Seasonal changes of metals in willow (Salix sp.) stands for phytoremediation on dredged sediment

Fast growing biomass plants such as Salix species are promising for use in phytoremediation of contaminated land. This study assessed the seasonal variations and changes with stand age in metal concentrations of S. fragilis L. and S. triandra L. grown in field conditions on contaminated dredged sediment substrates with comparable properties. A lesser proportion of total soil Cd was extractable by ammonium-acetate in the 6-year-old stand (6%) compared to the 1-year-old stand (17%). This suggests that the potential to remove metals from the site declines with tree age. Metal concentrations in willow biomass compartments decreased with stand age. Concentrations of Cd and Zn in leaves, wood, and bark increased toward the end of the growing season, irrespective of the species. Only Cd behavior offered limited prospects for targeting effective removal of the metal from the sediment through repeated harvest. The most efficient removal of Cd would require the combined harvest of stems and leaves; at the same time the risk of spreading Cd and Zn to the surroundings with leaf fall would be avoided.