Shifts in phytoplankton communities in inland waterways: Insights from the Beijing–Hangzhou Grand Canal, China

Abstract Phytoplankton play a crucial role in maintaining the health of river ecosystems, and their communities are closely linked to river hydrodynamics. In inland waterways, disturbances generated by ship propellers alter flow dynamics and may affect phytoplankton communities. To clarify it, phytoplankton communities in the Zhenjiang section of the Beijing–Hangzhou Grand Canal (BHGC) in China, the world's longest canal, were studied and compared them with its undisturbed tributaries. The results revealed major alternations in seasonal patterns of phytoplankton communities in the BHGC, shifting the peak of phytoplankton density from spring to autumn and the lowest diversity from summer to autumn. Ship disturbances increased water turbidity and created optimal N/P ratios, which provided Cyanobacteria with a competitive advantage in autumn. The proliferation of Cyanobacteria resulted in a phytoplankton density in the BHGC, exceeding that in the tributaries by more than tenfold, accompanied by a decrease in diversity to its lowest level. Due to habitat alterations, functional groups emerged that are resilient to strong disturbances and high turbidity. The findings add to the understanding of the impact of ship traffic on river ecosystems.