Abstract

Keywords

acid deposition; critical levels; critical loads; forest; ICP-Forests Level II; LWF; nitrogen risk assessment; tropospheric ozone; Switzerland

Abstract

Air pollution affects forest health through atmospheric deposition of acidic and nitrogen compounds and elevated levels of tropospheric ozone (O-3). In 1985, a monitoring network was established across Europe and various research efforts have since been undertaken to define critical values. We measured atmospheric deposition of acidity and nitrogen as well as ambient levels of O-3 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 O-3 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, and 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 O-3, exceedance of critical levels was recorded on 12 plots, and led to the development of typical O-3-induced visible injury on trees and shrubs, but not for all plots due to (1) the site specific composition of O-3 sensitive and tolerant plant species, and (2) the influence of microclimatic site conditions on the stomatal behaviour, i.e., O-3 uptake.

LWF Classification

Network: LWF, Sites: Alptal Beatenberg Bettlachstock Celerina Chironico Isone Jussy Lausanne Lens Nationalpark Neunkirch Novaggio Othmarsingen Schänis Visp Vordemwald, Category: ISI,