Steady-state and dynamic assessment of forest soil acidification in Switzerland

The European steady-state Simple Mass Balance (SMB) model and the dynamic s oil acidification model SAFE were used to assess the risk of future forest soil acidification in Switzerland. 2010 deposition forecasts on a 150x150 k m grid resolution as well as corresponding ecosystem protection levels were obtained from RAINS model runs based on the 1999 Gothenburg Protocol oblig ations under the UN/ECE LRTAP Convention. Deposition values for 2010 on the national resolution were derived by scaling down present 1x1 km deposition values according to the deposition trends at the 150x150 km grid resolutio n. Meeting the Protocol obligations will reduce the percentage of Swiss for est ecosystems not protected against acidification between 1990 and 2010 fr om 41 to 4% according to the RAINS assessment and from 63 to 16% according to the assessment with the SMB at the 1x1 km resolution. The dynamic approa ch indicates, however, that soil conditions may not improve as much as thes e steady-state models suggest. By 2010, 39% of the sites considered will st ill have soil solution Bc/Al molar ratios below 1 at least in one soil laye r. Nevertheless, deposition reductions obtained from the implementation of the new protocol will prevent the major part of Swiss forest soils from fur ther acidification. Aiming at recovery of the more sensitive forest ecosyst ems would require emission reductions beyond the Protocol's obligations.