Biogeomorphology of tidal landforms: physical and biological processes shaping the tidal landscape

We analyse the equilibrium states and transient dynamics of tidal biogeomorphic systems, such as lagoons and estuaries, in response to variations in the governing physical and biological forcings, such as tidal range, wind climate, sediment supply, vegetation, and microphytobenthos growth, and rates of relative sea level rise (RSLR). We use a point model of the coupled elevation–vegetation dynamics, which retains the description of the chief processes shaping these systems. We observe that salt marshes exposed to large tidal ranges are more stable, and therefore more resilient to increasing rates of RSLR, than marshes subjected to low tidal ranges. Furthermore, subtidal platforms in macrotidal systems are less exposed to wind-induced erosion processes than their counterparts in systems with smaller tidal fluctuations. Notably, we find that vegetation crucially affects both the equilibrium marsh elevation, through dissipation of wind waves and organic accumulation, and marsh resilience to accelerations in RSLR rates. Moreover, the biomass production as a function of elevation associated with the presence of different vegetation species, as opposed to mono-specific vegetation covers, increases marsh stability and resilience in the face of increasing rates of RSLR. Finally, our results show that the existence and stability of equilibrium states fundamentally depend on the local wind and tidal regime, even within the same tidal system, with important biogeomorphic implications. In summary, our model analyses of physical and biological controls of tidal system dynamics highlight the importance of accounting for biogeomorphic feedback to obtain realistic representations of the system dynamics in response to climatic changes