Methane fluxes measured by eddy covariance and static chamber techniques at a temperate forest in central Ontario, Canada

Wang, Jonathan M.; Murphy, J. G.; Geddes, Jeffrey A.; Winsborough, C. L.; Basiliko, Nathan; Thomas, Sean C.

doi:10.5194/bg-10-4371-2013

Cited by 67 publications

(37 citation statements)

References 54 publications

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“…In that case, the measurement does not significantly disturb atmospheric mixing and increased mechanical turbulence potentially enhances vertical gas exchange. Such positive correlation between the downward CH 4 flux and WS, with higher sinks during the daytime, has been reported by Wang et al (2013). This is consistent with the results of our fan-speed test, described in Koskinen et al (2014) who measured CO 2 respiration by the same chamber system.…”

Section: Diurnal Variationsupporting

confidence: 92%

“…In drained peatland forests, significant correlations between CH 4 flux and temperature have been found in CH 4 -emitting ecosystems (Nykänen et al, 1998;Minkkinen and Laine, 2006), although the direction of the correlation has been found to differ between fens and bogs. In contrast, no significant correlations with temperature were found in peatland forests that mainly showed CH 4 uptake (Ojanen et al, 2010;Wang et al, 2013). Both CH 4 emission and uptake have been found to correlate with WTL (e.g., Bellisario et al, 1999;Ojanen et al, 2010).…”

Section: Driving Factors For the Ch 4 Effluxmentioning

confidence: 90%

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Methane exchange at the peatland forest floor – automatic chamber system exposes the dynamics of small fluxes

et al. 2017

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Abstract. We measured methane (CH 4 ) exchange rates with automatic chambers at the forest floor of a nutrient-rich drained peatland in 2011-2013. The fen, located in southern Finland, was drained for forestry in 1969 and the tree stand is now a mixture of Scots pine, Norway spruce, and pubescent birch. Our measurement system consisted of six transparent chambers and stainless steel frames, positioned on a number of different field and moss layer compositions. Gas concentrations were measured with an online cavity ring-down spectroscopy gas analyzer. Fluxes were calculated with both linear and exponential regression. The use of linear regression resulted in systematically smaller CH 4 fluxes by 10-45 % as compared to exponential regression. However, the use of exponential regression with small fluxes (< 2.5 µg CH 4 m −2 h −1 ) typically resulted in anomalously large absolute fluxes and high hour-to-hour deviations. Therefore, we recommend that fluxes are initially calculated with linear regression to determine the threshold for "low" fluxes and that higher fluxes are then recalculated using exponential regression. The exponential flux was clearly affected by the length of the fitting period when this period was < 190 s, but stabilized with longer periods. Thus, we also recommend the use of a fitting period of several minutes to stabilize the results and decrease the flux detection limit. There were clear seasonal dynamics in the CH 4 flux: the forest floor acted as a CH 4 sink particularly from early summer until the end of the year, while in late winter the flux was very small and fluctuated around zero. However, the magnitude of fluxes was relatively small throughout the year, ranging mainly from −130 to +100 µg CH 4 m −2 h −1 . CH 4 emission peaks were observed occasionally, mostly in summer during heavy rainfall events. Diurnal variation, showing a lower CH 4 uptake rate during the daytime, was observed in all of the chambers, mainly in the summer and late spring, particularly in dry conditions. It was attributed more to changes in wind speed than air or soil temperature, which suggest that physical rather than biological phenomena are responsible for the observed variation. The annual net CH 4 exchange varied from −104 ± 30 to −505 ± 39 mg CH 4 m −2 yr −1 among the six chambers, with an average of −219 mg CH 4 m −2 yr −1 over the 2-year measurement period.

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Section: Diurnal Variationsupporting

confidence: 92%

Section: Driving Factors For the Ch 4 Effluxmentioning

confidence: 90%

Methane exchange at the peatland forest floor – automatic chamber system exposes the dynamics of small fluxes

et al. 2017

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“…The first experiments with our multicopter took place at the measurement site Fendt (DE-Fen) of the TERENOpreAlpine (TERrestrial ENvironmental Observatory) observatory (Zacharias et al, 2011) during the ScaleX campaign (Wolf et al, 2017) in June and July 2015. This intensive campaign aimed to address atmosphere-land surface interactions across different scales with both measurements and modeling.…”

Section: Site Description and Instrumentationmentioning

confidence: 99%

“…The operation of towers is fixed to a certain location and the vertical information is limited to the height of the tower as well as to discrete levels at the tower. However, towers provide continuous recording of the investigated variables and are routinely used (e.g., Sasakawa et al, 2010;Wang et al, 2013;Andrews et al, 2014). With radiosondes, balloons or kites, information of meteorological conditions can be acquired for an extended vertical range, but these systems are expensive and the location of the vertical profiles is dependent on atmospheric conditions.…”

