Air pollution load of forest stands in Vojířov and the impact on soil and run-off water chemistry

Research plots in Vojířov were established in a spruce stand and in a mixed stand. They are situated south of Jindřichův Hradec, near the border with Austria, on the ridge sloping to the Třeboň basin, exposed to western winds. The soils (Haplic Podzols) have developed on deep overlaps of eolian sands, between boulders of mica granite. Since summer 1991, the chemistry of precipitation water and run-off water from the O-humus horizon has been studied. Bulk deposition has been measured in the open area by the hunter's cottage Dubovice, where the chemistry of water in a local spring has also been studied. During the investigation the deposition of air pollutants in throughfall water was higher in the spruce stand than under beech trees in the mixed stand. In 1996, an increased deposition of pollutants was observed due to long-term winter period and high precipitation. This load of the ecosystem influenced soil water chemistry, mainly the chemistry of water in the spring, expressed by decreased pH, increase in SO4-2, F-, Al, Mn, only slowly disappearing in the subsequent years. At the end of the nineties the emissions of H+ , S/ SO4-2, F-, N(NO3-+ NH4+) decreased more significantly under the spruce stand than under beech. On the contrary, pH of precipitation water decreased in the open area. Soil analyses, carried out in 1991 and 1999, confirmed certain improvement of bio-genous supply in the humus horizons and decrease in sorbed basic cations in the surface horizons of mineral soil, and increase in the supply in deeper horizons, but it still remains at a low level.