Application of an open-path eddy covariance methane flux measurement system to a larch forest in eastern Siberia

Abstract

Canopy-Scale methane (CH4) flux measurement over a larch forest in eastern Siberia was conducted by eddy covariance method using an open-path CH4 gas analyzer. Though the uncorrected flux showed strong CH4 uptake in the daytime, this changed to CH4 emission after density and spectroscopic effects were corrected. Random flux errors calculated from cross-covariance functions suggested that CH4 flux was nearly the same as the upper boundary of the limit of flux detection at the 95th percentile, being barely resolved by the measurement system; and that most of the daytime CH4 flux remained positive even after uncertainties due to random flux errors were taken into consideration. CH4 flux showed clear diurnal variation, representing emission in the daytime and near-zero in the nighttime, irrespective of wind direction. The daytime CH4 flux was dependent on both air temperature and volumetric soil water content. The CH4 flux from May 29, to June 12, was calculated as net emissions of 4.9–13.8 nmol m−2 s−1 in daily average, ranging between the forest floor and a mesotrophic fen near this site measured by static chambers in a previous study.