Anthropogenic activities disturb phytoplankton taxa and functional groups in an urban river

Anthropogenic activities have substantial impacts on river ecosystems, yet how phytoplankton taxa and functional groups respond to varying levels of anthropogenic activity in urban rivers remains poorly understood. Herein, we investigated the sensitivity of phytoplankton taxa and functional groups to anthropogenic disturbances in the Bahe River, which experiences increased anthropogenic activity intensity from upstream to downstream. We found that both phytoplankton composition and niche breadth exhibited distinct variations among the three reaches with different anthropogenic disturbances. Notably, we observed a marked increase in the abundance of potential bloom-forming species in the river section with the highest anthropogenic disturbance, suggesting that anthropogenic activities might promote the growth and proliferation of these species. Compared to geographical and physiochemical factors, anthropogenic activities were identified as the primary driver of changes in phytoplankton taxa and functional groups. Increasing levels of anthropogenic activities potentially led to higher concentrations of ammonium nitrogen and total phosphorus, further influencing niche differentiation among phytoplankton taxa and functional groups. Our study offers profound insights into the impacts of anthropogenic disturbances on phytoplankton, emphasizing the necessity of integrating watershed-scale human activity management into strategies for controlling phytoplankton in urban rivers.