Salt marshes, due to their capability to bury soil carbon (C), are potentially important regional C sinks. Efforts to restore tidal flow to former salt marshes have increased in recent decades in New England, as well as in some other parts of the world. In this study, we investigated CO2 and CH4 fluxes in tidally restricted and unrestricted wetlands in Cape Cod, MA. Plant aboveground biomass, CO2 gas flux, and pore water chemistry were measured in 2015 and 2016.
Results/Conclusions
We found that the elevation in restored marshes was generally 2-16 cm lower than their natural references. Restored marshes, where porewater had similar chemistry as the natural reference, usually had greater plant aboveground biomass, gross ecosystem production (GEP), ecosystem respiration (ER), as well as net ecosystem production (NEP) than natural. This effect was further confirmed at sites where the dominant plant species were the same in both tidally restricted and unrestricted wetlands. Methane flux was highly varied among vegetations, with the highest emission observed in tidal restricted Phragmite brackish. Our findings indicated that successful restoration of the tidally-restricted or diked marshes may generally result in greater plant biomass and NEP, possibly leading to a greater rate of soil C storage for a decade, at minimum, after restoration. We suggest that those differences are likely due to lower elevation and greater flooding frequency and duration in the recently restored marshes than the natural marsh. The inverse relationship between soil elevation and productivity may further suggest that sea level rise may lead to enhanced organic and mineral sedimentation in these marshes, extending marsh survival under the increased sea level, and recouping carbon stocks that were lost during decades of tidal restriction.