Comment:

Product of the optional Accretion module. Within the SLAMM model, “accretion” is used as a catch-all phrase to represent marsh-elevation change under different rates of sea-level rise, including shallow subsidence. Four separate accretion-feedback models are available for “regularly-flooded marsh,” “irregularly-flooded marsh,” “tidal flats,” and “tidal-fresh marsh” categories. Vertical movement of other habitats (Inland-Fresh Marsh, Mangrove, Swamps, and Beaches) are modeled as constants (“elevation gain in mm/year”) though with a minor source-code modification a feedback model as shown above can be (and has been) used for these categories when adequate data or models are available. A more sophisticated approach can be to first model accretion by calibrating a mechanistic accretion model such as the Marsh Equilibrium Model (MEM) (Morris et al. 2002). A mechanistic model can be calibrated using available physical and biological data affecting accretion (e.g. tide ranges, suspended sediment concentrations, concentration density of standing biomass, organic matter decay rates, belowground biomass, and observed accretion rates). Once the model calibration is established, results can be translated into polynomial curves that are a function of marsh elevation, and these curves can be entered into SLAMM.