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Constraints on methane oxidation in ice-covered boreal lakes
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology. Umea Univ, Dept Ecol & Environm Sci, Umea, Sweden.
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology. Uppsala University, Science for Life Laboratory, SciLifeLab.
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2016 (English)In: Journal of Geophysical Research - Biogeosciences, ISSN 2169-8953, E-ISSN 2169-8961, Vol. 121, no 7, 1924-1933 p.Article in journal (Refereed) Published
Abstract [en]

Boreal lakes can be ice covered for a substantial portion of the year at which time methane (CH4) can accumulate below ice. The amount of CH4 emitted at ice melt is partially determined by the interplay between CH4 production and CH4 oxidation, performed by methane-oxidizing bacteria (MOB). Yet the balance between oxidation and emission and the potential for CH4 oxidation in various lakes during winter is largely unknown. To address this, we performed incubations at 2 degrees C to screen for wintertime CH4 oxidation potential in seven lakes. Results showed that CH4 oxidation was restricted to three lakes, where the phosphate concentrations were highest. Molecular analyses revealed that MOB were initially detected in all lakes, although an increase in type I MOB only occurred in the three lake water incubations where oxidation could be observed. Accordingly, the increase in CO2 was on average 5 times higher in these three lake water incubations. For one lake where no oxidation was measured, we tested if temperature and CH4 availability could trigger CH4 oxidation. However, regardless of incubation temperatures and CH4 concentrations, ranging from 2 to 20 degrees C and 1-500M, respectively, no oxidation was observed. Our study indicates that some lakes with active wintertime CH4 oxidation may have low emissions during ice melt, while other and particularly nutrient poor lakes may accumulate large amounts of CH4 below ice that, in the absence of CH4 oxidation, will be emitted following ice melt. This variability in CH4 oxidation rates between lakes needs to be accounted for in large-scale CH4 emission estimates.

Place, publisher, year, edition, pages
2016. Vol. 121, no 7, 1924-1933 p.
National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:uu:diva-274393DOI: 10.1002/2016JG003382ISI: 000382581900015OAI: oai:DiVA.org:uu-274393DiVA: diva2:896413
Funder
Swedish Research CouncilSwedish Research Council FormasCarl Tryggers foundation
Note

De två första författarna delar förstaförfattarskapet.

Available from: 2016-01-21 Created: 2016-01-21 Last updated: 2017-11-30Bibliographically approved
In thesis
1. Greenhouse Gas Dynamics in Ice-covered Lakes Across Spatial and Temporal Scales
Open this publication in new window or tab >>Greenhouse Gas Dynamics in Ice-covered Lakes Across Spatial and Temporal Scales
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Lakes play a major role in the global carbon (C) cycle, despite making up a small area of earth’s surface. Lakes receive, transport and process sizable amounts of C, emitting a substantial amount of the greenhouse gases, carbon dioxide (CO2) and methane (CH4), into the atmosphere. Ice-covered lakes are particularly sensitive to climate change, as future reductions to the duration of lake ice cover will have profound effects on the biogeochemical cycling of C in lakes. It is still largely unknown how reduced ice cover duration will affect CO2 and CH4 emissions from ice-covered lakes. Thus, the primary aim of this thesis was to fill this knowledge gap by monitoring the spatial and temporal dynamics of CO2 and CH4 in ice-covered lakes. The results of this thesis demonstrate that below ice CO2 and CH4 were spatially and temporally variable. Nutrients were strongly linked to below ice CO2 and CH4 oxidation variations across lakes. In addition, below ice CO2 was generally highest in small shallow lakes, and in bottom waters. Whilst below ice CH4 was elevated in surface waters near where bubbles from anoxic lake sediment were trapped. During the ice-cover period, CO2 accumulation below ice was not linear, and at ice-melt incomplete mixing of lake waters resulted in a continued CO2 storage in bottom waters. Further, CO2 transported from the catchment and bottom waters contributed to high CO2 emissions. The collective findings of this thesis indicate that CO2 and CH4 emissions from ice-covered lakes will likely increase in the future. The strong relationship between nutrients and C processes below ice, imply that future changes to nutrient fluxes within lakes will influence the biogeochemical cycling of C in lakes. Since catchment and lake sediment C fluxes play a considerable role in below ice CO2 and CH4 dynamics, changes to hydrology and thermal stability of lakes will undoubtedly alter CO2 and CH4 emissions. Nevertheless, ice-covered lakes constitute a significant component of the global C cycle, and as such, should be carefully monitored and accounted for when addressing the impacts of global climate change.  

