REVERSING ACIDIFICATION IN A FORESTED CATCHMENT IN SOUTHWESTERN SWEDEN - EFFECTS ON SOIL SOLUTION CHEMISTRY

The exclusion of acid precipitation in whole-catchment experiments can provide valuable information to further our understanding of recovery processes of acidified soils. In this study, we focused on the revers ibility of acidification-induce changes in different soil horizons whe n anthropogenic deposition was excluded. A small forested catchment in the Gardsjon area in southwest Sweden was covered with a transparent roof in April 1991 and sprinkled with water that simulated preindustri al deposition levels, Within the roofed catchment and a reference catc hment the soil solution was studied using a centrifugation drainage te chnique. Sulfate concentrations in the O and E horizons decreased by 7 5 and 65%, respectively, within 3 mo after treatment, In the Bs horizo n, the sulfate concentration decreased more gradually, reaching about 52% of the pretreatment level in 1993 after 2.5 yr of treatment, The d ecline in sulfate concentrations in the runoff followed the pattern ob served in the Bs horizon, The net loss from the catchment during the f irst 2.5 yr of the treatment period represents approximately 9% of the phosphate-extractable sulfate pool. No increase in soil solution pH o ccurred until 1994. In 1993, Al concentrations were lower compared wit h those found in earlier samplings of the soil solution and runoff, Fl uctuations in Al concentrations were correlated most strongly with cha nges in ionic strength in the soil solution and runoff. Nitrate concen trations remained unchanged in the soil solution and runoff, Concentra tions of NO3- were, however, already low (<30 pmol L(-1)) before the e xclusion.