LEAF-LITTER DECOMPOSITION AND SOIL MICROARTHROPODS AFFECTED BY SULFUR-DIOXIDE FALLOUT

A field experiment was set up in northeastern Italy to investigate the effects of sulphur dioxide fallout on leaf litter decomposition rates and soil microarthropods. The pollution fallout, which affected part of the Po River delta, originated from the activity of an oil-fired po wer plant located at Isola Camerini (Porto Tolle, Rovigo). Four sampli ng sites, exposed to different amounts of pollutant fallout, were sele cted along the river bank. Two sites, located 1.5 km from the power-pl ant stack, received minimum sulphur dioxide fallout and were used as c ontrols; two high-deposition sites were about 13 km away from the powe r-plant settlement. Soil cores were taken to compare sulphur concentra tions in the upper layers of the sampling site soil profiles. Litter b ags filled with plant material of various types, laid down over two co nsecutive sampling periods, were used to study leaf litter decompositi on and sulphur accumulation on plant tissues. Microarthropods were ext racted from the litter bags by means of a modified Tullgren apparatus. Soil chemical analysis showed the highest sulphur concentrations at t he high pollutant deposition sites along the plume path. Litter bag dr y weight loss over time was reduced by sulphur accumulation in plant t issues. Sulphur accumulation in litter bags gave an indirect measure o f the differential pollutant deposition over the land. High-deposition sampling sites showed a significant reduction in the total number of some decomposers. Collembola, in particular, appeared to be a robust b io-indicator of pollutant fallout. Conclusions were drawn about the po ssible detrimental effects of sulphur compounds on soil and leaf chemi stry, litter decomposition and microarthropod decomposer populations. (C) 1997 John Wiley & Sons, Ltd.