Solute Transport In Porous Sediment Under A Verticle Water Disturbance

The problem of mass re-suspension and release from the sediment structure of ocean, river and lake by the disturbance of overlying water has attained more and more attraction from global researchers. Such mass re-suspension, especially pollutants release by the turbulent condition has dramatically influenced water environment as well as its’ eco-system.To examine mass transport in porous sediments during a turbulent flow, we established a simple sediment re-suspension device, made use of different size of sands as homogeneous sediments, and injected 500μg·cm-3 soluble Rhodamine B into different parts of the sediment as mass tracer, to observe mass transport during the turbulent condition.The research showed that pore-water pressure mainly influenced mass transporting vertically in homogeneous sediment. In the average particle size of 71μm medium, there was almost no convection phenomenon under 200 r·min-1 intensity disturbance, and mass transport was mainly diffusion, further more, such diffusion had no connection with its’ burial depth. While the affection depth of average particle size of 154μm, 311μm, 503μm and 646μm media under this turbulent intensity was respectively 7cm, 10 cm, 12 cm and 13 cm, and the utmost transporting velocity in each sediment was respectively 0.8mm·h-1, 1.8mm·h-1, 2.9mm·h-1 and 4.9mm·h-1. While in non-homogeneous sediments, pore-water pressure gradient will be generated under certain turbulent disturbance, such pressure gradient will further lead to mass transport with the pore-water flow in the porous sediment in horizontal direction. Moreover, such convection transport will relatively enhance with the increasing of particle size or the turbulent disturbance. When it reached 200r·min-1, the surface sediment structure was found to be damaged. Still, non-homogeneous structure would also enhance verticle transpotation of mass in the sediment as well as its’ affect depth. For example, the disturb depth in 646μm sediment was 13 cm under 200 r·min-1 disturbance, while it reached 15cm~16cm in its’ corresponding non-homogeneous structure, and as to a certain medium, different non-homogeneous structure had diverse influence on mass transportation. Meanwhile, the results showed that there was an optimal non-homogeneous structure for mass transport, in this thesis, 646μm-311μm structure was found to be the optimal one under 200r·min-1disturbance. Lastly, the research found that mass transport in 71μm medium at the inter-surface of the non-homogeneous structure was largely enhanced, and its’ maximum diameter increment was nearly 1.5~2 times of other points, which meaned that non-homogeneous structure has strong effect on mass diffusion and migration at the inter-surface.As in the real sediment environment in oceans and lakes, such water dynamic conditions are extremely complex, and different turbulent condition has its’ distinct affect on mass transport in porous sediment, so the conclusions from this thesis are mostly applied to verticle water disturbance condition.