Shifting Shores: Carbon Storage and Habitat Resilience in a Major Scottish Saltmarsh

Abstract Saltmarshes are dynamic but vulnerable coastal ecosystems that play an important role in blue carbon sequestration, nature conservation, and flood defence. Shifting river channels, rising sea levels and increased storm frequency threaten these habitats, potentially disrupting the delicate balance of accretion and erosion. However, this study of Caerlaverock merse, Scotland’s largest saltmarsh, reveals a habitat that adapts to environmental change through vertical and horizontal accretion and new terrace formation. An analysis of 293 cores shows an organic carbon (OC) stock of 43.6 ± 6.6 kt in the top 30 cm of saltmarsh sediment, with OC density increasing from pioneer through to upper saltmarsh zones. Analysis of high-resolution (25 cm) aerial photography revealed a net areal accretion of saltmarsh ranging from 2.8 to 16.6 hectares across two seasonally matched periods (2014–2018 and 2015–2021), highlighting the saltmarsh’s resilience in maintaining blue carbon stocks and critical ecosystem services. Nevertheless, because higher OC-content middle (3.85 ± 0.92 kg m −2 , top 30 cm) and lower (2.96 ± 1.03 kg m −2 ) saltmarsh is being eroded and replaced with lower OC-content pioneer saltmarsh (1.82 ± 0.48 kg m −2 ), there is a net OC loss in the short term, though with longer-term succession to lower and middle saltmarsh, this deficit will be reversed. These findings provide valuable insights for saltmarsh conservation and management in response to changing climatic conditions.