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Regulation of carbon dioxide emission from Swedish boreal lakes and the Gulf of Bothnia
Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
2005 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The global carbon cycle is subject to intense research, where sources and sinks for greenhouse gases, carbon dioxide in particular, are estimated for various systems and biomes. Lakes have previously been neglected in carbon balance estimations, but have recently been recognized to be significant net sources of CO2.

This thesis estimates emission of carbon dioxide (CO2) from boreal lakes and factors regulating the CO2 saturation from field measurements of CO2 concentration along with a number of chemical, biological and physical parameters. Concentration of dissolved organic carbon (DOC) was found to be the most important factor for CO2 saturation in lake water, whereas climatic parameters such as precipitation, temperature and global radiation were less influential. All lakes were supersaturated with and, thus, sources of CO2. Sediment incubation experiments indicated that in-lake mineralization processes during summer stratification mainly occurred in the pelagial. Approximately 10% of the CO2 emitted from the lake surface was produced in epilimnetic sediments.

The mineralization of DOC and emission of CO2 from freshwaters was calculated on a catchment basis for almost 80,000 lakes and 21 major catchments in Sweden, together with rates of sedimentation in lakes and export of organic carbon to the sea. The total export of terrestrial organic carbon to freshwaters could thereby be estimated and consequently also the importance of lakes for the withdrawal of organic carbon export from terrestrial sources to the sea. Lakes removed 30-80% of imported terrestrial organic carbon, and mineralization and CO2 emission were much more important than sedimentation of carbon. The carbon loss was closely related to water retention time, where catchments with short residence times (<1 year) had low carbon retentions, whereas in catchments with long residence times (>3 years) a majority of the imported TOC was removed in the lake systems.

The Gulf of Bothnia was also studied in this thesis and found to be a net heterotrophic system, emitting large amounts of CO2 to the atmosphere on an annual basis. The rate of CO2 emission was depending on the balance between primary production and bacterial respiration, and the system was oscillating between being a source and a sink of CO2.

Place, publisher, year, edition, pages
Umeå universitet , 2005. , 24 p.
Keyword [en]
Physical geography and sedimentology, lakes, boreal, Gulf of bothnia, CO2, NEE, DOC, mineralization, sediment, catchment, net heterotrophy
Keyword [sv]
Naturgeografi och sedimentologi
National Category
Physical Geography
Research subject
Physical Geography
Identifiers
URN: urn:nbn:se:umu:diva-453ISBN: 91-7305-818-1 (print)OAI: oai:DiVA.org:umu-453DiVA: diva2:143496
Public defence
2005-03-11, KB3B1, KBC-huset, Umeå universitet, Umeå, 10:00
Opponent
Supervisors
Available from: 2005-02-17 Created: 2005-02-17 Last updated: 2011-03-21Bibliographically approved
List of papers
1. The catchment and climate regulation of pCO2 in boreal lakes
Open this publication in new window or tab >>The catchment and climate regulation of pCO2 in boreal lakes
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2003 (English)In: Global Change Biology, Vol. 9, no 4, 630-641 p.Article in journal (Refereed) Published
Abstract [en]

The regulation of surface water pCO2 was studied in a set of 33 unproductive boreal lakes of different humic content, situated along a latitudinal gradient (57°N to 64°N) in Sweden. The lakes were sampled four times during one year, and analyzed on a wide variety of water chemistry parameters. With only one exception, all lakes were supersaturated with CO2 with respect to the atmosphere at all sampling occasions. pCO2 was closely related to the DOC concentration in lakes, which in turn was mainly regulated by catchment characteristics. This pattern was similar along the latitudinal gradient and at different seasons of the year, indicating that it is valid for a variety of climatic conditions within the boreal forest zone. We suggest that landscape characteristics determine the accumulation and subsequent supply of allochthonous organic matter from boreal catchments to lakes, which in turn results in boreal lakes becoming net sources of atmospheric CO2.

Identifiers
urn:nbn:se:umu:diva-4405 (URN)10.1046/j.1365-2486.2003.00619.x (DOI)
Available from: 2005-02-17 Created: 2005-02-17 Last updated: 2010-11-10Bibliographically approved
2. Contribution of sediment respiration to summer CO2 emission from boreal and subarctic lakes
Open this publication in new window or tab >>Contribution of sediment respiration to summer CO2 emission from boreal and subarctic lakes
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2005 (English)In: Microbial Ecology, ISSN 0095-3628, E-ISSN 1432-184X, Vol. 50, no 4, 529-535 p.Article in journal (Refereed) Published
Abstract [en]

