Community Structure Of Phytoplankton And Its Relation With Environmental Factors In Taihu Lake,china

Taihu Lake is located in the lower reaches of the Yangtze River Delta.It is the third largest freshwater lake in China and the center of the Jiangnan water network.Its water quality is related to the safety of drinking water in the cities around Taihu Lake.Since 2003,there have been frequent outbreaks of cyanobacteria in Taihu Lake.During the ten years of national governance of Taihu Lake,the overall water quality has improved,but the cyanobacteria bloom has not yet been cured,and large-scale cyanobacteria blooms will still occur.Seasonal sampling survey of phytoplankton was taken in Taihu Lake from 2017 to 2018.The spatial and temporal distribution of phytoplankton community structure in Taihu Lake was analyzed.The temporal and spatial variation of phytoplankton and the correlation with environmental factors were compared.Meiliang Lake was conducted investigation monthly to analyze the interannual variation of phytoplankton community structure.This research explored the changes of various species of cyanobacteria during the outbreak of Taihu Lake bloom,providing basic data and basis for improving water quality and controlling cyanobacteria in Taihu Lake.The main results are as follows:1.From 2017 to 2018,289 species(including varieties and deformations)of phytoplankton were identified in Taihu Lake,belonging to 7 gates and 114 genera.Among them,the species of green algae are the most,with 42 species belonging to 42 genera,accounting for 43.3% of the total species,followed by diatoms,with 42 species belonging to 42 genera,accounting for 31.1% of the total species,and 33 species of 7 genera of cyanobacteria.11.4% of the total species,22 species of 11 genera of Cyanophyta,accounting for 7.6% of the total species,and fewer species of Jincaomen,Dinophyta and Cryptophyta,5 species,8 species,5 genera and 6 species.There are 5 species in 2 genera,accounting for 2.8%,2.1% and 1.7% of the total species.The seasonal variation of the number of species of phytoplankton is not obvious,the number of species in summer is the highest,and the number of species in autumn is the least.The number of species in each sampling point in Taihu Lake is not much different.The number of species in the lake waters is higher than the number of species in the surrounding lakes.2.The density of phytoplankton in Taihu Lake was 3110.4×104 cell/L in 2017,and its in 2018 was higher than that in 2017,which was 4067.5×104 cell/L.The density of phytoplankton in Taihu Lake showed obvious seasonal changes,with the highest density in summer and the lowest density in winter.Similarly,the density of phytoplankton in Taihu Lake is spatially different,with the highest density in the western waters,followed by the northern waters,and the lowest in the eastern waters.The average biomass in 2017 was 2.49 mg/L,and the average biomass in 2018 was equivalent to 2017,which was 2.46 mg/L.Like the change in density,the biomass of phytoplankton in Taihu Lake also showed a change in time,with the highest biomass in summer.Similarly,the phytoplankton biomass in Taihu Lake showed spatial distribution differences,with the largest biomass in the western waters,followed by the northern waters,and the smallest in the eastern waters.3.During 2017-2018,Microcystis spp.,Cryptomonas erosa and Chlamydomonas sp.were the dominant species of Taihu Lake in the whole year,Stephanodiscus hantzschii),Dinobryon sp.,Synura sp.,and Peridinium sp.were the dominant species in Taihu Lake in winter.4.The average biomass of cyanobacteria of Taihu Lake in 2017 was 0.89 mg/L.The average biomass of cyanobacteria in 2018 was equivalent to that of 2017,which was 1.28 mg/L.In the same year,the biomass of cyanobacteria increased first and then decreased,reaching a peak in summer(August).From February to August 2017,the biomass of Anabeana in Taihu Lake was higher than that of Microcystis.From October 2017 to August 2018,the biomass of Microcystis was higher than that of Anabeana.In November 2018,Anabeana has the same biomass as Microcystis.The cyanobacteria biomass in the western and northern areas of Taihu Lake is high,the biomass of Microcystis is higher than that of Anabeana.The cyanobacter biomass of the lake center is the second,the cyanobacteria of the southern and eastern lake had low biomass,and the biomass of Anabeana is higher than that of Microcystis.5.The average biomass of diatoms in Taihu Lake in 2017 was 0.38 mg/L.The average biomass of diatoms in Taihu Lake in 2018 was less than that in 2017,which was 0.34 mg/L.In the same year,the diatom biomass has a seasonal change,showing a trend of decreasing first and then increasing,reaching a peak in the summer of the same year(August),and the largest amount of diatom in summer(August),autumn(October or November)The diatom has the smallest biomass.The diatoms of the sampling points near the shore of the northern and southern waters are large,and the average biomass of the diatom of other sampling points did not present much difference.There was a significant negative correlation between diatom biomass and chemical oxygen demand.6.The green algae were observed in Taihu Lake in all seasons and sampling points.The biomass has no obvious regularity in time and space distribution.There was a significant positive correlation between the biomass of green algae and total nitrogen.Cryptophyta exhibited seasonal changes and peaks in winter(February).The cryptophyta biomass near the shore in the northern waters was large,and the cryptophyta biomass at other sampling points did not show not much differences.The cryptophyta biomass presented significant positive correlation with transparency,and significant negative correlation to the total phosphorus and chemical oxygen demand The biomass of Chrysophyta,Dinophyta and Euglenophyta showed obviously seasonal changes.Thebiomass of Chysophyta was the largest in February.The biomass of Dinophyta were large in February and August.And the biomass of Euglenophyta was the largest in February,but it was small in other seasons.