The increase in wastewater-sourced resistome elevated the prevalence and risk of riverine antibiotic resistance in wet season

Frequent rainfall events can trigger sewer overflows and surface runoff, facilitating the spread of antimicrobial resistance (AMR) to downstream aquatic environments. However, the dynamic hydrologic conditions during rainfalls complicate the behavior of antibiotic resistance genes (ARGs), making it challenging to trace their sources and assess associated risks. Here, we integrated global resistome data to investigate the distribution, sources, and AMR risks of ARGs in the Xiangjiang River during the wet season, in comparison to the dry season. The number of detected ARGs increased by 11% in water and 9% in sediment during the wet season. Despite dilution by river discharge, both absolute and relative abundances of total ARGs were significantly elevated during the wet season, indicating substantial external ARG inputs. Source tracking revealed that soil was the dominant contributor in both seasons (average 61.7%), while the proportion of wastewater-derived ARGs rose significantly in the wet season (average 30.6%) and positively correlated with ARG abundance, suggesting wastewater as a primary driver of ARG influx. Additionally, the increased detection of Risk Rank I and emerging ARGs in river water highlights heightened AMR risks during the wet season. In contrast, sediment ARG profiles were relatively stable across seasons, with fewer ARGs traced back to river water during the wet season (average 51.0%) compared to the dry season (65.5%). The low abundance and rarity of high-risk and emerging ARGs suggest minimal AMR risks in sediment. Overall, our findings underscore the critical role of rainfall-driven wastewater input in shaping riverine AMR dynamics.