Sediment archives urban-rural divergence in antibiotic resistance gene contamination within a freshwater lake

Freshwater lakes are critical ecosystems for sustaining biodiversity and human well-being, yet increasing anthropogenic activities threaten their ecological safety through pollution such as antibiotic resistance genes (ARGs). Previous studies on ARG pollution in aquatic systems have largely overlooked the distinct impacts of urban versus rural landscapes, limiting targeted mitigation strategies. Here, we investigate the urban-rural heterogeneity of ARG pollution in Chaohu lake, a major urban-rural junction lake in China, using shotgun metagenomic sequencing and Bayesian source-tracking approaches. Our findings reveal significant spatiotemporal variations in ARG abundance, with urban-adjacent regions (western lake) exhibiting 1.22- to 1.25-fold higher ARG levels than rural-adjacent areas (eastern lake) in water and sediments, respectively. Notably, a significant distance-decay relationship of ARG profiles was observed in sediments, highlighting that sediments act as a stable environmental archive recording the urban-rural divergence. Agricultural activities were identified as the dominant source lake-wide, contributing over 60 % of the total ARG load, thereby surpassing urban sewage inputs. Meanwhile, the abundance of mobile genetic elements (MGEs), particularly transposases, was significantly higher in the western lake, indicating a greater potential for horizontal gene transfer. The presence of multidrug-resistant, ARG-carrying pathogens, such as Stenotrophomonas maltophilia and Pseudomonas putida, was significantly enriched in these areas, correlating with higher ecological and health risks as quantified by the antibiotic resistome risk index. These results underscore the urgent need for landscape-specific management strategies to curb ARG dissemination, prioritizing agricultural non-point source control in urban-rural transitional zones to safeguard freshwater ecosystems and human health.