Abstract: To understand the spatial distribution pattern and key driving factors of benthic macroinvertebrates, surveys were conducted in the Anning River and its tributaries between June and July 2018. The spatial pattern of benthic macroinvertebrates along the longitudinal gradient of the river was analyzed. In total, 57 species of benthic macroinvertebrates belonging to 34 families of 5 phyla were identified, among which aquatic insects (44 species) were dominant taxa. Species richness in the mainstream of the Anning River was lower than that in its tributaries. The dominant species in the mainstream were Limnodrilus hoffmeisteri, Baetis sp., Aethalopsyche sp. and Physa acuta, while the dominant species in the tributaries were Cheumatopsychesp.,Drunellasp1, Heptagenia sp. and Stenopsyche sp. The macroinvertebrate density in the mainstream was nearly equal to that in its tributaries, but it decreased along the longitudinal gradient fromupstream to downstream. The results of canonical correspondences analysis (CCA) showed that the density of dominant macroinvertebrate species in the Anning River was closely related to water temperature, pH and substrate types.

Key words: Anning River, benthic macroinvertebrates, longitudinal gradient, spatial distribution pattern, environmental factor.