Distinct effects of sediment regulation on phytoplankton community assembly in the tributaries and mainstream of the Three Gorges Reservoir

Abstract

Sediment regulation (SR) maintains the water storage capacity of the Three Gorges Reservoir (TGR), but the influences of SR on riverine phytoplankton communities, especially in the upper reservoir, have not yet been investigated. In this study, the first description of the membership of the phytoplankton community was provided, together with hydrodynamic and environmental factors before, during, and after implementation of SR in the TGR region was investigated. A total of 84 taxa of phytoplankton from 6 phyla were recorded during the three stages of SR. There were no significant impacts of SR on phytoplankton assemblages in the mainstream. But in the tributaries, the replacement components of beta diversity increased from 0.39 to 0.63, and the biomass reduced from 1.36 to 0.49 mg/L. Bray-Curtis distances revealed that phytoplankton community in the mainstream and tributaries became more similar after SR (PERMANOVA, p = 0.592). Based on the investigated environmental variables, stochastic processes play a vital role in structuring the phytoplankton community in the TGR region, although SR decreased the relative importance of stochastic processes for phytoplankton assembly in the tributaries. This study indicates that SR plays a critical role in accelerating turnover rates within phytoplankton communities in tributaries, which has important implications for preventing phytoplankton bloom, and more significantly, for maintaining river–reservoir system sustainable development.