Modeling of Microscale Variations in Methane Fluxes

Dissertation for the degree of Doctor of Technology to be presented with due permission for public examination and debate in Auditorium 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. Publications The dissertation consists of the present summary article and the following papers: [I] Kettunen, A. (2000). Short-term carbon dioxide exchange and environmental factors in a boreal fen.correlation analysis of the dynamics of methane emissions from a boreal peatland. Predicting variations in methane emissions from boreal peatlands through regression models. (1999). Methane production and oxidation potentials in relation to water table fluctuations in two boreal mires. The author is responsible for developing the theoretical framework of the study, and for the modeling and data analyses presented in all papers. She is also responsible for the interpretation of the results and has written all the …