Variations in the transport, distribution, and budget of ²¹⁰Pb in sediment over the estuarine and inner shelf areas of the East China Sea due to Changjiang catchment changes

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 210Pb 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 210Pbex activity in the surficial sediments of the CSD‐ZFCMB decreased significantly after 2003 and that the surficial and vertical distribution of the 210Pbex activity in the CSD changed substantially due to intensified sediment redistribution. The 210Pb contribution of the Changjiang catchment to the CSD‐ZFCMB is not negligible. Due to the trapping effect of the TGD, 76 ± 49% of the 210Pb supply from the Changjiang upstream areas was retained in the TGD, resulting in the 210Pb flux into the sea decreased substantially. Furthermore, our findings demonstrate that the cross‐shelf plume provides a major conduit for the transport of 210Pb over the East China Sea. The variation in the 210Pb budget in the sediment of the CSD‐ZFCMB also indicated that the influence of Changjiang catchment changes on the 210Pbex and supported 210Pb activities will become more significant in the future. In addition, the rate of 210Pb burial in the sediments of the ZFCMB decreased, whereas the retention index of 210Pb and the amount of 210Pb retained in the CSD increased significantly, suggesting that after 2003, the material transfer function of the CSD weakened.

Distribution pattern and mass budget of sedimentary polycyclic aromatic hydrocarbons in shelf areas of the Eastern China Marginal Seas

“…[] successfully constructed the mass budget of black carbon in the BS, and Gao et al . [] developed a preliminary estimate of the 210 Pb budget for the ECS. However, relevant studies in large‐scale marginal sea systems are scarce.…”

“…An export ratio of sediments was defined and calculated as export flux divided by input flux. We calculated an export ratio of 21%, which is very close to the value of 20% proposed by Gao et al [2017]. Thus, the mass budget of PAHs for the ECMSs highlights the fate of PAHs on an extended regional scale and further clarifies the importance of PAHs transportation among subregions of the ECMSs.…”

Shifts in the Distribution and Fate of Sedimentary Polycyclic Aromatic Hydrocarbons Within the Estuarine‐Inner Shelf Areas of the East China Sea: Response to Human‐Induced Catchment Change

“…Grain-size variations from 1982-2014 showed that sediment coarsening occurred not only in the Changjiang Estuary but had also expanded to the entire estuarineinner shelf areas (Gao et al, 2019). Previous studies also demonstrated that material deposited in the estuarine-inner shelf regions of the ECS was likely to lag behind changes in the Changjiang River catchment by about 3 years (Gao et al, 2017;Hu et al, 2012). Therefore, samples collected in 2006 could reflect the sedimentary environment in the CSD around 2003, representing the situation before the construction of the TGD.…”

“…In addition to dam construction, the Water and Soil Conservation Project implemented in the high sediment yield region of the upper Changjiang basin in the 1980s could be another factor resulting in abrupt reductions in sediment loads (Dai & Lu, ). Such drastic reductions in sediment discharge have caused significant changes in the sedimentary environment and hydrodynamics of the ECS's estuarine‐inner shelf regions (Gao et al, ; Wang et al, ; Yang et al, ). In addition, reservoir interception of coarse‐grained sediment from upper reaches has induced channel erosion in the middle and lower reaches, substantially changing the sediment component reaching the ECS (Gao et al, ; Yang et al, ).…”

Distribution and source of Pu in the sediments of the seas and estuaries of China—a review

“…For example, the sediments from the Luan River and Hai River are deposited in the central Bohai Bay, and clay particles are derived to the southeastern region (Hu et al 2010) where the 239+240 Pu activities are significantly higher than other areas (Zhuang et al 2019). Moreover, the Yangtze River also carries a large amount of sediments deposited in the Yangtze River estuary, and forms two large-scale mud deposits (Changjiang Subaqueous Delta and Zhejiang-Fujian Coastal Mud Belt) (Gao et al 2017). The two mud deposits have exceptionally higher 239+240 Pu activities and 240 Pu/ 239 Pu atom ratios than their surroundings.…”