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824 Ergebnisse:

Pan-Arctic concentrations of mercury and stable isotope ratios of carbon (δ(13)C) and nitrogen (δ(15)N) in marine zooplankton.
The Science of the total environment (2016)
Corinne Pomerleau, Gary A Stern, Monika Pućko, Karen L Foster, Robie W Macdonald, Louis Fortier

Zooplankton play a central role in marine food webs, dictating the quantity and quality of energy available to upper trophic levels. They act as "keystone" species in transfer of mercury (Hg) up through the marine food chain. Here, we present the first Pan-Arctic overview of total and monomethylmercury concentrations (THg and MMHg) and stable isotope ratios of carbon (δ(13)C) and nitrogen (δ(15)N) in selected zooplankton species by assembling data collected between 1998 and 2012 from six arctic regions (Laptev Sea, Chukchi Sea, southeastern Beaufort Sea, Canadian Arctic Archipelago, Hudson Bay and northern Baffin Bay). MMHg concentrations in Calanus spp., Themisto spp. and Paraeuchaeta spp. were found to increase with higher δ(15)N and lower δ(13)C. The southern Beaufort Sea exhibited both the highest THg and MMHg concentrations. Biomagnification of MMHg between Calanus spp. and two of its known predators, Themisto spp. and Paraeuchaeta spp., was greatest in the southern Beaufort Sea. Our results show large geographical variations in Hg concentrations and isotopic signatures for individual species related to regional ecosystem features, such as varying water masses and freshwater inputs, and highlight the increased exposure to Hg in the marine food chain of the southern Beaufort Sea.

Apical dominance ratio as an indicator of the growth conditions favouring Abies alba natural regeneration under Mediterranean environment
European Journal of Forest Research (2016)
Francesco Ripullone, Tiziana Gentilesca, Marco Lauteri, Angelo Rita, Anna Rita Rivelli, Aldo Schettino, Marco Borghetti

As reported in several studies, the presence of Abies alba Mill (silver fir) has been declining throughout its natural range over a large part of mountainous belt in the Mediterranean area. In such a context, regeneration establishment depends mainly on the occurrence of a suitable combination of water and light availability. Thus, before planning any forest management practice, it is essential to investigate on the optimal microclimate conditions influencing the success of natural regeneration of silver fir. To this aim, changes in growth and photosynthesis together with C, N and O isotope compositions have been investigated on silver fir naturally recruited saplings, growing in mixed stands with Fagus sylvatica on Apennine mountains (southern Italy). The apical dominance ratio (ADR, ratio between apical shoot length and length of first whorl lateral twigs) has been used as an indicator for microclimate conditions in which saplings grow. Based on the range of ADR values (i.e. from 0.10 to 1.30), saplings were distributed in four classes. As expected, increases in height, root collar diameter and radial growth correspond to enhancing ADR values, gaining the optimal conditions in class IV. This latter also displayed the best performance in terms of maximum CO2 assimilation at saturating light (A max) and water-use efficiency as assessed by carbon isotope discrimination analysis. Conversely, class I and II seem to display the highest performance in terms of CO2 respiration rate (R d) and absolute water loss saving as assessed by the application of oxygen isotopes. We conclude that, in relatively mild Mediterranean areas, forest managers should promote silvicultural treatments favouring light conditions and migration of saplings towards class IV of ADR. This class represents the optimal microclimate for regeneration establishment of silver fir.
Schlagworte: C , N , O , soi , EA

Latitudinal variation in ecological opportunity and intraspecific competition indicates differences in niche variability and diet specialization of Arctic marine predators
Ecology and Evolution (2016)
David J. Yurkowski, Steve Ferguson, Emily S. Choy, Lisa L. Loseto, Tanya M. Brown, Derek C. G. Muir, Christina A. D. Semeniuk, Aaron T. Fisk

