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651.
Methane Production, Emission and Possible Control Measures in the Rice Agriculture 总被引:19,自引:0,他引:19
Wang Mingxing Shangguan Xingjian Shen Renxing Wassmann Reiner Seiler Wolfgang 《大气科学进展》1993,10(3):307-314
In the rice field methane is produced in the soil layer with depths of 2-25 cm. The vertical profile of methane production rate in the paddy soil during the water covering period differs from that in the paddy soil in dry phase. Only a small part, about 30%. of the produced methane is emitted to the atmosphere through rice plant, air bubbles, and molecular diffusion. Therefore, the methane emission rate from the rice field depends not only on the methane production rate in the soil, but also on the transport efficiency of the rice plant, air bubble formation that in turn depends on the production rate, and molecular diffusion.Field measurements show that methane emission rates from a particular rice field have very large diurnal, seasonal and interannual variations, which are related to soil characteristics, water regime, farming procedure, local climate, and rice growing activities. The relationship between the methane emission rate and the above mentioned factors is very complicated. The emission rate 相似文献
652.
Bernd R. Schöne Nicholas A. Page David L. Rodland Jens Fiebig Sven Baier Samuli O. Helama Wolfgang Oschmann 《International Journal of Earth Sciences》2007,96(3):525-540
We present the results of sclerochronologically calibrated growth and stable isotope analyses of the freshwater bivalve Margaritifera falcata collected from an agricultural, suburban setting near Vancouver, BC. The oxygen isotope range of shell aragonite can be explained by the temperature range during the growing season, assuming the water δ 18O composition remained constant. However, shell growth is strongly influenced by local summer precipitation and potentially runoff of nutrient-rich stormwater. About 44% of the variability of annual shell growth can be explained by amounts of local summer (June–September) rainfall. Local winter precipitation and El Niño–Southern Oscillation (ENSO) strength during the preceding year exert a weak, but significant control on shell growth. In combination, summer and winter precipitation can explain up to 50% of the variability in annual shell growth. Spectral analyses substantiate the effect of precipitation on shell growth and demonstrate that shell growth and ENSO are coupled by precipitation. Common spectral density was found at periods of 6.5–9 years, particularly between 1985 and 2004. Higher frequency oscillation corresponding to periods of 3–5 years occurred during the early 1970s, early to mid 1980s, and later 1990s. These results suggest that skeletal records of bivalve mollusks provide suitable archives of ENSO-coupled precipitation in areas where other climate proxies such as tree-rings and speleothems may not be available. 相似文献
653.
Quantitative characterization of plastic deformation of zircon and geological implications 总被引:1,自引:1,他引:0
Steven M. Reddy Nicholas E. Timms Wolfgang Pantleon Patrick Trimby 《Contributions to Mineralogy and Petrology》2007,153(6):625-645
The deformation-related microstructure of an Indian Ocean zircon hosted in a gabbro deformed at amphibolite grade has been
quantified by electron backscatter diffraction. Orientation mapping reveals progressive variations in intragrain crystallographic
orientations that accommodate 20° of misorientation in the zircon crystal. These variations are manifested by discrete low-angle
(<4°) boundaries that separate domains recording no resolvable orientation variation. The progressive nature of orientation
change is documented by crystallographic pole figures which show systematic small circle distributions, and disorientation
axes associated with 0.5–4° disorientation angles, which lie parallel to rational low index crystallographic axes. In the
most distorted part of the grain (area A), this is the [100] crystal direction. A quaternion analysis of orientation correlations confirms the [100] rotation axis
inferred by stereographic inspection, and reveals subtle orientation variations related to the local boundary structure. Microstructural
characteristics and orientation data are consistent with the low-angle boundaries having a tilt boundary geometry with dislocation
line [100]. This tilt boundary is most likely to have formed by accumulation of edge dislocations associated with a 〈001〉{100}
slip system. Analysis of the energy associated with these dislocations suggest they are energetically more favorable than
TEM verified 〈010〉{100} slip. Analysis of minor boundaries in area A indicates deformation by either (001) edge, or [100](100) and [001](100) screw dislocations. In other parts of the grain, cross slip on (111), and (112) planes seems likely. These data provide the first detailed microstructural analysis of naturally deformed zircon
and indicate ductile crystal-plastic deformation of zircon by the formation and migration of dislocations into low-angle boundaries.
