The occurrence, dissemination and assembly processes of antibiotic resistance genes (ARGs) in urban water ecosystems are far from being understood. Here, we examined the diversity and abundance of ARGs in urban water ecosystems including landscape ponds, drinking water reservoirs, influents (IFs) and effluents (EFs) of wastewater treatment plants of a coastal city, China through high-throughput quantitative PCR. A total of 237 ARGs were identified, where multidrug, aminoglycoside and beta-lactamase resistance genes were the most abundant. Urban ponds had a comparatively high diversity and large numbers of shared ARGs with IFs and EFs. The average absolute abundance of ARGs (1.38 × 107 copies/mL) and mobile genetic elements (MGEs) (4.19 × 106 copies/mL) in ponds were only one order of magnitude lower than those of IFs, but higher than those of EFs and reservoirs. Stochastic processes dominated the ARG community assembly in IFs and ponds due to the random horizontal gene transfer caused by MGEs. These results imply that urban ponds are hotspots of ARGs. We further identified 25, 3, and 11 indicator ARGs for tracing the ARG contamination from IFs, EFs and ponds, respectively. Our study represents the first to highlight the role of urban ponds in the dissemination of ARGs.
