AVERAGE CRITICAL LOADS FOR NITROGEN AND SULFUR AND ITS USE IN ACIDIFICATION ABATEMENT POLICY IN THE NETHERLANDS

Atmospheric deposition of N and S on terrestrial and aquatic ecosystem s causes effects induced by eutrophication and acidification. Effects of eutrophication include forest damage, NO3 pollution of groundwater and vegetation changes in forests, heathlands and surface waters due t o an excess of N. Effects of acidification include forest damage, grou ndwater pollution, and loss of fish populations due to Al mobilization . Critical loads (deposition levels) for N and S on terrestrial and aq uatic ecosystems in the Netherlands related to these effects have been derived by empirical data and steady-state acidification models. Crit ical loads of N generally vary between 500 and 1500 mol(c) ha-1 yr-1 f or forests, heathlands and surface waters and between 1500 and 3600 fo r phreatic groundwaters. Critical loads of total acid (S and N) vary b etween 300 to 500 mol(c) ha-1 yr-1 for phreatic groundwaters and surfa ce waters and between 1100 to 1700 mol ha-1 yr-1 for forests. On the b asis of the various critical loads a deposition target for total acid of 1400 mol(c) ha-1 yr-1 has been set in the Netherlands from which th e N input should be less than 1000 mol(c) ha-1 yr-1. This level, to be reached in the year 2010, implies an emission reduction of 80-90% in SO2, NO(x) and NH3 in the Netherlands and of about 30% in neighboring countries compared to 1980 emissions.