2024 CSDMS meeting-043


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Quantifying Methane Emissions in a Tidal Marsh System: Insights from a Morphodynamic Model

Eric Dammann, (He/Him),Montclair State University Montclair New Jersey, United States. dammanne1@montclair.edu
Jorge Lorenzo-Trueba, Montclair State University Montclair New Jersey, United States. lorenzotruej@montclair.edu
Charles Schutte, Rowan University Glassboro New Jersey, United States. schutte@rowan.edu

Tidal marshes store blue carbon because biomass production by vegetation exceeds organic matter decomposition. When methanogenic microorganisms drive decomposition, organic biomass decomposes into methane, a greenhouse gas with a higher warming potential than carbon dioxide. As sulfate availability increases sulfate-reducers outcompete methanogens, and methane production decreases. Such a shift from methanogenesis to sulfate reduction as the predominant decompositional pathway can occur within tidal marshes experiencing sea level rise (SLR), as marsh inundation by saline water increases. Additionally, SLR can lead to changes in marsh morphology and extent. To address this interplay, we adapt a cross-shore numerical model for the evolution of a marsh-lagoon system to predict methane emissions over decadal time scales and under different SLR scenarios, via the addition of a novel biogeochemical module. We compute total methane emissions by integrating the methane flux at each location over the width of the marsh platform, which is controlled by the rate of SLR, the wave energy in the lagoon, and the rate of marsh upland migration. We calculate the methane flux at a given location as a function of its distance from the edge of the marsh/lagoon boundary and the labile carbon available for decomposition. We test the morphodynamic component of the model on marshes along the Great Bay near the outlet of the Mullica River in southern New Jersey. The model can reproduce the magnitude of morphological change seen in the historical data from 1986-2020. In particular, the model captures that the marsh is eroding faster at the marsh/lagoon boundary than it is being gained by landward migration of the marsh/mainland boundary. Preliminary results of the coupled biogeochemical and morphodynamic model show that generally methane emissions increase with higher rates of SLR, however certain environmental conditions allow for scenarios in which higher rates of SLR lead to lower methane emissions.