• Energy Research

While peatland C cycling is generally well covered, understanding of the role of soil fertility in driving the spatial variation of C fluxes within peatlands remains scattered. Our aim was to examine the relative effects of fertility and microtopography on CO2 and CH4 exchange within a boreal fen and to link these effects to the spatial variation in plant and soil attributes. Fertility zones (eutrophic, mesotrophic, oligotrophic) were judged by moss species appearances, and the growing season CO2 and CH4 exchange was measured by static chambers for microforms (string, Sphagnum lawn, flark) and fertility zones and by eddy covariance technique for the entire ecosystem in three years. Plant leaf area index, plant functional type biomasses, soil C and N concentrations and litter decomposition were measured at study plots placed on the microforms and fertility zones. We found that higher fertility led to greater fluxes in both gases: the eutrophic zone had 111% higher net ecosystem CO2 exchange, 102% higher gross primary production, 83% higher ecosystem respiration and 93% higher CH4 emissions than the oligotrophic zone. Peat N concentration was lowest in the eutrophic zone, indicating fast N cycling. The relative importance of microtopography and fertility differed between the two gases: while microform explained 31-39% and fertility 10-15% of total variation in CO2 exchange, microform explained 14% and fertility 36% of variation in CH4 exchange. These results show that growing season CO2 and CH4 fluxes can be significantly affected by within-fen variation of fertility and that CH4 emissions can be more closely associated with fertility than microtopography. It seems that understanding of within-site variation in soil nutrient availability is highly relevant for predicting current and future C exchange in peatlands.

We analysed the effect of the 2018 European drought on greenhouse gas (GHG) exchange of five North European mire ecosystems. The low precipitation and high summer temperatures in Fennoscandia led to a lowered water table in the majority of these mires. This lowered both carbon dioxide (CO 2 ) uptake and methane (CH 4 ) emission during 2018, turning three out of the five mires from CO 2 sinks to sources. The calculated radiative forcing showed that the drought-induced changes in GHG fluxes first resulted in a cooling effect lasting 15–50 years, due to the lowered CH 4 emission, which was followed by warming due to the lower CO 2 uptake. This article is part of the theme issue ‘Impacts of the 2018 severe drought and heatwave in Europe: from site to continental scale’.