The fluxes and controlling factors of NO and CH emissions from freshwater marsh in Northeast China.

Nitrous oxide (NO) and methane (CH) 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 NO and sink of CH, while the SW marsh is sink of NO and source of CH. Remarkably, we observed a NO emission peak under Eh of −300 to −100 mV, and CH emission peak under Eh of +300 to +400 mV, which indicate additional sources of NO and CH for the freeze-thaw induced emission peaks of NO and CH observed between late July and early August. Further study shows that the additional NO and CH were emitted under the frozen soil after thawing. [ABSTRACT FROM AUTHOR]