Sedimentary records of recent anthropogenic eutrophication and metal contamination in Zhelin Bay, an important mariculture area in Southern China.

Dinoflagellate cysts (dinocysts), biogenic elements and metals were analyzed from sediment cores collected from Zhelin Bay of the South China Sea in December 2008 to understand the environmental changes over the past 50years. Dinocyst concentrations ranged from 0cysts/g to 770cysts/g, and they were dominated by heterotrophic taxa. There was a clear increase trend upcore for biogenic elements, except for biogenic silica. Metals originated from both the lithogenic source and human activities, and significantly increased after 1985-1995. Environmental changes in the past 50years can be divided into three stages: (1) before 1985, during which biogenic elements, cyst flux and metals were low; (2) from 1985 to the early 2000s, characterized by an obvious increase of dinocysts, TOC, TN and most metals, while TOC/TN and BSi decreased; and (3) after 2000, the period of rapid increase of dinocysts, TOC and TN but decrease of certain contamination metals.