Dissolved Organic Matter Export from Surface Sediments of a New England Salt Marsh

Salt marshes sequester a large amount of carbon via sedimentation, but seasonal and climate change impacts on sediment carbon biogeochemistry are not well-understood. This study investigates the export of dissolved organic carbon (DOC) and chromophoric dissolved organic matter (CDOM) from New England salt marsh sediment seasonally and under possible expected drought conditions. Surface sediment total organic carbon (TOC) values shifted seasonally depending on the overlying dominant plant species suggesting that vegetation and inundation frequency and duration are key factors in sediment TOC fluctuations. Fall sediment samples leached more DOC than summer samples, were compositionally similar to the estuarine water column, and compositionally different from fresh plant matter. Thus, the seasonal TOC pulse incorporated into surface sediments could be a dominant source of DOC to the estuary in the fall and that summer contributions are presumed to be from upstream DOM sources based on optical properties. Sediments leached more DOC under drought than non-drought conditions due to induced cracking in the sediment enhancing organic matter degradation. This study suggests the majority of DOM exported laterally from salt marshes comes from surface sediments (versus plant matter) and that temperature and sea-level rise could affect seasonal and drought pulses of DOC from the marsh.