Dynamic change of watershed sediment sources during implementation of the “grain for green” project in the coarse sandy areas of the Chinese Loess Plateau

A quantitative assessment of sediment sources is crucial for understanding soil erosion trends and enhancing soil erosion prevention and control measures. The environmental elements, such as vegetation, land use, and rainfall, etc., of the Chinese Loess Plateau (CLP) changed significantly after the implementation of “Grain for Green” (GFG) project. However, the response of sediment sources to the environmental changes in different periods remains unclear. In this study, sediment yields and sources were investigated by using the composite fingerprinting method. Forty flood couplets and their sediment yields corresponding to the 20-year period after the GFG project were established in Shagouba watershed, Shaanxi Province, China. Results showed that the thicker flood couplets, the higher percentage of silt and clay particles. Following the GFG project, the cumulative sediment yields during the first period (2000–2010) was 91,760 t, and in the second period (2011–2019) was 77,940 t. The sediment contributions changed from the first period that gully (48.73%) > shrub sandy land (28.82%) > sloping farmland (12.06%) > forestland and grassland (8.58%) > road (1.81%), to the second period that gully (47.33%) > shrub sandy land (26.40%) > forestland and grassland (10.27%) > road (9.02%) > sloping farmland (6.98%). The gully always contributes the most sediment, thus implementing measures such as safeguarding gully heads and constructing bio-valley mills in channels were recommended to mitigate gully erosion. This study provides a scientific basis for evaluating the effects of the GFG project on the CLP , and theoretical support for the scientific management of small watersheds.