Sulfur inputs and outputs for two European beech forests growing on different soil substrates

Using a flux-balance approach, the S budget of two heavily polluted beech (Fagus sylvatica L.) forest ecosystems growing on acid and calcareous soil substrates was investigated. Total S deposition (dry and wet fall) at both sites was large (2.3 and 3.2 kequiv. ha(-1).year-1 at the calcareous and acidic beech forest sites, respectively). The contribution of dry deposition to the total S deposition in both stands was significant; dry deposition of S exceeded the deposition of S even in bulk precipitation. The atmospheric input of S exceeded, at both sites, the forest S requirements by 6-7 times. Consequently, at the acidic beech forest site, phytotoxins like A13, (2 kequiv. ha(-1).year(-1) were released with seepage water, neutralizing the acid input. At the calcareous beech forest site, leaching of huge amounts of Ca2+ (15 kequiv.ha(-1).year(-1)) and HCO3-(12 kequiv.ha(-1).year(-1) was significant enough to offset the effects of acid precipitation. About 20% of the atmospheric S input in both beech stands accumulated in the vegetation. The S input-output balance in the acidic beech forest indicated a slight tendency towards S accumulation in the soil in the form of AlOHSO4. The S budget in the calcareous beech forest stand was more or less balanced