Seasonal sedimentation dynamics modulate contemporary particulate nutrient burial efficiencies in the Three Gorges Reservoir, China

: Sedimentation and associated nutrient burial in reservoirs pose significant threats to ecological stability and long-term operational sustainability. The Three Gorges Reservoir (TGR) in China represents a large river-type reservoir that has experienced substantial sedimentation since its impoundment; however, the efficiency of particulate nutrient burial associated with this sedimentation remains unquantified. In the present study, monthly suspended sediment load records from the TGR’s upstream (Cuntan and Beibei) and downstream (Yichang) hydrological stations (2003–2024) were used to estimate the reservoir’s sedimentation load. Time-integrated suspended sediment samples from the main channel and a sedimentary core from a representative section were collected. Their physicochemical properties, including particle-size distribution, total organic carbon (TOC), total nitrogen (TN), and total phosphorus (TP) concentrations, were subsequently determined. Results indicate that the mean annual burial fluxes for the 2003-2024 period were 1.61 Mt·yr -1 for TOC, 0.10 Mt·yr -1 for TN, and 0.09 Mt·yr -1 for TP, corresponding to burial efficiencies of 50.88%, 26.55%, and 50.51%, respectively. Nutrient burial efficiencies in the TGR exhibited significant seasonal variation, with wet-season values of 85.93% (TOC), 46.37% (TN), and 85.08% (TP) substantially exceeding dry-season values of 38.92%, 21.32%, and 38.79%, respectively. The findings herein demonstrate that high wet-season sedimentation rates drive the substantial burial of particulate nutrients in the TGR. This underscores the necessity of ongoing monitoring of sedimentary nutrient dynamics and the development of management strategies aimed at modulating sediment retention to mitigate potential ecological risks.