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

Nitrous oxide (N 2 O) and methane (CH 4 ) 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 N 2 O and sink of CH 4 , while the SW marsh is sink of N 2 O and source of CH 4 . Remarkably, we observed a N 2 O emission peak under Eh of −300 to −100 mV, and CH 4 emission peak under Eh of +300 to +400 mV, which indicate additional sources of N 2 O and CH 4 for the freeze-thaw induced emission peaks of N 2 O and CH 4 observed between late July and early August. Further study shows that the additional N 2 O and CH 4 were emitted under the frozen soil after thawing.