Enhanced soil, ground water and surface water acidification by elevated deposition of S and N compounds is one of the most important large-scale environmental problems today. This thesis deals with the quantification of:(i) natural and man-induced sources of acidification in agricultural soils and forest soils in the Netherlands;(ii) present impacts of atmospheric S and N deposition on the solution chemistry of acid sandy forest soils in the Netherlands;(iii) various buffermechanisms (i.e. mineral weathering, cation exchange and AI dissolution) in acid sandy soils in the Netherlands;(iv) average critical deposition levels (loads) for N and acidity (N and S) for forests, heathlands, ground water and surface water in the Netherlands;(v) spatial variability in critical loads for N, S and acidity and the degree by which these loads are exceeded at present on forests in the Netherlands and in Europe;(vi) long-term impacts of acidic deposition on representative non-agricultural soils;(vii) spatial variability in long-term impacts of acidic deposition on forest soils in the Netherlands and in Europe. Quantification was performed on the basis of interpretation of literature information, combined with field research (i and ii), laboratory research (iii), and model research, (iv, v, vi and vii). In order to derive critical loads, steady-state soil models were developed, i.e. a one-layer model (START) for application on a European scale and a multi-layer model (MACAL) for application on a national scale. Similarly, two dynamic soil models were developed to assess the long-term soil response to acidic deposition, i.e. a onelayer model (SMART) for application in Europe and a multi-layer model (RESAM) for application in the Netherlands.Results showed that:(i) the contribution of acid deposition to soil acidificatiom in the Netherlands is dominant in non- calcareous forest soils (≥80%), intermediate in non-calcareous agricultural soils (≤50%) and minor in calcareous soils (≤20%);(ii) S0 4 behaves conservative in Dutch forest ...