Finnish Forest Research Institute  Metla

Media release 19.10.2005

Only slight indication of forest acidification

Only slight indication of acidification in upland forest soils was detectable in samples taken during the past few decades. Hence, sulphur and nitrogen depositions due to emissions from industry and traffic do not seem to have a noticeable effect on soil properties. These findings were reported in a study made at the Finnish Forest Research Institute.

The aim of the research was to establish, if upland soil properties have changed during a follow-up period of 12 - 28 years. The materials in the study comprised soil samples collected from 54 upland test plots in southern Finland, from the organic top layer and the lower mineral soil layer. The oldest samples had been collected during 1965 - 1981 and the most recent ones in 1993. In addition to the soil data, also the annual total emissions of e.g. sulphur and nitrogen were assessed during the study period.

The concentrations of soil organic matter in the organic and mineral layers had increased during the study period, which caused changes in most of the examined soil variables. During the 12 - 28 -year study period, acidification of forest soil was manifested as an increase in aluminium concentrations in the mineral soil layer and as a decrease in calcium, magnesium and potassium concentrations especially in the organic layer.

The changes in soil properties, except for sulphur concentrations, could not be explained to be due to sulphur or nitrogen emissions. The reduced sulphur concentrations in the organic layer are likely to be connected with the reduction in sulphur emissions since the 1980s. Unchanged or decreased soil nitrogen concentrations suggest that there is no threat of excessive nitrogen deposition in forests of southern Finland in the foreseeable future.

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