Seasonal distribution patterns of 7Be and 210Pb in surface sediments in the Changjiang Estuary, China and their implication

The estuarine-inner shelf region of the East China Sea (ECS) is heavily impacted from the riverine input from the Changjiang River. In this study, the grain size and activities of radionuclides (7Be and 210Pb) of surface sediments collected from the Changjiang Estuary to the southern inner shelf of the ECS in June and November 2010, were measured to provide the study of the sources and the transportation pathways of surface sediments in this region. The results indicated that the grain size of surface sediments ranged from 8.1 to 251.1 μm and from 5.8 to 128.3 μm with an average of 85.1 μm and 56.6 μm in June and November 2010, respectively. Relatively large particle sizes were observed in the northwest and southeast of our study area. Meanwhile, the grain size increased offshore. The activities of 7Be in the surface sediments were high in the nearshore stations and the activities of 210Pbex in the surface sediments increased from north to south. For 7Be, more than 90% was decayed before deposition into the surface sediment. However, most 210Pb (99%) was deposited into the sediment. Both7Be and 210Pb need to be input into the inner shelf by boundary scavenging processes to balance the budget.