Copper and nickel mobility in podzolic forest soils subjected to heavy metal and sulphur deposition in Western Finland

The distribution of copper and nickel down the soil profile has been investigated at 4 plots along a heavy metal and sulphur gradient extending for a distance of up to 8 km from a copper smelter in Western Finland. Emissions from the smelter have earlier been at a relatively high level, but were considerably reduced at the beginning of the 1990ʹs prior to the start of the experiment. Soil samples were taken in 1991, and soil water quality has been monitored using zero-tension lysimeters (5, 20 and 40 cm depth) during the growing season in 1992–1994. The organic layer and mineral soil on the plot nearest to the smelter contains considerable amounts of Cu and Ni. The Cu/Ni ratio in the organic layer was much higher than that in the underlying mineral soil, indicating that Cu is more strongly adsorbed in the organic layer than Ni. Copper concentrations in percolation water showed a peak at 20 cm depth, while for Ni the concentrations at 40 cm were higher than those at 5 cm. The lower Cu and Ni concentrations at 5 cm depth could be signs of a gradual detoxification of the surface, i.e. the gradual leaching of the mobile Cu and Ni components down to greater depths.