uu.seUppsala University Publications
Change search
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
The role of sediments in the carbon cycle of boreal lakes
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Inland waters are active sites of carbon (C) processing and emitters of carbon dioxide (CO2) and methane (CH4) to the atmosphere. In the boreal zone, where surface waters receive large quantities of organic carbon (OC) from surrounding forests and wetlands, lakes and streams act as strong sources of these greenhouse gases. Lake sediments provide the only long-term sink of C in boreal inland waters, through burial of OC. However, mineralization of OC counteracts the efficiency of lake sediments in removing C from the short-term C cycle. In this context, this thesis provides a better insight into the dual role of boreal lake sediments as C source and C sink.

The presented work is based on empirical assessments of OC burial and OC mineralization rates in boreal lakes. The temporal variability of OC burial and the stability of the buried OC was assessed on both centennial and millennial timescales. The quantitative importance of sediment OC burial and mineralization in comparison both to other C fluxes within the lake, and to C fluxes within the tributary stream network, was quantified. By simulating the effect of climate change on water temperature, we also gauged the potential future efficiency of lake sediments in storing C.

The results demonstrate that OC mineralization in sediments dominates three-fold over OC burial when observed at a whole-basin and annual scale. The contribution of sediment OC mineralization to annual C emission from the assessed study lake was, however, found to be small (16%), when compared to OC mineralization in the water column (37%) and catchment import of C (47%). Furthermore, C emission from headwater streams was found to dominate greatly over the lake C emission, mainly triggered by the higher gas transfer velocity of streams compared to lakes.

On a long-term (Holocene) scale, the continuous OC burial flux results in a large amount of C stored in sediments. The temporal variability of this OC accumulation was found to vary across lakes, with, however, time-dependent patterns: On a millennial scale, smaller lakes exhibited a higher variability than larger lakes of the study area. For the last century, similar variability and a trend to increased OC accumulation was found for most study lakes, irrespective of their size. Analysis of lignin phenols in the accumulated OC did not indicated post-depositional degradation, independent of the age of the sediment OC, implying that sediments are a very stable sink for land-derived OC in boreal lakes.

Simulation of warming water temperatures in boreal lakes resulted in declines of the OC burial efficiency BE (OCBE; OC burial/OCdeposition) up to 16%, depending, however, on basin morphometry. Predicted declines in OCBE were higher for the more shallow lake compared to the deeper lake.

In conclusion, this thesis illustrates that sediments play, despite a small quantitative impact on aquatic C cycling, an important role as a very stable C sink in boreal lakes. However, the efficiency of this C sink is likely to be reduced in the future.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2015. , 42 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1279
National Category
Environmental Sciences
Identifiers
URN: urn:nbn:se:uu:diva-261157ISBN: 978-91-554-9318-9 (print)OAI: oai:DiVA.org:uu-261157DiVA: diva2:849764
Public defence
2015-10-16, Ekmans salen, Norbyvägen, Uppsala, 10:00 (English)
Opponent
Supervisors
Available from: 2015-09-25 Created: 2015-08-31 Last updated: 2015-10-01
List of papers
1. Uncoupled organic matter burial and quality in boreal lake sediments over the Holocene
Open this publication in new window or tab >>Uncoupled organic matter burial and quality in boreal lake sediments over the Holocene
Show others...
2015 (English)In: Journal of Geophysical Research - Biogeosciences, ISSN 2169-8953, E-ISSN 2169-8961, Vol. 120, no 9, 1751-1763 p.Article in journal (Refereed) Published
Abstract [en]

Boreal lake sediments are important sites of organic carbon (OC) storage, which have accumulated substantial amounts of OC over the Holocene epoch; the temporal evolution and the strength of this Holocene carbon (C) sink is, however, not well constrained. In this study we investigated the temporal record of carbon mass accumulation rates (CMARs), and assessed qualitative changes of terrestrially derived OC in the sediment profiles of seven Swedish boreal lakes, in order to evaluate the variability of boreal lake sediments as a C sink over time.

CMARs were resolved on a short-term (centennial) and long-term (i.e. over millennia of the Holocene) time scale, using radioactive lead (210 Pb) and carbon (14C) isotope dating. Sources and degradation state of terrestrially derived OC were identified and characterized by molecular analyses of lignin phenols.

