Characteristics of benthic macroinvertebrate community structure and their driving factors in middle and lower reaches of Hanjiang River

To investigate the structural characteristics and key drivers of benthic macroinvertebrate communities under prolonged low-flow conditions, a comprehensive survey was conducted in August 2025.Sampling was carried out at 25 sites located in the main stream and tributary confluences of the middle and lower reaches of the Hanjiang River, where both benthic macroinvertebrates and environmental parameters were collected.The community structure was assessed using the Shannon-Wiener diversity index, Margalef richness index and Pielou evenness index.Differences in community composition between the mainstem and tributary confluences were examined using principal coordinate analysis (PCoA) and permutational multivariate analysis of variance (PERMANOVA).The effects of environmental factors were analyzed via the Mantel test, canonical correspondence analysis (CCA), and hierarchical partitioning.The results showed that a total of 50 benthic macroinvertebrate species were identified, with an average density of 97.2 ind./m² and an average biomass of 17.19 g/m².The dominant species were Macrobrachium sp., Caridina sp., and Bellamya sp.A significant difference in community structure was observed between the mainstem and tributary confluences (p < 0.05).Both density and biomass were significantly higher in the confluences than in the mainstem (p < 0.05), while no significant differences were found in the diversity indices.Water temperature was a key environmental factor driving changes in community structure.The synergistic effects between water temperature and the proportion of sandy substrate, as well as between water temperature and orthophosphate, exert significant impacts on the benthic macroinvertebrate community.The research results can provide a scientific basis for ecological early warning and adaptive management in the Hanjiang River Basin under the background of drought.