Phytoplankton Community Structure And Environmental Driving Factors In Donghu Reservoir

The implementation of the South-to-North Water Diversion Project is of great significance for alleviating the shortage of water resources in the northern part of China and realizing the rational allocation of water resources.In the process of water transfer,it is the key to ensure the normal operation of the South-to-North Water Diversion Project and the safety of water supply along the line in the water quality condition and the growth and distribution of phytoplankton community.Among them,the reservoir can realize the reasonable allocation of the incoming water,adjust the transport water,and prevent the multiple water environment risks in the main canal and improve the water supply safety.Donghu Reservoir is an important storage reservoir for the Jiaodong main line project of the South-to-North Water Diversion Project.It shoulders the heavy responsibility of supplying water to Jinan,Zhangqiu,Zibo and Binzhou.Therefore,it is of great significance for the study of water quality and phytoplankton community structure.In this study,the water quality of the reservoir and the community structure characteristics of phytoplankton were analyzed for a long timeline（April 2014^December2017）after the start of Donghu Reservoir.Two sampling points were set up in the reservoir to study the water quality index of the Donghu Reservoir,the composition of the phytoplankton community structure,the density change,and the dominant algae species,and revealed the succession pattern of the phytoplankton community structure in the Donghu Reservoir.Non-metric multidimensional scaling（NMDS）and cluster analysis have identified the similarity and cluster similarity of phytoplankton community structure in different months;through redundancy analysis（redundancy analysis）,RDA)identified the main environmental driving factors affecting the phytoplankton community structure change in Donghu Reservoir.In the physical and chemical indicators of the Donghu Reservoir,there is no significant difference in water temperature,and other indicators have a certain change with time,but the range of variation is small.According to the water eutrophication index method,the eutrophication level of the reservoir is evaluated.The Donghu Reservoir belongs to the middle nutrient-light eutrophic water body.During the study period,Donghu Reservoir detected a total of 187 species of phytoplankton in 89 families,including Chlorophyta,Diatom,Cyanophyta,Euglenophyta,Cryptophyta,Huangzao,Dinoflagellate and Jincaomen.Among them,Chlorophyll detected the most species,accounting for 42.2%of the total detected species,followed by diatoms（22.5%）,cyanobacteria（16.6%）and Euglena（10.2%）,and other species detected phytoplankton The number of species is small.The number of phytoplankton detected in each year was also slightly different.The number of species detected in 2016 was the highest,and the least in 2014.The range and monthly mean value of total cell density of phytoplankton in Donghu Reservoir from 2014 to 2017 were 341.7⁴600.0×10⁴ cells·L^-1(2147.3×10⁴ cells·L^-1)and46.7¹437.5×10⁴ cells·L^-1(510.5×10⁴ cells·L^-1),46.65⁸50.6×10⁴ cells·L^-1(346.7×10⁴cells·L^-1),78.3¹370.9×10⁴ cells·L^-1(364.3×10⁴ cells·L^-1).The change of phytoplankton density has certain seasonal characteristics,and the summer and autumn seasons are significantly higher than the winter and spring seasons.However,the seasonal succession of phytoplankton varies from year to year.The dominant species of phytoplankton in different years of Donghu Reservoir are also different.In 2014,the dominant species of phytoplankton were mainly Pseudomonas aeruginosa,Chlorella vulgaris and Synedra acus.In 2015,Chlorella vulgaris and Microcystis aeruginosa were used.In 2016,Chlorella vulgaris、Synedra acus and Chroomonas acuta were the main species.In 2017,they were dominated by Fragilaria capucina and Chlorella vulgaris.As a whole,Chlorella vulgaris and Synedra acus have higher frequency as dominant species,and other dominant algae species alternate.Through the study of the diversity index and evenness of phytoplankton,it is found that the Donghu Reservoir is mostly in a state of micro-polluting to slight pollution.The phytoplankton community structure in Donghu Reservoir is greatly affected by environmental factors,including nitrogen salt and permanganate index,and the main environmental impact factors in different years are different.In addition,the water depth change caused by water transfer also has a certain impact on the phytoplankton community structure.