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824 Ergebnisse:

Isotope signatures of N2O emitted from vegetable soil: Ammonia oxidation drives N2O production in NH4+-fertilized soil of North China
Scientific Reports (2016)
Wei Zhang, Yuzhong Li, Chunying Xu, Qiaozhen Li, Wei Lin, P. M. Smith, O. Edenhofer, S. A. Montzka, E. J. Dlugokencky, J. H. Butler, R. Prinn, P. Smith, B. Metz, S. K. Lam, R. Well, H. Flessa, X. Lu, X. T. Ju, V. Römheld, H. W. Hu, X. Zhu, M. Burger, T. A

Nitrous oxide (N2O) is a potent greenhouse gas. In North China, vegetable fields are amended with high levels of N fertilizer and irrigation water, which causes massive N2O flux. The aim of this study was to determine the contribution of microbial processes to N2O production and characterize isotopic signature effects on N2O source partitioning. We conducted a microcosm study that combined naturally abundant isotopologues and gas inhibitor techniques to analyze N2O flux and its isotopomer signatures [δ15Nbulk, δ18O, and SP (intramolecular 15N site preference)] that emitted from vegetable soil after the addition of NH4+ fertilizers. The results show that ammonia oxidation is the predominant process under high water content (70% water-filled pore space), and nitrifier denitrification contribution increases with increasing N content. δ15Nbulk and δ18O of N2O may not provide information about microbial processes due to great shifts in precursor signatures and atom exchange, especially for soil treated with NH4+ fertilizer. SP and associated two end-member mixing model are useful to distinguish N2O source and contribution. Further work is needed to explore isotopomer signature stability to improve N2O microbial process identification.
Schlagworte: nitrogen , oxygen , soil , gashead

Iron-bound organic carbon in forest soils: quantification and characterization
Biogeosciences (2016)
Qian Zhao, Simon R Poulson, Daniel Obrist, Samira Sumaila, James J Dynes, Joyce M Mcbeth, Yu Yang

Iron oxide minerals play an important role in stabi-lizing organic carbon (OC) and regulating the biogeochem-ical cycles of OC on the earth surface. To predict the fate of OC, it is essential to understand the amount, spatial vari-ability, and characteristics of Fe-bound OC in natural soils. In this study, we investigated the concentrations and charac-teristics of Fe-bound OC in soils collected from 14 forests in the United States and determined the impact of ecogeo-graphical variables and soil physicochemical properties on the association of OC and Fe minerals. On average, Fe-bound OC contributed 37.8 % of total OC (TOC) in forest soils. Atomic ratios of OC : Fe ranged from 0.56 to 17.7, with val-ues of 1–10 for most samples, and the ratios indicate the importance of both sorptive and incorporative interactions. The fraction of Fe-bound OC in TOC (f Fe-OC) was not re-lated to the concentration of reactive Fe, which suggests that the importance of association with Fe in OC accumulation was not governed by the concentration of reactive Fe. Con-centrations of Fe-bound OC and f Fe-OC increased with lat-itude and reached peak values at a site with a mean annual temperature of 6.6 • C. Attenuated total reflectance–Fourier transform infrared spectroscopy (ATR-FTIR) and near-edge X-ray absorption fine structure (NEXAFS) analyses revealed that Fe-bound OC was less aliphatic than non-Fe-bound OC. Fe-bound OC also was more enriched in 13 C compared to the non-Fe-bound OC, but C / N ratios did not differ sub-stantially. In summary, 13 C-enriched OC with less aliphatic carbon and more carboxylic carbon was associated with Fe minerals in the soils, with values of f Fe-OC being controlled by both sorptive and incorporative associations between Fe and OC. Overall, this study demonstrates that Fe oxides play an important role in regulating the biogeochemical cycles of C in forest soils and uncovers the governing factors for the spatial variability and characteristics of Fe-bound OC.
Schlagworte: carbon , geol , elem

Spring Nitrogen Uptake, Use Efficiency, and Partitioning for Growth in Iris germanica ‘Immortality’
HortScience (2016)
Xiaojie Zhao, Guihong Bi, Richard L. Harkess, Jac J. Varco, Eugene K. Blythe

