Intermediate-scale community-level flux of CO₂ and CH₄ in a Minnesota peatland: putting the SPRUCE project in a global context

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.