The fluxes and controlling factors of N2O and CH4 emissions from freshwater marsh in Northeast China

Abstract: Nitrous oxide (N₂O) and methane (CH₄) emissions were measured using a static chamber method in two adjacent plots of freshwater marsh predominated by Calamagrostis angustifolia, one is seasonal waterlogged (SW) and the other without surface water accumulation (NW), in Sanjiang Plain wetland (47°35’N, 133°31’E), northeast China, during 2002–2004. The diurnal and seasonal flux variations of both gases were significantly correlated with 5-cm-soil temperature. The NW marsh is a source of N₂O and sink of CH₄, while the SW marsh is sink of N₂O and source of CH₄. Remarkably, we observed a N₂O emission peak under Eh of −300 to −100 mV, and CH₄ emission peak under Eh of +300 to +400 mV, which indicate additional sources of N₂O and CH₄ for the freeze-thaw induced emission peaks of N₂O and CH₄ observed between late July and early August. Further study shows that the additional N₂O and CH₄ were emitted under the frozen soil after thawing.