Individual specialization (IS), where individuals within populations irrespective of age, sex, and body size are either specialized or generalized in terms of resource use, has implications on ecological niches and food web structure. Niche size and degree of IS of near-top trophic-level marine predators have been little studied in polar regions or with latitude. We quantified the large-scale latitudinal variation of population- and individual-level niche size and IS in ringed seals (Pusa hispida) and beluga whales (Delphinapterus leucas) using stable carbon and nitrogen isotope analysis on 379 paired ringed seal liver and muscle samples and 124 paired beluga skin and muscle samples from eight locations ranging from the low to high Arctic. We characterized both within- and between-individual variation in predator niche size at each location as well as accounting for spatial differences in the isotopic ranges of potential prey. Total isotopic niche width (TINW) for populations of ringed seals and beluga decreased with increasing latitude. Higher TINW values were associated with greater ecological opportunity (i.e., prey diversity) in the prey fish community which mainly consists of Capelin (Mallotus villosus) and Sand lance (Ammodytes sp.) at lower latitudes and Arctic cod (Boreogadus saida) at high latitudes. In beluga, their dietary consistency between tissues also known as the within-individual component (WIC) increased in a near 1:1 ratio with TINW (slope = 0.84), suggesting dietary generalization, whereas the slope (0.18) of WIC relative to TINW in ringed seals indicated a high degree of individual specialization in ringed seal populations with higher TINWs. Our findings highlight the differences in TINW and level of IS for ringed seals and beluga relative to latitude as a likely response to large-scale spatial variation in ecological opportunity, suggesting species-specific variation in dietary plasticity to spatial differences in prey resources and environmental conditions in a rapidly changing ecosystem.
Schlagworte: C , N , ec , EA

The origin and evolution of thermogenic gases in organic-rich marine shales
Journal of Petroleum Science and Engineering (2016)
Yongqiang Xiong, Li Zhang, Yuan Chen, Xiaotao Wang, Yun Li, Mingming Wei, Wenmin Jiang, Rui Lei

In order to better understand the generation and primary source of mature thermogenic gas in shale, and to evaluate the residual gas generation potential of the shale at different maturity levels, we performed pyrolysis experiments on an organic-rich marine shale and its kerogens prepared by artificial maturation. The results indicate that the thermal maturation of organic matter in the shale can be divided into four stages: oil generation (<0.6–1.0% EasyRo), condensate generation (1.0–1.5% EasyRo), wet gas generation (1.5–2.2% EasyRo), and dry gas generation (2.2–4.5% EasyRo). Thermogenic methane is produced mainly during wet gas and dry gas generation, while most of the C2+ hydrocarbon gases are produced during condensate and wet gas generation. The kerogen at a thermal maturity of >3.0% EasyRo still has methane generation potential. Whether or not gas generation potential of a highly mature kerogen has a commercial significance depends on its organic matter richness, thermal maturity internal and some other geological factors, such as caprock sealing property, reservoir physical property, and tectonic movement. In addition to the gas produced from kerogen cracking, gas is also generated from the secondary cracking of residual bitumen as maturation progresses. Early hydrocarbon expulsion during oil generation likely has a considerable effect on the amount and δ13C values of the late-generated shale gas. The lower the oil expulsion efficiency of a shale, i.e., the more retained bitumen, then the higher the productivity of post-mature shale gas and comparative enrichment of the latter in 12C.

Verifying the geographical origin of poultry: The application of Stable Isotope and Trace Element (SITE) Analysis
Food Control (2016)
Gareth Rees, Simon D. Kelly, Paul Cairns, Henriette Ueckermann, Stephan Hoelzl, Andreas Rossmann, Michael J. Scotter

Stable isotope and elemental analysis, together with statistical processing of the resultant data has been used to determine the geographical origin of poultry and hence provide a means to verify poultry labels originating from major producing countries/regions. Multivariate statistical analysis has demonstrated that 18 variables, including carbon, hydrogen and nitrogen stable isotope ratios and elemental concentrations of magnesium, thallium, rubidium and molybdenum, are important parameters in poultry origin determination. Using cross-validated discriminant analysis 88.3% of poultry geographical origins were correctly classified (n = 339). Individual correct- classification rates were as follows; China, 100% (n = 36); Brazil, 94.1% (n = 101); Europe 92% (n=87); Chile 82.6% (n =46); Thailand, 70.3% (n = 46) and Argentina 50% (n = 10). The main identification errors were associated with miss-classification of Argentinean samples with those originating from Chile and Thailand. Carbon stable isotope ratios of chicken meat indicate the quantity of maize in the diet and this leads to useful discrimination between a large proportion of European poultry and poultry reared in locations such as South America, Thailand and China where maize feeding predominates. The use of poultry carbon isotope values as a simple ‘screening’ parameter to differentiate European poultry meat from other major importers is not as reliable as for the differentiation of European and South American beef. However carbon isotope ratios will be useful in most instances to corroborate suspicion of mislabelling of non corn-fed European poultry. The stable isotopes of hydrogen and oxygen in chicken meat change in a similar way to surface waters around the globe. Our findings support the hypothesis that the global isotopic variation of stable isotopes in drinking water and feed are transferred into animal tissue and can be used to help establish an animal’s geographic origin. This is a significant finding and mirrors our observations for beef skeletal muscle δ2H ‰ and δ18O ‰ values. These systematic variations can be exploited to give a ‘low-resolution’ indication of an animal’s geographic origin (e.g. Northern Europe versus the tropics).

