Effects of dam regulation on macroinvertebrate communities in the Yarlung Zangbo River: A functional trait perspective.

Understanding the disturbance of dam regulation on the structure and function of benthic macroinvertebrates, as well as its underlying pathways, is crucial for comprehending the impact of dams on river ecosystems. As an alpine river, the Yarlung Zangbo River (YZR) is facing significant ecological challenges from cascade hydropower development owing to its inherently fragile ecosystem. This study aimed to examine changes in the taxonomic and functional diversity of macroinvertebrates in the free-flowing reach upstream of the cascade dams and two regulated reaches in the midstream of the YZR. Through RLQ and fourth-corner analysis, key environmental variables influencing the functional traits of macroinvertebrates were identified and integrated into a partial least squares structural equation model (PLS-SEM) to elucidate the impact pathways through which dam regulation affects macroinvertebrates. The results indicated that while there was no significant difference in taxonomic α-diversity between the free-flowing and regulated reaches, functional α-diversity exhibited higher sensitivity to these changes and showed significant differences. Total functional β-diversity of the regulated reach closer to the dam was higher than that of both the natural-flowing reach and the regulated reach farther from the dam, while total taxonomic β-diversity exhibits the opposite trend. In addition, the impact of flow fluctuations on the functional α-diversity of macroinvertebrates was primarily realized through indirect effects, specifically by altering partial water quality parameters (e.g., dissolved total nitrogen (DTN) and electric conductivity (EC)) and taxonomic α-diversity, which in turn influenced functional α-diversity. This research enhances the understanding of the mechanisms through which hydropower stations influence the taxonomic and functional diversity of macroinvertebrates in alpine rivers, while providing critical insights for further hydropower development and management in the YZR.