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.
Highlights
Salt marshes provide valuable ecosystem services including habitat provision and storm protection (e.g., Chmura & Burdick, 2012; Barbier et al, 2013)
Salt marshes have been recognized for their value as highly effective carbon (C) sinks (Chmura et al, 2003; Mcleod et al, 2011) and the term ‘‘blue carbon’’ has been coined for the C stored in salt marshes, mangroves and seagrass beds (Nellemann et al, 2009)
Due to its high SGWP, even small fluxes of N2O can offset a portion of the blue carbon benefit associated with a marsh restoration project
Summary
Salt marshes provide valuable ecosystem services including habitat provision and storm protection (e.g., Chmura & Burdick, 2012; Barbier et al, 2013). Salt marshes have been recognized for their value as highly effective carbon (C) sinks (Chmura et al, 2003; Mcleod et al, 2011) and the term ‘‘blue carbon’’ has been coined for the C stored in salt marshes, mangroves and seagrass beds (Nellemann et al, 2009). Unlike freshwater wetlands which can be significant sources of CH4 (Bridgham et al, 2013), salt marshes are typically negligible sources of CH4 and N2O. The former is due to the presence of abundant sulfate in marsh soils that hinders CH4 production (Poffenbarger, Needelman & Megonigal, 2011). Where the supply of N as NO3− is minimal, N2O emissions are negligible (Chmura, Kellman & Guntenspergen, 2011)
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