Carbon balance of a Finnish bog: temporal variability and limiting factors based on 6 years of eddy-covariance data.

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From: Biogeosciences(Vol. 18, Issue 16)
Publisher: Copernicus GmbH
Document Type: Article
Length: 445 words

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Abstract :

Pristine boreal mires are known as substantial sinks of carbon dioxide (CO.sub.2) and net emitters of methane (CH.sub.4). Bogs constitute a major fraction of pristine boreal mires. However, the bog CO.sub.2 and CH.sub.4 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 CO.sub.2 and CH.sub.4 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 CO.sub.2 and CH.sub.4 EC flux (FCH4) measurements and identifies the environmental factors controlling the ecosystem-atmosphere CO.sub.2 and CH.sub.4 exchange. A 6-year average growing season (May-September) cumulative CO.sub.2 exchange of -61 ± 24 g C m.sup.-2 was observed, which partitions into mean total respiration (Re) of 167 ± 33 (interannual range 146-197) g C m.sup.-2 and mean gross primary production (GPP) of 228 ± 46 (interannual range 193-257) g C m.sup.-2, while the corresponding FCH4 amounts to 7.1 ± 0.7 (interannual range 6.4-8.4) g C m.sup.-2 . The contribution of October-December CO.sub.2 and CH.sub.4 fluxes to the cumulative sums was not negligible based on the measurements during one winter. GPP, Re and FCH4 increased with temperature. GPP and FCH4 did not show any significant decline even after a substantial water table drawdown in 2011. Instead, GPP, Re and FCH4 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 -73 g C m.sup.-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 g C m.sup.-2 in 2011 due to elevated Re, and by about 40 g C m.sup.-2 in 2012 due to limited GPP. The cumulative growing season sums of GPP and CH.sub.4 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 CO.sub.2 and CH.sub.4 fluxes and the EC footprint composition was found despite the apparent variation in fluxes with wind direction.

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Gale Document Number: GALE|A672366094