Micrometeorological measurements of methane flux at a boreal forest in central Alaska

Methane (CH_4) flux at a black spruce forest in central Alaska was determined by applying the three types of modified gradient method. One type used the eddy diffusivity obtained by CO_2 flux and CO_2 gradient. Others established the flux gradient relationship assuming Monin-Obukhov similarity. The wind speed and temperature profile functions were corrected for the influence of the roughness sublayer, and then applied to the modified gradient methods. More than 70% of the data were rejected by the strict quality control and a continental climate, such as calm wind. Although the diurnal variations of CH_4 flux by the three methods were different, the seasonal variation showed similar tendency; a weak emission on snowpack, an obvious emission around spring thaw, and CH_4 uptake in the late growing season. As calculated CH_4 flux was in the same range as with previous studies conducted by the chamber measurement