Dissertation > Environmental science, safety science > Environmental pollution and its prevention > Water pollution and its control > Lakes and reservoirs

Transference and Temporal-spatial Distribution of Typical Contamination after the Three Gorges Reservoir Impoundment

Author ZhangKe
Tutor ZhangZhi;ChenGangCai
School Chongqing University
Course Environmental Engineering
Keywords Three Gorges Reservoir Contamination Transference Distribution
CLC X524
Type Master's thesis
Year 2008
Downloads 206
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The Three Gorges Reservoir started water storage in June 2003, and water level of the dam fluctuated around 135 meters. Since then, parts of the Yangtze River became a typical channel reservoir, consequently, flow velocity of the water in this area sharply decreased as hydraulic condition changed. All of these would seriously impair its transport and diffusion capacity for contaminants. With the same load of nitrogen and phosphor as well as the same discharge method, water quality of the Three Gorges Reservoir would definitely deteriorate. The structure and function of local aquatic ecosystem would be influenced by changing hydraulic condition. As a matter of fact, eutrophication phenomenon has already occurred in backwater area of some tributaries, which indicated that low velocity of water flow might lead to eutrophication.This study aims at the removal and distribution of organic contamination (BOD5, CODMn), nutrient (N,P) and heavy metal(Cu,Pb,Cd) in main stream after Three Gorges Reservoir impoundment. The trophic state of tributaries is studied. Analizing the removal and distribution of contimination at 135m water level is very important to forcast the changing of contamination at 175m water level in 2009. It forcast the changing trent of contamination after 175m impoundment. The research result would be beneficial to protect the water quality of the Three Gorges Reservoir.Through these studies, some main conclusions were drawn as follows:①Concentration of BOD5 were retained low level which preceded surface water standardⅠand CODMn changed fromⅡ~Ⅳin diverse season. The variation of BOD5 and CODMn ranged from 0.1~1.3mg/L and 1.8~6.3mg/L respectively. Horizontal concentration of DO, BOD5 and CODMn in reservoir area were lower than upstream area. In flood season, concentration of CODMn were higher than normal and dry season. In reservoir area, the lower concentration of BOD5 were due to long retained time and COD due to particulate deposition. On vertical direction, variation of BOD5 and CODMn were not notable and organic pollutant were not layered.②Concentration of TP, NH3-N, NO2-N, NO3-N, TN ranged from 0.06~0.34mg/ L,0.01~0.72mg/L,0.002~0.100mg/L,0.76~2.09mg/L,0.855~2.52mg/L,respectively. TP value of reservoir area is normal beyond upstream. Due to particulate deposition, concentration of TP in flood season is higher than normal and dry season. The main form of phosphorus is dissolved phosphorus in normal and dry season. Particle phosphorus is main forms of phosphorus in flood season. TP retains low level in dry and normal season. In flood season, water body quality is only surface water standard III. Pollution of nitrogen is serious in Three-gorge reservoir. Concentration of NO2- N,NO3-N, TN is higher in normal season than in dry and flood seasons. NO3-N is the main form of TN and the rate of NO3-N in TN ranged from79%~90%. The rate of NO2-N in TN is the most lowest and ranges below 3.5%.③The concentration of Pb and Cu in flood season is higher than in normal and dry seasons. Concentration of Cd is not distinct different in diverse season. Horizontal concentration of heavy metal is not distinct different. Concentration of Cd is preceded surface water standardⅡand Pb and Cu is changed from the standardⅡtoⅣin diverse season.④The water body of tributaries is polluted at various levels. The concentration of nutrient in tributaies is beyond the concentration of eutrophication and TN is abundant. The rate of TN and TP showed that eutrophication are limited by TP in a part of tributaries. The concentration of CODMn is low except Zhuxi river. Chla is different in each tributary and the degree of eutrophication is more serious than before the Three Gorges Reservoir impoundment.⑤Concentration of COD, TP and heavy metal would be decreased in Three Gorges Reservoir area after 175m impoundment and disolved COD would be changed hardly, eutrophication trend of tributaries would be more serious with the decreasing of flow velocity. Diatoms as one of the dominated species in some tributaries would be substituted by blue and green algae.

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