Heavy metals in the benthic foraminifera from the coastal lagoons,Red Sea,Egypt: indicators of anthropogenic impact on environment (case study)     

Hashem Abbas Madkour  Mohamed Youssef Ali 《Environmental Geology》2009,58(3):543-553

Concentrations of Fe, Mn, Zn, Cu, Pb, Ni, and Cd were measured in several species and genera of Recent benthic foraminifera from three coastal lagoons, namely Abu-Shaar, Umm al-Huwaytat, and Marsa Shuni lagoons located along the Egyptian Red Sea coast. Spatially significant differences in the metal concentrations of benthic foraminifera were recorded among different sites. However, some foraminiferal species display deformation in their coiling, general shape of chambers and the apertures. Abu-Shaar and Umm al-Huwaytat lagoons are virtually influenced by anthropogenic activities while Marsa Shuni lagoon is affected by natural inputs. Benthic foraminifer shows high concentrations of Fe and Mn, especially in Umm al-Huwaytat lagoon. Foraminiferal black tests support this result and reflect selectivity for iron absorption. Among the metals analyzed, Cd, Pb, and Cu showed significant high concentrations in benthic foraminifera at the study areas. The anthropogenic activities and natural inputs are responsible for the abnormalities in benthic foraminifera. Therefore, benthic foraminifera can be used as a good indicator of the environmental changes.  相似文献   

软土地区超长抗拔桩成桩选型研究     

安景波  赵思远  邓志辉 《岩土工程技术》2009,23(6):284-287

对软土地区长抗拔桩中常用的常规直桩、扩底桩、注浆直桩的承载力性状进行了比较分析,研究了不同桩型的荷载传递规律和承载力提高机理,并引出其荷载一位移的理论计算公式,认为抗拔桩存在“有效桩长”。通过对某沿海城市不同超长抗拔桩的现场抗拔试验,分析比较了各种桩型在30mm上拔位移控制值下的单桩承载力和桩侧摩阻力分布规律,认为超过“有效桩长”的设计是不经济的,注浆直桩可以提高安全系数,宜优先选用注浆直桩。  相似文献   

Chemistry of Zircon in Rare Metal Granitoids and Associated Rocks, Eastern Desert, Egypt     

Hamdy M. Abdalla    Hossam Helba    Hiroharu Matsueda 《Resource Geology》2009,59(1):51-68

Typological study, including paragenic, morphological, textural, and chemical characteristics of zircon from nine rare metal granitic stocks and associated greisens, was carried out in order to identify the metallogenic processes of their host granitoids. The investigated zircon‐bearing granitoids and type occurrences can be categorized into magmatically and metasomatically specialized types. The magmatic type includes: (i) peralkaline, Zr + Nb‐enriched, A₁‐granite (e.g. Um Hibal); (ii) metaluminous, Nb + Zr + Y‐enriched, A₂‐type alkali granite (e.g. Hawashia and Ineigi); and (iii) peraluminous, Ta ≥ Nb + Sn + Be ± W‐enriched, Li‐albite granite (e.g. Nuweibi, Igla and Abu Dabbab). The metasomatized granites are Nb>>Ta + Sn + Zr + Y + U ± Be ± W‐enriched and hydrothermally altered alkali feldspar granite (i.e. apogranite; e.g. Um Ara, Abu Rusheid, and Um Naggat). Zircon of peralkaline granite is characteristically equant with well‐developed pyramidal faces and short prisms (i.e. pseudo‐octahedral form) with length/width ratios in the range of 2:1–1:1. It is of Zr_0.990Hf_0.007SiO₄ composition and is associated with hypersolvus assemblage consisting of alkali feldspar, quartz, aegirine and minor reibeckite. Zircon of metaluminous alkali granites is of Zr_0.99Hf_0.01SiO₄ composition and is associated with sub‐ to transolvus assemblage of K‐feldspar, quartz, plagioclase and annite‐siderophyllite mica. It is prismatic with length/width ratios in the range of 5:1–3:1, doubly terminated with small pyramidal faces. Compositionally, zircon of Li‐albite granite ranges between Zr_0.925Hf_0.075SiO₄ and Zr_0.705Hf_0.295SiO₄. It is idiomorphic with a simple combination of prism and bipyramidal terminations with a length/width ratio of 3:1–2:1. This zircon commonly exhibits a normal zoning with rims consistently higher in Hf than cores. The higher Hf content, of this zircon coupled with its association with topaz, tantalite and lithian micas (e.g. zinnwaldite and Li‐white mica), indicates a higher solubility of Hf‐fluoride complexes and their more stabilized state at lower temperature in Li‐ and F‐rich sodic melts. Zircon of apogranite association ranges in composition between Zr_0.967Hf_0.013SiO₄ in the lower unaltered alkali feldspar granite zone and Zr_0.805Hf_0.064(Y, U, Th, heavy rare‐earth elements) [HREE])_0.125SiO₄ in the apical metasomatized (i.e. microclinized, albitized, and greisenized) apogranite zones. This compositional change appears to reflect a roofward increasing in μ_KF, μ_NaF, and μ_HF of the exsolved fluids. Columbite, xenotime, thorite, cassiterite, beryl and fluorite are common associates of this zircon. This zircon is of bipyramidal to typical octahedral form with complete absence of prism concurrently with conspicuous development of pyramid, thus the zircon crystals have a length/width ratio of 1:1–0.5:1. The neoformed metasomatic zircon commonly exhibits either normal or reverse zoning with rims consistently different in Hf, U, Y, and HREE than cores, reflecting disequilibrium conditions (e.g. sudden change in P, T, salinity, and pH) between the growing crystals and the exsolved fluids.  相似文献   

