The long-term spatial and temporal variations of sediment loads and their causes of the Yellow River Basin

The erosion, deposition and transport processes of sediment alter the basin surface environment, and affect the function and structure of ecosystems. The sediment loads showed a significant decreased trend under the impacts of climate changes and human activities in the Yellow River Basin (YRB). Understanding the sediment transport patterns and causes is a prerequisite of sediment management and ecological restoration of the river basins. This study explored the sediment long-term fluctuation characteristics and the influences of various driving factors on the sediment variations based on the sediment loads data from the source region to the delta of the YRB. We found that the sediment fluxes showed a significant decreasing trend in the mainstream and tributaries of the YRB. The average sediment loads of the upper basin decreased to 42.88 +/- 26.14 Mt/yr in 2000-2019, which is less than 30% of the average value recorded before 1968. Compared with 1950-1968, the sediment loads in the middle and lower reaches decreased by approximately 88% and 89% from 2000 to 2019, respectively. In addition, the middle reaches of the Yellow River (YR) is in a persistent degradation state prior to 2000, the source-to-sink relationships of sediment downstream the Huayuankou station are changing frequently due to the operation of Sanmenxia and Xiaolangdi reservoirs. According to the sediment rating curves (SRCs), the sediment transport regimes have changed at time scale along the mainstream of the YR in recent three decades. Moreover, the human activities (reservoir constructions, water-soil conservation, etc.) are the dominant factors for explaining the progressively reduction trend of sediment loads, the contributions of human activities to sediment reduction was approximately 93% in recent two decades in the YRB. Precipitation and temperature are the predominant meteorological factors affecting sediment variations, and ENSO is the dominant teleconnection pattern for explaining the multiscale characteristics of sediment loads in the lower reaches of the YRB. The findings of this study could provide effective reference for the ecological restoration and sediment management of the YRB.