Purification Effects on β-HCH Removal and Bacterial Community Differences of Vertical-Flow Constructed Wetlands with Different Vegetation Plantations

This study aimed to investigate the removal of beta-hexachlorocyclohexane (beta-HCH) at realistic concentration levels (10 mu g/L) in different plant species in constructed wetlands (Acorus calamus, Canna indica, Thalia dealbata, and Pontederia cordata) and the structure of the rhizosphere microbial community response of each group during summer and winter. Results showed that all groups of constructed wetlands had very good decontamination efficiency against beta-HCH in water (90.86-98.17%). The species that most efficiently purified beta-HCH in water was A. calamus in summer (98.17%) and C. indica in winter (96.64%). Substrate sorption was found to be the major pathway for beta-HCH removal from water in the constructed wetlands. The ability of the wetland plants to absorb and purify beta-HCH was limited, and C. indica had the strongest absorptive capacity among the four plant species. The mean beta-HCH removal from the matrix of the planted plants increased by 5.8% compared with that of the control treatment (unplanted plants). The average beta-HCH content in the plant rhizosphere substrate was 4.15 mu g/kg lower than that in the non-rhizosphere substrate. High-throughput sequencing analysis revealed significant differences (P < 0.05) in the Chao1 and ACE indices of microbes in the substrate of four wetlands during summer and winter. At the genus level, the constructed wetlands with vegetation plantations showed higher microbial abundance than the constructed wetlands without vegetation plantations. In winter, the bacterial community structure of each constructed wetland was quite different, but no dominant flora in the bacterial community structure obviously changed. In summer, the bacterial community structure at the same stage was relatively small. The abundance of Actinobacteria and Sphingomonas remarkably increased over time in summer.