Impacts des dépôts atmosphériques acides sur l'eau des sols forestiers

Abstract

Impacts of atmospheric acid deposition on soil solutions in forests After a massive input of acidifying components on the environment in the middle of the 20th century, atmospheric acid deposition has decreased as a result of sulphur emission reduction. The continuous acid input might affect the chemistry of soils and drainage waters and accelerate soil acidification. In the framework of the Swiss Long-Term Forest Ecosystem Research (LWF), we examined whether acid deposition has continued to decline in the last ten years in different forest ecosystems and how the chemistry of soil water reacted to the improvement in air quality. Acid deposition decreased significantly at only three out of the nine study sites. Sulphur deposition declined at all sites, but due to the relatively low sulphur load compared to nitrogen deposition, it did not contribute to decrease acid deposition. Chemistry of soil solution remained quite constant since the beginning of the measurements about ten years ago. We did not observe any acidification of soil solution in six out of eight sites. In contrast, changes in soil solution chemistry at two sites showed a rapid acidification. At three sites, the deeper soil layer released large amount of sulphate coupled with base cations, which likely contributed to deplete the soil in nutrients. The analysis of the base saturation in 1039 soil profiles across Switzerland shows a high risk of relatively fast acidification of soil solution in almost 20% of sites.