Abstract: To explore the characteristics of phytoplankton functional groups and assess their influencing factors in Wuchang Lake, water samples were quarterly collected from December 2019 to October 2020. The composition and succession characteristics of phytoplankton functional groups were analyzed. Canonical correspondence analysis (CCA) and variance partitioning analysis were used to assess the key driving environmental factors. Water quality was evaluated by assemblage index (Q) and trophic level index (TLI). The results showed that 343 phytoplankton species from nine phyla were detected in Wuchang Lake. According to the functional group classification, phytoplankton could be divided into 25 functional groups, among which 18 (A, B, D, P, MP, T, T_B, S1, S_N, X3, Y, E, H1, J, L_O, M, W1 and W2) were the dominant functional groups. The seasonal succession of dominant functional groups was P, E (winter) → W1, MP (spring) → D, L_O (summer) → D (autumn). CCA results showed that environmental variables played an important role in the succession of phytoplankton functional groups. Depth, water temperature, electrical conductivity, transparency, total nitrogen, ammonium nitrogen, nitrate nitrogen and nitrite nitrogen were the main environmental factors. The Q value of different seasons was summer (2.28) < spring (2.30) < autumn (2.67) < winter (3.02), indicating lake water quality was in a mediumgood range. The TLI value of different seasons was winter (59.85) < autumn (59.91) < summer (62.12) < spring (65.74), indicating the lake was at a state of light-moderate eutrophication. The two evaluation results showed that water quality was better in winter. The changes in phytoplankton functional groups could reveal the succession characteristics of phytoplankton community and reflect the state of water environment in Wuchang Lake, which will be instructive for lake water quality evaluation and ecological protection.

Key words: phytoplankton, functional group, environmental factor, assemblage index, trophic level index.