Distribution and Sources of Organic Carbon in Surface Intertidal Sediments of the Rudong Coast, Jiangsu Province, China

In this study, total organic carbon (TOC), total nitrogen (TN), and stable carbon isotopes (delta C-13) were measured in surface intertidal saltmarsh and bare tidal flat sediments along the Rudong coast. The distribution and sources of organic carbon were examined under different depositional environments based on C/N ratios and a two-terminal mixing model. The results showed that the average TOC content of the vegetated saltmarsh sediments, bare tidal flat areas near vegetation (BF1), and bare tidal flat areas far from vegetation (BF2) were 4.05, 2.72, and 1.22 mg/g, respectively. The mean delta C-13 value within the vegetated saltmarsh area was -22.37 parts per thousand, and the C/N ratio was 9.3; the corresponding values in the BF1 area were -23.27 parts per thousand and 7.95, respectively; and in the BF2 area, the corresponding values were -21.91 parts per thousand and 5.36, respectively. These C/N ratios reflect an increasing marine contribution with distance from the vegetated zone. Combined with the two-terminal mixing model, the organic carbon in the vegetated saltmarsh sediments was dominated by terrestrial sources, while the bare tidal flat sediments were more influenced by marine sources, and the bare tidal flat sediments nearer to the vegetated zone (BF1) were influenced by a combination of vegetation, marine sources, and other terrestrial factors.