白洋淀超微真核藻的空间分布特征及关键影响因子

超微真核藻个体微小、比表面积大,具有高效的碳吸收速率,对水体初级生产力具有重要的贡献.目前对淡水超微真核藻的认知还非常有限.于2017年5月对白洋淀进行采样调查,结合流式细胞术和高通量测序技术探究了白洋淀超微真核藻群落结构的空间分布特征及关键环境影响因子.结果表明,白洋淀超微真核藻的平均丰度为7.59×104cells/ml,且随着营养水平的升高呈现先增加后降低的变化趋势.回归分析表明,超微真核藻丰度在中营养水平水域主要受溶解性总磷和TN/TP影响,在富营养水域主要与盐度有关.测序比对结果表明在纲水平上白洋淀超微真核藻主要以绿藻纲Chlorophyceae、硅藻纲Bacillariophyceae、中心硅藻纲Coscinodiscophyceae、金藻纲Chrysophyceae为主,不同区域差异不大.但在操作分类单元(Operation Taxonomy Units,OTU)水平上,超微真核藻群落结构在白洋淀不同营养状态湖区存在显著差异,中营养水域主要类群为栅列藻科Scenedesmaceae,近囊胞藻属Paraphysomona sp.,定鞭藻纲Haptophyceae和甲藻纲Dinophyceae为主,而富营养水域主要类群为红球藻科Haematococcaceae,金藻纲的Chromulinale sp.和Chrysophycea sp..Bioenv分析表明,对超微真核藻群落组成影响最大的环境因子是溶解性总氮、溶解性总磷、TN/TP、硝态氮、溶解氧.本研究表明超微真核藻的群落结构存在较明显的环境异质性,对白洋淀水体富营养化状态有很好的指示.     

西藏易贡滑坡物质运动全过程数值模拟研究

2000年4月9日20时05分，西藏波密县易贡乡发生的大型山体崩滑，造成极大危害。在野外调查基础上，运用离散单元法模拟该崩滑体破坏、运动的全过程，此次灾害为扎木弄沟源头的山体崩塌，振动引起沟内崩坡积物发生沙土液化而随崩塌体一起运动，形成高速碎屑流的破坏运动机制，与实际情况较为吻合。     

Turbulence Closures In Neutral Boundary Layer Over Complex Terrain

In this work, three turbulence closure models, Mellor andYamada level 2.5, E - l and E - implemented in a circulation model, are compared in neutral condition over complex terrain. They are firstly applied to a one-dimensional case on flat terrain and then to a schematic two-dimensional valley. The simulation results, in terms of wind field and turbulent kinetic energy, are tested against measurements from a wind-tunnel experiment. The empirical constants defining the characteristic length scales of the closures are modified based on turbulence parameters estimated in the experiment. The formulation of the diffusion coefficients is analysed to explain the differences among the various closures in the simulation results. Regarding the mean flow, both on flat and complex terrain, all the closures yield satisfactory results. Concerning the turbulent kinetic energy, the best results are obtained by E - l and E - closures.     

时间平均基流中准定常波的传播及多向折射

应用几何光学中的射线理论，直观地讨论了准定常波在时间平均基流中的传播，解释了定常 传播的纬向非均匀性。结果表明：折射指数平方可表示为基流绝对对基流流函数的微商，定常波的传播路径与折射指数平方的空间分布有着密切的关系。     

1998年中国洪灾成因初探

对１９９８年发生在我国长江流域及东北地区的特大暴雨及洪涝灾害的预测进行了总结 ,并对其形成原因进行了初步的分析与探讨,强调了越赤道气流异常及地磁场异常是形成这次特大洪涝灾害的诸多重要自然原因中的两个重要原因。     

Modelling increased soil cohesion due to roots with EUROSEM

As organic root exudates cause soil particles to adhere firmly to root surfaces, roots significantly increase soil strength and therefore also increase the resistance of the topsoil to erosion by concentrated flow. This paper aims at contributing to a better prediction of the root effects on soil erosion rates in the EUROSEM model, as the input values accounting for roots, presented in the user manual, do not account for differences in root density or root architecture. Recent research indicates that small changes in root density or differences in root architecture considerably influence soil erosion rates during concentrated flow. The approach for incorporating the root effects into this model is based on a comparison of measured soil detachment rates for bare and for root‐permeated topsoil samples with predicted erosion rates under the same flow conditions using the erosion equation of EUROSEM. Through backwards calculation, transport capacity efficiencies and corresponding soil cohesion values can be assessed for bare and root‐permeated topsoils respectively. The results are promising and present soil cohesion values that are in accordance with reported values in the literature for the same soil type (silt loam). The results show that grass roots provide a larger increase in soil cohesion as compared with tap‐rooted species and that the increase in soil cohesion is not significantly different under wet and dry soil conditions, either for fibrous root systems or for tap root systems. Power and exponential relationships are established between measured root density values and the corresponding calculated soil cohesion values, reflecting the effects of roots on the resistance of the topsoil to concentrated flow incision. These relationships enable one to incorporate the root effect into the soil erosion model EUROSEM, through adapting the soil cohesion input value. A scenario analysis shows that the contribution of roots to soil cohesion is very important for preventing soil loss and reducing runoff volume. The increase in soil shear strength due to the binding effect of roots on soil particles is two orders of magnitude lower as compared with soil reinforcement achieved when roots mobilize their tensile strength during soil shearing and root breakage. Copyright © 2008 John Wiley & Sons, Ltd.     

