Vervaeke P, Tack F M G, Lust N, Verloo M
Department of Applied Analytical and Physical Chemistry, Laboratory of Analytical Chemistry and Applied Ecochemistry, Ghent University, Coupure Links 653, 9000 Ghent, Belgium.
J Environ Qual. 2004 May-Jun;33(3):976-83. doi: 10.2134/jeq2004.0976.
Willow (Salix spp.) stands are often proposed as vegetation covers for the restoration and stabilization of contaminated and derelict land. Planting willows on dredged sediment disposal sites for biomass production can be an alternative to traditional capping techniques. However, with the introduction of willow stands on dredged sediment disposal sites, the possibility of increased contaminant availability in the root zone must be acknowledged as it can increase the risk of leaching. Two trials investigated the availability of Cd, Zn, Cu, and Pb in the root zones of willows grown on contaminated sediment. To assess the effects of willow root growth on metal extractability and mobility, bulk and rhizosphere sediment samples were extracted with deionized water, ammonium acetate at pH 7, and ammonium acetate-EDTA at pH 4.65. A rhizobox experiment was used to investigate the short-term effect of willow roots on metal availability in oxic and anoxic sediment. Longer-term effects were assessed in a field trial. The rhizobox trial showed that Cd, Zn, and Cu extractability in the rhizosphere increased while the opposite was observed for Pb. This was attributed to the increased willow-induced oxidation rate in the root zone as a result of aeration and evapotranspiration, which masked the direct chemical and biological influences of the willow roots. The field trial showed that Cu and Pb, but not Cd, were more available in the root zone after water and ammonium acetate (pH 7) extraction compared with the bulk sediment. Sediment in the root zone was better structured and aggregated and thus more permeable for downward water flows, causing leaching of a fraction of the metals and significantly lower total contents of Cd, Cu, and Pb. These findings indicate that a vegetation cover strategy to stabilize sediments can increase metal availability in the root zone and that potential metal losses to the environment should be considered.
柳树（柳属植物）林常被提议作为受污染废弃土地修复和稳定的植被覆盖物。在疏浚沉积物处置场种植柳树以生产生物质可作为传统覆盖技术的替代方法。然而，随着柳树林引入疏浚沉积物处置场，必须认识到根区污染物有效性增加的可能性，因为这会增加淋溶风险。两项试验研究了生长在受污染沉积物上的柳树根区镉、锌、铜和铅的有效性。为评估柳树根系生长对金属提取率和迁移率的影响，用去离子水、pH值为7的醋酸铵以及pH值为4.65的醋酸铵 - 乙二胺四乙酸对大量沉积物和根际沉积物样本进行提取。采用根箱试验研究柳树根对有氧和缺氧沉积物中金属有效性的短期影响。在田间试验中评估长期影响。根箱试验表明，根际中镉、锌和铜的提取率增加，而铅的情况则相反。这归因于通气和蒸散导致根区柳树诱导的氧化速率增加，这掩盖了柳树根的直接化学和生物影响。田间试验表明，与大量沉积物相比，水和醋酸铵（pH值为7）提取后，根区的铜和铅（而非镉）更易提取。根区的沉积物结构更好且团聚，因此对向下水流的渗透性更强，导致一部分金属淋溶，镉、铜和铅的总含量显著降低。这些发现表明，稳定沉积物的植被覆盖策略可增加根区金属的有效性，应考虑潜在的金属向环境中的流失。
