at several deposits. Hydrothermal flake graphite from pegmatites, skarns, and veins are distinct from graphite in schist-hosted deposits and have δ 13 C values that cluster around −7‰ to −5‰, consistent with deposition from igneous CO 2 . Covariation of carbon and oxygen stable isotopes and U-Pb zircon geochronology are not compatible with precipitation from fluids derived from country rock metapelites or marbles. Some graphite districts elsewhere show compelling evidence for remobilization and redeposition of sedimentary-derived carbon as hydrothermal graphite, sometimes as thick veins producing world-class, high-grade deposits. In the Adirondacks, there is evidence for two generations of graphite mineralization with distinct carbon sources: syngenetic graphite with an organic origin in Shawinigan quartz schists and epigenetic graphite with an igneous origin in Ottawan skarns and pegmatites.

New York↗

USGS2009

A lacustrine carbonate record of Holocene seasonality and climate

Annually laminated (varved) Holocene sediments from Derby Lake, Michigan, display variations in endogenic calcite abundance reflecting a long-term (millennial-scale) decrease in burial punctuated with frequent short-term (decadal-scale) oscillations due to carbonate dissolution. Since 6000 cal yr B.P., sediment carbonate abundance has followed a decreasing trend while organic-carbon abundance has increased. The correlation between organic-carbon abundance and the sum of March-April-October-November insolation has an r 2 value of 0.58. We interpret these trends to represent a precession-driven lengthening of the Holocene growing season that has reduced calcite burial by enhancing net annual organic-matter production and associated calcite dissolution. Correlations with regional paleoclimate records suggest that changes in temperature and moisture balance have impacted the distribution of short-term oscillations in carbonate and organic-matter abundance superimposed on the precession-driven trends.

Michigan↗