SOURCES OF SPATIAL VARIATION IN METHANE EMISSION FROM MIRES IN NORTHERN SWEDEN - A MECHANISTIC APPROACH IN STATISTICAL MODELING

Methane emissions from sis mires in northern Sweden were measured usin g a closed chamber technique during the frost free season in 1992. The average methane flux over the measurement period, calculated either f or each mire or for different plant communities within one mire, range d from 9 to 83 mg CH4 m(-2) d(-1). The emission rate on each occasion was related to physical and chemical environmental variables, both in a general data set for all mires (n=836) and in subdata sets for indiv idual mires, using multiple linear regression. The variables with sign ificant contributions to the models were water table, standing water a bove the vegetation surface, peat temperatures, and principal componen ts of the near infrared reflectance spectra of peat samples reflecting variations in organic chemical composition. To account for the actual contribution of methane production and methane oxidation, variables d escribing the active parts of the vertically distributed potentials of methane production or oxidation were constructed. The interaction ter ms between these variables, respectively, describing the active propor tion of methanogens and methanotrophs, and the temperature values repr esenting the anoxic and oxic parts of the profile were significantly c orrelated to the methane emission rate; positively for the production zone and negatively for the consumption zone. By using this mechanisti c approach, a significant temperature effect in both the methane produ ction and consumption zone was detected. These constructed temperature variables explain 21% of the variance in the logarithmically transfor med methane fluxes using the entire data set (n=836) but only 5% of th e variance using peat temperatures from fixed depths. Adding variables describing the organic chemical composition of the peat to the models improved the predictability in 10 of the 11 model sets tested, decrea sing the unexplained variance by maximally 50% for a poor fen communit y model and increasing R-2 from 0.40 to 0.68. In the general model, R- 2 increased from 0.42 to 0.49 with the inclusion of organic chemical c omposition. The explained variance in the final models, including the substrate variables, ranged from R-2=0.49 to R-2=0.75, with one except ion, Torsmyran (R-2=0.36) which is a mire that most closely relates to an eccentric ombrotrophic bog among the mires studied.