Greenhouse gas fluxes in two drained Northern peatlands inferred from eddy covariance and automatic light-dark chambers

Peatlands store large amounts of organic carbon, which become subject to increased microbial decomposition and mineralization to primarily CO₂ upon drainage.  Drained peatlands are often characterized by horizontal variability in soil water content and saturation, with drier parts closer to drainage ditches. CH₄ production should take place in the wetter parts, while respiratory CO₂ production should dominate in drier parts.

We investigate two neighboring, drained ombrotrophic bogs in Norway close to Trysil, Innlandet, 61.1”N 12.25”E, 640 m a. s. l. One site (South) on an upper slope is about 45 m higher than the other site (North) in a saddle-like flattening.  We use an automated, ecosystem-level, light-dark chamber method to examine the seasonality of CO₂, CH₄ and N₂O fluxes at different microsites along the water table gradient from center of drained patches to the drainage ditches in order to relate GHG fluxes to small scale spatial heterogeneity. With eddy covariance CO₂ and CH₄ flux measurements, we integrate GHG fluxes of CO₂ and CH₄ over a larger spatial scale.

We here present a comparative analysis of the first two years of measurements, where we examine shifting spatial patterns of GHG production at different scales and relate them to soil conditions. The automated chambers (five chambers within each footprint of each eddy flux tower) showed higher spatial variability for CH₄ fluxes than for CO₂ with higher CH₄ emissions in the wetter plots furthest away from ditches, i.e. CH₄ fluxes correlate well to water table depth at both sites. N₂O emissions were observed only in very short events during the early summer of year 1.

While the CO₂ fluxes compared very well between the two investigated sites during the first two years of investigation, the CH₄ fluxes were higher in the lower and wetter of the two sites (North).  Only in the South site, the CH₄ fluxes correlated well with the spatial coverage of well-drained versus less well-drained patches. We will present results on how the spatial variability changed with the seasonality of soil temperatures and the water table. Overall, there was a good alignment of fluxes measured with eddy flux and chamber technologies.

During fall 2021, the drainage ditches were filled and natural hydrology restored at the South site. In following years, GHG fluxes will be monitored continuously at both sites to determine the effect of the restoration on the GHG budget of the ecosystem.