Characteristics and source tracing of organic carbon in intertidal sediments of wetland in Yangtze Estuary, China

Abstract Background: Wetland ecosystem is characterized by water-land interaction and plays an important role in regional energy and material circulation. In the context of global climate change, the study of wetland carbon storage and carbon cycle has become a focus of academic attention. The characteristics of organic carbon in sediments and its source is a key problem in the study of carbon cycle in wetlands. Results: In this study, the characteristics of total organic carbon (TOC), total nitrogen (TN) accumulation, and stable carbon isotope (δ13C) in the vegetation and soil were investigated for the three dominant salt marsh vegetation Phragmites australis (PA), Spartina alterniflora (SA), Scirpus mariqueter (SM) of the coastal wetlands of Chongming Dongtan in the Yangtze River Estuary. The results showed that the mean value of TOC and TN concentrations in the surface sediments of wetland were 1.39 ± 0.34% and 0.091± 0.024%, respectively. The carbon stable isotope (δ13C) mean value of sediment was -24.17±1.51‰. The TOC of the sediment in the three saltmarsh plant communities was in the order of SA (1.76 ± 0.38%) > PA (1.45 ± 0.37%) > SM (0.96 ± 0.44%). The simulation results of the three end-member mixing equations showed that the organic carbon in sediments was mainly derived from suspended particles (42.44 ± 20.89%) and vegetation (34.50 ± 25.23%). The contribution rate of microalgae is lower (23.06 ± 4.62%). Conclusion: The organic carbon in sediments of wetland in Yangtze Estuary are the result of mixed input of terrestrial organic carbon and marine organic carbon. Organic carbon in sediments was mainly derived from suspended particles and vegetations. The results provide preliminary knowledge of the distribution and sources of sedimentary organic carbon for better understanding the sediment transport and deposition in this region.