This study investigated how spring nitrogen (N) application affects N uptake and growth performance in tall bearded (TB) iris ‘Immortality’ (Iris germanica L.). Container-grown iris plants were treated with 0, 5, 10, 15, or 20 mM N from 15NH415NO3 through fertigation using a modified Hoagland’s solution twice a week for 6 weeks in Spring 2013. Increasing N rate increased plant height, total plant dry weight (DW), and N content. Total N content was closely related to total plant DW. The allocation of N to different tissues followed a similar trend as the allocation of DW. In leaves, roots, and rhizomes, increasing N rate increased N uptake and decreased carbon (C) to N ratio (C/N ratio). Leaves were the major sink for N derived from fertilizer (NDFF). As N supply increased, DW accumulation in leaves increased, whereas DW accumulation in roots and rhizomes was unchanged. This indicates increasing N rate contributed more to leaf growth in spring. Nitrogen uptake efficiency (NupE) had a quadratic relationship with increasing N rate and was highest in the 10 mM N treatment, which indicates 10 mM was the optimal N rate for improving NupE in this study.

Journal of Petroleum Geology (2016)
Gao Zhiqian, Fan Tailiang, Ding Qunan, Hu Xiaolan

This paper presents outcrop, petrographic, geochemical, well log and seismic data which together characterise the third-order T78 unconformity located between the carbonate-dominated Lower Ordovician Penglaiba and Yingshan Formations in the Tarim Basin, NW China. Unconformities in Lower Palaeozoic carbonates in this basin are of increasing interest because major reserves of hydrocarbons have recently been discovered at the North Slope field (> 1000 × 106 brls oil and ∼ 3050× 108 m3 gas). The reservoir here consists of karstified Lower Ordovician carbonates bounded by a third-order unconformity. The T78 unconformity in Tarim Basin represents a short-term exposure surface (< 1 Ma) controlled both by sea-level changes and by palaeogeographic location within the basin, and the intensity of karstification varies laterally. The unconformity has had a major influence on porosity development in the underlying Penglaiba Formation carbonates. At two measured outcrop sections at the NW basin margin (Penglaiba and Shuinichang), dissolution porosity was observed in karstified and dolomitised carbonates below the T78 unconformity surface. A seismic profile shows the presence of reflection anomalies below the unconformity which are interpreted as karst-related palaeo-caverns. Geochemical data indicate that the T78 unconformity is associated with anomalies in stable isotope ratios and in heavy mineral and trace element profiles. Thus there are negative excursions in δ13C and δ18O ratios within the carbonate rocks immediately below the unconformity surface. Similarly, concentrations of major and trace elements such as Li, K, Ti, Rb, Th, Sr, V and Ni are significantly reduced in the underlying carbonates, while there is an anomalously high content of haematite-limonite.
Schlagworte: carbon , oxygen , geol , oilg , gashead

C, O, Sr and Nd isotope systematics of carbonates of Papaghni sub-basin, Andhra Pradesh, India: Implications for genesis of carbonate-hosted stratiform uranium mineralisation and geodynamic evolution of the Cuddapah basin
Lithos (2016)
Nurul Absar, B.M. Nizamudheen, Sminto Augustine, Shreyas Managave, S. Balakrishnan

The Cuddapah basin (CB) is one of a series of Proterozoic basins that overlie the Archaean cratons of India, and contains a unique stratiform carbonate-hosted uranium mineralisation. In the present work, we discuss stable (C, O) and radiogenic (Nd, Sr) isotope systematics of carbonates of the Papaghni sub-basin in order to understand uranium ore forming processes and geodynamic evolution of the CB. Uranium mineralised dolomites (UMDs) of the basal Vempalle Formation show a significantly lighter (~1.5‰) C-isotope signature compared to that of open-marine stromatolitic sub-tidal facies, suggesting input of isotopically lighter carbon through in situ remineralisation of organic matter (OM). This implies deposition in a hydrologically-restricted, redox-stratified lagoonal basin wherein exchange with open oceanic dissolved inorganic carbon (DIC) was limited. Persistent bottom water anoxia was created and maintained through consumption of dissolved oxygen (DO) by decaying OM produced in oxidised surface water zone. Significantly more radiogenic εNd(t) of UMD (−6.31±0.54) compared to that of Dharwar upper crust (−8.64±3.11) indicates that dissolved constituents did not originate from the Dharwar craton, rather were derived from more juvenile exotic sources — possibly from a continental arc. Dissolved uranyl ions (U+6) were introduced to the basin through fluvial run-off and were reduced to immobile uranous ions (U+4) at the redox interface resulting in precipitation of pitchblende and coffinite. Carbonate horizons of upper Vempalle Formation and Tadpatri Formation show progressively more radiogenic Nd isotope compositions signifying increased juvenile arc contribution to the Papaghni sub-basin through time, which is also corroborated by the presence of younger zircons (1923±22Ma) in Pulivendla quartzites. We propose that the Papaghni sub-basin opened as a back-arc extensional basin at ~2Ga as a result of westerly-directed subduction of oceanic crust beneath the eastern Indian continental margin. The ‘Papaghni’ back-arc basin eventually evolved to ‘upper Cuddapah’ foreland basin with collision of the Dharwar craton and Napier block of Antarctica at ~1.6Ga, possibly, during the final stage of amalgamation of the Columbia supercontinent.
Schlagworte: carbon , oxygen , geol , mulitcarb

