Evaporation from seasonally frozen bare and vegetated ground at various groundwater table depths in the Ordos Basin,Northwest China     

Zaiyong Zhang  Wenke Wang  Chengcheng Gong  Zhoufeng Wang  Lei Duan  Tian‐chyi Jim Yeh  Peiyuan Yu 《水文研究》2019,33(9):1338-1348

In cold climates, the process of freezing–thawing significantly affects the ground surface heat balance and water balance. To better understand the mechanism of evaporation from seasonally frozen soils, we performed field experiments at different water table depths on vegetated and bare ground in a semiarid region in China. Soil moisture and temperature, air temperature, precipitation, and water table depths were measured over a 5‐month period (November 1, 2016, to March 14, 2017). The evaporation, which was calculated by a mass balance method, was high in the periods of thawing and low in the periods of freezing. Increased water table depth in the freezing period led to high soil moisture in the upper soil layer, whereas lower initial groundwater levels during freezing–thawing decreased the cumulative evaporation. The extent of evaporation from the bare ground was the same in summer as in winter. These results indicate that a noteworthy amount of evaporation from the bare ground is present during freezing–thawing. Finally, the roots of Salix psammophila could increase the soil temperature. This study presents an insight into the joint effects of soil moisture, temperature, ground vegetation, and water table depths on the evaporation from seasonally frozen soils. Furthermore, it also has important implications for water management in seasonally frozen areas.  相似文献   

全球变化中的地球化学基线值研究及中国的研究现状   总被引：1，自引：0，他引：1  

陈静生  尹玉军 《地球科学进展》1991,6(2):36-39

介绍了“全球地球化学制图”(IGM)项目及其在中国的进展情况。展望了我国地球化学基线值研究工作方向及研究重点。  相似文献   

3种水稻土时间序列黏粒矿物的组合特征与物源指示意义     

韩光中 《地理科学》2016,36(8):1277-1284

对南方丘陵区3种不同母质水稻土时间序列黏粒矿物的X-射线衍射（XRD）进行分析发现：① 紫色砂页岩（PS）母质起源土壤的黏粒矿物以高岭石类似矿物为主;第四纪红黏土（RC）母质起源土壤的黏粒矿物以高岭石类似矿物、伊利石类似矿物与三羟铝石为主;红砂岩（RS）母质起源土壤的黏粒矿物以1.4 nm过渡矿物、高岭石类似矿物与三羟铝石为主。② 这3种母质土壤种稻后黏粒矿物的变化大体可分为2种情况。RC与RS母质的起源土壤种稻后,土壤黏粒矿物的变化相对较小,伊利石类似矿物相对含量有所增加,这可能主要与钾肥的持续施用有关。PS母质的起源土壤种稻后,土壤黏粒矿物变化相对较大,表现为高岭石类似矿物相对含量降低,低结晶度的伊利石或次生绿泥石与三羟铝石相对含量上升。PS母质发育的土壤种稻后脱钾明显且主要集中在原生矿物部分。这种原生矿物的脱钾作用对土壤黏粒含量和黏粒矿物的类型都有较大影响。③ 起源土壤的黏粒矿物通常会被水稻土所继承,并在水稻土发育过程中相对稳定,可以用其来指示起源土壤（或母质）的物源组分。  相似文献   

面向自然连续面群边线的协同化简方法     

张付兵  孙群  朱新铭  马京振 《地球信息科学学报》2022,24(4):631-642

自然连续面群边线化简是地形图中自然面状要素和地理国情普查数据中自然图斑自动制图综合的重要实施步骤。现有面要素边线化简算法大多以线化简算法为基础,未有效化简弯曲特征、保持面积平衡和满足图面视觉清晰性要求,且化简结果存在共享边界不一致、边线自相交和边线之间相交的拓扑问题。为此,结合自然连续面群表达特点和化简要求,本文提出一种面向自然连续面群边线的协同化简方法。首先将自然连续面群转换为拓扑数据结构组织,以待化简弧段及其相邻弧段为基础构建约束Delaunay三角网,标识化简区域;其次利用弧段双侧层次多叉树模型渐进式退化条带状弯曲、化简细小弯曲;最后自适应夸大狭窄“瓶颈”,实现边线的协同化简。以河南省某区域1:5万地形图中的植被与土质面要素进行化简实验,相较于对比方法,该方法能够有效保持自然连续面群边线化简前后的拓扑一致性、要素之间的面积平衡,充分化简目标尺度下的局部不清晰细节,化简结果精度高。  相似文献   

Organochlorine Pesticide Residues in Soils and Sediments of the Herbert and Burdekin River Regions, North Queensland – Implications for Contamination of the Great Barrier Reef     

J. E. Cavanagh  K. A. Burns  G. J. Brunskill  R. J. Coventry 《Marine pollution bulletin》1999,39(1-12):367-375

Organochlorine pesticides were widely used in the Australian sugarcane industry from the early 1950s until the late 1980s. Erosion of sugarcane soils and subsequent transport of sediment bound contaminants in river run-off to the Great Barrier Reef lagoon is a growing concern as the cane industry continues to expand. Organochlorine pesticide residues can be used as tracers to examine the worst-case scenario of the spatial extent to which currently used, though less persistent, organic agricultural pesticides might extend. The coastal alluvial flood-plains of the Herbert and Burdekin Rivers in North Queensland have sugarcane growing as the major coastal land-use. Sediment cores and surface sediment samples were collected from near-shore coastal regions of the Herbert and Burdekin Rivers. In addition, soil samples from cane-fields in the two catchments were collected. Analyses of the marine surface sediment samples and three sediment cores revealed the absence of detectable concentrations of organochlorine pesticides (<5 pg/g). However, easily detectable concentrations were found in the sugarcane soil samples (0.01–45 ng/g).  相似文献   

