Evaluation of diffuse and preferential flow pathways of infiltrated precipitation and irrigation using oxygen and hydrogen isotopes

Subsurface-water flow pathways in three different land-use areas (non-irrigated grassland, poplar forest, and irrigated arable land) in the central North China Plain were investigated using oxygen (¹⁸O) and hydrogen (²H) isotopes in samples of precipitation, soils, and groundwater. Soil water in the top 10 cm was significantly affected by both evaporation and infiltration. Water at 10–40 cm depth in the grassland and arable land, and 10–60 cm in poplar forest, showed a relatively short residence time, as a substantial proportion of antecedent soil water was mixed with a 92-mm storm infiltration event, whereas below those depths (down to 150 cm), depleted δ¹⁸O spikes suggested that some storm water bypassed the shallow soil layers. Significant differences, in soil-water content and δ¹⁸O values, within a small area, suggested that the proportion of immobile soil water and water flowing in subsurface pathways varies depending on local vegetation cover, soil characteristics and irrigation applications. Soil-water δ¹⁸O values revealed that preferential flow and diffuse flow coexist. Preferential flow was active within the root zone, independent of antecedent soil-water content, in both poplar forest and arable land, whereas diffuse flow was observed in grassland. The depleted δ¹⁸O spikes at 20–50 cm depth in the arable land suggested the infiltration of irrigation water during the dry season. Temporal isotopic variations in precipitation were subdued in the shallow groundwater, suggesting more complete mixing of different input waters in the unsaturated zone before reaching the shallow groundwater.

     

Efficacy of Coagulants and Ballast Compounds in Removal of Cyanobacteria (<Emphasis Type="Italic">Microcystis</Emphasis>) from Water of the Tropical Lagoon Jacarepaguá (Rio de Janeiro,Brazil)

Eutrophication is considered the most important water quality problem in freshwaters and coastal waters worldwide promoting frequent occurrence of blooms of potentially toxic cyanobacteria. Removal of cyanobacteria from the water column using a combination of coagulant and ballast is a promising technique for mitigation and an alternative to the use of algaecides. In laboratory, we tested experimentally the efficiency of two coagulants, polyaluminium chloride (PAC) and chitosan (made of shrimp shells), alone and combined with two ballasts: red soil (RS) and the own lagoon sediment, to remove natural populations of cyanobacteria, from an urban brackish coastal lagoon. PAC was a very effective coagulant when applied at low doses (≤8 mg Al L^?1) and settled the cyanobacteria, while at high doses (≥16 mg Al L^?1) large flocks aggregated in the top of test tubes. In contrast, chitosan was not able to form flocks, even in high doses (>16 mg L^?1) and did not efficiently settle down cyanobacteria when combined with ballast. The RS itself removed 33–47 % of the cyanobacteria. This removal was strongly enhanced when combined with PAC in a dose-dependent matter; 8 mg Al L^?1 was considered the best dose to be applied. The lagoon sediment alone did not promote any settling of cyanobacteria but removal was high when combined with PAC. Combined coagulant and ballast seems a very efficient, cheap, fast and safe curative measure to lessen the harmful cyanobacteria bloom nuisance in periods when particularly needed, such as around the 2016 Olympics in Jacarepaguá Lagoon.     

柴达木盆地西部新生界陆相湖盆碳酸盐岩沉积环境与沉积模式*

利用野外露头、岩心、测井录井和分析化验资料,对柴达木盆地西部(简称“柴西地区”)新生界干柴沟组湖相碳酸盐岩进行了研究,划分了其沉积微相类型,研究了其分布规律,分析其形成环境和控制因素,并建立了相应沉积模式。该区湖相碳酸盐岩在垂向上与碎屑岩频繁互层,湖相碳酸盐岩包括颗粒灰岩、藻灰岩、泥晶灰岩和混积岩4大类11种,划分出了灰泥坪、颗粒滩、藻丘(礁)、浅湖湾以及(半)深湖泥灰岩相等5种沉积微相。通过分析不同碳酸盐岩及其微相时空展布特征,认为其发育主要受控于湖盆构造运动、湖平面变化、陆源碎屑注入、古气候与古水介质条件、古地貌与古水深环境,并在此基础上建立了柴西湖相碳酸盐岩的沉积模式。研究认为柴达木盆地西部干柴沟组沉积时期,湖盆为典型咸化湖盆,构造活动相对稳定,湖平面上升达到峰值。碳酸盐岩主要发育在湖侵期,高频湖平面变化形成了碳酸盐岩与碎屑岩频繁互层。在枯水期,盆地坡折处发育碎屑岩滩坝或三角洲前缘沉积;在湖侵期,盆地坡折处发育了鲕粒滩及藻灰岩,盆地洼陷区发育泥灰岩或灰质泥岩。     

