Cyanobacterial Diversity And Temporal And Spatial Variability Of Cyanobacterial Community Composition In Lake Taihu

Rapid development of industry and agriculture in Taihu basin and decades of nutrition input causes severe eutrophication in Lake Taihu, resulting in frequently occurred cyanobacterial blooms in recent years, which have seriously affected sustainable development of social economy. Previous studies on cyanobacterial blooms in Lake Taihu often focused on the variation patterns or abundance of one genus (especially Microcystis) at one sampling site (like Meiliang Bay) during the bloom season. Few studies were conducted to analyse temporal and spatial variability of cyanobacterial community composition in Lake Taihu.To fully understand the cyanobacterial diversity and temporal and spatial variability of cyanobacterial community composition in Lake Taihu, in this study, water samples were monthly collected at five sites of Lake Taihu (East Lake, South Lake, West Lake, Zhushan Bay and Meiliang Bay) during one year, and physicochemical parameters of all samples were determined in situ and in laboratory following the national standards. Water samples of January, March, June and September (a total of 20 samples) were chosen to analyse temporal and spatial variability of cyanobacterial community composition at different sampling sites and sampling time by PCR-DGGE. Multivariate statistical analyses of PCA and RDA were conducted to analyse the relationships between cyanobacterial community compositions and environmental factors.DGGE analysis results showed that Microcystis, Synechococcus and Cyanobium were the dominant genera of cyanobacteria during the study period at all five sites, with Microcystis and Synechococcus being the two most dominant cyanobacteial genera. The diversity of Synechococcus was higher than that of Microcystis, while the abundance of Synechococcus was lower than that of Microcystis. Abundance of Microcystis was higher at East Lake and South Lake in January and March, whereas it was higher at the other three sites in June and September, indicating that cyanobacterial blooms occurred in summer and autumn were not only related with cyanobacterial abundance in winter and spring. In this study, we also found the dominance of two genera of picocyanobacteria(Synechococcus and Cyanobium) in Lake Taihu, which were seldomly found and neglected in previous studies.Three potentially MC-producing cyanobacterial genera of Microcystis, Anabaena, and Planktothrix were widespread in eutrophic lakes.In this study, Anabaena was the dominant cyanobacteria in winter and spring but not detected in summer and autumn. From winter to summer, Anabaena was gradually replaced by some other dominant cyanobacteria (e.g. Microcystis). Planktothrix was also not found in the four study months. Thus, Microcystis was the only MC-producing genus of cyanobacteria being present in the cyanobacterial blooms in Lake Taihu.The Chl-a concentration (representing cyanobacterial abundance) in Meiliang Bay was higher than those in West Lake and Zhushan Bay, indicating a higher risk of cyanobacterial bloom outbreak in Meiliang Bay. However, the eutrophication level in Meiliang Bay was lower than those in West Lake and Zhushan Bay, suggesting that the outbreak of cyanobacterial bloom was not only related to the trophic status but also related to some other environmental factors such as the wind direction and geographic locations.RDA indicated that the cyanobacterial community was significantly correlated with NO3"-N, CODMn, and NHU+-N in January and March, whereas it was correlated with water temperature in June and September. Thus limiting the nutrient input especially N and C loading in Lake Taihu will be a key factor in controlling the growth of cyanobacteria.Data from this study should be useful in the development of strategies in addressing future cyanobacterial bloom outbreaks in Lake Taihu.