Effect of restoration on saltmarsh carbon accumulation in Eastern England

Wetland soils are globally important carbon stores, and natural wetlands provide a sink for atmospheric carbon dioxide (CO₂) through ongoing carbon accumulation. Recognition of coastal wetlands as a significant contributor to carbon storage (blue carbon) has generated interest into the climate change mitigation benefits of restoring or recreating saltmarsh habitat. However, the length of time a re-created marsh will take to become functionally equivalent to a natural (reference) system, or indeed, whether reference conditions are attainable, is largely unknown. Here, we describe a combined field chronosequence and modelling study of saltmarsh carbon accumulation and provide empirically based predictions of changes in the carbon sequestration rate over time following saltmarsh restoration. Carbon accumulation was initially rapid (average 1.04 t C ha^-1 yr^-1 during the first 20 years), slowing to a steady rate of around 0.65 t C ha^-1 yr^-1 thereafter. The resulting increase in C stock gave an estimated total C accumulation of 74 t C ha^-1 in the century following restoration. This is approximately the same as our observations of natural marsh C content (69 t C ha^-1), suggesting that it takes approximately 100 years for restored saltmarsh to obtain the same carbon stock as natural sites.