The Effect of Land Use on Greenhouse Gas Emissions Along Salinity Gradients in Pacific Northwest Coastal Wetlands

Coastal wetlands can sequester carbon at high rates, but these are offset by the emission of greenhouse gases (GHG). To analyze the effect of land use and environmental predictor variables on GHG emission in coastal wetlands, we measured seasonal in situ trace gas fluxes in 11 restored, 6 reference, and 5 disturbed pasture sites in the Tillamook and Coos Bay, OR. The effects of land use on GHG emissions could be largely explained by physicochemical variables. Pastures had greater CO2 emissions and lower CH4 emissions. The restored marshes had lower CO2 emissions overall and higher CH4 emissions in Tillamook. Methane emissions were partially controlled by salinity, with methanogenesis almost completely inhibited when salinity > 18 ppt. Nitrous oxide (N2O) emissions were sporadic and irregular. Our results indicate that restoration of mesohaline and freshwater coastal wetlands may enhance methane emissions, which may offset any positive climate benefits of soil carbon sequestration