Abstract
Rigorous studies of recovery from soil acidification 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 at different soil depths) and foliar chemistry from three decades ago. It was hypothesized that declining acidic deposition is reflected in soil and foliar chemistry. Top soil pH within the stemflow area increased significantly by 0.6 units in both H2O and KCl extracts from 1984 to 2012. Exchangeable Ca and Mg increased markedly in the stemflow area and to a lower extent in the top soil of the between trees area. Trends of declining base cations in the lower top soil were probably caused by mobilization of organic S and associated leaching with high amounts of sulfate. Contents of C, N and S decreased markedly in the stemflow area from 1984 to 2012, suggesting that mineralization rates of organic matter increased due to more favorable soil conditions. It is concluded that the top soil will continue to recover from acidic deposition. However, in the between trees areas and especially in deeper soil horizons recovery may be highly delayed. The beech trees of the Vienna Woods showed no sign of recovery from acidification although S deposition levels decreased. Release of historic S even increased foliar S contents. Base cation levels in the foliage declined but are still adequate for beech trees. Increasing N/nutrient ratios over time were considered not the result of marginally higher N foliar contents in 2012 but of diminishing nutrient uptake due to the decrease in ion concentration in soil solution. The mean foliar N/P ratio already increased to the alarming value of 31. Further nutritional imbalances will predispose trees to vitality loss.
Highlights
Reversibility of acidification is an extremely important topic, for both political and scientific reasons
The beech trees of the Vienna Woods showed no sign of recovery from acidification S deposition levels decreased
Large decreases in acidic deposition may enable soils to restore pools of exchangeable bases reduced during the period of high leaching rates
Summary
Reversibility of acidification is an extremely important topic, for both political and scientific reasons. The topic is politically important because billions have been invested in cleaning up the emissions that cause Acid Rain, so it is worthwhile to know how much improvement has been achieved. Acidification research has moved down the agenda, the topic is scientifically important because acid precursor emissions, and their subsequent removal, represent a profound large-scale perturbation to biogeochemical cycles (Likens et al, 1996). Revisiting the Acid Rain topic is worthy, since in many regions mass balance estimates of S are negative due to release of previously stored S, delaying the recovery of pH of soils and surface waters, depending on soil properties (e.g., see review by Watmough et al, 2005; references therein; Likens et al, 2002, 2013)
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