Formation of iron plaque in the roots of Spartina alterniflora and its effect on the immobilization of wastewater-borne pollutants

Iron plaque (IP) plays an important role in the absorption of heavy metals (HMs) and nutrients in wetland plants. The present study aims to investigate the effect of IP in Spartina alterniflora on the immobilization of wastewater borne HMs and nutrients. The physiological responses and effect of IP formation on the uptake of HMs, nitrogen (N), and phosphorus (P) were studied in S. alterniflora subjected to different synthetic wastewater (SW) levels and waterlogging durations. Results showed that IP formed in roots of S. alterniflora increased significantly with increasing SW concentration but decreased under prolonged waterlogging. Increasing the waterlogging time enhanced the alcohol dehydrogenase activity and the ethylene content in the roots of S. alterniflora. HMs including Cu, Pb, and Cr, did not significantly accumulate in the IP, despite that the IP content increased with the increasing of SW levels. The SEM–EDX analysis revealed that IP formed on the surface of S. alterniflora did absorb HMs such as Cu, Zn, and Cr. At a fixed level of SW, the amount of HMs that accumulated in the DCB extract was substantially proportional to the IP concentration in the root. Increasing of the SW level enhanced the accumulation of P in the leaves and roots of S. alterniflora. In conclusion, IP formed on S. alterniflora helped immobilize SW pollutants, including HMs and P, and the formation of IP and its effect on pollutant immobilization were influenced by the waterlogging conditions.