2025 CSDMS meeting-102
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Theoretically and Empirically based modeling of the evolution of multi-species marshes
Conner Lester1, A. Brad Murray1, Morgan Alexander1, Nathaniel Blackford1, Andrea D’Alpaos2, Orencio Duran3, Marco Marani2, Tegan Blount2, Daniella Rubio1, Sonia Silvestri4, Zhicheng Yang1,5
1Duke University, USA 2 University of Padova, Italy 3 Texas A&M University, USA 4 University of Bologna, Italy 5 University of Georgia, USA Corresponding author: abmurray@duke.edu
1 Introduction
We have developed a simple, empirically and theoretically based approach to modeling how coastal marshes respond to changes in the rate of sea level rise (SLR) and sediment concentration. This approach produces plan view distributions of elevations and the densities of multiple marsh species and bare soil, for any combination of suspended sediment concentration in a channel network and SLR rate, for specific marshes.
2 Modeling Approach
The approach involves techniques to detect the spatial distributions of fractional cover and biomass densities of multiple marsh species from satellite observations. These techniques were developed using a combination of field observations and drone and airborne lidar and multispectral data from the East Coast of the United States and the Venice Lagoon, and can be applied to any coastal environment with similar mixes of vegetation types. Biomass density can be treated as a function of elevation, resulting in the realized niches of observed vegetation species, or mixtures of species.
The approach also involves results showing that, within marsh basins, tidal current velocities and rates of inorganic sediment deposition are essentially independent of biomass. Given this simplification, and the relationship between biomass density and elevation (realized niches), solving for equilibrium depths and biomass densities as a function of distance from the nearest channel becomes straightforward (Figure 1).
The rate of change of depth D (below high-water level) is given by:
∂D/∂t=R-A_inorg-A_org (1)
where R is the rate of SLR, Ainorg and Aorg are the rates of accretion of inorganic and organic sediment, respectively. Ainorg is equal to DC, where C is sediment concentration. In Figure 1 equilibrium depths (∂D/∂t=0;R-A_inorg=A_org) are graphically determined.
Figure 1: (Top) Hypothetical relationship between Aorg (proportional to biomass density) and D for multiple species (different colors) and mixtures of species. (Bottom) Graphical representation of equilibria in Equation (1) for some future R. Slanting lines represent Ainorg at different nondimensional distances from a channel (with C decreasing with distance from a channel). Intersections between the slanting lines and the curve represent equilibrium depths at different distances from a channel. Sections of the curve that are not intersected by slanting lines represent topographic steps and abrupt vegetation zonation. (Equilibria are unstable when the local slope of the curve is more negative than the slope of the intersecting line.)
Acknowledgments
Supported by the US NSF Geomorphology and Land Use Dynamics program (2016068), and AA, MM, and SS were also supported by the RETURN Extended Partnership and received funding from the European Union Next-GenerationEU (National Recovery and Resilience Plan – NRRP, Mission 4, Component 2, Investment 1.3 – D.D. 1243 2/8/2022, PE0000005).| [[Image:|300px|right]] |
