Seasonal dynamics of Cyanophyta and related affecting factors in Dianshan Lake

In order to understand the Cyanophyta community and its relations with environmental factors in Dianshan Lake, a survey was conducted at nine sampling sites from May 2009 to April 2010. Canonical correspondence analysis (CCA) was made to explore the relationships between recorded Cyanophyta species and environmental factors by CANOCO 4.5, and ordination diagrams were drawn with the results of CCA. During the study period, a total of 15 genera and 46 species of Cyanophyta were recorded, among which, Microcystis spp. made up of 69.9%, followed by Oscillatoria spp., accounting for 20.55%. The Cyanophyta had a distinct seasonal abundance, ranging from 9.0×10⁴ to 7.6×10⁶ cells • L^-1. The cell density of cyanobacteria had a strong relevance to water chlorophyll a, total N (TN), and trophic state indices TSI_M(chl-a) and TSI_M(TN), indicating that the water TN content in the lake greatly affected the algal cell density, and in return, the algal cell density and relative abundance affected the water chlorophyll content and transparency. CCA analysis showed that in spring, the water body was more greatly affected by water temperature, biological oxygen demand, and TP, while in summer, TP, biological oxygen demand, and transparency were the most important environmental factors affecting the water body. However, none of the factors played the most important role in affecting Cya- nophyta community in autumn. In winter, the Cyanophyta species positively correlated with water NH₄⁺-N and TN. M. aeruginosa and O. tenuis were regarded as the dominant species of the whole lake algae species. M. aeruginosa was significantly positively correlated with water temperature and TN and negatively correlated with water pH, while O. tenuis appeared in four seasons and was significantly affected by water temperature and pH. The relationships between algae dynamics and environmental factors were as follows: in spring and winter, cyanobacterial communities were most affected by water temperature; in summer, they were significantly affected by water TP and TN; while in autumn, water transparency was the most relevant factor. This study showed a highlight to understand the seasonal dynamics of cyanobacteria, and could help manage the environment of lake ecosystems.