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Abstract:
The research site was located at a typical taiga forest in central Alaska (64 o 51'58.57"N, 147 o 51'19.93"W), which stands on discontinuous permafrost. The vegetation of this site is composed of black spruce, short shrub, vascular plants, lichen and moss. The height of the black spruce around the observation tower was up to 6 m, but most were less than 1.5 m, and the density including short trees was 5000 trees/ha. The shrub height was less than 0.8 m, and the forest floor was tussock tundra with a height about 0.2-0.3 m. The permafrost soil thawed from spring to mid summer with the maximum depth of around 0.5 m. CO2 flux and energy balance (sensible heat and latent heat) were measured by an eddy correlation method using an open path CO2/H2O fluctuation meter (LiCor, LI7500) and a sonic anemometer (Campbell, CSAT-3). CH4 concentration was measured by a FID-GA (Flame Ionized Detector type-Gas Analyzer: Horiba, FIA-510). Ambient air at two heights of the tower (2 and 8 m) was sampled continuously with the CH4 analyzer, and the CH4 concentration at each height was measured. The CH4 flux was determined by the modified gradient method (Miyata et al., 2000), by using 30-min average data concentrations, sensible heat flux, friction velocity, and atmospheric stability.