Dynamics and fate of blue carbon in a mangrove–seagrass seascape: Influence of landscape configuration and land-use change

Context: Seagrass meadows act as efficient natural carbon sinks by sequestering atmospheric CO and through trapping of allochthonous organic material, thereby preserving organic carbon (C ) in their sediments. Less understood is the influence of landscape configuration and transformation (land-use change) on carbon sequestration dynamics in coastal seascapes across the land–sea interface. Objectives: We explored the influence of landscape configuration and degradation of adjacent mangroves on the dynamics and fate of C in seagrass habitats. Methods: Through predictive modelling, we assessed sedimentary C content, stocks and source composition in multiple seascapes (km-wide buffer zones) dominated by different seagrass communities in northwest Madagascar. The study area encompassed seagrass meadows adjacent to intact and deforested mangroves. Results: The sedimentary C content was influenced by a combination of landscape metrics and inherent habitat plant- and sediment-properties. We found a strong land-to-sea gradient, likely driven by hydrodynamic forces, generating distinct patterns in sedimentary C levels in seagrass seascapes. There was higher C content and a mangrove signal in seagrass surface sediments closer to the deforested mangrove area, possibly due to an escalated export of C from deforested mangrove soils. Seascapes comprising large continuous seagrass meadows had higher sedimentary C levels in comparison to more diverse and patchy seascapes. Conclusion: Our results emphasize the benefit to consider the influence of seascape configuration and connectivity to accurately assess C content in coastal habitats. Understanding spatial patterns of variability and what is driving the observed patterns is useful for identifying carbon sink hotspots and develop management prioritizations. 2 org org org org org org org org org