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A novel approach based on flow cytometric sorting followed by construction of 18S rRNA clone libraries was used to study the diversity of eukaryotic picophytoplankton of lakes. The composition of eukaryotic picophytoplankton community appeared highly variable in three lakes. Eukaryotic picophytoplankton was dominated by Cryptophyta in the Lake Xuanwu, and was mainly composed of Cryptophyta and Chrysophyta in the Lake Zixia. In the Lake Taihu, four phyla were discovered, including Cryptophyta, Chrysophyta, Bacillariophyta and Chlorophyta. Meanwhile, the diversity of eukaryotic picophytoplankton differed in various lake regions. In the Meiliang Bay, Chrysophyta was the dominant, and the other three phyla were found in the Gonghu Bay. In the central lake, all of those four phyla were discovered, implying this region contained the highest diversity. The canonical correspondence analysis between the diversity of eukaryotic picophytoplankton and environmental factors revealed the concentration of total phosphorus had the highest important impact on the eukaryotic picophytoplankton communities.

The old town area of Kaixian county was flooded and showed reservoir characteristics after the water level of Three Gorges Reservoir got 172. 8 m in December 2008. The aquatic ecology and nutritional status of Kaixian drawdown area after water storage are still rarely reported. To understand the current water environment and changes in algal community structure of Kaixian drawdown area after 172.8 m water level, the algal composition, abundance, biomass distribution and changes of its sampling spots including Hanfeng Lake were observed twice during winter storage period in January and December 2009. The trends in phytoplankton community structure were analyzed and the water quality assessment of nutritional status was carried out. The results indicated that 6 phylums, 37 genera, 69 species of phytoplankton in total were identified in the two sampling, and the dominant species were Dinophyta and Cryptophyta. The cell density and biomass in December 2009 were lower than those in January 2009. The evaluation results of algal population structure and pollution indicators showed that the nutrition level of Kaixian drawdown area during the winter storage period was mesotrophic to eutrophic type, while diversity analysis result indicated moderate pollution.