Abstract
Peatland measurements of CO2 and CH4 flux were obtained at scales appropriate to the in situ biological community below the tree layer to demonstrate representativeness of the spruce and peatland responses under climatic and environmental change (SPRUCE) experiment. Surface flux measurements were made using dual open-path analyzers over an area of 1.13 m2 in daylight and dark conditions along with associated peat temperatures, water table height, hummock moisture, atmospheric pressure and incident radiation data. Observations from August 2011 through December 2014 demonstrated seasonal trends correlated with temperature as the dominant apparent driving variable. The S1-Bog for the SPRUCE study was found to be representative of temperate peatlands in terms of CO2 and CH4 flux. Maximum net CO2 flux in midsummer showed similar rates of C uptake and loss: daytime surface uptake was −5 to −6 µmol m−2 s−1 and dark period loss rates were 4–5 µmol m−2 s−1 (positive values are carbon lost to the atmosphere). Maximum midsummer CH4-C flux ranged from 0.4 to 0.5 µmol m−2 s−1 and was a factor of 10 lower than dark CO2–C efflux rates. Midwinter conditions produced near-zero flux for both CO2 and CH4 with frozen surfaces. Integrating temperature-dependent models across annual periods showed dark CO2–C and CH4–C flux to be 894 ± 34 and 16 ± 2 gC m−2 y−1, respectively. Net ecosystem exchange of carbon from the shrub-forb-Sphagnum-microbial community (excluding tree contributions) ranged from −3.1 gCO2–C m−2 y−1 in 2013, to C losses from 21 to 65 gCO2–C m−2 y−1 for the other years.
Highlights
Peatlands currently represent a major global carbon sink sensitive to climate change, the effect of future warming on the fate of stored carbon (C) is largely unknown (Gorham 1991; Bubier and Moore 1994; Tarnocai and Stolbovoy 2006; Heijmans et al 2008)
In this study we addressed the question: how representative is the SPRUCE peatland in terms of CO2 and CH4 flux for known peatlands? We characterized the spatial heterogeneity of peat surface CO2 and CH4 fluxes within the S1-Bog prior to SPRUCE treatment initiation
The autotrophic shrub, forb, sedge and Sphagnum moss community took up CO2 when Photosynthetically active radiation (PAR) reached 194 lmol quanta m-2 s-1 and became light saturated above 1000–1200 lmol quanta m-2 s-1
Summary
Peatlands currently represent a major global carbon sink sensitive to climate change, the effect of future warming on the fate of stored carbon (C) is largely unknown (Gorham 1991; Bubier and Moore 1994; Tarnocai and Stolbovoy 2006; Heijmans et al 2008). Current projections of future climate conditions suggest that temperate peatlands may experience 4–6 °C warming by the end of the 21st century (IPCC 2013). Mechanistic models are powerful tools that can be leveraged to project future carbon dynamics in peatlands (Tian et al 2010; Wania et al 2010; Riley et al 2011), but provide a solution only if they can be parameterized and benchmarked with appropriate. Kolka Forestry Sciences Laboratory, USDA Forest Service, Northern Research Station, Grand Rapids, MN 55744, USA
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