Minimum estimates of dislocation density in the low-angle boundaries are of the order of ∼3.1010 cm−2. This value is sufficiently high to have a marked effect on the geochemical behavior of zircon, via enhanced bulk diffusion
and increased dissolution rates. Therefore, crystal plasticity in zircon may have significant implications for the interpretation
of radiometric ages, isotopic discordance and trace element mobility during high-grade metamorphism and melting of the crust. 相似文献
654.
The concentrations of platinum-group elements (PGE), Co, Re,Au and Ag have been determined in the base-metal sulphide (BMS)of a section of the Merensky Reef. In addition we performeddetailed image analysis of the platinum-group minerals (PGM).The aims of the study were to establish: (1) whether the BMSare the principal host of these elements; (2) whether individualelements preferentially partition into a specific BMS; (3) whetherthe concentration of the elements varies with stratigraphy orlithology; (4) what is the proportion of PGE hosted by PGM;(5) whether the PGM and the PGE found in BMS could account forthe complete PGE budget of the whole-rocks. In all lithologies,most of the PGE (65 up to 85%) are hosted by PGM (essentiallyPtFe alloy, PtPd sulphide, PtPd bismuthotelluride).Lesser amounts of PGE occur in solid solution within the BMS.In most cases, the PGM occur at the contact between the BMSand silicates or oxides, or are included within the BMS. Pentlanditeis the principal BMS host of all of the PGE, except Pt, andcontains up to 600 ppm combined PGE. It is preferentially enrichedin Pd, Rh and Co. Pyrrhotite contains, Rh, Os, Ir and Ru, butexcludes both Pt and Pd. Chalcopyrite contains very little ofthe PGE, but does concentrate Ag and Cd. Platinum and Au donot partition into any of the BMS. Instead, they occur in theform of PGM and electrum. In the chromitite layers the whole-rockconcentrations of all the PGE except Pd are enriched by a factorof five relative to S, Ni, Cu and Au. This enrichment couldbe attributed to BMS in these layers being richer in PGE thanthe BMS in the silicate layers. However, the PGE content inthe BMS varies only slightly as a function of the stratigraphy.The BMS in the chromitites contain twice as much PGE as theBMS in the silicate rocks, but this is not sufficient to explainthe strong enrichment of PGE in the chromitites. In the lightof our results, we propose that the collection of the PGE occurredin two steps in the chromitites: some PGM formed before sulphidesaturation during chromitite layer formation. The remainingPGE were collected by an immiscible sulphide liquid that percolateddownward until it encountered the chromitite layers. In thesilicate rocks, PGE were collected by only the sulphide liquid. KEY WORDS: Merensky Reef; Rustenburg Platinum Mine; sulphide; platinum-group elements; image analysis; laser ablation ICP-MS 相似文献
655.
