Generally speaking, in mesotrophic lakes, Pyrrophyta, Cryptophyta, and Bacillariophyta are the dominant species, and in eutrophic lakes, Chlorophyta and Cyanophyta are the dominant species [21]. From this, a conclusion can be drawn that Chlorella sp. and Microcystis selleck chemicals Navitoclax incerta Lemm. which belong to the Chlorophyta and Cyanophyta phyla, respectively, are becoming the dominant species, indicating that Baiyangdian Lake had become eutrophic and organic matters tended to increase year by year.3.3. Relationship between Phytoplankton and Environmental FactorsNine environment factors, chemical oxygen demand (COD), potassium permanganate index (CODMn), total nitrogen (TN), total phosphorus (TP), chlorophyll a (Chla), pH, dissolved oxygen (DO), secchi depth (SD), and temperature, were selected in the eight sampling sites.

The Pearson correlation analysis showed that no significant correlation was observed between phytoplankton cell density and environmental factors in spring (Table 2). In summer (Table 3), phytoplankton cell density was greatly influenced by DO (r = 0.813, P = 0.014), Chla (r = 0.818, P = 0.024), and TP (r = 0.833, P = 0.010), and there was a positive correlation between them. According to this, the best environment factor combination could not be identified which influenced the space distribution of phytoplankton in Baiyangdian Lake in summer, and DO, Chla, and TP were probably the important factors which influenced the space distribution of phytoplankton in Baiyangdian Lake in summer. The main reason for this is that summer is usually the time for algal bloom occurrence in eutrophic lakes.

In the sampling Sites 3 and 7, because breeding industry and crop farming were flourishing, the concentration of nutrients in water was high, while algae bloom, DO, and the phytoplankton cell density were low. In the sampling Sites AV-951 5 and 1, because the water was open and far from pollution source, the water quality was good and the phytoplankton cell density was low.Table 2Correlation analysis between phytoplankton density and environmental factors of Baiyangdian Lake in spring.Table 3Correlation analysis between phytoplankton density and environmental variables of Baiyangdian Lake in summer.Phytoplankton cell density varied greatly from season to season mainly due to the water temperature.