Soil acidification by acid rain in forest ecosystems: A case study in northern Italy

The elemental composition of rainwater, throughfall, stemflow and soil solution of a forest ecosystem in northern Italy was investigated in order to assess the impact of industrial emissions of acidic oxides. For rainfall, pH average is approx. 5.2 and in three-quarters of the samples collected most of the acidity is associated with anthropogenic components. Indeed, the contribution of anthropic NH4+ and NO3- to the total ionic charge was estimated to average 30%: ammonia-N is a critical acidification input, especially during spring. Interception of rain by vegetation induces substantial modifications in water chemistry, and soil acidification occurs at the base of plants and decreases with distance from the plants. Elemental concentrations in soil solution decrease with depth. Furthermore, in the B horizon competition between ammonia and nutrients sometimes arises to effectively counteract the uptake of nutrients by plants. At present, acidification effects on vegetation and soils are negligible. Potential phytotoxic hazard, however, may arise with persisting anthropogenic emissions. (C) 1998 Elsevier Science B.V. All rights reserved.