At each site along the European north-south transect studied, a predominant pool of nitrogen (N) is in the organic form. The processes of mineralisation followed by nitrification and anthropogenic deposition will, in addition, combine and provide the inorganic forms ammonium (NH4 −) and nitrate (NO3 −) in amounts and ratios which will depend upon local conditions of soil, climate and pollutant deposition. While Aheden, the most northerly site of the transect, supports little net mineralisation (see Cotrufo et al., Chap. 13, this Vol.) and receives virtually no pollutant N (see Persson et al., Chap. 2, this Vol.), the southern Scandinavian and central European sites have experienced considerable inputs of NH4 - and NO3 − deposition over recent years.