Quantifying Land-based and Aquaculture-Derived Pollutant Loads in Xuan Dai Bay, Vietnam: A Source-based Assessment for Sustainable Aquaculture

Coastal water quality is affected by multiple pollution sources, and their contributions to receiving waters depend on pollutant generation, transport pathways, and delivery processes. This study developed a source-based assessment of pollutant loads in the Xuan Dai Bay area, Vietnam, using 2025 activity data for aquaculture, domestic wastewater, crop cultivation, livestock farming, and stormwater runoff. Annual loads of biochemical oxygen demand (BOD), chemical oxygen demand (COD), total nitrogen (TN) and total phosphorus (TP) were estimated using source-specific emission factors and delivery coefficients. Total generated loads were estimated at 3,945.54 tonnes per year (t yr⁻¹) of BOD, 10,711.35 t yr⁻¹ of COD, 1,447.66 t yr⁻¹ of TN, and 318.95 t yr⁻¹ of TP. After the proposed delivery factors were applied, the estimated loads reaching the bay were 1,577.79, 3,955.95, 716.31 and 193.73 t yr⁻¹, respectively. Aquaculture was the dominant source of estimated delivered TN and TP, contributing 70.44% and 82.12%, respectively, while livestock farming was an important source of organic loads. The results demonstrate that source rankings can change when pollutant transport is considered alongside generation. Although the estimates provide an initial basis for prioritizing pollution-control measures, uncertainty in emission factors and delivery coefficients limits their precision. Local validation and hydrodynamic assessment are needed to refine source attribution and support future assessments of environmental carrying capacity.