Studies On Phytoplankton And Eutrophication Status Of Qingshan Lake In Nanchang, Jiangxi

Qingshan Lake,as one of the eight urban lakes in Nanchang city,had suffered from water eutrophication and annual cyanobacterial blooms have occurred frequently since 2008.However,very scarce information on phytoplankton composition and eutrophication status were available in Q ingshan Lake.In order to provide scientific basis for restoration of the lake phytoplankton composition,abundance and dynamics in Q ingshan Lake were examined from May 2015 to May 2016,and eutrophication status was evaluated as well.In addition,the succession and competition between Scenedesmus and Microcystis sepcies was also investigated combining the field survey and laboratory experiment at differernt temperatures and initial cell densities.The results were shown as followings:1.A total of 112 species belonging to 73 genera,7 phylum of phytoplankton were identified.Chlorophyta,cyanophyta and bacillariophyta were the main taxa,containing 56 species,24 species and 20 species,respectively.The numbers of euglenophyta,pyrrophyta,cryptophyta and chrysophyta species were 5,3,3 and 1,respectively.2.The cell densities of phytoplankton in the lake were in the range between 1.29×108cells/L to 8.38×108cells/L,and cyanobacteria dominated in cell number during whole year.The average biomass was 7.32mg/L,with the dominance by Chlorophyta or bacillariophyta.3.After microbial restoration by adding multiple bacterial strains into the lake,the first dominant species in cell density shifted from Microcystis spp.to Merimopedia minima or Monoraphidium sp.,The first dominant species in biomass shifted from Microcystis spp.to Scenedesmus sp.or Melosira granulata or Stephanodiscus neoastraea.4.The average species richness of phytoplankton was 38.8,and Pielou’s index ranged from 0.51 to 0.72,and Shannon wiener index as 2.25 in average and the mean Margalef index as 1.91.The biodiversity of phytoplankton in Q ingshan Lake was in the order as Autumn> Winter> Spring> Summer.5.Real-time quantitative PCR targeting on Microcystis spp.and microsystin-producing Microcystis showed that there existed large numbers of Microcystis and toxic Microcystis gene copies in the water,implying the potential water quality and safety problem in summer.6.The average concentrations of total nitrogen(TN)and total phosphorus(TP)were 1.51mg/L and 0.165mg/L,respectively,The average concentrations of nitrate nitrogen and ammonium nitrogen were 0.106mg/L and 0.043mg/L.The average transparency was 0.355 m,and the mean concentrations of dissolved oxygen as 10.439mg/L.The concentrations of Chlorophyll a was 72.77μg/L in average,and the variation of the Chla concentration was patterned as Autumn> Summer > Spring> Winter.7.Qingshan Lake was in a meso-eutrophic status,and water eutrophicaiton had not been improved,and the variation of TLI(Σ)was: Summer>Spring>Autumn>Winter.8.In the interspecies competition study,Scenedesmus bijuga had a competitive advantage when the ratio of Scenedesmus/Microcystis cells was above 1 and the temperature below 25℃,otherwise Scenedesmus bijuga lost the advantage under other conditions.