Discovery of the early Jurassic Gajia mélange in the Bangong–Nujiang suture zone: Southward subduction of the Bangong–Nujiang Ocean?

International Journal of Earth Sciences - Mélange records a series of geological processes associated with oceanic subduction and continental collision. This paper reports for the first time...     

松辽盆地增强型地热系统开发选区评价

干热岩是一种新型清洁能源,其开发利用区的确定十分重要。笔者首先通过对松辽盆地热源、资源量、导热、聚热、地震活动5个方面资料的收集,提出了松辽盆地增强型地热系统开发选区适宜性评价方法;然后选取8项评价因子,利用ArcGIS 10.2平台将松辽盆地划分为26个评价单元,根据打分法和层次分析法(AHP)求取每个因子的权重;最后,对26个选区进行综合评价,将其分成适宜、较适宜、一般适宜、较不适宜和不适宜5个等级。结果表明:松辽盆地干热岩开发适宜区和较适宜区主要集中在盆地中部的大安—大庆一带,确定的适宜选区范围对今后干热岩开发工作具有一定指导作用。     

孟加拉盆地东部褶皱带差异构造变形及成因

基于野外地质调查和地震资料分析,证实了孟加拉盆地东部褶皱带发育底部和中部两套滑脱层。底部滑脱层在整个褶皱带均发育,而中部滑脱层仅发育于北段—中段的陆上和陆架区,在中段的陆坡-洋盆区及南段则不发育。中部滑脱层的发育受古陆坡富泥沉积控制。北段—中段主要发育滑脱褶皱及被断层突破的滑脱褶皱,而南段主要发育泥底辟和泥火山构造。孟加拉盆地东部褶皱带滑脱层系及构造样式的差异变形特征主要受区域挤压作用、沉积作用以及地层流体超压等方面存在着差异的共同影响。     

二元同位素测温技术及其在白云岩储层成因研究中的应用——以塔里木盆地中下寒武统为例

作为近年来新兴的实验技术,二元同位素(D47)测温技术已被应用于碳酸盐岩成岩环境的研究中。简要介绍了二元同位素测温技术的原理及应用方法,并以塔里木盆地中下寒武统白云岩为例,优选11块样品,测试其D47值和白云石的碳氧同位素,并计算出样品的成岩温度和古流体的δ~(18)O值。综合分析认为:样品中,颗粒白云岩形成于低温准同生—浅埋藏环境,成岩流体为海水;细晶白云岩为深埋藏成岩环境中原岩受到了高温重结晶作用的改造,成岩流体为地下热卤水;孔缝中的白云石胶结物是深埋藏成岩环境富镁热卤水沉淀作用的产物。研究证明二元同位素测温技术可以较好地恢复白云岩的成岩温度,减少储层成因的多解性,它为今后储层成因研究提供了一种新的手段和依据。     

