Longitudinal patterns of phytoplankton distribution in a tributary bay under reservoir operation

To investigate longitudinal patterns of phytoplankton distribution influenced by reservoir operation, weekly surveys were carried out in the mainstream of the Yangtze River and Xiangxi Bay of the TGR from February, 2008 to February, 2009. Using cluster analysis based on chlorophyll a, transparency, and relative water column stability, the longitudinal patterns in different water level fluctuations periods were identified. The mainstream zone, lacustrine zone, transitional zone and riverine zone could be successively distinguished from the mouth to the end of Xiangxi bay, but distinct differences existed in different periods, including the location and extent of each zone. In Periods I (spring) and II (summer and early autumn, flood season), the mainstream zone was relatively short, while in Periods III and IV (autumn and winter seasons), it became longer. At the end of Xiangxi Bay, it presented characteristics of a transitional zone in Periods I, III, and IV, while in Period II it could be recognized as the riverine zone. The correlations among chlorophyll a, transparency, and relative water column stability differed from the Yangtze River to longitudinal zones of Xiangxi Bay, influenced by various features of these regions.