Section: Introductionmentioning

confidence: 99%

Simultaneous multicopter-based air sampling and sensing of meteorological variables

et al. 2017

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Abstract. The state and composition of the lowest part of the planetary boundary layer (PBL), i.e., the atmospheric surface layer (SL), reflects the interactions of external forcing, land surface, vegetation, human influence and the atmosphere. Vertical profiles of atmospheric variables in the SL at high spatial (meters) and temporal (1 Hz and better) resolution increase our understanding of these interactions but are still challenging to measure appropriately. Traditional ground-based observations include towers that often cover only a few measurement heights at a fixed location. At the same time, most remote sensing techniques and aircraft measurements have limitations to achieve sufficient detail close to the ground (up to 50 m). Vertical and horizontal transects of the PBL can be complemented by unmanned aerial vehicles (UAV). Our aim in this case study is to assess the use of a multicopter-type UAV for the spatial sampling of air and simultaneously the sensing of meteorological variables for the study of the surface exchange processes. To this end, a UAV was equipped with onboard air temperature and humidity sensors, while wind conditions were determined from the UAV's flight control sensors. Further, the UAV was used to systematically change the location of a sample inlet connected to a sample tube, allowing the observation of methane abundance using a ground-based analyzer. Vertical methane gradients of about 0.3 ppm were found during stable atmospheric conditions. Our results showed that both methane and meteorological conditions were in agreement with other observations at the site during the ScaleX-2015 campaign. The multicopter-type UAV was capable of simultaneous in situ sensing of meteorological state variables and sampling of air up to 50 m above the surface, which extended the vertical profile height of existing tower-based infrastructure by a factor of 5.

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“…Since the 1970s, a variety of direct or indirect experimental approaches have been used for the assessment of volatile pollutant flux to the atmosphere. Vapour fluxes can be directly measured at the soil-air interface using static flux chambers (recent examples include Wang et al 2013;Pihlatie et al 2013;Parker et al 2013a;Sihota et al 2013;Collier et al 2014;Gallego et al 2014;Happell et al 2014;Miola et al 2015) or using open or closed dynamic flux chambers (recent examples include Ma et al 2013;Parker et al 2013a;Parker et al 2013b;Sihota et al 2013;Carpi et al 2014;Liu et al 2014;Miola et al 2015). By definition, dynamic flux chambers differ from static flux chambers by the presence of a more or less high forced air flow passing through the measuring device (Hudson and Ayoko 2008).…”

mentioning

confidence: 99%

Evaluation of VOC fluxes at the soil-air interface using different flux chambers and a quasi-analytical approach

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et al. 2015

Water Air Soil Pollut

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Dense nonaqueous-phase liquids (DNAPLs) spilled on the soil migrate vertically depending upon gravity and capillary forces through the unsaturated zone of the porous aquifer, forming a vapour plume. These volatile organic compounds (VOCs) can be transferred by advection-diffusion to the groundwater or to the atmosphere. Evaluating DNAPL vapour fluxes at the soil-air interface is one of the key challenges in the remediation of contaminated sites. This work discusses the results of a large-scale vapour plume experiment with a well-defined trichloroethylene (TCE) spill, including a sequential raising and lowering of the water table, where the TCE vapour fluxes at the soil surface were experimentally quantified in two ways: (i) directly, with measurements at the soil-air interface using different flux chambers at various operational modes under both transient and steady-state conditions of the vapour plume, and (ii) indirectly, using a quasi-analytical approach based on soil gas measurements. It was shown that upward displacement of the water-air front during the controlled raising of the water table (approximately 10 cm h −1 ) increased the TCE vapour flux measured at the soil surface by factors of 4 to 10. Under steady-state transport conditions, TCE vapour fluxes measured using five types of flux chambers and three operational modes were similar. The effects of the flux chamber geometry, the accumulation of TCE vapours in the chamber headspace or the air recirculation at a low flow rate on the measured TCE vapour fluxes were low. At steady-state transport conditions, TCE vapour fluxes measured with the flux chambers and estimated using the quasianalytical approach were of the same order of magnitude. However, under transient conditions of the vapour plume, the TCE vapour flux predicted by the quasi-analytical approach greatly underestimated or overestimated the real TCE vapour flux at the soil-air interface.

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Methane fluxes measured by eddy covariance and static chamber techniques at a temperate forest in central Ontario, Canada

Cited by 67 publications

References 54 publications

Methane exchange at the peatland forest floor – automatic chamber system exposes the dynamics of small fluxes

Methane exchange at the peatland forest floor – automatic chamber system exposes the dynamics of small fluxes

Simultaneous multicopter-based air sampling and sensing of meteorological variables

Evaluation of VOC fluxes at the soil-air interface using different flux chambers and a quasi-analytical approach

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