Spatial gradients in dissolved carbon due to tidal marsh outwelling into a Chesapeake Bay estuary

Tidal marshes have been previously shown to affect fluxes of carbon and nutrients in adjacent estuaries by acting as sources, sinks or transformers of compounds transported in water exchanged between the marsh and estuary. Relative to information on the amount and direction of these exchanges, much less is known about the distribution and fate of the distinctive dissolved organic compounds derived from marshes, and the spatial extent to which this 'marsh signature' affects optical and biogeochemical variability in the estuary. In the present study we address the spatial distribution of both dissolved organic carbon (DOC) and dissolved inorganic carbon (DIC), as well as other biogeochemical components, in the Rhode River estuary-marsh complex of the Chesapeake Bay. High-spatial-resolution transects showed that the marshes are a major source of DOC, DIC and pCO(2) to the adjacent estuary and atmosphere, and that they seem to trap algae and other suspended particulate matter while releasing high-molecular-weight, aromatic-rich, highly colored dissolved organic matter (CDOM) into the estuary through tidal flushing. These processes result in strong variability in water characteristics considerably beyond the marsh-estuary interface. Non-conservative mixing in CDOM with salinity was probably due to both intense processing of the more labile marsh-exported components, as well as to mixing with other terrestrial and wetland inputs into the estuary. Despite the possible role of the adjacent subtidal mudflat as a sink for some of the material released from the marshes, the marsh signature was distinguishable from the regional estuarine background over a distance of more than 1 km into the river.