Responses of the phytoplankton community in the Yangtze River estuary and adjacent sea areas to the impoundment of the Three Gorges Reservoir

The phytoplankton community in river estuaries is subject to complex physical and chemical stresses. The construction of the Three Gorges Dam (TGD) has dramatically changed the hydro-environmental conditions, including hydrological regimes and water quality in the Yangtze River estuary (YRE), which could have a significant impact on the estuarine ecosystem. To evaluate the effects of hydro-environmental alterations on the phytoplankton community in YRE, sampling campaigns were conducted in the area during 2010–2011; meanwhile, historical data before TGD construction and during the TGD filling period were collected. Seasonal variations showed that diatoms dominated the community throughout the sampling period, and the most important environmental factors affecting the phytoplankton community were silicate, total suspended solids and phosphate. With respect to differences in the three phases (before TGD construction, during TGD filling and after TGD filing), the abundance of phytoplankton showed an increasing trend: the proportions of diatom species numbers declined, while the proportions of Dinophyta species numbers increased. The position of phytoplankton abundance maximum moved inwards to the estuary of the Yangtze River after the impoundment of the TGD.The changes of water transparency, silicate/phosphorus/nitrogen ratio and salinity profile due to interception of sediment and alteration of discharge by Three Gorges Dam significantly affected the community structure and spatial distribution of phytoplankton in the Yangtze River Estuary