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824 Ergebnisse:

Modifications to the azide method for nitrate isotope analysis
Rapid Communications in Mass Spectrometry (2016)
Ying Tu, Yunting Fang, Dongwei Liu, Yuepeng Pan

Rationale The azide method for measuring the stable isotope ratios of nitrate (NO3−) is easy to set up. However, the method requires spongy cadmium (Cd) or activated Cd powder which are not easy to prepare, and a toxic azide buffer is used. We aimed to use Cd powder directly to simplify preparation and to substantially reduce the azide dose. Methods The reaction conditions were optimized in order to maximize the NO3− reduction yield. The original azide buffer was diluted by 10- to 10000-fold with or without addition of sodium acetate to reduce O-exchange between nitrite (NO2−) and H2O. The isotope ratios of the produced nitrous oxide (N2O), used to examine the overall reaction performance, were measured using a purge and cryogenic trap system coupled to an isotope ratio mass spectrometer. Results It was found that Cd powder could be directly used to reduce NO3− to NO2−. A 100-fold diluted azide buffer could be used to reduce NO2− to N2O when only the δ15N value was measured, and the diluted azide buffer with sodium acetate when both δ15N and δ18O values were measured. Using the modified method, the standard deviations of the δ15N and δ18O measurements of international NO3− standards were 0.1 to 1.0‰ and often better than 0.3‰ (3 replicates). Conclusions Compared with the original azide method, the techniques described here can reduce preparation time by using Cd powder without activation in the first reaction step and substantially (by >60-fold) reduce the dose of extremely toxic reagents containing azide by incorporating sodium acetate in the second reaction step. Our modified method is suitable for samples with small volume (5 mL), being different from previous methods in which 50 or 70 mL samples were used.

High-resolution trace element and stable/radiogenic isotope profiles of late Pleistocene to Holocene speleothems from Dim Cave, SW Turkey
Palaeogeography, Palaeoclimatology, Palaeoecology (2016)
Ezgi Ünal-İmer, James Shulmeister, Jian-Xin Zhao, I. Tonguç Uysal, Yue-Xing Feng

Multiple climate-sensitive trace element/Ca and stable isotope (O and C) profiles derived from Dim Cave speleothems (S-SW Turkey) provide evidence of climatic changes and define a series of palaeohydrological conditions for the period ~9–90kyr. Dim Cave speleothem Mg/Ca, Sr/Ca, U/Ca, Ba/Ca, and Y/Ca ratios demonstrate similar patterns over glacial–interglacial scales, in agreement with δ18O and δ13C records. Three episodes of more positive moisture balance (71–63kyr, 51–40kyr, and 18–10kyr) were observed based on Y/Ca (and to a lesser extent Zr/Ca), 87Sr/86Sr ratios, calcite micromorphology, and growth rates. Increasing concentrations of Y and Zr (and U) and elevated 87Sr/86Sr ratios are attributed to enhanced levels of terrestrial input during these periods. Correlations between δ13C, δ18O and Mg/Ca during 40–18kyr (corresponding with the lowest growth rate of ~0.8mm/kyr), 63–51, and 80–71kyr (relatively low growth rates), as well as co-varying and enhanced Mg/Ca, Sr/Ca, and to a lesser extent Ba/Ca, ratios point to the prior calcite precipitation, wall–rock interaction, and preferential dolomite dissolution over calcite in the host dolomitic limestone during these periods. This relationship suggests that water–rock interactions are maximised during episodes of slower drip rates of water through the karst under drier conditions. Chondrite-normalized rare earth element and yttrium (REY) patterns of the stalagmites reveal seawater signatures closely linked to the dolomitic limestone. Excluding the aragonite formation during ~80–75kyr, which is an autogenic effect, trace element/Ca ratios appear to respond to millennial scale global cooling periods such as Heinrich events.

