水体垂向扰动条件下溶质在沉积介质中的迁移研究

发布时间：2017-12-28 14:01

本文关键词：水体垂向扰动条件下溶质在沉积介质中的迁移研究　出处：《清华大学》2015年硕士论文　论文类型：学位论文

【摘要】：上覆水体的扰动对海洋、河流、湖泊等水体沉积物中物质的再悬浮和释放已逐渐受到全球学者的关注。这种在水动力条件下导致的物质的迁移和再悬浮过程,尤其是污染物质的释放过程严重的影响着水体的环境和生态平衡。为了研究在上覆水体扰动条件下物质在沉积介质中的迁移,本实验建立了简单的沉积物再悬浮发生装置,并分别利用不同粒径大小的沙粒作为均质沉积物,同时利用500μg·cm-3的溶解性罗丹明B作为示踪剂,观测研究在垂向紊流扰动条件下溶质在不同沉积介质中的迁移情况。实验表明,在均匀沉积介质中,水流的垂向扰动主要影响溶质的垂向迁移,而溶质的水平对流迁移十分微弱。在200 r·min-1的扰动强度下,在平均粒径为71μm介质中,溶质几乎不发生对流迁移现象,以自由扩散迁移为主,且扩散的强度与埋深没有直接关系;而该扰动强度对平均粒径为154μm,311μm,503μm和646μm均匀沉积介质的扰动影响深度分别达到了7cm,10cm,12cm和13cm;在各均匀介质中最大迁移速率分别达到了0.8 mm·h-1、1.8 mm·h-1、2.9 mm·h-1和4.9 mm·h-1,且随着埋深的加深,物质前迁移减弱。而在非均匀介质中,上覆水体的扰动将在非均匀介质中产生的横向孔隙水紊动压强增大,从而导致溶质随着水流发生跨介质的横向对流迁移,且一定范围内随着扰动的增强和颗粒粒径的增大,溶质的这种横向对流迁移也相应增强。当扰动强度达到300 r·min-1以上时,沉积层表层颗粒已发生了大量再悬浮-再沉淀现象,破坏了表层沉积层结构。研究还发现非均匀结构将会增大溶质在介质中的垂向迁移以及同一扰动强度对介质的影响深度,如200r·min-1的扰动强度对646μm均匀沉积介质影响深度为13cm,而对其各类非均匀结构的影响深度达到了15cm~16cm;并且对于同一种沉积介质,不同的非均匀组合对溶质迁移的影响也不同。同时,研究还表明,不同的沉积介质间存在着一个最利于溶质迁移的结构组合,在本实验组中,646μm介质与311μm介质构成的非均匀结构在200r·min-1的扰动强度下最利于物质的迁移。另外,实验发现在非均质边界处,溶质在71μm介质中的扩散迁移大大增强,其最大扩散直径增量几乎是其它各点的1.5倍~2倍,说明扰动条件下非均匀结构对溶质的扩散迁移也有明显的增强效果。由于自然条件下水动力条件十分复杂,不同的扰动环境对物质的迁移影响也存在着较大的差异,因此该论文得出的结论适用于水体的垂向扰动。
[Abstract]:The disturbance of overlying water has gradually attracted the attention of global scholars for the resuspension and release of material in marine, river, lake and other water sediments. The migration and resuspension of substances, especially the release of pollutants, seriously affect the environment and ecological balance of water under hydrodynamic conditions. In order to study the disturbance transfer conditions in sedimentary material medium in overlying water, this experiment established a simple sediment resuspension generator, and then different particle size of sand as homogeneous sediments, while using 500 g cm-3 dissolved Luo Danming B as tracer, observation and study of disturbance migration conditions the solute in different deposition medium to turbulent flow in the vertical. The experimental results show that the vertical migration of the solute is mainly influenced by the vertical disturbance of the flow in the homogeneous sedimentary medium, while the horizontal convection migration of the solute is very weak. In the perturbation strength 200 r min-1, the average particle size of 71 m in the medium, there is almost no solute convection phenomenon, migration dominated by free diffusion, and the diffusion of the strength and depth of no direct relationship; and the disturbance intensity on the average particle size of 154 m, 311 m, influence the depth of disturbance 503 m and 646 m respectively, the uniform deposition of medium 7cm, 10cm, 12cm and 13cm; in the homogeneous medium maximum migration rate reached 0.8 mm - H-1, mm - 1.8 H-1, 2.9 mm H-1 and 4.9 mm H-1, and with the depth of the material before deepened. Migration weakened. While in non homogeneous medium, transverse pore water turbulence disturbance of overlying water will result in inhomogeneous medium dynamic pressure increases, which leads to the solute water flow with transverse convection cross media migration, and within a certain range with the increasing of the size of the particle and enhance the disturbance, the migration of the solute is transverse convection the corresponding enhancement. When the intensity of the disturbance reaches more than 300 R. Min-1, a large number of re - suspension and re precipitation phenomena have occurred in the surface layer of the sedimentary layer, which destroys the structure of the surface layer. The study also found that non uniform structure will increase the solute in the medium vertical migration and the influence of disturbance intensity on the same medium depth, such as disturbance intensity of 200R - 646 m min-1 on the uniform deposition medium influence depth is 13cm, and the influence of various kinds of non uniform structure depth reached 15cm~16cm; and for the same the sedimentary medium, different non uniform combination effects on solute migration are different. Meanwhile, the study also shows that there is a structural combination that is most conducive to solute transport among different sedimentary media. In this experimental group, the non-uniform structure composed of 646 mu m medium and 311 m medium is most conducive to the migration of matter under the intensity of 200R min-1. In addition, it is found that the diffusion and transport of solute in the medium of 71 M can be greatly enhanced at the heterogeneous boundary. The maximum diffusion diameter increment is almost 1.5 times ~2 times of the other points, indicating that the heterogeneous structure has obvious enhancement effect on the solute diffusion and migration under the condition of disturbance. Because of the complexity of hydrodynamic conditions under natural conditions, the influence of different disturbance environments on material migration is also quite different. Therefore, the conclusions drawn in this paper are applicable to vertical disturbance of water bodies.
【学位授予单位】：清华大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：X52

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