Quantifying preferential flow in soils: A review of different techniques

Preferential flow (PF) in soil has both environmental and human health implications since it favours contaminant transport to groundwater without interaction with the chemically and biologically reactive upper layer of soil. PF is, however, difficult to measure and quantify. This paper reviews laboratory and field techniques, such as breakthrough curves, dye tracing, and scanning techniques, for evaluating PF in soil at different scales. Advanced technologies, such as scanning techniques, have increased our capability to quantify transport processes within the soil with minimal soil disturbance. Important issues with respect to quantifying PF concern large-scale studies, frozen soil conditions, tracing techniques for particles and gases, a lack of simple mathematical tools for interpreting field data, and the lack of a systematic approach for comparing PF data resulting from different measurement techniques. Also, more research is required to quantify the relative importance of the various PF processes that occur in soil rather than the integrated result of all PF processes in soils.     

Restrictions on Deep Flow Across the Shelf-break and the Role of Submarine Canyons in Facilitating such Flow

The shelf-break acts as a separator between the coastal ocean and the open ocean. Circulation (particularly deep near-bottom flow) is restricted from crossing the bathymetry. Eddies become elongated in the region of the shelf-break restricting exchange. An estimate of the horizontal eddy diffusivity over the shelf-break of less than 10m²s^-1 is found from a numerical model. Various mechanisms are responsible for the weak cross-isobath flow that does occur. One is the increase of the Rossby number over small-scale topography such as submarine canyons. Along-shore flow (in the direction opposite to Kelvin wave propagation) generates upwelling through submarine canyons. A review of upwelling through submarine canyons is given. The deep cross-shelf flow generated by the canyons is shown to be as significant as the wind-driven upwelling in some regions. Examples for the reduction of flow across the shelf-break and for upwelling through canyons are taken from the West Coast of Vancouver Island.     

供水管网渗漏分析研究

渗漏管网的流分析是进行供水管网震后功能评价，从而实现在系统层次进行抗震设计的基础。在正常使用阶段，渗漏也是供水管网设计必须考虑的问题。本文介绍了供水管网渗漏分析的两类基本模型，在此基础上，给出了考虑渗漏模型的供水管网流分析的实施步骤。为了比较无渗漏模型和渗漏模型的差异及不同渗漏模型对计算结果的影响，对一典型供水管网进行了无渗漏管网模型的流分析和不同渗漏模型的带渗漏管网的流分析。分析结果表明，合理的渗漏模型是正确评价供水管网服务能力的基础。     

The dynamics of natural pipe hydrological behaviour in blanket peat

Natural soil pipes are found in peatlands, but little is known about their hydrological role. This paper presents the most complete set of pipe discharge data to date from a deep blanket peatland in Northern England. In a 17.4‐ha catchment, we identified 24 perennially flowing and 60 ephemerally flowing pipe outlets. Eight pipe outlets along with the catchment outlet were continuously gauged over an 18‐month period. The pipes in the catchment were estimated to produce around 13.7% of annual streamflow, with individual pipes often producing large peak flows (maximum peak of 3.8 l s^?1). Almost all pipes, whether ephemerally or perennially flowing, shallow or deep (outlets > 1 m below the peat surface), showed increased discharge within a mean of 3 h after rainfall commencement and were dominated by stormflow, indicating good connectivity between the peatland surface and the pipes. However, almost all pipes had a longer period between the hydrograph peak and the return to base flow compared with the stream (mean of 23.9 h for pipes, 19.7 h for stream). As a result, the proportion of streamflow produced by the pipes at any given time increased at low flows and formed the most important component of stream discharge for the lowest 10% of flows. Thus, a small number of perennially flowing pipes became more important to the stream system under low‐flow conditions and probably received water via matrix flow during periods between storms. Given the importance of pipes to streamflow in blanket peatlands, further research is required into their wider role in influencing stream water chemistry, water temperature and fluvial carbon fluxes, as well as their role in altering local hydrochemical cycling within the peat mass itself. Enhanced piping within peatlands caused by environmental change may lead to changes in the streamflow regime with larger low flows and more prolonged drainage of the peat. Copyright © 2012 John Wiley & Sons, Ltd.