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The role of inland waters in the carbon cycle at high latitudes
Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. (Arcum)
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Understanding the drivers of climate change requires knowledge about the global carbon (C) cycle. Although inland waters play an important role in the C cycle by emitting and burying C, streams and lakes are in general overlooked in bottom-up approached C budgets. In this thesis I estimated emissions of carbon dioxide (CO2) and methane (CH4) from all lakes and streams in a 15 km2 subarctic catchment in northern Sweden, and put it in relation to the total catchment C exchange. I show that high-latitude aquatic systems in general and streams in particular are hotspots for C emission to the atmosphere. Annually, the aquatic systems surveyed in this study emitted about 10.8 ± 4.9 g C m-2 yr-1 (ca. 98 % as CO2) which is more than double the amount of the C laterally exported from the catchment. Although the streams only covered about 4% of the total aquatic area they emitted ca. 95% of the total aquatic C emission. For lake emissions, the ice break-ups were the most important annual events, counting for ca. 45% of the emissions. Overall, streams dominated the aquatic CO2 emission in the catchment while lakes dominated CH4 emission, 96 % and 62 % of the totals, respectively. When summing terrestrial and aquatic C fluxes together it showed that the aquatic emissions alone account for approximately two thirds of the total annual catchment C loss. The consequence of not including inland waters in bottom-up derived C budgets is therefore a risk of overestimating the sink capacity of the subarctic landscape. However, aquatic systems can also act as C sinks, by accumulating C in sediment and thereby storing C over geological time frames. Sediment C burial rates were estimated in six lakes from a chronology based on 210Pb dating of multiple sediment cores. The burial rate ranged between 5 - 25 g C m-2 yr-1, which is of the same magnitude as lake C emissions. I show that the emission:burial ratio is about ten times higher in boreal compared to in subarctic-arctic lakes. These results indicate that the balance between lakes C emission and burial is both directly and indirectly dependent on climate. This process will likely result in a future increase of C emissions from high-latitude lakes, while the C burial capacity of these same lakes sediments weaken.

Place, publisher, year, edition, pages
Umeå: Umeå universitet , 2014. , 17 p.
Keyword [en]
lakes, streams, carbon (C), carbon dioxide (CO2), methane (CH4), dissolved inorganic carbon (DIC), boreal, sub-arctic, arctic, emission, sediments, burial, budget
National Category
Earth and Related Environmental Sciences
Research subject
Limnology; Earth Sciences with Specialization Environmental Analysis; Physical Geography
Identifiers
URN: urn:nbn:se:umu:diva-84541ISBN: 978-91-7459-781-3 (print)OAI: oai:DiVA.org:umu-84541DiVA: diva2:685004
Public defence
2014-01-31, KBC - huset, Stora hörsalen, (KB3B1), Umeå Universitet, Umeå, 10:00 (English)
Opponent
Supervisors
Funder
Swedish Research Council, 621-385 2008-4390
Available from: 2014-01-10 Created: 2014-01-08 Last updated: 2016-11-14Bibliographically approved
List of papers
1. Integrating carbon emissions from lakes and streams in a subarctic catchment
Open this publication in new window or tab >>Integrating carbon emissions from lakes and streams in a subarctic catchment
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2013 (English)In: Journal of Geophysical Research: Biogeosciences, ISSN 2169-8953, Vol. 118, no 3, 1200-1207 p.Article in journal (Refereed) Published
Abstract [en]

Northern inland waters emit CO2 and CH4 to the atmosphere but the importance of these emissions is poorly understood due to a lack of integrated catchment-scale estimates of carbon (C) emissions from lakes and streams. In this study we quantified the annual emission of CO2 and CH4 from 27 lakes and 23 stream segments in a 15km(2) subarctic catchment in northern Sweden. All lakes and streams were net sources of C to the atmosphere on an annual basis. Streams dominated (96%) the aquatic CO2 emission while lakes (61%) dominated the aquatic CH4 emission. Total aquatic C emission from the catchment was estimated to be 9.1gCm(-2)yr(-1) (98% as CO2). Although streams only accounted for 4% of the aquatic area in the catchment, they accounted for 95% of the total emission. The C emissions from lakes and streams were considerably larger than previously reported downstream waterborne export of C from the catchment, indicating that the atmospheric losses of C in the aquatic systems are an important component in the catchment C balance.

