Separation of Gaseous and Particupate Dry Deposition of Sulfur at a Forest Edge in Denmark

Throughfall deposition of SO2−4 and Na+ to a spruce [Picea abies (L.) Karst.] forest edge in Denmark was measured during 1 yr. The deposition of both SO2−4 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 SO2−4-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.