Impacts of urban wastewater discharge on seagrass meadows (Zostera noltii)     

Susana Cabaço  Raquel MachásVasco Vieira  Rui Santos 《Estuarine, Coastal and Shelf Science》2008

The abiotic disturbance of urban wastewater discharge and its effects in the population structure, plant morphology, leaf nutrient content, epiphyte load and macroalgae abundance of Zostera noltii meadows were investigated in Ria Formosa coastal lagoon, southern Portugal using both univariate and multivariate analysis. Four sites were assessed, on a seasonal basis, along a gradient from a major Waste Water Treatment Works (WWTW) discharge to a main navigation channel. The wastewater discharge caused an evident environmental disturbance through the nutrient enrichment of the water and sediment, particularly of ammonium. Zostera noltii of the sites closest to the nutrient source showed higher leaf N content, clearly reflecting the nitrogen load. The anthropogenic nutrient enrichment resulted in higher biomass, and higher leaf and internode length, except for the meadow closest to the wastewater discharge (270 m). The high ammonium concentration (158–663 μM) in the water at this site resulted in the decrease of biomass, and both the leaf and internode length, suggesting a toxic effect on Z. noltii. The higher abundance of macroalgae and epiphytes found in the meadow closest to the nutrient source may also affect the species negatively. Shoot density was higher at the nutrient-undisturbed site. Two of the three abiotic processes revealed by Principal Component Analysis were clearly related to the WWTW discharge, a contrast between water column salinity and nutrient concentration and a sediment contrast between both porewater nutrients and temperature and redox potential. A multiple regression analysis showed that these abiotic processes had a significant effect on the biomass-density dynamics of meadows and on the overall size of Z. noltii plants, respectively. Results show that the wastewater discharge is an important source of environmental disturbance and nutrients availability in Ria Formosa lagoon affecting the population structure, morphology and N content of Z. noltii. This impact is spatially restricted to areas up to 600 m distant from the WWTW discharge, probably due to the high water renewal of the lagoon.  相似文献   

Episodic Quaternary volcanism in France and Germany     

David A. G. Nowell  M. Chris Jones  David M. Pyle 《第四纪科学杂志》2006,21(6):645-675

Intra‐plate volcanism in western Europe shows statistically significant episodicity during the Quaternary period. By comparing the known ages for eruptions in France and Germany, which are compiled here, with a composite oxygen isotope record, we have investigated the link between this episodic volcanism and the climate record over the last two million years. We show that increased volcanism between 415–400 ka and 17–5 ka correlates with warming phases at the end of the last Weichselian (Devensian) and earlier Elsterian (Anglian) glacial stages. The three significant caldera explosions in the eastern Eifel, Germany, are all associated with warming phases at the onset of interglacials. The growth and decay of nearby ice sheets suggest that surface changes in continental mass distribution during glacial Milankovich cycles could provide a mechanism for this correlation by means of the distal effects of flexural loading on the lithosphere. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

Analytical solutions for a three‐invariant Cam clay model subjected to drained loading histories     

Dunja Peri&#x; 《国际地质力学数值与分析法杂志》2006,30(5):363-387

Analytical solutions are derived for a three‐invariant Cam clay model subjected to proportional and circular drained loading histories. The solutions are presented for a specific volume, and volumetric and generalized shear strains. In the case of a proportional loading only straight effective stress paths are considered while in the case of a circular loading the maximum possible change in Lode's angle is π/3 due to plastic isotropy. Additionally, a concept of deviatoric stiffness is devised and an analytical expression for the generalized hardening modulus is derived. Qualitative and quantitative analyses are carried out in the form of direct comparisons between analytical solutions for drained and undrained loading histories thus offering an improved understanding of the three‐invariant model. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

Inclined load capacity of suction caissons     

C. P. Aubeny  S. W. Han  J. D. Murff 《国际地质力学数值与分析法杂志》2003,27(14):1235-1254

A simplified method of analysis for estimating lateral load capacity of suction caisson anchors based on an upper bound plasticity formulation is presented. The simplification restricts the analysis to caissons in uniform and linearly varying undrained strength profiles; nevertheless, its computational efficiency permits quick evaluation of a number of parameters affecting load capacity. The validity and limitations of the simplified formulation are demonstrated through comparisons to more rigorous finite element solutions. A series of sensitivity studies demonstrate the effects of various soil conditions and loading parameters. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

Response of saturated porous media to cyclic thermal loading     

E. Blond  N. Schmitt  F. Hild 《国际地质力学数值与分析法杂志》2003,27(11):883-904

The response of a semi‐infinite saturated porous medium subjected to a harmonic thermal loading on its free face is studied herein. The pressure diffusion equation that governs the fluctuation of the interstitial pressure is established. It allows us to obtain prevalent parameters, i.e. the thermal and fluid mass diffusivities and the coefficient of relative bulk variation. Closed‐form solutions of the maximum fluid pressure P_max and its location x_cr are derived. It is shown that the location x_cr of P_max is localized and depends on the diffusivity ratio and the frequency of the thermal loading while the magnitude of P_max depends on the diffusivity ratio and the thermal amplitude. Master curves for x_cr and P_max versus diffusivity ratio are built. It follows that three regimes can be distinguished: namely, thin spalling, thick spalling or in‐depth cracking and no cracking. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

