Seasonal dynamics and key drivers of pharmaceutical pollution in a peri-urban watershed

Peri-urban ecosystems are strongly influenced by their natural environmental conditions and surrounding landscape. However, landscape patterns and landscape-related variables driving pharmaceutical pollution in peri-urban watersheds with rapid urbanization remain poorly understood. Herein, we investigated the occurrence and spatiotemporal distribution of 28 pharmaceuticals and their potential influencing factors in a peri-urban watershed (Zhangxi River Watershed) in Zhejiang province, Eastern China. Paraxanthine (detection frequency 97 %, mean concentration 223.07 ng/L) and anhydro-erythromycin (95 %, 4.01 ng/L) were the most prevalent compounds. Total pharmaceutical concentrations (sum of all target compounds) were significantly higher in the wet season (summer and autumn) than in the dry season (spring and winter; P < 0.05). Information theoretic-based analysis revealed that landscape pattern and dissolve organic matter were the main drivers of watershed-scale pharmaceutical pollution rather than water quality parameters and topographic characteristics. Correlation analysis showed that total pharmaceutical concentrations were more highly correlated with landscape pattern during the dry season than the wet season. The importance analysis and indicator interaction analysis revealed that interspersion and juxtaposition index (IJI), mean patch size (AREA-MN), patch density (PD), terrestrial humic-like substances C2, dissolved organic carbon (DOC) and fluorescent dissolved organic matter (FDOM) played a vital role in the occurrence and distribution of pharmaceutical in the watershed. Maintaining natural landscape is conducive to reduce antibiotic concentration in Zhangxi River. These results suggest that landscape patterns and dissolved organic matter strongly influence pharmaceutical pollution in the peri-urban ecosystem at a watershed scale.