As a basis for experimentation, inputs and outputs of biogeochemicals were observed in coniferous stands in Denmark, the Netherlands, Germany and Ireland. The range of deposition observed is characteristic of populated regions of northwest Europe, from only moderately polluted Atlantic areas through decreasing marine influence and increasing deposition of anthropogenic nitrogen and sulphur. In intensive agricultural regions, ammonium inputs are high enough to cause nitrogen saturation of ecosystems, and nitrificationacidification is a major soil process. Co-deposition of ammonia and sulphur dioxide may be significantly increasing loads of N and S in forests in the region. Input-outputs are balanced for seasalts in the maritime sites, and sulphur outputs from the rooting zone also reflect the inputs to a large degree on these sites. Mobilisation of cations, notably aluminium, apparently occurs as a result of acidity generated by nitrogen transformations.