Effect of salinity on greenhouse gas production and emission in marsh soils during the decomposition of wetland plants

Purpose Salinity and vegetation can significantly affect the productions and emissions of greenhouse gases (GHGs) in wetland soils. We aim to investigate the effect of salinity on the productions and emissions of GHGs in marsh soils during the decomposition of wetland plants under different scenarios. Methods Soils and wetland plants collected from a freshwater marsh (FM) and a saline marsh (SM) in the Louisiana Barataria Basin estuary were incubated under different levels of salinity treatment for 180 days. Gas and soil samples were periodically collected and analyzed for CO2, CH4, and N2O and for TN, TC, and DOC contents, respectively. Results CH4 and CO2 production rates reached maximums on day 30 as the decomposition processed. The increment of CH4 and CO2 production rates in SM soils was greater than in FM soils. The CH4 and CO2 production rates were generally more significantly correlated with DOC than with TC. Reducing salinity inhibited the productions and emissions of CO2 and N2O but significantly promoted those of CH4 in SM soils, while in FM soils, increasing salinity significantly decreased the CO2 production and emission but had no significant effect on CH4 and N2O. The CO2-equivalent cumulative emissions increased by 41% as the salinity decreased by 17.7% in saline marsh, and the percent contribution of CH4 emissions to CO2-equivalent cumulative emissions increased from 15 to 47%. Conclusion Our results suggested the potential that the diversion of Mississippi River water to the wetlands might promote the production and emission of CH4 in saline marsh.