Soil drainage water solute chemical composition showed not only increased losses of inorganic N with increasing N input but also substantially increased organic N losses from the soil system. These losses are important for water bodies both from the eutrophication and acidification view points, and may also be relevant in the context of trace metal transport via chelation. Preliminary studies showed that physical parameters such as hydraulic conductivity, bulk density and porosity could be important to assessment of damage occurring due to acidic N pollution load. Reduced soil microbial activity was clearly demonstrated from peat micromorphological studies and decomposition experiments. The micromorphological studies showed the thickening of the porous surface horizon in grossly polluted areas, where the decomposition process is slowed significantly. Under these conditions, however, NH4+ and NO3- leaching from microcosms is reduced, with greater use being made by biota of atmospheric N inputs as N mineralisation decreases. Two biotic components were studied. Enchytraeid worms showed sensitivity to soil acidity in the long term. Mycorrhizal infection studies showed that increasing N input, especially in the form of NH4+, could be injurious even in the short to mid term. Both studies suggested that more attention is needed in this area. aSignificant accumulation of NH4+ in peat was found in this study. Toxicity effects of high NH4+-N to plants or microflora may be manifesting themselves via discouraging infection in the Calluna root system. New plant generation for high NH4+- N treatment was also poor. It is suggested that, among the N species in N inputs, NH4+ could be most damaging.