Epigenetic geochemical dynamics and driving mechanisms of chemical elemental distribution patterns in soil in Southwest China

The Earth's surface is a complex system involving mutual interactions of its many components, including mountains, rivers, forests, farmlands, lakes and grasses. The interaction and mutual feedback of chemical elements in Earths surface layer can drive changes in chemical elemental distribution patterns. In this study, we evaluated the mechanisms and interactions driving the distribution patterns of macroelements, probiotics, halogens and heavy metals in soils in Southwest China, based on a systematic geochemical land-quality survey at a scale of 1250000. The results showed that the parent material determines the natural state of chemical elements in land resources. Epigenetic geochemical dynamics reshapes the distribution patterns of chemical elements in top soil; biogeochemical processes drive the evolutionary trends of land quality; and human activities, such as mining, disrupt the natural evolution of chemical elemental distribution patterns. The establishment of an epigenetic geochemical dynamics theory allows the construction of a framework for understanding the Earths surface layer and promoting technological innovations for the comprehensive geochemical investigation of land resources.     

北部湾盆地福山凹陷深湖重力流成因分类、发育机制及沉积模式

福山凹陷为北部湾盆地南缘海南隆起斜坡上的一个新生代断陷湖盆。本文充分利用岩心、测井以及覆盖整个研究区的高分辨率三维地震资料,以层序地层学、沉积学等多种理论为指导,结合沉积岩石学、地震沉积学等相关技术,于古近系流沙港组SQEls₂EST+LST时期,在福山凹陷识别出4种深湖重力流沉积岩相类型;通过岩相组合及其转换特征、砂分散体系、地震相分析,对该时期沉积体系展布特征进行细致剖析,进而建立福山凹陷深湖重力流发育机制和沉积模式：西部地区发育以浊流为主、具有典型浊积水道的湖底扇沉积;而东部地区则以砂质碎屑流沉积形成的远端孤立朵体为主。     

Numerical simulation of the undrained stability of slopes in anisotropic fine-grained soils

The undrained stability of slopes in anisotropic fine-grained soils is studied in this paper using the finite element method (FEM). A constitutive model is presented, able to account for the observed variation of undrained strength with loading direction. The model is able to encompass the different strength distributions observed in normally, slightly overconsolidated and heavily overconsolidated soils. A series of stability analyses have been performed to explore the effect of the type of undrained strength anisotropy on the stability and failure mechanisms of slopes of different inclinations. In addition, a real case study of the failure of an underwater slope is analysed with the numerical approach presented. It suggests that, by considering undrained strength anisotropy, the failure can be satisfactorily explained.     

DYNAMIC RESOURCES OF RIVER SEDIMENTS

The currently enforced Bulgarian water legislation [the Water Act (1999), the Environmental Protection Act (2002), etc.] requires conducting special studies for accurate assessments of sand and gravel flux along the rivers, prior to the issue of the license for operation of the quarries, where they will be dredged. The activity of a quarry necessitates special investigations because of the large dimensions of the damages inflicted on the environment. Ours studies have shown that there are two types of river reaches, in which abstraction of sand and gravel is performed. The first one refers usually to the plain area river reaches. The other type is mountainous with high rate of sediment load, which consists of coarse solid matter. The “on-the-spot” study on the environmental impact of the sand and gravel dredging has revealed that in the area of the quarry the riverbed cuts into the alluvial sediments to about 6-7 m and this ditch has spread by attenuation at a distance of more than 25 km upstream. Downstream the pit the picture is replicated and at the 8th km a local scour on the riverbed, amounting to more than 1.80-2.00 m, has been measured near the foundation of a massive bridge in the centre of city of Plovdiv. Such assessments of dynamic resources of sand and gravel materials are expected to serve for the purposes of gradual limitation of this activity in river sections close to renewable resources. The amount of sediment load, which may be abstracted in the area of the Orizare quarry in Bulgaria on a yearly basis has been calculated as 6000 m^3/a. It ensures that the resources will not be exhausted and irreversible distortion of the riverbed will be prevented. This is an environmentally safe limit.     

TRANSPORT OF GRAVELS WITH DIFFERENT RANGES OF GRAIN SIZES IN A STEEP CHANNEL

An understanding of the transport mechanism of gravel-bed rivers is very important for the river management and engineering works. The main objective of this study was to conduct a series of laboratory experiment in a steep flume to investigate the particle segregation and the transport rate of nonuniform gravel. Median sizes of 15 mm and 7.5 mm, and gradation coefficients of 1.5 and 2.0 were selected for the particle size distributions of nonuniform gravel. In addition to the 36 sets of data collected in this study, 635 sets of existing data for gravel with both nonuniform and nearly uniform sizes were analyzed. According to the results of the sieve analysis and the related theory, hiding functions for both particle size distributions of this study were derived. An attempt was made to develop an Einstein-type transport relationship for nonuniform gravel using dimensionless parameters with mean size as a representative particle size. A modified Schoklitsch-type sediment transport equation with a critical unit flow discharge was also developed to reasonably predict the transport rate of gravels. In addition, an artificial neural network (ANN) model with a back-propagation network (BPN) algorithm was also applied in this study.     

