Abstract
The closed chamber technique has been widely employed to detect methane emissions, despite little being known about whether the absence or presence of light will impact the flux estimation. Here, we employed a laser greenhouse gas analyzer with an opaque—transparent chamber pair to measure the methane emission rate in a boreal peatland complex. Microtopography (i.e., hummocks and hollows) in natural and drained peatlands, and plant communities (i.e., grasses and shrubs) in a pasture converted from natural peatlands, were considered to cover the local heterogeneity. Our results indicated that opaque chambers (0.58–0.78 g CH4 m−2 during the growing season) measured a significantly higher (∼2–3 times) methane emission at the hummocks than transparent chambers (∼0.24 g CH4 m−2); however, a similar phenomenon was not found at the hollows or at other measurement plots. Gross photosynthesis explained 44%–47% of the temporal variation of the ‘artificial bias’ (the difference in methane flux obtained by the opaque versus transparent chambers) at the hummocks. Additionally, both water table depth and surface soil moisture significantly explained spatial variations of methane emissions. Our study suggests that microtopography has a significant influence on the artificial bias in methane emission estimation and the artificial properties of a chamber (transparency/opacity) method can be vitally important in some cases (i.e., hummocks), and negligible in others (i.e., hollows). The observed connection between the photosynthesis process and the ‘artificial bias’ of closed chambers (opaque versus transparent) can be used to improve methane flux modeling. Separate parameterization schemes are needed for methane transportation under the presence or absence of light.
Highlights
At the hummocks of drained peatlands, the opaque chambers estimated a net emission of 0.58 ± 0.16 (SE) g CH4 m−2 across the growing season, while the transparent chambers showed a net emission of 0.24 ± 0.10 g CH4 m−2
No significant difference in CH4 fluxes between the opaque and transparent chambers was found for other sites
No correlation was found between the difference in air temperature and CH4 flux obtained by opaque versus transparent chambers (figures 2(c), (d))
Summary
Data from chamber based measurements have been taken as an important source of examining spatial variability and environmental controls of methane emission from various ecosystems, including wetland ecosystems. Either opaque (Davidson et al 2008, Guckland et al 2009) or transparent (Cao et al 2008, Mastepanov et al 2008) chambers were employed to conduct the chamber enclosure measurement, even though clear plastic chambers can lead to high temperatures as a result of a long covering period (Chanton & Whiting 1995), while an opaque chamber might impact CH4 emission estimation over 30 min coverage since stomata started to close after 30 min (Morrissey et al 1993). The blockage of light under opaque chambers potentially impacts the production, transportation, or emission process of CH4. Our specific objectives were: (1) to investigate the difference between opaque and transparent chambers for measuring CH4 fluxes within a short covering period (three minutes); and (2) to identify if a similar phenomenon exists among different communities or hummocks and hollows in boreal peatlands
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