METHANE EMISSION FROM FORESTED SWAMPS IN XIAOXING’AN MOUNTAINS, NORTHEASTERN CHINA

Aims Our major objectives were to quantify methane fluxes and variations during growing season and understand key factors controlling methane fluxes in five natural forested swamps. Methods We measured methane fluxes from natural forested swamps in Xiaoxing’an Mountains from early June to late October 2007, using the static opaque chamber and gas chromatography technique. Important findings We observed large seasonal variations in methane fluxes in Alnus sibirica swamp, Larix gmelinii-moss swamp and Larix gmelinii-Sphagnum spp. swamp, but smaller variations in Betula platyphylla swamp and Larix gmelinii-Carex schmidtii swamp. Episodic flux was detected in Larix gmelinii-Sphagnum spp. swamp, which greatly influenced methane fluxes during the growing season. Alnus sibirica swamp, Larix gmelinii-moss swamp and Larix gmelinii-Sphagnum spp. swamp were sources of atmospheric methane, but Betula platyphylla swamp and Larix gmelinii-Carex schmidtii swamp were sinks, and the average methane emission rates during the growing season were (56.08 ± 200.38), (15.34 ± 14.89), (0.64 ± 0.88), (–0.88 ± 1.76) and (–0.94 ± 3.00 ) mg·m–2·d–1, respectively. Average methane emission rates were higher with higher water table among the forested swamps, except for Larix gmelinii-Sphagnum spp. swamp. There was a critical point of atmospheric methane source or sink when the water table was at –34.5 ～ –30.8 cm; forested swamps with average water table below this value were atmospheric methane sinks. Effects of temperature on methane fluxes were complex, as temperature may show positive or negative and significant or non-significant correlations. Aboveground biomass of trees may be the best indicator of methane emissions from these forested swamps, because there were strong negative correlations between them.