DETERMINING CARBON STOCKS IN NORTHERN SALT MARSHES

Salt marshes store large amounts of organic carbon, termed ‘Blue Carbon,’ which they accumulate over millennia. Ongoing losses of salt marsh area to disturbance and sea level rise can release carbon in these stores back into the atmosphere, but the magnitude of such losses is difficult to estimate as few marsh-wide carbon stocks have been developed. Much of the current research into salt marsh carbon storage has focused on burial rates and surface stocks often limited to depth of 30 cm or less. To accurately estimate marsh-carbon stocks we need to document peat depths which are related to marsh morphology, antecedent topography, and geomorphic processes (ice, spit migration, panne formation, etc.).

We are investigating whether specific types of marsh have typical depths, bulk density and carbon content starting with salt marshes on lagoons protected by barrier beaches and those associated with migrating spits on the coast of the Maine and eastern Canada, sampling depths and collecting cores at key locations. The presence of non-marsh subsurface deposits and freshwater marsh deposits can complicate the estimation of salt marsh carbon stocks. Over wash deposits from barriers and spits can be misinterpreted as the base of the marsh or skew measurements of bulk density from which carbon density, thus carbon stocks are derived. Freshwater marsh deposits are often found below the salt marsh deposit. It is not clear whether they should be calculated as part of the Blue Carbon stock, but these older deposits may be susceptible to loss if the overlaying salt marsh deposit is lost. Dealing with these complications is vital before developing regional carbon stock estimates.