The doctoral dissertations of the former Helsinki University of Technology (TKK) and Aalto University Schools of Technology (CHEM, ELEC, ENG, SCI) published in electronic format are available in the electronic publications archive of Aalto University - Aaltodoc.
Aalto

Modeling of Microscale Variations in Methane Fluxes

Anu Kettunen

Dissertation for the degree of Doctor of Technology to be presented with due permission for public examination and debate in Auditorium E at Helsinki University of Technology, Espoo, Finland, on the 17th of January, 2003, at 12 o'clock noon.

Overview in PDF format (ISBN 951-22-6304-1)   [270 KB]
Dissertation is also available in print (ISBN 951-22-6255-X)

Abstract

The current study analyzes the different modes of variation in methane fluxes from different microsites of a boreal mire. The results emphasize the importance of microsite characteristics, water table and vegetation cover for methane fluxes. Water level affects the moisture and oxygen profiles in peat matrix which are reflected to methane production and oxidation rates and the corresponding microbial populations. Vascular plants promote methane production by providing substrates in the form of root exudates and fine root litter, enhance methane oxidation by transporting oxygen to water saturated peat layers and accelerate methane transport by liberating methane from peat to the atmosphere via the aerenchymous tissue. The model presented in this study connects the methane fluxes to the seasonal photosynthetic cycle of plants at the microsite level while the thermal and hydrological conditions in peat are used as an operational framework. Overall, the model dynamically combines the microbial processes in peat to changing environmental factors in the level of peatland ecosystem. Sensitivity analysis of the model reveals the importance of substrate supply to methane fluxes. Furthermore, the model outcome is sensitive to increased capability of the vascular plants to transport oxygen downwards. Lack of oxygen and partly methane keep methane oxidation at a very low level. Any changes in model parameters or environmental conditions that compensate for these lacks have a remarkable decreasing effect on simulated flux. Simulated methane flux decreases considerably if the duration of simulated dry period increases, threshold for a dramatic change lying between 4 and 6 weeks of drought. Increase in air temperature enhances methane flux especially if the effect of increased temperature on gross primary production is taken into account.

This thesis consists of an overview and of the following 5 publications:

  1. Kettunen, A., 2000. Short-term carbon dioxide exchange and environmental factors in a boreal fen. Verh. Internat. Verein. Limnol. 27, 1446-1450. © 2000 E. Schweizerbart'sche Verlagsbuchhandlung. By permission.
  2. Kettunen, A., Kaitala, V., Alm, J., Silvola, J., Nykänen, H. and Martikainen, P. J., 1996. Cross-correlation analysis of the dynamics of methane emissions from a boreal peatland. Global Biogeochemical Cycles 10 (3), 457-471. © 1996 American Geophysical Union. By permission.
  3. Kettunen, A., Kaitala, V., Alm, J., Silvola, J., Nykänen, H. and Martikainen, P. J., 2000. Predicting variations in methane emissions from boreal peatlands through regression models. Boreal Environment Research 5, 115-131. © 2000 Finnish Environment Institute. By permission.
  4. Kettunen, A., Kaitala, V., Lehtinen, A., Lohila, A., Alm, J., Silvola, J. and Martikainen, P. J., 1999. Methane production and oxidation potentials in relation to water table fluctuations in two boreal mires. Soil Biology and Biochemistry 31, 1741-1749. © 1999 Elsevier Science. By permission.
  5. Kettunen, A., 2002. Connecting methane fluxes to vegetation cover and water table fluctuations at microsite level: A modeling study. Systems Analysis Laboratory Research Reports E10, November 2002. © 2002 by author.

Keywords: boreal peatlands, microsites, vegetation cover, water table, photosynthetic carbon cycle, methane production and oxidation potentials, flux dynamics, correlation techniques, regression and process-based models

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© 2003 Helsinki University of Technology

Last update 2011-05-26