<p>Mangrove ecosystems exhibit substantial carbon sequestration capabilities. This study investigates carbon burial processes in mangrove blue carbon ecosystems by analyzing a sediment core from the Maowei Sea Mangrove Reserve (MSMR) in Guangxi, China. MSMR sediments consist primarily of sand and silt. The sediment organic carbon (SOC) and sediment nitrogen (SN) ranged from 0.36% to 1.87% (mean 0.96%) and 0.02% to 0.10% (mean 0.05%), respectively. The C/N ratio varied from 12.05 to 25.89 (mean 18.64), δ¹³C values from −26.63‰ to −24.68‰ (mean −25.56‰), and δ¹⁵N values from 2.63‰ to 7.17‰ (mean 4.37‰). The average sediment mass accumulation rate was 0.84 cm/a. The sediment fluxes (SF) [g/(cm²·a)] and OC burial fluxes (OCBF) [g/(m²·a), in terms of C] were from 0.59–1.20 (mean 0.92) and 3.65×10¹–2.01×10² (mean 8.55×10¹), respectively. SF and OCBF were reduced due to the construction of reservoirs from 1940s to 1960s. From 1990s to 2010s, OCBF decreased with the reduction in sediment concentration of Qinjiang River entering the sea, while SF increased due to the expansion of mangrove area and the siltation of the bare flat front. After 2010s, SF influenced by the dredging project in Maowei Sea, leading to a decrease trend. Source analysis of organic matter revealed the terrestrial OC contribution was dominant, averaging 6.63× 10¹ [g/(m²·a), in terms of C]. The results of this study demonstrate the changes in sediment carbon burial rates caused by both natural and human activities occurring in the mangrove wetland transition zones. In the future, it is noted that the long-term impact of major projects, such as the newly built Pinglu Canal, on carbon storage in downstream coastal wetlands.</p>