Spatiotemporal variations and driving factors of streamflow and sediment load across different geomorphic conditions in a sediment-laden river of the Loess Plateau

The Beiluo River Basin, situated within the Loess Plateau, is a major source of coarse sediment. Variations in streamflow and sediment transport have a major effect on sediment regulation, water resource management, and the maintenance of regional ecological stability. The combined impacts of climate change and human activities have recently caused a notable reduction in both streamflow and sediment transport. Previous studies have emphasized basin-scale alterations, while the hydrological and sediment responses and their pathway relationships under distinct geomorphic units remain insufficiently understood. Different geomorphic units differ substantially in topography, soil properties, and vegetation conditions, resulting in distinct hydrological and sediment responses and consequently influence ecological restoration and soil conservation effectiveness. Therefore, this study selected three representative geomorphic units, including the hilly gully area (HG), hilly gully–tableland gully area (HTG), and hilly gully–tableland gully–terrace plain area (HTP), to investigate the differences in water–sediment variations and their driving factors. Hydrological records from Liujiahe, Jiaokouhe, and Zhuangtou stations between 1962 and 2022 showed significant decreases in streamflow along with sediment load in HG, HTG, and HTP units. Moreover, the influencing factors of streamflow and sediment load variations differed among the three geomorphic units. The dynamics of water and sediment were notably affected by precipitation in the HTG and HTP units. Vegetation cover in the HG unit significantly influenced streamflow but showed no significant direct effect on sediment load, whereas in the HTG and HTP units, it showed significant direct influences on both variables. Land use primarily affected water and sediment indirectly by influencing vegetation cover and streamflow across the three geomorphic units. Moreover, during the research period, the primary contributor to the reductions in streamflow and sediment load were anthropogenic activities. This study showed that different geomorphic units have distinct driving factors and pathway relationships for hydrological and sediment processes. The findings can enhance our understanding of the differences in water–sediment responses under different geomorphic conditions and provide scientific support for water resource management and ecological restoration.