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Photosynthesis overrides photo-oxidation in CO2 dynamics of Arctic permafrost streams
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

Global warming is mobilising large amounts of organic carbon (C) from arctic soils into streams, where it can be mineralized to CO2 and released to the atmosphere. Photo-chemical degradation is thought to drive this mineralization, yet this process has not been quantitatively integrated with biological processes, like photosynthesis and respiration, that also influence CO2 dynamics in aquatic ecosystems. We measured CO2 and δ13C-DIC concentrations at diel resolution in two northern Alaska streams, and coupled this with whole-system metabolism estimates to assess the effect of different light-dependent processes on stream C dynamics. CO2 concentrations decreased by up to 500 ppm from night to day, a pattern counter to the hypothesis that photodegradation is the dominant source of dissolved CO2. Instead, the observed decrease in CO2 concentration during daytime was explained by photosynthetic rates in streams, which ranged from 0.04 to 0.17 g C m-2 d-1, and were also strongly correlated with diurnal changes in the isotopic composition of dissolved inorganic C. However, photosynthetic rates were larger than the observed diel change in CO2, suggesting that metabolic estimates are partly masked by CO2 production from photo-oxidation. The difference between expected and observed daytime CO2 concentrations suggests 1 – 30 mmol C m3 d-1 may be generated from photo-oxidation, a range that corresponds well to laboratory measurements of this process. Overall, stream net ecosystem production was a source of CO2, with rates ten times greater than published photo-oxidation rates for arctic aquatic ecosystems and accounted for 27-83% of CO2 evasion. Our results suggest that aquatic metabolic activity has a significant effect on CO2 dynamics and emissions from arctic stream networks.

National Category
Environmental Sciences Geosciences, Multidisciplinary
Identifiers
URN: urn:nbn:se:umu:diva-158881OAI: oai:DiVA.org:umu-158881DiVA, id: diva2:1315363
Available from: 2019-05-13 Created: 2019-05-13 Last updated: 2019-06-13
In thesis
1. Biophysical controls on CO2 evasion from Arctic inland waters
Open this publication in new window or tab >>Biophysical controls on CO2 evasion from Arctic inland waters
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

CO2 evasion to the atmosphere from inland waters is a major component of the global carbon (C) cycle. Yet spatial patterns of CO2 evasion and the sources of C that fuel evasion remain poorly understood. In this thesis, I use detailed measurements of biological and physical drivers of CO2 evasion to assess how C is transformed and evaded from inland waters in the Arctic (Northern Scandinavia and Alaska). I found that lake size was a master variable controlling lake CO2 evasion in an Arctic catchment and that large lakes play a major role at the landscape scale. In stream networks, I found that catchment topography shapes patterns of CO2 evasion by dictating unique domains with high lateral inputs of C, other domains where biological processes were dominant, and domains where physical forces promoted degassing to the atmosphere. Together, these topographically driven domains created a strong spatial heterogeneity that biases regional and global estimates of CO2 evasion. Further, I found that photosynthetic activity in Arctic streams can produce a large change in CO2 concentrations from night to day, and as a result CO2 evasion is up to 45% higher during night than day. The magnitude of the diel change in CO2 was also affected by the turbulence of the stream and photo-chemical production of CO2. Overall, this thesis offers important insights to better understand landscape patterns of CO2 evasion from inland waters, and suggests that stream metabolic processes largely determine the fate of the C delivered from Arctic soils.

Place, publisher, year, edition, pages
Umeå: Umeå Univeristy, 2019. p. 32
Keywords
Inland waters, carbon dioxide, organic carbon, inorganic carbon, arctic, CO2 evasion, DOC, DIC, streams, metabolism, oxygen
National Category
Physical Geography Geosciences, Multidisciplinary Environmental Sciences
Research subject
Limnology
Identifiers
urn:nbn:se:umu:diva-158882 (URN)978-91-7855-075-3 (ISBN)
Public defence
2019-06-14, Carl Kempe Salen, KBC, Umeå University, Umeå, 09:30 (English)
Opponent
Supervisors
Available from: 2019-05-24 Created: 2019-05-13 Last updated: 2019-05-23Bibliographically approved

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Rocher-Ros, Gerard

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