Change search
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • 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
Lake Fluxes of Methane and Carbon Dioxide
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL. (Meteorologi, AWEP)
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Methane (CH4) and carbon dioxide (CO2) are two important greenhouse gases. Recent studies have shown that lakes, although they cover a small area of the globe, can be very important natural sources of atmospheric CH4 and CO2. It is therefore important to monitor the fluxes of these gases between lakes and the atmosphere in order to understand the processes that govern the exchange.

By using the eddy covariance method for lake flux studies, the resolution in time and in space of the fluxes is increased, which gives more information on the governing processes.

Eddy covariance measurements at a Swedish lake revealed a diel cycle in the fluxes of both CH4 and CO2, with higher fluxes during nighttime than daytime. The high nighttime CO2 fluxes could to a large extent be explained with enhanced transfer velocities due to waterside convection. For the diel cycle of CH4 flux it was suggested that waterside convection could enhance the transfer velocity, transport CH4 rich water to the surface, as well as trigger ebullition.

Simultaneous flux measurements of CH4 and CO2 have been presented using both the eddy covariance method and the floating chambers method of which the latter is the traditional measuring method for lake fluxes. For CO2 the two methods agreed well during some periods but differed considerably during others. Disagreement between the methods might be due to horizontal heterogeneity in partial pressure of CO2 in the lake. The methods agreed better for the CH4 flux measurements. However, it is clear that due to the discontinuous nature of the floating chambers, this method will likely miss important high flux events.

The main conclusions of this thesis are:

1) the two gas flux methods are not directly comparable and should be seen as supplementary to each other

2) waterside convection enhances the fluxes of both CH4 and CO2 over the water-air surface. If gas flux measurements are not conducted during nighttime, potential high flux periods might be missed and estimates of the total amount of gas released from lakes to the atmosphere may be biased.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2015. , 41 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1221
Keyword [en]
air-lake gas exchange, carbon dioxide, eddy covariance, floating chambers, methane, waterside convection
National Category
Natural Sciences Meteorology and Atmospheric Sciences
Research subject
Meteorology
Identifiers
URN: urn:nbn:se:uu:diva-241984ISBN: 978-91-554-9152-9 (print)OAI: oai:DiVA.org:uu-241984DiVA: diva2:784579
Public defence
2015-03-20, Hambergsalen, Villavägen 16, Uppsala, 10:00 (English)
Opponent
Supervisors
Available from: 2015-02-26 Created: 2015-01-19 Last updated: 2015-03-18Bibliographically approved
List of papers
1. Diurnal cycle of lake methane flux
Open this publication in new window or tab >>Diurnal cycle of lake methane flux
2014 (English)In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 119, no 3, 236-248 p.Article in journal (Refereed) Published
Abstract [en]

Air-lake methane flux (FCH4) and partial pressure of methane in the atmosphere (pCH4a) were measured using the eddy covariance method over a Swedish lake for an extended period. The measurements show a diurnal cycle in both FCH4 and pCH4a with high values during nighttime (FCH4 ≈ 300 nmol m−2 s−1pCH4a ≈ 2.5 µatm) and low values during day (FCH4 ≈ 0 nmol m−2 s−1pCH4a ≈ 2.0 µatm) for a large part of the data set. This diurnal cycle persist in all open water season; however, the magnitude of the diurnal cycle is largest in the spring months. Estimations of buoyancy in the water show that high nighttime fluxes coincide with convective periods. Our interpretation of these results is that the convective mixing enhances the diffusive flux, in analogy to previous studies. We also suggest that the convection may bring methane-rich water from the bottom to the surface and trigger bubble release from the sediment. A diurnal cycle is not observed for all convective occasions, indicating that the presence of convection is not sufficient for enhanced nighttime flux; other factors are also necessary. The observed diurnal cycle of pCH4a is explained with the variation of FCH4 and a changing internal boundary layer above the lake. The presence of a diurnal cycle of FCH4 stresses the importance of making long-term continuous flux measurements. A lack of FCH4measurements during night may significantly bias estimations of total CH4 emissions from lakes to the atmosphere.

Keyword
Methane, lake, eddy correlation, eddy covariance, diurnal cycle
National Category
Meteorology and Atmospheric Sciences Climate Research Geosciences, Multidisciplinary
Research subject
Meteorology
Identifiers
urn:nbn:se:uu:diva-224896 (URN)10.1002/2013JG002327 (DOI)000334534500005 ()
Funder
Swedish Research Council Formas, 2009-1692
Available from: 2014-05-23 Created: 2014-05-23 Last updated: 2017-12-05
2. Comparison of floating chamber and eddy covariance measurements of lake greenhouse gas fluxes
Open this publication in new window or tab >>Comparison of floating chamber and eddy covariance measurements of lake greenhouse gas fluxes
Show others...
2014 (English)In: Biogeosciences Discussions, ISSN 1810-6277, E-ISSN 1810-6285, Vol. 11, 4225-4233 p.Article in journal (Refereed) Published
Abstract [en]