The distribution of nitrogen speciation and sources of nitrate in the north of Taihu Lake
Environmental Earth Sciences (2016)
Da Li, Xia Jiang, Kun Wang, Binghui Zheng

Meiliang Bay and Gonghu Bay, in the north of Taihu Lake, are important water sources for the city of Wuxi, and increased eutrophication now threatens the safety of drinking water. The distribution of nitrogen (N) speciation and source of N in the surface waters in the north of Taihu Lake is studied, which was an important first step in controlling N pollution. The result shows that the average concentration of ammonia (NH4+) and nitrate (NO3−) of surface water in Meiliang Bay was 0.32 and 0.35 mg/L, while 0.21 and 0.74 mg/L of Gonghu Bay, in which both bays had serious nitrate pollution. The concentrations of NH4+ and NO3− in the surface water of the two bays had a trend of gradual decrease from north to south. The maximum concentrations of NH4+ and NO3− of two bays were observed near the inflowing rivers, and the maximum concentrations of NH4+ in surface water of two bays were 0.49 and 0.61, and 0.77 and 1.38 mg/L of NO3−. The concentration of NH4+ in the interstitial water of the two bays had a trend of gradual decrease from west to east, but NO3− had the opposite tendency. The maximum concentrations of NH4+ in the interstitial water of the two bays were 5.88 and 4.64, and 3.58 and 7.18 mg/L of NO3−. The exchangeable NH4+ content in the sediment of Meiliang Bay had a trend of gradual decrease from north to south, but Gonghu Bay showed the reverse. The exchangeable NO3− content in the sediment of Meiliang Bay had a trend of gradual decrease from east to west, but a decreasing trend from north to south was observed in Gonghu Bay. The maximum concentrations of exchangeable NH4+ were determined, and the values were 96.25 and 74.90 mg/kg, as well as NO3− with the values of 12.06 and 7.08 mg/kg. Chemical fertilizer and domestic sewage were the major sources of nitrate in surface water of Gonghu Bay, contributing 39.16 and 47.79%, respectively. Domestic sewage was the major source of nitrate in Meiliang Bay, contributing 84.79%. The denitrification process in Gonghu Bay was more apparent than in Meiliang Bay. Mixing and dilution processes had important effects on changing the concentration of nitrate transportation in the two bays.

Solar-, monsoon- and Kuroshio-influenced thermocline depth and sea surface salinity in the southern Okinawa Trough during the past 17,300 years
Geo-Marine Letters (2016)
Libo Wang, Jun Li, Jingtao Zhao, Helong Wei, Bangqi Hu, Yanguang Dou, Zhilei Sun, Liang Zou, Fenglong Bai

Factors influencing millennial-scale variability in the thermocline depth (vertical mixing) and sea surface salinity (SSS) of the southern Okinawa Trough (OT) during the past 17,300 years were investigated based on foraminifer oxygen isotope records of the surface dweller Globigerinoides ruber sensu stricto and the thermocline dweller Pulleniatina obliquiloculata in the AMS 14C dated OKT-3 core. The thermocline depth is influenced by surface thermal buoyancy (heat) flux, in turn controlled by the annual mean insolation at 30°N and the strength of the East Asian winter monsoon (EAWM). Strong insolation and weak EAWM tend to increase buoyancy gain (decrease buoyancy loss), corresponding to shallow thermocline depths, and vice versa. Regional SSS is influenced by the global ice volume, the Kuroshio Current (KC), and vertical mixing. A deep thermocline coincides with a high SSS because strong vertical mixing brings more, saltier subsurface KC water to the surface, and vice versa. Local SSS (excluding the global ice volume effect) became lower in the northern OT than in the southern OT after ~9.2 ka, implying that Changjiang diluted water had stronger influence in the northern sector. SSS show no major changes during the Bølling/Allerød and Younger Dryas events, probably because the KC disturbed the North Atlantic signals. This argues against earlier interpretations of sea surface temperature records of this core. Wavelet and spectral analyses of the Δδ18OP-G (δ18O of P. obliquiloculata minus G. ruber s.s.) and δ18Olocal records display 1,540-, 1,480-, 1,050-, 860-, 640-, and 630-year periods. These are consistent with published evidence of a pervasive periodicity of 1,500 years in global climate as well as EAWM and KC signatures, and a fundamental solar periodicity of 1,000 years and intermediary derived periodicity of 700 years.