Carbonatite associated with ultramafic diatremes in the Avon Volcanic District, Missouri, USA: Field, petrographic, and geochemical constraints
Lithos (2016)
Ethan J. Shavers, Abduwasit Ghulam, John Encarnacion, David L. Bridges, Patrick B. Luetkemeyer

Here we report field, petrographic, and geochemical analyses of the southeast Missouri Avon Volcanic District intrusive rocks and present the first combined textural and geochemical evidence for the presence of a primary magmatic carbonatite phase among ultramafic dikes, pipes, and diatremes of olivine melilitite, alnöite, and calciocarbonatite. The δ13CVPDB values measured for primary calciocarbonatite as well as carbonates in olivine melilitite and alnöite rocks range from -3.8‰ to -8.2‰, which are within the typical range of mantle values and are distinct from values of the carbonate country rocks, 0.0‰ -1.3‰. The carbonate oxygen isotope compositions for the intrusive lithologies are in the range of 21.5‰ to 26.2‰ (VSMOW), consistent with post-emplacement low temperature hydrothermal alteration or kinetic fractionation effects associated with decompression and devolatilization. Metasomatised country rock and breccia-contaminated igneous lithologies have carbonate δ13CVPDB values gradational between primary carbonatite values and country rock values. Unaltered sedimentary dolomite breccia and mafic spheroids entrained by calciocarbonatite and the lack of microstratigraphic crystal growth typical of carbonate replacement, also exclude the possibility of hydrothermal replacement as the cause of the magmatic-textured carbonates. Rare earth element (REE) patterns for the alnöite, olivine melilitite, and carbonatite are similar to each other with strong light REE enrichment and heavy REE depletion relative to MORB. These patterns are distinct from those of country rock rhyolite and sedimentary carbonate. These data suggest that rocks of the Avon Volcanic District represent a single ultramafic carbonatite intrusive complex possibly derived from a single mantle source.

Thyroid hormones correlate with field metabolic rate in ponies, Equus ferus caballus.
The Journal of experimental biology (2016)
Lea Brinkmann, Martina Gerken, Catherine Hambly, John R Speakman, Alexander Riek

During winter free living herbivores are often exposed to reduced energy supply at the same time that energy needs for thermoregulation increase. Several wild herbivores as well as robust horse breeds reduce their metabolism during times of low ambient temperature and food shortage. Thyroid hormones (TH) affect metabolic intensity and a positive effect of TH on basal metabolic rate (BMR) has been demonstrated in mammals and birds. As BMR and field metabolic rate (FMR) are often assumed to be intrinsically linked, TH may represent a reliable indicator for FMR. To test this hypothesis, ten Shetland pony mares were kept under semi-extensive central European conditions. During the winter month one group was fed 60% and one group 100% of their maintenance energy requirements. We measured FMR, locomotor activity, resting heart rate and TH levels in summer and winter. FMR, locomotor activity, resting heart rate and total T3 concentrations decreased substantially in winter compared to summer, whereas total T4 increased. Feed restriction led to a reduced FMR and resting heart rate, while TH and locomotor activity were not affected. Across both seasons FMR, resting heart and locomotor activity were positively correlated with total T3 but negatively and more weakly related with total T4.
Schlagworte: H , O , med , GH

Increased water use efficiency does not prevent growth decline of Pinus canariensis in a semi-arid treeline ecotone in Tenerife, Canary Islands (Spain)
Annals of Forest Science (2016)
Patricia Brito, Thorsten E. E. Grams, Rainer Matysssek, Maria S. Jimenez, Agueda M. Gonzalez-Rodríguez, Walter Oberhuber, Gerhard Wieser

Intrinsic water use efficiency of Pinus canariensis (Sweet ex Spreng.) growing at a semi-arid treeline has increased during the past 37 years. Tree ring width by contrast has declined, likely caused by reduced stomatal conductance due to increasing aridity. Context Rising atmospheric CO2 concentration (C a ) has been related to tree growth enhancement accompanied by increasing intrinsic water use efficiency (iWUE). Nevertheless, the extent of rising C a on long-term changes in iWUE and growth has remained poorly understood to date in Mediterranean treeline ecosystems. Aims This study aimed to examine radial growth and physiological responses of P. canariensis in relation to rising C a and increasing aridity at treeline in Tenerife, Canary Islands, Spain. Methods We evaluated temporal changes in secondary growth (tree ring width; TRW) and tree ring stable C isotope signature for assessing iWUE from 1975 through 2011. Results Precipitation was the main factor controlling secondary growth. Over the last 36 years P. canariensis showed a decline in TRW at enhanced iWUE, likely caused by reduced stomatal conductance due to increasing aridity. Conclusion Our results indicate that increasing aridity has overridden the potential CO2 fertilization on tree growth of P. canariensis at its upper distribution limit.

