Fate of Organic Carbon Shaped by Iron Minerals in Coastal Wetlands: Mechanisms and Implications

Coastal wetlands are premier blue carbon sinks, yet the stability and fate of their organic carbon (OC) are profoundly shaped by complex biogeochemical interactions with iron minerals. This review provided a systematic analysis of iron-mediated OC dynamics by resolving the "coastal syndrome"─the synergistic regulation of Fe-OC interactions by salinity fluctuations, tidal hydrodynamics, and halophytic vegetation. We elucidated how iron minerals govern OC fate through multipathway stabilization (adsorption, coprecipitation, and aggregation) and simultaneous mineralization driven by redox transitions, including Fe(III) reduction and Fe(II)-catalyzed reactive oxygen species (ROS) production. Crucially, we emphasize the active role of OC as a redox mediator─acting as electron shuttles and complexing agents─that regulates iron transformation and bioavailability. Also, we synthesized microscale mechanisms and responses to environmental drivers, emphasizing dynamic regulation of interactions between iron minerals and OC by salinity fluctuations, tidal hydrodynamics, vegetation rhizospheres, and their joint effects. Integrating these mechanistic insights, we proposed a transition toward a unified, multifactor coupling framework to better predict and manage the carbon sink functionality of coastal wetlands. This review offered a mechanistic basis for linking saltwater intrusion, iron redox dynamics, and microbial metabolism to carbon sequestration in coastal blue carbon ecosystems.