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排序方式: 共有226条查询结果,搜索用时 15 毫秒
221.
Huguette C. Emvoutou Béatrice Ketchemen Tandia Suzanne Ngo Boum Nkot Rodrigue C. S. Ebonji Yvon B. Nlend Georges E. Ekodeck Christine Stumpp Piotr Maloszewski Serigne Faye 《Environmental Earth Sciences》2018,77(5):219
Douala city, located in the littoral province of Cameroon, receives abundant rainfall quantities due to its geographical position in the Gulf of Guinea and bears considerable surface water and groundwater resources. Due to socioeconomic development and rapid demographic growth in the city and its consequences of unplanned urbanization and improper sanitation system, these water resources are poorly protected and managed. Streams in the Wouri watershed receive large amounts of wastewater discharge, and hundreds of boreholes have been drilled into the aquifer system without any management plan. A detailed hydrodynamic and hydrogeochemistry study in Douala town and its environs was conducted to get a better insight into the groundwater system functioning in order to provide information for the sustainable management and protection of the groundwater resource. Two field campaigns were carried out with 187 samples collected and analyzed for major ions, stable isotopes (18O, 2H), and tritium 3H. The results of the sampling have shown that the weathering of silicate minerals is the dominant geochemical process affecting groundwater chemistry in this system. However, acid rainfall in the humid climate has also caused carbonate mineral dissolution, amorphous silica deposition, and ion exchange reactions to occur in aquifers in the region. The various water types identified were categorized into four major clusters C1 to C4, based on the major ion composition and the local hydrogeological conditions. Environmental isotope data reveal that modern-to-submodern waters occur in the phreatic Quaternary/Mio-Pliocene and Oligocene/Upper Eocene aquifers, respectively. These results corroborate with the conceptual model built where modern groundwater types indicated silicate mineral weathering and calcite dissolution (C1 and C2), whereas submodern groundwater mostly showed silica deposition, ion exchange, and, to a lesser extent, carbonate mineral dissolution (C3 and C4). This improved understanding of the aquifer system functioning is essential to provide a reasonable basis for effective control measures and sustainable water management. 相似文献
222.
Philippe Blanc Hélène Gailhanou Jacques Rogez Georges Mikaelian Hitoshi Kawaji Fabienne Warmont Stéphane Gaboreau Sylvain Grangeon Jean-Marc Grenèche Philippe Vieillard Claire I. Fialips Eric Giffaut Eric C. Gaucher F. Claret 《Physics and Chemistry of Minerals》2014,41(8):603-615
In the context of the deep waste disposal, we have investigated the respective stabilities of two iron-bearing clay minerals: berthierine ISGS from Illinois [USA; (Al0.975FeIII0.182FeII1.422Mg0.157Li0.035Mn0.002)(Si1.332Al0.668)O5(OH)4] and chlorite CCa-2 from Flagstaff Hill, California [USA; (Si2.633Al1.367)(Al1.116FeIII0.215Mg2.952FeII1.712Mn0.012Ca0.011)O10(OH)8]. For berthierine, the complete thermodynamic dataset was determined at 1 bar and from 2 to 310 K, using calorimetric methods. The standard enthalpies of formation were obtained by solution-reaction calorimetry at 298.15 K, and the heat capacities were measured by heat-pulse calorimetry. For chlorite, the standard enthalpy of formation is measured by solution-reaction calorimetry at 298.15 K. This is completing the entropy and heat capacity obtained previously by Gailhanou et al. (Geochim Cosmochim Acta 73:4738–4749, 2009) between 2 and 520 K, by using low-temperature adiabatic calorimetry and differential scanning calorimetry. For both minerals, the standard entropies and the Gibbs free energies of formation at 298.15 K were then calculated. An assessment of the measured properties could be carried out with respect to literature data. Eventually, the thermodynamic dataset allowed realizing theoretical calculations concerning the berthierine to chlorite transition. The latter showed that, from a thermodynamic viewpoint, the main factor controlling this transition is probably the composition of the berthierine and chlorite minerals and the nature of the secondary minerals rather than temperature. 相似文献
223.
Influence of bioturbation by the polychaete Nereis diversicolor on the structure of bacterial communities in oil contaminated coastal sediments 总被引:1,自引:0,他引:1
Cuny P Miralles G Cornet-Barthaux V Acquaviva M Stora G Grossi V Gilbert F 《Marine pollution bulletin》2007,54(4):452-459
Patterns of change in the structure of bacterial communities monitored by ribosomal intergenic spacer analysis (RISA) in oil contaminated sediments inhabited or not by the marine polychaete Nereis diversicolor were studied during 45 days under laboratory conditions. Results supported by principal component analysis showed a marked response of the bacterial communities to the oil contamination and to the presence of N. diversicolor. Phylogenetic affiliation of specific RISA bands showed that, in the contaminated sediments, the presence of the marine polychaetes favoured the development of bacteria which may play an active role in natural bioremediation processes of oil polluted environments. 相似文献
224.
