Composition and variability of soil solutions as a measure of human impact on protected woodland areas

A study was made of the sandy and loamy soils of the woodland areas of the Wielkopolski National Park (Poland) affected by acid rain. The basic properties of the soils were determined, revealing their strong acidification, poor buffering power, and the possibility of aluminium release. An analysis was made of the content of soluble, exchangeable, organic, amorphous, and free forms of aluminium. The concentration of exchangeable aluminium exceeded that of the form dissolved in soil water several times to tens of times. In soil solutions Ca/Al ratios in some horizons show very low values that could induce a nutrient deficit. In the sandy profiles the ratio even drops below the critical level of 0.1. In the surface horizon the dominant cation at all the sites is the aluminium ion. An analysis of anions shows a dominance of sulphate and chloride ions. In autumn nitrites were recorded at all depth levels, while in spring only in the surface layers. The highest fluoride concentrations were found to occur in profiles situated the closest to the emission source of fluorine compounds. The markedly higher concentrations of ammonium than nitrate ions can lead to increased acidification and eutrophication of the soil.