Carbon dioxide, methane and nitrous oxide fluxes from former peat extraction fields currently used for cranberry (Vaccinium macrocarpon) and highbush blueberry (Vaccinium corymbosum) plantations

Under the umbrella of international and European Union climate policies and agreements aimed at achieving climate neutrality and thus reducing greenhouse gas (GHG) emissions from drained organic soils (including the Paris agreement, the European Green Deal and the Nature Restoration Law), it is urgently necessary to estimate GHG fluxes from former peat extraction fields to provide measurement-based recommendations for further management of these areas. In addition, there is lack of quantitative estimates of contribution of peatland plant cultivation, including berries, to total GHG emissions and climate change mitigation. Here, we compared carbon dioxide (CO₂), methane (CH₄), and nitrous oxide (N₂O) fluxes from nutrient-poor organic soils (Histosols) in former peat extraction fields currently used for cranberry (Vaccinium macrocarpon) and highbush blueberry (Vaccinium corymbosum) plantations, active peat extraction fields and pristine raised bogs. GHG flux measurements were conducted over two years using a manual chamber technique at 16 study sites (at least three sites of each land-use type) across 11 different raised bogs in the hemiboreal vegetation region of Europe (in Latvia). Across the studied land-use types, mean annual net CO₂ fluxes, calculated as the difference between the annual soil heterotrophic respiration and the annual C input into soil with plant litter, ranged from near zero (-0.07 ± 0.68 t CO₂-C ha^-1 y^-1) in the pristine raised bogs to 1.56 ± 0.19 t CO₂-C ha^-1 y^-1 in active peat extraction fields. Furthermore, net CO₂ fluxes had the largest contribution to total GHG emissions in both active peat extraction fields and berry plantations. The lowest annual CH₄ fluxes were observed in cranberry plantations (6.65 ± 1.77 kg CH₄-C ha^-1 yr^-1), while the highest were in pristine raised bogs (128.0 ± 27.5 kg CH₄-C ha^-1 yr^-1), where CH₄ fluxes accounted for the largest share of total GHG emissions. Annual N₂O fluxes did not exceed 0.65 ± 0.33 kg N₂O-N ha^-1 yr^-1 (in highbush blueberry plantations) and made a relatively low contribution to total GHG emissions compared to net CO₂ and CH₄ fluxes. Across the studied land-use types, the highest total GHG fluxes (the sum of annual net CO₂, CH₄ and N₂O fluxes considering global warming potential values for a 100-year time horizon) were observed in active peat extraction fields (6.23 t CO₂ eq. ha^-1 yr^-1), while the lowest were in cranberry plantations (1.50 t CO₂ eq. ha^-1 yr^-1).

Acknowledgments: The research was conducted within the scope of the European Commission LIFE Climate Action Programme Project “Peatland restoration for greenhouse gas emission reduction and carbon sequestration in the Baltic Sea region” (LIFE21 - CCM - LV - LIFE PeatCarbon, Project number: 101074396).