Place, publisher, year, edition, pages
Wiley-Blackwell, 2013
Keyword
subarctic, streams, lakes, CO2, CH4, emission
National Category
Earth and Related Environmental Sciences
Identifiers
urn:nbn:se:umu:diva-82832 (URN)10.1002/jgrg.20092 (DOI)000325549900019 ()
Funder
Swedish Research Council, 621-2008-4390
Note

We acknowledge the contributions of NSERC (Canada), the Abisko Scientific Research Station (Sweden), Swedish Research Council, Swedish Environmental Protection Agency, and the Lund University GIS Centre for the funding of the lidar and DEM survey [cf. Hasan et al. 2012].

Available from: 2013-11-11 Created: 2013-11-11 Last updated: 2016-05-17Bibliographically approved
2. High emission of carbon dioxide and methane during ice thaw in high latitude lakes
Open this publication in new window or tab >>High emission of carbon dioxide and methane during ice thaw in high latitude lakes
2013 (English)In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 40, no 6, 1123-1127 p.Article in journal (Refereed) Published
Abstract [en]

The winter period is seldom included in the estimates of aquatic-atmospheric carbon exchange. In this study we quantified the flux of carbon dioxide (CO2) and methane (CH4) over 3 years from 12 small subarctic lakes. The lakes accumulated consistent and high amounts of CO2 and CH4 (56–97% as CO2) over the winter, resulting in a high flux during ice thaw. The CO2 flux during ice thaw increased with increasing mean depth of the lakes, while the CH4 flux was high in lakes surrounded by mires. The ice thaw period was quantitatively important to the annual gas balances of the lakes. For nine of the lakes, 11 to 55% of the annual flux occurred during thaw. For three of the lakes with an apparent net annual CO2 uptake, including the thaw period reversed the balance from sink to source. Our results suggest that the ice thaw period is critically important for the emissions of CO2 and CH4 in small lakes.

Place, publisher, year, edition, pages
John Wiley & Sons, 2013
Keyword
lakes, carbon fluxes, winter
National Category
Biological Sciences
Identifiers
urn:nbn:se:umu:diva-71370 (URN)10.1002/grl.50152 (DOI)
Available from: 2013-05-27 Created: 2013-05-27 Last updated: 2017-12-06Bibliographically approved
3. Strong climate impact on the carbon emission – burial balance inhigh latitude lakes
Open this publication in new window or tab >>Strong climate impact on the carbon emission – burial balance inhigh latitude lakes
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

Lakes play an important role in the global carbon (C) cycle by burying C in sediments and emitting CO2 and CH4 to the atmosphere. The strengths of these fundamentally different pathways are critical for quantifying effects of lakes upon the climate system. In this study, based on new high-resolution estimates in combination with literature data, we show a generally ten times higher emission:burial ratio in boreal compared to subarctic-arctic lakes. These results suggest a major bioclimatic impact on C cycling in lakes, as lakes in warmer boreal regions emit more and store relatively less C than lakes in colder arctic regions. Thus, our results reveal a previously unforeseen longterm climate feedback: if predictions of the northward expansion of the boreal biome are correct, C emissions of high latitude lakes may increase four-fold, corresponding to 14% of present global lake C evasion to the atmosphere. Such effects are of major importance for understanding feedbacks of climate warming on the continental source-sink function at high latitudes

 

 

National Category
Geosciences, Multidisciplinary
Research subject
Earth Sciences with Specialization Environmental Analysis; Limnology
Identifiers
urn:nbn:se:umu:diva-84499 (URN)
Funder
Swedish Research Council, 621-385 2008-4390
Note

Submitted

Available from: 2014-01-08 Created: 2014-01-08 Last updated: 2014-01-09
4. A weak C sink at high latitudes: support from an integrated terrestrial – aquatic C balance
Open this publication in new window or tab >>A weak C sink at high latitudes: support from an integrated terrestrial – aquatic C balance
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

High latitude ecosystems have served as net sinks of atmospheric carbon (C) in the Holocene time perspective. However, the ongoing climate warming makes it questionable if high latitude landscapes still function as net C sinks. In this study we used multiyear high resolution C flux data to estimate an integrated terrestrial-aquatic C balance of a sub-arctic catchment. The results indicate large inter annual variability in C fluxes and suggest that the C sink function of this landscape is weak, especially when also accounting for the often neglected C losses from aquatic systems. In fact, our results suggest that it is more likely that the studied catchment serves as a net source of C rather than a net sink. These results highlight the importance of inland waters in the C cycle and that the strength of the C sequestering in the contemporary sub-arctic environment is much weaker than often assumed.

National Category
Earth and Related Environmental Sciences
Research subject
Earth Sciences with Specialization Environmental Analysis
Identifiers
urn:nbn:se:umu:diva-84536 (URN)
Funder
Swedish Research Council, 621-385 2008-4390
Note

Submitted

Available from: 2014-01-08 Created: 2014-01-08 Last updated: 2014-01-09Bibliographically approved

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