The greenhouse gas exchange of a drained peatland forest: first insights from eddy-covariance measurements of CO2, CH4 and N2O fluxes in Estonia

While covering only about 3% of the global land surface, peatlands store approximately one-third of all terrestrial carbon (C) and 12–21% of global soil organic nitrogen (N). Pristine peatland soils typically function as minor sinks for carbon dioxide (CO₂), moderate sources of methane (CH₄), and minor to moderate sources of nitrous oxide (N₂O). However, over the past century, extensive drainage of peatlands for forestry, particularly in temperate and boreal regions, has substantially altered the dynamics of greenhouse gases (GHG).

The lowering of the groundwater table has a crucial impact on soil GHG exchange with aerobic conditions inhibiting methanogenesis, thereby reducing CH₄ flux, while simultaneously increasing N₂O flux and accelerating peat decomposition. These changes transform peatlands from carbon sinks to net carbon sources and intensify their N₂O emissions. However, actively growing tree stands may partially offset soil carbon losses through sequestration and indirectly modulate CH₄ and N₂O fluxes by altering soil moisture and microbial activity.

While the net ecosystem exchange of drained peatland forest soils is relatively well studied, there's limited knowledge regarding ecosystem-scale GHG fluxes, especially in the transitional hemiboreal forest zone. In this study, we present the first years of eddy-covariance measurements of CO₂, CH₄, and N₂O fluxes from a drained peatland forest in Eastern Estonia. The site, drained in the early 1970s via an open-ditch network, is dominated by Downy Birch (Betula pubescens, 64%) and Norway Spruce (Picea abies, 36%). The current soil profile, classified as Drainic Eutric Histosol, features a peat layer approximately one meter thick and a moderate C:N ratio (15.1) in the upper soil horizon. Our findings contribute to the growing body of knowledge on peatland forest GHG fluxes, offering valuable data for managing forested peatlands in a changing climate.