SEPARATION OF GASEOUS AND PARTICULATE DRY DEPOSITION OF SULFUR AT A FOREST EDGE IN DENMARK

Throughfall deposition of SO42- and Na+ to a spruce [Picea abies (L.) Karst.] forest edge in Denmark was measured during 1 yr. The deposition of both SO42- and Na+ was highly elevated at the forest edge with Na+ showing the steepest gradient. Using Na+ as a model-substance for the deposition of particles and assuming that 6 to 24% of the SO42--deposition in throughfall inside the stand originated from particles, the relative contribution of particulate and gaseous S to the throughfall deposition at the forest edge could be estimated. The deposition of particulate S showed a strong dependence on the distance to the forest edge. Thus, particulate S contributed 25 to 100% of the net throughfall deposition under the front tree, whereas particulate S only contributed 6 to 24% inside the stand. The gaseous deposition showed a more moderate dependence on the forest edge and did not exceed the change in leaf area index.