Impact of the spread of invasive alien species in saltmarshes sedimentary carbon sinks

The proliferation of invasive alien species (IAS) is one of the main threats to the conservation of estuarine habitats, including saltmarshes. Differences between IAS and their native counterparts in structural traits (e.g. plant size, biomass allocation, shoot stiffness) and chemical composition (e.g. nutrient and lignin content) can affect the accumulation and long-term storage of organic carbon (OC) in saltmarsh sediments. However, the impact of IAS colonization on sedimentary carbon sinks in saltmarshes remain largely unexplored, particularly in Europe. Existing studies are scarce and focus primarily on the herbaceous species Spartina alterniflora, while no research has yet assessed the impact of the spread of woody shrub species such as Baccharis halimifolia, one of the main IAS in European estuaries. This study examines organic carbon (OC) stocks, ²¹⁰Pb-derived accumulation rates and the molecular composition of the organic matter (i.e. through pyrolysis techniques) in 12 sediment cores sampled across native saltmarsh (i.e. Juncus maritimus and Spartina maritima) and invasive saltmarsh communities (i.e. Spartina alterniflora, Spartina anglica and Baccharis halimifolia) in the Gulf of Biscay. The results of this study serve as a basis for the implementation of conservation and restoration actions in saltmarsh environments that address both biodiversity and climate change mitigation goals.