We found that CMARs varied substantially on both short-term and long-term scales, and that the variability was mostly attributed to sedimentation rates and uncoupled from the OC content in the sediment profiles. The lignin phenol analyses revealed that woody material from gymnosperms was a dominant and constant OC source to the sediments over the Holocene. Furthermore, lignin-based degradation indices, such as acid-to-aldehyde ratios, indicated that post-depositional degradation in the sediments was very limited on longer time scales, implying that terrestrial OC is stabilized in the sediments on a permanent basis.

Keyword
organic carbon, accumulation rates, radiocarbon dating, lead dating, lignin phenols, carbon sink
National Category
Environmental Sciences
Research subject
Biology with specialization in Limnology
Identifiers
urn:nbn:se:uu:diva-260660 (URN)10.1002/2015JG002987 (DOI)000363332900004 ()
Funder
Swedish Research Council Formas
Available from: 2015-09-07 Created: 2015-08-21 Last updated: 2017-12-04Bibliographically approved
2. The role of sediments in the carbon budget of a small boreal lake
Open this publication in new window or tab >>The role of sediments in the carbon budget of a small boreal lake
Show others...
2016 (English)In: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 61, no 5, 1814-1825 p.Article in journal (Refereed) Published
Abstract [en]

We investigated the role of lake sediments as carbon (C) source and sink in the annual C budget of a small (0.07 km2), shallow (mean depth 3.4 m), and humic lake (mean DOC concentration 17 mg L-1) in boreal Sweden. Organic carbon (OC) burial and mineralization in sediments were quantified from 210Pb-dated sediment and laboratory sediment incubation experiments, respectively, and upscaled to the entire basin and to one whole year, by using sediment thickness derived sub-bottom profiling, basin morphometry, and water column monitoring data of temperature and oxygen concentration. Furthermore, catchment C import, open water metabolism, photochemical mineralization as well as carbon dioxide (CO2) and methane (CH4) emissions to the atmosphere, were quantified to relate sediment processes to other lake C fluxes. We found that on a whole-basin and annual scale, sediment OC mineralization was three times larger than OC burial, and contributed about 16% to the annual CO2 emission from the lake to the atmosphere. Remaining contributions to the CO2 emission were attributed to water column metabolism (31%), photochemical mineralization (6%), and catchment imports via inlet streams and inflow of shallow groundwater (47%). We conclude that on an annual and whole-basin scale 1) sediment OC mineralization dominated over OC burial, 2) water column OC mineralization contributed more than sediments to lake CO2 emission, and 3) catchment import of C to the lake was greater than lake-internal C cycling. 

Keyword
mineralization, burial, carbon dioxide, methane, emission, photomineralization
National Category
Environmental Sciences
Research subject
Biology with specialization in Limnology
Identifiers
urn:nbn:se:uu:diva-260666 (URN)10.1002/lno.10336 (DOI)000383621800019 ()
Funder
EU, European Research CouncilSwedish Research Council FormasSwedish Research Council
Available from: 2015-09-07 Created: 2015-08-21 Last updated: 2017-07-11Bibliographically approved
3. Carbon dioxide evasion from headwater systems strongly contributes to the total export of carbon from a small boreal lake catchment
Open this publication in new window or tab >>Carbon dioxide evasion from headwater systems strongly contributes to the total export of carbon from a small boreal lake catchment
Show others...
2015 (English)In: Journal of Geophysical Research - Biogeosciences, ISSN 2169-8953, E-ISSN 2169-8961, Vol. 120, no 1, 13-28 p.Article in journal (Refereed) Published
Abstract [en]

