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Boreal Lake Sediments as Sources and Sinks of Carbon
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Inland waters process large amounts of organic carbon, contributing to CO2 and CH4 emissions, as well as storing organic carbon (OC) over geological timescales. Recently, it has been shown that the magnitude of these processes is of global significance. It is therefore important to understand what regulates OC cycling in inland waters and how is that affected by climate change. This thesis investigates the constraints on microbial processing of sediment OC, as a key factor of the carbon cycling in boreal lakes.

Sediment bacterial metabolism was primarily controlled by temperature but also regulated by OC quality/origin. Temperature sensitivity of sediment OC mineralization was similar in contrasting lakes and over long-term. Allochthonous OC had a strong constraining effect on sediment bacterial metabolism and biomass, with increasingly allochthonous sediments supporting decreasing bacterial metabolism and biomass. The bacterial biomass followed the same pattern as bacterial activity and was largely regulated by similar factors. The rapid turnover of bacterial biomass as well as the positive correlation between sediment mineralization and bacterial biomass suggest a limited effect of bacterial grazing. Regardless of the OC source, the sediment microbial community was more similar within season than within lakes.

A comparison of data from numerous soils as well as sediments on the temperature response of OC mineralization showed higher temperature sensitivity of the sediment mineralization. Furthermore, the low rates of areal OC mineralization in sediments compared to soils suggest that lakes sediments are hotspots of OC sequestration.

Increased sediment mineralization due to increase in temperature in epilimnetic sediments can significantly reduce OC burial in boreal lakes. An increase of temperature, as predicted for Northern latitudes, under different climate warming scenarios by the end of the twenty-first century, resulted in 4–27% decrease in lake sediment OC burial for the entire boreal zone.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis , 2011. , 39 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 823
Keyword [en]
boreal lakes, allochthonous, lake sediments, sediment mineralization, bacterial production, bacterial biomass, carbon cycle
National Category
Ecology
Research subject
Limnology
Identifiers
URN: urn:nbn:se:uu:diva-150709ISBN: 978-91-554-8072-1OAI: oai:DiVA.org:uu-150709DiVA: diva2:410284
Public defence
2011-05-31, Friessalen, Evolutionary Biology Centre (EBC), Norbyvägen 18, Uppsala, 10:00 (English)
Opponent
Supervisors
Available from: 2011-05-10 Created: 2011-04-04 Last updated: 2011-07-01Bibliographically approved
List of papers
1. Temperature-controlled organic carbon mineralization in lake sediments
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2010 (English)In: Nature, ISSN 0028-0836, E-ISSN 1476-4687, Vol. 466, no 7305, 478-481 p.Article in journal (Refereed) Published
Abstract [en]

Peatlands, soils and the ocean floor are well-recognized as sites of organic carbonaccumulation andrepresentimportant global carbon sinks(1,2). Although the annual burial of organic carbon in lakes and reservoirs exceeds that of ocean sediments(3), these inland waters are components of the global carbon cycle that receive only limited attention(4-6). Of the organic carbon that is being deposited onto the sediments, a certain proportion will be mineralized and the remainder will be buried over geological timescales. Here we assess the relationship between sediment organic carbon mineralization and temperature in a cross-system survey of boreal lakes in Sweden, and with input froma compilation of published data from awide range of lakes that differ with respect to climate, productivity and organic carbon source. We find that the mineralization of organic carbon in lake sediments exhibits a strongly positive relationship with temperature, which suggests that warmer water temperatures lead to more mineralization and less organic carbon burial. Assuming that future organic carbon delivery to the lake sediments will be similar to that under present-day conditions, we estimate that temperature increases following the latest scenarios presented by the Intergovernmental Panel on Climate Change(7) could result in a 4-27 per cent (0.9-6.4 Tg Cyr(-1)) decrease in annual organic carbon burial in boreal lakes.