Numerical simulation of the critical scale of oasis maintenance and development in the arid regions of Northwest China   总被引：3，自引：0，他引：3  

GAO Yanhong  CHEN Yuchun  Lü Shihua 《大气科学进展》2004,21(1):113-124

Oasis is a special geographic landscape among the vast desert/Gobi in Northwest China (NWC). The surface sensitive heat flux and latent heat flux at Zhangye Oasis during 1 to 11 August 1991 are simulated using the NCAR nonhydrostatic mesoscale model MM5 Version 3. The horizontal grid resolution is set as 1km. By comparing the simulation results with HEIFE observations, it is proved that the model can be used to simulate the surface energy and water mass exchange of arid and semiarid regions in NWC.Based on the above results, the influence of different oasis scales on the local atmospheric field near the ground surface, and the critical scale of oasis maintenance, in NWC are studied dynamically. The following conclusion is obtained: the local thermal circulation between the oasis and the desert/Gobi is formed in the oasis downstream if the oasis scale is larger than 4 km. This local thermal circulation between the oasis and the desert adjacent to the oasis helps to conserve water vapor over the oasis. At the sametime, it transfers the abundant water vapor from the oasis into the desert/Gobi near to the oasis to supply relatively plentiful water vapor for desert crops to grow on the fringe of the oasis. So, it is advantageous for oasis extension. However, if the scale of the oasis is smaller than 4 km, it is not easy for the local thermal circulation between the oasis and the desert/Gobi to take shape. This study provides a new standpoint for oasis maintenance and development.  相似文献   

厦门西港沉积环境变化及重金属的污染累积   总被引：1，自引：0，他引：1  

李桂海  曹志敏  蓝东兆  许江  关伟 《地球科学》2008,33(1):124-130

通过测定柱状沉积物中的重金属、有机碳和硫化物含量, 结合沉积物粒度分析及现代沉积速率, 重现了厦门西港近70a的沉积环境变化及重金属的污染历史, 探讨了沉积环境对重金属累积过程的影响.结果表明, 厦门西港污染指示元素为Cu, Zn, Pb, As, 富集程度依次为As > Cu > Zn > Pb, 元素Cr, Cd和Hg在研究海域内没有富集现象.综观70a来, 厦门西港沉积物组成变化较大, 沉积环境变化明显, 重金属含量的垂向变化特征与当时的水动力、沉积环境变化紧密相关.研究表明, 沉积物来源越稳定, 沉积物粒径越小, 分选性越好, 则沉积物中重金属含量越高; 同时, 各层位的绝大部分重金属与有机碳和硫化物呈显著正相关关系.   相似文献   

