Modeling Marsh Dynamics Using a 3-D Coupled Wave-Flow-Sediment Model

Abstract

Salt marshes are dynamic biogeomorphic systems that respond to external physical factors, including tides, sediment transport, and waves, as well as internal processes such as autochthonous soil formation. Predicting the fate of marshes requires a modeling framework that accounts for these processes in a coupled fashion. In this study, we implement two new marsh dynamic processes in the 3-D COAWST (coupled-ocean-atmosphere-wave sediment transport) model. The processes added are the erosion of the marsh edge scarp caused by lateral wave thrust from surface waves and vertical accretion driven by biomass production on the marsh platform. The sediment released from the marsh during edge erosion causes a change in bathymetry, thereby modifying the wave-energy reaching the marsh edge. Marsh vertical accretion due to biomass production is considered for a single vegetation species and is determined by the hydroperiod parameters (tidal datums) and the elevation of the marsh cells. Tidal datums are stored at user-defined intervals as a hindcast (on the order of days) and used to update the vertical growth formulation. Idealized domains are utilized to verify the lateral wave thrust formulation and show the dynamics of lateral wave erosion leading to horizontal retreat of marsh edge. The simulations of Reedy and Dinner Creeks within the Barnegat Bay estuary system demonstrate the model capability to account for both lateral wave erosion and vertical accretion due to biomass production in a realistic marsh complex. The simulations show that vertical accretion is dominated by organic deposition in the marsh interior, whereas deposition of mineral estuarine sediments occurs predominantly along the channel edges. The ability of the model to capture the fate of the sediment can be extended to model to simulate the impacts of future storms and relative sea-level rise (RSLR) scenarios on salt-marsh ecomorphodynamics.

A Minimalist Model of Salt-Marsh Vegetation Dynamics Driven by Species Competition and Dispersal

“…This can create potential hotspots for biodiversity (Elsey-Quirk et al, 2019) and determine changes in vegetation distribution according to the ability of individual species to tolerate such stresses, which in turn depends on the specific vegetation traits (Leonard and Croft, 2006;Van Wesenbeeck et al, 2008;Schoutens et al, 2020;Schulte Ostermann et al, 2021). On the one hand, some of the abiotic factors, especially the hydrodynamic ones, could be included rather easily in the model, for example by weighting the habitat quality based on stresses calculated from hydrodynamic models or, alternatively, as a function of the distance of each site from marsh edges exposed to the action of waves and currents (see for example Gourgue et al, 2021a;Kalra et al, 2021). On the other hand, however, most of the biotic factors affecting vegetation dynamics are difficult to conceptualize, as they depend on the community ecology of marsh fauna (Gaskins et al, 2020;Burdick et al, 2021;Pennings and He, 2021).…”

“…Our model can be coupled with virtually any hydromorphodynamic model to simulate the intertwined evolution of marsh halophytes and topographic gradients under varying rates of relative sea-level rise and sediment supply. If the models employ different types of grids or spatial resolutions, the coupling can also be performed using subgrid schemes together with appropriate multiscale coupling techniques (e.g., Gourgue et al, 2021a;Gourgue et al, 2021b;Kalra et al, 2021). The evolution of marsh topography at each site will be obtained by a combined geomorphological balance between erosion and sedimentation, computed by the morphodynamic model, and organic production by halophytic vegetation, calculated by the vegetation model.…”

“…First, fundamental species niches are typically approximated by the realized ones. Therefore, although field studies suggest performances of individual species to increase steadily with elevation in the absence of competition, habitat quality and vegetation performances are typically assumed to peak at an optimum marsh elevation, and to decrease as elevation moves away from such optimum (Morris et al, 2002;Morris, 2006;Morris, 2007;D'Alpaos et al, 2007;Kirwan and Murray, 2007;Kirwan and Guntenspergen, 2010;Fagherazzi et al, 2012;Da Lio et al, 2013;Marani et al, 2013;Kirwan et al, 2016;Geng et al, 2021;Kalra et al, 2021;Sgarabotto et al, 2021). Second, competition in numerical models of marsh vegetation dynamics, with few exceptions (e.g., Marani et al, 2006), does not occur by direct species interaction.…”

Modeling the Dynamics of Salt Marsh Development in Coastal Land Reclamation

“…Details on model coupling can be found in Warner et al (2010). For the application presented in this work, we adopted the sediment transport and marsh routines presented in Kalra et al (2021). Updated model framework can be found in supplemental materials (Figure S5 in Supporting Information S1)…”

“…In this work, we use a coupled vegetation‐hydrodynamic‐morphological model to study the development of a marsh via vegetation colonization and its relationship with forcing conditions. The Coupled‐Ocean‐Atmosphere‐Wave‐Sediment Transport (COAWST) Modeling System (Warner et al., 2010) is used, with a newly developed vegetation module (Kalra et al., 2021). We were able to simulate marsh development in an idealized basin and monitor sediment fluxes and feedbacks with vegetation through a varying range of sediment, SLR, and tidal conditions.…”