Abstract: Qiandao Lake is one of China’s ten major reservoirs and the most important strategic source of drinking water in the Yangtze River Delta region. An investigation was conducted on the water quality and the community structure of phytoplankton at 8 sampling sites in Qiandao Lake of Southeast China in January 2010. The photosynthetic activity of phytoplankton was measured by Phyto-PAM (Pulse Amplitude Modulation) and Water-PAM. The water quality indicators were in accordance with the requirements of the water environmental function zones except TN. There was a stratification of water temperature, physical and chemical indicators in winter. The thermocline depth was between 25-40 m. Diatoms, cyanobacteria, green algae, cryptophyta, dinoflagellates, and golden algae were observed in winter. Dominant phytoplankton groups were Diatoms (Melosira and Cyclotella). They accounted for 60% of the total density. Chlorophyll a concentration varied from 1.4 to 5.7 μg·L^-1. The results suggested that the photosynthetic activity of phytoplankton was active in winter. Diatoms had the maximum photosynthetic activity, secondly cyanobacteria, and finally green algae. There were significant horizontal and vertical spatial differences in photosynthetic activity. The light saturation intensity of phytoplankton in Qiandao Lake ranged between 700-1000 μmol·s^-1·m^-2. The results also suggested that the high photosynthetic activity of diatoms relate to the outbreak of diatom bloom in Qiandao Lake in spring.

Key words: ACCase, walnut, fat, G6PDH, Pyruvate Kinase.