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Marsh morphodynamics models are usually calibrated using sparse short-term measurements. Hence, their ability to predict long-term trajectories (centuries to millennia) is highly uncertain. Here I improved an existing model for marsh ecomorphodynamics and used it to hindcast the whole morphodynamic trajectory (2500 years) of an actual salt marsh in New England (USA). The model includes enough processes – among which tidal currents and waves, sand and mud transport, and vegetation population dynamics – to simulate a realistic marsh analogue that closely matches the modern topobathymetry and stratigraphy. Marsh trajectory is highly sensitive to initial bathymetry, mud supply from the nearshore, wave erosion processes, and vegetation dynamics. Each one of these factors is important yet difficult to calibrate on its own. Matching the long-term evolution with the stratigraphic record provides a global constraint for the processes and parameters in the model, increasing the confidence in future long-term predictions. This type of comparison complements those made at short times scales, and it should be used more routinely. [ABSTRACT FROM AUTHOR]

High-lying vegetated marshes and low-lying bare mudflats have been suggested to be two stable states in intertidal ecosystems. Being able to identify the conditions enabling the shifts between these two stable states is of great importance for ecosystem management in general and the restoration of tidal marsh ecosystems in particular. However, the number of studies investigating the conditions for state shifts from bare mudflats to vegetated marshes remains relatively low. We developed a GIS approach to identify the locations of expected shifts from bare intertidal flats to vegetated marshes along a large estuary (Western Scheldt estuary, SW Netherlands), by analyzing the interactions between spatial patterns of vegetation biomass, elevation, tidal currents, and wind waves. We analyzed false-color aerial images for locating marshes, LIDAR-based digital elevation models, and spatial model simulations of tidal currents and wind waves at the whole estuary scale (~326 km²). Our results demonstrate that: (1) Bimodality in vegetation biomass and intertidal elevation co-occur; (2) the tidal currents and wind waves change abruptly at the transitions between the low-elevation bare state and high-elevation vegetated state. These findings suggest that biogeomorphic feedback between vegetation growth, currents, waves, and sediment dynamics causes the state shifts from bare mudflats to vegetated marshes. Our findings are translated into a GIS approach (logistic regression) to identify the locations of shifts from bare to vegetated states during the studied period based on spatial patterns of elevation, current, and wave orbital velocities. This GIS approach can provide a scientific basis for the management and restoration of tidal marshes.