Phytoplankton community structures and environmental limitation in Fuxian Lake

The species composition and cell density of phytoplankton and chlorophyll a content were studied with reference to environmental factors sampled in spring, summer and autumn in 2001 in Fuxian Lake (24 degrees 21'-24 degrees 38'N, 102 degrees 49'12-102 degrees 57'26"E). The phytoplankton from Fuxian Lake included 78 species belonging to 40 genera 25 family, 7 phyla. Chlorophytes was predominant, with consisted of 43.5% of total species number. Species number of phytoplankton and cell density, and chlorophyll a appeared visible monthly variation. Phytoplankton cell density was highest at water layer of 0-20m. The average cell density of phytoplankton was on 18th September (342.73x10(3)cells/dm(3) ) > on 13th September (235.67x 10(3) cells/dm(3)) > on 14th August (80.10x10(3) cells/dm(3))> on 26th May (52.46x10(3) cells/dm(3)). The main predominant phytoplankton species was Mougeotia bloodlei, which accounted for 42.94%-84.94%. of total cell density of phytoplankton. Therefore the monthly variation of the cell density of Mougeotia bloodlei controlled the overall density of phytoplankton directly. The change of dominant species from 1990 to present study was Mougeotia bloodlei (Chlorophyta) from Aphanizomenon flos-aquae (Cyanophyta). The community structures of phytoplankton were consists of Mougeotia bloodlei, Chroococcus spp., Cyclotella spp., Ceratium hirundinella and Dinobryon sertularia. The cell density of phytoplankton was positively correlated with chlorophyll a concentration, and negatively correlated with the concentration of nutrient salts (PO43-, NO3- and SiO32-).