【作者】 王岩；

【导师】 陈友媛；

【作者基本信息】 中国海洋大学 ， 环境工程， 2010， 硕士

【摘要】 优先流是土体在整个入流边界上接受补给,但补给只通过少部分土体的快速运移。如今,近海水域的污染问题越来越严重,从陆源带来的大量污染物质在波浪引起的水体运动和渗流作用下,在潮滩沉积物中发生着入渗、迁移和转化,而生物洞穴引发的优先流则加快了这些物质的迁移转化,加大了近海水域的污染。因此研究生物洞穴造成的优先流路径对污染物质在沉积物中的迁移转化规律具有重要的理论意义和实际应用价值。本文首先通过均质土柱与人工模拟大孔隙土柱的对比试验来揭示土壤优先水流的特征并初步研究非吸附性溶质优先迁移的运动,进一步研究土壤初始水分含量、粘粒含量、溶质施加方式、进水浓度、不同价态阳离子等对溶质优先迁移过程的影响,最后通过二维土槽试验来研究溶质优先迁移的时空分布规律。通过对比均质土柱和人工模拟大孔隙土柱的硝态氮穿透曲线,较早的初始穿透、峰值出现时间早和较高的回收率都说明人工模拟大孔隙土柱中存在优先水流。土壤优先水流的特征表现为能够快速穿透土体,其穿透曲线表现出不对称性、拖尾和出流速率具有较大的波动性。干土条件使得大孔隙对水流和溶质运移的贡献更大,减少了水流与基质间的相互作用,溶质优先运移的特征更明显；粘粒含量对溶质优先运移的影响也很大,随着粘粒含量的降低,初始穿透时间变早,出现峰值的时间也越早,峰值越大,优先流的各项特征越明显；在间歇式溶质施加方式的间隙阶段,在低渗透性介质中的溶质可以向优先流通道的边界扩散,在下一循环开始的时候可以恢复成向下渗透的水流的一部分,从而相比连续式溶质施加方式,溶质的回收率得到提高；进水浓度增大,溶质运移过程中的溶质势增大,导致出流变快,总时间变短,同时加快了溶质在土壤中的运移速度,从而使出流时间提前,达到平衡和完成运移的时间也大大缩短；硝态氮在供试土样中的迁移受不同价态阳离子的影响极小。利用二维土槽进行溶质优先迁移试验,研究了溶质优先迁移过程中非吸附性溶质(NO3-N)和吸附性溶质(H2PO4-P)的时空分布规律。NO3-N在沉积物中迁移时,表层硝态氮浓度随时间而降低,表明水及溶质随时间向下迁移了,硝态氮的浓度分布随时间变得越来越均匀,随着深度的增加在横剖面上的分布越来越不均匀；H2P04-在土样中运移时被土颗粒吸附,因此表层总磷浓度较高,到开挖土壤剖面的第二层,浓度明显降低,以下各层浓度都较低。与硝态氮的运移规律相似,总磷的浓度分布也是随着时间的推移越来越均匀,随深度越来越不均匀。由二维图像可以更直观地看出硝态氮和总磷在土槽中的浓度分布。更多还原

【Abstract】 Preferential flow is the rapid migration that the inflow boundary in the soil to accept the supplies, but the supplies only by a small part of the soil. Nowadays, the pollution problems of the offshore waters become more and more serious, the serious pollution caused by land-based sources of material is occuring infiltration, migration and transformation under the wave induced motion of water and seepage in intertidal sediments, and preferential flow caused by biological caves accelerates migration and transformation of these substances, increases pollution of coastal waters. So the study on preferential flow path caused by the biological cave has important theoretical and practical value for the transformation and migration law of contaminants in sediments.Firstly, we revealled the characteristics of the preferential flow in the soil and took preliminary study on the preferential transport of non-adsorption solute through homogeneous soil columns and columns with artificial macropores comparative test, and further studied the effects of the initial soil water content, clay content, solute application method, influent concentration, different valence cations on the solute preferential transport process, and finally reserched the spatial and temporal distribution law of solute preferential transport through the two-dimensional soil bin tests.By comparing nitrate breakthrough curves of the homogeneous soil column and soil column with artificial macropore, earlier initial penetration time, earlier peak times and higher recovery rates show that preferential flow presents in soil column with artificial macropores. Soil preferential flow is characterized by penetrating the soil quickly, the breakthrough curves show asymmetry, tailing and the flow rate has large fluctuation.Dry soil conditions make more contributions of large pores to water flow and solute transport, and reduce the interactions between the flow and the matrix, and make the characteristics of solute preferential transport clearer; clay content also has great effects on the transport of water and solute. With the decrease of clay content, the initial penetration time becomes earlier, as well as the time when the solute concentration reach the peak value. Moreover, the peak value gets bigger.the more obvious of the characteristics of preferential flow; in the gap phase of the intermittent solute application method, solute in low-permeability medium can diffuse to preferential flow channel boundary, when the next cycle starts, it can be resumed a part of the downward infiltration of water, then gets a higher solute recovery rates compared to the continuous solute application method; the bigger the influent concentration, the bigger the solute potential of solute transport process, resulting in faster flow, shorter total time, while speeding up the solute transport rate in the soil, Thus advances the effluent time, reduces the time to balance and complete the migration; the migration of nitrate in the soil samples is little affected by the cations of different valence.Using two-dimensional soil tank to study solute preferential transport, we investigated the temporal and spatial distribution law of the preferential migration of the non-adsorption solute (NO3-N) and adsorption solute (H2PO4-P).When NO3-N transported in the sediment, surface nitrate concentrations decreased with time, which indicated that water and solutes moved downward over time, and nitrate concentration become more uniform with time, andwith the depth increase the distribution is more uneven in the cross section; H2PO4- was adsorpted by soil particles when migrated in soil samples, so surface total phosphorus concentration was higher, when to the second layer of the soil profile, total phosphorus concentrations were lower, and so do the others. Be similar to the Nitrate transport law, total phosphorus concentration is more uniform over time, and more uneven with depth. By the two-dimensional image we can seen nitrate and total phosphorus concentration distribution in the soil tank more directly.更多还原