Phytoplankton functional groups succession and their driving factors in a shallow subtropical lake

The succession of phytoplankton functional groups and environmental variables were investigated from January to December 2018 in a shallow subtropical lake, East Taihu Lake, located in the Yangtze Delta of China. Altogether, 125 genera, 21 functional groups, and 7 predominant functional groups, D (Fragilaria acus, Synedra acus, and Nitzschia spp.), P (Fragilaria capucina and Aulacoseira granulate), MP (Oscillatoria spp., Diploneis ovalis, Gomphonema angustatum, Nitzschia palea, and Achnanthes spp.), Y (Cryptomonas ovata, Cryptomonas erosa, Chroomonas acuta, and Ceratium spp.), H2 (Anabaena spp.), M (Microcystis spp.), and W1 (Euglenoids spp.), were identified, and these predominant functional groups exhibited strong seasonal variations. Groups Y and W1 dominated from winter to spring when temperature and light were low. The external pollution load and high levels of nutrients entered the lake in June, allowing group M to become dominant, even ultimately triggering Microcystis blooming. Meanwhile, the abundance of aquatic plants in summer, combined with high levels of transparency and light availability, resulted in Group M being replaced by Group P and then Groups M and H2 rebounding in autumn. The redundancy analysis revealed that water temperature, nutrients, and light availability (Z(eu)/Z(mix)) were the key factors promoting phytoplankton succession. The ecological assessment results demonstrated a good ecological status based on the assemblage index (Q average = 3.0). This work emphasizes the fact that temperature, nutrients, and light were the driving factors for phytoplankton dynamics, and aquatic plants and external pollution were important external factors for the succession of phytoplankton.