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824 Ergebnisse:

Depositional Environment of the Lower Cretaceous (Upper Albian) Winton Formation At Isisford, Central-West Queensland, Australia, Inferred From Sandstone Concretions
Journal of Sedimentary Research (2016)
Caitlin E. Syme, Kevin J. Welsh, Eric M. Roberts, Steven W. Salisbury

Numerous vertebrate and plant fossils have been found in ex-situ sandstone concretions near Isisford in central-west Queensland since the mid-1990s. These concretions are found in the Lower Cretaceous portion (upper Albian, 100.5–102.2 Ma) of the Winton Formation. The lower most Winton Formation is thought to have formed in a fluvial channel or flood-basin setting proximal to the Eromanga Sea, but due to the scarcity of good exposures, the local depositional environment at Isisford has not been ascertained. Minimal compression of vertebrate and plant fossils, a lack of grain suturing, predominantly cement-supported fabric, and fractures running through calcite cement, as well as fossil bone and framework grains, indicates that concretions formed during early diagenesis (pre-compactional or syndepositional). Calcite stable-isotope δ18OVPDB values range from −12.25 to −4‰, indicating mixed marine and meteoric pore waters, and δ13CVPDB values range from −5.3 to 4.1‰, indicative of both sulfate reduction and methanogenesis of organic material (including decaying vertebrate soft tissues) in the burial environment. The mixed marine and freshwater signature suggests a marginal marine setting, possibly deltaic or estuarine, connected to the regressive epicontinental Eromanga Seaway at around 102–100 Ma. This is not inconsistent with the lithology from nearby cores, coupled with Isisford fossil-vertebrate ecology (personal observation). Our research demonstrates the utility of investigating ex-situ concretions to refine paleoenvironments at localities where little or no outcrop is available and traditional facies analysis is impractical.
Schlagworte: carbon , oxygen , geol , mulitcarb

Diagenetic alteration affecting δ18O, δ13C and 87Sr/86Sr signatures of carbonates: A case study on Cretaceous seep deposit from Yarlung-Zangbo Suture Zone, Tibet, China
Chemical Geology (2016)
Hongpeng Tong, Qinxian Wang, Jörn Peckmann, Yuncheng Cao, Linying Chen, Weide Zhou, Duofu Chen

Seep carbonates provide excellent records of past seepage activities, and have been commonly considered to preserve primary, unaltered stable carbon isotope signatures. However, late diagenetic reactions may overprint original isotopic compositions, but the mode and effect of such alterations are poorly understood. In particular, there are significant uncertainties regarding how carbon and strontium isotopic compositions of seep carbonates respond to diagenesis. This study reports recently discovered Cretaceous hydrocarbon-seep deposits from the Yarlung-Zangbo Suture Zone, Tibet, China that have experienced substantial diagenetic alteration that is shown by recrystallization and secondary veins. Unitary linear recursive analysis was applied to δ13C values and 87Sr/86Sr ratios of the seep carbonates to evaluate the degree of secondary modification and to quantitatively constrain the compositions of primary carbonates and late diagenetic fluids. The δ18O values range from −11.8‰ to −2.2‰, δ13C values from −34.1‰ to −12.9‰ and 87Sr/86Sr ratios from 0.706221 to 0.706808. The heterogeneity in isotopic compositions and the observation that the most negative δ18O values occur in samples with the most extensive recrystallization indicate significant and spatially heterogeneous modification of isotope compositions during late diagenesis. The linear correlations between δ13C values and δ18O values for matrix micrites (R2=0.54), and between bulk carbonate 87Sr/86Sr ratios and δ18O values (R2=0.85) are best explained by burial diagenetic overprinting of oxygen, strontium, and even carbon isotopic compositions rather than by meteoric water hypergenesis. Extrapolated values of δ13C and ratios of 87Sr/86Sr against a δ18O value of −2‰ (average value of calcite precipitated in isotopic equilibrium with coeval Cretaceous seawater) that would characterize the primary carbonate, give an end member δ13C value of −34‰ and an end member 87Sr/86Sr ratio of 0.7072. The end member isotopic values obtained by this extrapolation suggest that the primary seep carbonates with low δ13C values and high 87Sr/86Sr ratios were formed by anaerobic oxidation of methane near the seafloor. In contrast, the measured δ18O values and 87Sr/86Sr ratios reflect late diagenetic fluids represented by burial pore water characterized by a low 87Sr/86Sr ratio and high temperature. Our findings reveal that δ13C values can only be moderately and 87Sr/86Sr ratios can be significantly altered during late diagenesis, and show that it is possible to quantitatively assess the primary composition of diagenetically altered seep carbonates.
Schlagworte: carbon , oxygen , geol , gashead

