[Burial, source characteristics and influencing factors of organic carbon in mangrove sediments at the mouth of the Oujiang River Estuary, China].

Abstract

Mangrove forests are crucial coastal "blue carbon" ecosystems, known for their significant carbon sequestration capabilities to "carbon neutrality" and mitigating global climate change. We used ²¹⁰Pb radioisotope dating to analyze sedimentation rates in the sediments of the Oujiang River Estuary mangrove forest, to calculate organic carbon burial rate, and to assess the characteristics and sources of organic carbon burial. The results showed that the average total organic carbon content in the sediments was 1.4 %, generally decreasing with depth. The average organic carbon burial rate was 26.2 Mg C·hm^-2·a^-1, slightly higher than the global average for mangrove forests. By contrast, the organic carbon content in the core sediments (0-150 cm) was 37.4 Mg C·hm^-2, slightly lower than the global average. The stable carbon and nitrogen isotope distribution characteristics and the stable isotope mixing model (SIMMR) indicated that organic carbon originated from a mix of marine and terrestrial sources. Marine sources, such as suspended organic particles and phytoplankton, contributed 45.6% and 10.6%, respectively, while terrestrial sources, including sedimentary organic matter and leaf litter, accounted for 31.5% and 12.3%, respectively. Overall, the Oujiang River Estuary mangrove forest had a high organic carbon burial rate, with significant variations in carbon content at different depths influenced by tidal influences. Additionally, the input of external suspended organic particles was an important contributor to sediment organic carbon burial.