Carbon storage and sequestration in Irish saltmarsh habitats

Coastal wetlands are recognised for the vital role they play in climate change mitigation and adaptation. In particular, coastal wetlands are efficient ecosystems for sequestering and storing carbon. Regional estimates of carbon stocks and rates of carbon accumulation are often lacking, particularly for the temperate Northeastern Atlantic region. To address this knowledge gap, I conducted a national carbon stock assessment of 23 saltmarshes in Ireland to determine the magnitude of their carbon inventory and to understand the variability between different morphology types. The carbon density per hectare was 145.28 ± 2.58 Mg Corg ha-1 resulting in a carbon stock of over 950,000 Mg Corg, with the main drivers of variability being the composition and origin of the substrate. To understand the annual increase in carbon stock, I analysed the sediment and carbon accumulation rates of 13 saltmarshes of varying geographical locations through marker horizons and radiometric dating. Through these techniques, the annual present and historic carbon accumulation rate were estimated as 0.018 ± 0.002 g Corg cm-2 and 0.0077 ± 0.0005 g Corg cm-2, respectively. Lastly, I determined the contribution of an invasive species (Spartina anglica) on the carbon storage and accumulation rates. Areas of S. anglica swards were found to store 78.4 ± 6.0 Mg Corg ha-1, and a national total of 105,918 ± 8,106 Mg Corg. Spartina anglica-dominated areas were also found to annually accumulate 40% more sediment and 15% more carbon. Overall, the saltmarshes of Ireland have a below average carbon density and an average carbon accumulation rate on a global scale. This research provides the backbone for Tier 2 data for IPCC National Inventory Reporting and expands our understanding of carbon dynamics in saltmarsh ecosystems in the temperate Northeastern Atlantic region. This will ultimately underpin improved management for the protection and restoration of these habitats.