JIN Hui-jun, WU Jie, CHENG Guo-dong, NAKANO Tomoko, SUN Guang-you
The areal extent of cold freshwater wetlands on the Tibetan Plateau is estimated to be 0.133×106 km2, suggesting a significant methane potential. Methane fluxes from wet alpine meadows, peatlands, Hippuris vulgaris mires and secondary marshes were 43.18,12.96,-0.28 and 45.90 mg·m-2·d-1, respectively, based on the transection studies at the Huashixia Permafrost Station from July to August 1996. Average CH4 flux in the thaw season was extrapolated to be 5.68 g·m-2 according to the areal percentage of wetland areas in the Huashixia region. CH4 fluxes at four fixed sites, representative of similar ecosystems, ranged from-19.384 to 347.15 mg·m-2·d-1, and the average CH4 fluxes varied from 6.54 to 71.97 mg·m-2·d-1 at each site from April to September 1997. CH4 emissions at each site during the entire thaw season was estimated from 1.21 to 10.65 g·m-2, displaying strong spatial variations. Seasonal variations of CH4 fluxes were also observed at the four sites. It is found that CH4 bursted in the early thaw season, and increased afterwards with rising soil temperatures. Episodic fluxes were observed in summer, which influenced the average CH4 flux considerably. Annual CH4 emissions from cold wetlands on the plateau were estimated at about 0.7~0.9 Tg based on the distribution of wetlands, representative CH4 fluxes, and number of thaw days. The centers of CH4 releasing are located in the sources of the Yangtze and Yellow Rivers, and Zoige Peatlands.