Temporal and Spatial Variations of Phytoplankton Community Structure in Lake Erhai, a Chinese Plateau Lake, with Reference to Environmental Factors

Temporal and spatial variations of phytoplankton community in Lake Erhai were investigated from May 2010 to April 2011. A total of 124 species belonging to 8 phyla and 72 genera were recorded, among which Chlorophyta (74) ranked the first, followed by Bacillariophyta (24) and Cyanophyta (17). Total phytoplankton density ranged from 27.7 × 105 to 442.1 × 105 cells/L, with annual average value of 196.3 × 105 cells/L. The range of total phytoplankton biomass was between 0.68 mg/L and 3.25 mg/L, with annual average value of 2.31mg/L. In winter and spring, the dominant species were Fragilaria capucina and Aulacoseira granulata, while it changed into Cyclotella meneghiniana, Microcystis (M. aeruginosa, M. wesenbergii and M. viridis) and Psephonema aenigmaticum in summer and autumn. Phytoplankton biomass in the southern zone of the lake was significantly higher than those in the northern and middle zones of the lake. Two-way ANOVA showed that the influences of temporal (F = 43.75, P < 0.001), spatial variability (F = 14.85, P < 0.001), and their interaction (F = 2.74, P < 0.001) on phytoplankton biomass in Lake Erhai were all significant. Redundancy analysis revealed that water temperature, transparency, nutrient concentration and crustacean zooplankton were main environmental factors affecting phytoplankton community structure.