Sedimentary dinoflagellate cyst records of human-induced environmental changes in Daya Bay, the northern South China Sea

High resolution dinocyst records were established in sediment core to detect human-induced environmental changes in Daya Bay, the South China Sea. The grain was homogeneous except at depths of 17-18 cm, where the clay proportion increased dramatically from similar to 40% to similar to 80%. The Pb-210 activity varied from 25.1 Bq kg(-1) to 78.5 Bq kg(-1) and showed temporary interruption at depths 17-18 cm associated with 1978, while dinocysts showed no obvious hiatus. Totally 36 cyst species were identified, with the highest species richness (20) and cyst abundance (900 cysts g(-1)) occurring at 7-cm depth, associating with severe blooms of Scrippsiella acuminate from 1998 to 2000 in Daya Bay. Cyst assemblages showed high similarity (>70%), especially in the interrupted and upper layers, indicating similar marine-originated for these intervals. Moreover, autotrophic and heterotrophic cysts dominated alternately before and after 1978, indicating high potential of the cysts to trace human-induced environmental changes in Daya Bay.