DEM simulations of sandstone under true triaxial compressive tests

Numerically simulated true triaxial compression tests (σ ₁ ≥ σ ₂ ≥ σ ₃) are conducted in this study to elucidate the failure mechanism of sandstone using 3D discrete element method (DEM), in particular the effect of the intermediate principal stress (σ ₂). Eight series of tests (σ ₃ = 0, 10, 20, 30, 40, 50, 70, and 100 MPa) are conducted. Within each series, σ ₂ is varied from σ ₂ = σ ₃ to σ ₂ = σ ₁ from test to test. For each test, σ ₁ is raised monotonically to failure while keeping σ ₂ and σ ₃ constant. The DEM simulations reveal the effect of σ ₂ on the variations of peak stress, Young’s modulus, failure plane angles, the brittle–ductile transition, and the evolution of failure modes, the effect beyond the well-understood effect of σ ₃. The simulation is in qualitative agreement with the results obtained experimentally. Detailed analyses performed on the particle-scale responses further the understanding of the microscopic mechanisms. The distribution of contact force becomes more homogeneous with the increase of σ ₃, which leads to the resulting damage being more localized rather than diffused. The interaction between contact force distribution and coalescence of cracks determines the processes and patterns of fracturing in the sample scale. σ ₂ is found to affect the microscopic stress distribution as well as structure evolution, and this effect weakens with the increase of σ ₃.     

Three-dimensional DEM investigation of critical state and dilatancy behaviors of granular materials

The critical state is significant to the mechanical behaviors of granular materials and the foundation of the constitutive relations. Using the discrete element method (DEM), the mechanical behaviors of granular materials can be investigated on both the macroscopic and microscopic levels. A series of DEM simulations under true triaxial conditions have been performed to explore the critical state and dilatancy behavior of granular materials, which show the qualitatively similar macroscopic responses as the experimental results. The critical void ratio and stress ratio under different stress paths are presented. A unique critical state line (CSL) is shown to indicate that the intermediate principal stress ratio does not influence the CSL. Within the framework of the unique critical state, the stress–dilatancy relation of DEM simulations is found to fulfill the state-dependent dilatancy equations. As a microscopic parameter to evaluate the static determinacy of the granular system, the redundancy ratio is defined and investigated. The results show that the critical state is very close to the statically determinate state. Other particle-level indexes, including the distribution of the contact forces and the anisotropies, are carefully investigated to analyze the microstructural evolution and the underlying mechanism. The microscopic analysis shows that both the contact orientations and contact forces influence the mechanical behaviors of granular materials.     

The human impact on the transformation of juniper forest landscape in the western part of the Pamir-Alay range (Tajikistan)

Detailed analyses were conducted of human impact on juniper forest landscapes occurring within the Zarafshan Range (Pamir-Alay). Juniperus seravschanica and J. semiglobosa belong to forest-forming species in Central Asia. At present, juniper forests all over Tajikistan are seriously threatened as a result of excessive logging and cattle grazing. The aim of this paper is to present juniper forest transformation as a result of human activities as well as the diversity of soil properties in the organic and humus horizons in the altitudinal system of soil zonation. Three groups of phytocoenoses were distinguished: those with a dominant share of Juniperus seravschanica; those with a dominant share of J. semiglobosa; and mixed. Associations with Juniperus seravschanica and J. semiglobosa feature several variants of phytocoenoses with dominant species: Artemisia lehmanniana, A. dracunculus, Eremurus olgae, Festuca sulcata, Ligularia thomsonii, Stipa turkestanica, Thymus seravschanicus, and Ziziphora pamiroalaica. The collected soil samples differ in their granulometric composition. Gravelly cobble fractions >2 mm are dominant; the share of sandy particles <2 mm is much lower (about 10–20%). Fraction 0.5–0.05 attains 35% on average. The Corg content of the soil varied from 0.26 to 11.40% in the humus horizon (A) and from 4.3 to 25% in the organic (O). Similar relationships were reported in the case of Ntot concentration. A clear relationship can be observed between concentrations of Corg and Ntot. Soil pH varied, ranging from very low acidic (pH 5.5) to neutral (pH 8.5). The content of available P varied; high concentrations were noted in organic (O) (40.46–211 mg kg^?1) and mixed horizons (OA) (2.61–119 mg kg^?1). Maximum accumulations of Pavail (1739.6 mg kg^?1) and Ptot (9696 mg kg^?1) were observed at a site heavily affected by intense grazing. Concentrations of Mgavail varied from 116 to 964 mg kg^?1. Most of the analysed soil profiles lacked an organic horizon; only thin humus occurred.