Inland waters are hotspots for carbon (C) cycling and therefore important for landscape C budgets. Small streams and lakes are particularly important; however, quantifying C fluxes is difficult and has rarely been done for the entire aquatic continuum, composed of connected streams and lakes within the same catchment. We investigated carbon dioxide (CO2) evasion and fluvial fluxes of dissolved inorganic carbon and dissolved organic carbon (DIC and DOC) in stream and lake systems within the 2.3km(2) catchment of a small boreal lake. Our results show pronounced spatial and temporal variability in C fluxes even at a small spatial scale. C loss from the catchment through CO2 evasion from headwaters for the total open water-sampling period was 9.7g C m(-2) catchment, dominating the total catchment C loss (including CO2 evasion, DIC, and DOC export from the lake, which were 2.7, 0.2, and 5.2g C m(-2) catchment, respectively). Aquatic CO2 evasion was dominated by headwater streams that occupy similar to 0.1% of the catchment but contributed 65% to the total aquatic CO2 evasion from the catchment. The importance of streams was mainly an effect of the higher gas transfer velocities than compared to lakes (median, 67 and 2.2cmh(-1), respectively). Accurately estimating the contribution of C fluxes from headwater streams, particularly the temporal and spatial dynamics in their gas transfer velocity, is key to landscape-scale C budgets. This study demonstrates that CO2 evasion from headwaters can be the major pathway of C loss from boreal catchments, even at a small spatial scale.

National Category
Climate Research
Identifiers
urn:nbn:se:uu:diva-241585 (URN)10.1002/2014JG002706 (DOI)000349899200002 ()
Available from: 2015-01-13 Created: 2015-01-13 Last updated: 2017-12-05Bibliographically approved
4. Decreased efficiency of sediment carbon burial in boreal lakes at warming lake water temperatures
Open this publication in new window or tab >>Decreased efficiency of sediment carbon burial in boreal lakes at warming lake water temperatures
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Organic carbon (OC) burial in lake sediments is a fundamental process for aquatic carbon (C) cycling since it removes C from the active cycling pool. Here, we address the effect of lake warming on the OC burial efficiency (OCBE) of sediments in boreal humic lakes to evaluate the impact of warmer water temperatures and altered water column stratification patterns on the OCBE with respect to future climate change. Present-day water column conditions of temperature and oxygen concentration were monitored in two small (<0.1 km2) boreal lakes in central and southwestern Sweden over an annual cycle. Furthermore, OC burial, sediment OC mineralization, the OCBE, and lake CO2 and CH4 emission to the atmosphere, were quantified on a whole-basin scale and for a whole year. Then, future temperature and stratification patterns were simulated in both lakes by adjusting present-day temperature and oxygen conditions according to projected air temperature warming scenarios, in order to quantify the net effect on the OCBE. Present-day conditions were found to be similar in the two study lakes, with annual OC mineralization (~1 t C yr-1) exceeding annual OC burial (<0.5 t C yr-1) at least by a factor of two, returning whole-basin OC burial efficiencies of 28 and 25%, respectively. Also, annual CO2 and CH4 emission was found to be of similar magnitude in both study lakes (6-7 t C yr-1) surpassing sediment C fluxes by at least 5 times. The different lake warming scenarios (RCP 2.6, 4.5 and 8.5, corresponding to increase in annual mean air temperature of 1.5-4.5 °C) caused moderate decreases in the OCBE of 5-16% and 3-11% for each lake, respectively. The more pronounced decreases in OCBE were obtained for the more shallow lake, related to a higher proportion of sediments being affected by warming in the epilimnion. Our results suggest that warmer surface water temperatures in the future are likely to reduce the efficiency of the lake sediment C sink, thereby affecting the long-term C balance of the boreal forest biome.

National Category
Environmental Sciences
Research subject
Biology with specialization in Limnology
Identifiers
urn:nbn:se:uu:diva-260668 (URN)
Available from: 2015-09-07 Created: 2015-08-21 Last updated: 2015-10-01

Open Access in DiVA

fulltext(1151 kB)151 downloads
File information
File name FULLTEXT02.pdfFile size 1151 kBChecksum SHA-512
6dd98aba28bbe112b95de5f6b33812036cb58316cccd0d504142957eb7c2eee4f2aad6d2cdf7fad2d65f354c119588927fca828716fe83cda66ed9200898e6eb
Type fulltextMimetype application/pdf
Buy this publication >>

By organisation
Limnology
Environmental Sciences

Search outside of DiVA

GoogleGoogle Scholar
Total: 151 downloads
The number of downloads is the sum of all downloads of full texts. It may include eg previous versions that are now no longer available

isbn
urn-nbn

Altmetric score

isbn
urn-nbn
Total: 1419 hits
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf