Continuous measurement of methane flux over a larch forest using a relaxed eddy accumulation method

Abstract

We measured the methane flux of a forest canopy throughout a year using a relaxed eddy accumulation (REA) method. This sampling system was carefully validated against heat and CO 2 fluxes measured by the eddy covariance method. Although the sampling system was robust, there were large uncertainties in the measured methane fluxes because of the limited precision of the methane gas analyzer. Based on the spectral characteristics of signals from the methane analyzer and the diurnal variations in the standard deviation of the vertical wind velocity, we found the daytime and nighttime precision of halfhourly methane flux measurements to be approximately 1.2 and 0.7 μg CH 4 m −2 s −1 , respectively. Additional uncertainties caused by the dilution effect were estimated to affect the accuracy by as much as 0.21 μg CH 4 m −2 s −1 on a half-hourly basis. Diurnal and seasonal variations were observed in the measured fluxes. The biological emission from plant leaves was not observed in our studies, and thus could be negligible at the canopy-scale exchange. The annual methane sink was 835±175 mg CH 4 m −2 year −1 (8.35 kg CH 4 ha −1 year −1 ), which was comparable to the flux range of 379-2,478 mg CH 4 m −2 year −1 previously measured in other Japanese forest soils. This study indicated that the REA method could be a promising technique to measure canopy scale methane fluxes over forests, but further improvement of precision of the analyzer will be required.

Methane uptake in a temperate forest soil using continuous closed-chamber measurements

“…The nighttime data under calm conditions were eliminated using a friction velocity (u * ) threshold (0.3 m s −1 ), but we have also shown the fluxes without this threshold (Ueyama et al, 2012b(Ueyama et al, , 2013. Further details on the HREA method are provided in previous papers (Ueyama et al, 2012a(Ueyama et al, ,b, 2013.…”

“…The mean canopy height is approximately 25 m. The soil is classified as coarse volcanic ash with 0.43 ± 0.11 g cm −3 of soil bulk density (Urakawa et al, 2015). Further details about the study site are provided in our previous publications (Ueyama et al, 2012a(Ueyama et al, , 2013Mochizuki et al, 2014;Takahashi et al, 2015).…”

Spatial and seasonal variations of CO2flux and photosynthetic and respiratory parameters of larch forests in East Asia

“…Fuji in central Japan (Ueyama et al 2012). The stand age was 45-50 years old at the time of the measurement.…”

Influences of various calculation options on heat, water and carbon fluxes determined by open- and closed-path eddy covariance methods

“…FHK is a planted Japanese larch (L. kaempferi) forest located in Fujiyoshida, Japan (Ueyama et al, 2012). The terrain at this site has a slope of 3Á48, and the canopy is homogeneous.…”