Leaching of metals from forest soils as influenced by tree species and management

Abstract

The leaching of metals (Na, K, Mg, Ca, Fe, Mn, Al, Cu, Zn, Cd, Pb, Cr and Ni) in a brown forest soil (Sjöbo) and a podzol (Horröd) with adjacent stands of spruce, beech and an open regeneration area in South Sweden were quantified using lysimeter techniques. The two localities differed in soil properties: glacifluvial sand deposit at Sjöbo; acid glacial till, poor in carbonates, at Horröd. Generally, the leaching of base cations was greatest from the brown forest soil, while the leaching of Al was greater from the podzol. Soil solution pH was lowest in the spruce forests, highest in the regeneration areas. The spruce increased soil acidification and leachability of metals most pronouncedly in the podzol. Soil acidification and leaching of metals were usually less under beech than under spruce. Soil solution metal concentrations were generally lowest in the regeneration areas, as was the outflow of metals. In an opening outside the spruce canopy at Horröd, soil acidification did not penetrate as deep as beneath the canopy; also the metal flux was considerably lower in the opening. In the spruce soil at Sjöbo and in all soils at Horröd, Al was the metal most clearly affected by variations in soil acidity. The solubility of Al increased suddenly within a small pH range (4.5-4.0) in the B horizon. Concentration of Al in soil solution increased from 2 to 10 mg l −1 when pH decreased from 4.4 to 4.2. In the brown forest soil at Sjöbo, particularly in the beech stand and in the regeneration area, the increase of base cation concentrations corresponded to the soil acidity in this pH range.