Research On The Structure And Formation Mechanism Of Phytoplankton Functional Groups In Key Waters Of The Three Gorges Reservoir

Since the completion of the 175 m experimental water storage,the inter-annual water level of the Three Gorges Reservoir fluctuates at 145-175 m at sea level.For functions such as flood control and power generation,anthropogenic water level regulation has seriously affected the ecosystem health of the reservoir.A series of environmental problems such as eutrophication and loss of biodiversity have affected the ecological value and service function of reservoirs.Therefore,quantitative assessment of the ecological status of the Three Gorges Reservoir,and exploration of the ecological status and the correlation between the biological community and the environmental situation are the prerequisites for the current management of the ecological problems of the Three Gorges Reservoir.Phytoplankton are one of the main producers in freshwater ecosystems and are widely used in biological monitoring and ecosystem health assessment due to their sensitivity to the environment.This study was carried out in the entire reservoir area of the Three Gorges Reservoir and in the Xiangxi Bay.Based on the phytoplankton aggregation index,the ecological status of the Three Gorges Reservoir was evaluated from the time and space scales.And the relationship between the composition and stability of the planktonic functional group and the environmental situation is analyzed.The result is as follows:1.In this study,the phytoplankton aggregation index combined with the evaluation results of the nutritional status of the Three Gorges Reservoir was used to comprehensively analyze the changes in the grouping of phytoplankton functional groups and their impact on the ecological status under different nutritional status.Based on the field monitoring survey results of a total of173 sampling points in the main stream of the Yangtze River in the Three Gorges Reservoir and its tributaries and reservoir bays in the spring of 2015,a total of 61 species(including varieties)of phytoplankton were identified,belonging to 16 functional groups.The overall ecological status of the Three Gorges Reservoir is in a moderate state,among which,the proportion of the sample points with the ecological evaluation results of the main stream of the Yangtze River and the tributaries of the reservoir bay being moderate or above is 94% and 69%,respectively.The Q index was significantly negatively correlated with the nutritional status index,but the nutritional status corresponding to the Q index in a certain range(1.5-2.5)changed greatly.2.The main content of this chapter is to divide water level fluctuation events on short time scales into 3 days,7 days,14 days,and the interval between two sampling days(18 days-43 days,with an average of 30 days).The water level fluctuation events are divided into three types: the magnitude of the water level change,the frequency of strong water level fluctuations and the rate of change.Based on the phytoplankton aggregation index,the ecological status of the Three Gorges Reservoir from April 2010 to March 2015 was evaluated,and the environmental factors affecting the ecological status of the main stream and tributaries of the Three Gorges Reservoir were analyzed in combination with changes in the environmental situation.The results show that the ecological status of the main stream and tributaries of the Three Gorges Reservoir is at a moderate level,and the inter-annual fluctuations are not very different.The ecological status of the main stream fluctuates more than the tributaries during the year.The main ecological condition influencing factor is the decline of water level.Comparing the physical and chemical factors and the influence state,the index of water level fluctuation has the greatest influence on the ecological state.3.The main content of this study is to analyze the effects of the characteristics of water level fluctuations on phytoplankton communities,and to compare physical and chemical factors to see whether water level fluctuations are the dominant factor.The research results show that the divided water level index has a significant correlation with the physical and chemical factors of the main stream and tributaries of the reservoir,the composition of the main phytoplankton functional groups and the stability of phytoplankton.Comparing the physical and chemical factors,the water level index plays a leading role in the three.In addition,a two week was a time scale that could significantly affect physicochemical factors,functional group composition,and phytoplankton stability.Regarding the index types,the frequency of strong water level fluctuations was the main factor affecting physicochemical factors,functional group composition and phytoplankton stability.4.The ecological status of Xiangxi Bay,Daning River and Xiaojiang Bay,the typical tributaries of the Three Gorges Reservoir,was quantitatively evaluated by using phytoplankton functional group method.The results showed:(1)the B and X2 functional groups represented by cyclophyllum and cyanophyllum were the dominant species,followed by LM and H1 functional groups represented by cerodinacea and anabaena.(2)The ecological status of Xiangxi Bay,Daning Bay and Xiaojiang Bay showed a trend of deterioration from the estuary to the upper reaches of the river,and the sampling in spring avoided the blurriness of the differences of ecological status among the samples caused by algae blooms.(3)The ecological status of Xiangxi Bay is better than that of Daning Bay than Xiaojiang Bay,and the main factors affecting the ecological status of Xiangxi Bay are nutrient concentration.