A COMPARISON OF SITES IN THE EXMAN PROJECT, WITH RESPECT TO ATMOSPHERIC DEPOSITION AND THE CHEMICAL-COMPOSITION OF THE SOIL SOLUTION AND FOLIAGE

Forest stands, throughfall and the composition of the soil solution in six coniferous forest plantations in Europe were compared as part of the EXMAN project, which was established to quantify biogeochemical cy cles and the effects of atmospheric deposition on coniferous forest ec osystems. Even though the EXMAN stands and sites are broadly similar, they represent a wide range of climatic conditions and levels of pollu tant deposition. The EXMAN project incorporates treatment of forest pl ots and in this paper the untreated control plots are compared. The re sults show marked differences in ionic composition of water between si tes, most clearly expressed in throughfall fluxes. At the German and D utch sites, ionic inputs demonstrate a strong human influence. Through fall at the Danish and Irish sites is dominated by ions of marine orig in. Hydrogen ions are not the most important cations in precipitation at any site, and at only one site (Selling, Germany) was the hydrogen ion flux in throughfall greater than in precipitation. The influence o f atmospheric deposition on the composition of the soil water is very evident for most major ions. Exceptions to this are ammonium and nitra te, the complexity of whose behaviour demonstrates the need for greate r understanding of nitrogen transformation and uptake in coniferous fo rest ecosystems.