Intertidal marsh as a source of dissolved inorganic carbon and a sink of nitrate in the Satilla River‐estuarine complex in the southeastern U.S.

Total dissolved inorganic carbon (DIC), total alkalinity (TA), pH, and nitrate + nitrite (NO x ) data collected during the summer of 1996 in the Satilla River estuary in the southeastern U.S. were used to assess fluxes of DIC and NO x between intertidal marshes and estuarine waters and to model system NO x dynamics. Nitrate and nitrite are produced in the low‐salinity portion of the estuary. The intertidal marshes are sites of intensive respiration that export DIC to the estuary and remove NO x . An integrated view is presented on the nitrification and denitrification processes in the marsh/estuarine complex and their relationship to CO 2 generation rates. The distribution of NO x in the marsh and estuarine waters indicates that all NO x generated in the marsh‐estuary system is removed in the intertidal marshes, most likely via denitrification. Model analysis of NO x and river flow data for three seasons indicates that NO x distribution in the estuarine water is also determined by river flow rates. Export fluxes of NO x to the coastal ocean are insignificant in all seasons when compared to NO x production rates in the entire system; however, they are significantly higher than NO x inputs from the river end member in October 1996. Although only a small fraction (~10%) of DIC generated in the marshes is exported to the coastal sea and around 90% is lost to the atmosphere, it represents a nearly threefold increase in riverine DIC flux to the ocean.