Dispersal and mobility of heavy metals in relation to tree survival in an aerially contaminated woodland soil

Nearly a century of metal deposition adjacent to a metal refinery in Prescot, north-west England has led to highly elevated metal levels in soils at a dominantly Acer pseudoplatanus woodland, but with incongruously and perplexingly few detrimental effects on trees. Dispersal and speciation of Cu, Cd, Zn, Pb and Ni in soil was found to be extremely variable, but spatial patterns of metals were inter-related and also related to soil pH and soil organic matter. These soil variables were all generally higher in soil directly beneath trees than in soil between trees, and were particularly high beneath the spreading canopy of Aesculus hippocastanum. It is argued that this heterogeneous dispersal and availability of metals in soils may explain the survival of mature trees and the successful establishment of seedlings within the woodland. Differing speciation and mobility has allowed high disappearance rates of metals since recent closure of the refinery, which may result in soil recovery at a faster rate than previously thought.