Drivers of blue carbon dynamics in saltmarsh ecosystems

Political and economic interest in blue carbon as a natural climate solution has grown exponentially in recent years. In particular, the effective management of coastal wetlands, including saltmarshes, via conservation and restoration, is an attractive climate change mitigation tool. However, to become a scalable natural climate solution, a better understanding of the drivers governing blue carbon dynamics is required. Therefore, this thesis sought to identify drivers of blue carbon dynamics to guide effective coastal management. Work to investigate the influence of sea-level rise on carbon accumulation and stocks, and to determine major fine-scale drivers responsible for carbon stock variability between restored saltmarshes was conducted. Societal perceptions of blue carbon and coastal wetlands were also explored to address the growing need for trans-disciplinary approaches to ensure the longevity of blue carbon management.

Sea-level rise was a dominant control on saltmarsh carbon accumulation rates and drove spatial and temporal patterns across the 20th century. However, evidence from a regional study showed declines in carbon stock when saltmarshes were unable to keep pace with more recent rates of sea-level rise. Further research is required as global sea-level rise continues to accelerate. Work to identify fine-scale drivers of carbon stocks in restored saltmarshes found sites elevated above mean high water neap tidal levels had significantly higher carbon stocks, likely driven by suitable conditions for mature vegetation communities, including key plant species. Together, these findings can inform future restoration schemes that aim to maximise blue carbon stocks. Finally, a limited public awareness of blue carbon and a low connection with coastal wetlands was found, with implications for societal support of coastal wetland management. Targeted education and outreach campaigns, based on sociodemographic characteristics, are recommended.

Overall, this thesis has contributed new knowledge to progress blue carbon science and guide effective saltmarsh management for climate change mitigation.