Nitrogen exchange between a southeastern USA salt marsh ecosystem and the coastal ocean

Abstract

The salt marsh ecosystem at North Inlet, South Carolina, USA consistently exported dissolved inorganic nitrogen via tidal exchange with the coastal Atlantic Ocean. Concentrations centrations of NH 4 + and NO 3 - +NO 2 - displayed distinct tidal patterns with rising values during ebb flow. These patterns suggest the importance of biogeochemical processes in the flux of material from the salt marsh. NH 4 + export peaked during the summer (15 to 20 mg m-2 tide-1) during a net balance of tidal water exchange. Remineralization of NH 4 + within the salt marsh system appears to be contributing to the estimated annual net export of bout 4.7 g NH 4 + -N m-2 yr-1. NO 3 - +NO 2 - exports were higher in the fall and winter of 1979 (2 to 4 mg N m-2 tide-1). The winter export coincided with a considerable net export of water with no distinctive concentration patterns, suggesting a simple advective export. However, the fall peak of NO 3 - +NO 2 - export occurred during a period of net water balance in tidal exchange and an insignificant freshwater input from the western, forested boundary. During the summer and fall, tidal concentration patterns were particularly apparent, suggesting that nitrification within the salt marsh system was contributing to the estimated annual net export of ca 0.6 g NO 3 - +NO 2 - -N m-2 yr-1.