Fluxes of carbon dioxide (CO2) and methane (CH4) from lakes may have a large impact on the magnitude of the terrestrial carbon sink. Traditionally lake fluxes have been measured using the floating chamber (FC) technique; however, several recent studies use the eddy covariance (EC) method. We present simultaneous flux measurements using both methods at lake Tämnaren in Sweden during field campaigns in 2011 and 2012. Only very few similar studies exist. For CO2 flux, the two methods agree relatively well during some periods, but deviate substantially at other times. The large discrepancies might be caused by heterogeneity of partial pressure of CO2 (pCO2w) in the EC flux footprint. The methods agree better for CH4 fluxes. It is, however, clear that short-term discontinuous FC measurements are likely to miss important high flux events.

National Category
Natural Sciences Earth and Related Environmental Sciences Meteorology and Atmospheric Sciences Climate Research Geosciences, Multidisciplinary
Identifiers
urn:nbn:se:uu:diva-229778 (URN)10.5194/bg-11-4225-2014 (DOI)000341104400012 ()
Available from: 2014-08-13 Created: 2014-08-13 Last updated: 2017-12-05Bibliographically approved
3. Diel cycle of lake-air CO2 flux from a shallow lake and the impact of waterside convection on the transfer velocity
Open this publication in new window or tab >>Diel cycle of lake-air CO2 flux from a shallow lake and the impact of waterside convection on the transfer velocity
2015 (English)In: Journal of Geophysical Research - Biogeosciences, ISSN 2169-8953, E-ISSN 2169-8961, Vol. 120, no 1, 29-38 p.Article in journal (Refereed) Published
Abstract [en]

Two years of eddy covariance measurements of lake carbon dioxide (CO2) fluxes reveal a dielcycle with higher fluxes during night. Measurements of partial pressure in the air (pCO2a) and in the water(pCO2w), during 4 months, show that the high nighttime fluxes are not explained by changes in the differencebetween pCO2a and pCO2w. Analyzing the transfer velocity (k600,meas), which is a measure of the efficiencyof the gas transfer, with respect to wind speed, shows that variations in wind speed do not explain thediel cycle. During nighttime, when the fluxes are high, the wind is normally low. Thus, a solely wind-basedparameterization of the transfer velocity (ku,CC) results in large errors compared to k600,meas, especially forwind speeds lower than 6ms1. The mean absolute percentage error between ku,CC and k600,meas is 79%. By subtracting ku,CC from k600,meas, we investigate how waterside convection influence k600,meas. Our resultsshow that the difference (k600,measku,CC) increases with increasing waterside convection. Separating thetransfer velocity parameterization in two parts, one depending on the wind speed and one depending onwaterside convection, the mean absolute percentage error compared to the measurements reduces to 22%. The results in this paper show that the high nighttime CO2 fluxes can, to a large extent, be explained bywaterside convection and that a transfer velocity parameterization based on both wind speed and watersideconvection better fits the measurements compared to a parameterization based solely on wind speed.

National Category
Earth and Related Environmental Sciences
Identifiers
urn:nbn:se:uu:diva-241576 (URN)10.1002/2014JG002781 (DOI)000349899200003 ()
Available from: 2015-01-13 Created: 2015-01-13 Last updated: 2017-12-05Bibliographically approved
4. Methane fluxes from a small boreal lake measured with eddy covariance method
Open this publication in new window or tab >>Methane fluxes from a small boreal lake measured with eddy covariance method
Show others...
(English)Manuscript (preprint) (Other academic)
National Category
Natural Sciences
Identifiers
urn:nbn:se:uu:diva-241981 (URN)
Available from: 2015-01-19 Created: 2015-01-19 Last updated: 2015-03-11

Open Access in DiVA

fulltext(698 kB)398 downloads
File information
File name FULLTEXT01.pdfFile size 698 kBChecksum SHA-512
6ee8fef7b1ad34a12a1c0aee9be30e4dd9c07cb0a6f22e0188e6831aa2c02cd7bac890cf1bfd00f3ff994a1980f86e45d067781001e42a4bbe64d04da4ca4bc2
Type fulltextMimetype application/pdf
errata(93 kB)12 downloads
File information
File name ERRATA01.pdfFile size 93 kBChecksum SHA-512
e6eb11dfc770853d69a88796f3b9053ca7d0b78d781c0eb6f88a140b6cdaf831376e41964df53208ddca7b9dd60fdde351bebc46f84ce32a596b83b02b083146
Type errataMimetype application/pdf
Buy this publication >>

Search in DiVA

By author/editor
Podgrajsek, Eva
By organisation
LUVAL
Natural SciencesMeteorology and Atmospheric Sciences

Search outside of DiVA

GoogleGoogle Scholar
Total: 398 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: 1428 hits
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • 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