Assessment of the effects of land use change on water quality and quantity in the Nam Ngum River Basin using the Better Assessment Science Integrating point and Non-point Sources 4.0 model

Abstract

The Better Assessment Science Integrating Point and Nonpoint Sources 4.0 model (BASINS 4.0) was used to simulate the relationships between land use practices and water quality and quantity of the Nam Ngum River Basins in Lao PDR. The results of the simulation revealed that BASINS 4.0 performed consistently well in simulating water quantity and quality of Nam Ngum River Basin after calibration, with percent mean error for annual flow volume and total sediment loads being approximately -3.70 and 2.90%, respectively. The simulation of baseline conditions revealed that urban land segment (0.0215% of total land area) yields the highest total sediment load, contributing 40.7% of annual sediment loads. The agricultural land segment (39.98% of total land area) contributed approximately 93.16 and 72.64% of annual total nitrogen and phosphorus loads, respectively. Six land use scenarios were developed to simulate the effects of potential land use changes in the Nam Ngum River Basin. The simulation of these scenarios indicated that urbanization has the most impact on runoff, increasing as percent coverage of urban areas increased. The study also found that sediment loads reduced by 21.03% when the forest coverage area increased from 38 to 70%. Total nitrogen and phosphorus loads increased by 16.44 and 8.73%, respectively, when agriculture land coverage area rose from 50.32 to 60%. The study also showed that total sediment and nitrogen and phosphorus loads were reduced significantly when Best Management Practices were implemented concurrently with the expansion of forest area, with total sediment, nitrogen and phosphorus loads reduced by 46.76, 67.90, and 43.45%, respectively. Overall, the results of the study demonstrated that BASINS 4.0 can be used as an effective planning tool for water resource managers who are managing the Nam Ngum River Basin.