COMPARISON OF ACIDIC DEPOSITION TO SEMINATURAL ECOSYSTEMS IN DENMARK - COASTAL HEATH, INLAND HEATH AND OAKWOOD

Acidic deposition to coastal heath, inland heath and oak wood in Denma rk was determined from analysis of bulk precipitation and throughfall measurements for up to 3 yrs. The analysis aimed to determine the tota l annual sulphur and nitrogen deposition to the three different ecosys tems. Total nitrogen deposition is especially difficult to assess due to uptake of nitrogen by the canopy, and difficulties in determining t he dry deposition of each nitrogen species. An NHx-uptake estimation m odel is presented which assumes co-deposition of NHx + H+ and SOx + NO y and exchange of NHx + H+ for the leached Mg2+, Ca2+ and K+ in the ca nopy. This approach makes it possible to estimate the dry deposition o f reduced nitrogen (NHx). Dry deposited oxidized nitrogen (NOy) still remains unquantified with the throughfall method, and therefore this t erm is estimated from a generalized micro-meteorological model. Total annual nitrogen deposition was 29.0 kg ha(-1) yr(-1) for the oak wood, 18.3 kg ha(-1) yr(-1) for the inland heathland and 13.5 kg ha(-1) yr( -1) for the coastal heathland. The total annual acidic deposition (the sum of H+, SOx, NOy and NHx) was 3202 mol(c) ha(-1) for the oak wood, 2228 mol(c) ha(-1) for the inland heathland, and 2060 mol(c) ha(-1) f or the coastal heathland. However, this acid load has different effect s on the ecosystems depending on the actual bio-geochemical reactions. The potential maximum acidification estimated for the oak wood (5512 mol(c) ha(-1) yr(-1)) was almost twice as high as for the inland heath land (3815 mol(c) H+ ha(-1) yr(-1)) and for the coastal heathland (338 3 mol(c) H+ ha(-1) yr(-1)). (C) 1998 Elsevier Science Ltd. All rights reserved.