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Emission of methane from northern lakes and ponds
Stockholm University, Faculty of Science, Department of Geological Sciences.
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 [en]
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: urn:nbn:se:su:diva-126823ISBN: 978-91-7649-362-5 (print)OAI: oai:DiVA.org:su-126823DiVA: diva2:907899
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: 2017-02-24Bibliographically approved
List of papers
1. Climate-sensitive northern lakes and ponds are critical components of methane release
Open this publication in new window or tab >>Climate-sensitive northern lakes and ponds are critical components of methane release
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2016 (English)In: Nature Geoscience, ISSN 1752-0894, E-ISSN 1752-0908, Vol. 9, 99-105 p.Article, review/survey (Refereed) Published
Abstract [en]

Lakes and ponds represent one of the largest natural sources of the greenhouse gas methane. By surface area, almost half of these waters are located in the boreal region and northwards. A synthesis of measurements of methane emissions from 733 lakes and ponds north of ~50° N, combined with new inventories of inland waters, reveals that emissions from these high latitudes amount to around 16.5 Tg CH4 yr−1 (12.4 Tg CH4-C yr−1). This estimate — from lakes and ponds alone — is equivalent to roughly two-thirds of the inverse model calculation of all natural methane sources in the region. Thermokarst water bodies have received attention for their high emission rates, but we find that post-glacial lakes are a larger regional source due to their larger areal extent. Water body depth, sediment type and ecoclimatic region are also important in explaining variation in methane fluxes. Depending on whether warming and permafrost thaw cause expansion or contraction of lake and pond areal coverage, we estimate that annual water body emissions will increase by 20–54% before the end of the century if ice-free seasons are extended by 20 days. We conclude that lakes and ponds are a dominant methane source at high northern latitudes.

Keyword
Biogeochemistry, Climate-change impacts
National Category
Earth and Related Environmental Sciences
Research subject
Geochemistry
Identifiers
urn:nbn:se:su:diva-126816 (URN)10.1038/ngeo2578 (DOI)000369324600010 ()
Funder
Swedish Research Council, 2007-4547
Available from: 2016-02-16 Created: 2016-02-16 Last updated: 2017-11-30Bibliographically approved
2. Multiyear measurements of ebullitive methane flux from three subarctic lakes
Open this publication in new window or tab >>Multiyear measurements of ebullitive methane flux from three subarctic lakes
2013 (English)In: Journal of Geophysical Research - Biogeosciences, ISSN 2169-8953, E-ISSN 2169-8961, Vol. 118, no 3, 1307-1321 p.Article in journal (Refereed) Published
Abstract [en]

Ebullition (bubbling) from small lakes and ponds at high latitudes is an important yet unconstrained source of atmospheric methane (CH4). Small water bodies are most abundant in permanently frozen peatlands, and it is speculated that their emissions will increase as the permafrost thaws. We made 6806 measurements of CH4 ebullition during four consecutive summers using a total of 40 bubble traps that were systematically distributed across the depth zones of three lakes in a sporadic permafrost landscape in northernmost Sweden. We identified significant spatial and temporal variations in ebullition and observed a large spread in the bubbles' CH4 concentration, ranging from 0.04% to 98.6%. Ebullition followed lake temperatures, and releases were significantly larger during periods with decreasing atmospheric pressure. Although shallow zone ebullition dominated the seasonal bubble CH4 flux, we found a shift in the depth dependency towards higher fluxes from intermediate and deep zones in early fall. The average daily flux of 13.4mg CH4 m(-2) was lower than those measured in most other high-latitude lakes. Locally, however, our study lakes are a substantial CH4 source; we estimate that 350kg of CH4 is released via ebullition during summer (June-September), which is approximately 40% of total whole year emissions from the nearby peatland. In order to capture the large variability and to accurately scale lake CH4 ebullition temporally and spatially, frequent measurements over long time periods are critical.

