基于多元统计分析的渔山列岛潮间带软体动物功能群和次级生产力比较   总被引：1，自引：0，他引：1  

徐鹏  刘好真  刘懂  焦海峰  王一农  尤仲杰 《海洋与湖沼》2018,49(1):151-159

渔山列岛于2008年成为国家级海洋生态保护区,为了解渔山列岛保护区内潮间带软体动物次级生产力的时空变化。于1982年和2010年的3个季节(春、夏、冬)在渔山列岛进行潮间带软体动物调查,采用多元统计分析软体动物时空差异,以Brey经验公式计算分析软体动物次级生产力(P值,P/B值)。结果表明,年际间物种食性结构发生了明显的改变,1982年潮间带软体动物对次级生产力贡献率最大的物种有单齿螺(Monodonta labio)、锈凹螺(Chlorostoma rustica),占软体动物总次级生产力的42.88%,2010年潮间带软体动物对次级生产力贡献率最大的物种有覆瓦小蛇螺(Serpulorbis imbricata)、条纹隔贻贝(Septifer virgatus),占软体动物总次级生产力的75.96%。1982年,年均栖息密度为2758ind/m2,年均生物量为2100.26g/m2,年均次级生产力为240.04g/(m2·a),年均P/B值为0.63a–1;2010年,年均栖息密度为699ind/m2,年均生物量为1101.85g/m2,年均次级生产力为94.82g/(m2·a),年均P/B值为0.55a–1。多因素方差分析表明软体动物次级生产力年际间差异显著(F=5.761,P0.05),季节间和潮位间差异都不显著(F=0.135,P0.05;F=2.076,P0.05),P/B的值较低,表明该海域软体动物世代更替速度较慢,2010年的P/B值(0.55a–1)低于1982年的P/B值(0.63a–1),表明近30年来群落结构受到影响。  相似文献   

Beaver dam analogues drive heterogeneous groundwater–surface water interactions     

Jeffrey Wade  Laura Lautz  Christa Kelleher  Philippe Vidon  Julianne Davis  Julio Beltran  Casey Pearce 《水文研究》2020,34(26):5340-5353

Beaver dam analogues (BDAs) are a cost-effective stream restoration approach that leverages the recognized environmental benefits of natural beaver dams on channel stability and local hydrology. Although natural beaver dams are known to exert considerable influence on the hydrologic conditions of a stream system by mediating geomorphic processes, nutrient cycling, and groundwater–surface water interactions, the impacts of beaver-derived restoration methods on groundwater–surface water exchange are poorly characterized. To address this deficit, we monitored hyporheic exchange fluxes and streambed porewater biogeochemistry across a sequence of BDAs installed along a central Wyoming stream during the summer of 2019. Streambed fluxes were quantified by heat tracing methods and vertical hydraulic gradients. Biogeochemical activity was evaluated using major ion porewater chemistry and principal component analysis. Vertical fluxes of approximately 1.0 m/day were observed around the BDAs, as was the development of spatially heterogeneous zones of nitrate production, groundwater upwelling, and anaerobic reduction. Strong contrasts in hyporheic zone processes were observed across BDAs of differing sizes. This suggests that structures may function with size-dependent behaviour, only altering groundwater–surface water interactions after a threshold hydraulic step height is exceeded. Patterns of hyporheic exchange and biogeochemical cycling around the studied BDAs resemble those around natural beaver dams, suggesting that BDAs may provide comparable benefits to channel complexity and near-stream function over a 1-year period.  相似文献   

Three-dimensional finite element simulation of fracture propagation in rock specimens with pre-existing fissure(s) under compression and their strength analysis     

Ramin Pakzad  Shanyong Wang  Scott W. Sloan 《国际地质力学数值与分析法杂志》2020,44(10):1472-1494

A FORTRAN program, consistent with the commercially available finite element (FE) code ABAQUS, is developed based on a three-dimensional (3D) linear elastic brittle damage constitutive model with two damage criteria. To consider the heterogeneity of rock, the developed FORTRAN program is used to set the stiffness and strength properties of each element of the FE model following a Weibull distribution function. The reliability of the program is assessed against available experimental results for granite cylindrical specimens with a throughgoing, flat and inclined fissure. The calibration procedure of the material parameters is explained in detail, and it is shown that the compressive to tensile strength ratio can have a substantial influence on the failure response of the specimens. Numerical simulations are conducted for models with different levels of heterogeneity. The results show a smaller load bearing capacity for models with less homogeneity, representing gradual coalescence of fully damaged elements forming throughout the models during loading. The maximum load bearing capacity is studied for various combinations of inclination angles of two centrally aligned, throughgoing and flat fissures of equal length embedded in cylindrical models under uniaxial and multiaxial loading conditions. The key role of the compressive to tensile strength ratio is highlighted by repeating certain simulations with a lower compressive to tensile strength ratio. It is proven that the peak loads of the rock models with sufficiently small compressive to tensile strength ratios containing two throughgoing fissures of equal length are similar, provided that the minimum inclination angles of the models are the same. The results are presented and discussed with respect to the existing experimental findings in the literature, suggesting that the numerical model applied in this study can provide useful insight into the failure behaviour of rock-like materials.  相似文献   

