Spatial-Seasonal Assessment of Surface Water Quality in Can Gio, Vietnam Using the Water Quality Index

This study evaluates the spatial and seasonal variation of surface water quality in the Can Gio estuary, a core area of the Can Gio Mangrove Biosphere Reserve in Southern Vietnam, using the VN-WQI water quality index. Fourteen monitoring sites were sampled during the dry and rainy seasons, and major physicochemical, nutritional, heavy metal, and microbiological indicators were analyzed according to national standards. The evaluation results showed that the VN-WQI value ranged from 68 to 83 (from moderate to good) in both the weighted VN-WQI and unweighted VN-WQI (the weighted VN-WQI provides a more sensitive indication of organic and nutrient pollution than the unweighted index). The main polluting parameters contributing to water quality degradation were organic and microbiological indicators, particularly BOD5, COD, ammonium, nitrite, phosphate, total coliforms, and Escherichia coli. The data used in this study were derived from secondary monitoring datasets . In particular, the sample collection points near aquaculture areas and human activities (CG5, CG8, CG9, CG10, CG11, and CG12) have a lower VN-WQI index than the rest of the points. The results of these studies contribute to helping the state management agency in charge of the environmental control pollution as well as monitoring surface water quality to protect the biosphere reserve as well as the mangrove ecosystem.