Ecosystem metabolism and greenhouse gas production in a mesotrophic northern temperate lake experiencing seasonal hypoxia
Biogeochemistry (2016)
Kateri R. Salk, Peggy H. Ostrom, Bopaiah A. Biddanda, Anthony D. Weinke, Scott T. Kendall, Nathaniel E. Ostrom

Many lacustrine systems, despite management efforts to control eutrophication, are hypoxic during stratified periods. Hypoxia is a major concern, not only for its impact on aquatic life but also for its potential to stimulate production of the greenhouse gases, methane (CH4) and nitrous oxide (N2O). We investigated the drivers of hypoxia in Muskegon Lake, a temperate dimictic freshwater estuary that experiences frequent hypolimnetic mixing due to atmospheric forces, riverine inputs, and intrusion of oxic water from coastal upwelling in Lake Michigan. Primary production and respiration (R) rates obtained from a δ18O mass balance model were similar to other mesotrophic environments (0.56–26.31 and 0.57–13.15 mmol O2 m−3 day−1, respectively), although high P/R (≥2 in mid-summer) indicated there is sufficient autochthonous production to support hypoxia development and persistence. The isotopic enrichment factor for respiration (εobs) varied markedly and was least negative in August of both sampling years, consistent with high R rates. Hypoxic conditions were associated with accumulation of N2O but not CH4, and emissions of N2O are among the highest reported from lakes. The average N2O site preference value of 25.4‰ indicates that the majority of N2O was produced by nitrification via hydroxylamine oxidation, despite the presence of resilient hypoxia. While it has been hypothesized that denitrification acts as a sink for N2O in hypoxic lakes, it is clear that Muskegon Lake functions as a strong source of N2O via nitrification. Further considerations of lakes as global sources of N2O thus warrant a closer evaluation of nitrification-fueled N2O production.
Schlagworte: nitrogen , oxygen , ecol , gashead

Organic geochemical evidence of postglacial paleoenvironmental evolution of the Comeya peatland (Asturias, N Spain)
International Journal of Coal Geology (2016)
Justyna Urbańczyk, A. Bechtel, Angeles G. Borrego

Comeya peatland is located in Picos de Europa National Park (N. Spain) at 851m above sea level, representing the continuous postglacial infill of a hollow (growth rate=0.4mm/yr) during the last 15,000cal.yrBP. Three intervals can be distinguished in the profile: the bottom one, with ash content close to 90%, which is previous to the peatland installation in the area and is followed by an interval with oscillating ash content (30–60%) probably related to alluvial fan sedimentation. The uppermost one corresponds to the peat deposit with ash content generally close to 10%. The present day vegetation consists of Sphagnum species with herbaceous plants and heathers. The study comprises the analysis of some biomarkers with potential as palaeoenvironmental proxies quantified by gas chromatography/mass spectrometry, supported by bulk δ13C and δ15N isotopic. The biomarker assemblage is dominated by the n-alkanes and methyl-ketones with medium-to-high molecular weight and odd number of carbons. The biomarker ratios indicate an enrichment in Sphagnum characteristic compounds at 120–250cm (3150–6350cal.yrBP) reflecting more humid conditions. This episode coincides with higher C/N atomic ratio, higher values of δ13C and lower of δ15N. The wetter conditions of this interval are also shown by the depleted δD values of the n-alkane, particularly those related with mosses as (n-C23 and n-C25) and the enriched δ13C values of both n-alkanes and methyl-ketones. Segregation of δ13C values has been observed for homologues series in Comeya peat with medium molecular weight n-alkanes typical of mosses living in waterlogged environments, being enriched in δ13C values compared with higher molecular weight n-alkanes typical of woody and herbaceous plants of drier habitats. This study has shown a slight enrichment of δ13C values of methyl-ketones compared to n-alkanes, the differences being not conclusive to support a common or different origin for both compound classes.
Schlagworte: carbon , nitrogen , geol , elem

