Effect of acid deposition on quantity and quality of dissolved organic matter in soil-water.

The aim of this study was to explore how acid deposition may affect the concentration and quality of dissolved organic matter (DOM) in soil-water. This was done by a small-scale acidification experiment during two years where 0.5 x 0.5 m(2) plots were artificially irrigated with water with different sulfuric acid content, and soil water was sampled using zero-tension lysimeters under the O-horizon. The DOM was characterized using absorbance, fluorescence, and size exclusion chromatography analyses. Our results showed lower mobility of DOM in the high acid treatment. At the same time, there was a significant change in the DOM quality. Soil water in the high acid treatment exhibited DOM that was less calored, less hydrophobic, less aromatic, and of lower molecular weight, compared to the low add treatment. This supports the hypothesis that reduction in sulfur deposition is an important driver behind the ongoing brownification of surface waters in many regions.