IMHE OpenIR  > 山地表生过程与生态调控重点实验室
紫色土坡地产流过程及胶体迁移研究
Alternative TitleHydrological Processes and Colloid Transport in the Sloping Farmland of Purple Soil
Language中文
张维
Thesis Advisor唐翔宇
2015
Degree Grantor中国科学院大学
Place of Conferral北京
Degree Name博士
Degree Discipline土壤学
Keyword胶体迁移 紫色土 坡耕地 产流
Abstract胶体是介于泥沙和溶质之间的悬浮颗粒,广泛存在于地下环境中,是多种污染物在多孔介质和裂隙介质中迁移的载体。地块尺度自然胶体释放及迁移的研究非常缺乏,尤其是有关胶体随地表与裂隙潜流的迁移机理与动态研究还未见报道。长江上游紫色土地区坡耕地土壤侵蚀及水土流失是造成三峡库区乃至长江流域地表水、地下水环境质量下降的重要原因之一。本研究以川中丘陵区典型小流域紫色土坡耕地(24 m2、1500 m2)为对象,研究了坡地地表径流、壤中流及泥岩裂隙潜流中自然胶体原位释放与迁移的机理、动态及其与坡地产流的关系,同时查明了从坡地到小流域地表水出口断面的浅层地下水(6口不同使用功能的井)中胶体的季节变化动态。主要结果和结论如下: 紫色土坡耕地产流机理及径流特征 降雨入渗过程中,雨水主要驱替浅层土壤(0-10 cm)中的孔隙水,20 cm土层土壤旧水滞留时间最长,难以被驱替。紫色土坡地中活塞流及壤中流可以同时发生,活塞流主要发生在10-20 cm土层,且雨前土壤越湿润、降雨强度越大越有利于活塞流发生;优先流主要发生在20-30 cm的犁底层。最大降雨强度超过土壤饱和导水率时,土壤大孔隙是产流的主要通道,反之,介孔是主要通道。综合裂隙潜流流量、DOC浓度、稳定性氧同位素(δ18O)及坡地土水势等指标的动态变化可以全面深入地揭示裂隙潜流产流机理以及产流过程中水源的变化。紫色土坡地地表径流主要是超渗产流,岩土界面土层饱和时才产生侧向壤中流,是蓄满产流。泥岩裂隙潜流是紫色土坡地最主要产流方式,雨水对裂隙潜流及壤中流的初始穿透有重要贡献。 紫色土坡耕地自然胶体原位释放及迁移特征 降雨强度及其时间分配是决定紫色土坡地深层裂隙潜流中胶体对降雨响应的最重要因子。干湿交替以及持续干旱时间是影响土层中胶体源累积量的主要因素。雨水直接击溅侵蚀是地表径流中胶体释放、分散与迁移的主要机理。裂隙潜流中胶体的释放与迁移主要是发生在土层未饱和阶段,气-液界面(AWI)对胶体的富集及其随产流入渗前锋推进的过程中对胶体的释放是产流初始响应段胶体迁移的主要原因;随着产流进行,雨水混合土壤前期水对土壤介孔(土层未完全饱和时)或者大孔隙(土层饱和时)内壁胶体的水力剪切、裹挟是胶体释放与迁移的最主要机理。地表径流中的胶体浓度显著高于裂隙潜流中的胶体浓度,后者略高于壤中流中的胶体浓度。壤中流胶体浓度呈现逐渐降低和长拖尾的特点,裂隙潜流中胶体浓度呈现出快速上升、快速下降及长拖尾的特点,且胶体浓度峰早于裂隙潜流径流峰。 紫色土坡耕地径流中胶体性质 地表径流与泥岩裂隙潜流中颗粒粒径分布(PSD)呈单峰型分布,壤中流可能会出现双峰型PSD。地表径流的细颗粒(< 10 微米)含量普遍大于80%,显著高于壤中流及裂隙潜流中的细颗粒比例。裂隙潜流中胶体以团聚体存在,以< 100 微米颗粒为主,粒径峰值介于4-12 微米。产流初期细颗粒比例大于85%,随产流进行,细颗粒比例逐渐减小。紫色土坡地径流中胶体的矿物组成以原生矿物为主,其有机质含量略高于紫色土,且显著高于母岩,土壤是径流中胶体的主要来源。紫色土中胶体在形成过程中可能有CaCO3等胶结物粘结矿质胶体颗粒与有机质,促进颗粒的多级团聚,形成具有一定水稳性的胶体。 川中丘陵区典型小流域浅层地下水中胶体的季节变化 总的来说,雨季前及雨季初期浅层井中胶体浓度相对雨季期间浓度更高。井水中胶体浓度介于0.2-15 mg/L,数量浓度介于10的7次方到9次方(个/L)数量级之间,胶体以团聚体形式存在。水化学因素如井水电导率、二价阳离子含量(Ca2+、Mg2+)、DOC浓度及人为扰动是影响胶体浓度的主要因素。
Other AbstractColloids are suspending particles falling in between sediments and solutes. They are ubiquitous in subsurface geologic media and usually act as transport vehicles for various contaminants. Field studies of subsurface transport of colloids are still rare, particularly for the sloping lands. It has been widely reported that soil erosion or soil and water loss from sloping farmlands in purple soil region in the upper Yangtze River is the main reason for surface and subsurface water quality degradation in the Three Gorges Reservoir area or even the whole Yangtze River basin. Colloid release mechanisms and transport dynamics in surface runoff, subsurface lateral flow and underflow/fracture flow from sloping farmlands of purple soil (1500 m2 and 24 m2) in a typical small watershed in the hilly area of central Sichuan Basin were studied. Moreover, colloid variations in the shallow well water were investigated in the same small watershed. The major results are as follows: Flow generation mechanisms and flow characteristics in the sloping farmland of purple soil Rainwater mainly displaces pre-event soil water in the shallow layer (0-10 cm). Soil water at 20 cm in soil profile shows the longest residence time and could hardly been displaced. Piston flow and preferential flow could occur simultaneously in the sloping farmland. Piston flow mainly occurs in 10-20 cm layer and the good soil wetness and large rainfall intensity favors the occurrence of piston flow. Preferential flow mainly occurs at 20-30 cm layer. When the maximum rainfall intensity is larger than soil Ks-LPL, soil macropores act as the main conductors for flow, otherwise, soil mesopores are the main flow conductors. Dissolved organic carbon