GROWTH AND TRACE-METAL ABSORPTION BY PHRAGMITES-AUSTRALIS IN WETLANDS CONSTRUCTED FOR LANDFILL LEACHATE TREATMENT

Phragmites australis (common reed) grew well in the presence of high concentrations of NH4+-N (300 mg/l), BOD (300 mg/l), Fe (30 mg/l), Mn (1.5 mg/l) and K (500 mg/l). Other metals were not particularly elevated with the pH of the landfill leachate being 7-7.2. Reed standing crop continued to increase in the two years after leachate applications began, ranging to about 1100, 100, and 1000 g/m(2) dry wt. for shoots, roots and rhizomes, respectively. Nutrient elements like N, K, Ca, and Mg were absorbed to normally sufficient levels, while tissue P was low at 0.04%. Metals were not translocated to and accumulated by shoots or rhizomes, but exhibited elevated levels in roots. Fe, Cu, Zn, Pb, and Cd were at levels of 3700, 65, 45, 12 and 0.2 mg/kg respectively, but the roots acted as effective filters for transport of metals to the shoots and rhizomes. Only P and Zn accumulation by plants approached total amounts in leachate entering the constructed beds. SEM and X-ray microanalysis showed Fe accumulation on root surfaces, with Fe and other metals at lower concentrations inside the root tissue. The rhizosphere may provide a particularly effective, locally oxidized environment for metal precipitation and adsorption outside the root.