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 (CH<sub>4</sub>), nitrous oxide (N<sub>2</sub>O) and soil respiratory carbon dioxide (CO<sub>2</sub>) measured at nine European peatlands (<i>n</i> = 4) and shrublands (<i>n</i> = 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<sup>−1</sup>. 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. <br><br> The shrublands were generally sinks for atmospheric CH<sub>4</sub>, whereas the peatlands were CH<sub>4</sub> sources, with fluxes ranging from −519 to +6890 mg CH<sub>4</sub>-C m<sup>−2</sup> yr<sup>−1</sup> across the studied ecosystems. At the peatland sites, annual CH<sub>4</sub> emission increased with mean annual air temperature, while a negative relationship was found between net CH<sub>4</sub> uptake and the soil carbon stock at the shrubland sites. Annual N<sub>2</sub>O fluxes were generally small ranging from −14 to 42 mg N<sub>2</sub>O-N m<sup>−2</sup> yr<sup>−1</sup>. Highest N<sub>2</sub>O emission occurred at the sites that had highest nitrate (NO<sub>3</sub><sup>−</sup>) concentration in the soil water. Furthermore, experimentally increased NO<sub>3</sub><sup>−</sup> deposition led to increased N<sub>2</sub>O efflux, whereas prolonged drought and long-term drainage reduced the N<sub>2</sub>O efflux. Soil CO<sub>2</sub> emissions in control plots ranged from 310 to 732 g CO<sub>2</sub>-C m<sup>−2</sup> yr<sup>−1</sup>. Drought and long-term drainage generally reduced the soil CO<sub>2</sub> efflux, except at a hydric shrubland where drought tended to increase soil respiration. <br><br> In terms of fractional importance of each greenhouse gas to the total numerical global warming response, the change in CO<sub>2</sub> efflux dominated the response in all treatments (ranging 71–96%), except for NO<sub>3</sub><sup>−</sup> addition where 89% was due to change in CH<sub>4</sub> 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 CO<sub>2</sub> fluxes

Dual controls on carbon loss during drought in peatlands

“…2), possibly mainly from AR. As in other wooded peatlands 7,8,11 , drainage did not raise SR ( Supplementary Fig. 2), although more reactive nitrogen was available in drained sites compared with restored sites (Supplementary Table 3).…”

“…These hydrologic shifts often threaten carbon stores, changing peatlands from a carbon sink to a carbon source by increasing decomposition 2,3,[14][15][16] ; concomitantly, the crucial peat-forming Sphagnum mosses are replaced by shrubs/trees 2,10,12 with possibly substantial feedbacks on climate change 6,10 . However, recent evidence showed that in some peatlands drought had little impact or even decreased CO 2 emission and increased carbon accumulation [7][8][9][10][11][17][18][19] (Supplementary Table 1). These contrasting results raise uncertainty on the future fate of peat carbon and question the conventional theory that anoxia is the key to sustaining peat carbon.…”

Comparison of soil greenhouse gas fluxes from extensive and intensive grazing in a temperate maritime climate

“…For example, a recent analysis of CH 4 flux measurements made across different soil types and land-uses in the UK showed that AMo CH 4 fluxes (37 µg m −2 h −1 ) were at the top end of the range of CH 4 fluxes reported for mineral soils (17 to 40 µg m −2 h −1 ), rather than peatlands (17 to 1580 µg m −2 h −1 ) (Levy et al, 2012). The largest CH 4 fluxes in that analysis were recorded from the deep peats in the flow country (Loch More) (peat depth = 4 m), but also from a lowland raised bog, Whim Bog within 2 km of AMo (peat depth = 6 m) (Levy et al, 2012;Carter et al, 2012). Methane fluxes at Loch More and Whim Bog were at least 50 times larger than those at AMo, and were similar to those measured in northern Finland (Drewer et al, 2010;Lohila et al, 2011).…”

Intermediate-scale community-level flux of CO2 and CH4 in a Minnesota peatland: putting the SPRUCE project in a global context

“…Roulet et al (2007) for a range of northern Ontario peatlands. In an extensive synthesis of data for a broad range of European peatlands Carter et al (2012) also recorded annual CH 4 flux to be between 0.5 to 6.8 gCH 4 -C m -2 y -1 . Estimated night CO 2 -C losses from the S1-Bog are over 40 times higher than the CH 4 -C losses, suggesting a minimal role for CH 4 -C efflux in the overall NEE from the bog.…”