Abstract:

The carbon balance of high-latitude terrestrial ecosystems plays an essential role in the atmospheric concentration of trace gases, including carbon dioxide (CO₂) and methane (CH₄). Increasing levels of atmospheric methane have contributed to ~20 % of the observed global warming since the pre-industrial era. Rising temperatures in the Arctic are expected to promote the release of methane from Arctic ecosystems. Still, existing methane flux data collection efforts are sparse and highly scattered, and further attempts to assess the landscape fluxes over multiple years are needed.

Here we use multiyear monitoring from automated flux chambers located on the fringe of a fen area in the center of Zackenberg Valley, northeast Greenland, from July and August (2006–2019). Direct measurements of methane fluxes showed high variability, with mean July–August fluxes ranging from 0.26 to 3.41 mg CH₄ m⁻² h⁻¹. Methane fluxes based on manual chamber measurements are available from campaigns in 1997, 1999–2000, and in shorter periods from 2007–2013 and have been summarized in several published studies. Fluxes from the multiyear monitoring were combined with fluxes from the most common vegetation types, measured in 2007, and a detailed vegetation cover map to assess the methane flux on a landscape-scale and its variability over time.

July–August landscape fluxes, estimated in the current study for the 2006–2019 period, were low compared to previous estimations. For the full study area covering the valley floor, the net methane source during these months was estimated as 0.06 to 0.83 mg CH₄ m⁻² h⁻¹ and as 0.26 to 3.45 mg CH₄ m⁻² h⁻¹ for the central fen-rich areas.

A 2017–2018 erosion event indicates that some fen and grassland areas along the river in the center of the valley are becoming unstable following pronounced fluvial erosion and a prolonged period of permafrost warming. Although such physical disturbance in the landscape can disrupt the current ecosystem–atmosphere flux patterns, even pronounced future erosion along the river is unlikely to impact methane fluxes at a landscape-scale significantly. Instead, projected changes in future climate in the valley play a more critical role. The results show that multiyear landscape methane fluxes are highly variable at a landscape-scale and stress the need for long-term spatially distributed measurements in the Arctic.