Anthropogenic activities strongly influence river habitat conditions and surrounding landscape patterns. A major challenge is to understand how these changes impact microbial community composition and structure. Here, a comprehensive analysis combining physicochemical characteristics in sediment with sequencing targeting the V4 region of the 16S rRNA gene was conducted to test the hypothesis that diverse habitat conditions induce dissimilarity of microbial community composition and structure in a regulated urban river. The results suggested that observed species richness and Shannon–Wiener diversity had a decreasing variation along the land use intensified gradient, while beta diversity also revealed significant separation of microbial community structure between headwaters and urban reaches. Total nitrogen (TN), total phosphorus (TP), oxidation–reduction potential (ORP) and total organic carbon (TOC) in sediment were the dominant factors in structuring bacterial and archaeal community assemblages. Further analysis in dominant fecal-associated bacteria indicated that elevated nutrient concentrations may significantly (p < 0.05) increase the relative abundance of Clostridium and Acinetobacter in sediment. The findings highlight the pivotal roles of alpha diversity and fecal-associated bacteria in understanding the dynamics of microbial communities in a regulated urban river ecosystem.

Long-term wastewater and reclaimed water irrigation systems constitute the major processes in local water circulation, which concomitantly introduce plenty of undesirable substances that can threaten water quality, ecosystem functions and human health. At the Southeast Reclaimed Water Irrigation Region (SRWIR) of Beijing, wastewater irrigation was adopted from 1969 to 2002, and second-treated effluents (reclaimed water) has been used thereafter. Polycyclic aromatic hydrocarbons (PAHs) were the most ubiquitously detected contaminant in wastewater and reclaimed water and are reported to be carcinogenic. Hence, we measured the concentrations of dissolved sixteen United States Environmental Protection Agency (USEPA) priority PAHs in surface water and groundwater at the SRWIR to characterize their spatial and temporal variations, and to clarify the role of reclaimed water to natural water. The concentration of 16 individual PAHs in reclaimed water, rivers and groundwater varied from 339.4 to 636.2 ng/L, 359.1 to 3,435.0 ng/L and 216.5 to 488,205.2 ng/L, respectively. The lower aromatic rings of PAHs prevailed in aquatic environments rather than the higher ones. Thereinto, naphthalene was the predominant isomer within the highest concentration reached to 486,600 µg/L. The groundwater samples had higher PAHs concentrations at Tongzhou district which attributed to the higher vulnerability of aquifer. Additionally, strong correlations between PAHs and total nitrogen, nitrate, dissolved oxygen and electrical conductivity suggested those potential factors affecting the photo degradation and/or biodegradation of PAHs. The relationship identified between PAHs concentrations and physical and chemical indices would help us to enhance the understanding migration and transformation of PAHs spatially and temporally, enable us to assess the potential risks of the environmental pollutants to aquatic organisms and human water supplies.