Phytoplankton Community in a Large Shallow Eutrophic Lake (Lake Dianchi, Southwest China)

Monthly investigation is executed during April 2006 to May 2007, focusing on the abundance and composition of phytoplankton in a large (300 km²) shallow (mean depth 4.4 m) eutrophic lake (Lake Dianchi). The presence of phytoplankton in northern bay was the highest, while that in the southern part the lowest, and center part and northern part conditions represented an intermediate state between these two. Phytoplankton communities dominated by cyanobacteria, and Microcystis bloom occurred in the whole year. Annual average phytoplankton cell number was 8.7 times 10⁷ cells L^-1, of which 93.6% was Microcystis, 4.5% were Chlorophyta and 0.3% was Aphanizomenon. Comparative studies of our investigation against conditions in the past indicate that phytoplankton abundance and diversity decreased and cell miniaturization occurs in 2006 - 2007.