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 reversibility of acidification-induce changes in different soil horizons when 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 preindustrial deposition levels, Within the roofed catchment and a reference catchment the soil solution was studied using a centrifugation drainage technique. Sulfate concentrations in the O and E horizons decreased by 75 and 65%, respectively, within 3 mo after treatment, In the Bs horizon, the sulfate concentration decreased more gradually, reaching about 52% of the pretreatment level in 1993 after 2.5 yr of treatment, The decline in sulfate concentrations in the runoff followed the pattern observed in the Bs horizon, The net loss from the catchment during the first 2.5 yr of the treatment period represents approximately 9% of the phosphate-extractable sulfate pool. No increase in soil solution pH occurred until 1994. In 1993, Al concentrations were lower compared with those found in earlier samplings of the soil solution and runoff, Fluctuations in Al concentrations were correlated most strongly with changes in ionic strength in the soil solution and runoff. Nitrate concentrations remained unchanged in the soil solution and runoff, Concentrations of NO3- were, however, already low (<30 pmol L(-1)) before the exclusion.