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824 Ergebnisse:

Comparing watershed black locust afforestation and natural revegetation impacts on soil nitrogen on the Loess Plateau of China.
Scientific reports (2016)
Zhao Jin, Xiangru Li, Yunqiang Wang, Yi Wang, Kaibo Wang, Buli Cui

This study examined a pair of neighbouring small watersheds with contrasting vegetations: artificial forestland and natural grassland. Since 1954, afforestation which mainly planted with black locust has been conducted in one of these watersheds and natural revegetation in the other. The differences in soil total N, nitrate, ammonium, foliar litterfall δ(15)N and dual stable isotopes of δ(15)N and δ(18)O in soil nitrate were investigated in the two ecosystems. Results showed that there was no significant difference in soil total N storage between the two ecosystems, but the black locust forestland presented higher soil nitrate than the grassland. Moreover, the foliar litterfall N content and δ(15)N of the forestland were significant higher than the grassland. These results indicate that 60 years of watershed black locust afforestation have increased soil N availability. The higher nitrate in the forestland was attributed to the biological N fixation of black locust and difference in ecosystem hydrology. The dual stable isotopes of δ(15)N and δ(18)O revealed that the two ecosystems had different sources of soil nitrate. The soil nitrate in the forestland was likely derived from soil N nitrification, while the soil nitrate in the grassland was probably derived from the legacy of NO3(-) fertiliser.

Characterization of a site contaminated by chlorinated ethenes and ethanes using multi-analysis
Environmental Earth Sciences (2016)
Dugin Kaown, Seong-Chun Jun, Rak-Hyeon Kim, Shin Woosik, Kang-Kun Lee

Chlorinated ethenes and ethanes are the most commonly detected groundwater contaminants in industrial areas. Compound-specific stable isotope analysis combined with hydrogeological, and geochemical analyses was applied to identify contaminant sources and to monitor the natural degradation processes of chlorinated ethenes and ethanes in an industrial area of Asan, Korea. The concentrations of the detected trichloroethene (TCE) and 1,1,1-trichloroethane (1,1,1-TCA) ranged from 0.004 to 5.8 mg/L and from non-detected to 1.8 mg/L in August 2013. TCE concentrations correspond to 65–87 % of the molar fraction of the volatile organic compounds. Most of the flow system in the study area is aerobic with dissolved oxygen (DO) ranging 0.1–8.3 mg/L. The highest concentration of TCE (5.8 mg/L) and the most depleted δ13C and δ37Cl values (−27.1 and −1.7 ‰, respectively) were observed in the well near an electrical parts company, indicating a source area. The slight enrichments in both the carbon and chlorine isotopic values of contaminants in some wells can be explained by isotopic shifts caused by degradation processes in the study area. 1,1-dichloroethene (1,1-DCE) was present in higher concentrations than cis-DCE and trans-DCE. The concentrations of 1,1-DCA, the biotic degradation product of 1,1,1-TCA, were much lower than those of 1,1-DCE due to the limited anaerobic conditions of the study area. High correlations of 1,1-DCE and 1,1,1-TCA in the study area indicated that some 1,1-DCE might be the dehydrohalogenation product of 1,1,1-TCA. Further isotopic analysis of 1,1,1-TCA are recommended to identify the degradation pathway of 1,1,1-TCA. Hydrogeochemical, VOCs, and dual isotope data showed that dilution with an insignificant rate of biodegradation is the main process attenuating VOCs in the groundwater system. Thus, an active remediation plan is necessary to reduce contaminant concentration in the study area.

Effects of HCl pre -treatment , drying , and storage on the stable isotope ratios of soil and sediment samples
Rapid Communications in Mass Spectrometry (2016)
Min-Seob Kim, Won-Seok Lee, K. Suresh Kumar, Kyung-Hoon Shin, Wayne Robarge, Minseok Kim, Sang Ryong Lee