基于剪胀效应的桩底嵌岩锚杆荷载传递分析法   总被引：2，自引：0，他引：2  

赵明华  龙照  邹新军 《岩土力学》2008,29(7):1938-1942

针对基桩竖向承载力自锚法测试体系中桩底嵌岩锚杆的受力特点,基于锚固体-岩石作用的剪胀机制,建立了适合于桩底嵌岩锚杆的荷载传递函数,并由此推导出锚杆临界锚固长度的解析解。然后,基于该解答探讨了桩底嵌岩锚杆锚固段摩阻力沿锚固长度的分布规律及其影响,并提出可近似考虑各因素综合影响效果的? 值。工程算例对比分析结果表明,其计算结果与实测值吻合较好。  相似文献   

K0固结软黏土的临界不排水强度研究     

王秋生 《岩土力学》2008,29(12):3179-3185

临界状态土力学中孔隙比-平均有效压力 坐标下 压缩线和临界状态线可以简化为平行的直线,倾斜的椭圆屈服面是能够考虑土体各向异性的数学表达最简单的屈服面形式。结合临界状态土力学理论和倾斜的椭圆屈服面方程,给出了轴对称和平面应变情况下 固结软黏土的临界不排水强度比的解析式,通过一些试验数据对这些解析式进行了验证,最后给出了便于工程应用的临界不排水强度比关于有效内摩擦角的简易表达式。  相似文献   

爆破振动作用下城门洞形衬砌的临界振速研究   总被引：3，自引：0，他引：3  

易长平  卢文波  张建华  张爱平 《岩土力学》2008,29(8):2203-2208

根据应力波理论,采用复变函数方法,对爆破振动作用下城门洞形衬砌的应力和振速分布进行了研究,进而求解了入射波入射角度不同时衬砌的临界振速。首先将城门洞形衬砌映射为一个内径为1,外径大于1的圆环,再求解稳态P波作用下圆环的动态响应;计算结果表明：入射波的入射方向对于城门洞形衬砌的临界振速有较大的影响,入射角度为90?时,衬砌的临界振速最大,入射角为0?时次之,入射角为270?时最小。  相似文献   

地震作用下加筋土坡临界高度研究   总被引：1，自引：0，他引：1  

林永亮  李新星 《岩土力学》2008,29(Z1):394-398

以塑性极限分析理论为基础,假定破裂面为对数螺旋面,考虑加筋机理和地震力的作用,提出了加筋土坡临界高度的计算模型。应用该计算模型,不仅能考虑地震力的作用,而且能考虑不同的加筋机理对临界高度的影响。通过与前人静力试验结果的对比发现,基于复合加筋机理得到的临界高度比基于单一加筋机理得到的临界高度要偏大,且更接近于实测值,表明了该理论及其求解方法的有效性和可靠性。通过对地震作用下加筋边坡的临界高度分析表明,地震力作用下摩擦加筋机理对临界高度基本没有影响,主要是准粘聚力机理在起作用。该方法可对加筋边坡临界高度的设计提供有益的指导和参考。  相似文献   

大降雨型滑坡临界雨量及潜势预报模型研究   总被引：8，自引：3，他引：5  

王仁乔  周月华王丽 谌伟 《气象科技》2005,33(4):311-313

通过对湖北省1975～2002年发生的194次滑坡个例进行分析发现：滑坡时间主要发生在5-8月,占全年总次数的80％左右,与多年月平均雨量分布比较一致;滑坡区域主要位于湖北西部山地,高频中心在三峡库区;滑坡与前期降雨尤其是大降雨关系非常密切,大降雨型滑坡占滑坡总次数的63．1％。利用实效雨量计算方法,确定了大降雨型滑坡临界雨量,以此为依据建立了潜势预报模型。  相似文献