Effects of local land-use policies and anthropogenic activities on water quality in the upstream Sesan River Basin, Vietnam

Study region: This study focuses on the upstream Sesan River Basin in the Central Highlands of Vietnam. Study focus: Local land-use policies and human activities can significantly affect hydrology and increase the magnitude of erosion and nutrients in downstream areas. The effects in terrestrial regions on water quality of the target area were evaluated during the 2000–2018 period using the SWAT (Soil and Water Assessment Tool) with updated land-use conditions following the local policy decisions and agricultural practices in different periods. New hydrological insights for the regions: This study indicates that the implementation of the local land-use policies, along with extensive anthropogenic activities, has had significant effects on the downstream aquatic environment as compared with the period before the implementation of the land-use policies. Higher annual sediment, total nitrogen (TN), and total phosphorus (TP) loadings were found upstream from the Poko Watershed, where range land predominated, and in southern and southwestern Dakbla Watershed, where arable land and permanent cropland predominated. Arable land had the highest proportion of sediment and nutrient loadings into the reach, especially in the 2005–2009 period (conducting afforestation, agricultural expansion, and urbanization) and in the 2010–2014 period (applying crop conversion policy involving a shift from mixed forests to rubber forests). Understanding the watershed characteristics along with the combination of spatial land use, local land-use policies, and agricultural practices will support the implementation of regional land use and water resources management strategies more comprehensively.