National Category
Biological Sciences
Identifiers
urn:nbn:se:uu:diva-135652 (URN)10.1038/nature09186 (DOI)000280141200033 ()
Note

Correction in Nature, vol. 466, issue 7310, doi 10.1038/nature09383

Available from: 2010-12-08 Created: 2010-12-07 Last updated: 2014-10-30Bibliographically approved
2. Microbial biomass and community composition in boreal lake sediments
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2011 (English)In: Limnology and Oceanography, ISSN 0024-3590, Vol. 56, no 2, 725-733 p.Article in journal (Refereed) Published
Abstract [en]

We used phospholipid fatty acids (PLFA) to determine microbial biomass and community structure in the sediments of eight boreal lakes with different loadings of allochthonous organic carbon and total phosphorus (TP) in the water during the course of a year. The total concentration of PLFA, an estimate of the microbial biomass, depended more on TP, a proxy for pelagic primary production, but not on dissolved organic carbon, a proxy for terrestrial organic carbon input. The composition of PLFAs varied considerably over time, demonstrating seasonal dynamics in microbial community composition. When PLFA profiles in all lakes andseasons are compared, community composition is more similar within season than within lakes.

 

National Category
Ecology
Research subject
Limnology
Identifiers
urn:nbn:se:uu:diva-150710 (URN)10.4319/lo.2011.56.2.0725 (DOI)000290677800027 ()
Available from: 2011-04-04 Created: 2011-04-04 Last updated: 2014-01-17Bibliographically approved
3. Constrained microbial processing of allochthonous organic carbon in boreal lake sediments
Open this publication in new window or tab >>Constrained microbial processing of allochthonous organic carbon in boreal lake sediments
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2012 (English)In: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 57, no 1, 163-175 p.Article in journal (Refereed) Published
Abstract [en]

We investigated sediment bacterial metabolism in eight lakes with different inputs of allochthonous and autochthonous organic carbon in south-central Sweden. Sediment bacterial production, mineralization and biomass were measured on a seasonal basis and along a lake depth gradient together with different water and sediment characteristics. Sediment bacterial metabolism was primarily controlled by temperature but also regulated by organic carbon quality/origin. Metabolism was positively correlated to measures of autochthonous influence on the sediment organic carbon, but did not show a similar increase with increasing input of allochthonous organic carbon.  Hence, in contrast to what is currently known for the water column, increasing amounts of terrestrial organic carbon do not result in enhanced sediment bacterial metabolism.  Meio- and macrobenthic invertebrate biomass were at most weakly correlated to bacterial metabolism and biomass, suggesting limited control of sediment bacteria by grazing. We suggest that the bacterial metabolism in boreal lake sediments is constrained by low temperatures and by the recalcitrant nature of the dominant organic carbon, resulting in sediments being an effective sink of organic carbon.

Keyword
allochthonous organic carbon, microbial metabolism, lake sediments
National Category
Ecology
Research subject
Limnology
Identifiers
urn:nbn:se:uu:diva-150712 (URN)10.4319/lo.2012.57.1.0163 (DOI)000298321300014 ()
Available from: 2011-04-04 Created: 2011-04-04 Last updated: 2016-04-22Bibliographically approved
4. Mineralization of organic carbon in lake sediments: temperature sensitivity and a comparison to soils
Open this publication in new window or tab >>Mineralization of organic carbon in lake sediments: temperature sensitivity and a comparison to soils
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

Temperature alone can explain a great amount of variation in sediment organic carbon (OC) mineralization. Studies on decomposition of soil OC suggest that the temperature sensitivity is different for the decomposition of labile and recalcitrant OC, but lake sediments with different contributions of labile and recalcitrant components have been reported to show similar temperature sensitivities. Sediment mineralization is typically measured in short-term incubations. However, whether the mineralization of OC in sediments dominated by recalcitrant and labile OC have different temperature sensitivities at the longer term is not clear. Here we show that during 5 months of continuous incubation of contrasting boreal lake sediments, sediment mineralization was strongly dependent on temperature and OC quality/origin but temperature sensitivity was similar across lakes and over time. Sediment mineralization showed low overall rates in spite of low apparent activation energy (Ea) compared to published rates of soil and litter mineralization. The fraction of the total OC pool that was lost during 5 months varied between 0.4 and 14%. The non-buried sediment OC pool was lost slowly, with apparent turnover times between 2.5 and 32 years. At a large scale, lake sediments, by showing lower mineralization rates than soils are more effective as carbon sinks.

 

Keyword
lake sediment, mineralization, temperature sensitivity, organic carbon, turnover time
National Category
Ecology
Research subject
Limnology
Identifiers
urn:nbn:se:uu:diva-150714 (URN)
Available from: 2011-04-04 Created: 2011-04-04 Last updated: 2016-03-05

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