RATIONALE: Stable isotope (δ13C, δ15N, δ34S values) analysis has become increasingly important for tracing contaminant sources in environments. Pretreatment of environmental samples allows accurate analysis of stable isotope ratios. The pretreatment of a sample and its subsequent preservation could either contaminate or create experimental artifacts affecting the validity of the resulting C/N ratios and the elemental isotopic contents of a sample. METHODS: The effects of acid pretreatment (0.1, 0.5, 1, 2, 5, 13 M HCl) and exposure period (2, 6, 12, 24, and 48 h) on the stable isotopic ratios of marine sediment (MS), river sediment (RS) and terrestrial soil (TS) samples were evaluated. The effects of storage temperatures (–80, –20 and 2°C), storage duration (1 week, 1 to 12 months) and washing steps (1, 2, 3, 5, 7 or 12 times) on the stable isotopic ratios were also considered. The %C, %N and %S, as well as the δ13C, δ15N, and δ34S values, of each sample were measured using continuous flow Elemental Analyzer/Isotope Ratio Mass Spectrometry (EA/IRMS). RESULTS: The HCl treatment was applicable for δ13C analysis. However, the acid concentration and duration of exposure that brought about total removal of carbonate for the three sample types varied; e.g. the TS sample required stronger acid and a shorter exposure time. Storage time also had an effect: the δ13C values were lower and the δ15N and δ34S values higher after storage for 300 days. CONCLUSIONS: HCl pretreatment effectively eliminates carbonates and thereby helps δ13C analysis of the organic fraction. HCl pretreatment is not recommended for δ15N and δ34S analysis. Freeze-drying of samples is recommended rather than oven drying. A temperature-dependent change in the isotopic ratios of long-term stored samples was observed during this study; therefore, relatively short-term storage (–80°C) of freeze-dried samples is preferable

Chemical weathering and the role of sulfuric and nitric acid in carbonate weathering: isotopes ( 13 C, 15 N, 34 S and 18 O) and chemical constraints
Journal of Geophysical Research: Biogeosciences (2016)
Cai Li, Hongbing Ji

Multiple isotopes (13C-DIC, 34S and 18O-SO42−, 15N and 18O-NO3−) and water chemistry were used to evaluate weathering rates and associated CO2 consumption by carbonic acid and strong acids (H2SO4 and HNO3) in a typical karst watershed (Wujiang River, Southwest China). The dual sulfate isotopes indicate that sulfate is mainly derived from sulfide oxidation in coal stratum and sulfide-containing minerals, and dual nitrate isotopes indicate that nitrate is mainly derived from soil N and nitrification. The correlation between isotopic compositions and water chemistry suggests that sulfuric and nitric acids, in addition to carbonic acid, are involved in carbonate weathering. The silicate and carbonate weathering rates are 7.2 t km−2 yr−1 and 76 t km−2 yr−1, respectively. In comparison with carbonate weathering rates (43 t km−2 yr−1) by carbonic acid alone, the subsequent increase in rates indicates significant enhancement of weathering when combined with sulfuric and nitric acid. Therefore, the role of sulfuric and nitric acid in the rock weathering should be considered in the global carbon cycle.
Schlagworte: C , N , O , S , ge , EA , GH

Identification of nitrate sources in groundwater using a stable isotope and 3DEEM in a landfill in Northeast China.
The Science of the total environment (2016)
Zhifei Ma, Yu Yang, Xinying Lian, Yonghai Jiang, Beidou Xi, Xing Peng, Kun Yan

The groundwater was sampled in a typical landfill area of the Northeast China. Coupled stable isotope and three dimensional excitation-emission matrix (3DEEM) were applied to dentify diffused NO3(-) inputs in the groundwater in this area. The results indicated that combined with the feature of groundwater hydrochemistry and three-dimensional fluorescence technology can effectively identify the nitrate pollution sources. The nitrate was derived from manure and sewage by δ(15)N and δ(18)O-NO3(-) values of groundwater in the different periods. The excitation-emission matrix fluorescence spectroscopy was further evidence of groundwater DOM mainly which comes from the landfill. The protein-like was very significant at the sampling points near the landfill (SPNL), but only fulvic acid-like appeared at downstream of the landfill groundwater sampling points (DLGSP) in the study area. Partial denitrification processes helped to attenuate nitrate concentration in anaerobic environment.

