Understanding watershed sources of pollution in Vinh Long Province, Vietnamese Mekong Delta

We explore point source (PS) and non-point source (NPS) pollution impacts on surface water quality in Vinh Long Province, Vietnam. We used data from 60 surface water quality monitoring stations across dry, transitional, and wet seasons from 2017 to 2021, in addition to sampling data collected from 12 wastewater outlets from June to October 2021 to determine the sources of pollution loads. Surface water quality was assessed using both the water quality index (WQI) and the Vietnamese standards QCVN 08:2015, whilst cluster analysis (CA) and principal components analysis (PCA) were used to evaluate spatial variation and key influencing factors. We observed seasonal variation in surface water quality, with a decline in quality during the rainy season. Moreover, the water quality parameters such as chemical oxygen demand (COD), biochemical oxygen demand (BOD5), total nitrogen (TN), and total phosphorus (TP) frequently exceeded the QCVN 08:2015 standard. Across, the different monitoring fixed points and seasons, COD levels were found to range from 8.94 to 15.14 mg/L, while TN levels varied between 0.24 and 0.53 mg/L. The cluster analysis categorized the monitoring fixed points into three groups, based on their water quality parameters, while PCA identified four principal components that explain 69% of the variance, distinguishing between pollution sources and seasonal factors. Our findings emphasize that poor water quality in many areas is affected by non-point source pollution, underscoring the need for watershed and land management. The results and applied methodologies provide insights for watershed management, policy development, and adaptation, applicable to regions facing similar environmental challenges. Article Highlights Pinpointing and quantifying sector-specific sources of pollution is essential to effective water resource management. Methods exist by which to use water quality data to begin to identify primary sources of pollution in complex watersheds. Water quality declined during the rainy seasons of 2017 to 2021, emphasizing non-point sources (NPS) as as leading causes of the decline.