The estuarial wetlands of the Yellow River Delta possess significant carbon (C) sink capacity,influenced by frequent channel shifts of the Yellow River. These changes have altered the hydrological conditions and vegetation characteristics of estuarial wetlands in different rive channels,potentially impacting the source of soil organic carbon (SOC) in these wetlands. However,research examining the impact of river channel alterations on SOC sources in the Yellow River Delta remains scarce. This study aimed to investigate the distribution and traceability characteristics of SOC in a Suaeda salsa wetland and a mudflat in both the abandoned channel in 1996 and the current channel in the Yellow River Delta. The results indicated that (1) The soil C/N ratio in the two wetlands varied from 26 to 54,significantly higher in the abandoned channel wetland than in the active river channel (P<0.05). Additionally,the soil C/N ratio varied significantly along the soil depth (P<0.05). The natural ¹³C abundance (δ¹³C) of SOC ranged from -25.30‰ to -22.03‰,with the δ¹³C values in the Mudflat of the two river channels being significantly higher than of S.salsa (P<0.05). However,the δ¹³C values showed a gradual decrease trend with the increase of soil depth. (2) Calculations from the Bayesian mixed model showed that overall,SOC in the wetlands of the Yellow River Delta originated mainly from local plants (40%-67%),followed by marine phytoplankton (23%-40%),while the relative contribution of terrestrial particulate organic matter (POM) was the smallest. (3) Statistical analysis showed that the sources of SOC in the wetlands of the Yellow River Delta were affected by both channel and plant type. Specifically,the contribution of local plants to SOC in the S.salsa was greater than that in the Mudflat (P<0.05),the contribution of marine phytoplankton differed significantly between the two river channels and between the two plant types (P<0.05),while the contribution of terrestrial POM was affected by the interaction between river channels and plant types (P<0.05). This study revealed the traceability characteristics and driving factors of SOC in the estuarial wetlands in the Yellow River Delta,enhancing our comprehension of the soil carbon cycle in these wetlands and offering vital scientific insights for the management of blue carbon sinks.