Remediation of heavy metal conta- minated forest soil in Finland using recycled organic matter and native woody plants

Introduction The Harjavalta area (Figure 1) is one of the areas most seriously polluted by heavy metals in Finland. Copper smelting first started in 1945, and nickel smelting in 1959. The smelted ore concentrates contain sulphur, trace metals and arsenic. Although emissions of SO2 and heavy metals from the smelters have been strongly reduced in recent years (Figure 2), the topsoil of neighbouring forested sites still contains 50 years‟ accumulation of a wide range of heavy metals (Derome & Lindroos 1998; Uhlig et al. 2001). Microbial activity and litter mineralization are strongly retarded (Fritze et al. 1996), the Scots pine trees (photo 1) are suffering from serious defoliation and growth retardation (Nieminen et al. 2000), and fine root mortality is high (Helmisaari et al. 1999). The understorey vegetation is almost completely degraded (Salemaa et al. 2004). This enhances the wind erosion of metal-contaminated particles, decreases the water-holding capacity of the soil and may facilitate the leaching of heavy metals (Derome & Nieminen 1998) into the groundwater. Even though viable seeds have been found in forests close to the smelter, high concentrations of heavy metals inhibit seedling rooting (Salemaa & Uotila 2001). Also the thick undecomposed litter layer (McEnroe & Helmisaari 1999), shortage of nutrients (Derome & Lindroos 1998) and extremely dry conditions make natural revegetation difficult.