Objective  Archaea plays an important role in the biogeochemical cycle of elements in various environments. The aim of this study was to explore the relationship between the archaeal community structures and the environmental factors and to explore how the characteristics of archaeal community structures indicating sediment environments in urban river sediments.

  Method  16S rRNA gene-based Illumina MiSeq sequencing was used to investigate archaeal community structures in the different reaches in the Shiwuli River, and redundancy analysis (RDA) and correlation analysis between archaeal community indices and environmental factors were conducted to explore the driving factors affecting archaeal community structures and archaeal diversities.

  Result  The first dominant phylum (relative abundance 51.93% ~ 96.02%) was Euryarchaeota, and the second dominant phyla were Thaumarchaeota (relative abundance 3.22% ~ 42.47%) and Bathyarchaeota (relative abundance 0.17% ~ 22.49%) in all river surface sediments. The relative abundance of Euryarchaeota in the upstream and midstream was significantly higher than that in the downstream, while the relative abundance of Thaumarchaeota and Bathyarchaeota in the downstream was higher than that in the midstream and upstream, especially for the relative abundance of Bathyarchaeota (except for sampling site C7 separated from the river by lower dam). Except for Nitrososphaeria at class level at sampling site C3 at the confluence of Weixi River and Shiwuli River, the first dominant archaea were Mehtanomicrobia and their relative abundance was higher in the downstream than that in the midstream and upstream. Except for Thermococci at sampling site C7, the second dominant archaea in the midstream and upstream were Methanobacteria, while the dominate archaea were different among the three sampling sites in the downstream. At the genus level, the relative abundances of Methanocella and Rice_Cluster_I were significantly higher in the downstream than those in the other reaches, while those of Methanosaeta and Methanobacterium in the midstream and upstream were significantly higher than those in the downstream. There was no significant difference in the total abundance of archaea among different river reaches, but the archaeal diversities in the downstream were higher than those in the upstream and midstream. Soil pH, total organic carbon, available potassium, total phosphate, C/N and C/P were the environmental factors affecting the distribution of sediment archaeal community in the river, and pH, total phosphate and C/P were the important environmental factors affecting the sediment archaeal diversities.

  Conclusion  In general, the archaeal community structures and diversities in the different river reaches of Shiwuli River were significantly distinct, reflecting the difference in the surface sediment environment which owned high nutrient and pollution in the midstream/upstream, and low nutrient and pollution in the downstream.