Combined effect of matrix dams and paddy field drainage ditches on nitrogen and phosphorus removal

Context Nitrogen and phosphorus contaminants from paddy field drainage flow into the receiving bodies of water, posing a risk of eutrophication. To mitigate this pollution risk, several technologies, including constructed wetlands, ecological revetments and ecological floating beds, have been introduced in drainage ditches. However, the capacity of these technologies to intercept pollutants need to reconstruct the existing ditch structure. Aims This study aimed to optimise the interception and purification capabilities of drainage ditches through matrix dams. Methods A hydrodynamic and water-quality numerical model was established using the Mike 21 software, and the comprehensive ability of purifying pollutants by the interception of matrix dams and drainage ditches was evaluated. Key results We found that the overall average flow rate was reduced by 84% in the paddy field drainage ditch after introducing matrix dams, and pollutant concentrations decreased progressively from upstream to downstream. Total nitrogen concentrations were reduced by exceeding 60%, with a maximum reduction in total dissolved nitrogen concentrations of 84.3%. Conclusions Results indicated that the the combined deployment of drainage ditches and matrix dams is effective in removing nitrogen and phosphorus pollutants from paddy field drainage. Implications This study can provide a theoretical foundation for the practical implementation of matrix dams.