Closing the salt marsh dissolved organic carbon (DOC) outwelling budget: sediment fluxes

Outwelling of dissolved and particulate matter from salt marshes has been observed for decades, but has been difficult to quantify due to the dynamic and heterogeneous nature of these systems. In addition to quantifying the total dissolved organic carbon (DOC) outwelling from the Neponset Salt Marsh in Boston, Massachusetts by examining the DOC exported from the mouth of the estuary to Boston Harbor, this study has attempted to delineate the DOC outwelling by source. Direct leaching from the above- and below-ground vegetation accounted for~20% of the total export while photodissolution from resuspended sediment could account for ~25% of the total export. This presentation will focus on the contributions from marsh sediment leaching. Incubating sediments from three different heights (low marsh, Spartina-dominated areas) and replicating tidal fluctuations led to sediment contributions of 30-45% of the total outwelling budget, varying with the height of the marsh sediments. The changing influence of salt marshes on carbon export over tidal cycle, season, and climate change will be discussed.