concentration and δ18O dynamics in combination with soil water potential could be used to apportion water sources of fracture flow at different stages. Surface flow is infiltration excess overland flow for the most time and subsurface lateral flow is saturation flow. Underflow or fracture flow is the major flow pattern in sloping farmlands. Rainwater shows a large contribution in underflow or fracture flow breakthrough. Colloid release mechanisms and transport dynamics in sloping farmlands Rainfall intensity and its distribution during the rainfall determine fracture flow colloid response to rainfall events. Dry and wet cycles and the drying intervals between two events have a large influence on colloid pool accumulation. Rainwater splash leads to colloid release, dispersion and transport in surface runoff. Colloid release and transport occurred mainly during the period when soil layer was not completely saturated. Air-water interface adsorb colloids due to its larger surface tension than that in water-solid interface. The moving AWI driving by the infiltration fronts releases its associated colloids, which is responsible for colloid release and transport at the early subsurface flow response stage. As the saturation increase in the soil, hydraulic shearing and scouring of colloids from soil mesopores and macropores by the mixing flow of rainwater and pre-event soil water becomes the most important contribution for subsurface colloid release and transport mechanism. Colloid concentrations in surface runoff are much larger than that in subsurface flow. Colloid concentration in subsurface lateral flow shows gradual decrease and long tailing, while it shows a fast increase followed by the fast decrease and long tailing in underflow. Characteristics of colloids in runoff of sloping farmlands of purple soil Particle size distribution (PSD) in surface runoff and underflow or fracture flow is unimodal and a bimodal PSD pattern may appear for subsurface lateral flow. Small particles with diameters < 10 um account for a major portion (> 80%) in surface runoff, which is significantly larger than that in subsurface flow. Particles in fracture flow are <100 um and the peak percentage falls between 4-12 um. Proportions of small particles with diameters <10 um are larger than > 85% at the early response stage but could decrease to less than 40 % at the receding stage. Colloids in underflow or fracture flow contain a large part of secondary mineral and their organic content is a little larger than that in the purple soil and significantly larger than that in the mudrock. Therefore, colloid may be formed in the multi aggregation processes in which mineral colloids and organic matters are bonded by cements such as CaCO3. Seasonal variations of colloids in shallow well waters In general, larger colloid concentrations were found in well waters during the period right before the rainy season and at the early rainy season as compared with that during the rainy season. Colloid concentration in different well waters varied from 0.2 mg/L to 15 mg/L and colloids existed in aggregates. Anthropogenic disturbances and water chemistries e.g. conductivity, cation (Ca2+、Mg2+) concentrations and DOC concentration have a large effect on colloid concentrations.
Document Type学位论文
Identifierhttp://ir.imde.ac.cn/handle/131551/15062
Collection山地表生过程与生态调控重点实验室
Affiliation中国科学院成都山地灾害与环境研究所
Recommended Citation
GB/T 7714
张维. 紫色土坡地产流过程及胶体迁移研究[D]. 北京. 中国科学院大学,2015.
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