Effects of acid deposition on forest soils in northernmost Russia: Modelled and field data

In addition to strong natural stresses forest ecosystems in the Kola Subarc tic, Russia, receive high loads of sulphur and heavy metals from the nickel smelter. To estimate soil response to acid deposition we compared the soil field data along a pollution gradient and simulated time effects. Multivar iate technique was applied to investigate spatial distribution of soil fiel d data. Time response of soils to acid deposition was evaluated with the SM ART model. According to field observations there is no evidence for strong soil acidification effects close to the smelter. Concentrations of exchange able Ca and base saturation increase, while acidity decrease in lower soil mineral horizons towards the pollution source. However, some features seem to reflect the early stages of the started acidification. Most soil profile s have low pH values. Despite increasing of exchangeable Ca and Mg towards the smelter in lower mineral horizons due to geological inheritance, they d o not reveal the same trends in the upper ones. Concentration of exchangeab le K in organic horizons decreases towards the smelter, thus confirming the starting acidification. As result, exchangeable base cations are depleted in the considerable part of shallow soil profiles. According to model simul ation the present acid load does not effect considerably on forest soils in background areas, however, dramatic shift in soil chemistry near the smelt er is expected within several decades. Due to low pool of exchangeable base cations and low weathering rate continued acid deposition can lead to incr eased soil acidification and nutrient imbalance.