Impact of reduced precipitation and increased temperature on CH4 emission from peatland in Western Poland

Peatlands play a key role in the global carbon cycle and the greenhouse gas balance of the biosphere, due to the amount of stored organic carbon and rather big methane (CH₄) emissions. Climate change can make these very valuable and vulnerable ecosystems a net emitter of greenhouse gases to the atmosphere. The question is however, how the anticipated climate changes may impact the methane emission. Will it decrease due to expected drier conditions, or other processes and factors may play a role leading to higher emissions? To answer this question we carried out a field climate manipulation experiment at Rzecin peatland in Poland to assess how, increased temperature and reduced precipitation may impact the CH₄ emission. The field site consists of three times replicated treatments [control (CO); simulated warming (W); reduced precipitation (RP), and warming & RP (WRP)]. Temperature (T) was increased year around with infrared heaters (400Wx4 per site), while precipitation was reduced with an automatic curtain working during growth seasons at night. The average yearly peat (at 5 cm depth) and air temperatures (at 30 cm) increased at manipulated plots by ca. 1.0^oC and 0.4^oC, respectively, while the precipitation was reduced from 24% in 2017 to 38% in 2016. Methane and carbon dioxide fluxes were measured with an automated prototyped mobile chamber system equipped with LGR and Picarro gas analyzers.

                Here we present data from three years; very dry and warm 2015 (417 mm, 9.5°C), more wet and colder 2016 (678 mm, 8.9°C) ad very wet and warm 2017 (929 mm, 9.3°C). The net CH₄ emissions at the control site were at the same rate of 25 gC·m^-2yr^-1 for both 2015 and 2016 years, and significantly higher (by 55%) in the very wet 2017 (39 gCH₄-C·m²·yr^-1). This may indicate that 1) temperature and precipitation play a role in driving the methane emissions from peatland, 2) increase of methane emissions due to higher precipitation can be compensated by lower temperature leading to smaller emission, 3) at more wet and warm years methane emissions may be higher than presently. However, our manipulation clearly indicated that at manipulated sites (W, WRP and RP) methane fluxes were significantly higher (by 28%) than on control plots for both 2015 and 2016 years, while no significant differences between sites exposed for manipulation were found for wet and warm 2017 (although peat temperatures at W, WRD and RD were higher than on CO). This can indicate that in conditions of a high level of groundwater in peatland (due to high rainfall) the sensitivity of methane production processes to temperature changes caused by manipulations may be lower. On the other hand, we found that higher methane fluxes at the manipulated plots are significantly correlated to a higher biomass of vascular plants. This may indicate how important might be the plant species composition on peatland in defining the transport pathways of methane to the atmosphere and overall methane emissions with respect to anticipated climate change.

Research was funded within the NCN projects (017/25/N/ST10/02212, 72016/21/B/ST10/02271) and WETMAN project.