Sea-Level Rise Impact on Salt Marsh Sustainability and Migration for a Subtropical Estuary: GTMNERR (Guana Tolomato Matanzas National Estuarine Research Reserve)

Sea-level rise impacts on salt marsh for Guana Tolomato Matanzas National Estuarine Research Reserve are investigated using field measurements (six sites within the marsh) and a tide-marsh equilibrium model (Hydro-MEM). The hydrodynamic component of the model enables for prediction of spatially variable tidal data (mean low water and mean high water), which are coupled with a marsh equilibrium model (MEM) for prediction of spatially based biomass productivity of Spartina alterniflora. The field measurements corroborate the model results by way of prediction of relatively productive marsh at four of the six sites (percent coverage of Spartina alterniflora of 30–41%, canopy height of 0.27–0.67 m and simulated biomass density of greater than 750 g m−2 over at least half of the local area within 500-m radii of the measurement sites) and relatively limited marsh at the two other sites (percent coverage of Spartina alterniflora of 3–5%, canopy height of 0.11–0.29 m, and simulated biomass density of greater than 750 g m−2 over less than one-tenth of the local area within 500-m radii of the measurement sites). The model is applied in a coupled fashion for 50 years of time into the future using ten 5-year increments, where each increment of Hydro-MEM accounts for the natural accretion of the marsh, an update of the digital elevation model and bottom-friction parameterization, and the subsequent feedback to the hydroperiod and marsh productivity. Hydro-MEM is shown to exhibit rate-sensitivity with respect to sea-level rise exceeding the marsh accretion rate, whereby a sudden loss of marsh elevation occurs in such instances of marsh destabilization. Demonstrating rate-critical transition, the model proves flexible to account for the non-homogeneous and transient nature of the fast-slow variables, whereby the marsh migrates away from the tidal creeks and further into the upland zones. Practical implication of the model results is illustrated by identifying zones of lands into which marsh will be able to migrate and where existing marsh will not survive under increasing sea level. Post-analysis compares the final model output against land use/cover zonation to correct the 50-year simulation results of marsh productivity for elevation-appropriate regions but that are developed, freshwater, or otherwise inappropriate land type for salt-marsh habitat.