Seasonal succession of phytoplankton functional groups in a reservoir in central China

Zhushuqiao Reservoir is one of the main sources of drinking water for Changsha City, which is the capital of Hunan province in central China. Understanding phytoplankton functional groups and their relationships with the environment is critical for the sustainable management of the reservoir for the supply of drinking water. Therefore, phytoplankton and water samples were collected and analyzed seasonally in 2016 to detect these relationships, with a total of 23 functional groups of phytoplankton identified. The highest diversity of functional groups was observed in spring, while the lowest was in winter. Due to differences in the geographical position, as well as the hydrological and environmental conditions, upstream phytoplankton-community structures are different from those downstream, with the dominant functional groups having a clear seasonal succession. The succession dynamics of phytoplankton functional groups from upstream to downstream in spring were M (Microcystis aeruginosa) + Y (Cryptomonas sp.) -> S1 (Pseudanabaena limnetica) + L-M (Gomphosphaeria sp.) -> S1 + L-M + X1 (Chlorella sp.) -> X1 + X2 (chlamydomonas sp.) + F (Oocystis sp.) -> F + X1 + X2; X1, F and Lo (Peridinium sp.) were the co- dominant groups from summer to autumn, and group C (Melosira ambigua) was dominant in winter. The upstream assemblages of X1 + X2, X1 + F, S1 + L-M + M in spring and LO in summer can adapt to the rapid growth in eutrophic conditions with potential bloom threats. Water temperature, light and phosphorus were the primary factors regulat- ing the dominant functional groups, and the phytoplankton succession was seasonally dependent. These results may have implications for the management of future water resources in the Zhushuqiao Reservoir, such as the determination of the intake depth of drinking water, and the prevention of nutrient pollution