| Carbon, sulfur and heavy metals are some of the most reactive components of coastal marine sediments during early diagenesis. In this study, we examined the Total Organic Carbon (TOC), organic carbon to nitrogen ratio (C/N), Acid Volatile Sulfide (AVS), and heavy metal contents of four sediment cores collected from the Licun Estuary in the northeast of Jiaozhou Bay near Qingdao, China. Near the entrance of the river, sediment (argillaceous siltstone) TOC content was relatively high (TOC average of JZB-2 core was 1.87%) and was controlled by terrestrial input. The relatively low stream flow, weak water dynamics, and high biological productivity in the water column in this area favored the preservation and burial of organic carbon in the sediment. The concentrations of heavy metals (i.e., Cd, Cr, Cu, Fe, Pb, Sr, Zn, etc.) were high and correlated positively with both TOC and AVS contents. A short distance away from the entrance of the river, sediment was coarser (siltstone) and its TOC content was lower (TOC average of JZB-2 core was 1.02%) than sediment near the entrance. The relatively high C/N ratio (i.e., >>20) and weak C to N correlation indicated that sediment organic carbon content was controlled by both marine and terrestrial sources. The concentrations of heavy metals in sediment were low. The reactive fractions of Cd, Cu and Sr correlated positively with sediment TOC content, while the reactive fractions of Cr, Pb and Zn correlated positively with sediment organic nitrogen. This observation suggested that the mobility of some heavy metals was controlled by terrestrial organic matter. The SEM fractions of Fe and Zn correlated positively with sediment AVS content, indicating strong influence of sulfur cycling on the mobility of this group of heavy metals. In addition, a careful examination of the current methods of sediment organic content determination revealed an important artifact. A revised the method was presented.
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