How will sea level rise impact greenhouse gas fluxes from salt marsh soils?

Abstract:

Salt marshes are important blue carbon ecosystems that sequester large amounts of carbon mitigating the effects of climate change. This negative climate feedback, however, may be offset by soil emissions of the potent greenhouse gases CH₄ and N₂O, which some studies have shown to vary with marsh elevation and vegetation zone. Salt marshes of the northern Northwest Atlantic typically have unvegetated tidal flat at the lowest elevation, which transitions with increasing elevation to a grass zone (Spartina alterniflora), followed by a forb zone (Plantago maritima and Triglochin maritima) and then into another grass zone (Spartina patens). The increased flooding that occurs with climate-related sea level rise will cause a landward shift in these zones and we are aware of no studies comparing the greenhouse gas flux from the soil of all four zones. Here we present findings from a study conducted on a salt marsh at La Pocatière, Quebec, located on the St. Lawrence River estuary, which is typified by this zonation. Here the average annual temperature is 4.5 °C and the marsh is subject to extensive winter freeze. We measured greenhouse gas fluxes from the four different areas of the marsh to investigate differences in climate feedbacks between them and to determine how this feedback may shift with sea level rise.