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Mitigating Agricultural Emissions of Methane 总被引：7，自引：0，他引：7
A.R. Mosier J.M. Duxbury J.R. Freney O. Heinemeyer K. Minami D.E. Johnson 《Climatic change》1998,40(1):39-80
Agricultural crop and animal production systems are important sources and sinks for atmospheric methane (CH4). The major CH4 sources from this sector are ruminant animals, flooded rice fields, animal waste and biomass burning which total about one third of all global emissions. This paper discusses the factors that influence CH4 production and emission from these sources and the aerobic soil sink for atmospheric CH4 and assesses the magnitude of each source. Potential methods of mitigating CH4 emissions from the major sources could lead to improved crop and animal productivity. The global impact of using the mitigation options suggested could potentially decrease agricultural CH4 emissions by about 30%. 相似文献
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Widespread Plio-Pleistocene (2.43-0.06 Ma) tephra zones recognised in deep-sea cores from high latitudes (>60°) in the Southern Pacific Ocean were thought to have originated from calc-alkaline rhyolitic eruptions in New Zealand, some 5000 km distant. Electron microprobe analyses of the glasses reveal a wide diversity of alkalic felsic compositions, as well as minor components of basic and intermediate glasses, incompatible with a New Zealand Neogene source but similar to contemporaneous eruptives from the Antarctic region. Most tephra zones are trachytic; seven zones are peralkaline rhyolite. The rhyolitic zones represent a deep-sea record of widespread silicic eruptions from continental Antarctica, possibly Marie Byrd Land. The extent of these rhyolitic zones suggest a greater frequency of large explosive eruptions in Antarctica than previously documented. The coarse grain size of some of the shards (up to 3 mm), their great distance from the closest sources (>1600 km for some cores), and the presence of nonvolcanic ice-rafted debris indicate some of the glasses, especially the more basic compositions, may have been ice-rafted, contrary to previous suggestions of a fallout origin. 相似文献
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H. A. Wollenberg A. R. Smith D. F. Mosier S. Flexser M. Clark 《Pure and Applied Geophysics》1984,122(2-4):327-339
In the Long Valley caldera, where seismicity has continued essentially uninterrupted since mid-1980 and uplift is documented, samples of water from hot, warm, and cold springs have been collected since September, 1982, and their222Rn concentrations analyzed. Concurrently, rocks encompassing the hydrologic systems feeding the springs were analyzed for their radioelement contents, because their uranium is the ultimate source of the222Rn in the water.The222Rn concentration in the springs varies inversely with their temperature and specific conductance. High concentrations (1500 to 2500 picocuries per liter) occur in dilute cold springs on the margins of the caldera, while low contents (12 to 25 pCi/l) occur in hot to boiling springs. Springwater radon concentrations also correlate slightly with the uranium content of the encompassing rocks.A continuous monitoring system was installed in August, 1983, at a spring issuing from basalt, to provide hourly records of radon concentration. A gamma detector is submerged in a natural pool, and we have observed that the radioactivity measured in this manner is due almost entirely to the222Rn concentration of the water. Initial operation shows diurnal and semidiurnal variations in the222Rn concentration of the springwater that are ascribed to earth tides, suggesting that those variations are responding to small changes in stress in the rocks encompassing the hydrologic system. 相似文献
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The reason some VMS deposits contain more gold or other metals than others might be due to the influence of intrusions. A new approach examining this possibility is based on examining the information about many VMS deposits to test statistically if those with associated intrusions have significantly different grades or amounts of metals. A set of 632 VMS deposits with reported grades, tonnages, and information about the observed presence or absence of subvolcanic or plutonic intrusive bodies emplaced at or after VMS mineralization is statistically analyzed.Deposits with syn-mineralization or post-mineralization intrusions nearby have higher tonnages than deposits without reported intrusions, but the differences are not statistically significant. When both kinds of intrusions are reported, VMS deposit sizes are significantly higher than in the deposits without any intrusions. Gold, silver, zinc, lead, and copper average grades are not significantly different in the VMS deposits with nearby intrusions compared to deposits without regardless of relative age of intrusive. Only zinc and copper contents are significantly higher in VMS deposits with both kinds of intrusive reported. These differences in overall metal content are due to significantly larger deposit sizes of VMS deposits where both intrusive kinds are observed and reported, rather than any difference in metal grades. 相似文献
