Meteorological responses of carbon dioxide and methane fluxes in the terrestrial and aquatic ecosystems of a subarctic landscape

• Published in: Biogeosciences
• Main Authors: L. Heiskanen, J.-P. Tuovinen, H. Vekuri, A. Räsänen, T. Virtanen, S. Juutinen, A. Lohila, J. Mikola, M. Aurela
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Publications 2023
• Subjects: Ecology; QH540-549.5; Life; QH501-531; Geology; QE1-996.5; Kaamanen; Northern Finland; Subarctic
• Online Access: https://doi.org/10.5194/bg-20-545-2023; https://doaj.org/article/80f02c027cf6474d9268777c442ec505

The subarctic landscape consists of a mosaic of forest, peatland, and aquatic ecosystems and their ecotones. The carbon ( C ) exchange between ecosystems and the atmosphere through carbon dioxide ( CO 2 ) and methane ( CH 4 ) fluxes varies spatially and temporally among these ecosystems. Our study area in Kaamanen in northern Finland covered 7 km 2 of boreal subarctic landscape with upland forest, open peatland, pine bogs, and lakes. We measured the CO 2 and CH 4 fluxes with eddy covariance and chambers between June 2017 and June 2019 and studied the C flux responses to varying meteorological conditions. The landscape area was an annual CO 2 sink of − 45 ± 22 and − 33 ± 23 g C m −2 and a CH 4 source of 3.0 ± 0.2 and 2.7 ± 0.2 g C m −2 during the first and second study years, respectively. The pine forest had the largest contribution to the landscape-level CO 2 sink, − 126 ± 21 and − 101 ± 19 g C m −2 , and the fen to the CH 4 emissions, 7.8 ± 0.2 and 6.3 ± 0.3 g C m −2 , during the first and second study years, respectively. The lakes within the area acted as CO 2 and CH 4 sources to the atmosphere throughout the measurement period, and a lake located downstream from the fen with organic sediment showed 4-fold fluxes compared to a mineral sediment lake. The annual C balances were affected most by the rainy peak growing season in 2017, the warm summer in 2018, and a heatwave and drought event in July 2018. The rainy period increased ecosystem respiration (ER) in the pine forest due to continuously high soil moisture content, and ER was on a level similar to the following, notably warmer, summer. A corresponding ER response to abundant precipitation was not observed for the fen ecosystem, which is adapted to high water table levels, and thus a higher ER sum was observed during the warm summer 2018. During the heatwave and drought period, similar responses were observed for all terrestrial ecosystems, with decreased gross primary productivity and net CO 2 uptake, caused by the unfavourable growing conditions and ...