Air pollution affects forest health through atmospheric deposition of acidic and nitrogen compounds and elevated levels of tropospheric ozone (O3). In 1985, a monitoring network was established across Europe and various research efforts have been undertaken to define critical values. We measured atmospheric deposition of acidity and nitrogen as well as ambient levels of O3 on 12, 13, and 14 plots, respectively, in the framework of the Swiss Long-Term Forest Ecosystem Research (LWF) in the period from 1995 to 2002. We estimated the critical loads of acidity and of nitrogen using the steady state mass balance approach and calculated the critical O3 levels using the AOT40 approach. The deposition of acidity exceeded the critical loads on 2 plots and almost reached them on 4 plots. The median of the measured molar ratio of base nutrient cations to total dissolved aluminium (Bc/Al) in the soil solution was higher than the critical value of 1 for all depths, also at the plots with an exceedance of the critical load of acidity. For nitrogen, critical loads were exceeded on 8 plots and deposition likely represents a long-term ecological risk on 3 to 10 plots. For O3, exceedance of critical levels was recorded on 12 plots and lead to the development of typical O3-induced visible injury on trees and shrubs, but not for all plots due to (i) the site specific composition of O3 sensitive and tolerant plant species and (ii) the influence of microclimatic site conditions on the stomatal behaviour, i.e. O3 uptake.
critical loads, critical levels, nitrogen, acid deposition, tropospheric ozone, forest, risk assessment, LWF, ICP-Forests Level II, Switzerland
Waldner P., Schaub M., Graf Pannatier E., Schmitt M., Thimonier A., Walthert L., (accepted). Atmospheric deposition and ozone levels in Swiss forests: are critical values exceeded?. In: Paoletti E., Schaub M., Bytnerowicz A. (eds.). Air Pollution and Global Change: Key Studies of the Effects on Forest Vegetation. Environmental Monitoring and Assessment (Special Issue).