Chemical transportation of heavy metals in the constructed wetland impacted by acid drainage was investigated seasonally using a combination of the selective sequential extraction of the sediments with elemental analysis of the emergent vegetation in the wetland. Manganese was dissolved from sediments in the constructed wetland by the contact with acid drainage, and then precipitated again as ionexchangeable forms. It was expected that a part of Mn and Fe bound to oxides were flown out of the wetland as suspended particulate matters. It was observed that there is passive absorption of Mn in leaves of Phragmites austlaris in the upstream of the wetland. The transportation of Cu clearly showed the seasonal variation: there was the decomposition of organic substances with high molecular weights by soil microorganisms in summer. Therefore, Cu was complexed to the humic substances, and dramatically adosorbed onto the roots of Phragmites austlaris in down stream of the wetland. It was also observed that there is active absorption of Fe in roots and leaves of Phragmites austlaris. Most of the zinc was strongly bounded to the sediments, therefore, scarcely uptaken to the vegetation. It was also found that there were heavy metal distributions between plant organs.

No abstract

Heavy metal contents in representative emergent vegetations, Phragmites australia and Typha latifolia, were investigated from March 2002 to December 2003 in a constructed wetland in Kaminokuni, Hokkaido, Japan. Typha latifolia was more effective to Mn 2+ sorption than Phragmites australis. Manganese was accumulated in leaves in Typha latifolia, upto 14 mg/g-dry weight. Accumulation of Mn in leaves of Typha latifolia was likely the result of activated demand of Mn in photosynthesis during summer and autumn. In contrast, Fe, Zn and Cu distributions were markedly localized and mostly concentrated in root sections of both plants in all seasons. They increase in Fe, Zn and Cu contents in roots of vegetations may be a protection mechanism against excess uptake of unnecessary heavy metals in aerial parts of the plants.