Greenhouse Gas Production in Disturbed, Restored, and Reference Estuaries along a Salinity Gradient in Oregon, USA

There is substantial interest in restoring coast wetlands because of their high rates of soil carbon sequestration, but this positive climatic effect can be offset by emissions of greenhouse gases (GHG). It is also expected that GHG emissions will depend substantially on salinity levels in coastal wetlands, so restoration of different types of coastal wetlands may have very different climate mitigation effects. However, few studies have quantified GHG emissions in disturbed, restored, and reference coastal wetlands along salinity gradients. We investigated the effects of land use and salinity on the seasonal emission of methane, nitrous oxide, and carbon dioxide with a portable gas analyzer in 6 restored (in 2016-2017), 3 reference, and 3 agricultural field sites in Tillamook Bay, Oregon, USA. dioxide and methane emissions were greater in disturbed sites than in reference marshes, but did not differ from restored marshes. Nitrous oxide fluxes were generally below our limit of detection. Soil temperature, water table, and pH were significantly correlated with carbon dioxide emissions. Methane emissions were significantly correlated with salinity, water table, and pH. Overall our preliminary results that indicate that estuarine wetland restoration does not necessarily enhance GHG emissions, possibly because of increasing salinity with restored tidal influence. Our GHG emission data will be combined with soil carbon sequestration data in the future to provide a complete greenhouse gas forcing for this case study.