Petrogenesis and Ni-Cu sulphide potential of mafic-ultramafic rocks in the Mesoproterozoic Fraser Zone within the Albany-Fraser Orogen, Western Australia
Precambrian Research (2016)
W.D. Maier, R.H. Smithies, C.V. Spaggiari, S.J. Barnes, C.L. Kirkland, S. Yang, Y. Lahaye, O. Kiddie, C. MacRae

The Albany Fraser orogen is located along the southern and southeastern margins of the Archean Yilgarn Craton. The orogen formed during reworking of the Yilgarn Craton, along with variable additions of juvenile mantle material, from at least 1810 Ma to 1140 Ma. The Fraser Zone is a 425 km long and 50 km wide geophysically distinct belt near the northwestern edge of the orogen, hosting abundant sills of predominantly metagabbroic non-cumulate rocks, but including larger cumulate bodies, all emplaced at c. 1300 Ma. The gabbroic rocks are interpreted to have crystallised from a basaltic magma that had ∼8.8% MgO, 185 ppm Ni, 51 ppm Cu, and extremely low contents of platinum-group elements (PGE, <1 ppb). Levels of high field-strength elements (HFSE) in the least enriched rocks indicate that the magma was derived from a mantle source more depleted than a MORB source. Isotope and trace element systematics suggest that the magma was contaminated (εNd 0 to -2 throughout, La/Nb around 3) with small (<10%) amounts of crust before and during ascent and emplacement. Larger bodies of cumulate rocks show evidence for additional contamination, at the emplacement level, with country-rock metasedimentary rocks or their anatectic melts. The area has been the focus of considerable exploration for Ni-Cu sulphides following the discovery of the Nova deposit in 2012 in an intrusion consisting of olivine gabbronoritic, noritic and peridotitic cumulates, interlayered with metasedimentary rocks belonging to the Snowys Dam Formation of the Arid Basin. Disseminated sulphides from a drillcore intersecting the structurally upper portion of the intrusion, above the main ore zone, have tenors of ∼ 3-6.3% Ni, 1.8-6% Cu and mostly <500 ppb PGE, suggesting derivation from magma with the same composition as the regional Fraser Zone metagabbroic sills, at R factors of ∼1500. However, the Nova rocks tend to have higher εSr (38-52) and more variable δ34S (-2 to +4) than the regional metagabbros (εSr 17-32, δ34S around 0), consistent with the geochemical evidence for enhanced crustal assimilation of the metasedimentary country-rock in a relatively large magma staging chamber from which pulses of sulphide bearing, crystal-charged magmas were emplaced at slightly different crustal levels. Preliminary investigations suggest that the critical factors determining whether or not Fraser Zone mafic magmas are mineralised probably relate to local geodynamic conditions that allow large magma chambers to endure long enough to sequester country-rock sulphur.

Changing distributions of sea ice melt and meteoric water west of the Antarctic Peninsula
Deep Sea Research Part II: Topical Studies in Oceanography (2016)
Michael P. Meredith, Sharon E. Stammerjohn, Hugh J. Venables, Hugh W. Ducklow, Douglas G. Martinson, Richard A. Iannuzzi, Melanie J. Leng, Jan Melchior van Wessem, Carleen H. Reijmer, Nicholas E. Barrand

The Western Antarctic Peninsula has recently undergone rapid climatic warming, with associated decreases in sea ice extent and duration, and increases in precipitation and glacial discharge to the ocean. These shifts in the freshwater budget can have significant consequences on the functioning of the regional ecosystem, feedbacks on regional climate, and sea-level rise. Here we use shelf-wide oxygen isotope data from cruises in four consecutive Januaries (2011–2014) to distinguish the freshwater input from sea ice melt separately from that due to meteoric sources (precipitation plus glacial discharge). Sea ice melt distributions varied from minima in 2011 of around 0 % up to maxima in 2014 of around 4–5%. Meteoric water contribution to the marine environment is typically elevated inshore, due to local glacial discharge and orographic effects on precipitation, but this enhanced contribution was largely absent in January 2013 due to anomalously low precipitation in the last quarter of 2012. Both sea ice melt and meteoric water changes are seen to be strongly influenced by changes in regional wind forcing associated with the Southern Annular Mode and the El Niño–Southern Oscillation phenomenon, which also impact on net sea ice motion as inferred from the isotope data. A near-coastal time series of isotope data collected from Rothera Research Station reproduces well the temporal pattern of changes in sea ice melt, but less well the meteoric water changes, due to local glacial inputs and precipitation effects.

