Greenhouse gas emissions from intact riparian wetland soil columns continuously loaded with nitrate solution: a laboratory microcosm study

In this study, we aimed at determining greenhouse gas (GHG) (CO2, CH4, and N2O) fluxes exchange between the soil collected from sites dominated by different vegetation types (Calamagrostis epigeios, Phragmites australis, and Carex schnimdtii) in nitrogenous loaded riparian wetland and the atmosphere. The intact soil columns collected from the wetland were incubated in laboratory and continuously treated with \( {\mathrm{NO}}_3^{-} \)-enriched water simulating downward surface water percolating through the soil to become groundwater in a natural system. This study revealed that the soil collected from the site dominated by C. epigeios was net CO2 and N2O sources, whereas the soil from P. australis and C. schnimdtii were net sinks of CO2 and N2O, respectively. The soil from the site dominated by C. schnimdtii had the highest climate impact, as it had the highest global warming potential (GWP) compared with the other sites. Our study indicates that total organic carbon and \( {\mathrm{NO}}_3^{-} \) concentration in the soil water has great influence on GHG fluxes. Carbon dioxide (CO2) and N2O fluxes were accelerated by the availability of higher \( {\mathrm{NO}}_3^{-} \) concentration in soil water. On the other hand, higher \( {\mathrm{NO}}_3^{-} \) concentration in soil water favors CH4 oxidation, hence the low CH4 production. Temporally, CO2 fluxes were relatively higher in the first 15 days and reduced gradually likely due to a decline in organic carbon. The finding of this study implies that higher \( {\mathrm{NO}}_3^{-} \) concentration in wetland soil, caused by human activities, could increase N2O and CO2 emissions from the soil. This therefore stresses the importance of controls of \( {\mathrm{NO}}_3^{-} \) leaching in the mitigation of anthropogenic N2O and CO2 emissions.