Response of Phytoplankton Community Structure to Vegetation Restoration after Removal of Purse Seine in Shengjin Lake

Aquatic vegetation has been restored since the removal of seine nets from the lake surface of Shengjin Lake in 2018. Through four seasons of phytoplankton sampling surveys from 2019–2020, we analyzed spatial and temporal changes in phytoplankton communities, water quality, and aquatic plant recovery in conjunction with previous research literature to reveal the response mechanisms of phytoplankton community structure to rapidly recovering aquatic vegetation. The results showed that the Secchi depth increased (0.4 m to 0.7 m), the concentration of total phosphorus decreased (0.053 mg/L to 0.41 mg/L), the species of aquatic plants (5 species to 16 species), phytoplankton species (210 species to 254 species) and cell density increased after the removal of the seine. Since the removal of the seine of Shengjin Lake, the aquatic vegetation cover has exceeded 80%, the phytoplankton biodiversity has increased, and the water quality has recovered to II-III water status. Our results show that aquatic plants improve water quality through direct and indirect effects and influence phytoplankton community structure together with the water environment, which can provide guidance for the restoration situation of the middle and lower reaches of the Yangtze River through-river lake ecosystems.