Arboreal Legume Litter Nutrient Contribution to a Tropical Silvopasture
Agronomy Journal (2016)
Valéria Xavier de Oliveira Apolinário, José Carlos Batista Dubeux, Mário de Andrade Lira, Everardo V. S. B. Sampaio, Silvânia Oliveira de Amorim, Nalígia Gomes de Miranda e Silva, James P. Muir

Legumes contribute to pasture sustainability through symbiotic N2 fixation, which may increase primary productivity and animal performance in low-input systems. Litterfall is the main way of cycling nutrients from tree legumes. We quantified gliricidia [Gliricidia sepium (Jacq.) Kunth ex Walp.] and sabiá (Mimosa caesalpiniifolia Benth) litter deposition, along two 336-d cycles, in a signalgrass (Brachiaria decumbens Stapf.) pasture. Litterfall was produced throughout the year but concentrated in the dry season. Sabiá produced slightly greater (P < 0.0001) litterfall amounts in the two cycles (10,790 kg ha–1) than gliricidia (10,420 kg ha–1) but the overall average N concentration of gliricidia (21.5 g kg–1) was greater than that of sabiá (18.8 g kg–1). Nitrogen amounts cycled through the litter were greater for gliricidia in both cycles (105 and 109 kg N ha–1) than for sabiá (87 and 98 kg N ha–1). The proportions of litter N that were derived from the atmosphere by symbiotic fixation were similar (P ≥ 0.05) in both species (55%) and varied little along the two cycles. Lignin concentration, which influences decomposition, was similar in both species, averaging 238 and 214 g kg–1 in the two cycles for gliricidia and 233 and 246 g kg–1 for sabiá. Greater N concentration, lower C/N ratio and lower lignin concentration indicate that gliricidia litter may have a faster cycling rate than sabiá litter. Sabiá could be a more promising species for soil cover and protection because of its slower litter decomposition rate.
Schlagworte: carbon , nitrogen , food , soil , elem

One-century decline of mollusk diversity as consequence of accumulative anthropogenic disturbance in a tropical estuary (Cuban Archipelago)
Marine Pollution Bulletin (2016)
Maickel Armenteros, Misael Díaz-Asencio, Raúl Fernández-Garcés, Carlos Alonso Hernández, Yusmila Helguera-Pedraza, Yoelvis Bolaños-Alvarez, Claudia Agraz-Hernández, Joan-Albert Sanchez-Cabeza

In order to infer changes in sediments and mollusk assemblages for the last century, we used biogeochemical data from two 210Pb dated cores collected in Sagua La Grande estuary, Cuban Archipelago. We found evidences of cumulative anthropogenic disturbance during the last century, causing considerable depletion of mollusk assemblage diversity and enhancement of the dominance of deposit feeding species. The sequence of impacts assessed was i) eutrophication due to nutrient releases from urban settlements, ii) habitat alteration due to water channeling and damming, and iii) mercury pollution. These successive impacts caused a steady diversity depletion from ca. 70 mollusk species in 1900 to less than five in 2010. Only two species persisted in the estuary: Nuculana acuta and Finella dubia. Hurricanes did not impact the molluscan fauna in the long term. The effects of the anthropogenic impacts suggest that the resilience of this estuarine system is compromised.
Schlagworte: carbon , nitrogen , ocea , poll , elem

