Sea-Level Rise Impact on a Salt Marsh System of the Lower St. Johns River

The impact of sea-level rise on salt marsh sustainability is examined for the lower St. Johns River and associated salt marsh (Spartina alterniflora) system. A two-dimensional hydrodynamic model, forced by tides and sea-level rise, is coupled with a zero-dimensional marsh model to estimate the level of biomass productivity of S. alterniflora across the salt marsh landscape for present day and anticipated future conditions (i.e., when subjected to sea-level rise). The hydrodynamic model results show mean low water (MLW) to be highly spatially variable with a SD of +/- 0.18 m and mean high water (MHW) to be less spatially variable with a SD +/- 0.03 m. The spatial variability of MLW and MHW is particularly evident within the tidal creeks of the salt marsh. MLW and MHW are sensitive to sea-level rise and respond in a nonlinear fashion (i.e., MLW and MHW elevate by an amount that is not proportional to the level of sea-level rise). The coupled hydrodynamic-marsh model results illustrate the spatial heterogeneity of biomass productivity and indicate marsh vulnerability to sea-level rise. The model is then used to demonstrate an application of engineered accretion that can help sustain a marsh that is exposed to sea-level rise. DOI: 10.1061/(ASCE)WW.1943-5460.0000177. (C) 2013 American Society of Civil Engineers.