Sensitivity and complexity of the Yangtze River’s sediment dynamics

The Yangtze River, the world’s longest river flowing entirely within one country, has experienced a 60%–99% decline in sediment load since the late 1970s. Climate change and human activities are widely acknowledged to be drivers of this decline in sediment load. However, which tributaries are most sensitive to the driving factors and how to understand the complexity of sediment dynamics remain poorly understood. Based on estimates of the relative impact of driver-related factors on sediment load reduction from eight regression models, the current study developed the sediment load sensitivity index (SSI), which assesses the sensitivity of the sediment load across the Yangtze River over the past 30 years. The complexity of the sediment dynamics caused by dam construction in the Yangtze River basin was also investigated. The current results show that the annual sediment load decreased by 85% between 1988 and 2018, with reductions most pronounced after major dam construction (e.g., the Three Gorges Dam). Human activities, particularly reservoir construction and the intensity of ecological engineering, accounted for 28.62%–97.22% of the observed decline, while climate variability explained approximately 5.62% of the reduction in sediment load. The current results also show that the sensitivity of sediment load increased significantly in Dongting Lake (DTL) and the middle mainstream of the Yangtze River (MMYR). Nevertheless, the complexity of sediment load series immediately downstream of mega dams has simplified, resulting in an enhanced impact of sediment inputs from downstream tributaries on sediment load time series in the downstream reaches of the Yangtze River. By integrating the sediment load sensitivity index with entropy analysis, the current study demonstrates how dams alter sediment regimes in the Yangtze River and provides a quantitative framework for assessing human impacts on sediment dynamics in other large river systems.