Recent eutrophication and human disturbance in Daya Bay, the South China Sea: Dinoflagellate cyst and geochemical evidence

Recent trends in eutrophication and human disturbance were evaluated using dinoflagellate resting cysts and geochemical parameters. Analyses were performed on three sediment cores from Daya Bay, South China Sea covering the past hundred years. Changes in cyst assemblages as well as geochemical parameters including biogenic silica (BSi), organic carbon (OC) and total nitrogen (TN) reflected environmental change in the area. The clear increase in overall cyst concentration and the prominence of Scrippsiella cysts suggested an increase in cultural eutrophication which began in the 1970s and become evident since 1985. Large fluctuation in cyst assemblages and BSi in the upper 22 cm signaled the influence of construction and operation of nuclear power stations on phytoplankton community and environments, with an increase in the early stage of construction, a rapid decline in the late stage of construction and early operation, and then a sharp increase thereafter. High Alexandrium cyst abundance in shallowest sediments was consistent with high PSP levels and PSP events in the area, and the persistent toxicity suggests recurrent seeding from the rich cyst bed in these surface sediments.

► Dinocyst and geochemical analyses provided evidences for environment changes.
► Predominance of Scrippsiella cyst reflected the influence of cultural eutrophication.
► Sharp decrease in cyst and BSi was the results of nuclear power station construction.
► Increase in cyst and BSi displayed the increasing temperature on phytoplankton.