Deposition of Atmospheric Pollutants and its Impact on Forest Ecosystems of the Northern Tyrolean Limestone Alps

1996

S. 131-144

42 Lit. Ang.

Unselbständiges Werk

200052094

The present subproject of the interdisciplinary project "Achenkirch Altitude Profiles" focuses on the deposition of long-term effective atmospheric pollution and its impact on forest ecosystems of two spruce (mixed wood) stands (Picea abies) located at altitudes of 1400m and 1050m. The deposition input was monitored by bulk sampling of throughfall and the soil water was investigated by lysimetry. The results obtained during a two-years period (August 1992 to July 1994) indicate very little input by deposition of atmospheric pollutants. Deposition rates under the canopy were 9-12kg N ha hoch-1 year hoch-1 and 7-8kg S ha hoch-1 year hoch-1. Proton rates ranged from 0.1-0.3 kmol H hoch+ ha hoch-1 year hoch-1. No indication of a correlation between stress and altitude was observed along the given difference in elevation (350m). It is very unlikely that soil acidification is the cause of a decreased vitality, especially since the buffering capacities of the investigated soils are very high. The significance of the proton buffering and of the increased leaching of nutrients from the canopy is, however, evident by the fact that leaching reduces the stand's pool of elements needed for the formation of the foliage by approximately 22 to 78% (K, 72-78%; Mg, 36-40%; Ca, 22-24%). Renewed uptage of these elements requires a higher amount of energy and transfers the buffering effect to the ecotoxicologically highly sensitive area of the immediate rhizosphere. The highest mean annual nitrate concentrations of the soil solution amounts to only 2.8 mg l hoch-1 year hoch-1. This fact and N foliar analyses prove that nitrogen is the limiting element for stand growth. As the investigated spruce stands are not nitrogen-saturated, the nitrogen inputs measured serve to meet the N demand of the stands. Nitrate leaching therefore does not cause soil acidification or associated nutrient losses.