Assessing the effect of human activity on sediment load in the Second Songhua River Basin, Northeast China, based on the SWAT model

Human activity is a significant factor contributing to sediment load changes. Many studies have assessed the effect of human activity on sediment load using mathematical statistical methods, such as linear regression, without considering the physical processes of sediment transport. This study aims to use a distributed hydrological model to reconstruct the sediment load under natural conditions and assess the effect of human activity on sediment load in the Second Songhua River Basin (SSRB), Northeast China. The double cumulative curve method is applied to identify the point where the relationship between precipitation and runoff with sediment load changes abruptly. In addition, it employs the Soil and Water Assessment Tool (SWAT) to simulate sediment load under natural conditions to quantify the impact of human activities on sediment load. The results indicated that precipitation and runoff exhibit insignificant changes (P > 0.05), while the sediment load shows a significant decrease (P < 0.001) in the SSRB. Ens and R² are greater than 0.4, and Re is less than 10 % on annual and monthly scales. These outcomes demonstrated that the SWAT model can effectively simulate runoff and sediment load in the SSRB. From 1978–2014, human activities led to a decrease of 2.11 × 10⁵ t in sediment load, accounting for 57.02 % of the total sediment load. The decrease in sediment load is primarily caused by water conservancy projects, which reduce sediment load in the basin by trapping upstream sediment and regulating flood flows. These results can provide references for soil and water conservation and disaster warning in the basin.