T. Schneider (Editor). Acidification Research. Evaluation and Policy Applications 0 1992 Elsevier Science Publishers B.V. All rights resewed 319 SCENARIO ANALYSIS WITH THE DUTCH ACIDIFICATION SYSTEMS (DAS) MODEL An example for forests and forest soils A. Tiktak", A.H. Bakema", K.F. de Boer", J.W. Erisman", J.J.M. van Grinsven", C. van Heerden", G.J. Heij', J. Kros', F.A.A.M. de Leeuw", J.G. van Minnen", C. van der Salmb, J.C.H. Voogdb and W. de Vriesb " National Institute of Public Health and Environmental Protection (RIVM). PO BOX 1, 3720 BA BILTHOVEN, The Netherlands The Winand Staring Centre for integrated land, soil and water research (SC-DLO). PO-BOX 125, 6700 AC WAGENINGEN, The Netherlands Abstract Within the framework of the Dutch Priority Programme on Acidification, the DAS model has been developed. This model aims at evaluating the effects of acidification abatement strategies on a number of receptor systems in the Netherlands and describes the entire causality chain from emissions to effects in a regionalized way. Effects of three emissioddeposition scenarios on forest soils and forests are described. The emissioddeposition scenarios are based on political measures as announced in the Netherlands Environmental Policy Plan+ for the period 1990- 2000. For the period aRer 2000, three deposition targets have been chosen. Emission reductions between 1990 and 2000 cause a reduction of the average deposition to the Netherlands of about 50%. This reduction is mainly caused by reduction of Dutch agricultural NH, emissions, although considerable reductions are also foreseen for NO, and SO, emissions in the Netherlands and other European countries. Deposition reductions lead to a fast increase of the pH value and decrease of the A13+ concentration and A13+/Ca2+ ratio in the soil solution, decreasing the risk for indirect forest damage. The exceedance of a critical A13+ concentration of 0.2 rn~l,.m-~ and a critical molar A13+/Ca2+ ratio of 1.0 reduces from about 75% and 65% of the considered forest area at present to about 40% and 30% in the year 2000. When further deposition reductions are established, the exceedance of these parameters will become negligible in the year 2050. When deposition is kept constant after 2000, the critical A13+ concentration and Al3+/Ca2+ ratio will still be exceeded in a considerable area of forest soil in 2050. As a result of the