Effect of land-use change on CH4 and N2O emissions from freshwater marsh in Northeast China

The wetlands play an important role in global carbon and nitrogen storage, and they are also natural sources of greenhouse gases such as methane (CH4) and nitrous oxide (N2O). Land-use change is an important factor affecting the exchange of greenhouse gases between wetlands and the atmosphere. However, few studies have investigated the effect of land-use change on CH4 and N2O emissions from freshwater marsh in China. Therefore, a field study was carried out over a year to investigate the seasonal changes of the emissions of CH4 and N2O at three sites (Deyeuxia angustifolia marsh, dryland and rice field) in the Sanjiang Plain of Northeast China. Marsh was the source of CH4 showing a distinct temporal variation. Maximum fluxes occurred in June and the highest value was 20.69 ± 2.57 mg CH4 m−2 h−1. The seasonal change of N2O fluxes from marsh was not obvious, consisted of a series of emission pulses. The marsh acted as a N2O sink during winter, while became a N2O source in the growing season. The results showed that gas exchange between soil/snow and the atmosphere in the winter season contributed greatly to the annual budgets. The winter season CH4 flux was about 3.24% of the annual flux and the winter uptake of N2O accounted for 13.70% of the growing-season emission. Conversion marsh to dryland resulted in a shift from a strong CH4 source to a weak sink (from 199.12 ± 39.04 to −1.37 ± 0.68 kg CH4 ha−1 yr−1), while increased N2O emissions somewhat (from 4.07 ± 1.72 to 4.90 ± 1.52 kg N2O ha−1 yr−1). Conversion marsh to rice field significantly decreased CH4 emission from 199.12 ± 39.04 to 94.82 ± 9.86 kg CH4 ha−1 yr−1 and N2O emission from 4.07 ± 1.72 to 2.09 ± 0.79 kg N2O ha−1 yr−1.