HEAVY-METAL ACCUMULATION BY OLD-FIELD PLANT-SPECIES DURING RECOVERY OF SLUDGE-TREATED ECOSYSTEMS

Concentrations of heavy metals in old-field plant species were compare d among untreated reference subplots, unlimed sludge-treated subplots and limed sludge-treated subplots during the 4th yr of ecosystem recov ery following long-term (11-yr) nutrient enrichment. Althougth results varied on a metal-specific and species-specific basis, liming was ove rall successful in reducing metal concentrations in old-field plant sp ecies. For example, concentrations of Cd in leaves and roots and conce ntrations of Fb and Zn in roots of Ambrosia trifida were significantly lower in plants collected from limed compared to unlimed sludge-treat ed subplots. Liming significantly reduced concentrations of Cd in leav es and roots of Solidago canadensis, and in the leaves, roots, and see ds of Setaria faberii to levels found in untreated reference subplots. Liming also significantly reduced concentrations of Cu in the roots o f Solidago canadensis, Pb in the roots and seeds of Setaria faberii, a nd Zn in the roots and leaves of S. faberii to reference levels. Chang es in plant species composition during secondary succession may also i ndirectly reduce metal uptake since the annual Ambrosia trifida accumu lated Cd and Zn in leaves, roots and seeds at levels two to thr ee tim es greater than did the perennial Solidago canadensis.