Abstract
Rigorous studies on long-term changes of heavy metal distribution in forest soils since the implementation of emission controls are rare. Hence, we resampled 97 old-growth beech stands in the Vienna Woods. This study exploits an extensive data set of soil (infiltration zone of stemflow and between trees area) and foliar chemistry from three decades ago. It was hypothesized that declining deposition of heavy metals is reflected in soil and foliar total contents of Pb, Cu, Zn, Ni, Mn and Fe. Mean soil contents of Pb in the stemflow area declined at the highest rate from 223 to 50 mg kg−1 within the last three decades. Soil contents of Pb and Ni decreased significantly both in the stemflow area and the between trees area down to 80–90 cm soil depth from 1984 to 2012. Top soil (0–5 cm) accumulation and simultaneous loss in the lower soil over time for the plant micro nutrients Cu and Zn are suggested to be caused by plant uptake from deep horizons. Reduced soil leaching, due to a mean soil pH (H2O) increase from 4.3 to 4.9, and increased plant cycling are put forward to explain the significant increase of total Mn contents in the infiltration zone of beech stemflow. Top soil Pb contents in the stemflow area presently exceed the critical value at which toxicity symptoms may occur at numerous sites. Mean foliar contents of all six studied heavy metals decreased within the last three decades, but plant supply with the micro nutrients Cu, Zn, Mn and Fe is still in the optimum range for beech trees. It is concluded that heavy metal pollution is not critical for the studied beech stands any longer.
Highlights
Anthropogenic emissions of air pollutants and subsequent deposition of heavy metals are known to cause negative effects on chemical and biological processes in soils
It is concluded that heavy metal pollution is not critical for the studied beech stands any longer
The most striking result of this study was the decrease of Pb in the stemflow area from 223 to 50 mg kg−1 from 1984 to 2012, a decrease by 78% (Fig. 3), which was basically expected in the light of reported temporal trends in vehicular and industrial emissions in Austria and cited results of other studies that compared present and past heavy metal contents in soils
Summary
Anthropogenic emissions of air pollutants and subsequent deposition of heavy metals are known to cause negative effects on chemical and biological processes in soils. In the northern hemisphere, large areas were polluted by various heavy metals via atmospheric deposition from industrial and traffic emission sources including power generation (Bergkvist et al, 1989; Steinnes and Friedland, 2006). Long-term acidification of terrestrial ecosystems caused a reduction of cation exchange capacity and increasing mobilization of heavy metals in soils with decreasing pH (Blake et al, 1999; McKenzie, 1980). Though atmospheric deposition of these heavy metals decreased in many regions, current releases via mobilization of this legacy may still represent a potential danger for forest ecosystems (Friedland, 1992)
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