Study on the Community Dynamics and Diversity of Phytoplankton in Tiegang Reservoir (China)

Tiegang Reservoir is an important drinking water source in Shenzhen, and its water quality status and water ecological health affect the phytoplankton succession pattern in the reservoir. The opposite can also be reflected by the biomass and diversity of phytoplankton. In this study, based on the phytoplankton monitoring data of the reservoir from 2019 to 2020, combined with the physicochemical parameters of the reservoir water body during the same period, we analysed the spatial and temporal characteristics of the phytoplankton in Tiegang Reservoir, analysed the phytoplankton diversity, and evaluated the drinking water safety level. The results showed that 7 phytoplankton phyla were detected in Tiegang Reservoir, of which cyanobacteria and diatoms were the dominant taxa, and green algae were the subdominant species. The results showed that the total cell abundance in Tiegang Reservoir ranged from 8.78 to 36.51 × 106 cells/L. Cyanobacteria, diatoms and green algae are dominant algae. And cell abundance of other algae was very low. The phytoplankton density in the surface layer was not much different from that in the transmissive layer, but both were higher than the phytoplankton bio-density in the bottom layer. In Tiegang Reservoir, cyanobacteria dominated from May to November, with the proportion of 56.27 to 78.36%; diatoms dominated from December to April of the following year, with the proportion of 45.12 to 58.98%; and green algae were at a low level throughout the year, with the proportion of 5.21 to 13.79%. The risk of diatom outbreaks in winter is high, which can easily cause clogging of the filter tanks in waterworks and threaten the safety of water supply. In summer, there is a certain risk of cyanobacterial outbreaks, and the dominant cyanobacteria are Microcystis spp. and Chlorella spp., which produce algal toxins that are harmful to human health. Overall, the risk to the safety of drinking water in Tioga Reservoir is low, with a few periods of moderate risk. The risk level of drinking water safety at the four sites was ranked as Sample 3 > Sample 2 > Sample 4 > Sample 1. The risk of cyanobacteria was mainly in the months of May to July, and the risk of diatoms was mainly in the months of January to February.