Longitudinal Differences of Phytoplankton Community during a Period of Small Water Level Fluctuations in a Subtropical Reservoir Bay (Xiangxi Bay,Three Gorges Reservoir,China)

The Three Gorges Reservoir (TGR) had a great inflow discharge with small water level fluctuations in the flood season of the year 2008, when a large‐scale cyanobacterial bloom broke out in Xiangxi Bay (a tributary bay behaving like a lake) for the first time after the construction of the TGR impoundment. To compare spatiotemporal longitudinal differences of phytoplankton community structure during this period, weekly surveys were performed in Xiangxi Bay. The cyanobacterial bloom lasted from June 6 to July 18, 2008, with Microcystis aeruginosa as the dominant species. During this bloom the species diversity, evenness and community change rate was relatively low. The probable causes for the interruption of the bloom were precipitation and water temperature. In the non‐cyanobacterial bloom period (July 25 to September 26, 2008) many other species dominated the community including Stephanodiscus hantzschii and Cryptomonas ovata, with higher values of species diversity, evenness and community change rate. As for the longitudinal differences, the community structure in the riverine zone was different from that in other zones, indicating the important effect of inflow from the upstream of Xiangxi Bay. The management actions in Xiangxi Bay should prevent blooms in the mainstream, lacustrine and transitional zone. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)