Effects of the geometry of two‐dimensional fractures on their hydraulic aperture and on the validity of the local cubic law          下载免费PDF全文

Ahmad Hajjar  Luc Scholtès  Constantin Oltéan  Michel Antoine Buès 《水文研究》2018,32(16):2510-2525

Flow through rough fractures is investigated numerically in order to assess the validity of the local cubic law for different fracture geometries. Two‐dimensional channels with sinusoidal walls having different geometrical properties defined by the aperture, the amplitude, and the wavelength of the walls' corrugations, the corrugations asymmetry, and the phase shift between the two walls are considered to represent different fracture geometries. First, it is analytically shown that the hydraulic aperture clearly deviates from the mean aperture when the walls' roughness, the phase shift, and/or the asymmetry between the fracture walls are relatively high. The continuity and the Navier–Stokes equations are then solved by means of the finite element method and the numerical solutions compared to the theoretical predictions of the local cubic law. Reynolds numbers ranging from 0.066 to 66.66 are investigated so as to focus more particularly on the effect of flow inertial effects on the validity of the local cubic law. For low Reynolds number, typically less than 15, the local cubic law properly describes the fracture flow, especially when the fracture walls have small corrugation amplitudes. For Reynolds numbers higher than 15, the local cubic law is valid under the conditions that the fracture presents a low aspect ratio, small corrugation amplitudes, and a moderate phase lag between its walls.  相似文献   

基于ASP.NET MVC的海域海岸带整治修复项目信息管理系统的设计和实现          下载免费PDF全文

于新宇  李家  郝杰  闫吉顺 《海洋开发与管理》2018,35(2):71-73+93

文章在国家大力开展海域海岸带整治修复的背景下,利用Visual Studio 2013开发平台和SQL Server 2014数据库软件,采用ASP.NET MVC架构设计海域海岸带整治修复项目信息管理系统,实现整治修复项目信息的快速录入,并可进行查询、展示和互动等操作。相比传统信息管理系统,本系统大大提高了可维护性、可扩展性、灵活性和封装性,可促进我国海域海岸带整治修复项目信息管理实现现代化。  相似文献   

The bivalve Lembulus bicuspidatus may enhance denitrification in shelf sediment at the Angola–Benguela Frontal Zone     

A Neumann  A Flohr 《African Journal of Marine Science》2018,40(1):91-96

We collected living individuals of the bivalve Lembulus bicuspidatus, which shows an unusual preference for the oxygen-deficient habitat found at the Angola–Benguela Frontal Zone of the southeastern Atlantic. With a series of incubation experiments with ¹⁵N-labelled nitrate as a tracer in combination with membrane-inlet mass spectrometry, we studied the potential contribution of L. bicuspidatus to nitrate reduction in the upper sediment layer. Our preliminary results suggest that L. bicuspidatus enhances nitrate reduction if the oxygen concentration is sufficiently low. The Lembulus-mediated nitrate reduction rate is then similar to the rate of microbial nitrate reduction in the surrounding sediment.  相似文献   