结构性软土的损伤及其对地基沉降的影响   总被引：5，自引：2，他引：3  

孙红  赵锡宏 《岩土力学》1999,20(1):19-21,26

通过室内试验,研究了软粘土的结构性及其在受力过程中的损伤特性,并讨论结构损伤对地基瞬时沉降和固结沉降的影响。计算结果表明,常规方法低估地基的瞬时沉降,夸大地基的固结沉降。  相似文献   

FEM validation of a double porosity elastic model for consolidation of structurally complex clayey soils     

C. Callari  F. Federico 《国际地质力学数值与分析法杂志》2000,24(4):367-402

Laboratory consolidation of structured clayey soils is analysed in this paper. The research is carried out by two different methods. The first one treats the soil as an isotropic homogeneous equivalent Double Porosity (DP) medium. The second method rests on the extensive application of the Finite Element Method (FEM) to combinations of different soils, composing 2D or fully 3D ordered structured media that schematically discretize the complex material. Two reference problems, representing typical situations of 1D laboratory consolidation of structured soils, are considered. For each problem, solution is obtained through integration of the equations governing the consolidation of the DP medium as well as via FEM applied to the ordered schemes composed of different materials. The presence of conventional experimental devices to ensure the drainage of the sample is taken into account through appropriate boundary conditions. Comparison of FEM results with theoretical results clearly points out the ability of the DP model to represent consolidation processes of structurally complex soils. Limits of applicability of the DP model may arise when the rate of fluid exchange between the two porous systems is represented through oversimplified relations. Results of computations, obtained having assigned reasonable values to the meso‐structural and to the experimental apparatus parameters, point out that a partially efficient drainage apparatus strongly influences the distribution along the sample and the time evolution of the interstitial water pressure acting in both systems of pores. Data of consolidation tests in a Rowe's cell on samples of artificially fissured clays reported in the literature are compared with the analytical and numerical results showing a significant agreement. Copyright © 2000 John Wiley & Sons, Ltd.  相似文献   

改性粘土辅助沉水植物修复技术维持清水稳态的原位研究   总被引：1，自引：0，他引：1  

汤鑫  曹特  倪乐意  谢平 《湖泊科学》2013,25(1):16-22

在富营养湖泊治理实践中,修复沉水植被被认为是改善水质的长效措施,而壳聚糖改性粘土是短期快速改善水质的有效手段.本研究利用改性粘土辅助沉水植被修复,旨在探索改善水质的长效方案.2011年5-11月在太湖梅梁湾开展了四组不同处理(对照、水草、水草+粘土、粘土)围隔实验,在水草(盖度13.0%)和水草+粘土(盖度52.3%)围隔中不同程度重建了苦草群落.实验期内每3 d一次的水质监测表明,粘土处理可显著改善水质,水体总氮(TN)、总磷(TP)、正磷酸盐(PO34--P)和叶绿素a(Chl.a)含量分别比对照下降了20.7%、74.6%、31.0%和80.4%,透明度(SD)升高了90.4%;粘土辅助植被修复改善水质效果最长稳,水体TN、TP、PO34--P和Chl.a含量分别比对照下降了36.2%、64.0%、28.6%和71.1%,SD升高了76.4%;低盖度苦草群落单独处理对水质改善效果不显著.在三种处理中,粘土辅助植被修复改善底质效果最好,使间隙水的TN、TP、PO34--P、NH4+-N分别比实验前下降了15.6%、61.7%、55.8%和82.8%.本研究表明改性粘土辅助沉水植被修复可作为重富营养水体中水质改善的整合技术,但其长期生态效应仍需谨慎评估.  相似文献   

An averaging procedure for layered materials     

A. Niemunis  C. Karcher  T. Theile 《国际地质力学数值与分析法杂志》2000,24(10):837-851

In order to model thin‐layered soils a special averaging procedure is proposed. It works with very few restrictions imposed on the constitutive equations used for individual materials. General considerations are followed by an example from open pit mining industry. Geometrical non‐linearity is considered. The proposed method is not necessarily restricted to the problems of soil mechanics. It could also be applied on composite materials. Copyright © 2000 John Wiley & Sons, Ltd.  相似文献   

A first Holocene leaf wax isotope-based paleoclimate record from the semi-humid to semi-arid south-eastern Caucasian lowlands     

Marcel Bliedtner  Roland Zech  Jana Zech  Imke Schäfer  Hans von Suchodoletz 《第四纪科学杂志》2020,35(5):625-633

The Holocene paleoclimate of the Caucasus region is rather complex and not yet well understood: while existing studies are mainly based on pollen records from high-altitude and humid lowland regions, no records are available from the semi-humid to semi-arid south-eastern Caucasian lowlands. Therefore, this study investigated compound-specific δ²H and δ¹³C isotopes of leaf wax biomarkers from Holocene floodplain soils in eastern Georgia. Our results show that the leaf wax δ²H signal from the paleosols mostly reflects changes in the moisture source and its isotopic composition. Depleted δ²H values before ~8 cal ka bp change towards enriched values after ~5 cal ka bp and become again depleted after ~1.6 cal ka bp. This trend could be caused by Holocene changes of the isotopic compositions of the Black and eastern Mediterranean Sea, and/or by varying contribution of both moisture sources linked with the North Atlantic Oscillation. The leaf wax δ¹³C signal from the paleosols directly indicates varying local water availability and drought stress. Depleted δ¹³C values before ~8 and after ~5 cal ka bp indicate wetter local conditions with higher water availability, whereas more enriched values during the middle Holocene (~8 until at least 5 cal ka bp ) indicate drier conditions with increased drought stress.  相似文献