A geochemical record of environmental changes in sediments from Sishili Bay, northern Yellow Sea, China: Anthropogenic influence on organic matter sources and composition over the last 100Â years

- Increased TOC and TN in the sediment cores indicated a eutrophic trend since 1975.
- Marine organic matter sources dominated in Sishili Bay.
- Scallop culture displayed mitigation on eutrophication pressures in Sishili Bay.
- Increased fertilizer use well matched eutrophic process in Sishili Bay in 1975.

Total organic carbon (TOC), total nitrogen (TN), δ13C and δ15N were measured in sediment cores at three sites in Sishili Bay, China, to track the impacts of anthropogenic activities on the coastal environment over the last 100 years. The increased TOC and TN in the upper section of sediment cores indicated a eutrophic process since 1975. In comparison, the TOC and TN in the sediment core near to a scallop aquaculture area displayed a much slower increase, indicating the contribution of scallop aquaculture in mitigating eutrophication. Combined information from δ13C, δ15N and TOC:TN indicated an increased terrestrial signal, although organic matter sources in Sishili Bay featured a mixture of terrestrial and marine sources, with phytoplankton being dominant. Increased fertilizer use since 1970s contributed to the eutrophic process in Sishili Bay since 1975, and increased sewage discharge from 1990s has added to this process.