Yi-Zeng Yang Yan Wang Ri-Sheng Ye Shuang-Qing Li Jian-Feng He Wolfgang Siebel 《International Geology Review》2017,59(1):62-79
The relationship among magmatism, large-scale metallogenesis of Southeast China, and subduction of the Pacific plate has long been debated. The lower Yangtze River belt (LYRB) in the northeastern edge of Southeast China is characterized by intense late Mesozoic magmatism and associated polymetallic mineralization such as copper, gold, iron, tungsten, molybdenum, etc. The copper-related adakitic rocks (148–130 Ma) in this belt are the oldest episode of magmatism and intruded as small intermediate-acid intrusive bodies. The Huayuangong granitoids (HYG), located in the southern part of this belt, however, are copper-barren. Three granitoid samples from this pluton give zircon U–Pb ages of 126.4 ± 1.6 Ma, 125.9 ± 1.9 Ma, and 126.2 ± 1.2 Ma, respectively. The HYG has A-type affinity with metaluminous to weakly peraluminous, high FeOT/(FeOT+MgO) ratios, and high Zr+Nb+Ce+Yb contents. Meanwhile, 10 late Mesozoic mafic samples from the LYRB exhibit similar trace element characteristics to those of ‘continental arc andesite’ (CAA) and suggest an enriched lithospheric mantle source with depletion in high field strength elements (e.g. Nb, Ta, Zr, Hf, and Ti) and enrichment of large ion lithophile elements (e.g. Rb, Th, U, and Pb). Although the HYG exhibits similar Sr–Nd isotope composition with the mafic dikes, distinct whole-rock Pb isotope ratios imply that the granitoids and mafic magmas originated from heterogeneous mantle sources. Compared with coeval Baijuhuajian A-type rocks that are exposed along the Jiang–Shao fault of Southeast China, the HYG shows enriched Hf isotope ratios of zircon with εHf(t) values ranging from ?4.8 to ?11.1. In the Yb/Ta versus Y/Nb diagram, being different from the major asthenospheric mantle-origin Baijuhuajian pluton, a large range of and high Y/Nb ratios as well as high Zr contents of the HYG pluton suggest a magmatic source of mixing between the asthenospheric and enriched crustal component in the LYRB. Compared with early-stage copper-related adakitic rocks (148–130 Ma) with subduction-related affinities and high oxygen fugacity, the copper-barren HYG has with-plate A-type affinities and lower oxygen fugacity. Summarizing, the production of early-stage (i.e. subduction related) adakitic rocks followed by late-stage A-type granitoids in the LYRB is ascribed to the rollback of the Palaeo-Pacific plate beneath Southeast China and associated with asthenospheric upwelling and lithospheric thinning during the late Mesozoic era. 相似文献
656.
Distribution of Natural and Synthetic Estrogenic Steroid Hormones in Water Samples from Southern and Middle Germany Natural and synthetic hormones can reach surface waters via domestic sewage effluents. For drinking water production, bank filtration of river waters is a common procedure and hormone contaminations can potentially reach groundwater levels and drinking water sources. In order to analyse steroid hormones in the different aquatic compartments (raw sewage and effluent, surface water, groundwater, raw and drinking water) of South and Middle Germany, a sensitive analytical method was developed and employed to detect the natural steroid hormones estradiol (E2) and estrone and the synthetic estrogen ethinylestradiol (EE2). Samples which were taken in two subsequent series were subjected to clean‐up and enrichment procedure and subsequently analysed by HPLC‐MS. The limit of quantitation for the method was determined to be 0.05 to 0.5 ng/L, depending on the matrix. By treating the samples with glucuronidases/arylsulfatases, conjugates were amenable to analysis and the sum of conjugates and unconjugated steroids was calculated. In raw sewage, the median of the concentrations of the unconjugated steroids was 7 ng/L for EE2, 1.5 ng/L for E2, and 5.5 ng/L for estrone. After cleavage of conjugates, the medians of total steroids were 9.5 ng/L (EE2), 3 ng/L (E2), and 13 ng/l (estrone). Conjugates therefore contributed up to 50 % of the total steroid concentration in raw sewage. In treated effluents, the concentrations of steroids were much lower than in the raw sewage. The medians of free steroids were determined to be 0.3 ng/L for EE2, 0.2 ng/L for E2, and 2.5 ng/L for estrone. Overall the medians in the effluent were thus less than 10% of those in the influent. Conjugates still contributed significantly (40% and more) to the steroid concentrations (medians: EE2: 0.5 ng/L, E2: 0.8 ng/L, and estrone: 8 ng/L). 相似文献
657.
