Abstract: A seasonal investigation was conducted on the plankton community structure at five sampling profiles (S1-S3 for discharge area and S4-S5 for non-discharge area) in the areas with high and medium tide levels of the mudflat wetland of Hangzhou Bay in April (spring), July (summer), October （autumn), 2010 and January (winter), 2011, aimed to understand the characteristics of the plankton community and their relationships with environmental factors. In the wetland, the annual average density of phytoplankton was 3278 ind·L^-1, being dominated by Oscillatoria (69.2%) and Ulothrix (17.2%), and the biomass was 0.039 mg·L^-1, being dominated by Coscinpdoscus (66.2%) and Nitzschia (23.5%). The annual average density of zooplankton was 54.4 ind·L^-1, being dominated by Rotifera (68.1%) and Copepoda (29.5%), and the biomass was 0.268 mg·L^-1, being dominated by Copepoda (61.2%) and Rotifera (23.9%). The dominant species of each group of plankton were Oscillatoria, Brachionus calyciflorus, Diaphanosoma brachyurum, Sinocalanus dorrii, and Nematodes, respectively. The water nutrient concentrations and the biomass of plankton community were much higher at the profiles S2-S3 than at the other profiles, and much higher in the areas with medium tide level than with high tide level. The water NH₄⁺-N concentration was significantly linearly correlated with phytoplankton biomass and zooplankton biomass, and the pollution index had a significant positive correlation with rotifers biomass (P<0.001). The areas with medium tide level were seriously polluted by inland discharge, whereas the significant increase of rotifer biomass and the decline of zooplankton species richness were the important characteristics of the plankton community.

Key words: bioaccumulation, stable isotopes, food web, heavy metal, Daya Bay.