Lignin analysis of sediments from around 2,000 to 1,000 years ago (Jiulong River estuary, southeast China)

In this work, a sediment core collected from the Jiulong River estuary in southeastern China was subjected to 14C dating of foraminifera, as well as lignin, total organic carbon, and stable carbon isotope (δ13C) analyses in order to determine the impacts of climate change and human activities on the sedimentary organic matter in this area from around 2,000 to 1,000 years ago. The ratios of lignin parameters syringyl/vanillyl and cinnamyl/vanillyl ranged from 1.60 to 8.63 and 0.11 to 0.45, respectively, and the lignin phenol vegetation index ranged from 25.14 to 1740.14, indicating the presence of non-woody angiosperms. The ratio of vanillic acid/vanillin ranged from 0.42 to 2.04, indicating medium to high degrees of oxidative degradation. The vertical distribution profile showed a similar historical sedimentary trend with locations at higher latitudes along the Zhejiang-Fujian Mud Area, with the lower abundance of total lignin from around 2400 to 2000 BP being attributed to the decreasing temperature during this period. However, all the lignin parameters showed higher values and greater fluctuations due to increasing temperatures after 2000 BP, and human activity has probably had the greatest impact in the most recent 1,000 years.