Source identification and distribution reveals the potential of the geochemical Antarctic sea ice proxy IPSO25
Nature Communications (2016)
S. T. Belt, L. Smik, T. A. Brown, J.-H. Kim, S. J. Rowland, C. S. Allen, J.-K. Gal, K.-H. Shin, J. I. Lee, K. W. R. Taylor, C. Parkinson, D. Cavalieri, J. Turner, S. Stammerjohn, R. Massom, D. Rind, D. Martinson, J. Turner, T. J. Bracegirdle, T. Phillips,

The presence of a di-unsaturated highly branched isoprenoid (HBI) lipid biomarker (diene II) in Southern Ocean sediments has previously been proposed as a proxy measure of palaeo Antarctic sea ice. Here we show that a source of diene II is the sympagic diatom Berkeleya adeliensis Medlin. Furthermore, the propensity for B. adeliensis to flourish in platelet ice is reflected by an offshore downward gradient in diene II concentration in >100 surface sediments from Antarctic coastal and near-coastal environments. Since platelet ice formation is strongly associated with super-cooled freshwater inflow, we further hypothesize that sedimentary diene II provides a potentially sensitive proxy indicator of landfast sea ice influenced by meltwater discharge from nearby glaciers and ice shelves, and re-examination of some previous diene II downcore records supports this hypothesis. The term IPSO25—Ice Proxy for the Southern Ocean with 25 carbon atoms—is proposed as a proxy name for diene II.
Schlagworte: geol , clim , gaschrom

Unraveling migratory connectivity of two European diving ducks: a stable isotope approach
European Journal of Wildlife Research (2016)
Alain Caizergues, Steven L. Van Wilgenburg, Keith A. Hobson

Quantifying the strength of migratory connectivity or the degree to which breeding and wintering populations are connected is crucial for conservation and management of migratory birds. Using stable hydrogen isotope ratios of secondary flight feathers (δ2Hf), we assessed the breeding origins/locations of 666 common pochards (Aythya ferina) and 190 tufted ducks (A. fuligula) captured in France during the 2005–2006 and 2008–2009 wintering seasons. Isotopic values of common pochards wintering on Grand-lieu Lake (western France) displayed a marked bimodal spatial distribution supportive of strong contributions of both northern (60–65° of latitude) and central European (45–55° of latitude) origins. According to the temporal distribution of δ2Hf values, the presence of common pochards of northern origin reached a maximum at the peak of the wintering season (December–January). In contrast, tufted duck did not display a clear bimodal pattern in δ2Hf, with individuals displaying a more northerly origin (60–70° of latitude), likely of Russian and Scandinavian origin. First-year individuals had more northern origins than adults, suggesting that either isotopic discrimination differed among age groups or, more probably, that some adults may undergo moult at latitudes lower than that of their breeding ground. Tufted ducks with northerly δ2Hf values were observed early in the season in individuals sampled in eastern France and late in the season in those sampled in western France. The effects of winter severity on the distribution of individuals over the wintering range were supported for the tufted duck with more northerly values recorded during harsh winters. Management implications of these results are discussed.
Schlagworte: hydrogen , ecol , elem

Temperature dependence of CO2 emissions rates and isotopic signature from a calcareous soil
Journal of Arid Environments (2016)
Tiphaine Chevallier, Laurent Cournac, Salwa Hamdi, Tahar Gallali, Martial Bernoux

In the context of climate change, studies have focused on the temperature dependence of soil CO2 emissions. Although calcareous soils cover over 30% of the earth's land surface, few studies have considered calcareous soils where soil inorganic carbon (SIC) makes the analysis of the C fluxes at the soil to air interface more complex. This study tested how temperature could affect the contributions of soil organic carbon (SOC) and SIC to the CO2 emitted from a calcareous soil. The soil pH, CO2 emissions and δ13C signatures of CO2 were measured after soil incubations at 4 temperatures (20 °C, 30 °C, 40 °C and 50 °C). The CO2 emissions and the δ13C signature of the emitted CO2 increased with temperature. The proportion of SIC-derived CO2 in these emissions seemed to be stimulated by temperature. Three processes were discussed: (1) isotopic fractionations, (2) temperature impacts on SIC- and SOC-derived CO2, and (3) isotope exchanges between SIC- and SOC-derived CO2. The use of δ13C signature analysis to determine the contribution of SIC and SOC to the total CO2 emissions from soil is not straightforward. An increase in the SIC signature of emitted CO2 does not directly imply an increase in SIC as a source of CO2.