The use of mycorrhiza for eco‐engineering measures in steep alpine environments: effects on soil aggregate formation and fine‐root development

Steep erosion‐prone and vegetation‐free slopes are widespread in alpine areas and are often discussed since they have a high socio‐economic damage potential. We present an eco‐engineering approach to test whether a mycorrhizal inoculum improves the establishment of hedge brush layers and in turn soil structural stability on a steep, coarse‐grained vegetation‐free slope in the eastern Swiss Alps. We established (i) mycorrhizal and (ii) non‐mycorrhizal treated eco‐engineered research plots on a field experimental scale, covering a total area of approximately 1000 m² on an east‐northeast (ENE) exposed slope, where many environmental parameters can be regarded as homogeneous. After a full vegetation period, we quantified soil aggregate stability, the formation of water stable aggregates and the fine‐root development. Our results illustrate that the establishment of brush layers without mycorrhizal inoculum increased aggregate stability significantly. Against our expectation and glasshouse experiments, the addition of mycorrhizal inoculum did not have a statistically significant effect after one vegetation period although it tended to increase aggregate stability. Analogously, root length density (RLD) tended to be higher at the non‐mycorrhizal treated site. Aggregate stability was significantly correlated with RLD. Studies on a bigger field experimental scale are inevitable, complement glasshouse studies and lead to a better understanding for a successful application of sustainable eco‐engineering measures in alpine environments. Based on our results and considering the fact that the response time in natural ecosystems may be slower than in laboratory approaches, we conclude that long‐term field studies are necessary to validate results gained through laboratory experiments. Copyright © 2014 John Wiley & Sons, Ltd.     

Application of perfectly matched layers in the transient analysis of dam–reservoir systems

The transient analysis of dam–reservoir systems by employing perfectly matched layers has been investigated. In previous studies, boundary conditions of the PML region in the reservoir have been neglected. In this paper, they are incorporated completely in the formulation. Moreover, a technique is introduced to involve the effect of incident waves caused by vertical ground motions at the reservoir bottom in the analysis. Performing several numerical experiments indicates that applying boundary conditions of the PML domain and utilizing the proposed method for vertical excitation cases reduce the computational cost significantly and make the PML method a very efficient approach for the transient analysis of dam–reservoir systems.     

Fate of the Evros River suspended particulate matter in the northern Aegean Sea

Evros River is the most important river flowing into the North Aegean Sea (eastern Mediterranean) in terms of freshwater discharge, and the second largest one of Eastern Europe after the Danube River. Salinity and temperature measurements, together with suspended particulate matter concentrations were obtained in various depths at 14 stations in the adjacent Alexandroupolis Gulf during four seasons (June 1998, September 1998, February 1999 and March 2000) in order to investigate the particle dynamics and distributions in the northern Aegean Sea. Analysis of the collected data, together with particle observations under the scanning electron microscope and study of satellite images showed that, under certain circumstances driven by the hydrological and wind regime of the area, the Evros River particulate matter, with the associated pollutants, can be transferred far away from the estuary and implicitly comprise a hazardous factor for the environmental status of the northern Aegean Sea. This fact, combined with the future construction of the Burgas-Alexandroupolis pipeline, may cause a negative impact on the studied natural ecosystem.     

Recovery of benthic macroinvertebrate and epilithic communities following a large flood,in an unstable,braided, New Zealand river

Benthic macroinvertebrates and small stones were collected from a riffle in the Ashley River, North Canterbury, New Zealand, on 12 occasions within a 132‐day period following a particularly large flood in 1986. Despite the occurrence of smaller floods during this period, benthic macroinvertebrate communities and stone surface organic layers recovered rapidly. Mean concentration of stone surface organic carbon increased from 0.23 g/m² to 1.01 g/m² stone surface in the first 23 days after the flood and chlorophyll a concentration increased from 0.13 mg/m² (day 3) to 9.2 mg/m² by day 132. Minor floods during the recovery period had little effect on organic layer biomass. Mean faunal density increased from 230/m² to 7920/m² during this time and taxon richness from 7 to 21 per 5 benthic samples. Immediately after the flood and throughout the study period the fauna was dominated by larvae of Deleatidium (Ephemeroptera: Leptophlebiidae), Hydora (Coleoptera: Elmidae), and Chironomidae. Re‐establishment of Deleatidium populations in previously denuded brands was effected by oviposition, egg‐hatching, and larval immigration. Minor braids are likely to represent important epicentres from which recolonisation proceeds.     