Wolfgang Glatzel Carsten Obach 《Monthly notices of the Royal Astronomical Society》1999,308(1):147-152
The hydrodynamic interaction of an accretion disc with its central object is reanalysed within the framework of the slim-disc approximation. Arguments are presented against an interpretation of the total angular momentum flux as an eigenvalue of the system. A simple intuitive consideration is provided, which shows that the central object may be in a state of stationary rotation even if the disc imposes the constraint of a finite angular momentum flux into it. It is argued that equilibrium rotation is characterized by vanishing viscous torque rather than by zero total angular momentum flux. As a consequence, the central object can be in a state of stationary rotation below the break-up limit, although its angular momentum increases. Despite accretion, even for positive total angular momentum flux and subcritical rotation, central objects are spun down within a considerable range of their parameters. The results are illustrated by application to FU Orionis systems. 相似文献
658.
We present the results of a re-examination of a [Ne II] line emission data cube (λ 12.8μm) and discuss the kinematic structure of the inner 3×4 pc of the Galaxy. The quality of [Ne II] as a tracer of ionized gas is examined by comparing it to radio data. A three-dimensional representation of the data cube allows us to disentangle features which are projected onto the same location on the sky. A model of gas streams in different planes is fitted to the data. We find that most of the material is located in a main plane which itself is defined by the inner edge of the Circum-Nuclear Disk in the Galactic Center. Finally, we present a possible three-dimensional model of the gas streams. 相似文献
659.
The Born approximation is applied to the modelling of the propagation of deeply turning longperiod body waves through heterogeneities in the lowermost mantle. We use an exact Green's function for a spherically symmetric earth model that also satisfies the appropriate boundary conditions at internal boundaries and the surface of the earth. The scattered displacement field is obtained by a numerical quadrature of the product of the Green's function, the exciting wavefield and structural perturbations. We study three examples: scattering of longperiod P waves from a plume rising from the coremantle boundary (CMB), generation of longperiod precursors to PKIKP by strong, localized scatterers at the CMB, and propagation of corediffracted P waves through largescale heterogeneities in D". The main results are as follows: (1) the signals scattered from a realistic plume are small with relative amplitudes of less than 2 per cent at a period of 20 s, rendering plume detection a fairly difficult task; (2) strong heterogeneities at the CMB of appropriate size may produce observable longperiod precursors to PKIKP in spite of the presence of a diffraction from the PKP B caustic; (3) corediffracted P waves ( P diff ) are sensitive to structure in D" far off the geometrical ray path and also far beyond the entry and exit points of the ray into and out of D"; sensitivity kernels exhibit ringshaped patterns of alternating sign reminiscent of Fresnel zones; (4) P diff also shows a nonnegligible sensitivity to shear wave velocity in D"; (5) down to periods of 40 s, the Born approximation is sufficiently accurate to allow waveform modelling of P diff through largescale heterogeneities in D" of up to 5 per cent. 相似文献
660.
The k-ε turbulence model which relates the eddy viscosity to turbulent kinetic energy, k, and to the rate of its dissipation, ε, and determines the distribution of these two quantities from modeled transport equations, is employed in calculating the vertical structure of wave-induced turbulent flows in two-dimensional estuaries. The empirical constants in this model are given the standard values cited in the literature and used successfully for calculating a large variety of steady flows; they are not tuned to the oscillating flows. The free surface elevation and the eddy-viscosity distribution are also calculated as a part of the solution. First, calculations performed for oscillatory laminar flows are compared with analytic solutions to ensure the proper performance of the numerical scheme. The turbulent flow in a laboratory-estuary model with one end closed, and in the Humber Estuary is simulated with the numerical model, and the results are compared with the corresponding flume and field measurements. The influence of frequency and roughness is thereby investigated. The results indicate that the time and space variation of the velocity field and the phase lag between the surface slope and the horizontal velocity can be predicted satisfactorily in wave-induced turbulent flows. 相似文献