Modifying hydrodynamics offers a pathway to enhance ecosystem function of the Qinghai-Tibet Plateau rivers

The effects of climate change on ecosystems were particularly pronounced in alpine regions. Most studies on alpine river ecosystems were conducted in the temperate and Arctic regions, primarily focusing on the effects of meltwater runoff variation, with limited attention on the subtropical regions, e.g., the Qinghai-Tibetan Plateau (QTP). Rivers on the QTP are experiencing significant environmental shifts due to both hydrological and hydrodynamic changes, which are altering the ecosystem characteristics of these highland rivers. However, understanding gaps still remain in the biodiversity, community composition and structure stability of these ecosystems, as well as their key ecological driving force. Using macroinvertebrates as indicator species, we characterized biodiversity, community structures and food web stability within river networks of the middle-lower Yarlung Tsangpo Basin, a typical alpine river basin along QTP’s margin. The mainstem (Yarlung) and two tributaries, i.e., Nyang River and Parlung Tsangpo River, exhibited increasing gradients of hydrodynamic intensity and meltwater runoff. We found that taxonomic structures of macroinvertebrates were different across spatial and temporal scales, with hydrodynamic intensity, rather than water temperature reported in the temperate and arctic regions, as the primary factor driving taxonomic composition. Biodiversity showed consistent unimodal response patterns to hydrodynamic intensity across scales. Specifically, γ diversity, representing the regional biodiversity, was highest in Nyang River, which was characterized by moderate hydrodynamic intensity among rivers. Within each river basin, α diversity also peaked at the moderate hydrodynamic intensity on the basin’s range. Regarding food web structure, we observed similar functional feeding groups’ composition but variable complexity and stability across rivers, and found that the effect of hydrodynamic intensity on the structure stability surpassed that of basal food sources. As hydrodynamic intensity increased, structural complexity also increased, while stability followed a unimodal response, with the food web being most stable at moderate hydrodynamic intensity. These findings highlight hydrodynamic conditions as the most critical ecological driver in subtropical alpine rivers. It is suggested that moderating hydrodynamic intensity may be an effective strategy to maintain high biodiversity, functional complexity, and food web stability, offering a promising approach for ecological optimization in high-altitude alpine rivers affected by ongoing climate change and anthropogenic activities.