Efficiency of Phragmites australis under different times of wastewater irrigation in the soil–plant–water system

This study investigates the impact of wastewater irrigation on soil–plant–water system at the vegetative, flowering, and reproductive stages of Phragmites australis for two and four days (in each stage) in the coastal saline area of Urmia Lake. The concentrations of potentially toxic elements were detected in irrigated water, soil, and plant (aboveground and belowground) tissues, and transfer factor and bioaccumulation factor were calculated. The shoot biomass was significantly increased with increasing wastewater exposure, up to four days after the flowering stage. All potentially toxic elements concentrations in belowground (roots and rhizomes) tissues were higher than aboveground (leaves and stems) tissues. Fe showed the maximum concentrations in all organs at different growth stages due to the higher level contents in soil and water. Fe was found to be the least mobile at the reproductive stage and presented in the following order: roots > rhizomes > leaves ≥ stems. By contrast, Zn and Cd metals which are quickly transported in plants exhibited the same trend. Pb was accumulated at the flowering stage as follows: rhizomes > roots > stems > leaves. The toxic threshold was exceeded by Zn, Fe, Cu, and Cd in roots; Fe in rhizomes, and leaves; Cd in rhizomes; and Ni in roots. There was more efficiency in the removal of chemical oxygen demand (61.09%), biochemical oxygen demand (73%), total suspended solids (50%), and ammoniacal nitrogen (59.5%) at the reproductive stage. Therefore, P. australis could be an efficient and valuable tool for the phytoextraction and phytostabilization of metals if harvested at the proper time of growth in high potentially toxic elements polluted coastal ecosystems.