# Responses of Macroinvertebrate Communities to Heterogeneity Among Typical Reaches in the Upper Yangtze River

## TL;DR

This study explores how different river sections in the upper Yangtze River affect benthic macroinvertebrate communities through changes in water flow and sediment conditions.

## Contribution

The study identifies a 'dual-pathway' mechanism linking flow velocity to macroinvertebrate distribution via direct and indirect ecological effects.

## Key findings

- Macroinvertebrate communities differ significantly in richness and diversity across canyon, anabranching, and Reef–Tuo river reaches.
- Flow velocity directly influences rheophilic taxa and indirectly affects sediment-preferring taxa through sediment dynamics.
- Stable low-velocity zones in anabranching and Reef–Tuo reaches serve as refugia for benthic communities.

## Abstract

Benthic macroinvertebrates are important indicators of river ecosystem health, and their spatial distribution is highly sensitive to environmental heterogeneity. In large mountainous rivers characterized by complex geomorphology and strong hydrodynamics, habitat structural diversity may influence community structure through multi‐pathway mechanisms. This study focused on three representative reaches of the upper Yangtze River—the Canyon, Anabranching, and Reef–Tuo reaches. By integrating two‐dimensional hydrodynamic simulations, in situ measurements of water and sediment conditions, and benthic community surveys, we systematically analyzed the effects of environmental factors on community composition. Non‐metric multidimensional scaling (NMDS) and redundancy analysis (RDA) revealed significant differences in community richness, diversity, and functional group composition among reaches. Partial least squares path modeling (PLS‐PM) further demonstrated a “dual‐pathway” ecological mechanism: flow velocity not only directly promoted the abundance of rheophilic taxa but also indirectly influenced the distribution of sediment‐preferring taxa by altering sediment condition. Hydrodynamic simulation results further validated the spatial basis of this mechanism. Flow velocity gradients were strongly shaped by geomorphic features, and notably, stable low‐velocity zones persisted in the Anabranching and Reef–Tuo reaches. These areas served as important refugia for benthic communities, reinforcing the ecological applicability of the “dual‐pathway” mechanism in complex river segments.

This study examines how hydraulic and geomorphological heterogeneity shape benthic macroinvertebrate communities in the mountainous upper Yangtze River. Integrating field measurements with hydrodynamic modeling, it identifies distinct community patterns across canyon, anabranching, and Reef–Tuo reaches, driven by flow velocity, sediment dynamics, and nutrient retention. Findings underscore both direct and indirect pathways through which physical habitat structure influences biodiversity.