Stage-specific response of litter decomposition to N and S amendments in a subtropical forest soil
Biology and Fertility of Soils (2016)
Yehong Xu, Jianling Fan, Weixin Ding, Roland Bol, Zengming Chen, Jiafa Luo, Nanthi Bolan

Nitrogen (N) and sulfur (S) deposition are important drivers of global climate change, but their effects on litter decomposition remain unclear in the subtropical regions. We investigated the influences of N, S, and their interactions on the decomposition of 13C-labeled Pinus massoniana leaf litter. An orthogonal experiment with three levels of N (0, 81, and 270 mg N kg−1 soil) and S (0, 121, and 405 mg S kg−1 soil) was conducted. We traced the incorporation of 13C-litter into carbon dioxide (CO2), dissolved organic C (DOC), and microbial phospholipids. Over the 420-day incubation, litter decomposition did not respond to low N and S additions but increased under high levels and combined amendments (NS). However, litter-derived CO2 emissions were enhanced during the first 56 days, with a positive interaction of N × S. N additions promoted fungal growth, while S stimulated growth of Gram-positive bacteria, fungi, and actinobacteria. Increased decomposition was related to higher litter-derived DOC and fungi/bacteria ratio. Inversely, N and/or S amendments inhibited decomposition (N > NS > S) from day 57 afterwards, possibly due to C limitation and decreased abundances of Gram-negative bacteria and actinobacteria. These results suggested that N deposition interacted with S to affect litter decomposition, and this effect depended on N and S deposition levels and litter decomposition stage.

Not so deserted…paleoecology and human subsistence in Central Iberia (Guadalajara, Spain) around the Last Glacial Maximum
Quaternary Science Reviews (2016)
José Yravedra, Marie-Anne Julien, Manuel Alcaraz-Castaño, Verónica Estaca-Gómez, Javier Alcolea-González, Rodrigo de Balbín-Behrmann, Christophe Lécuyer, Claude Hillaire Marcel, Ariane Burke

In contrast to the coastal areas of the Iberian Peninsula, the Upper Palaeolithic settlement of central Iberia, dominated by the Spanish plateau, is poorly known. Traditional models assume a total or virtual depopulation of the interior of the Iberian Peninsula during the Last Glacial. In this paper we present a detailed investigation of human-environment interactions through the first zooarchaeological, taphonomic and isotopic study of the key site of Peña Capón, a rock shelter located in the south-eastern foothills of the Central System range that contains a multi-layered deposit dated to marine isotope stage 2 (MIS 2). Analyses of the faunal assemblages of the Proto-Solutrean (3) and Middle Solutrean (2) layers show that human preferentially hunted horse, deer and iberian ibex living in the vicinity of the rock shelter. Isotope geochemistry of the animal remains of Peña Capón provides us with the first detailed intra-tooth multi-proxy analysis for this time period in south-western Europe, providing estimates of climatic conditions, seasonal flucturation of diet, as well as patterns of seasonal mobility. Our results indicate that human presence at Peña Capón was apparently restricted to relatively warm intervals around the LGM or reflects the presence of an ecological refuge, and provide us with evidence of recurrent human presence in the Iberian interior during the Upper Paleolithic prior to the Magdalenian.

Significant difference in hydrogen isotope composition between xylem and tissue water in Populus euphratica.
Plant, cell & environment (2016)
Liangju Zhao, Lixin Wang, Lucas A Cernusak, Xiaohong Liu, Honglang Xiao, Maoxian Zhou, Shiqiang Zhang

Deuterium depletions between stem water and source water have been observed in coastal halophyte plants and in multiple species under greenhouse conditions. However, the location(s) of the isotope fractionation is not clear yet and it is uncertain whether deuterium fractionation appears in other natural environments. In this study, through two extensive field campaigns utilizing a common dryland riparian tree species Populus euphratica Oliv., we showed that no significant δ(18) O differences were found between water source and various plant components, in accord with previous studies. We also found that no deuterium fractionation occurred during P. euphratica water uptake by comparing the deuterium composition (δD) of groundwater and xylem sap. However, remarkable δD differences (up to 26.4‰) between xylem sap and twig water, root water and core water provided direct evidence that deuterium fractionation occurred between xylem sap and root or stem tissue water. This study indicates that deuterium fractionation could be a common phenomenon in drylands, which has important implications in plant water source identification, palaeoclimate reconstruction based on wood cellulose and evapotranspiration partitioning using δD of stem water.
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Critical analysis of hydrogen production from mixed culture fermentation under thermophilic condition (60 °C).
Applied microbiology and biotechnology (2016)
Hang Zheng, Raymond J Zeng, Cathryn O'Sullivan, William P Clarke