Composition of stable carbon and nitrogen isotopes in five wetland plants and sediments from the Pearl River estuary, South China
Chemistry and Ecology (2016)
S. Y. Miao, L. D. Long, W. Q. Tao, Q. C. Zeng, J. H. Chen, J. L. Huang, Q. H. Wu, Y.J. Tang

ABSTRACTThis study sampled five plant species and adjoining sediments from the Qi’ao (Zhuhai) and Nansha (Guangzhou) coastal wetlands located in the Pearl River estuary, South China. The compositions of stable carbon and nitrogen isotopes as well as the content of carbon and nitrogen in the samples were analysed. Differences in carbon/nitrogen (C/N) ratio, and habitat feature were compared between exotic plants (Spartina alterniflora, Sonneratia apetala, and Laguncularia racemosa) and native mangroves (Aegiceras corniculatum and Acrostichum aureum). The results showed that for Qi’ao, which is nearer the sea, the conductivity of the sediments at this location was approximately two times higher than that at Nansha (more inland). The composition of both δ13C and δ15N in sediments was also higher at Qi’ao (−26.52‰ to −23.83‰ and 6.25‰ to 11.53‰, respectively) as compared to Nansha (−29.30‰ to −27.43‰ and 3.34‰ to 4.73‰, respectively). Overall, the exotic plants S. alterniflora and S. apetala at Qi’ao and S. a...

A late Miocene methane-seep deposit bearing methane-trapping silica minerals at Joetsu, central Japan
Palaeogeography, Palaeoclimatology, Palaeoecology (2016)
Yusuke Miyajima, Yumiko Watanabe, Yukio Yanagisawa, Kazutaka Amano, Takashi Hasegawa, Norimasa Shimobayashi

The modern Japan Sea is characterized by active methane seeps associated with gas hydrates, but their ancient counterparts are not fully understood. This study describes a newly discovered methane-seep carbonate block, the ‘Nakanomata Seep Deposit’, from the upper Miocene Nodani Formation in Joetsu City, central Japan. The age of this deposit is constrained to 7.5–6.5Ma based on its fossil diatom assemblage. The deposit contains molluscan fossils typical of methane seeps, including vesicomyid and bathymodiolin bivalves, and provannid gastropods, and it retains an almost entirely aragonitic mineralogy, despite its Miocene age. It is composed of clotted microcrystalline aragonite containing nodules and intraclasts, and is crosscut by vein-like networks of voids and cavities rimmed with acicular aragonite. The δ13C values of the carbonate phases are as low as −41.1‰ and the presence of lipid biomarkers (pentamethylicosane and crocetane) suggests that the deposit originated from the anaerobic oxidation of methane. It is suggested that an initially diffuse methane seepage formed the micritic nodules, followed by a more rapid and intense methane seepage that led to the development of abundant voids in the sediment; finally, the sediment was cemented by microcrystalline aragonite and void-lining acicular aragonite. The seep deposit also contains peculiar globular silica minerals and authigenic quartz. During their precipitation, these globular silica minerals may have trapped methane gas bubbles, and the minerals may be pseudomorphs after silica clathrate. Sufficient increase in pH and supersaturation of silica, which led to the dissolution and subsequent precipitation of these silica minerals, could have resulted from the degassing of carbon dioxide, promoted by an effective supply of methane, and its supersaturation, thus forming gas bubbles.

Seasonal dynamics of δ 13 C of C-rich fractions from Picea abies (Norway spruce) and Fagus sylvatica (European beech) fine roots
Plant, Cell & Environment (2016)
Alex Paya, Thorsten E. E. Grams, Taryn L. Bauerle

The (13/12) C ratio in plant roots is likely dynamic depending on root function (storage vs. uptake), but to date, little is known about the effect of season and root order (an indicator of root function) on the isotopic composition of C-rich fractions in roots. To address this, we monitored the stable isotopic composition of one evergreen (Picea abies) and one deciduous (Fagus sylvatica), tree species' roots by measuring δ(13) C of bulk, respired and labile C, and starch from 1(st) /2(nd) and 3(rd) /4(th) order roots during spring and fall root production periods. In both species, root order differences in δ(13) C were observed in bulk organic matter, labile, and respired C fractions. Beech exhibited distinct seasonal trends in δ(13) C of respired C, while spruce did not. In fall, 1(st) /2(nd) order beech roots were significantly depleted in (13) C, whereas spruce roots were enriched compared to higher order roots. Species variation in δ (13) C of respired C may be partially explained by seasonal shifts from enriched to depleted C substrates in deciduous beech roots. Regardless of species identity, differences in stable C isotopic composition of at least two root order groupings (1(st) /2(nd) , 3(rd) /4(th) ) were apparent, and should hereafter be separated in belowground C-supply-chain inquiry.