Identification of the earlier human-induced sedimentation change in Daya Bay, northern South China Sea using 210Pb and 137Cs

Highlights: • A two-stage distribution of ²¹⁰Pb was observed in a sediment core in Daya Bay. • The hiatus was confined to late 1977 using ¹³⁷Cs and ²¹⁰Pb techniques. • Anthropogenic perturbation was earlier than general recognition in Daya Bay. - Abstract: Over the past 30 years, the rapid development of the Chinese economy resulted in environmental problems, especially in coastal areas. To discern the effects of anthropogenic activities, ²¹⁰Pb and ¹³⁷Cs were examined in the sediment from Daya Bay, northern South China Sea. The specific activity of ¹³⁷Cs showed a clear maximum, corresponding to 1963. ²¹⁰Pb specific activity varied from 25.1 to 78.5 Bq kg^{− 1}. ²¹⁰Pb distribution showed a hiatus at 18–19 cm with 5–6 cm of older sediment (> 150 years), indicating direct land-originating material over a short timescale rather than natural processes. This event was attributed to the human-induced redistribution of sediment during reclamation. Based on the ¹³⁷Cs-labeled 1963 and ²¹⁰Pb-chronologies, this event was confined to late 1977, earlier than the generally recognized significant anthropogenic activities. Thus, information archived in the sediment or in records prior to the 1970s would be better environmental background in Daya Bay.