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Fantastic Wetlands and Why to Monitor Them: Demonstrating the Social and Financial Benefit Potential of Methane Abatement through Salt Marsh Restoration in Massachusetts, U.S.A.
Citation:
Reilly, A., N. Merrill, K. Mulvaney, P. Colarusso, AND E. Burman. Fantastic Wetlands and Why to Monitor Them: Demonstrating the Social and Financial Benefit Potential of Methane Abatement through Salt Marsh Restoration in Massachusetts, U.S.A. RAE Coastal & Estuarine Summit 2022, New Orleans, LA, December 04 - 08, 2022.
Impact/Purpose:
Salt marshes can be a source of excess methane, a powerful greenhouse gas. This study estimates the greenhouse gas benefits of restoring freshening salt marsh. Freshening referes to marsh, whose salinity is lower than natural due to human factors, like road culverts. We estimate the monetary benefits of restoring salt marsh to nature salinity using the social cost of carbon and equivalents.
Description:
Salt marsh restoration has the potential to reduce greenhouse gas emissions thereby providing an opportunity for blue carbon crediting, but implementation has been restricted to date because of limited data and validation. Salt marshes are critical coastal ecosystems that provide a slate of ecosystem services, including fish and wildlife habitat, recreation, greenhouse gas (GHG) storage, and more. Freshening salt marshes are sources of methane emissions, which presents an opportunity for states to address this source of potent GHG emissions if restored to their more saline state. In this paper, we demonstrate the potential scale of methane emissions that could be avoided if salinity-reducing impairments are mitigated by applying findings from six salt marsh restoration sites in Massachusetts combined with meta-analyses of the salt marsh salinity-methane relationship. Of the six sites selected, restoration at three sites were successful in improving salinity. We found that restoration of these impaired salt marshes (22.7 hectares total) may have contributed to abating 239 - 435 metric tons (Mts) of CO2-equivalent emissions annually (0.20 – 0.42 Mts methane-hectare-1-year-1), resulting in $277,576 - $602,930 in social benefit value by 2050. Our approach and findings demonstrate the potential benefits in developing consistent accounting methodologies to better track, prioritize, and implement wetlands restoration strategies to mitigate methane emissions, increase carbon sequestration, and contribute toward state-level GHG emissions reduction targets. A significant limitation in estimating GHG benefits, however, is the lack of coordinated, widespread monitoring strategies. While not insurmountable, these challenges will need to be addressed for methane emissions reductions and carbon sequestration through salt marsh restoration to be demonstrated as an effective strategy. We conclude that while carbon crediting may offer benefits to marsh restoration and state GHG emission targets, there remain significant concerns about the potential lack of project monitoring, which could undermine the social benefits that carbon crediting would afford. In the worst case, this could result in the offsetting of actual GHG emissions with credits that are supported by indirect and less-than-rigorous monitoring data.
