Seasonal water level fluctuations regulate the source, distribution, and risk of antibiotics in the largest...

Seasonal water fluctuations in floodplain-lake occur globally, yet their effect on spatiotemporal distribution of antibiotics in the lakes remains poorly understood. This study explores how seasonal water level fluctuations and resulting shifts in land use and environmental factors influence antibiotic sources, distribution, and ecological risks in the largest floodplain-lake (Poyang Lake) in China. The lake was divided into three areas based on water level dynamics: high-water level (HWL) area, fluctuating water level (FWL) area, and dish-shaped lake (DSL) area. In the FWL and DSL areas, seasonal water level fluctuations exerted significant regulatory effects on antibiotic distribution in both water and sediments, while was negligible in the HWL area. Additionally, water level had stronger regulatory effects on the antibiotic distributions in water compared to sediments. The spatial heterogeneity of antibiotic in sediment was weaker compared to water. Under the regulation of water level, the concentrations and ecological risks of antibiotic in water were significantly higher in the FWL and HWL areas than that in the DSL area in dry season (p ​​< 0.05). Antibiotic sources also varied spatially in the water, with animal excreta contributing less in the HWL area (mean 81.2 % and 62.1 %, respectively) than in the DSL (mean 94.2 % and 78.2 %, respectively) and FWL areas (mean 90.0 % and 77.1 %, respectively) during the wet and dry seasons, whereas medical wastewater contributed more in the HWL area (mean 18.8 % and 37.9 %, respectively) than other areas. These findings underscore the role of water level in shaping antibiotic in floodplain-lakes, offering critical insights to address this pressing environmental challenge.