Stable isotopic and elemental characteristics of recent tufa from a karstic Krka River (south‐east Slovenia): useful environmental proxies?
Sedimentology (2016)
Saša Zavadlav, Boštjan Rožič, Matej Dolenec, Sonja Lojen

Tufa samples from 16 consecutive barrages along a 13 km section of a groundwater-fed Krka River (Slovenia) were analysed for their petrographical, mineralogical, elemental and stable carbon (δ13C) and oxygen (δ18O) isotope composition, to establish their relation to current climatic and hydrological conditions. Waters constantly oversaturated with calcite and the steep morphology of the Krka riverbed stimulate rapid CO2 degassing and subsequent tufa precipitation. The carbon isotope fractionation (Δ13C) between DIC and tufa in the Krka River evolves toward isotopic equilibrium being controlled by continuous CO2 degassing and tufa precipitation rate downstream. The Δ13C increased from 1.9 to 2.5‰ (Vienna PeeDee Belemnite); however, since tufa precipitation rates remain similar downstream, the major controlling factor of carbon isotope exchange is most probably related to the continuous 12CO2 degassing downstream leaving the carbon pool enriched in 13C. In the case of oxygen, the isotope fractionation was found to be from 1.0 to 2.3‰ smaller than reported in the literature. The observed discrepancies are due to different precipitation rates of calcite deposits as Krka tufas on cascades grow relatively faster compared to slowly precipitated calcite deposits in cave or stream pools. Due to non-equilibrium oxygen isotope exchange between Krka tufa and water, the δ18O proxy showed from 1.2 to 8.2°C higher calculated water temperatures compared to measured water temperatures, demonstrating that δ18O proxy-based temperature equations are not reliable for water temperature calculations of fast growing tufa on cascades. Because Mg is bound to the terrigenous dolomite fraction in the Krka tufa samples, the Mg/Ca was also found to be an unreliable temperature proxy yielding over up to 20°C higher calculated water temperatures.
Schlagworte: carbon , oxygen , geol , gashead

Short-term and seasonal soil nitrogen dynamics and recovery by bermudagrass irrigated with 15N labelled swine lagoon effluent
Plant and Soil (2016)
Jiuquan Zhang, Jac J. Varco, Ardeshir Adeli

Aim Rapid and efficient utilization of swine (Sus scrofa domestucus) lagoon effluent nitrogen (N) by crops is necessary to minimize N losses and environmental pollution. The objective of this study was to determine the dynamics and fate of effluent N applied to bermudagrass (Cynodon dactylon (L.) pers.) using 15N tracer technology as influenced by irrigation date. Methods Anaerobic swine lagoon effluent was labeled with enriched (15NH4)2SO4 and applied to an acid silty clay soil. Microplots (1 × 1 m) were established for each irrigation event (main plots) and soil was sampled and bermudagrass was harvested on day 0, 1, 2, 3, 7, and 14 (subplots) following irrigation. Soil sampling coincided with harvests to monitor effluent derived 15N transformations. Results Application in July when bermudagrass growth was most active resulted in a plant 15N recovery of 59 %. Crop recoveries for June and September irrigation events were equal at 33 %. Nitrification of effluent NH4+-N occurred rapidly within 24 h to 48 h following application. Rapid losses of effluent 15N within 1 d suggest a high probability for NH3 volatilization, while losses following rainfall and high soil moisture content in June infer denitrification was most active. Lack of 15N detection in the 30 to 60 cm soil depth indicated a low probability of leaching losses, while unaccounted for 15N was 45, 5, and 30 % for irrigation events in June, July, and September, respectively. Conclusion Bermudagrass recovery, dynamics and fate of effluent N applied to an acid soil varied with environmental conditions affecting crop growth and N uptake and soil N transformations.
Schlagworte: nitrogen , soil , poll , elem

