TEMPORAL AND SPATIAL VARIATION OF PHYTOPLANKTON FUNCTIONAL GROUPS AND MAIN DRIVING FACTORS IN THE THREE GORGES RESERVOIR, CHINA

The Three Gorges Reservoir (TGR) is a deep, canyon-reservoir created in consequence of the Changjiang (Yangtze) River's impoundment by the Three Gorges Dam in southwest China. To study the spatio-temporal dynamics of phytoplankton functional groups and the main driving factors in this large subtropical reservoir, field samplings were conducted in five sections along the longitudinal axis of the TGR in summer (August 2012), autumn (December 2012), winter (January2013), and spring (April 2013), respectively. Twenty-nine phytoplankton functional groups were identified among 246 phytoplankton species. There were obvious seasonal and spatial differences in both the biomass and composition of the phytoplankton functional groups. The algal biomass in the mainstream was at low level during the study period and the dominant functional groups included groups B, D, P, and MP, which adapted to mixed and turbid water condition. In comparison with the mainstream, the algal biomass in the tributaries was higher in during the flood seasons (spring and summer) and the dominant groups switched to X2, L-O, and P, which prefer meso-eutrophic environments and standing water. In the dry seasons (autumn and winter), the dominant groups in the tributaries were B, D, P, L-O, and Y. Group L-O and Y can swim to optimal light and nutrients layers with the help of flagella. The study suggests that hydrological regimes such as mixing, water flow, water temperature, and thermal structure played an important role in determining the biomass and community structure of phytoplankton, and shows the value of phytoplankton functional groups in studying algal spatio-temporal dynamics in the TGR