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Biophysical controls on CO2 evasion from Arctic inland waters
Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.ORCID iD: 0000-0001-7853-2531
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 [en]
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: urn:nbn:se:umu:diva-158882ISBN: 978-91-7855-075-3 (print)OAI: oai:DiVA.org:umu-158882DiVA, id: diva2:1315375
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
List of papers
1. Large lakes dominate CO2 evasion from lakes in an arctic catchment
Open this publication in new window or tab >>Large lakes dominate CO2 evasion from lakes in an arctic catchment
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2017 (English)In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 44, no 24, p. 12254-12261Article in journal (Refereed) Published
Abstract [en]

CO2 evasion from freshwater lakes is an important component of the carbon cycle. However, the relative contribution from different lake sizes may vary, since several parameters underlying CO2 flux are size dependent. Here we estimated the annual lake CO2 evasion from a catchment in northern Sweden encompassing about 30,000 differently sized lakes. We show that areal CO2 fluxes decreased rapidly with lake size, but this was counteracted by the greater overall coverage of larger lakes. As a result, total efflux increased with lake size and the single largest lake in the catchment dominated the CO2 evasion (53% of all CO2 evaded). By contrast, the contribution from the smallest ponds (about 27,000) was minor (<6%). Our results emphasize the importance of accounting for both CO2 flux rates and areal contribution of various sized lakes in assessments of CO2 evasion at the landscape scale.

Place, publisher, year, edition, pages
American Geophysical Union (AGU), 2017
National Category
Geophysics Oceanography, Hydrology and Water Resources
Identifiers
urn:nbn:se:umu:diva-144858 (URN)10.1002/2017GL076146 (DOI)000422954700049 ()
Available from: 2018-02-22 Created: 2018-02-22 Last updated: 2019-05-13Bibliographically approved
2. Landscape process domains drive patterns of CO2 evasion from river networks
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2019 (English)In: Limnology and Oceanography Letters, ISSN 2378-2242, Vol. 4, no 4, p. 87-95Article in journal, Letter (Refereed) Published
Abstract [en]

Streams are important emitters of CO2 but extreme spatial variability in their physical properties can make upscaling very uncertain. Here, we determined critical drivers of stream CO2 evasion at scales from 30 to 400 m across a 52.5 km2 catchment in northern Sweden. We found that turbulent reaches never have elevated CO2 concentrations, while less turbulent locations can potentially support a broad range of CO2 concentrations, consistent with global observations. The predictability of stream pCO2 is greatly improved when we include a proxy for soil‐stream connectivity. Catchment topography shapes network patterns of evasion by creating hydrologically linked “domains” characterized by high water‐atmosphere exchange and/or strong soil‐stream connection. This template generates spatial variability in the drivers of CO2 evasion that can strongly bias regional and global estimates. To overcome this complexity, we provide the foundations of a mechanistic framework of CO2 evasion by considering how landscape process domains regulate transfer and supply.

Place, publisher, year, edition, pages
John Wiley & Sons, 2019
National Category
Geosciences, Multidisciplinary
Identifiers
urn:nbn:se:umu:diva-158874 (URN)10.1002/lol2.10108 (DOI)000474692600001 ()
Funder
Swedish Research Council, 2013‐5001
Available from: 2019-05-13 Created: 2019-05-13 Last updated: 2019-08-12Bibliographically approved
3. Stream metabolism controls diel patterns and evasion of CO2 in Arctic streams
Open this publication in new window or tab >>Stream metabolism controls diel patterns and evasion of CO2 in Arctic streams
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

Streams play an important role in the global carbon (C) cycle, accounting for a large portion of CO2 evaded from inland waters despite their small areal coverage. However, the relative importance of different terrestrial and aquatic processes driving CO2 production and evasion from streams remains poorly understood. In this study, we measured O2 and CO2 continuously in tundra-dominated streams in northern Sweden to estimate daily metabolic rates and CO2 evasion simultaneously and thus provide insight into the role of stream metabolism as a driver of C dynamics in Arctic streams. Our results show that aquatic biological processes control CO2 concentrations and evasion at multiple time scales. Photosynthesis caused a marked decrease in CO2 concentrations during the day, with up to a 900-ppm difference between day- and night-time values with the magnitude of this diel variation being strongest at the low-turbulence streams. These diel patterns in CO2 concentrations in turn influenced evasion, with up to 45% higher rates at night. Throughout the summer, CO2 evasion was sustained by ecosystem respiration, which was one order of magnitude higher than gross primary production. Furthermore, in most cases the contribution of stream respiration exceeded CO2 evasion, suggesting that some stream reaches serve as net sources of CO2, creating longitudinal heterogeneity in C production and loss within this stream network. Overall, our results provide the first link between stream metabolism and CO2 evasion in the Arctic and demonstrate that stream metabolic processes are key drivers of the transformation and fate of terrestrial organic matter exported from these landscapes.

National Category
Geosciences, Multidisciplinary
Research subject
Limnology
Identifiers
urn:nbn:se:umu:diva-158880 (URN)
Available from: 2019-05-13 Created: 2019-05-13 Last updated: 2019-06-13
4. Photosynthesis overrides photo-oxidation in CO2 dynamics of Arctic permafrost streams
Open this publication in new window or tab >>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:nbn:se:umu:diva-158881 (URN)
Available from: 2019-05-13 Created: 2019-05-13 Last updated: 2019-06-13

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