Alkalinity enhancement and carbon capture potential in blue carbon ecosystems

Blue carbon ecosystems (BCEs) such as seagrass meadows, and mangrove forests provide a wide range of ecosystem services including, but not limited to, coastal protection and fisheries enhancement. By transferring carbon dioxide to organic biomass and ultimately burying it in the sediment, BCEs have the potential to also serve as sites of economically viable carbon dioxide removal. Most BCE studies have focused on the potential role and complications of enhanced organic carbon storage. In contrast the potential impact that these ecosystems may have on altering the benthic flux of alkalinity and dissolved inorganic carbon is more poorly constrained. We provide a new look at how BCE can affect shallow marine alkalinity budgets using a newly constructed time-dependent sediment diagenetic model that simulates the cycling of carbon (in both organic and inorganic forms), iron, sulfur, nitrogen and methane in seagrass and mangrove ecosystems. We found that restoring mangroves and seagrass ecosystems can, on an annual basis, foster significant 'permanent' atmospheric carbon dioxide removal through ocean alkalinity enhancement with only a minor increase in diffusive methane fluxes.