Using multi-isotopes (34S, 18O, 2H) to track local contamination of the groundwater from Hongshan-Zhaili abandoned coal mine, Zibo city, Shandong province
International Biodeterioration & Biodegradation (2016)
Jianwei Zhou, Qiuxia Zhang, Fengxin Kang, Yanpeng Zhang, Lei Yuan, Dong Wei, Shanghua Lin

The Hongshan-Zhaili coal mine was extensively mined for several decades, lies in Zibo city, Shandong province. After closed in 1994, the coal strata water level raised above the Ordovician limestone water level, then led to the cross strata pollution, which greatly affected the normal use of local people. The Ordovician limestone aquifer is the important drinking water aquifer for local community which covered under the coal strata. Thirty-two domestic water wells near the former coal mine were sampled for water chemistry and stable-isotope analysis of water and dissolved SO42−. Groundwater plots close to the Global Meteoric Water Line and reveals evidence of recharging from atmospheric precipitation. The analysis of sensitive components NO3−, SO42−, 34S in groundwater shows an oxidation environment, promoting the pyrite oxidation. The result of 34S isotopes indicates that the Ordovician limestone water SO42− mainly derived from the atmospheric precipitation SO42−, and the contamination of the Ordovician limestone water from coal strata water has occurred locally in the study area, the Ordovician limestone water is enriched in SO42− and depleted 34S in sulfate.
Schlagworte: hydrogen , oxygen , sulfur , poll , elem

Short-term contributions of cover crop surface residue return to soil carbon and nitrogen contents in temperate Australia
Environmental Science and Pollution Research (2016)
Xiaoqi Zhou, Hanwen Wu, Guangdi Li, Chengrong Chen

Cover crop species are usually grown to control weeds. After cover crop harvest, crop residue is applied on the ground to improve soil fertility and crop productivity. Little information is available about quantifying the contributions of cover crop application to soil total carbon (C) and nitrogen (N) contents in temperate Australia. Here, we selected eight cover crop treatments, including two legume crops (vetch and field pea), four non-legume crops (rye, wheat, Saia oat, and Indian mustard), a mixture of rye and vetch, and a nil-crop control in temperate Australia to calculate the contributions of cover crops (crop growth + residue decomposition) to soil C and N contents. Cover crops were sown in May 2009 (autumn). After harvest, the crop residue was placed on the soil surface in October 2009. Soil and crop samples were collected in October 2009 after harvest and in May 2010 after 8 months of residue decomposition. We examined cover crop residue biomass, soil and crop total C and N contents, and soil microbial biomass C and N contents. The results showed that cover crop application increased the mean soil total C by 187–253 kg ha−1 and the mean soil total N by 16.3–19.1 kg ha−1 relative to the nil-crop treatment, except for the mixture treatment, which had similar total C and N contents to the nil-crop control. Cover crop application increased the mean soil microbial biomass C by 15.5–20.9 kg ha−1 and the mean soil microbial biomass N by 4.5–10.2 kg ha−1. We calculated the apparent percentage of soil total C derived from cover crop residue C losses and found that legume crops accounted for 10.6–13.9 %, whereas non-legume crops accounted for 16.4–18.4 % except for the mixture treatment (0.2 %). Overall, short-term cover crop application increased soil total C and N contents and microbial biomass C and N contents, which might help reduce N fertilizer use and improve sustainable agricultural development.
Schlagworte: carbon , nitrogen , soil , elem

