Elevated depositions of non-marine sulphate (SO42-) and inorganic nitrogen (N), as a consequence of air pollution, resulted in a progressive acidification and eutrophication of Flemish forests. Since the 1980s emission abatement reduced the acidifying and eutrophying emissions and depositions in Flanders. This thesis aimed to evaluate the impact of the evolution in depositions on soil solution chemistry, using long-term data collected in 5 plots of the ICP Forests monitoring (Level II) network in Flanders. The sharp decrease of SO42- and ammonium (NH4+) depositions made that abiotic N status started to improve and acidification slowed down during the past two decades. However, N depositions are still far above the critical loads for ectomycorrhiza and epiphytic lichens. Given the still very low soil pH (3.5‒4.5) unfavourable for microbial life, the generally observed tendency of increased dissolved organic carbon (DOC) and nitrogen (DON) mobility is likely a direct result of lowered ionic strength and partly rise in pH. Abiotic recovery is delayed by a simultaneous decrease in the deposition of base cations (Ca2+, K+ and Mg2+) and SO42- desorption. Biotic recovery is lagging behind on the changes in soil solution chemistry, as indicated by the stable but unbalanced tree mineral nutrition. Acidification and eutrophication will likely continue to produce after-effects for many decades. The results from this thesis indicate that the Programmatic Approach to Nitrogen (PAS) is partly missing its target for oxidized N compounds and that extra measures will be necessary to bring NOx emissions at an acceptable level.