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A weak C sink at high latitudes: support from an integrated terrestrial – aquatic C balance
Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
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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: urn:nbn:se:umu:diva-84536OAI: oai:DiVA.org:umu-84536DiVA: diva2:684962
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
In thesis
1. The role of inland waters in the carbon cycle at high latitudes
Open this publication in new window or tab >>The role of inland waters in the carbon cycle at high latitudes
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
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:nbn:se:umu:diva-84541 (URN)978-91-7459-781-3 (ISBN)
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

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Citation style
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