Variation in Sink and Source Level of METHANE0 at Black Spruce Forest on Permafrost in Interior Alaska

Methane (CH4) is effective greenhouse gas in ecosystem, and the large uncertainty in the strength of source and sink with their temporal variability requires comprehensive observational studies. We conducted continuous CH4 flux observation at a black spruce forest in interior Alaska by several methods of eddy correlation, gradient-aero-dynamic, and relaxed eddy accumulation. There are anaerobic hollows and air-rich moss layer at forest floor on permafrost, which provides heterogeneous distribution of CH4 sink and source. Therefore, the observed stand-level CH4 flux showed complicated time series and strength between sink and source, which was seldom consistent among three methods depend on different footprint, source spots and seasonal weather change. To clarify the local strength of source/sink level, we applied a cavity ring-down spectroscopy gas analyzer (FMA200, Los Gatos Research, USA) to measure small concentration differences of CH4, CO2 and H2O simultaneously between inside and outside of dynamic chambers. Chamber measurement system is similar to Pape et al.(2009). Most chamber locations of sphagnum-moss, feather-moss, and sedge showed CH4-sink with daily variation of air-temperature (up to -0.15 mgCH4 m-2 h-1 in midday). Hollow, where pond was surrounded by sedge and moss, was CH4-source (high emission in nighttime of 0.25 mgCH4 m-2 h-1), but the pond emitted almost same level of 1 mgCH4 m-2 h-1 without daily variation (small change of water temperature). Locality of CH4-flux was quite large, and the comparison of CH4-flux between pond and hollow suggested that a considerable level of CH4 was emitted from the limited source points, most of which was oxidized by methanotrophic bacteria at aerobic surface, especially around hollow.