Spatio-temporal Variation Of Lake Environment And Diatom Distribution Of Fuxian Lake In 2015

Lake sytems,an important component of the earth surface system,are susceptible to climate change and human activities,including their water quality and community distribution.The Yunnan-Guizhou Plateau is one of the five major lake distribution regions in China and many lakes from this region have experienced the degradation of environmental functioning and ecosystem health.Fuxian Lake,the deepest lake in Yunnan Province,is home to 9% of China's strategic freshwater resources with current water quality generally being oligotrophic.However,it has experienced a slow process of eutrophication and a long-term decline in ecosystem health due to the increasing impact of regional warming and catchment development.In order to effectively protect this lake,it is necessary to systematically evaluate community distribution and biodiversity of key lake biota,their spatial and temporal variation,as well as their key environmental factors.Here,we investigated the diatom community and physico-chemical parameters for surface waters of 16 sampling sites across the lake basin in Fuxian in 2015.The results of this high-resolution lake survey included:1)A total of 31 genera and 167 species of diatoms were detected in Fuxian with the dominant species being the planktonic taxa.The common taxa included Cyclotella ocellata,Fragilaria crotonensis,and Aulacoseira granulata,however,the endemic species Cyclotella rhomboideo-elliptica,the once dominant diatom species in Fuxian,was nearly extirpated in 2015.In addition,the diatom biomass fluctuated obviously across seasons with the maximum biomass found in March of 2015.Over the spatial scale,there existed difference in diatom biomass between sites,but their variation is smaller than that found at the time scale.2)The monthly change of diatom community structure showed obvious seasonal succession in all of the 16 sampling sites of Fuxian.The dominant species in January and February was F.crotonensis and was A.granulata in March,respectively.In April,C.ocellata and F.crotonensis were abundant,while C.ocellata absolutely dominanted during the rest of the year(i.e.relative abundance of ~80%).On the spatial scale,diatom community structure was highly consistent across the lake basin.The results of principal component analysis(PCA)and t-test indicated that diatom community structure varied significantly at temporal scale but not over the spatial scale.3)Redundancy analysis(RDA)and variation partitioning further revealed that the main driving factors included meteorological and physical factors(i.e.water temperature,wind speed,precipitation,and water transparency),which altogether accounted for 16% of the total variance in the spatio-temporal change of diatom community.Further analyses indicated that the duration of thermal stratification and thickness in deep water lakes played an important role in affecting the organization of diatom communities.Meanwhile,lake-water nutrient level and ion concentrations also exerted an important influence on community structuring,which explained 15.2% and 9.3% of the diatom community variability,respectively.4)The diatom ? diversity results showed an obvious seasonal fluctuation in Fuxian Lake.The diatom species richness remained higher in early spring and summer,but was relatively low in late spring and autumn.the seasonal trend of Shannon and the Pielou index showed a similar pattern with relatively high diversity values found in both winter and spring and relatively low values occurring in autumn and winter.Water temperature,a significant driver for diatom community structure,showed no significant correlation with diatom diversity index(p>0.05).While the soluble orthophosphate,Ca ion and wind speed were all positively correlated with Shannon index and Pielou index(p<0.05,r>0.64).Furthermore,there was a significant negative correlation between water transparency and species richness(p<0.05,r=-0.59).On the spatial scale,diatom diversity showed a negative correlation with water depth and distance to shore in Fuxian Lake.Diatom ? diversity(as referred by Jaccard dissimilarity index)between samples displayed relatively high values in summer and winter but relatively low values in spring and autumn.In summary,water temperature and catchment development have significantly shaped diatom distribution and ecosystem health of Fuxian Lake.Therefore,measures should be taken not only to control catchment input of pollutant but also to actively mitigate the long-term impact of climate change for sustainable protection and ecological remediation of Fuxian Lake.