Distributions and sources of organic biomarkers in surface sediments from the Changjiang (Yangtze River) Estuary, China

Surface marine sediments, collected from four sites of the Changjiang Estuary, China, have been analyzed for total organic carbon (TOC) and total nitrogen (TN) content, δ 13C values of organic matter, n-alkanes and isoprenoid hydrocarbons, fatty acids, aliphatic alcohols and sterols, acyclic methyl ketones and sterones. The dissolvable organic matter (DOM) is the highest at the most eastern site (site 17), with the lower TOC and TN contents due to the long time degradation. The distributions of various compounds indicate that the organic matter at all four sites is derived from marine autogenic and terrestrial origins at different proportions. At the site of the boundary of turbidity maximum (site 8), the organic matter originates from the autogenic and terrestrial sources are fairly equal. At the site close to the river mouth (site 11), the terrestrial input is the predominant source of the organic matter. At the most eastern site (site 17), the organic matter is mainly from ancient Changjiang River delta residue sediment. At the southern site of the Changjiang Estuary (site 26), the contribution of the marine autogenic organisms to the organic matter is significant. In addition, the microbial activities appear higher at site 11 than at the other three sites, as reflected from the distributions of various dissolvable organic matter compounds in anoxic sediments.