Estimating current and future saltmarsh areas and carbon storage in Irish Blue Carbon habitats

Saltmarshes protect the coast against storm surges and erosion, are important ecosystems for breeding and sheltering birds and fishes, and sequester large amounts of carbon in their soils. Natural plant colonisation of mudflats as well as future sea-level rise will contribute to new saltmarsh formation and additional managed realignment projects can improve national capacities to meet climate targets. In this study, we’re investigating the current and future extent of saltmarshes in Ireland and estimate their carbon storage potential. The areas of current saltmarshes are identified based on literature and openly available GIS data. The potential natural development and expansion of existing saltmarshes is analysed using mean and extreme water level data from marine tidal gauges and topographic elevation data of the adjacent terrestrial areas. Further, carbon storage in up to 1 m deep soils was determined in various types of saltmarshes in a nationwide field campaign and upscaled to estimate future blue carbon potential. Results show that e.g. saltmarshes in County Dublin could increase from 181 ha to 227 ha due to natural saltmarsh expansion, with a potential increase of stored carbon by 22,688 Mg C_org and avoiding the emission of 83,264 t CO₂. However, saltmarsh depth plays a significant role in carbon sequestration. Thus, when considering carbon storage in only 10 cm deep soils the estimated carbon storage increase is reduced to 1,588 Mg C_org and 5,828 t CO₂ emission avoided. Further, our results indicate that Irish saltmarsh plants sequester less carbon than species in China or the United States, thus lowering global blue carbon estimates. Results of this study will serve as a basis for managers and policymakers estimating carbon credit potentials of saltmarshes and planning Managed Realignment projects.