Chemistry of soil solutions under different kinds of vegetation in the vicinity of a thermal power station

The influence of atmospheric deposition on the chemical characteristics of soil solutions in a small catchment area in NW Spain was studied. The soils, developed from slates, were sampled from seven sites supporting different forms of vegetation (deciduous and pine forest and heath). Soil solutions were extracted, by the column displacement method, from soil samples collected monthly from March 1992 until November 1993. The solutions were acidic with a low content of basic cations. The most common ions in all horizons were Cl(-) and Na(+), due to marine influence. In the surface horizons (0-10 cm), relatively high concentrations of SO(2-)4 (150-380 micromol litre(-1)) and Zn (approximately 2 micromol litre(-1)) were obtained, with good correlation between the two ions. These results, along with the prevalence of inorganic forms of Al (50-90% of total Al), were related to the effects of acidic deposition in the catchment area. The more rapid breakdown of litter in the soils under deciduous forest explains the greater ionic concentrations obtained in these solutions.