Sources, pathways, and mitigatoon strategies for excess nitrogen loading in the Red River Delta, northern Vietnam

The Red River Delta (RRD), Vietnam, like many large river systems worldwide, faces significant pollution due to human activities. Tracing pollution sources, quantifying waste flows, and assessing their distribution across regions remain major challenges. Material Flow Analysis (MFA) is an effective tool to address these issues, providing valuable insights for policymakers and supporting practical mitigation strategies. We employ MFA to assess the potential nitrogen pollution in the RRD estuary, providing an overview of nitrogen sources and pathways and quantifying their relative significance at the provincial level. Our analysis reveals that rice fields and fish ponds are the primary nitrogen sources, accounting for 53–74% and 21–32% of total nitrogen inputs to surface water, respectively. Based on sensitivity analysis, we propose mitigation measures, including a 10% reduction in chemical fertilizer use, improved fishpond drainage at harvest, increasing domestic wastewater collection to 50–70%, and enhancing treatment efficiency for livestock manure to 50%. These measures could reduce total nitrogen loads to the RRD by 13–58%. The accuracy of our simulations is supported by secondary data and field studies. A comparison of the simulated and estimated nitrogen loads suggests substantial nitrogen retention within the delta, estimated at approximately 63%.