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Importance of water temperature and thermal stratification dynamics for temporal variation of surface water CO2 in a boreal lake
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.
Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
2010 (English)In: Journal of Geophysical Research, ISSN 0148-0227, Vol. 115, no G02024, 10PP- p.Article in journal (Refereed) Published
Abstract [en]

Variation of the surface water CO2 concentration is likely to be the result of biological activity and physical processes as water mixing and gas exchange with the atmosphere. Here we have studied the variations in surface water CO2 during the ice-free period in the humic Lake Merasjärvi in northern Sweden. Meteorological, hydrological and limnological data were collected using data logging equipment permitting high time-resolution. The surface water of the lake was supersaturated with respect to CO2 throughout the study period. There were, however, considerable diurnal and longer-term temporal variations of the surface water CO2 concentrations. Partial least squares (PLS) models were used to link the logged CO2 data to the multivariate dataset. On the longer-term time scale (analyzed with 24h means of the logged data) high concentrations of surface water CO2 were best related to the depth and temperature of the upper warmer layer (epilimnion), and to erosion of the underlying colder layer (hypolimnion). The diurnal variation (analyzed with 30 minute means of the logged data) was best related to the thermal dynamics within the epilimnion, which regulated the surface water access to CO2 stores within this layer. Variables related to CO2 emission and photosynthesis (wind and PAR), showed only weak correlations to variations of the surface water CO2 concentration. Accordingly, the CO2 flux, measured with the eddy-covariance technique, was not correlated to the surface water CO2 concentration.

Place, publisher, year, edition, pages
2010. Vol. 115, no G02024, 10PP- p.
Keyword [en]
lake, carbon dioxide, PLS, thermal stratification, boreal
National Category
Earth and Related Environmental Sciences
Research subject
Physical Geography
Identifiers
URN: urn:nbn:se:umu:diva-26965DOI: 10.1029/2009JG001085ISI: 000279310300001OAI: oai:DiVA.org:umu-26965DiVA: diva2:275324
Available from: 2009-11-04 Created: 2009-11-04 Last updated: 2011-10-17Bibliographically approved
In thesis
1. Production and emission of CO2 in two unproductive lakes in northern Sweden
Open this publication in new window or tab >>Production and emission of CO2 in two unproductive lakes in northern Sweden
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Unproductive lakes are one of few natural landscape compartments with net release of carbon to the atmosphere. Lakes also generally decrease the net terrestrial carbon uptake, since most of the CO2 production in unproductive lakes are derived from organic carbon produced on land (e.g. in forests). High latitude lakes are predicted to be particularly affected by the global climate change. The carbon cycling in these lakes and their role in the landscape are therefore important to study.

In this thesis, carbon turnover processes were studied in two lakes above the arctic circle (Lake Diktar-Erik and Lake Merasjärvi) in year 2004 and 2005. Both lakes were net heterotrophic, with large variations in CO2 concentrations both on shorter (30min) and longer (24h) time-scales. The pelagic habitat supported a major part of the net production of CO2, with larger dynamics in the CO2 production than the sediments. The CO2 variations of the surface water were related to respiration of allochthonous organic carbon, and were affected by the concentration and quality of the DOC, as well as the whole lake water temperatures, and vertical water movements.

The emission of CO2 from Lake Merasjärvi was measured with the eddy covariance tech­nique. The results showed that the gas transfer rate during moderate winds were higher than expected, causing the two most commonly used models to underestimate the long term fluxes of CO2 from the lake.

Taken together, the results of the thesis show that the studied lakes contributed to bring terrestrial organic carbon back into the atmosphere, driven by a substantial internal CO2 production based on mineralization of allochthonous organic carbon. Major results are that the eddy covariance technique indicated that commonly used models tend to underestimate the net release rate of CO2 from lakes to the atmosphere, and that the lake CO2 dynamics can be the results of interactions between biogeochemical and physical processes in the lake water.

Place, publisher, year, edition, pages
Umeå: Institutionen för Ekologi, miljö och geovetenskap, Umeå universitet, 2009. 28 p.
Keyword
lake, carbon dioxide, organic carbon, inorganic carbon, boreal, arctic, DOC, DIC, CO2, emission, thermal stratification, allochthonous organic carbon
National Category
Ecology Physical Geography
Research subject
Physical Geography
Identifiers
urn:nbn:se:umu:diva-26967 (URN)978-91-7264-878-4 (ISBN)
Public defence
2009-12-03, Naturvetarhuset hörsal N450, Johan Bures Väg, Umeå universitet, Umeå, 10:00 (Swedish)
Opponent
Supervisors
Available from: 2009-11-12 Created: 2009-11-04 Last updated: 2009-11-13Bibliographically approved

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