Investigation of summer plankton community structure in Yuqiao Reservoir,Tianjin

In July of 2011,the water quality and the structures of plankton community were investigated in Yuqiao Reservoir to evaluate its trophic state.The comprehensive trophic level index(TLI(∑)) is 45.8,which indicates the reservoir is mesotrophic.59 phytoplankton species in total have been identified.The average phytoplankton abundance is 312.40 × 104cells / L,and the average biomass is 5.30 mg / L.The phytoplankton community is mainly composed by Cyanophyta and Chlorophyta.Microcystis aeruginosa,Microcystis flos-aquae and Pediastrum simplex var.duodenarium are dominated species.Total of 16 zooplankton species have been identified.The average zooplankton abundance is 53.2 ind./ L,and the average biomass is 11.58 mg / L.The zooplankton community is mainly composed of Bosmina longirostris and Cyclops vicinus.Based upon the analyses of the Shannon-Wiener index,Pielou index and Margalef index,the reservoir is between medium pollution level and heavy pollution level,which is similar to the evaluation results of nutritional status using TLI(∑).Comparative analysis has been carried out between historical data and the present investigation,and the results show that both abundance and biomass of phytoplankton have been increased,and zooplankton species have reduced while zooplankton biomass has increased.This indicates the evolution of Yuqiao Reservoir from a Bacillariophyta-Cyanophyta dominated reservoir into a Bacillariophyta-Chlorophyta dominated reservoir,and finally into a Cyanophyta-Chlorophyta dominated reservoir.