Bio-hydrogen production from mixed culture fermentation (MCF) of glucose was studied by conducting a comprehensive product measurement and detailed mass balance analysis of their contributions to the final H2 yield. The culture used in this study was enriched on glucose at 60 °C through a sequential batch operation consisting of daily glucose feeds, headspace purging and medium replacement every third day in serum bottles for over 2 years. 2-Bromoethanesulfonate (BES) was only required during the first three 3-day cycles to permanently eliminate methanogenic activity. Daily glucose feeds were fully consumed within 24 h, with a persistent H2 yield of 2.7 ± 0.1 mol H2/mol glucose, even when H2 was allowed to accumulate over the 3-day cycle. The measured H2 production exceeded by 14 % the theoretical production of H2 associated with the fermentation products, dominated by acetate and butyrate. Follow-up experiments using acetate with a (13)C-labelled methyl group showed that the excess H2 production was not due to acetate oxidation. Chemical formula analysis of the biomass showed a more reduced form of C5H11.8O2.1N1.1 suggesting that the biomass formation may even consume produced H2 from fermentation.

Breeding origins and pattern of migration of Bluethroats Luscinia svecica wintering from Iberia to Senegal as revealed by stable isotopes
Bird Study (2016)
Juan Arizaga, Steven L. Van Wilgenburg, Daniel Alonso, Jose A. Cortés, Michel Leconte, Hamid Rguibi, Thijs Valkenburg, Pablo Vera, Keith A. Hobson

ABSTRACTCapsule: Stable isotope analyses reveal some degree of migratory connectivity of Bluethroat populations wintering from Iberia to West Africa.Aims: To identify the probable breeding origins of Bluethroats wintering from Iberia to Senegal.Methods: Bluethroat feathers (P1) were sampled from individuals at their wintering areas. These feathers were then analysed for stable H isotopes (δ2H). We assigned individual Bluethroats to approximate geographic origin using likelihood-based assignment procedures.Results: We observed spatial segregation between different Bluethroat populations. At wintering sites north of the Sahara Desert, Bluethroats wintering to the west came from further west origins than those which overwintered to the east. Bluethroats from central-eastern Europe overwintered either within the circum-Mediterranean region or in Senegal. We found no clear evidence supporting a sub-Saharan wintering range for birds breeding in Iberia (Luscinia svecica azuricollis subspecies).Conclusion: North ...

Constraining the role of iron in environmental nitrogen transformations: Dual stable isotope systematics of abiotic NO2- reduction by Fe(II) and its production of N2O
Geochimica et Cosmochimica Acta (2016)
Carolyn Buchwald, Kalina Grabb, Colleen M. Hansel, Scott D. Wankel

Despite mounting evidence for biogeochemical interactions between iron and nitrogen, our understanding of their environmental importance remains limited. Here we present an investigation of abiotic nitrite (NO2-) reduction by Fe(II) or ‘chemodenitrification,’ and its relevance to the production of nitrous oxide (N2O), specifically focusing on dual (N and O) isotope systematics under a variety of environmental conditions. We observe a range of kinetic isotope effects that are regulated by reaction rates, with faster rates at higher pH (∼8), higher concentrations of Fe(II) and in the presence of mineral surfaces. A clear non-linear relationship between rate constant and kinetic isotope effects of NO2- reduction was evident (with larger isotope effects at slower rates) and is interpreted as reflecting the dynamics of Fe(II)-N reaction intermediates. N and O isotopic composition of product N2O also suggests a complex network of parallel and/or competing pathways. Our findings suggest that NO2- reduction by Fe(II) may represent an important abiotic source of environmental N2O, especially in iron-rich environments experiencing dynamic redox variations. This study provides a multi-compound, multi-isotope framework for evaluating the environmental occurrence of abiotic NO2- reduction and N2O formation, helping future studies constrain the relative roles of abiotic and biological N2O production pathways.