四川攀枝花昔格达组及其下伏河流砾石的地球化学特征以及对物源的制约

位于扬子地块西缘的攀枝花地区昔格达组湖相沉积及其下伏河流相砾石比较发育。湖相沉积具有较高的SiO2含量和Al2O3/SiO2比值,显示其载体沉积物具有较高成熟度,表明经历了长距离的搬运。主元素、稀土(REE)和微量元素分析结果揭示昔格达组湖相沉积物源形成于典型的大陆岛弧构造背景,主要来自松潘-甘孜造山带义敦岛弧花岗岩区。Eu/La?Yb/La判别图与Zr/Y比值进一步证实昔格达组湖相沉积分别来自于金沙江上游及雅砻江上游,说明昔格达古湖形成时金沙江上游已被袭夺。昔格达组下伏河流相砾石REE、微量元素分析结果显示其形成于被动大陆边缘构造背景,说明其是由雅砻江经扬子板块边缘花岗岩区携载而来。昔格达组湖相沉积与其下伏河流相砾石的不同物源特征表明伴随着昔格达古湖的形成,金沙江河流经历了演化史上的巨变。     

卵砾石地层金刚石钻头的试验研究

卵砾石地层钻进是钻探的难题之一,不仅钻进速度低,钻头的使用寿命短,而且钻探成本高。针对卵砾石地层钻进,开展了新型结构钻头的试验研究,研制成一种金刚石-聚晶体复合型钻头,现场试验表明,钻头的钻进速度能够≮1.8 m/h,使用寿命能够达到50 m,钻探成本较低。     

Active Soils of the Niger Delta in Road Pavement Design and Construction

Active soils existing to irreplaceable extents (both laterally and vertically) within the freshwater zone of the Niger delta are known and have been shown to be highly undesirable in their natural forms for road construction. This is because they swell extensively in the rainy season and shrink proportionately in the dry months together with any structure including road pavement constructed with or placed on them. In this paper, four samples of these soils collected from across the Niger delta were subjected to chemical stabilization with slaked-lime and calcium chloride (CaCl₂) to reduce swelling potential while resulting mixtures (corresponding to tolerable swelling limits) were stabilized with Portland cement to improve strength. First, swell indicator (i.e. 24-h free swell index) was found to diminish with increasing stabilizer content while for combined plot (independent of location/percentage fines), about 10.7% and 6% slaked-lime and CaCl₂ were found to be required to achieve the minimum (2.5% free swell) tolerable, normal or non-swell soil condition. Under this condition and for individual soil materials, addition of cement was found to enhance continual increase in MDD, soaked-CBR and durability index such that the soil becomes better compactible, stronger and more durable with increasing cement content. About 2.6% and 14.6% cement contents were found needed to respectively produce sub-base and base-course materials in roadworks with the latter much more durable than the former. The graphs so obtain could also constitute a complete graphical model for preparing deltaic active soils for use as road pavement materials.     

Analysing laser‐scanned digital terrain models of gravel bed surfaces: linking morphology to sediment transport processes and hydraulics

The grain‐scale topography of a sediment surface is a key component of a fluvial system, affecting aspects including sediment transport, flow resistance and ecology. However, its effect is hard to quantify because of the need for grain‐scale elevation data from in situ fluvial gravel surfaces which are difficult to collect. The sediment surface properties are, therefore, commonly estimated as a function of the sediment grain‐size distribution; however, because of additional factors, such as grain packing and shape, there is not necessarily a unique relationship between the two. A new methodology has been developed that uses terrestrial laser scanning to collect grain‐scale topographic data from in situ fluvial gravel surfaces, from which digital terrain models are created. This paper investigates methods of analysing such digital terrain models, and possible sedimentological interpretations that can be drawn from the analysis. Eleven digital terrain models from exposed gravel surfaces in two contrasting rivers (the River Feshie and Bury Green Brook) were analysed by calculating: the distribution of surface elevations, semivariograms, surface inclinations, surface slopes and aspects and grain orientation. The distribution of surface elevations and surface slope and aspect analysis were found to be most informative. In the River Feshie, grain‐size was interpreted as being a dominant control on sediment surface structure and gravel imbrication was identified. In Bury Green Brook, the location of the digital terrain models within the riffle–pool sequence was the dominant control on surface structure and grain orientation. Such digital terrain models therefore provide a new approach to measuring and quantifying the topography of fluvial sediment surfaces.     

广州市公园表层土壤中有机氯农药的分布特征

通过测定广州市典型公园的冬季和夏季表层土壤样品中有机氯农药(OCPs)含量,研究了OCPs的残留现状和潜在生态风险,并与附近地区相比较,结合当地所处的地理位置对土壤中OCPs的分布特征进行了探讨。冬季和夏季土壤中,六六六类(HCHs)的残留水平分别为0.29~6.26 ng/g和0.60~8.07ng/g,平均值分别为2.06和2.44 ng/g;滴滴涕类(DDTs)的残留水平分别为3.27~38.8 ng/g和1.46~35.5 ng/g,平均值分别为12.4和12.5 ng/g。两类OCPs都未超过国家土壤环境质量标准一级自然背景值。较低的α-HCH/γ-HCH比值和γ-HCH>β-HCH,有可能仍有林丹的使用所致。一些公园可能有新的外源DDTs的输入。历史悠久且距离市中心较近的公园土壤中OCPs含量明显偏高。对于大多数新建且相对偏僻的公园而言,表层土壤一般都未见明显的OCPs污染。