This study shows the influence of acid rain on the chemistry of surface waters in two small basins. The basins present similar altitudes and climates, only one is forested, and the forest decline has been clearly established. In both basins, rain water is polluted by acids (H+, so24-,N03). This acid input is neutralized in soils but the efficiency of that neutralization varies from one basin to another: (a) in the non forested basin, the alkalinity of surface water dominates the anionic charge, (b) in the forested basin, the strong acid anions still dominate the anionic charge of a just neutralized solution. The chemistry of surface water in the forested basin cannot be explained only by the incident rainfall and its partial evaporation. There appears to be a major input of pollutant through dry deposits in throughfall
