LAUSR

Abstract Hydrology, water quality and biological pressures can influence structure and function of stream and river ecosystems. However, in practice, identifying the shared effects of factors on communities instead of isolated effects is a challenging task. Benthic macroinvertebrate community can reflect bottom conditions of streams and is less disturbed by river flows and human activities. Therefore, it is suitable to analyze the shared effects of hydromorphological and physico-chemical parameters. Benthic macroinvertebrate based Multi-Metric Index (B-MMI) was built to evaluate overall status and the effects on three biological traits were calculated, including diversity and abundance (D/A), sensitivity and tolerance to pollutions (S/T) and functional feeding groups (FFGs). Redundancy Analysis (RDA) was performed to evaluate the percentage of explained variance of 18 hydromorphological and physico-chemical parameters on invertebrate community. Our analysis showed that the two facets of the environment have high shared explained variances (28.2%–44.5%). Relatively, physico-chemical parameters have higher contributions on B-MMI than hydromorphological parameters. Seasonal analysis showed the shared effects are higher in dry season than wet season. S/T characteristics are most sensitive to seasonal shared effects, which in wet season can best show the isolated effects of the two facets of the environment. At the catchment-scale, middle stretches had higher B-MMI values since stony substrate and less disturbed land use types. And reach studies showed channel morphology contributed more in stony reaches while bottom conditions contributed more in silty and sandy reaches. Our findings consequently give rise to concern to the integrity index of benthic invertebrate community, which allows to show large shared effects of hydromorphological and physico-chemical factors. Besides catchment scale, reach scale also help add the perspective of substrate diversity and heterogeneity in habitat restoration and conservation.