Summer carbon dioxide and water vapor fluxes across a range of northern peatlands

Abstract

[1] Northern peatlands are a diverse group of ecosystems varying along a continuum of hydrological, chemical, and vegetation gradients. These ecosystems contain about one third of the global soil carbon pool, but it is uncertain how carbon and water cycling processes and response to climate change differ among peatland types. This study examines midsummer CO 2 and H 2 O fluxes measured using the eddy covariance technique above seven northern peatlands including a low-shrub bog, two open poor fens, two wooded moderately rich fens, and two open extreme-rich fens. Gross ecosystem production and ecosystem respiration correlated positively with vegetation indices and with each other. Consequently, 24-hour net ecosystem CO 2 exchange was similar among most of the sites (an average net carbon sink of 1.5 ± 0.2 g C m À2 d À1 ) despite large differences in water table depth, water chemistry, and plant communities. Evapotranspiration was primarily radiatively driven at all sites but a decline in surface conductance with increasing water vapor deficit indicated physiological restrictions to transpiration, particularly at the peatlands with woody vegetation and less at the peatlands with 100% Sphagnum cover. Despite these differences, midday evapotranspiration ranged only from 0.21 to 0.34 mm h À1 owing to compensation among the factors controlling evapotranspiration. Water use efficiency varied among sites primarily as a result of differences in productivity and plant functional type. Although peatland classification includes a great variety of ecosystem characteristics, peatland type may not be an effective way to predict the magnitude and characteristics of midsummer CO 2 and water vapor exchanges.

Assessing the spatial variability in peak season CO<sub>2</sub> exchange characteristics across the Arctic tundra using a light response curve parameterization

“…Similarly, a high inter-site variability of summertime NEE has been documented in another comparison study (Lund et al, 2010) on northern wetlands in northern Europe and North America. This is contrary to quantified variability in seven Canadian sites (Humphreys et al, 2006), where the rates of peak season NEE were comparable.…”

“…This suggested that ecosystem (AMAP, 1998) respiration is a stronger driver of CO 2 flux variability in the Arctic tundra during peak season than the assimilation parameters. Yet comparable variability in photosynthesis and ecosystem respiration was found in seven Canadian Boreal peatlands (Humphreys et al, 2006) during peak season while in northern wetlands (Lund et al, 2010) and Canadian tundra ecosystems, variability in NEE was driven mainly by photosynthesis. This may be because our study is comprised of a wide range of climate and ecosystem settings as opposed to northern wetlands (Lund et al, 2010) and the Canadian Boreal peatlands (Humphreys et al, 2006) and the Canadian tundra .…”

“…Quantum sensors LiCor Inc., USA) have been used to measure PPFD (unit: µmol m −2 s −1 ). For Kytalyk, where there were no direct PPFD measurements, estimates were made from global incoming radiation assuming a linear relationship (Jacovides et al, 2003). Table 1 summarizes ecosystem characteristics and EC instrumentation and setup across sites in this study.…”

Shifting environmental controls on CH<sub>4</sub> fluxes in a sub-boreal peatland

“…The cut-off for spike detection is lower than the typical 3-5 SD range reported by others (e.g. Baldocchi et al, 1997;Humphreys et al, 2006;Vickers and Mahrt, 1997) because, given the above time constant, the recursive mean is more responsive to coherent transient departures from the long-term mean compared to block averaging. Sonic anemometer wind vectors were mathematically rotated based on the tilt correction algorithms presented by Wilczak et al (2001), also known as the planar fit method.…”

Advances in Canadian Peatland Hydrology, 2003-2007

“…Nearby forests had a significant impact on pond evaporation through sheltering and turbulence influences and thus forest management can play an important role in wetland ET and its hydrology. Humphreys et al (2006) compared peak growing season ET rates from six wetlands located in central and western Canada and found that maximum ET rates between sites varied from 0.21 to 0.34 mm hr -1 . They suggested that this small range was due to off-setting controls on ET across the various wetland types, in particular where increases in vascular plant leaf area decreased the importance of moss (or surface) evaporation and vice versa.…”