重力坝层间抗滑稳定体系的动力可靠度分析方法

受明显的层状结构影响,加之材料参数和动荷载的双重随机性,动力条件下碾压混凝土重力坝的层间抗滑稳定可靠度问题值得关注。考虑地震波频谱特性、峰值加速度、坝体材料参数的随机性,统计概化出地震作用下坝体的潜在滑动失效路径;在特定地震动作用下,基于随机有限元分析结果,采用刚体极限状态判断准则和响应面法构建失效路径的动力抗滑稳定功能函数,进而求得其抗滑稳定可靠指标;接着考虑不同失效路径的相关性,用Ditlevsen窄界限公式估算体系的可靠度;最后,考虑地震动荷载的随机性,采用基于全概率公式的数值拟合积分方法求解大坝抗滑稳定体系的动力可靠度。研究结果表明,动力条件下,当水平地震系数大于0.2时,重力坝层间抗滑体系可靠度不再由建基面失效路径决定,而是由下游折坡处层面的失效路径决定。该方法数学意义明确,实用性强。     

天津地区覆盖层土动力学参数统计分析

收集天津地区近年来有代表性的具有完整土动力学参数作为实验数据的地震安全性评价报告66份,用两种统计方法按不同深度统计分析粉质黏土、黏土、粉土、砂土、淤泥质土等的实测土动力学参数,给出动剪切模量比和阻尼比平均值。选取2个典型工程场地,构建土层分析模型,进行土层地震反应分析计算。结果表明,本文得到的统计2值在天津地区具有一定的代表性和适用性,与实测值结果更为接近。对于获得原状土样困难的场地,特别是对于较薄的夹层土,可参照统计2结果进行分析计算。     

Nearshore bar migration and sediment-induced buoyancy effects

A 1-D General Ocean Turbulence Model that includes the effects of sediment-induced stratification is shown to simulate the observed onshore and offshore migration of a nearshore sandbar. The only two free parameters of the model, the bed reference concentration and the sediment diffusivity, are taken from the literature, rather than tuned to the data used here. The model results suggest that predictions of onshore bar migration, in which wave-induced sediment transport confined to within a few centimeters of the bottom dominates, are not greatly affected by accounting for buoyancy effects. The model results also suggest that both mean flows and waves transport sediment during offshore bar migration, with different components of transport dominating at different cross-shore locations across the bar-trough bathymetry. Neglecting the effects of sediment-induced stratification results in higher model skill during the largest waves, likely because the excess turbulence production simulated by the non-stratified model is counterbalanced by neglected breaking-wave-generated turbulence. Considering both onshore and offshore migration, the model that includes sediment-induced stratification has higher skill than the model without stratification.     

钱塘江盾构越江隧道最小覆土厚度的确定

钱塘江洪水冲刷河床与大潮回淤交替出现,必将影响盾构越江隧道安全。如何合理地确定越江隧道的埋深,既确保隧道安全,又降低工程造价,是一个迫切需要解决的问题。已有的研究成果认为,300年一遇的罕见洪水冲刷河床的最大深度可达16 m,据此初步选择了河床冲刷后最小埋深分别为3.5 m和4.0 m两种隧道埋设方案,开展了隧道抗上浮研究。研究结果表明,考虑隧道周围土体和管片环间纵向螺栓的剪切抗浮效应时,两种方案均能够满足抗浮要求。但施工期刚脱出盾尾的管片环在未硬化注浆体的浮力作用下,大大增加隧道上浮的可能性,需要加强施工期的管理工作,减少对周围土体扰动。     

近30年南京市浅层地温场变化规律研究

在收集南京市单一观测站点近50年气温资料和近30年浅层地温数据的基础上,对南京市地温变化趋势及其与气温变化的相关性进行了分析,对不同深度定时地温变化、日均地温伞年变化、地温日较差变化等进行了比较,同时也对地温变化对城市浅层土工程性质可能带来的影响进行了分析.结果表明:地温场与气温场变化规律基本一致,但存在一定的滞后现象;南京市月均地温变化规律基本相同,最高值出现在7,8月份,最低值出现在1,2月份;近30年来浅层地温场总体呈现上升趋势,其中地表上升最大值达2.8℃,0～20 cm土层温度变化幅度比较接近,上升最大值达2.0℃,40 cm处最大值达1.75℃;30年来地表最大温差高达84.5℃,40 cm深度最大地温差也超过27.5℃,因此多年地温变化对城市浅层土工程性质的影响不容忽视.     

Macrodynamics of α2 dynamos

Abstract

Two distributions of the α-effect in a sphere are considered. The inviscid limit is approached both by direct numerical solution and by solution of a simpler nonlinear eigenvalue problem deriving from asymptotic boundary layer analysis for the case of stress-free boundaries. The inviscid limit in both cases is dominated by the need to satisfy the Taylor constraint which states that the integral of the Lorentz force over cylindrical (geostrophic) contours in a homogeneous fluid must tend to zero. For a small supercritical range in α, this condition can only be met by magnetic fields which vanish as the viscosity goes to zero. In this range, the agreement of the two approaches is excellent. In a portion of this range, the method of finite amplitude perturbation expansion is useful, and serves as a guide for understanding the numerical results. For larger α, evidence from the nonlinear eigenvalue problem suggests both that the Taylor state exists, and that the transition from small to large amplitude can require a finite amplitude (oscillatory) instability in accord with the findings of Soward and Jones (1983). However, solutions of the full equations have not been found which are independent of viscosity at larger values of α.