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Large isotopic variations and similarities in methane ebullition from northern lakes
Stockholm University, Faculty of Science, Department of Geological Sciences.
Stockholm University, Faculty of Science, Department of Geological Sciences.
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

Lakes are abundant in northern, high latitude landscapes and considered a substantial source of atmospheric methane (CH4). In spite of this, little is known about how CH4 release mechanisms relate to underlying organic sources and biogenic production pathways in different types of water bodies. Here, we present a substantial, multiyear dataset of the stable isotopes of CH4 ebullition from three interconnected, subarctic post-glacial lakes. The δ13C-CH4 and δD-CH4 vary from -78.4 to -53.1‰ and from -369.8 to -218.8‰, respectively. Overall, these observations suggest predominantly acetoclastic methanogenesis in the shallow zones, possibly fueled by in-situ plant production, and a shift towards a mix with hydrogenotrophy at depth. The bubbles’ δ13C-CH4 are similar to most of those reported from other northern natural systems, but we found differences in δD-CH4, possibly due to evaporation-driven fractionation over summer. Stable isotopes provide valuable information about underlying organic sources and production pathways, however, due to large overlaps they may not be effective in reducing uncertainties in emissions potentials among different water body types, and in general between lakes and wetlands.

Keyword [en]
northern lakes, methane emission, ebullition, stable isotopes
National Category
Earth and Related Environmental Sciences
Research subject
Geochemistry
Identifiers
URN: urn:nbn:se:su:diva-126822OAI: oai:DiVA.org:su-126822DiVA: diva2:903504
Funder
Swedish Research Council, 2007-4547
Available from: 2016-02-16 Created: 2016-02-16 Last updated: 2016-03-22Bibliographically approved
In thesis
1. Emission of methane from northern lakes and ponds
Open this publication in new window or tab >>Emission of methane from northern lakes and ponds
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Northern lakes and ponds are abundant and emit large amounts of the potent climate forcer methane to the atmosphere at rates prone to change with amplified Arctic warming. In spite of being important, fluxes from surface waters are not well understood. Long-term measurements are lacking and the dominant and irregular transport mode ebullition (bubbling) is rarely quantified, which complicate the inclusion of lakes and ponds in the global methane budget. This thesis focuses on variations in emissions on both local and regional scales. A synthesis of methane fluxes from almost all studied sites constrains uncertainties and demonstrates that northern lakes and ponds are a dominant source at high latitudes. Per unit area variations in flux magnitudes among different types of water bodies are mainly linked to water depth and type of sediment. When extrapolated, total area is key and thus post-glacial lakes dominate emissions over water bodies formed by peat degradation or thermokarst processes. Further, consistent multiyear measurements in three post-glacial lakes in Stordalen, northern Sweden, reveal that seasonal ebullition, primarily driven by fermentation of acetate, can be predicted by easily measured parameters such as temperature and heat energy input over the ice-free season. Assuming that most water bodies respond similarly to warming, this thesis also suggests that northern lakes and ponds will release substantially more methane before the end of the century, primarily as a result of longer ice-free seasons. Improved uncertainty reductions of both current and future estimates rely on increased knowledge of landscape-level processes related to changes in aquatic systems and organic loading with permafrost thaw, as well as more high-quality measurements, seldom seen in contemporary data. Sampling distributed over entire ice-free seasons and across different depth zones is crucial for accurately quantifying methane emissions from northern lakes and ponds.

Place, publisher, year, edition, pages
Stockholm: Institutionen för geologiska vetenskaper, 2016. 42 p.
Series
Meddelanden från Stockholms universitets institution för geologiska vetenskaper, 361
Keyword
lakes, ponds, water bodies, methane, fluxes, ebullition, stable isotopes, arctic, subarctic, carbon cycling, climate change
National Category
Earth and Related Environmental Sciences
Research subject
Geochemistry
Identifiers
urn:nbn:se:su:diva-126823 (URN)978-91-7649-362-5 (ISBN)
Public defence
2016-04-29, William-Olssonsalen, Geovetenskapens hus, Svante Arrhenius väg 14, Stockholm, 10:00 (English)
Opponent
Supervisors
Funder
Swedish Research Council, 2007–4547
Note

At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 4: Manuscript.

Available from: 2016-04-06 Created: 2016-02-16 Last updated: 2016-03-23Bibliographically approved

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Wik, MartinThornton, BrettCrill, Patrick M.
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