Abstract To investigate the impact of changes in the Changjiang catchment on the estuarine coast‐shelf sedimentary system, variations in the transport, distribution, and budget of 210 Pb in the sediment of the Changjiang subaqueous delta (CSD) and the Zhejiang‐Fujian coastal mud belt (ZFCMB) system were analyzed before and after the impounding of the Three Gorges Dam (TGD). The results indicate that the 210 Pb ex activity in the surficial sediments of the CSD‐ZFCMB decreased significantly after 2003 and that the surficial and vertical distribution of the 210 Pb ex activity in the CSD changed substantially due to intensified sediment redistribution. The 210 Pb contribution of the Changjiang catchment to the CSD‐ZFCMB is not negligible. Due to the trapping effect of the TGD, 76 ± 49% of the 210 Pb supply from the Changjiang upstream areas was retained in the TGD, resulting in the 210 Pb flux into the sea decreased substantially. Furthermore, our findings demonstrate that the cross‐shelf plume provides a major conduit for the transport of 210 Pb over the East China Sea. The variation in the 210 Pb budget in the sediment of the CSD‐ZFCMB also indicated that the influence of Changjiang catchment changes on the 210 Pb ex and supported 210 Pb activities will become more significant in the future. In addition, the rate of 210 Pb burial in the sediments of the ZFCMB decreased, whereas the retention index of 210 Pb and the amount of 210 Pb retained in the CSD increased significantly, suggesting that after 2003, the material transfer function of the CSD weakened.
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