Atmospheric input of nitrogen compounds may have an impact on both terestrial and aquatic ecosystems in the Alpine area. Nitrogen (N) can act as a fertilizer for forest ecosystems, enhancing forest growth. On the other hand, high N loads can determine nutrient imbalances, changes in the composition of ground vegetation, and increased sensitivity to other stress factors (Dise and Wright, 1995; Gundersen et al. 1998). The Western European Alps are affected by high N deposition (usually above 15 kg N ha-1 y-1 as the sum of ammonium and nitrate). Some long-term studies at the catchment scale in the Alps showed increasing evidence of soil N saturation with consequent leaching of nitrate to surface water (Rogora et al. 2001).
Several research programs for the monitoring of atmospheric depsotion in the Alpine countries have been launched in the last few decades. To monitor the atmospheric deposition onto forest, national programs in many European countries sample and analyze bulk and throughfall deposition as part of the International Cooperative Programme on Assessment and Monitoring of Air Pollution Effects on Forests (ICP Forests) (EC-UN/ECE, 1998). Results from the ICP Forests network of Italy, Switzerland and France are gathered in this paper in order to:
(i) investigate geographical variability in the deopsition of nitrogen compounds;
(ii) assess temporal trends of N deposition in response to changes in the atmospheric emission;
(iii) discuss the potential relationship between the status of N deposition and its effects on
forest ecosystems in the alpine and subalpine areas.
No obvious gradients were identified in N deposition in relation to geographical attributes such as altitude or latitude. The highest loads were recorded in areas in the foothills of the Alps, such as the pre-alpine area in North-Western Italy and the area of Canton Ticino, Switzerland.
Nitrate in atmospheric depostion has not decreased significantly in last decade, both as concentration and flux. Ammonium depostion has slightly decreased at few sites. The deposition of N is still well above the estimated critical loads of nutrient N at most of the sites.
Present N deposiktion were compared to estimates of deposition reduction by 201 according to the reduction of NO3 deposition envisaged by the Protocol, a sharp decreas of N input also in reduced form will be needed to reach the goal of critical loads.
Dise, N. B. and Wright, R. F. (1995). Nitrogen leaching from European forests in relation to nitrogen deposition. Forest Ecology and Management 71, 153-161.
Gundersen, P., Emmentt, B. A., Kjonaas, O. J., Koopmans, C. J., and Tietaema, A. (1998). Impact of nitrogen deposition on nitrogen cycling in forests: a synthesis of NITREX data. Forest Ecology and Management 101, 37-55.
Rogora, M. Marchetto, A., Mosello, R. (2001). Trends in the chemistry of atmopheric deposition and surface waters in the Lago Maggiore watershed. Hydrol. Hearth System Sci. 5, 379-3990.
EC-UN/ECE, 1998: De Vries, W., Reinds, J., Deelstra, H. D., Klap, J. M., Vel, E. M.: Intensive Monitoring of Forest Ecosystems in Europe, 1998 Technical Reoport, EC, UN/ECE, Brussels, Geneva, 104 pp.
UN-ECE, 1999: Protocol to the 1979 Convention on Long-range Transboundary Air Pollution to abate acidification, autrophication and ground-level ozone. United Nations, Economic Commission for Euzrope, Geneva, Switzerland.