Spatio-temporal Distribution And Environmental Drivers Of Phytoplankton Community And Diversity In Fuxian Lake

Lakes serve as an important geographic unit and changes in water environment can alter community distribution and biodiversity pattern.At present,the degradation of ecosystem and the loss of water resources,as a result of lake eutrophication,have become one of the major environmental problems in Yunnan.Fuxian Lake,the largest deepest lake of Yunnan with a long geological history,is home to ~ 9% of national strategic freshwater resources.However,the lake-water nutrient level has increased in recent years due to catchment development and the expansion of agriculture and tourism,potentially changing ecosystem structure and biodiversity patterns.Therefore,it is urgently needed to evaluate the spatio-temporal distribution of lake organisms as well as the pattern of biodiversity,so as to provide important basic data and scientific basis for the management and restoration of this large plateau lake.Phytoplankton,the key primary producer in lake food webs,can be used reliably to indicate water quality and ecosystem health.Here,we conducted algal and limnological surveys through basin-wide and monthly sampling in 2015,to uncover the spatio-temporal pattern of phytoplankton distribution and to identify the key drivers through multivariate analyses.Furthermore,the relationship between lake productivity and algal diversity was explored.The main results derived from this thesis include:1)The phytoplankton community in Fuxian Lake is dominated by Chlorophyta throughout the year of 2015,with Mougeotia sp.and Cyclotella ocellata as the dominant species.When compared to the previous studies,algal taxa that prefer high nutrient levels were increased with a concurrent decrease in oligotrophic taxa.2)The phytoplankton biomass and community structure displayed obvious temporal changes in Fuxian Lake.Phytoplankton biomass mainly were generally higher in spring and summer with lower levels in autumn and winter.Chlorophyta was dominated throughout the year with Cyanophyta,Bacillariophyta,Pyrrophyta and Chrysophyta showing strong fluctuation between seasons.Over space,phytoplankton biomass showed significant differences between the north and south parts of the lake basin in March,May,August and November,respectively,with generally higher biomass found in the northern part.The existed no significant difference in algal structure during rainy seasons,but significant difference between both parts of the basin was often found in dry seasons.3)The multivariate analyses(such as variance portioning)showed that nutrients,temperature and the ion concentration were among the key environmental drivers in shaping the changes of phytoplankton community structure in Fuxian Lake.The ion content accounted for the largest proportation of the total variance in community changes,partly due to the complex geological background of Fuxian Lake.4)There existed strong relationships between the productivity and algal diversity(PDR)in Fuxian Lake,varying both over time and space.The PDR based on algal ?-diversity was generally positive over spatio-temporal scale.While the relationship between average productivity and ?-diversity was generally negative spatio-temporal scale.While,the relationship between the magnitude in the change of productivity and ? diversity was correlated negatively and positively over time and space,respectively.