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Kinetics of arsenopyrite oxidative dissolution by oxygen 总被引：1，自引：0，他引：1
We used a mixed flow reactor system to determine the rate and infer a mechanism for arsenopyrite (FeAsS) oxidation by dissolved oxygen (DO) at 25 °C and circumneutral pH. Results indicate that under circumneutral pH (6.3-6.7), the rate of arsenopyrite oxidation, 10−10.14±0.03 mol m−2 s−1, is essentially independent of DO over the geologically significant range of 0.3-17 mg L−1. Arsenic and sulfur are released from arsenopyrite in an approximate 1:1 molar ratio, suggesting that oxidative dissolution by oxygen under circumneutral pH is congruent. Slower rates of iron release from the reactor indicate that some of the iron is lost from the effluent by oxidation to Fe(III) which subsequently hydrolyzes and precipitates. Using the electrochemical cell model for understanding sulfide oxidation, our results suggest that the rate-determining step in arsenopyrite oxidation is the reduction of water at the anodic site rather than the transfer of electrons from the cathodic site to oxygen as has been suggested for other sulfide minerals such as pyrite. 相似文献
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Patrick Forest 《Geoforum》2012,43(1):14-24
Water has been the source of many controversies in Canada. While the extensive literature on international water transfers has focused on the continental schemes aimed at diverting and transferring Arctic water southward, little has been written about the only existing bulk water transfers between borderland communities located along the Canadian and American border. This article introduces the concept of transboundary inter-local water supplies, and documents their spatialities, origins, modes of governance, and characteristics. For decades, these communities have engaged with the international realm to address water scarcity issues and the high costs associated with water infrastructure. Although small in scale, they constitute a different model of Canadian–American cross-boundary water cooperation. I argue, however, that these transfers are scale dependent; they cannot be scaled up because they are only possible because they are embedded within the local. Although such partnerships have often evolved informally, within grey areas of water governance, they have nonetheless been effective in providing freshwater to local border communities. 相似文献
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中国西北地区石羊河流域农业生态系统能值评价 总被引：1，自引：0，他引：1
通过能值方法分析了石羊河流域农业生态系统的资源环境基础和经济特征。结果表明,石羊河流域中下游凉州区和民勤绿洲的能值总投入呈降低趋势,能值投资率都偏高,生产成本较大;能值产出率低,对购买能值的利用效率不高;但能值自给率有所提高;环境载荷率高,农业生态环境所受压力较大,系统可持续发展指标表明两个绿洲经济系统极为不发达,属于消费型经济系统,并且人均可用能值和能值密度都呈降低趋势。 相似文献
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Alexandre Forest Jean-Éric Tremblay Yves Gratton Johannie Martin Jonathan Gagnon Gérald Darnis Makoto Sampei Louis Fortier Mathieu Ardyna Michel Gosselin Hiroshi Hattori Dan Nguyen Roxane Maranger Dolors Vaqué Cèlia Marrasé Carlos Pedrós-Alió Amélie Sallon Christine Michel Colleen Kellogg Jody Deming Elizabeth Shadwick Helmuth Thomas Heike Link Philippe Archambault Dieter Piepenburg 《Progress in Oceanography》2011,91(4):410-436
Major pathways of biogenic carbon (C) flow are resolved for the planktonic food web of the flaw lead polynya system of the Amundsen Gulf (southeast Beaufort Sea, Arctic Ocean) in spring-summer 2008. This period was relevant to study the effect of climate change on Arctic marine ecosystems as it was characterized by unusually low ice cover and warm sea surface temperature. Our synthesis relied on a mass balance estimate of gross primary production (GPP) of 52.5 ± 12.5 g C m−2 calculated using the drawdown of nitrate and dissolved inorganic C, and a seasonal f-ratio of 0.64. Based on chlorophyll a biomass, we estimated that GPP was dominated by phytoplankton (93.6%) over ice algae (6.4%) and by large cells (>5 μm, 67.6%) over small cells (<5 μm, 32.4%). Ancillary in situ data on bacterial production, zooplankton biomass and respiration, herbivory, bacterivory, vertical particle fluxes, pools of particulate and dissolved organic carbon (POC, DOC), net community production (NCP), as well as selected variables from the literature were used to evaluate the fate of size-fractionated GPP in the ecosystem. The structure and functioning of the planktonic food web was elucidated through inverse analysis using the mean GPP and the 95% confidence limits of every other field measurement as lower and upper constraints. The model computed a net primary production of 49.2 g C m−2, which was directly channeled toward