Uncertainty In Greenhouse Gas Emissions On Carbon Sequestration In Coastal and Freshwater Wetlands of the Mississippi River Delta: A Subsiding Coastline as a Proxy for Future Global Sea Level

Abstract Coastal marshes are an important component of the global carbon cycle, yet our understanding of how these ecosystems will respond to sea level rise (SLR) is limited. Coastal marsh hydrology varies based on elevation, distance from channel, and hydraulic properties, resulting in zones of unique water level oscillation patterns. These zones impact ecology and geochemistry and correspond to differences in carbon accumulation rates. These physical‐biogeochemical linkages enable use of a hydrological model to predict changes in marsh zonation, and in turn carbon accumulation, as well as groundwater‐surface water exchange under SLR. Here, we developed a calibrated hydrological model of a Delaware coastal marsh using HydroGeoSphere. We simulated three scenarios each of SLR, sediment accretion, and upland hydrologic response, and we quantified changes in the spatial coverage of different hydrologic zonations and groundwater‐surface water exchange. Results show that relative SLR reduces marsh area, carbon burial, and lateral water fluxes. However, the magnitudes of change are linked to the terrestrial groundwater table response as well as relative SLR. In scenarios where the upland water table does not change with SLR, the magnitude of decline in marsh area and carbon accumulation is reduced compared to scenarios where the upland water table keeps pace with SLR. In contrast, the reduction in lateral water flux is minimized in scenarios with an upland water table rise equal to SLR compared to scenarios where the upland water table is held at present‐day levels. This study highlights the importance of regional hydrologic setting in the fate of coastal marsh dynamics.

Biogeochemical Cycle

10.1029/2019wr026302

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Coastal Wetland Carbon Sequestration in a Warmer Climate

AGUFM (2016)

Genevieve L. Noyce P. Megonigal Matthew L. Kirwan Roy Rich Paul Dijkstra

Carbon sink

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Implications of Vegetation Shifts on Greenhouse Gas Production in a Coastal Salt Marsh