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 cycles and the effects of atmospheric deposition on coniferous forest ecosystems. Even though the EXMAN stands and sites are broadly similar, they represent a wide range of climatic conditions and levels of pollutant deposition. The EXMAN project incorporates treatment of forest plots and in this paper the untreated control plots are compared. The results show marked differences in ionic composition of water between sites, most clearly expressed in throughfall fluxes. At the German and Dutch sites, ionic inputs demonstrate a strong human influence. Throughfall at the Danish and Irish sites is dominated by ions of marine origin. 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 of atmospheric deposition on the composition of the soil water is very evident for most major ions. Exceptions to this are ammonium and nitrate, the complexity of whose behaviour demonstrates the need for greater understanding of nitrogen transformation and uptake in coniferous forest ecosystems.