dominant calanoid copepods (i.e. Calanus hyperboreus 20%, Calanus glacialis 10%, and Metridia longa 10%), other mesozooplankton (12%), microzooplankton (14%), detrital POC (18%), and DOC (16%). Bacteria required 29.9 g C m−2, a demand met entirely by the DOC derived from local biological activities. The ultimate C outflow comprised respiration fluxes (82% of the initial GPP), a small sedimentation (3%), and a modest residual C flow (15%) resulting from NCP, dilution and accumulation. The sinking C flux at the model limit depth (395 m) supplied 60% of the estimated benthic C demand (2.8 g C m−2), suggesting that the benthos relied partly on other C sources within the bottom boundary layer to fuel its activity. In summary, our results illustrate that the ongoing decline in Arctic sea ice promotes the growth of pelagic communities in the Amundsen Gulf, which benefited from a ∼80% increase in GPP in spring-summer 2008 when compared to 2004 – a year of average ice conditions and relatively low GPP. However, 53% of the secondary production was generated within the microbial food web, the net ecological efficiency of zooplankton populations was not particularly high (13.4%), and the quantity of biogenic C available for trophic export remained low (6.6 g C m−2). Hence it is unlikely that the increase in lower food web productivity, such as the one observed in our study, could support new harvestable fishery resources in the offshore Beaufort Sea domain. 相似文献
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福建省南平市林业技术开发试验示范区 《湿地科学与管理》2000,(1):36-40
<正> 南平林业技术开发试验示范区是在1990年5月南平市政府(原地区行署)与中国林科院签订了长期友好合作,共建技术开发试验区协议的基础上,于1992年8月林业部正式批准成立的。 南平林业技术开发试验示范区的范围为南平市所辖10个县(市、区)行政区域,总面积26031平方公里(263.18万公顷),总人口300万人。山地面积217.28万公顷,有林地 相似文献
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中国林业科学研究院林产化学工业研究所 《湿地科学与管理》2000,(3):19-23
<正> 1997年6月24日,中国林科院以科改字(1997)83号文批准我所深化科技体制改革试点方案。三年来,我们按照院批复指示精神,结合我所的具体实际,确立了以“市场为导向,效益为中心,科研为基础,产业为支柱” 相似文献
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Kosovichev A. G. Schou J. Scherrer P. H. Bogart R. S. Bush R. I. Hoeksema J. T. Aloise J. Bacon L. Burnette A. De Forest C. Giles P. M. Leibrand K. Nigam R. Rubin M. Scott K. Williams S. D. Basu Sarbani Christensen-dalsgaard J. DÄppen W. Duvall T. L. Howe R. Thompson M. J. Gough D. O. Sekii T. Toomre J. Tarbell T. D. Title A. M. Mathur D. Morrison M. Saba J. L. R. Wolfson C. J. Zayer I. Milford P. N. 《Solar physics》1997,170(1):43-61
The medium-l program of the Michelson Doppler Imager instrument on board SOHO provides continuous observations of oscillation modes of angular degree, l, from 0 to 300. The data for the program are partly processed on board because only about 3% of MDI observations can be transmitted continuously to the ground. The on-board data processing, the main component of which is Gaussian-weighted binning, has been optimized to reduce the negative influence of spatial aliasing of the high-degree oscillation modes. The data processing is completed in a data analysis pipeline at the SOI Stanford Support Center to determine the mean multiplet frequencies and splitting coefficients. The initial results show that the noise in the medium-l oscillation power spectrum is substantially lower than in ground-based measurements. This enables us to detect lower amplitude modes and, thus, to extend the range of measured mode frequencies. This is important for inferring the Sun's internal structure and rotation. The MDI observations also reveal the asymmetry of oscillation spectral lines. The line asymmetries agree with the theory of mode excitation by acoustic sources localized in the upper convective boundary layer. The sound-speed profile inferred from the mean frequencies gives evidence for a sharp variation at the edge of the energy-generating core. The results also confirm the previous finding by the GONG (Gough et al., 1996) that, in a thin layer just beneath the convection zone, helium appears to be less abundant than predicted by theory. Inverting the multiplet frequency splittings from MDI, we detect significant rotational shear in this thin layer. This layer is likely to be the place where the solar dynamo operates. In order to understand how the Sun works, it is extremely important to observe the evolution of this transition layer throughout the 11-year activity cycle. 相似文献
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<正> 衢州是浙江三大林区之一,人口238万,其中农业人口200万人,总面积88.47万公顷,林业用地62万公顷,有林地55.67万公顷,森林覆盖率65.4％。森林蓄积量1242万立方米,经济林10.67万公顷,竹林6万公顷,毛竹10700万株,林业生产在农业经济中占有重要的地位。 1985年衢州恢复地级市建制,辖四县一市一区。针对我市人口密度大,人均林地少, 相似文献
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