Abstract: As an important storage of freshwater resources, plateau lakes in Yunnan are facing multiple environmental stresses, such as eutrophication and heavy metal pollution. The structure and distribution pattern of aquatic communities have been changed with the intensification of catchment development. Phytoplankton, an important group of primary producer, are the basis of lake food webs. In this study, we identified the spatial pattern of algal communities and their driving factors during the summer of 2016, in eight and five lakes from the central and south of Yunnan, respectively. The results showed that 161 species of algae were identified, belonging to seven phyla and 73 genera. Cyanophyta was dominant in all the lakes except for lakes of Fuxian, Chaheihai and Changhu. Phytoplankton community of Dianchi Lake was significantly dissimilar with those in lakes of Chaheihai, Changhu, Yuehu, Yangzong, Changqiao and Qilu, with a Jaccard’s dissimilarity value of 0.98. Changqiao Lake was most similar to Datun Lake (0.19). Furthermore, phytoplankton community structure were dissimilar between lakes from the central and southern Yunnan (ANOSIM, R=0.27, P<0.05). The total biomass in lakes of south Yunnan was significantly higher than that of central Yunnan (t_test, P<0.05), with a mean biomass of 105.87 and 29.27 mg·L^-1, respectively. The results of Pearson correlation analysis showed that phytoplankton biomass was positively correlated with temperature, total phosphorus (TP), total nitrogen (TN), arsenic and electrical conductivity, and negatively related to elevation and transparency (P<0.05,n=13). The results of Canonical Correspondence Analysis (CCA) showed that TP, N:P ratio, Mn (magnesium), Ca (calcium), and spatial variable (PCNM1) wereamong the significant factors in driving phytoplankton distribution. The analyses of variation partitioning also displayed that the trophic level (TN, TP), spatial variable (PCNM5) and lake type (lake size) independently explained 30.35%, 4.90%, and 3.44% of the total variation in phytoplankton communities, respectively. Meanwhile, the interaction of human activities with spatial variable and lake type accounted for 6.52% and 4.27% of community variation, respectively. With the intensification of catchment development, lake eutrophication was the major driver in structuring phytoplankton communities, with both lake type and spatial distribution having relatively minor impacts on algal community structure. Our results highlight the importance of nutrient control for lake protection and ecological restoration, and thus provide basis for preventing algal blooms and biodiversity conservation in plateau lakes of Yunnan.

Key words: phytoplankton, community structure, spatial distribution, environmental factor.