Factors influencing the distribution of organic carbon in four different coastal sedimentary environments

Purpose Organic carbon (OC) plays an important role in the multimedium transport of pollutants and the carbon cycle. However, the distribution and fate of OC in coastal areas with multiple sedimentary environments, especially in underdeveloped coastal areas, have been underappreciated and lacked sufficient understanding.Materials and methods In this paper, the characteristics and fate of OC in four sedimentary environments (mangrove, sandy coast, bay, and estuary) in a coastal area in Guangdong, China, were compared. Dissolved organic carbon (DOC) and suspended sediment (SPS) concentrations in water phases as well as total organic carbon (TOC) content and grain size distribution in sediments were determined.Results and discussion The DOC concentrations and TOC contents were 0.006-13.66 mg L-1 and 0.04-9.51%, respectively, indicating a large spatial heterogeneity. The DOC levels showed an increasing trend into the bays and a decreasing trend along the estuaries, relating to hydrodynamic conditions for OC transport. The SPS concentrations were positively correlated with the TOC/DOC ratios in estuaries, confirming the carrier role of SPS in water-sediment systems. No significant differences in DOC concentrations were found under different water column depths, inferring that water-sediment ratios were not a limiting factor for DOC levels. The actual OC storage of the whole mangrove sedimentary environment was underestimated by 18.2% when calculated using the OC levels of the largest mangrove.Conclusion Our results suggest that the OC storage estimation in multiple sedimentary environments could be underestimated. This study provides new insight for management and protection of coastline eco-environments and the estimation of carbon stock in the hopes of adapting to climate change.