Development of a Long-term CO2 Flux Measurement System Using REA Method with Density Correction.

Hamotani, Ken; Monji, Nobutaka; Yamaguchi, Koji

doi:10.2480/agrmet.57.93

Cited by 13 publications

(17 citation statements)

References 10 publications

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“…Our REA method was validated by a comparison against CO 2 flux measurements using the EC method. Although previous studies only validated this method based on short-term measurements (Hamotani et al 2001;Ueyama et al 2009), we found that the performance of the REA method was suitable for measuring fluxes on the annual time scale. The data coverage of the REA method was also higher than that of the EC method, although the data coverage of the EC method would increase if the sampled air was fully dehydrated.…”

Section: Discussionmentioning

confidence: 94%

“…3 Amplitude spectral density of methane concentration measured by a gas analyzer (Model APHA360, Horiba, Japan) during calibration using a standard gas with a methane concentration 9 ppm. The dark and light gray areas represent the periods of 11 and 4 min, respectively downdraft signals based on the vertical wind velocity (Hamotani et al 2001;Ueyama et al 2009), which were consistent with the timing of switching the pumps for C up and C down in the REA sampling system. The relationship between σ w (T up -T down ) and the heat flux as measured by the EC method is shown in Fig.…”

Section: Determination Of the Empirical Coefficientmentioning

confidence: 95%

“…The slope of this relationship is the empirical constant b which was determined here to be approximately 0.53. In previous studies, this value was found to be 0.51-0.57 in forests (Hamotani et al 2001;Ueyama et al 2009). The high correlation coefficient (0.97) indicates that the REA system's use of a moving average of vertical wind velocity sufficiently separated the updraft and downdraft conditions.…”

Section: Determination Of the Empirical Coefficientmentioning

confidence: 99%

“…T up , T down , C up , and C down are the air temperature and the mean methane concentration in the updraft and downdraft, respectively. Finally, b is empirically determined using heat fluxes obtained through the use of the EC method and the mean air temperature of the updraft and downdraft (Hamotani et al 2001). …”

Section: Relaxed Eddy Accumulation Methodsmentioning

confidence: 99%

“…Because this method does not required a gas analyzer with a rapid response, unlike the EC method, it has begun to attract considerable attention for use in studies of trace gas fluxes (Simpson et al 1997;Nemitz et al 2001). An REA system was previously developed by our group (Hamotani et al 1996(Hamotani et al , 2001, and its precision and accuracy have been validated (Ueyama et al 2009). The REA system could be applicable to the measurement of methane fluxes in forest ecosystems, which could enable researchers to use methane gas analyzers for measurements at optimal integration times without high electric power requirements.…”

Section: Introductionmentioning

confidence: 99%

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

Ueyama

Hamotani

Nishimura

et al. 2012

Theor Appl Climatol

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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.

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Section: Discussionmentioning

confidence: 94%

Section: Determination Of the Empirical Coefficientmentioning

confidence: 95%

Section: Determination Of the Empirical Coefficientmentioning

confidence: 99%

Section: Relaxed Eddy Accumulation Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

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

Ueyama

Hamotani

Nishimura

et al. 2012

Theor Appl Climatol

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Measurement of methane flux over an evergreen coniferous forest canopy using a relaxed eddy accumulation system with tuneable diode laser spectroscopy detection

Sakabe

Hamotani

Kosugi

et al. 2011

Theor Appl Climatol

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Very few studies have conducted long-term observations of methane (CH 4 ) flux over forest canopies. In this study, we continuously measured CH 4 fluxes over an evergreen coniferous (Japanese cypress) forest canopy throughout 1 year, using a micrometeorological relaxed eddy accumulation (REA) system with tuneable diode laser spectroscopy (TDLS) detection. The Japanese cypress forest, which is a common forest type in warm-temperate Asian monsoon regions with a wet summer, switched seasonally between a sink and source of CH 4 probably because of competition by methanogens and methanotrophs, which are both influenced by soil conditions (e.g., soil temperature and soil moisture). At hourly to daily timescales, the CH 4 fluxes were sensitive to rainfall, probably because CH 4 emission increased and/or absorption decreased during and after rainfall. The observed canopy-scale fluxes showed complex behaviours beyond those expected from previous plot-scale measurements and the CH 4 fluxes changed from sink to source and vice versa.

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Nocturnal isoprene emission from mature trees and diurnal acceleration of isoprene oxidation rates near Quercus serrata Thunb. leaves

Miyama

Okumura

Kominami

et al. 2013

Journal of Forest Research

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Development of a Long-term CO2 Flux Measurement System Using REA Method with Density Correction.

Cited by 13 publications

References 10 publications

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

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

Measurement of methane flux over an evergreen coniferous forest canopy using a relaxed eddy accumulation system with tuneable diode laser spectroscopy detection

Nocturnal isoprene emission from mature trees and diurnal acceleration of isoprene oxidation rates near Quercus serrata Thunb. leaves

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