Source analysis of total nitrogen in a representative seaward river using the calibrated MIKE model

ABSTRACT In this study, the Jueju River, a representative seaward river in Nantong, Jiangsu Province, was analyzed for total nitrogen (TN) pollution sources. A calibrated MIKE model, using measured hydrological and water quality data, was developed to quantify the TN pollution at cross-sections, identify sensitive contributing areas, and prioritize pollution control strategies. The results revealed that TN concentrations in the Jueju River followed an overall ‘W-shaped’ trend annually, with a distinct ‘U-shaped’ pattern in 2022. Winter TN concentrations were consistently higher than those in other seasons. The seaward flux of TN was primarily sourced from upstream watershed areas, influenced by both the quantity of TN input from catchment units and transport distance. At the Huandong Gate section, catchment units 1, 2, and 3 were identified as the main contributors to TN pollution. Key pollution sources included centralized wastewater treatment plants, agricultural activities, and livestock farming, while unregulated rural domestic pollution also significantly impacted TN levels at the cross-section. These findings provide valuable insights for policymaking, emphasizing the need for strengthened management and control of TN pollution in seaward rivers, ultimately improving water quality in nearshore areas.