Response of predominant phytoplankton species to anthropogenic impacts in Lake Taihu

A year-long investigation of patterns in dominant phytoplankton species was conducted to reveal the response of the phytoplankton community to anthropogenic impacts in Lake Taihu. Microcystis spp. and Cyclotella meneghiniana were the predominant species throughout the lake. Another 14 taxa were codominant species in parts of the lake. In the northwest, the highest phytoplankton biovolume appeared and Microcystis spp. and C. meneghiniana alternately dominated. Aulacoseira granulata, Asterionella formosa and Synedra spp. codominated in succession with C. meneghiniana in winter and spring. Species diversity indices were highest in spring while lowest in summer and anthropogenic nutrient inputs were the key factors controlling the alternating dominance of phytoplankton species. In the Gonghu area (the northeast), Microcystis spp. and C. meneghiniana codominated all year long; the predominant species was determined by water transfer from the Yangtze River, where the codominant species took advantage of flushing and mixing. In the southwest and the lake center with weak anthropogenic impacts, internal nutrient release was the key factor affecting the codominance of Microcystis spp. and C. meneghiniana all year long as well as the codominance of A. granulata, Dolichospermum flos-aquae and Ceratium spp. in succession. It could be concluded that anthropogenic influences shaped the structure of the phytoplankton community and determined the composition of dominant species in Lake Taihu. Species diversity was significantly correlated with nutrient inputs. Not only exogenous P reduction, but also internal P source reduction should be undertaken to prevent harmful cyanobacterial bloom. Water transfer could be used as an emergency management for bloom control.