Heavy Metal Retention by Different Forest Species Used for Restoration of Post-Mining Landscapes, N. Greece

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Abstract
The main objective of this research was to study heavy metal absorption by the leaves of main forest species which were planted for that purpose at post-lignite mining landscapes in Northern Greece (Ptolemais, Prefecture of Kozani), as well as in a neighboring region (Kato Grammatiko), 30 km far from the mining area. Four species were studied; two conifers (Pinus nigra Arn., Cupressus arizonica Greene) and two broad-leaved (Robinia pseudoacacia L., Populus nigra L.). The four species varied in their leaf morphology (needles, scale-like leaves, blade, compound or simple, with rough or smooth surfaces). Eighty (80) leaf samples were collected, (10 from each tree species at either site). The heavy metal concentrations measured were iron (Fe), copper (Cu), chromium (Cr), nickel (Ni), cadmium (Cd), manganese (Mn), zinc (Zn) and cobalt (Co). Statistically significant differences (p = 0.01) were found between the lignite deposit and control areas and among the studied species. Higher concentrations were measured for the studied species at the lignite deposit. Moreover, no species demonstrated maximum absorption for all metals. The metal absorption pattern by coniferous trees’ leaves at the mining landscape was similar, with highest concentrations observed for iron and lowest for cobalt [iron (Fe) > zinc (Zn) > manganese (Mn) > copper (Cu) > chromium (Cr) > nickel (Ni) > cobalt (Co)]. Both broadleaved species absorbed highest concentrations of iron, but differed in the amount of the remaining metals [black locust: iron (Fe) > manganese (Mn) > zinc (Zn) > copper (Cu) > nickel (Ni) > chromium (Cr); black poplar: iron (Fe) > zinc (Zn) > manganese (Mn) > copper (Cu) > nickel (Ni) > chromium (Cr) > cobalt (Co)]. Cadmium was detected only in black poplar at both sites. In general, black pine was found to absorb the highest concentration of iron (Fe), and black poplar zinc (Zn). We discuss the importance of carefully selecting the appropriate mixture of tree species in order to achieve maximum habitat restoration effect at heavy metal polluted sites.