Christian Ruby Mustapha Abdelmoula Aurélien Renard Georges Ona-Nguema Jean-Marie R. Génin 《Geochimica et cosmochimica acta》2010,74(3):953-966
FeII-III hydroxycarbonate green rust GR(CO32−), FeII4 FeIII2 (OH)12 CO3·3H2O, is oxidized in aqueous solutions with varying reaction kinetics. Rapid oxidation with either H2O2 or dissolved oxygen under neutral and alkaline conditions leads to the formation of ferric oxyhydroxycarbonate GR(CO32−)∗, FeIII6 O12 H8 CO3·3H2O, via a solid-state reaction. By decreasing the flow of oxygen bubbled in the solution, goethite α-FeOOH forms by dissolution-precipitation mechanism whereas a mixture of non-stoichiometric magnetite Fe(3−x)O4 and goethite is observed for lower oxidation rates. The intermediate FeII-III oxyhydroxycarbonate of formula FeII6(1−x) FeIII6x O12 H2(7−3x) CO3·3H2O, i.e. GR(x)∗ for which x ? [1/3, 1], is the synthetic compound that is homologous to the fougerite mineral present in hydromorphic gleysol; in situ oxidation accounts for the variation of ferric molar fraction x = [FeIII]/{[FeII]+[FeIII]} observed in the field as a function of depth and season but limited to the range [1/3, 2/3]. The domain of stability for partially oxidized green rust is observed in the Eh-pH Pourbaix diagrams if thermodynamic properties of GR(x)∗ is compared with those of lepidocrocite, γ-FeOOH, and goethite, α-FeOOH. Electrochemical equilibrium between GR(x)∗ and FeII in solution corresponds to Eh-pH conditions close to those measured in the field. Therefore, the reductive dissolution of GR(x)∗ can explain the relatively large concentration of FeII measured in aqueous medium of hydromorphic soils containing fougerite. 相似文献
225.
The oceanic bottom boundary-layer model of Weatherly and Martin (1978) is used to study the vertical structure of the eddy diffusivity in a region with initially imposed bottom mixed-layer thickness. Because of near-bottom oceanic features, such as the Cold Filament (Weatherly and Kelley, 1982) and cold eddies (Ebbesmeyer et al., 1988), the bottom mixed-layer thickness is not the sole result of boundary-layer mixing; this is the incentive for this study. For a given geostrophic forcing and imposed mixed-layer depth, a formula for the eddy diffusion coefficient is found. This parameterization of the eddy diffusivity improves previous formulas used in oceanic and atmospheric boundary layers in the upper portion of the boundary layer. A simple model of a Cold Filament-like feature demonstrates the structure of the bottom boundary layer, the bottom mixed layer, and the relation between the two. A lens-like cross section of cold blobs, often used in analytical models, may be inappropriate if bottom friction is important. 相似文献
226.
阿尔金断裂带附近地壳结构的接收函数成像及其地球动力学意义 总被引:1,自引:1,他引:1
利用中法1995年布设在跨过阿尔金断裂剖面上的18个流动三分量地震台站记录到的近5个月的天然地震记录,经筛选得到533个高质量接收函数。通过速度分析和接收函数成像处理,得到了阿尔金断裂附近地壳结构的清晰图像。塔里木盆地的Moho界面非常清楚,近水平地位于~44km深度上。该界面以低缓的角度一直向南延伸到了阿尔金断裂附近的~70km的深度。阿尔金断裂以南柴达木盆地下面的Moho界面也十分清楚,近水平地位于~55km的深度上,在阿尔金断裂附近存在向上挠曲,并抬升到了~45km的深度上。在阿尔金断裂下方,Moho界面存在~15km的错断。塔里木盆地Moho之下还存在另一个震相,我们解释为沉积层多次波与可能来自Hales间断面转换波的复合震相。接收函数成像结果表明阿尔金断裂是一个超壳的岩石圈断裂,具有比较直立的产状和很狭窄的剪切变形带。根据这些结果,我们推测塔里木的下地壳可能要比柴达木的下地壳更硬,柴达木地壳增厚的原因可以部分归结于它有一个相对弱的下地壳,青藏高原隆升没有扩展到塔里木盆地是因为塔里木盆地具有更刚性的下地壳和岩石圈地幔。高原北部地壳变形应该是所谓青藏高原隆升的“硬”变形模式(Tapponnieretal... 相似文献