Variation Of Filamentous Cyanobacteria Communities And Its Environmental Driving Factors In Drinking Water Reservoir In Northern China

Cyanobacteria bloom has been a major global environmental problem resulted from water eutrophication.The cyanobacteria bloom not only destroys the ecosystem health of lakes and reservoirs,but also seriously threatens the safety of drinking water and endangers human health.Microcystis,Anabaena,Raphidiopsis and Pseudanabaena are generally considered as the main cyanobacteria populations causing cyanobacteria bloom in lakes and reservoirs.The cyanobacteria blooms in China are drived by Microcystis.However,in recent years,harmful filamentous cyanobacteria,such as Raphidiopsis and Pseudanabaena,have been reported as dominant bloom species in many countries and regions.Therefore,not only paying attention to Chroococcus blooms in lakes and reservoirs is essential,but also the phenomenon that filamentous cyanobacteria become dominant species and even lead to filamentous blooms during the high-risk period of blooms also needsfollow closely.However,the research of planktonic filamentous cyanobacteria population in reservoir-type water sources is few,and is mainly concentrated in tropical and subtropical areas.Therefore,this study focused on the northern reservoir-type water source and analyzed the water quality status together with the variation of planktonic filamentous cyanobacteria community.Meanwhile,this study explored the relationship between filamentous cyanobacteria and environmental factors,and the similarities and differences of cyanobacteria population structure.The research can fill margin the research gap regarding growth characteristics of filamentous cyanobacteria in reservoir-type water sources,and provide theoretical and technical support for the subsequent management of reservoirs,along with prevention and control of filamentous cyanobacteria bloom.In this study,taking Chengbei Reservoir located in Gaomi city,Shandong Province as an example,the water quality and phytoplankton were measured from April,2019 to December,2020.The water quality of the reservoir was evaluated by using the nutritional status index method.The variation of algae composition,density and dominant species abundance were analyzed.Through diversity index and evenness index,the uniformity and stability of phytoplankton population in reservoir were clarified.Using Non-metric multi-dimensional scale analysis and cluster analysis,the temporal and spatial similarity and difference of filamentous cyanobacteria population composition in reservoirs were compared.With RDA analysis,Pearson correlation analysis and Species response curve,the main environmental factors affecting the composition of cyanobacteria population were identified.The main conclusions were as follows:(1)Chengbei Reservoir is in eutrophication state of all year round and super-eutrophication in some months.Under the influence of rainfall and water transfer in 2019 and 2020,nitrogen nutrients changed greatly and total nitrogen obviously increased.A total of 231 species belonging to 97 genera,8 phyla,and 37 cyanobacteria species belonging to 21 genera have been observed in the reservoir.The composition of phytoplankton is abundant,and the density and proportion of algae in the reservoir fluctuate widely.(2)Filamentous cyanobacteria,being dominant species,account for more than 85%of the cyanobacteria detected,and Pseudanabaena limnetica is the dominant cyanobacteria in the four monitoring points of the reservoir.There is no obvious spatial difference in the distribution of cyanobacteria population in the reservoir,and the cyanobacteria population structure at the four detection points is basically the similar.The population structure of cyanobacteria in the reservoir exhibits obvious difference in time scale.From 2019 to 2020,the dominant cyanobacteria changed from Raphidiopsis sp.and Pseudanabaena sp.to Pseudanabaena sp.and Leptolyngbye sp.At the same time,the cyanobacteria population structure is quite different between summer-autumn and winter-spring due to the effect of temperature.(3)The main environmental factors affecting the cyanobacterial population structure were nitrogen nutrients and temperature.The dominant cyanobacteria in the reservoir is Pseudanabaena limnetica,and its density has significantly positive relationship with total nitrogen concetration,N/P ratio,nitrate nitrogen concetration,conductivity,turbidity and pH(p<0.01),while significantly negative relationship with CODMn(p<0.01).