基于“DEM-NDVI-土地覆盖分类”的天山博格达自然遗产地山地垂直带提取与变化分析     

冀欣阳  骆磊  王心源  李丽  万红 《地球信息科学学报》2018,20(9):1350-1360

本文基于Landsat影像数据获取天山博格达自然遗产地土地覆盖分类,结合归一化植被指数（NDVI）和数字高程模型（DEM）构建“DEM-NDVI-土地覆盖分类”散点图分析研究区植被受海拔和坡向的水热空间变化影响的分布特征,通过概率统计分析提取博格达遗产地山地垂直带,并结合研究区的气温、降水数据和NDVI变化特征分析垂直带变化的原因。研究结果表明：① 本文利用“DEM-NDVI-土地覆盖分类”散点图,揭示了研究区1989年和2016年的NDVI值和分类类别随着海拔上升的变化特征,其中NDVI值随着海拔上升呈现“倒U形”变化,而不同分类类别在一定的海拔区间内呈现出聚集效应,且不同分类类别有明显的高程界限。② 1989年和2016年博格达遗产地山地垂直带分带上限分别为：1278 m和1185 m（温带荒漠草原带）、1784 m和1759 m（山地草原带）、2706 m和2730 m（山地针叶林带）、3272 m和3293 m（高山草甸带）、3636 m和3690 m（高山垫状植被带）。③ 博格达遗产地1989年和2016年山地垂直带受区域气温升高和降雨增加的影响有较为明显的改变,其中温带荒漠草原带最为敏感,其上限变化最大,向下收缩93 m;山地针叶林带的分布范围则向两侧扩张49 m;山地草甸带带宽基本保持不变,但整体上移了约20 m;冰雪带则受到全球气候变暖的影响向上退缩54 m。  相似文献   

基于2 m格网点云数据的高精度DEM制作第三次国土调查坡度图     

李国华 《测绘通报》2020,(8):117-121

地形地貌随着时间的推移时刻发生变化，以高精度数字高程模型（EDE）数据制作坡度图，进而计算田坎系数，更精准地进行耕地面积计算及统计。以2 m格网点云数据生成的DEM数据为基础，按照第三次全国国土调查的相关技术要求，根据耕地坡度分级要求进行分级，生成坡度分级栅格数据图。对坡度分级栅格数据图进行矢量化，生成坡度分级矢量化数据。对矢量化数据进行图斑综合、界线平滑、拓扑重建、数据裁切等处理，制作完成调查区域坡度图及相关属性数据制作。并对生产的坡度图成果进行分析，找出不同尺度格网生产的坡度图的技术差异，并对高精度坡度的应用进行了展望。  相似文献   

Solution for a plane strain rough‐walled hydraulic fracture driven by turbulent fluid through impermeable rock          下载免费PDF全文

N. Zolfaghari  E. Dontsov  A. P. Bunger 《国际地质力学数值与分析法杂志》2018,42(4):587-617

The impact of turbulent flow on plane strain fluid‐driven crack propagation is an important but still poorly understood consideration in hydraulic fracture modeling. The changes that hydraulic fracturing has experienced over the past decade, especially in the area of fracturing fluids, have played a major role in the transition of the typical fluid regime from laminar to turbulent flow. Motivated by the increasing preponderance of high‐rate, water‐driven hydraulic fractures with high Reynolds number, we present a semianalytical solution for the propagation of a plane strain hydraulic fracture driven by a turbulent fluid in an impermeable formation. The formulation uses a power law relationship between the Darcy‐Weisbach friction factor and the scale of the fracture roughness, where one specific manifestation of this generalized friction factor is the classical Gauckler‐Manning‐Strickler approximation for turbulent flow in a rough‐walled channel. Conservation of mass, elasticity, and crack propagation are also solved simultaneously. We obtain a semianalytical solution using an orthogonal polynomial series. An approximate closed‐form solution is enabled by a choice of orthogonal polynomials embedding the near‐tip asymptotic behavior and thus giving very rapid convergence; a precise solution is obtained with 2 terms of the series. By comparison with numerical simulations, we show that the transition region between the laminar and turbulent regimes can be relatively small so that full solutions can often be well approximated by either a fully laminar or fully turbulent solution.  相似文献   

Micromechanical approach to effective viscoelastic properties of micro‐fractured geomaterials          下载免费PDF全文

Cássio B. Aguiar  Samir Maghous 《国际地质力学数值与分析法杂志》2018,42(16):2018-2046

The aim of this paper is to formulate a micromechanics‐based approach to non‐aging viscoelastic behavior of materials with randomly distributed micro‐fractures. Unlike cracks, fractures are discontinuities that are able to transfer stresses and can therefore be regarded from a mechanical viewpoint as interfaces endowed with a specific behavior under normal and shear loading. Making use of the elastic‐viscoelastic correspondence principle together with a Mori‐Tanka homogenization scheme, the effective viscoelastic behavior is assessed from properties of the material constituents and damage parameters related to density and size of fractures. It is notably shown that the homogenized behavior thus formulated can be described in most cases by means of a generalized Maxwell rheological model. For practical implementation in structural analyses, an approximate model for the isotropic homogenized fractured medium is formulated within the class of Burger models. Although the approximation is basically developed for short‐term and long‐term behaviors, numerical applications indicate that the approximate Burger model accurately reproduce the homogenized viscoelastic behavior also in the transient conditions.  相似文献