IMPACTS OF ACID DEPOSITION ON CONCENTRATIONS AND FLUXES OF SOLUTES INACID SANDY FOREST SOILS IN THE NETHERLANDS

This article summarizes the most important impacts of acid atmospheric deposition on the soil solution chemistry of acid sandy forest soils in the Netherlands, by comparing and interpreting data from soil solut ion monitoring studies (18 stands) and a national soil solution survey (150 stands). Major conclusions are: (i) in forest subsoils there is almost a 1:1 relationship between the concentrations of SO4 and NO3 an d those of H and Al, (ii) presumed critical Al concentrations (0.2 mol (c) m-3) and Al/Ca ratios (1.0 mol mol-1) are generally exceeded below 20 cm soil depth whereas NH4/K ratios sometimes exceed a presumed cri tical value (5 mol mol-1) in the upper 20 cm, (iii) SO4, NO3, Al and H concentrations decrease in the order: spruce forests > pine forests > deciduous forests, (iv) forest soils are invariably saturated with SO 4 (leaching equals deposition), (v) there is generally a relative larg e retention of N although there are indications that forest soils beco me N-saturated at total N inputs above 4.0 kmol(c) ha-1 yr-1, (vi) NH4 leaching is generally negligible but may become substantial above an NH4 input of 3.0 kmol(c) ha-1 yr-1, and (vii) Al mobilization is the m ajor buffer mechanism neutralizing the acidity produced from N transfo rmations. Conclusions (i), (iv) and (vi) imply that a decrease in atmo spheric inputs of S and N will give a nearly equivalent decrease in (H and) Al leaching.