Heavy metal accumulation by old-field plant species during recovery of sludge-treated ecosystems

Concentrations of heavy metals in old-field plant species were compared among untreated reference subplots, unlimed sludge-treated subplots and limed sludge-treated subplots during the 4th yr of ecosystem recovery following long-term (11-yr) nutrient enrichment. Although results varied on a metal-specific and species-specific basis, liming was overall successful in reducing metal concentrations in old-field plant species. For example, concentrations of Cd in leaves and roots and concentrations of Pb and Zn in roots of Ambrosia trifida were significantly lower in plants collected from limed compared to unlimed sludge-treated subplots. Liming significantly reduced concentrations of Cd in leaves and roots of Solidago canadensis, and in the leaves, roots, and seeds of Setaria faberii to levels found in untreated reference subplots. Liming also significantly reduced concentrations of Cu in the roots of Solidago canadensis, Pb in the roots and seeds of Setaria faberii, and Zn in the roots and leaves of S. faberii to reference levels. Changes in plant species composition during secondary succession may also indirectly reduce metal uptake since the annual Ambrosia trifida accumulated Cd and Zn in leaves, roots and seeds at levels two to three times greater than did the perennial Solidago canadensis.