Effect Of Impoundment On Community Structure Of The Phytoplankton In The Main Stream Of The Three Gorges Reservoir,in Chongqing

The Three Gorges Dam was altogether finished in 2009, whose capacity of water can reach 39.3 billion cubic meter.Contrast to primary water environment of Changjiang(Yangtze) river before impoundment of the Three Gorge Dam,water environment parameters are singnificant different in velocity of flow、the residence time of the water body、illumination、temprature.In order to accomplish the goal of floodprotectio、power generation、shipping,we regulate the water level of he Three Gorges Reservoir in the follow way:water level will reach 175 meter during dry season (winter) and fall down to 145m during rainy season (summer).Impoundment of the Three Gorges Reservoir forms three significant difference water types in the main stream of the Three Gorges Reservoir in Chongqing:Natural riverine zone (above 175m) where the change of water environment fluctuate with seasons, the river in upstream of Jiangjin area in Chongqing are belong to these water type.Transition zone (145-175m) where water environment is effected by season flood and impoundment.which locate in between Jiangjin and Fuling area in Chongqing.And analogous lacustrine zone where water level is below 145m throughout the year. The main stream in downstream of Fuling area in Chongqing are belong to these water type.They are different in velocity of flow, nutritive level (such as the concentration of N and P) and so on. Phytoplanktons,as primary producer of water ecosystem, are sensitive to the change of water quality and play a key role in keeping the balance and stabilization of wate ecosystem.For investigating the response to these changes of algae, The physical and chemical characters of water in the main stream were tested and surveys on the phytoplankton communities and in the Three Gorges Reservoir were carried out in September 2009(time before impoundment of the Three Gorge Reservoir), January (storage period), March (drainage period) September 2010(time before the second impoundment) and, January 2011. And try to explain effect of impoundment on community structure of the Phytoplankton in the main stream of the Three Gorges Reservoir of Chongqing; therefore, we can protect water resources scientifically and give early warning of water contamination with strong scientfic data. The result as follows:1. A total of 476 plankton species belonging to 7 phyla were identified, among which Bacillariphyta (63.9%) were dominant with Chlorophyta and Cyanophyta following. The phytoplanktons which were belonging to xanthophyta only account for 0.21%. Just like other subtropic riverine reservoir, the Three Gorges Reservoir is full with phytoplankton in Chlorophyta and Cryptophyta during spring, cyanophyta begin to increase in summer and autumn while Bacillariphyta dominate community of phytoplankton in winter. Yet different water types have change with seasons differently:During the investigation period, before impoundment of the Three Gorge Dam (sep.2009), Bacillariphyta was also in dominant position, and more cyanophyta became dominant species with the reduction of flow velocity, while in winter (January 2010 and 2011) bacillariphyta constituted an overwhelming superiority. In spring (March 2010) chlorophyta became dominant species in analogous lacustrine zone and algaes from chlorophyta became more important for water environment.the proportion of Chlorophyta also raised gradually and went up to 67.8% in analogous lacustrine zone in spring (March,2010).But in September 2010(before the second impoundment of the Three Gorges reservoir), Oscillatoria tenuis could be found in all water types and even the dominance degree of cyanophyta was beyond bacillariphyta greatly.Especially, the dominance degree of cyanophyta in all water types exceed the case in September 2009. And the proportion of Cyanophyta in phytoplankton even soars to 63.8% becoming main species. Such as Oscillatoria tenuis Ag whose dominance degree index was significant higher than any other species. Although Bacillariphyta were put one at an absolute predominance in the all water columns during winter, the abundance of algae in Chlorophyta in analogous lacustrine zone was larger than any other water types.The mean Shannon-Wiener diversity index in the main stream was 2.43, Margalef index was 2.22.The variation in analogous lacustrine zone was in summer and autumn>winter>spring. On the contrary, the index was the lowest in winter in natural riverine zone and transition zone. The evenness index changed between 0.52 and 0.85 and the evenness in spring was lowest than any other seasons.2. Refer to the physical and chemical character, flow velocity of different water typies reduced from natural riverine zone to analogous lacustrine zone and changed with different impound period. The mean of pH was 8.17 and Dissolved Oxygen (DO) changed 6.54-11.44 mg/L during the investigation. Total nitrogen (TN) of all sample point is between 1.43 mg/Land 3.55 mg/L and Total phosphorus (TP) was between 0.09 mg/L and 1.33 mg/L.The level of nitrogen and phosphorus nutrients were much higher than the international standard of eutrophication (0.2 mg/L and TP 0.02 mg/L) and were also a little higher than previous studies done by other researchers during initial water impoundment of reservoir.Accoding to PCA(principal component analysis) and correlation analysis between community parameters of phytoplanktons, flow velocity, transparency and the rate of nitrogen and phosphorus content were more important than other parameters of water quality to the communities of phytoplankton in the main stream of the Three Gorges Reservoir of Chongqing.3. We used indicator organism method of water column and the diversity index to assess water qualiy of the main stream of the Three Gorges Reservoir of Chongqing.the results indicated that, no matter which seasons and water types, the main stream of the Three Gorges Reservoir of Chongqing were full filled with algaes which suggested water quality belonged toβ-mesosaprobiczone. And in greater detail, in March and September,2010 the species which indicated water quality belonged toα-mesosaprobiczone were more than other investigation time. That mean the water pollution degree is more serious during these period. Compared to previous research, water qualiy of the main stream of the Three Gorges Reservoir of Chongqing became worse.Impoundment of the Three Gorges Reservoir cause great diference in water dynamics condition of different water types. And with the changes caused environment variables by seasons which mainly influence the illumination and temperature of water column, community of phytoplanktons in analogous lacustrine zone became unstability and are algal bloom were more likely to outbreaks.