Distribution and pollution assessment of biogenic elements in surface sediments from Qingdao coastal area

Thirty-three surface sediment samples were collected from Jiaozhou bay, Laoshan coastal area and Qingdao amphioxus reserve area in November 2017. Biogenic elements including total organic carbon (TOC), total nitrogen (TN), total phosphate (TP) and biogenic silica (BSi) were analyzed. Concentrations of TOC, TN, TP and BSi were in the range of 0.21%~1.43%, 0.02%~0.13%, 0.06%~0.15%, 0.26%~0.60%, respectively. TN and TP were high in Jiaozhou bay, and TOC was high in Laoshan coastal area. While, BSi was high in amphioxus reserve area. In addition, BSi in Jiaozhou bay showed a significant decreasing trend compared to the previous studies, indicating the decrease of diatom productivity. Based on the molar ratios of TOC/TN, TOC in Jiaozhou bay and amphioxus reserve area was originated from mixture inputs of terrestrial and marine sources, while was mainly originated from marine sources in Laoshan coastal area. Results from pollution assessment of biogenic elements indicated that TOC in the surface sediments from Qingdao coast belonged to the uncontaminated level, however TN and TP reached moderate pollution level.