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Quantifying landscape‐level methane fluxes in subarctic Finland using a multiscale approach

Hartley, Iain. P., Hill, Timothy. C., Wade, Thomas. J., Clement, Robert. J., Moncrieff, John. B., Prieto‐Blanco, Ana., Disney, Mathias. I., Huntley, Brian., Williams, Mathew., Howden, Nicholas. J. K., Wookey, Philip. A., Baxter, Robert.
Global change biology 2015 v.21 no.10 pp. 3712-3725
eddy covariance, lawns and turf, aerial photography, methodology, global warming, seasonal variation, forest soils, remote sensing, forests, uncertainty, greenhouse gas emissions, Betula pubescens var. pumila, ecosystems, land cover, temperature, prediction, methane production, plant communities, landscapes, methane, growing season, water table, lichens, Finland
Quantifying landscape‐scale methane (CH₄) fluxes from boreal and arctic regions, and determining how they are controlled, is critical for predicting the magnitude of any CH₄ emission feedback to climate change. Furthermore, there remains uncertainty regarding the relative importance of small areas of strong methanogenic activity, vs. larger areas with net CH₄ uptake, in controlling landscape‐level fluxes. We measured CH₄ fluxes from multiple microtopographical subunits (sedge‐dominated lawns, interhummocks and hummocks) within an aapa mire in subarctic Finland, as well as in drier ecosystems present in the wider landscape, lichen heath and mountain birch forest. An intercomparison was carried out between fluxes measured using static chambers, up‐scaled using a high‐resolution landcover map derived from aerial photography and eddy covariance. Strong agreement was observed between the two methodologies, with emission rates greatest in lawns. CH₄ fluxes from lawns were strongly related to seasonal fluctuations in temperature, but their floating nature meant that water‐table depth was not a key factor in controlling CH₄ release. In contrast, chamber measurements identified net CH₄ uptake in birch forest soils. An intercomparison between the aerial photography and satellite remote sensing demonstrated that quantifying the distribution of the key CH₄ emitting and consuming plant communities was possible from satellite, allowing fluxes to be scaled up to a 100 km² area. For the full growing season (May to October), ~ 1.1–1.4 g CH₄ m⁻² was released across the 100 km² area. This was based on up‐scaled lawn emissions of 1.2–1.5 g CH₄ m⁻², vs. an up‐scaled uptake of 0.07–0.15 g CH₄ m⁻² by the wider landscape. Given the strong temperature sensitivity of the dominant lawn fluxes, and the fact that lawns are unlikely to dry out, climate warming may substantially increase CH₄ emissions in northern Finland, and in aapa mire regions in general.