Study On Pollution Character And Water Environment Impact Of The Wet-dry Zones In The Three Gorges Reservoir

The environment problems of the Three Gorges Reservior have being cared since it was started. With the construction of the Three Gorges Project, the Three Gorges Reservior will be more than 600 kilometers in length, 1084 square kilometers in area, and will be able to hold about 44.57 billion cubic meters of water. The project will be the foremost tactic water resource in China. Since impounded in Jun 2003 , the water level of the Reservior has risen to 156 meters, and will reach 175 meters by the end of 2009. The Three Gorges Project adopts the scheme of storing fresh water and excluding the muddy water, that is, low-water in sumer and high-water in winter, which will form wet-dry zones with a drop of 30 meters in maximum water level in the areas along the river. The wet-dry zone has strong detoxifcation function , as liver to the reservoir. It is also a gallery for exchange things and energy between land and water system, take cushion to the water and protect to the shore . In the future, due to the alternate influence of land and water environment, the ecosystem structure will be acted up by both terrestrial ecosystems and aquatic ecosystems. Owing to the influence of industry sewage, living sewage, the lixiviate things of soil in the wet-dry zones and the falling of water self clean ability, the water quality of reservoir will be influenced and the fluctuation in stage will share a inverse relationship with the regression of river level in the natural state. Gradually, the attention is given to the aquatic environment problems, the geological environment problems and the healthy problems of people in the surrounding areas which the wet-dry zones face.The thesis rely on the number 03-96 item of Chongqing Sciene Committee and Chongqing Development Committee, which is research on ecosystem environment and rebuild mode of wet-dry zone. The thesis analyse the characteristic of N, P heavy metals and other pollutants in the wet-dry zone, investigete the impact to the reservoir and bring forward the prevention measure. Mostly study content are as follows.After impounding of the project, the wet-dry zone formed primarily and the wate level changed most obviously. Especially the anabranch water level is raisen great and the flow speed slow down obviously for holded up by the Yangtze River, and the rate of water eutrophication is raisen. The thesis chose the typical branch river, Xiaojiang river, to sample and research the eutrophication degree , and discover that the eutrophication of branch river are serious. The soil in wet-dry zones of the Reservoir is a constituent part of its habitat. Throμgh investigation and analysis of heavy metallic elements in the soil, we know that, the average content of Cadmium and Hg of purplish soil in eluvial horizons, the average content of Cadmium, Zinc and Hg in internal layer are both above that of the soil of the same kind and the same level in the whole country, and the average content of Zinc, Copper,Lead, Fluorid in eluvial horizons and internal layer of Chao soli shares the same result, while the average content of metal in the eluvial horizons and internal layer of limestone soil is under the level of whole country.The distributing character of Cd, Cr, As, Hg, Ni in soil of wet-dry zones display normal distribution basically(Sig.>0.05), while Pb, Zn and pH don't display this distribution. The content of pH, Cd and Cu take on significant correlation, which relativity are not prominent with other metal elements. The relativity coefficient of Cd and Cu in soil of wet-dry zones is 0.67, Pb and Ni is 0.786, As and Ni is 0.642, which take on significant correlation.On the basis of lab simulation experiment of immersion, we study the soaking-out laws of three heavy metallic elements (Cd, Hg and Pb), with the experimental data, set up the stripping rate equation of them. This paper uses one-dimensional water quality model, studies on wet-dry zones of Xiaojiang river, and forecasts the influence of the released heavy metallic elements on the water environment in the Reservoir.By analysising the soil of the wet-dry zone, we find the N content is about 0.06-0.28%, and the P conten is about 0.037-0.071%, which belong to the region of high content in China. In that soil the N, P content of the Chao soil and purple soil are higher than yellow soil. It has some plus interfix between the total N content of soil and PH, and has not distinct interfix between total N and total P, between total P and PH. The total N content has different distributing with area and the total P content has not the character.The thesis take the XiaoJiang river for research object, make use of one- dimension water quality model to forecast the impact of discharging N and P. When the wet-dry zone of the XiaoJiang river show up, the most N, P burthen with the erosive soil to water are 21.6 t and 9.64 t, which bring the most concentration of total N 0.02 mg/l and total P 0.01 mg/l to the water, which attenuate to 0.018 mg/l and 0.001 mg/l on 10 km of the river,Factors, such as Peripheral environment elements, management, etc, have a important influence on maintaining ecosystem stability in wet-dry zones and preventing the effect on the water environment of the TGR of environment problem broμght by wet-dry zones. In the end, this paper puts forward correlative measures about the prevention and cure of ecological environment problems in wet-dry zones of the TGR.