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Rainbow trout, Oncorhynchus mykiss, have been stocked in southwestern Australia since the 1930s. Trials at a research station maintained 868 tagged yearling O. mykiss (age: 14 months; standard length: 208 mm) for up to 375 days. The mean tag loss rate was 0.12% ± 0.040% per day for both single- and double-tagged fish. The tag loss rate was used to interpret tag return data from 7030 single-tagged yearlings stocked into three river systems in southwestern Australia. Recaptures indicated that O. mykiss survived into their second season in all rivers, with the maximum time at liberty of 21 months (longevity of at least 35 months). Upstream and downstream movements of O. mykiss increased with time, although 29% of recaptures were reported from the stocking site. Significantly more O. mykiss were recaptured from the Warren River, and differences remained even when corrected for stocking levels; angler effort had a marginal effect on return rates. Higher return rates from the Warren River may be due to availability of suitable habitat (stream cover, cooler water) for O. mykiss. Results allow the stocking regime to be reviewed to improve fishery performance. 相似文献
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Molecular data have shown that jellyfishes are more geographically restricted and evolutionarily divergent than previously thought. We examined genetic variation and divergence within the meroplanktonic barrel jellyfish Rhizostoma pulmo in the Mediterranean Sea; specific sampling areas were the northern Adriatic, western Mediterranean and Tunisian coast. A total of 19 sampling sites and 68 sequences of the mtDNA cytochrome c oxidase subunit I (COI) gene were used. Of the 68 COI sequences, 45 were newly collected specimens which originated from nine sampling sites along the Tunisian coast. A total of 24 haplotypes were obtained and the specimens sampled were characterised by relatively high levels of haplotype diversity (h = 0.866) and low levels of nucleotide diversity (π = 0.004). Haplotype network analysis showed the presence of three distinct phylogenetic lineages (populations), with separate geographic ranges in the northern Adriatic, western Mediterranean and Tunisian coast. The observed genetic differentiation between these three lineages was supported by the presence of significant genetic differentiation between the 19 populations (FST = 0.757, p < 0.001). The high level of genetic differentiation detected in the barrel jellyfish investigated could be attributed to either intrinsic and/or extrinsic barriers to genetic exchange between different populations that may have adapted to different environmental conditions. 相似文献
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ANDREAS DEHNERT FRANK PREUSSER JAN D. KRAMERS NAKI AKÇAR PETER W. KUBIK REGINA REBER CHRISTIAN SCHLÜCHTER 《Boreas: An International Journal of Quaternary Research》2010,39(3):620-632
Dehnert, A., Preusser, F., Kramers, J. D., Akçar, N., Kubik, P. W., Reber, R. & Schlüchter, C. 2010: A multi‐dating approach applied to proglacial sediments attributed to the Most Extensive Glaciation of the Swiss Alps. Boreas, Vol. 39, pp. 620–632. 10.1111/j.1502‐3885.2010.00146.x. ISSN 0300‐9483. The number and the timing of Quaternary glaciations of the Alps are poorly constrained and, in particular, the age of the Most Extensive Glaciation (MEG) in Switzerland remains controversial. This ice advance has previously been tentatively correlated with the Riss Glaciation of the classical alpine stratigraphy and with Marine Isotope Stage (MIS) 6 (186–127 ka). An alternative interpretation, based on pollen analysis and stratigraphic correlations, places the MEG further back in the Quaternary, with an age equivalent to MIS 12 (474–427 ka), or even older. To re‐evaluate this issue in the Swiss glaciation history, a multi‐dating approach was applied to proglacial deltaic ‘Höhenschotter’ deposits in locations outside the ice extent of the Last Glacial Maximum. Results of U/Th and luminescence dating suggest a correlation of the investigated deposits with MIS 6 and hence with the Riss Glaciation. Cosmogenic burial dating suffered from large measurement uncertainties and unusually high 26Al/10Be ratios and did not provide robust age estimates. 相似文献
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Two surface‐sediment sampling campaigns were carried out in November and December 2003, before and after a strong swell event, in the back‐reef area of a microtidal fringing reef on the western coast of La Reunion, Indian Ocean. The spatial distributions of the mean grain size, sorting and skewness parameters are determined, and grain‐size trend analysis is performed to estimate the main sediment transport pathways in the reef. The results of this analysis are compared with hydrodynamic records obtained in the same reef area during fair weather conditions and during swell events. Sediment dynamics inferred from the hydrodynamic records show that significant sediment erosion and transport occur only during swell events and under strongly agitated sea states. Under normal wave conditions, there is a potential for onshore sediment transport from the reef‐flat to the back‐reef, but this transport is episodic and occurs principally during high‐tide stages. Sediment transport trends revealed by the grain‐size trend analysis method show onshore and alongshore low‐energy transport processes that are in agreement with the hydrodynamic records. The grain‐size trend analysis method also provides evidence of an offshore high‐energy transport trend that could be interpreted as a real physical process associated with return flow from the shore to the reef. The impact of swell on the reef sediment dynamics is clearly demonstrated by onshore and alongshore transport. Considering different combinations of the vector transport trends computed through the grain‐size trend analysis approach, more realistic and pertinent results can be obtained by applying an exclusive OR operation (XOR case) on the vectors. The main results presented here highlight a trend towards the accumulation of carbonate sands in the back‐reef area of the fringing reef. These sediments can only be resuspended during extreme events such as storms or tropical cyclones. 相似文献