Combined use of open-air and indoor fumigation systems to study effects of SO2 on leaching processes in Scots pine litter.
Both an open-air fumigation system and a laboratory-based system were used to expose decomposing Scots pine (Pinus sylvestris L.) needles to controlled concentrations of SO(2) (arithmetic mean </= 48 nl litre(-1)) during a period, in total, of 301 days. The experimental design involved reciprocal litter transplants from 'clean' to 'polluted' air and vice versa, using the two fumigation systems. The objectives were (1) to observe the effects of SO(2) on leachate and litter chemistry, (2) to assess whether pollution-induced changes are reversible in clean air, and (3) to test the suitability of small-scale fumigation chambers (litter microcosms) compared with open-air systems in soil studies. Through the formation of SO(4)(2-) ions, dry-deposited SO(2) exhibited a marked capacity to remove 'base' cations (Ca(2+), Mg(2+) and K(+)) from decomposing pine needles, and also to acidify litter leachates (as indicated by proton fluxes from the litter). When litter was transferred from polluted air (48 nl litre(-1) SO(2), in the open-air system) to either clean or polluted air in the laboratory, the effects of prior exposure to SO(2) on leachate composition were still evident even after 86 days: the role of base cation depletion within the litter, caused by SO(4)(2-)-induced leaching, is discussed. Data for SO(4)(2-) fluxes in leachates collected from the small-scale chambers indicated that dry deposition velocities for SO(2) were not anomalously high within this fumigation system. It is therefore concluded that microcosm studies can provide information complementary to the open-air fumigation approach in soils research.
Wookey
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PA
Institute of Environmental and Biological Sciences, Division of Biological Sciences, University of Lancaster, Bailrigg, Lancaster LA1 4YQ, UK.
Ineson
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P