Carbon Sequestration Potential of Coastal Restored Wetlands

Predicting and understanding wetland radiative forcing is currently limited by incomplete and temporally coarse wetland carbon accounting, as well as a deficient understanding of how tidal exchange, elevation, and salinity gradients influence the transformation, import, and export of carbon compounds in wetlands (Anderson et al. 2016; Ferner 2011). Improving such knowledge and predictions is needed to guide management and policy decisions at local, regional, and national levels. Here we present CO2 and CH4 fluxes of the two longest running side-by-side restoring and reference salt marsh eddy covariance flux tower sites, located at the Billy Frank Jr. Nisqually National Wildlife Refuge in Puget Sound. We further analyze how wetland elevation, tidal variation, and salinity influence fluxes from each site. From 2017 to 2019 the reference wetland was a strong carbon sink, with high CO2 uptake and low CH4 release. The restoring site was a weak carbon source; however, annual CO2 uptake increased over the course of this study. Further, evidence from these sites suggests that how tides impact wetland carbon fluxes may differ by wetland elevation. These findings indicate novel/key parameters for wetland carbon and radiative forcing modelling, and also transform our approach of, and expectations for, wetland restoration.