28 Nov 2022
28 Nov 2022
Status: a revised version of this preprint is currently under review for the journal BG.

Dissolved organic matter composition regulates microbial degradation and carbon dioxide production in pristine subarctic rivers

Taija Saarela1, Xudan Zhu2, Helena Jäntti1, Mizue Ohashi3, Jun'ichiro Ide4, Henri Siljanen1, Aake Pesonen1, Heidi Aaltonen5, Anne Ojala6, Hiroshi Nishimura7, Timo Kekäläinen8, Janne Jänis8, Frank Berninger2, and Jukka Pumpanen1 Taija Saarela et al.
  • 1Department of Environmental and Biological Sciences, University of Eastern Finland, Kuopio, FI‑70210, Finland
  • 2Department of Environmental and Biological Sciences, University of Eastern Finland, Joensuu, FI‑80101, Finland
  • 3School of Human Science and Environment, University of Hyogo, Hyogo, 670-0092, Japan
  • 4Department of Applied Chemistry and Bioscience, Chitose Institute of Science and Technology, Chitose, 066-8655, Japan
  • 5Department of Agricultural Sciences, University of Helsinki, Helsinki, FI-00014, Finland
  • 6Natural Resources Institute Finland (Luke), Helsinki, FI-00790, Finland
  • 7Research Institute for Sustainable Humanosphere, Kyoto University, Kyoto, 606-8501, Japan
  • 8Department of Chemistry, University of Eastern Finland, Joensuu, FI‑80101, Finland

Abstract. Dissolved organic matter (DOM) degradation in freshwater rivers and streams plays a major role in the global carbon cycle. However, little is known about how the source and composition of riverine DOM contribute to the production of greenhouse gases, especially in high-latitude areas with a large proportion of carbon-rich peatlands. Here, we conducted for the first time the combination of molecular-level characterization of terrestrially derived DOM and the potential carbon dioxide (CO2) production measurements in pristine subarctic rivers of Finnish Lapland. 21-day incubation studies were conducted with water samples taken from two rivers differing in DOM content during spring and fall 2018. The changes in the DOM concentration and molecular composition, as well as the CO2 production, were measured. The DOM molecular characterization was carried out using Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). Our results demonstrate efficient mineralization of dissolved organic carbon (DOC) into CO2 in mineral soil associated clearwater river during the incubation, while significantly lower CO2 production per DOC was observed in the brown-water river surrounded by peatlands. The limited degradability in the brown-water river was caused by a large number of terrestrial and aromatic compounds (i.e., highly unsaturated and phenolic compounds, condensed aromatics, and polyphenolics) from surrounding peatlands. In the clearwater river, the percentage of formulas assigned to aliphatics decreased over the incubation, indicating microbial utilization of biolabile DOM. This study highlights the importance of energy-rich, biolabile molecular compounds and the contribution of clearwater systems in the DOM degradation dynamics of subarctic catchments.

Taija Saarela et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on bg-2022-225', Anonymous Referee #1, 28 Dec 2022
    • AC1: 'Reply on RC1', Taija Saarela, 30 Jan 2023
  • RC2: 'Comment on bg-2022-225', Anonymous Referee #2, 06 Jan 2023
    • AC2: 'Reply on RC2', Taija Saarela, 30 Jan 2023

Taija Saarela et al.

Taija Saarela et al.


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Short summary
This study investigated the molecular composition and carbon dioxide production of water samples collected from two subarctic rivers that represent contrasting types of catchment characteristics. The results highlight the role of clearwater environments in microbial degradation and greenhouse gas dynamics of subarctic catchments.