Interplay between saltmarsh carbon burial and lateral exchange in coastal wetlands: The role of biomorphodynamic feedback

Understanding the carbon sequestration of saltmarshes and the role of biomorphodynamic feedback are essential for the protection, management, and adaptation to climate change of coastal blue carbon ecosystems. We developed a biomorphodynamic model that simultaneously considers carbon vertical burial and lateral exchange of soil organic carbon and validated this model against field measurements. This model was then used to examine carbon dynamics in saltmarshes and to explore the integrated effects of hydrodynamics, vegetation growth, sediment transport, and morphological change on carbon sequestration and spatial patterns. We find that taking lateral transport of sediment and carbon into account results in a greater spatial gradient of carbon burial compared to that of biomass, especially near the marsh edge. This enhanced gradient is reflected in our field data. Hydrodynamics enhance the spatial heterogeneity of marsh carbon burial and exchange by suspending sediment at the production-governed edge and transporting carbon into the marsh where it deposits. In our study case, the transport loss at the saltmarsh front accounted for 43% of carbon production inputs, while carbon burial was only 40%. The carbon sequestration capacity of saltmarshes critically depends on the hydrodynamic complexity of the fringing zone, which in some cases can shift the role of saltmarshes from carbon sinks to sources. Our modeling framework facilitates more accurate predictions of how carbon sequestration responds to changes in landscape morphology and hydrodynamics, providing valuable insights for conservation strategies aimed at maximizing the climate change mitigation benefits of blue carbon ecosystems.