Greenhouse gas flux with reflooding of a drained salt marsh soil

Abstract

Salt marshes are highly effective carbon (C) sinks and bury more C per square meter annually than any other ecosystem. Reclamation and anthropogenic impacts, however, have resulted in extensive losses of salt marshes. Carbon credits can be generated and sold by restoring marshes, but only if C sequestration and net reductions in greenhouse gases (GHG) are reliably quantified. Restored marshes, however, may exhibit different patterns of GHG emissions than natural marshes and it is possible that they could temporarily become sources of N2O even in the usually N-limited estuarine environment. Research on short-term GHG flux following salt marsh restoration is limited to studies of two restored marshes which examined GHG flux more than six months after the return of tidal flooding. Here we report on a laboratory experiment in which soil cores collected from a drained agricultural marsh on the St. Lawrence Estuary were flooded with estuary water. Gas flux measurements immediately after flooding revealed small increases in N2O and CH4, but a large decline in CO2 yielding, from a climatic perspective, a net cooling effect over the observation period. In addition to restoring the land’s capacity to sequester C once a marsh develops, returning tidal flooding thus appears to have the added benefit of stemming large ongoing C losses. With more than 400 km2 of undeveloped dykeland, Eastern Canada is well positioned to restore large sections of marsh and contribute to reducing atmospheric CO2 concentrations.

Physiochemical Controls on the Horizontal Exchange of Blue Carbon Across the Salt Marsh‐Tidal Channel Interface

“…Tidal salt marshes store so‐called “blue carbon” (Nellemann et al., 2009) in high quantities relative to their land area (Chmura et al., 2003; Duarte et al., 2008, 2013) and could be used to mitigate climate change (Howard et al., 2017; IPCC, 2014; Macreadie et al., 2021; Serrano et al., 2019), but we are just beginning to understand C dynamics in these complex ecosystems. Most blue C studies focus on the distribution of C in the soil profile (Berthelin et al., 2022; Chmura et al., 2003; Gorham et al., 2021; Hinson et al., 2017; Spivak et al., 2019; Sun et al., 2019; J. Yu et al., 2014; Van De Broek et al., 2016) or vertical trace gas fluxes (Abdul‐Aziz et al., 2018; Capooci et al., 2019; Capooci & Vargas, 2022a; Diefenderfer et al., 2018; O’Connor et al., 2020; Tong et al., 2020; Vázquez‐Lule & Vargas, 2021; Wollenberg et al., 2018). Few studies focus on the lateral C flux, which is the inorganic and organic C imported and exported via tidal channels (Santos et al., 2021; Trifunovic et al., 2020).…”