Alekseychik, Pavel; Korrensalo, Aino; Mammarella, Ivan; Launiainen, Samuli; Tuittila, Eeva-Stiina; Korpela, Ilkka; Vesala, Timo

Pristine boreal mires are known as substantial sinks of carbon dioxide (inline-formulaCO2) and net emitters of methane (inline-formulaCH4). Bogs constitute a major fraction of pristine boreal mires. However, the bog inline-formulaCO2 and inline-formulaCH4 balances are poorly known, having been largely estimated based on discrete and short-term measurements by manual chambers and seldom using the eddy-covariance (EC) technique.

Eddy-covariance (EC) measurements of inline-formulaCO2 and inline-formulaCH4 exchange were conducted in the Siikaneva mire complex in southern Finland in 2011–2016. The site is a patterned bog having a moss–sedge–shrub vegetation typical of southern Eurasian taiga, with several ponds near the EC tower. The study presents a complete series of inline-formulaCO2 and inline-formulaCH4 EC flux (inline-formula M9inlinescrollmathml F chem normal CH normal 4 23pt14ptsvg-formulamathimgab687810aac214ba5f355fd0aa86f2fd bg-18-4681-2021-ie00001.svg23pt14ptbg-18-4681-2021-ie00001.png ) measurements and identifies the environmental factors controlling the ecosystem–atmosphere inline-formulaCO2 and inline-formulaCH4 exchange. A 6-year average growing season (May–September) cumulative inline-formulaCO2 exchange of inline-formula−61 inline-formula± 24 inline-formulag C m−2 was observed, which partitions into mean total respiration (Re) of 167 inline-formula± 33 (interannual range 146–197) inline-formulag C m−2 and mean gross primary production (GPP) of 228 inline-formula± 46 (interannual range 193–257) inline-formulag C m−2, while the corresponding inline-formula M20inlinescrollmathml F chem normal CH normal 4 23pt14ptsvg-formulamathimg3b23b2f6ff1912ba08777d77987e537a bg-18-4681-2021-ie00002.svg23pt14ptbg-18-4681-2021-ie00002.png amounts to 7.1 inline-formula± 0.7 (interannual range 6.4–8.4) inline-formulag C m−2. The contribution of October–December inline-formulaCO2 and inline-formulaCH4 fluxes to the cumulative sums was not negligible based on the measurements during one winter.

GPP, Re and inline-formula M25inlinescrollmathml F chem normal CH normal 4 23pt14ptsvg-formulamathimgd8bbbc44b841bc4b0d560790d27387ad bg-18-4681-2021-ie00003.svg23pt14ptbg-18-4681-2021-ie00003.png increased with temperature. GPP and inline-formula M26inlinescrollmathml F chem normal CH normal 4 23pt14ptsvg-formulamathimge7faee267f2d387a57bd161b24473195 bg-18-4681-2021-ie00004.svg23pt14ptbg-18-4681-2021-ie00004.png did not show any significant decline even after a substantial water table drawdown in 2011. Instead, GPP, Re and inline-formula M27inlinescrollmathml F chem normal CH normal 4 23pt14ptsvg-formulamathimgbb4584dfd3d333b1930088202eeb2343 bg-18-4681-2021-ie00005.svg23pt14ptbg-18-4681-2021-ie00005.png were limited in the cool, cloudy and wet growing season of 2012. May–September cumulative net ecosystem exchange (NEE) of 2013–2016 averaged at about inline-formula−73 inline-formulag C m−2, in contrast with the hot and dry year 2011 and the wet and cool year 2012. Suboptimal weather likely reduced the net sink by about 25 inline-formulag C m−2 in 2011 due to elevated Re, and by about 40 inline-formulag C m−2 in 2012 due to limited GPP. The cumulative growing season sums of GPP and inline-formulaCH4 emission showed a strong positive relationship.

The EC source area was found to be comprised of eight distinct surface types. However, footprint analyses revealed that contributions of different surface types varied only within 10 %–20 % with respect to wind direction and stability conditions. Consequently, no clear link between inline-formulaCO2 and inline-formulaCH4 fluxes and the EC footprint composition was found despite the apparent variation in fluxes with wind direction.

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Alekseychik, Pavel / Korrensalo, Aino / Mammarella, Ivan / et al: Carbon balance of a Finnish bog: temporal variability and limiting factors based on 6 years of eddy-covariance data. 2021. Copernicus Publications.

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