Abstract
Abstract. The patterned microtopography of subarctic mires generates a variety of environmental conditions, and carbon dioxide (CO2) and methane (CH4) dynamics vary spatially among different plant community types (PCTs). We studied the CO2 and CH4 exchange between a subarctic fen and the atmosphere at Kaamanen in northern Finland based on flux chamber and eddy covariance measurements in 2017–2018. We observed strong spatial variation in carbon dynamics between the four main PCTs studied, which were largely controlled by water table level and differences in vegetation composition. The ecosystem respiration (ER) and gross primary productivity (GPP) increased gradually from the wettest PCT to the drier ones, and both ER and GPP were larger for all PCTs during the warmer and drier growing season 2018. We estimated that in 2017 the growing season CO2 balances of the PCTs ranged from −20 g C m−2 (Trichophorum tussock PCT) to 64 g C m−2 (string margin PCT), while in 2018 all PCTs were small CO2 sources (10–22 g C m−2). We observed small growing season CH4 emissions (< 1 g C m−2) from the driest PCT, while the other three PCTs had significantly larger emissions (mean 7.9, range 5.6–10.1 g C m−2) during the two growing seasons. Compared to the annual CO2 balance (−8.5 ± 4.0 g C m−2) of the fen in 2017, in 2018 the annual balance (−5.6 ± 3.7 g C m−2) was affected by an earlier onset of photosynthesis in spring, which increased the CO2 sink, and a drought event during summer, which decreased the sink. The CH4 emissions were also affected by the drought. The annual CH4 balance of the fen was 7.3 ± 0.2 g C m−2 in 2017 and 6.2 ± 0.1 g C m−2 in 2018. Thus, the carbon balance of the fen was close to zero in both years. The PCTs that were adapted to drier conditions provided ecosystem-level resilience to carbon loss due to water level drawdown.
Highlights
Northern mires have sequestered substantial amounts of atmospheric carbon (C) since the last glacial period
The annual average temperature was close to the long-term value (−0.4 ◦C) in both years (−0.6 ◦C in 2017 and 0.4 ◦C in 2018), but in 2018 the monthly means of May, July and November were clearly higher than the reference values by 4.4, 5.4 and 6.5 ◦C, respectively (Fig. 2a)
In 2018, the daily mean temperatures rose to 10 ◦C already in early May, while in 2017 such temperatures were not recorded until early June
Summary
Northern mires have sequestered substantial amounts of atmospheric carbon (C) since the last glacial period. The C storage of these peat soils has been estimated to be 415 ± 150 Pg of C (Hugelius et al, 2020), which adds up to about 30 % of the global soil C This C storage has accumulated through the photosynthetic fixation of carbon dioxide (CO2) by mire vegetation, which in the long term has been larger than the release of C through plant respiration and peat decomposition. Understanding the annual variability in peatland C dynamics is essential, as the subarctic and arctic regions warm rapidly, 2–3 times as fast as the rest of the world (Masson-Delmotte et al, 2018) This is projected to result in increased evapotranspiration and altered precipitation patterns, affecting in turn the C balance of mires (Tarnocai, 2006)
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