Sulfur isotope constraints on marine transgression in the lacustrine Upper Cretaceous Songliao Basin, northeastern China
Palaeogeography, Palaeoclimatology, Palaeoecology (2016)
Hansheng Cao, Alan J. Kaufman, Xuanlong Shan, Huan Cui, Guijie Zhang

Organic-rich Cretaceous source rocks of the petroliferous Songliao Basin in northeast China are considered to be lacustrine in origin, but paleontological and organic geochemical evidence suggest episodic marine incursions. As a test of this hypothesis, we applied time-series measurements of elemental and isotopic abundances on core and cutting samples to evaluate fluctuations in the sulfur and carbon cycles across the Santonian-Campanian transition preserved in the upper Yaojia and lower Nenjiang formations. The data reveal a spike in pyrite sulfur abundance and a marked negative excursion in ??34S at the base of the Nenjiang Formation when the basin expanded to its maximal extent. The elemental and isotopic data suggest that flooding was associated with rapid marine transgression that enhanced sulfate concentrations, which promoted microbial sulfate reduction in anoxic bottom waters that were episodically euxinic. Subsequent restriction of the basin and a decline in marine influence is supported by progressive upsection 34S enrichment (up to 30???) in Nenjiang Member I, which are interpreted to reflect the distillation of sulfate through enhanced pyrite burial, followed by a gradual return to lacustrine conditions that prevailed in overlying strata.
Schlagworte: C , N , S , ge , EA

Source apportionment of atmospheric ammonia before, during, and after the 2014 APEC summit in Beijing using stable nitrogen isotope signatures
Atmospheric Chemistry and Physics Discussions (2016)
Yunhua Chang, Xuejun Liu, Congrui Deng, Anthony J Dore, Guoshun Zhuang

Stable nitrogen isotope composition (δ 15 N) offers new opportunities to address the 15 long-standing and ongoing controversy regarding the origins of ambient ammonia (NH 3), a vital precursor of PM 2.5 inorganic components, in the urban atmosphere. In this study, the δ 15 N values of NH 3 samples collected from various sources were constrained using a novel and robust chemical method coupled with standard elemental analysis procedures. Independent of the wide variation in mass concentrations (ranging from 33 (vehicle) to over 6000 (human excreta) μg m -3), different NH 3 sources 20 have generally different δ 15 N values (ranging from -52.0 to -9.6‰). Significantly high δ 15 N values are seen as a characteristic feature of all vehicle-derived NH 3 samples (-14.2±2.8‰), which can be distinguished from other sources emitted at environmental temperature (-29.1±1.7, -37.8±3.6, and -50.0±1.8‰ for livestock, waste, and fertilizer, respectively). The isotope δ 15 N signatures for a range of NH 3 emission sources were used to evaluate the contributions 25 of the different sources within measured ambient NH 3 in Beijing, using an isotope mixing model (IsoSource). The method was used to quantify the sources of ambient NH 3 before, during and after the 2014 APEC summit, when a set of stringent air quality control measures were implemented. Results show that the average NH 3 concentrations (the overall contributions of traffic, waste, livestock, and fertilizer) during the three periods were 9.1 (15.1, 31.2, 23.7, and 30.0%), 7.3 (8.8, 24.9, 14.3, and 30 1 Atmos. Chem. Phys. Discuss., doi:10.5194/acp-2016-432, 2016 Manuscript under review for journal Atmos. Chem. Phys. Published: 13 June 2016 c Author(s) 2016. CC-BY 3.0 License. 52.0%), and 12.7 (29.4, 23.6, 31.7, and 15.4%) μg m -3 , respectively, representing a 20.0% decrease first and then a 74.5% increase in overall NH 3 mass concentrations. During (after) the summit, the contributions of traffic, waste, livestock, and fertilizer decreased (increased) by 58.7 (234.2), 0.9 (-5.0), 41.0 (120.8), and -87.6% (-70.5%) when compared with periods before (during) the summit, respectively, signifying that future NH 3 control efforts in megacities like Beijing should prioritize traffic 35 sector as well as livestock breeding. The results show that isotope ratio measurements of NH 3 to be a valuable tool to quantify the atmospheric sources of NH 3 in urban atmospheres.
Schlagworte: N , po , GH