FIELD-SCALE CLEAN RAIN TREATMENTS TO 2 NORWAY SPRUCE STANDS WITHIN THE EXMAN PROJECT - EFFECTS ON SOIL SOLUTION CHEMISTRY, FOLIAR NUTRITIONAND TREE GROWTH

'Clean rain' treatments were performed in spruce forests at Klosterhed e, Denmark, and Selling, Germany, by replacement of ambient throughfal l water with artificial throughfall reducing the load of S (55-95%), N (70-90%) and acidity (ca. 90%). The induced strong reductions in SO42 -, input caused corresponding strong reductions in soil solution conce ntrations at Klosterhede and to a minor extent at Selling. The differe nce in response to the reduced input is suggested to be largely a cons equence of differences in storage capacity between the two sites. Redu ced input of N at Selling caused strong and immediate reduction in the soil solution concentration. At Klosterhede, N concentrations in the soil solution were already low prior to the treatment and no effects w ere recorded. The effects on soil acidification reflected by Al and H concentrations were slow and small although a slight improvement in ac id neutralising capacity (ANC) was observed at Klosterhede, mainly cau sed by a strong reduction in strong acid anions. The input reductions decreased the general ion activity in the soil solution and the accumu lation of base cations at both sites were consequently increased, With in the 6 yr of treatment at Klosterhede and the 2 yr at Selling, the e ffects on the soil solution chemistry were generally moderate. Accordi ngly, no significant changes in vegetation were observed apart from a water induced increase in growth rate at Klosterhede. (C) 1998 Elsevie r Science B.V.