Heavy metal accumulation in roots and substrates of different plants in constructed wetlands and their correlations with environmental factors

Abstract:

In order to study the effect of composite vertical subsurface flow constructed wetlands on the removal of heavy metals in pond aquaculture water, the correlation between different plant roots and their substrates near roots on heavy metal enrichment effect, different environmental factors and heavy metal enrichment rate were analyzed by measuring water quality index and heavy metal. The results showed that the removal efficiencies of Pb and Cu in constructed wetlands were 77.20% and 41.70%, respectively. Compared with other types of wetlands, the composite vertical subsurface flow constructed wetlands had some advantages for the removal of Pb and Cu; the As was released in wetland with an average release rate of 8.40%. The roots of Polygonum hydropiper and Thalia dealbata Fraser have enrichment effect on Cr, As, Pb and Cu, and the roots of Pontederia cordata L. have only enrichment of Cr and As. The substrates near the roots of Polygonum hydropiper, Pontederia cordata L., and Thalia dealbata Fraser have a good enrichment effect on chromium, and among them, the maximum rate of the concentration of Pontederia cordata L. to chromium is 0.987mg/(kg·d). The enrichment rate of Pb and Cu in Polygonum hydropiper root was negatively correlated with temperature and the enrichment rate of Cr and Cu was negatively correlated with pH; the enrichment rate of Cr and As in Pontederia cordata L. root was negatively correlated with temperature; the enrichment rate of Pb in Thalia dealbata Fraser root was negatively correlated with temperature and pH, the enrichment rate of Cu was negatively correlated with temperature. The results of this study provide a theoretical basis and reference for the application of composite vertical subsurface flow constructed wetlands and the selection of wetland plants from the perspective of heavy metal removal.