Using hydrogen isotopes of freshwater fish tissue as a tracer of provenance
Ecology and Evolution (2016)
David X. Soto, Keith A. Hobson, Leonard I. Wassenaar

Hydrogen isotope (δ2H) measurements of consumer tissues in aquatic food webs are useful tracers of diet and provenance and may be combined with δ13C and δ15N analyses to evaluate complex trophic relationships in aquatic systems. However, δ2H measurements of organic tissues are complicated by analytical issues (e.g., H exchangeability, lack of matrix-equivalent calibration standards, and lipid effects) and physiological mechanisms, such as H isotopic exchange with ambient water during protein synthesis and the influence of metabolic water. In this study, δ2H (and δ15N) values were obtained from fish muscle samples from Lake Winnipeg, Canada, 2007–2010, and were assessed for the effects of species, feeding habits, and ambient water δ2H values. After lipid removal, we used comparative equilibration to calibrate muscle δ2H values to nonexchangeable δ2H equivalents and controlled for H isotopic exchange between sample and laboratory ambient water vapor. We then examined the data for evidence of trophic δ2H enrichment by comparing δ2H values with δ15N values. Our results showed a significant logarithmic correlation between fork length and δ2H values, and no strong relationships between δ15N and δ2H. This suggests the so-called apparent trophic compounding effect and the influence of metabolic water into tissue H were the potential mechanisms for δ2H enrichment. We evaluated the importance of water in controlling δ2H values of fish tissues and, consequently, the potential of H isotopes as a tracer of provenance by taking account of confounding variables such as body size and trophic effects. The δ2H values of fish appear to be a good tracer for tracking provenance, and we present a protocol for the use of H isotopes in aquatic ecosystems, which should be applicable to a broad range of marine and freshwater fish species. We advise assessing size effects or working with fish of relatively similar mass when inferring fish movements using δ2H measurements.
Schlagworte: hydrogen , ecol , elem

Adaptation to a high protein diet progressively increases the postprandial accumulation of carbon skeletons from dietary amino acids in rats
American Journal of Physiology - Regulatory, Integrative and Comparative Physiology (2016)
Magdalena Stepien, Dalila Azzout-Marniche, Patrick C Even, Nadezda Khodorova, Gilles Fromentin, Daniel Tomé, Claire Gaudichon

We aimed to determine whether oxidative pathways adapt to the overproduction of carbon skeletons resulting from the progressive activation of amino acid (AA) deamination and ureogenesis under a high protein (HP) diet. Ninety-four male Wistar rats, of which 54 were implanted with a permanent jugular catheter, were fed a normal protein diet for one week and were then switched to an HP diet for 1, 3, 6 or 14 days. On the experimental day, they were given their meal containing a mixture of 20 U-[15N]-[13C] AA, whose metabolic fate was followed for 4 h. Gastric emptying tended to be slower during the first 3 days of adaptation. 15N excretion in urine increased progressively during the first 6 days, reaching 29% of ingested protein. 13CO2 excretion was maximal as early as the first day, and represented only 16% of the ingested proteins. Consequently, the amount of carbon skeletons remaining in the metabolic pools 4 h after the meal ingestion progressively increased to 42% of the deaminated dietary AA after 6 days of HP diet. In contrast, 13C enrichment of plasma glucose tended to increase from 1 to 14 days of the HP diet. We conclude that there is no oxidative adaptation in the early postprandial period to an excess of carbon skeletons resulting from AA deamination in HP diets. This leads to an increase in the postprandial accumulation of carbon skeletons throughout the adaptation to an HP diet, which can contribute to the sustainable satiating effect of this diet.