TRACE METAL UPTAKE AND ACID TOLERANCE OF PLANT SPECIES GROWING IN AN ACID MINE DRAINAGE SEEP

The Green Valley mine site is located northwest of Terre Haute, Indiana. Soil and plant samples were taken in May 2004 from 22 2’x 2’ plots across an acid mine-drainage seep. Plots were chosen to span the variation observed in plant communities, from low biodiversity and/or stunted growth to good growth. Soil pH ranged from less than 3 to slightly below neutral. Preliminary plant ICPMS data from an adjacent plot suggested that uptake of certain heavy metals was pH-dependent and could result in toxic levels of accumulation in plant tissues.

For this study, soil (n=43) and plant (n=92) samples were analyzed by ICPMS for concentration of trace elements. Phragmites grew well over a pH range from 2.4 to 4.8. In Phragmites high concentrations of Rb, Ni, and Cu were observed, especially at low pH. In Festuca pratense Ni and Mn concentrations were much higher in seeds than in plant tissues. Melilotus showed an increased uptake of Cs. Trace element uptake also varied between species within genera, even within the same plots. Concentrations of Se and Rb were higher and Cs was lower in one Solidago species than in another Solidago species. High plant concentrations of Rb and Cs may be explained by preferential uptake of these elements in place of K.

Given that different plants preferentially take up different trace elements and even species within genera differ, it is important to avoid extrapolating behavior across plant species. The trace element uptake of plants has important ramifications for agriculture and site remediation, as these elements are subject to food-chain amplification to possibly toxic levels due to the consumption of plants by livestock and wildlife.