Greenhouse gas balances change during development of land-uplift mires on the coast of the Gulf of Bothnia

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ANNUAL REPORT 2005

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Photo: Erkki Oksanen

Changes were observed in vegetation, water conditions, microbial communities and in dynamics of greenhouse gases (GHG) as mires age. During a dry period a young mire can be a methane sink releasing carbon dioxide, whereas during moister periods the same mire works as a methane emission source and a carbon dioxide sink. The development of the GHG balance was studied in five mires of different ages in Siikajoki on the land-uplift coast. The youngest site rose from the sea less than 100 years ago and the oldest one approximately 2500 years ago.

During an exceptionally dry growing season in 2003 the three youngest fens were methane sinks and emissions were measured only from the approximately 1000-year-old fen. During a moister season in 2004 all five sites emitted methane to the atmosphere. The composition of the methanogenic microbial communities present in peat was observed to change during the successional transect.

During a dry growing season the younger mires released carbon and only the oldest site was a carbon dioxide sink. In conditions where the water level stayed high keeping the peat layer moist, the carbon balance of young mires changed from negative to positive and all sites served as net sinks of carbon dioxide. This can partly be explained by the changes that occur in vegetation. As the mire ages, the grasses and sedges that dominate younger fens are replaced by mosses and shrubs.

The research was part of the research programme Greenhouse effects of the use of peat and peatland in Finland coordinated by the University of Helsinki, Department of Forest Ecology, with several academic departments and units of Metla involved.

Additional information: www.metla.fi/hanke/7115/index-en.htm

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