大同--运城高速公路某软基复合地基检测结果分析   总被引：2，自引：2，他引：0  

毛新虎 《地球科学与环境学报》2004,26(1):33-37

以山西大运高速公路某段软基处理为例,从挤密碎石桩的加固机理和破坏方式入手,通过对软基复合地基的原位测试结果分析,得出碎石桩不但提高了地基的承载力,增加了桩间土的强度,减少了地基沉降,而且消除或减轻了地基的液化,使复合地基承载力达到了设计要求,特别是为以后在高速公路修筑中的软基处理提供了参考资料.  相似文献   

风浪作用下入湖河口内源释放特征   总被引：5，自引：0，他引：5       下载免费PDF全文

许志波  卢信  胡维平  邓建才  袁旭音 《水科学进展》2011,22(4):574-579

采用Y型沉积物再悬浮发生装置模拟3种风速条件下典型入湖河流河口沉积物再悬浮和沉降过程.结果表明,随着风速的增大,水柱中悬浮物总量增加;3种风速条件下氨氮(NH₄+-N)增量均为负;小风和中风过程,正磷酸盐(PO₄3--P)总量呈减小趋势,大风过程,正磷酸盐总量出现了明显上升,相对于初始值增加了46%,在5.1~8.7m/s的某一模拟风速条件下PO₄3--P的释放和吸附达到动态平衡,其表观值与初始值相等.总氮(TN)和总磷(TP)总量随着风速的增加而增大,TN最大增量是初始总量的2倍,而TP则是17倍;风浪过后TN、TP总量基本恢复到初始值.典型风速过程中,营养盐垂向分布无明显规律.  相似文献   

渭河干流典型断面非点源污染监测与负荷估算   总被引：5，自引：0，他引：5       下载免费PDF全文

李家科  李怀恩  沈冰  秦耀民  董雯 《水科学进展》2011,22(6):818-828

渭河水质在较大程度上受非点源污染的影响,因此,有必要对其负荷和比重进行研究。2009年至2010年,对渭河干流关中段咸阳和临潼断面进行了洪水期和非洪水期水质水量同步监测。根据监测结果及水文站实测流量资料,分别采用改进的水文分割法和平均浓度法对两断面的非点源污染负荷进行了计算,分析了非点源污染的特点。结果表明:渭河干流关中段主要污染物为COD、NH₃-N和TN,两断面洪水期间各指标的平均浓度基本都小于平时的平均浓度;各指标非洪水期浓度变化总体上小于洪水期浓度变化幅度,量级较大的洪水水质变化幅度相对较小;改进的水文分割法和已被检验并被广泛采用的平均浓度法计算结果符合良好。2009年(枯水年,P=68%)渭河咸阳和临潼站各指标非点源污染所占比例基本在20%～30%左右;2009年渭河干流咸阳-临潼河段污染以点源污染为主,构成比例在80%以上。对比2006年(枯水年,P=69%),2009年临潼站COD、NH₃-N和TN年点源负荷分别减少11937t、791t和29t,渭河点源治理取得一定成效;此外,临潼站这两年的污染构成比例基本相同。非点源污染在渭河水污染中占较大比重,其对渭河水质的影响不容忽视。  相似文献   

后压浆CFG桩复合地基的应用     

张晓春  李金武  龙铁牛  许晖 《世界地质》2011,30(3):459-462

结合某高层建筑地基处理工程,介绍后压浆CFG桩复合地基的承载力计算和施工工艺。通过现场栽荷试验、低应变检测等试验分析加固效果,探讨后压浆技术应用于CFG桩的可行性。分析结果表明,桩端后压浆CFG桩可以明显提高地基的承载力,单桩竖向承载力较压浆前提高了一倍;低应变实测波形显示在桩端的桩一土界面上波形变化不明显,说明浆液向桩端四周扩散良好,有效加固了土层。  相似文献   

地震荷载作用下斜坡响应研究:以四川青川东山—狮子梁剖面为例   总被引：1，自引：0，他引：1  

王福海  王运生  孙刚  徐鸿彪  罗骑龙  李玉林 《现代地质》2011,25(1):142-150

在对青川地震监测剖面实测数据进行系统分析的基础上,运用大型通用有限元分析软件ANSYS建立东山—狮子梁监测剖面的数值模型,分析了地震作用下斜坡的动力响应规律。结果表明:地震荷载作用下,斜坡的地震响应不是单调的随斜坡高度的增加而增加,而是与斜坡地形地貌及岩体中裂隙的发育程度有密切关系;斜坡的地震响应由坡内向坡外逐渐增大,且坡向与地震波传播方向相同时斜坡的地震动力响应要大于坡向与地震波传播方向相反的情况。研究结果为地震荷载作用下边坡稳定性评价提供了理论支持,为提出更加合理的地震动稳定性评价方法提供依据。  相似文献