COUPLING OYSTER REEF WITH SALTMARSH ENHANCES CARBON STORAGE IN THE FACE OF SEA-LEVEL RISE

As some of the only hard substrate along the Atlantic and Gulf of Mexico coasts, oyster reefs are highly touted as green infrastructure for shoreline protection in the face of damaging storms and wave-induced erosion, particularly when coupled with fringing marsh. While the presence of an oyster reef may enhance the capacity of saltmarshes to protect coastal infrastructure, it is unclear how the proximity of these two habitats may impact other ecosystem services, like a reef’s capacity for growth and a marsh’s ability to sequester carbon. In an effort to obtain a greater understanding of the interaction of these adjacent habitats, transects of sediment cores and terrestrial lidar data were collected within different marsh and reef settings (i.e. oyster reefs connected to marsh, unprotected marsh, and isolated patch reefs) of Back Sound and North River Estuary, North Carolina. Sediments were analyzed for grain size and carbon content, and reef growth was measured from digital elevation models collected across 1- and 2-year time steps at various shoreline morphologies (e.g., fringing reef, groin reef, etc.). Sediment analyses indicated that reef presence has minimal effect on marsh sediment composition, and differences in sediment composition is driven more by geographic location of the marsh. Most notably, almost all fringing reefs began transgressing their respective marsh shorelines within the last century and preservation of the carbon-rich marsh sediment below the reef is high. Marsh is completely eroded in areas where shoreline transgression is progressing in the absence of a fringing reef. We have also observed preservation of marsh sediment below ancient (>4 ka) buried oyster reefs. In addition to reducing marsh-shoreline erosion rates, fringing oyster reefs increase the preservation potential of marsh organic carbon by capping the marsh during transgression. Erosion of marsh sediment will allow most of the buried organic carbon to be remineralized and released back into the atmosphere.