Preprints
https://doi.org/10.5194/bg-2022-69
https://doi.org/10.5194/bg-2022-69
 
06 Apr 2022
06 Apr 2022
Status: this preprint is currently under review for the journal BG.

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

Lauri Heiskanen1, Juha-Pekka Tuovinen1, Aleksi Räsänen2,3, Tarmo Virtanen2, Sari Juutinen2,4, Henriikka Vekuri1, Annalea Lohila1, Juha Mikola2,3, and Mika Aurela1 Lauri Heiskanen et al.
  • 1Climate System Research Unit, Finnish Meteorological Institute, Helsinki, Finland
  • 2Ecosystems and Environment Research Programme, Faculty of Biological and Environmental Sciences, University of Helsinki, Helsinki, Finland
  • 3Natural Resources Institute Finland (LUKE), Helsinki, Finland
  • 4University of Eastern Finland, Department of Geographical and Historical Studies, Joensuu, Finland

Abstract. 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 (CO2) and methane (CH4) fluxes varies spatially and temporally among these ecosystems. Our study area in Kaamanen in northern Finland covering 7 km2 of boreal subarctic landscape with upland forest, open peatland, pine bogs and lakes. We measured the CO2 and CH4 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 CO2 sink of -25.9 ± 65.7 and -41.3 ± 64.9 g C m-2, and a CH4 source of 2.4 ± 0.7 and 2.3 ± 0.7 g C m-2 during the first and second study year, respectively. The pine forest had the largest contribution to the landscape-level CO2 sink, -78.3 ± 50.8 and -118.9 ± 26.8 g C m-2, and the fen to the CH4 emissions, 7.0 ± 0.2 and 6.3 ± 0.3 g C m-2, during the first and second study year, respectively. The lakes within the area acted as CO2 and CH4 sources to the atmosphere throughout the measurement period, with an organic sediment lake located downstream from the fen showing sixfold fluxes compared to a mineral sediment lake. The annual C balances were affected most by the rainy peak growing season of 2017 and the heatwave and drought event in July 2018. The rainy period increased the ecosystem respiration of the pine forest due to continuously high soil moisture content. A similar flux response to abundant precipitation was not observed for the fen ecosystem, which is adapted to high water table levels. During the heatwave and drought period, similar responses were observed for all terrestrial ecosystems, with decreased gross primary productivity and net CO2 uptake, caused by the unfavourable growing conditions and plant stress due to the soil moisture and vapour pressure deficits. Additionally, the CH4 emissions from the fen decreased during and after the drought. However, the timing and duration of drought effects varied between fen and forest ecosystems, as C fluxes were affected sooner and had a shorter post-drought recovery time in the fen than forests. The differing CO2 flux response to weather variations showed that terrestrial ecosystems can have a contrasting impact on the landscape-level C balance in a changing climate, even if they function similarly most of the time.

Lauri Heiskanen et al.

Status: open (until 17 Jun 2022)

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Lauri Heiskanen et al.

Lauri Heiskanen et al.

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Short summary
We measured and modelled the CO2 and CH4 fluxes of the terrestrial and aquatic ecosystems of the subarctic landscape for two years. The landscape was an annual CO2 sink and a CH4 source. The forest had the largest contribution to the landscape-level CO2 sink and the peatland to the CH4 emissions. The lakes released 20 % of the annual net C uptake of the landscape back to the atmosphere. The C fluxes were affected most by the rainy peak growing season of 2017 and the drought event in July 2018.
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