Dianchi Lake is a typical plateau, unstratificated, eutrophic lake in southwest of China. It has been seriously polluted in the past decades. And it had not been investigated in the whole lake for phytoplankton since 1980s. Thus, a project was carried out to find out what happened to the phytoplankton biomass and its regime dominance in the lake now.In this study, Chlorophyll a (Chl. a) had been monthly investigated according to the national standard method at 40 sites in Dianchi Lake from September, 2001 to August, 2002. Cell density and phytoplankton species composition had been investigated bimonthly as well. The results showed that Chl. a increased from 0.015mg/L to 0.10mg/L (monthly average values) during January to August, 2002. Correspondingly, water temperature increased from 10 degrees C to 28 degrees C. Chlorophyll concentrations of the south sites were lower than the north ones. Site one had the highest chlorophyll a value in all sites. We concluded that the southwester prevailing over the Dianchi Lake played a very important role. The horizontal movement of phytoplankton should be wind-induced. The water blooms mainly composed by cyanobacterial species. The percentage sometimes reaches to 100%. And Microcystis aeruginosa was the most common species. But in the spring of 2002, the dominance species was changed. Aphanizomenon spp. became dominant (69%) in March. It showed an obvious evidence for the seasonal succession. Moreover, the investigation indicated that the Pearson Correlation were high significant between chlorophyll a and water temperature (0.736, p < 0.01), total nitrogen (0.970, p < 0.01) and chemical oxygen demand (0.929, p < 0.01). Therefore, we concluded that phosphor-us was no longer the limited nutrition factor in Dianchi Lake to phytoplankton growth, nitrogen has taken the place. CODMn which is considered the token of organism population level, become the main chemical factor affecting the algal biomass. All the results indicate that Dianchi Lake is extremely eutrophication now; the blooms can last for 9-10 months in the year; the water is polluted seriously, especially the organic pollution, and it became an important factor which could affect the phytoplankton biomass directly; the species are simplex I Microcystis, Anabaena and Aphanizouwnon were the most popular bloom-forming cyanobacteria.
Wan Neng (email@example.com) ; Song Li-Rong (firstname.lastname@example.org) ; Wang Ruo-Nan; Liu Jian-Tong.The spatio-temporal distribution of algal biomass in Dianchi Lake and its impact factors,Acta Hydrobiologica Sinica,2008,32(2):184-188