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 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.