Biological mechanisms driving the seasonal changes in the internal loading of phosphorus in shallow lakes   总被引：1，自引：6，他引：1  

XIE Ping 《中国科学D辑(英文版)》2006,49(Z1)

Because of the obvious importance of P as a nutrient that often accelerates growth of phytoplankton (including toxic cyanobacteria) and therefore worsens water quality, much interest has been devoted to P exchange across the sediment-water interface. Generally, the release mode of P from the sediment differed greatly between shallow and deep lakes, and much of the effort has been focused on iron and oxygen, and also on the relevant environmental factors, for example, turbulence and decomposition, but a large part of the P variation in shallow lakes remains unexplained. This paper reviews experimental and field studies on the mechanisms of P release from the sediment in the shallow temperate (in Europe) and subtropical (in the middle and lower reaches of the Yangtze River in China) lakes, and it is suggested that pH rather than DO might be more important in driving the seasonal dynamics of internal P loading in these shallow lakes, i.e., intense photosynthesis of phytoplankton increases pH of the lake water and thus may increase pH of the surface sediment, leading to enhanced release of P (especially iron-bound P) from the sediment. Based on the selective pump of P (but not N) from the sediment by algal blooms, it is concluded that photosynthesis which is closely related to eutrophication level is the driving force for the seasonal variation of internal P loading in shallow lakes. This is a new finding. Additionally, the selective pump of P from the sediment by algal blooms not only explains satisfactorily why both TP and PO4-P in the hypereutrophic Lake Donghu declined significantly since the mid-1980s when heavy cyanobacterial blooms were eliminated by the nontraditional biomanipulation (massive stocking of the filter-feeding silver and bighead carps), but also explains why TP in European lakes decreased remarkably in the spring clear-water phase with less phytoplankton during the seasonal succession of aquatic communities or when phytoplankton biomass was decreased by traditional biomanipulation. Compared with deep lakes, wax and wane of phytoplankton due to alternations in the ecosystem structure is also able to exert significant influences on the P exchange at the sediment-water interface in shallow lakes. In other words, biological activities are also able to drive P release from sediments, and such a static P release process is especially more prominent in eutrophic shallow lakes with dense phytoplankton.  相似文献   

Static and dynamic response of massive caisson foundations with soil and interface nonlinearities—validation and results     

Nikos Gerolymos  George Gazetas   《Soil Dynamics and Earthquake Engineering》2006,26(5):377-394

The static, cyclic, and dynamic response of a massive caisson foundation embedded in nonlinear layered or inhomogeneous soil and loaded at its top is investigated. The caisson is supported against horizontal displacement and rotation by four types of inelastic springs and dashpots, described with the BWGG model that was developed in the preceding companion paper [Gerolymos N, Gazetas G. Development of winkler model for static and dynamic response of caisson foundations with soil and interface nonlinearities. Soil Dyn Earthq Eng, submitted companion paper]. The prediction of the model is satisfactorily compared with results from 3D-finite element analysis. Some experimental corroboration of the method is provided with the help of a 1/3-scale lateral load test that had been conducted in the field by EPRI. An illustrative example of a caisson embedded in linearly-inhomogeneous clay and subjected to static and dynamic loading is analysed. Characteristic results are presented highlighting the role of soil inelasticity and its interplay with the two dominant interface nonlinearities: separation (gapping) of the caisson shaft from the surrounding soil, and uplifting of the base from the underlying soil.  相似文献   

碎石土地基湿陷性研究   总被引：1，自引：0，他引：1  

张管宏  谌文武  王生新 《岩土工程技术》2006,20(3):136-139

主要以甘南330 kV变电所碎石土地基的现场浸水载荷试验和室内实验为基础,根据湿陷变形的特征,分析了影响碎石土地基湿陷变形的主要影响因素,探讨了碎石土地基的湿陷机理。认为碎石等大骨架颗粒与细粒胶结物相填充的特殊结构是碎石土地基湿陷最主要的原因。碎石土由于浸水骨架颗粒之间抗剪、抗压强度降低而导致碎石土结构破坏,随之填充在骨架颗粒之间的细颗粒产生二次湿陷,两者引起土体体积减小所导致。  相似文献   

