Phytoplankton community structure in Lake Ulungur in Xinjiang Uygur Autonomous Region

The phytoplankton of Lake Ulungur was investigated seasonally from November, 2006 to July, 2007. A total of 164 phytoplankton species (including a number of unconfirmed species) was detected, which belonged to 90 genera, 8 phylum. Among them, Anabaena bergii was a new record species of cyanophyta in Xinjiang Uygur Autonomous Region, and two species of bacillariophyta, Chaetoceros sp. and Thalassionema sp., belonged to marine algal. In each season, the phytoplankton composition was dominated by Chlorophyta and Bacillariophyta, secondly dominated by Cyanophyta, Euglenophyta, Xanthophyta, Chrysophyta, Cryptophyta and Pyrrophyta. The number of phytoplankton species was the highest in autumn (141 species), followed by the summer (128 species) and spring (121 species), the lowest in winter (95 species). There was an obvious seasonal characteristiscs for the dominant species. Raphidiopsis sinensia, Teraёdron minimum, Selenastrum minutum, Chlorella vulgaris and Synedra acus were dominant species in the whole year, while Synedra ulna could only be found in spring, summer and autumn. Kirchneriella contorta and Chlorella ellipsoidea dominated in summer, and Chlorococcum infusionum and Treubaria crassispina dominated in winter. The standing crop of phytoplankton peaked only in summer with a biomass of 6.77mg/L and the minimum biomass of 1.45mg/L occurred in winter. Compared with historical data, the phytoplankton composition had remarkable changes. The growth of green alga and diatom were most notable, while the number of the phytoplankton increased many fold in the past 30 years.