Abstract:

Lihu lake，Taihu lake was investigated in winter (January 30th) and Spring (March 27th)，in 2007，respectively.Biological indexes such as similarity index，predominance index，diversity index and KolkwitzMorsson pollution system were used to analyze the community characteristic of phytoplankton.Furthermore，both biological indexes and physicalchemical indexes were used to evaluate the water quality of Lihu lake.Results showed that 88 species and varieties，and 8 phylum of phytoplankton were detected in water samples of Lihu lake；and green algae accounting for 5455% of the total species of phytoplankton were the most important component，and then followed by diatom which accounted for 1705% of the total species of phytoplanton.Although the dominant species were all green algae in winter and spring，there were some differences in species.〖WTBX〗Chlamydomonas microsphaera〖WTBZ〗 was dominant species in winter，and the dominance index changed from 7143% to 9628%.〖WTBX〗Pedinomonas minor〖WTBZ〗 and 〖WTBX〗Chlorella vulgaris〖WTBZ〗 were dominant species in spring，and the dominance index changed from 6702% to 8259%.The dominant indexes were all high in winter and spring，which meant that the dominant species were very obviously.The investigation also indicated that there was great difference in phytoplankton component between winter and spring，and the similarity index was only 030.Biological evaluation indicated that the water quality in winter was worse than that in spring，which was the same as the result evaluated by physicalchemical method.However，biological evaluation showed that the water quality states of Lihu lake were middle pollution in spring and heavy pollution in winter，and the pollution degrees evaluated by biological method in winter and spring were both more serious than that evaluated by physicalchemical method，which revealed the difference between the two evaluation methods.

Key words: Lihu Lake/ phytoplankton/ community characteristics/ water quality evaluation