Coastal wetland response to sea level rise in a marine and fluvial estuarine system

Abstract:

Coastal wetlands are at the risk of losing their productivity under increasing rates of sea level rise (SLR). Studies show that under extreme enough stressors, salt marshes will not have time to establish an equilibrium and may migrate landward (Donnelly and Bertness 2001; Warren and Niering 1993) or become open water.

In order to investigate salt marsh productivity under SLR scenarios, an integrated hydrodynamic-marsh model was incorporated to dynamically couple physics and biology. The hydrodynamic model calculates mean high water (MHW) and mean low water (MLW) within the river and tidal creeks by analysis of simulated tidal constituents. The response of MHW and MLW is nonlinear due to local changes in the salt marsh platform elevation and biomass productivity. Spatially-varying MHW and MLW are utilized in a biologic model that is a two-dimensional application of the Marsh Equilibrium Model (Morris et al. 2002) to capture the effects of the hydrodynamics on biomass productivity and accretion.

Including accurate marsh table elevations into the model is crucial to obtain accurate biomass productivity results. A lidar-derived Digital Elevation Model (DEM) is corrected by incorporating Real Time Kinematic (RTK) surveying elevation data. Additionally, salt marshes continually adapt themselves to reach an equilibrium, in which there are ideal ranges of relative SLR and depth of inundation to increase biomass productivity (Morris et al. 2002). The inputs of the model are updated using the biomass productivity results at each coupling time step to capture the interaction between the marsh and hydrodynamic models.

The hydro-marsh model is used to assess the effects of four projections of SLR (Parris et al., 2012) on salt marsh productivity for the year 2100 for the marine dominated Grand Bay, MS estuary and the fluvial dominated Apalachicola, FL estuary. The results show higher productivity under a low SLR scenario and less productivity under the intermediate low SLR. Most of the salt marshes become flooded and some of them migrate under higher SLR scenarios. These examples show how this tool can be used in any estuarine system to project salt marsh productivity and accretion under sea level change scenarios to better interpret responses and improve restoration and planning management decisions.