Antibiotic resistance profiles and associated factors in aquatic ecosystems with contrasting hydrodynamic settings

Antibiotic resistance genes (ARGs) are ubiquitous in aquatic ecosystems, but the ecological risk patterns and associated factors remain unclear across aquatic environments with contrasting hydrodynamic conditions. Using an integrated analytical framework, we explored interactions among antibiotics, microbial communities, mobile genetic elements (MGEs), and ARGs in a dynamic river and a slow-flow wetland. Antibiotics were widely detected in both systems, with generally higher total concentrations in the dynamic river (50.0-148.4 ng/L) than in the slow-flow wetland (2.5-101.7 ng/L). Total abundance of ARGs was also higher and more homogeneous in the dynamic river (49529.4-58542.5 RPKM) compared to the slow-flow wetland (24091.8-53003.0 RPKM), which exhibited greater spatial heterogeneity. Structural equation modeling (SEM) revealed different ARG-associated factor patterns in the two aquatic ecosystems with contrasting hydrodynamic settings. Bacterial communities and MGEs showed stronger associations with ARG variation in the Qiantang River, with standardized total effects (STEs) of 0.953 and 0.442, respectively, whereas antibiotics and MGEs showed stronger associations with ARG variation in the Xixi Wetland, with STEs of 0.816 and 0.747, respectively. Sulfamonomethoxine (SMM) was identified as the antibiotic most strongly associated with ARG variation in the wetland based on random forest analysis (importance score = 46.90%). This study indicates that the Qiantang River and Xixi Wetland exhibited distinct antibiotic resistance profiles and ARG-associated factor patterns, characterized by a host community-associated mode in the river and an antibiotic-associated mode in the wetland, with MGEs associated with ARG variation in both ecosystems.