Dry deposition and internal circulation of nitrogen, sulphur and base cations to a coniferous forest

The dry deposition of sulphur, nitrogen and base cations to a spruce stand was estimated during a five year period using a surrogate surface resemblin g needles, throughfall and bulk deposition measurements. The deposition was calculated from the ratio between the deposition of an ion and sodium on t he surrogate surface and the net throughfall of sodium to the forest. The d ry deposition represented a large fraction of the total atmospheric input o f base cations. For Na+, Mg2+, Ca2+, and K+ they were 66, 67, 53 and 42%, r espectively. The internal circulation was 95% of non-marine net throughfall fro K+ and 76% for Ca2+. The dry deposition of SO2 to the canopies regulat es the internal circulation of Ca2+. The dry deposition of SO2 to the canop ies regulates the internal circulation of Ca2+. The estimated dry depositio ns of ammonium and nitrate are close to the net throughfall of Kjeldahl-N a nd nitrate, respectively. The obtained deposition velocities are comparable to other studies. The calculated dry deposition of ammonium was compared t o the net throughfall of ammonium at three nearby forest stands receiving d ifferent ammonium amounts on the soils. No correlation to nitrogen level wa s found, but most ammonium was lost and converted to organic nitrogen in th e canopies of the wettest forest stand. (C) 1999 Elsevier Science Ltd. All rights reserved.