Functional trait responses of macroinvertebrate communities to low-head dams in headwater streams

Headwater streams are vital components of river basins, supporting water retention, hydrological regulation, purification, biodiversity, and ecological connectivity, thereby sustaining watershed integrity. Although headwater streams perform essential ecological functions, the prevalence of low-head dams is a common feature in mountainous catchments, while their effects on benthic macroinvertebrate community structure remain poorly understood. In this study, we examined how low-head dams influence macroinvertebrate communities in subtropical headwater streams by contrasting undisturbed upstream reference reaches with paired impoundment sites upstream of dams and scouring sites downstream of dams. Physical habitat conditions differed markedly among site types: impoundment reaches exhibited slower flow, wider channels, and finer sediments, whereas scouring reaches were characterized by high current velocities, exposed substrates, and increased presence of artificial materials. Consistent with these habitat changes, species richness declined in impoundment and scouring sites, and community composition differed significantly among site types. β-diversity partitioning revealed that species replacement, rather than richness differences, was the main driver of community differentiation. Functional trait analyses demonstrated pronounced trait-mediated responses: impoundment sites were dominated by long-lived, large-bodied, burrowing taxa with low drift propensity, whereas scouring sites supported small-bodied, highly mobile taxa with strong swimming ability, clinger or swimmer habits, and filter-feeding strategies. Multivariate analyses confirmed strong correlations between environmental gradients and multiple functional traits, highlighting the deterministic role of environmental filtering under altered hydrological conditions. These findings provide trait-based insights into the ecological consequences of low-head dams in headwater streams and underscore the importance of incorporating functional trait perspectives into sustainable management practices aimed at conserving biodiversity and maintaining ecosystem functioning in regulated headwater systems. • Low-head dams markedly alter macroinvertebrate community structure in headwater streams. • β-diversity differentiation was mainly driven by species replacement, not richness loss. • Impoundments favored long-lived burrowers, while scouring sites supported mobile clingers. • Functional traits showed strong linkages with hydrological and sedimentary gradients. • Findings provide trait-based insights for biodiversity conservation and river management.