Comparison of acidic deposition to semi-natural ecosystems in Denmark—Coastal heath, inland heath and oak wood

Acidic deposition to coastal heath, inland heath and oak wood in Denmark was determined from analysis of bulk precipitation and throughfall measurements for up to 3 yrs. The analysis aimed to determine the total annual sulphur and nitrogen deposition to the three different ecosystems. Total nitrogen deposition is especially difficult to assess due to uptake of nitrogen by the canopy, and difficulties in determining the dry deposition of each nitrogen species. An NHx-uptake estimation model is presented which assumes co-deposition of NHx+H+ and SOx+NOy and exchange of NHx+H+ for the leached Mg2+, Ca2+ and K+ in the canopy. This approach makes it possible to estimate the dry deposition of reduced nitrogen (NHx). Dry deposited oxidized nitrogen (NOy) still remains unquantified with the throughfall method, and therefore this term 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 molc ha-1 for the oak wood, 2228 molc ha-1 for the inland heathland, and 2060 molc ha-1 for the coastal heathland. However, this acid load has different effects on the ecosystems depending on the actual bio-geochemical reactions. The potential maximum acidification estimated for the oak wood (5512 molc ha-1 yr-1) was almost twice as high as for the inland heathland (3815 molc H+ ha-1 yr-1) and for the coastal heathland (3383 molcH+ ha-1 yr-1).