Dam-induced connectivity loss shapes benthic communities through water quality alterations in the Yangtze River Basin

Human activities, such as hydropower generation, irrigation, and flood control, have led to the extensive construction of dams, significantly impacting river ecosystems worldwide. These structures disrupt the river system and alter the natural flow characteristics of river channels, disrupting the continuity and connectivity of aquatic ecosystems. The loss of free-flowing river basins often leads to the deterioration of water conditions, including changes in temperature, dissolved oxygen levels, and nutrient concentrations, which negatively affect aquatic biodiversity. Benthic macroinvertebrates, being highly sensitive to alterations in their habitat, are particularly vulnerable to these changes. This study evaluated the impacts of river connectivity on water quality, and the diversity and community assembly of benthic macroinvertebrates in the Yangtze River Basin, the longest and largest watershed in China. The results indicated the following: (1) Dam-induced connectivity loss significantly affects benthic macroinvertebrate diversity and community composition. Reduced connectivity limits species dispersal, decreasing α-diversity while driving shifts in β -diversity along connectivity gradients, (2) Dam-induced connectivity changes influence benthic macroinvertebrate diversity primarily through water quality alterations. Further, reduced river connectivity modifies flow regimes, resulting in changes to key water quality parameters and degraded habitat conditions for benthic communities. Our findings provide crucial insights into the ecological consequences of river fragmentation and highlight the importance of maintaining connectivity for conserving aquatic biodiversity. • Dam construction drives spatial variation in river connectivity across the Yangtze River Basin. • Connectivity loss degrades water quality and reduces benthic biodiversity. • Water quality mediates the impact of connectivity loss on biodiversity. • Restoring connectivity and improving water quality are critical for aquatic biodiversity conservation.