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2016. 53 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1341
Keyword
carbon cycle, climate change, cryosphere, carbon dioxide, methane, lakes, winter limnology, methane oxidation, nutrients, catchment
National Category
Natural Sciences
Research subject
Limnology
Identifiers
urn:nbn:se:uu:diva-275018 (URN)978-91-554-9467-4 (ISBN)
Public defence
2016-03-18, Friessalen, Evolutionary Biology Centre (EBC), Norbyvägen 14, Uppsala, 13:15 (English)
Opponent
Supervisors
Available from: 2016-02-26 Created: 2016-01-28 Last updated: 2016-03-09
2. Life strategies for substrate assimilation by freshwater bacterioplankton
Open this publication in new window or tab >>Life strategies for substrate assimilation by freshwater bacterioplankton
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The availability of substrates is one of the most important environmental constraints on the diversity and functioning of microorganisms. Substrate quantity and quality as well as the metabolic features of heterotrophic microorganisms determine the efficiency, speed and type of transformation that can occur in nature. As such their interplay with the environment regulates how much carbon and energy is incorporated by bacteria and subsequently reaches higher trophic levels. In lakes the bulk substrate that is available for bacteria is composed of a complex mixture of compounds, varying in lability and distribution in the environment. This thesis addresses the coupling of organic substrates, their metabolic use and the composition and ecology of the microbial community. Controlled laboratory experiments with mixed bacterial communities in either batch cultures or chemostats were designed to shed further light on bacterial use of labile and quantitatively significant carbon compounds.

I show that different amino acid substrates only exert a minor influence on bacterioplankton community composition and growth. Hence the ability to use a wide range of such abundantly produced protein monomers seems to be widespread among freshwater bacteria. In contrast, when acetate was provided as the only carbon substrate, in either pulsed or continuous amendments, this very different substrate input mode had a strong effect on bacterial community composition. Biomass yield, for example, was twice as high when acetate was given in the form of pulses rather than provided continuously.

In another set of experiments, I show that the oxidation of the globally significant greenhouse gas methane is a process that can potentially take place at the water-ice interface of seasonally ice-covered lakes and was not constrained by temperature as suggested in previous studies. This work also suggests that methane oxidation in ice-covered lakes can be constrained by competition for nutrients between specialized methanotrophs and heterotrophic bacteria.

Combined these studies suggest that some labile substrates cause minor selection on bacterial community structure and functioning. This probably reflects the competitive advantage of using a broad range of low molecular weight substrates. However, as in the case of methanotrophs there is specialization for a specific low molecular weight substrate such as methane. In which case, competition with other community members i.e. for nutrients can constrain methane oxidation. In both cases it might however not depend just on the availability of substrate, but also on how substrates are distributed in time and space.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2016. 39 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1342
Keyword
lake, methane, bacteria, substrate, methanotrophs, pulse, chemostat
National Category
Natural Sciences
Identifiers
urn:nbn:se:uu:diva-275181 (URN)978-91-554-9470-4 (ISBN)
Public defence
2016-03-18, Friessalen, EBC, Norbyvägen 14, Uppsala, 09:00 (English)
Opponent
Supervisors
Available from: 2016-02-26 Created: 2016-02-01 Last updated: 2016-03-09

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