攀枝花钒钛磁铁矿区土壤重金属地球化学特征及污染评价   总被引：9，自引：0，他引：9  

庹先国  徐争启  滕彦国  穆克亮 《矿物岩石地球化学通报》2007,26(2):127-131

为了解攀枝花钒钛磁铁矿区土壤重金属的特征及污染程度,采集了矿区表层土壤样品和两个土壤剖面,用多种分析方法有针对性地分析了Cu、Pb、Zn、Ti、V、Co、Ni、As、Cd、Cr、Hg、Mn十二种元素。在分析分布特征基础上,对重金属进行了污染物负荷指数评价,结果发现:1)攀枝花钒钛磁铁矿矿区表层土壤大部分属于中等污染,少数属于强污染,个别达到了极强污染;2)Co、V、Cu、Cd、Ti几种元素的最高污染系数大,Zn、Mn、Ni、Cr四种元素的最高污染系数次之,Hg、Pb两种元素的最高污染系数较小,As的最高污染系数最小;3)从各区域的污染物负荷指数来看,排土场周围和朱矿采矿场下游附近污染程度较大,远离矿区以及矿区上游污染较小。  相似文献   

桩端土加固处理设计及检测方法的探讨     

张莲花  罗康 《岩土工程技术》2007,21(2):67-69,85

介绍了人工挖孔桩桩端土承载力不足进行旋喷桩处理的设计过程以及处理后检测过程中遇到的问题。桩端土处理设计可以遵循一般的地基处理设计方法和原则,并针对复合地基承载力检测和桩端土极限端阻力的检测中存在的差异和共同点,提出组合静载荷试验的思路和方法,并在工程中予以实施,并取得了较好的效果。  相似文献   

应用深层平板载荷试验选择桩端持力层     

张海峰  岳元元  娄志良 《岩土工程技术》2007,21(6):307-309

深层平板载荷试验是一种新兴的原位测试方法。通过安阳某工程人工挖孔扩底灌注桩深层平板载荷试验的现场实践,确定了不同土层地基土的承载力特征值,为设计单位选择持力层提供数据,并为甲方节省了大量建设资金。  相似文献   

广平地震台地磁异常与地震关系的研究     

张建国  曹轶  吕凤章  孙晴 《华北地震科学》2007,25(3):20-27

利用加卸载响应比、日变幅逐日比、空间相关分析法,研究分析了广平台1982-2006年地磁垂直分量观测资料与河北省及邻近地区Ms≥5.0地震之间的关系,发现它们之间有较好的对应关系;同时给出了适用于广平地磁台的地震分析预报参数,为今后广平台依磁报震提供了依据.  相似文献   

静海地震台地磁加卸载响应比与邻区地震关系研究     

庞群英  徐学恭  胡培元  宋金钟  田山 《地震地磁观测与研究》2007,28(1):52-56

研究分析了静海地磁台2002～2006年观测资料的加卸载响应比异常与邻区ML 4.0以上地震之间的关系,提出了适用于静海地磁台的地震分析预报异常形态特征和阈值判据.  相似文献   

动载作用下淤泥质软土流变模型与流变方程   总被引：3，自引：2，他引：3  

胡华 《岩土力学》2007,28(2):237-240

淤泥质软土在动态载荷作用下具有黏弹塑性流变力学特性。在理论分析和测试基础上，建立了黏弹塑性流变力学模型，并推导了新的流变方程和动态黏弹性流变参数。研究结论对分析动态载荷作用下软土流变力学响应与稳定性，探索软土加速流变并导致岩土地质灾害的动力学机制等具有重要的理论意义，对维护岩土工程的安全性等具有重要的工程意义。  相似文献   

冻结粉土动强度的荷载效应及长期极限动强度   总被引：4，自引：1，他引：3  

沈忠言 《冰川冻土》1998,20(1):42-45

荷载效应包括速率效应和疲劳效应两部分．速率效应使冻土的动强度和退荷回弹动弹模随应变速率加快而提高;疲劳效应使冻土的动强度随振频增加而下降,但在低应变速率下却使动强度略有提高．在高应变速率下动强度大于静强度,在低应变速度下动强度小于静强度,其间存在一个临界应变速率．通过动强度－破坏振次关系,可确定长期极限动强度．  相似文献