Satellite-derived turbidity dynamics reveal sediment regulation by the Three Gorges Dam and large river-connected lakes in the Yangtze River

Abstract

Study Region The Yangtze River is a large regulated river system with pronounced variations in hydrology, sediment transport, and river–lake interactions. This study focuses on the mainstem from Yibin to Shanghai, particularly reaches influenced by the Three Gorges Dam (TGD), Dongting Lake, and Poyang Lake. Study Focus An integrated satellite-driven framework was developed to reconstruct turbidity dynamics during 2016–2024. Landsat-8/9 imagery was combined with ensemble machine learning, causal inference, and GeoDetector analysis to characterize turbidity variability and identify environmental controls. The Voting Regressor achieved the best performance (R² = 0.934, RMSE = 5.221 NTU, MAE = 3.874 NTU, MAPE = 18.618%). New Hydrological Insights for the Region Basin-wide turbidity declined by 32.2% during 2016–2024, reaching a minimum in 2022 followed by a slight rebound in 2023–2024. Turbidity was generally higher during the low-water period than during the high-water period. Spatially, turbidity generally increased downstream but exhibited pronounced heterogeneity. A marked reduction occurred downstream of the TGD, whereas turbidity increased farther downstream in reaches influenced by Dongting Lake. Near the Yangtze–Poyang Lake confluence, turbidity showed a positive correlation with runoff (r = 0.54), contrasting with upstream reaches. Hydrological factors exerted the strongest influence, while meteorological and land-use factors mainly contributed through their interactions with hydrological conditions. These findings underscore the importance of considering reservoir regulation, river–lake interactions, and watershed environmental factors in understanding turbidity dynamics in large regulated rivers.