We measured sediment production of carbon dioxide (CO(2)) and methane (CH(4)) and the net flux of CO(2) across the surfaces of 15 boreal and subarctic lakes of different humic contents. Sediment respiration measurements were made in situ under ambient light conditions. The flux of CO(2) between sediment and water varied between an uptake of 53 and an efflux of 182 mg C m(-2) day(-1) from the sediments. The mean respiration rate for sediments in contact with the upper mixed layer (SedR) was positively correlated to dissolved organic carbon (DOC) concentration in the water (r(2) = 0.61). The net flux of CO(2) across the lake surface [net ecosystem exchange (NEE)] was also closely correlated to DOC concentration in the upper mixed layer (r(2) = 0.73). The respiration in the water column was generally 10-fold higher per unit lake area compared to sediment respiration. Lakes with DOC concentrations <5.6 mg L(-1) had net consumption of CO(2) in the sediments, which we ascribe to benthic primary production. Only lakes with very low DOC concentrations were net autotrophic (<2.6 mg L(-1)) due to the dominance of dissolved allochthonous organic carbon in the water as an energy source for aquatic organisms. In addition to previous findings of allochthonous organic matter as an important driver of heterotrophic metabolism in the water column of lakes, this study suggests that sediment metabolism is also highly dependent on allochthonous carbon sources.

Identifiers
urn:nbn:se:umu:diva-4406 (URN)10.1007/s00248-005-5007-x (DOI)
Available from: 2005-02-17 Created: 2005-02-17 Last updated: 2017-12-14Bibliographically approved
3. Role of lakes for organic carbon cycling in the boreal zone
Open this publication in new window or tab >>Role of lakes for organic carbon cycling in the boreal zone
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2004 (English)In: Global Change Biology, ISSN 1354-1013, E-ISSN 1365-2486, Vol. 10, no 1, 141-147 p.Article in journal (Refereed) Published
Abstract [en]

We calculated the carbon loss (mineralization plus sedimentation) and net CO2 escape to the atmosphere for 79 536 lakes and total running water in 21 major Scandinavian catchments (size range 437–48 263 km2). Between 30% and 80% of the total organic carbon that entered the freshwater ecosystems was lost in lakes. Mineralization in lakes and subsequent CO2 emission to the atmosphere was by far the most important carbon loss process. The withdrawal capacity of lakes on the catchment scale was closely correlated to the mean residence time of surface water in the catchment, and to some extent to the annual mean temperature represented by latitude. This result implies that variation of the hydrology can be a more important determinant of CO2 emission from lakes than temperature fluctuations. Mineralization of terrestrially derived organic carbon in lakes is an important regulator of organic carbon export to the sea and may affect the net exchange of CO2 between the atmosphere and the boreal landscape.

Place, publisher, year, edition, pages
Oxford: Blackwell Scientific, 2004
Keyword
boreal lakes, CO2 emission, mineralization, organic matter, terrestrial export, water residence time
Identifiers
urn:nbn:se:umu:diva-4407 (URN)10.1111/j.1365-2486.2003.00721.x (DOI)
Available from: 2005-02-17 Created: 2005-02-17 Last updated: 2017-12-14Bibliographically approved
4. Seasonal variation of CO2 saturation in the Gulf of Bothnia: Indications of marine net heterotrophy
Open this publication in new window or tab >>Seasonal variation of CO2 saturation in the Gulf of Bothnia: Indications of marine net heterotrophy
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2004 (English)In: Global Biogeochemical Cycles, ISSN 0886-6236, E-ISSN 1944-9224, Vol. 18, 4021-4028 p.Article in journal (Refereed) Published
Abstract [en]

Seasonal variation of pCO2 and primary and bacterioplankton production were measured in the Gulf of Bothnia during an annual cycle. Surface water was supersaturated with CO2 on an annual basis, indicating net heterotrophy and a source of CO2 to the atmosphere. However, the Gulf of Bothnia oscillated between being a sink and a source of CO2 over the studied period, largely decided by temporal variation in bacterial respiration (BR) and primary production (PP) in the water column above the pycnocline. The calculated annual respiration-production balance (BR-PP) was very similar to the estimated CO2 emission from the Gulf of Bothnia, which indicates that these processes were major determinants of the exchange of CO2 between water and atmosphere. The southern basin (the Bothnian Sea) had a lower net release of CO2 to the atmosphere than the northern Bothnian Bay (7.1 and 9.7 mmol C m−2 d−1, respectively), due to higher primary production, which to a larger extent balanced respiration in this basin.

Place, publisher, year, edition, pages
Washington, D.C: American Geophysical Union (AGU), 2004
National Category
Oceanography, Hydrology, Water Resources
Identifiers
urn:nbn:se:umu:diva-7841 (URN)10.1029/2004GB002232 (DOI)
Available from: 2008-01-13 Created: 2008-01-13 Last updated: 2017-10-24Bibliographically approved

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