LAUSR

Salt marshes provide a range of critical ecosystem services including high rates of carbon sequestration. Recent recognition of the importance of these ecosystems has led to an interest in restoring marshes that have been degraded by human activities. Tidal restriction from coastal development can alter salt marsh plant and animal communities as well as marsh biogeochemistry. However, much less is known about how tidal restriction, and subsequent tidal restoration, may alter greenhouse gas emissions. Since salt marshes typically have lower emissions of methane than freshwater wetlands, tidal restoration that increases the salinity in a restricted marsh could theoretically improve the net global warming potential of a marsh by lowering methane emissions. In this study, we examined the emissions of carbon dioxide, methane, and nitrous oxide at four temperate salt marshes, three of which had been restricted and subsequently restored. Greenhouse gas fluxes were poorly correlated with environmental parameters (biomass, temperature, moisture, sediment organic content, porewater salinity and pH, etc.) normally considered to be primary drivers of salt marsh biogeochemical processes. Carbon dioxide and nitrous oxide emissions and uptake were not influenced by the restriction and restoration history of the marshes. Despite comparable salinity, methane emissions in one partially restored marsh were 25 times higher than those in unimpacted reference sites 13+ years after restoration. However, methane emissions from the other restored sites were equal to or significantly lower than those from unimpacted reference sites. This study highlights that we cannot assume recovering ecosystems will function like unimpacted ones, especially if restoration is incomplete.