Synthesizing greenhouse gas fluxes across nine European peatlands and shrublands – responses to climatic and environmental changes

Abstract. In this study, we compare annual fluxes of methane (CH₄), nitrous oxide (N₂O) and soil respiratory carbon dioxide (CO₂) measured at nine European peatlands (n = 4) and shrublands (n = 5). The sites range from northern Sweden to Spain, covering a span in mean annual air temperature from 0 to 16 °C, and in annual precipitation from 300 to 1300 mm yr⁻¹. The effects of climate change, including temperature increase and prolonged drought, were tested at five shrubland sites. At one peatland site, the long-term (> 30 yr) effect of drainage was assessed, while increased nitrogen deposition was investigated at three peatland sites.

The shrublands were generally sinks for atmospheric CH₄, whereas the peatlands were CH₄ sources, with fluxes ranging from −519 to +6890 mg CH₄-C m⁻² yr⁻¹ across the studied ecosystems. At the peatland sites, annual CH₄ emission increased with mean annual air temperature, while a negative relationship was found between net CH₄ uptake and the soil carbon stock at the shrubland sites. Annual N₂O fluxes were generally small ranging from −14 to 42 mg N₂O-N m⁻² yr⁻¹. Highest N₂O emission occurred at the sites that had highest nitrate (NO₃⁻) concentration in the soil water. Furthermore, experimentally increased NO₃⁻ deposition led to increased N₂O efflux, whereas prolonged drought and long-term drainage reduced the N₂O efflux. Soil CO₂ emissions in control plots ranged from 310 to 732 g CO₂-C m⁻² yr⁻¹. Drought and long-term drainage generally reduced the soil CO₂ efflux, except at a hydric shrubland where drought tended to increase soil respiration.

In terms of fractional importance of each greenhouse gas to the total numerical global warming response, the change in CO₂ efflux dominated the response in all treatments (ranging 71–96%), except for NO₃⁻ addition where 89% was due to change in CH₄ emissions. Thus, in European peatlands and shrublands the effect on global warming induced by the investigated anthropogenic disturbances will be dominated by variations in soil CO₂ fluxes.