Measurement of methane and carbon dioxide fluxes from peatland ecosystems by the conditional‐sampling technique

Abstract

The conditional sampling method was used to measure methane (CH4) and carbon dioxide (CO2) fluxes from peatlands in northern Scotland. Preliminary data were obtained using a simple system. Subsequent automation made continuous nux-measurements possible. Observed CH4 fluxes were in the range -70 to +110 mu mol m(-2)h(-1) with a mean flux of 23 mu mol m(-2)h(-1). Peak photosynthetic CO2 fluxes were in the range -10 to -30 mmol m(-2) h(-1). Nocturnal respiration ranged from 0 to +10 mmol m(-2) h(-1). The conditional sampling observations showed reasonable agreement with measurements of flux by eddy-covariance, gradient and aircraft methods. Error analyses and laboratory tests were conducted to determine the precision of the flux-measurement system. The dominant error was associated with the determination of the mixing-ratio difference in conditionally-sampled updraught and downdraught air. The standard error of the difference for CH4 was typically 0.15 ng g(-1) (0.3 parts in 10(9) (p.p.b.))using a careful high-repetition sampling strategy with a modified gas chromatographic/flame ionization detector system. Under typical daytime atmospheric conditions this corresponded to a standard error in the flux measurement of 10 mu mol m(-2)h(-1), which is consistent with field observations. The empirical beta factor in the conditional sampling equation was found to be insensitive to changes in turbulence intensity and atmospheric stability. Simple upscaling models were used to estimate annual carbon-fluxes to Great Britain's peatlands of -0.5 Mt of carbon in the form of CO2 and 18 kt in the form of methane

Stability dependence of the relaxed eddy accumulation coefficient for various scalar quantities

“…This is either because the authors found no significant dependence on environmental parameters or because they did not specifically investigate this problem (partly because of the limited data sets available). The average b 0 values reported for unstable and near‐neutral daytime conditions range within 0.56–0.58 [ Pattey et al , 1993, 1995; Gao , 1995; Katul et al , 1996; Beverland et al , 1996a] and are thus comparable to the constant value of about 0.56 found in this study (compare Figure 7). The literature results were obtained from measurements over a variety of different surface/vegetation types, including bare soil, peatland, grassland, soybeans, corn, and deciduous forest.…”

An Atlantic blanket bog is a modest CO2 sink

“…The annual average air temperature was 10.51 (2003) [Beverland et al, 1996]) and measured over four consecutive years in a Canadian boreal raised bog (À76, À69, À68 and À10 g C m À2 y À1 [Lafleur et al, 2003]). A higher annual CO 2 balance was estimated for a boreal fen in Russia (À88 g C m À2 y À1 [Friborg et al, 2003]) while generally lower values were measured in six consecutive years in a subarctic fen in Finland (À4, À21, À8, À6, À37 and À53 g C m À2 y À1 [Aurela et al, 2004]).…”

“…[4] Studies of C dynamics in peatlands have been carried out mostly in boreal bogs and fens and in sub-arctic fens [Aurela et al, 2004;Friborg et al, 2003;Lafleur et al, 2003;Waddington and Roulet, 2000], some in arctic fens [Nordstroem et al, 2001] but very few studies of CO 2 fluxes have been performed in blanket bogs [Beverland et al, 1996;Chapman and Thurlow, 1996]. To our knowledge, no CO 2 measurements have been performed using the EC method in an Atlantic blanket bog over the full calendar year.…”

Impact of dust aerosols on the radiative budget, surface heat fluxes, heating rate profiles and convective activity over West Africa during March 2006

“…Here, we just detail the methodology used for estimating surface fluxes, based on the eddy covariance method, which is considered as the reference method for vertical flux scalar measurement (Beverland et al, 1996). This method is based on the direct high frequency measurement of the two components of the vertical flux of a scalar: the vertical wind speed "w" and the scalar itself, "c" here, which can be temperature, water vapor mixing ratio or CO 2 concentration.…”