Flow rates of ions in waters percolating through a model ecosystem with forest trees

From 1983-88 the long-term effects of low level exposure with O(3), SO(2) and simulated acid rain on mineral cycling in model ecosystems with spruce, fir and beech seedlings were investigated. Systems consisting of open-top chambers built above lysimeters were protected against the intrusion of ambient rain and dust. As part of the investigations on mineral cycling the fluxes of elements with water input and output of the canopy and soil compartments are presented. During the 5 year duration of the experiment, pronounced effects on canopy deposition and cation leaching were observed. Most noticeable were throughfall enrichment with sulfate through dry deposition of SO(2) as influenced by duration of needlewetting and factors promoting SO(2) oxidation. Depending on sulfur deposition, leaching of calcium, magnesium, manganese, zinc and ammonium from canopies was elevated, in total leading to enhanced soil input of acid. After 15 months, the water percolating the soils in the lysimeters of these treatments was acidified, with elevated flowrates of sulfate, manganese, calcium and magnesium. The results on canopy/soil leaching are compared to those from old conifer stands in the field.