Atmospheric deposition of N and S on terrestrial and aquatic ecosystems 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 to an excess of N. Effects of acidification include forest damage, groundwater pollution, and loss of fish populations due to Al mobilization. Critical loads (deposition levels) for N and S on terrestrial and aquatic ecosystems in the Netherlands related to these effects have been derived by empirical data and steady-state acidification models. Critical loads of N generally vary between 500 and 1500 mol(c) ha-1 yr-1 for forests, heathlands and surface waters and between 1500 and 3600 for phreatic groundwaters. Critical loads of total acid (S and N) vary between 300 to 500 mol(c) ha-1 yr-1 for phreatic groundwaters and surface waters and between 1100 to 1700 mol ha-1 yr-1 for forests. On the basis 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 the 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.
