Monitoring suspended sediment longitudinal fluctuations along the Pearl River

Climate change and intensified anthropogenic activities have profoundly altered sediment dynamics in large river systems, particularly across major Asian basins. Traditional hydrological station data, constrained by sparse spatial coverage, are insufficient to capture the continuous longitudinal variability of suspended sediment. To address this limitation, this study integrated satellite remote sensing with advanced model development to quantify suspended sediment concentration (SSC) dynamics across the Pearl River Basin (PRB). A high-accuracy SSC retrieval model was developed by fusing Sentinel-2 imagery with in-situ observations and optimized using a Bayesian calibration algorithm. The results reveal that: (1) Despite still high SSC in the upper PRB (median: 105 mg/L), cascade reservoirs cascade reservoirs substantially intercept suspended sediment, markedly reducing concentrations in midstream reaches; (2) Midstream reaches exhibit lower SSC levels (median: 15 mg/L), while downstream segments show a resurgence (65 mg/L) likely driven by local erosion and tributary inputs; (3) Dam operations have enhanced seasonal SSC disparities reservoir inflow and outflow, with higher retention during the monsoon season and lower during the dry season. These findings demonstrate that traditional hydrological observations fail to represent the pronounced longitudinal SSC variations induced by reservoir cascades, thereby overlooking critical processes shaping sediment transport from the headwaters to the estuary. The spatially continuous SSC maps derived in this study underscore the dual role of reservoirs as both sediment sinks and agents of downstream geomorphic adjustment and deltaic sediment redistribution. These findings offer a scientific basis for improving sediment monitoring and management in the PRB and other similar large river basins facing comparable hydroclimatic and anthropogenic pressures.