Keyword
methane, ebullition, high-latitude lakes
National Category
Environmental Sciences Ecology
Research subject
Geochemistry
Identifiers
urn:nbn:se:su:diva-96126 (URN)10.1002/jgrg.20103 (DOI)000325549900028 ()
Note

AuthorCount:4;

Available from: 2013-11-13 Created: 2013-11-11 Last updated: 2017-12-06Bibliographically approved
3. Energy input is primary controller of methane bubbling in subarctic lakes
Open this publication in new window or tab >>Energy input is primary controller of methane bubbling in subarctic lakes
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2014 (English)In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 41, no 2, 555-560 p.Article in journal (Refereed) Published
Abstract [en]

Emission of methane (CH4) from surface waters is often dominated by ebullition (bubbling), a transport mode with high-spatiotemporal variability. Based on new and extensive CH4 ebullition data, we demonstrate striking correlations (r(2) between 0.92 and 0.997) when comparing seasonal bubble CH4 flux from three shallow subarctic lakes to four readily measurable proxies of incoming energy flux and daily flux magnitudes to surface sediment temperature (r(2) between 0.86 and 0.94). Our results after continuous multiyear sampling suggest that CH4 ebullition is a predictable process, and that heat flux into the lakes is the dominant driver of gas production and release. Future changes in the energy received by lakes and ponds due to shorter ice-covered seasons will predictably alter the ebullitive CH4 flux from freshwater systems across northern landscapes. This finding is critical for our understanding of the dynamics of radiatively important trace gas sources and associated climate feedback.

Keyword
methane, ebullition, energy flux, subarctic lakes
National Category
Earth and Related Environmental Sciences
Research subject
Geochemistry
Identifiers
urn:nbn:se:su:diva-103320 (URN)10.1002/2013GL058510 (DOI)000332991000051 ()
Note

AuthorCount:6;

Available from: 2014-05-14 Created: 2014-05-12 Last updated: 2017-12-05Bibliographically approved
4. Large isotopic variations and similarities in methane ebullition from northern lakes
Open this publication in new window or tab >>Large isotopic variations and similarities in methane ebullition from northern lakes
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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
northern lakes, methane emission, ebullition, stable isotopes
National Category
Earth and Related Environmental Sciences
Research subject
Geochemistry
Identifiers
urn:nbn:se:su:diva-126822 (URN)
Funder
Swedish Research Council, 2007-4547
Available from: 2016-02-16 Created: 2016-02-16 Last updated: 2016-03-22Bibliographically approved
5. Biased sampling of methane release from northern lakes: A problem for extrapolation
Open this publication in new window or tab >>Biased sampling of methane release from northern lakes: A problem for extrapolation
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2016 (English)In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 43, no 3, 1256-1262 p.Article in journal (Refereed) Published
Abstract [en]

Methane emissions from lakes are widely thought to be highly irregular and difficult to quantify with anything other than numerous distributed measurement stations and long-term sampling campaigns. In spite of this, a large majority of the study sites north of 50°N have been measured over surprisingly short time periods of only one to a few days. Using long-term data from three intensively studied small subarctic lakes, we recommend that measurements of diffusive methane flux and ebullition should be made over at least 11 and 39 days scattered throughout the ice-free season using depth-stratified sampling at 3 and 11 or more locations, respectively. We further show that low temporal and spatial resolutions are unlikely to cause overestimates. Therefore, we argue that most sites measured previously are likely underestimated in terms of emission potential. Avoiding these biases seen in much of the contemporary data is crucial to further constrain large-scale methane emissions from northern lakes and ponds.

Keyword
northern lakes, methane, sampling bias, ebullition, diffusion, subarctic
National Category
Earth and Related Environmental Sciences
Research subject
Geochemistry
Identifiers
urn:nbn:se:su:diva-126819 (URN)10.1002/2015GL066501 (DOI)000372056600039 ()
Funder
Swedish Research Council, 2007–4547
Available from: 2016-02-16 Created: 2016-02-16 Last updated: 2017-11-30Bibliographically approved

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