Short- and long-term sediment transport in western Bohai Bay and coastal areas

Sediment cores (similar to 40-100 cm) were collected at 12 locations in the western Bohai Bay, the Haihe River estuary, the Yongding River estuary and the Tianjin Harbor, China, during 24-26 July 2007, and analyzed for Be-7 and Pb-210 activities. Due to localized hydrodynamic patterns and frequent disturbance from dredging activities, steady-state sedimentation features were not observed in this study. As demonstrated in the Be-7 and Pb-210 profiles, the temporal and spatial variations of these radionuclides support a non-steady state depositional environment in the study area. By comparing Be-7 and Pb-210 inventories in the sediments with those of the atmospheric source, we found that: 1) sediments dredged from the Tianjin Harbor or eroded from nearby estuarine and coastal areas are retained in the western Bohai Bay for relatively short intervals (several months), as reflected in the relatively high Be-7 inventories in the western Bohai Bay; 2) over the long-term (years to decades), Pb-210 inventories in the sediments imply that there is a net on-shore transport of sediments, and the sediments are mass-balanced in the entire study area. Overall, our results suggest that the sediments are retained in the estuaries and the western Bohai Bay despite local variability in sediment dynamics and disturbance due to human activities.