Sources and Transport of Terrigenous Organic Matters Along the East China Sea Inner Shelf: Insights from Lignin and Alkane Biomarkers

The area of East China Sea (ECS) inner shelf is an important sink of suspended particulates from Yangtze River (YR) and materials originated from YR basin. In this study, the parameters of lignin and alkane biomarkers in surface sediment samples from ECS inner shelf were determined to distinguish the sources and to trace the transport of terrigenous organic matters in the region. Our dataset showed that total alkanes with carbon numbers from 10 to 38 (T-alkanes) were significantly correlated to both TAR (terrigenous/aquatic ratio) and HMW/LMW (the ratio of high molecular weight to low molecular weight alkanes) ( r =0.88, P <0.05 for both), indicating that the majority of T-alkanes was predominantly originated from terrestrial sources, and T-alkanes are important constituents of terrestrial organic matters in the study area. The area was probably affected by petroleum pollution to a certain degree, as indicated by the values of carbon preference index (CPI), odd-over-even carbon number predominance (OEP) and the ratio of pristane to phytane (Pr/Ph). The values of Pr/n-C 17 and Ph/n-C 18 suggested a strong reductive sedimentary condition in the region with no obvious biodegradation. The content of eight lignin phenols (Σ8) decreased from the coast to the open sea, indicative of riverine input and hydrodynamic transport of terrigenous organic matters. Lignin degradation parameters presented an increasing trend from the coastline toward the open sea. The lignin vegetation parameters and alkane index (AI) suggested the predominance of non-woody angiosperms in the YR basin. The obvious correlation between Λ8 (Σ8 normalized to 100 mg organic carbon), TAR and HMW/LMW reveals the significantly concurrent input of lignin and alkanes from terrestrial sources.