Research On Screening Of Plant Species And The Effect Of Plant Community Modal For Ecological Remediation In A Lead-zinc Polluted Area

This study was conducted to investigate the pollution status of lead-zinc mining waste contaminated soil in Zixing lead-zinc mine region and the characteristics of native plant species regarding their abilities in accumulation and tolerance of heavy metals. Samples were also collected from the lead-zinc tailing ecological restoration project site to analyze the remediation effect of the designed plant community models and to monitor the treatment effect of the established ecological interception and purification system for control of soil erosion and heavy metal diffusion. The main results are summarized below:(1) The soil in the Pb-Zn tailing area is poor in nutrients and heavily contaminated by Pb, Zn, Cu as well as other heavy metals. The key task to improve the environment of the tailing waste polluted area is to restore the vegetation and landscape, reduce the soil heavy metal contents and control metal diffusion to nearby water environment.(2) In the present study, plant heavy metal concentration (C), quantity transfer coefficient (TQ) and accumulation (U) are used as basic indexes for identifying the natures of tolerance and accumulation capacity of plants to be used as phytoremediation species. The idea to use the three indexes is that C reflects the tolerance of plants to resist heavy metal toxicity; TQ reflects the ability of plants to transfer heavy metals from underground to upground while U reflects the capacity of plants to accumulate heavy metals. Based on the indexes, a phytoremediation plant assessment system is established. The significance of the assessment system is that it provides not only a theoretical ground but also a practical measure for screening of phytoremediation plant species for amending heavy metal polluted areas and evaluation of their ecological restoration function and efficiency.(3) The nature of native plant species were analyzed using plant heavy metal concentration (C), quantity transfer coefficient (TQ) and accumulation quantity (U) as three basic indexes. Pioneer native plants adapted to the polluted environment were screened including spring species Ixeris denticulate, Leonurus artemisia, Perilla frutescens, Erigeron annuu, Daucus carota, Solanumcarolinense, Boehmeria nivea, Miscanthus sinensis and Equisetum ramosissimum; Summer species womb doix miev, Leonurus artemisia, Rubus corchorifolius, Artemisia anomala S.Moore, Chrysanthemum indicum, Conyza canadensis, Setairaviridis and Equisetum ramosissimum; Autumn species Polygonum orientale, Erigeron annuus, Vicia multicaulis Ledeb, Humulus japonicus, Setairaviridis and Miscanthus sinensis; and winter species Ageratum conyzoides, Conyzabonariensis, Herba Bidentis Pilosa, Artemisia princeps Pomp, Miscanthus floridulus, Phragmitesaustralis, Miscanthus, Equisetum ramosissimum and Setairaviridis.(4) Five ecological-economic plant community models (I:Timber+native species; Ⅱ:Timber+landscape species;Ⅲ:Timber+energy species; IV:Precious timber+ ornamental plants; V:Industrial raw material+timber+landscape species) were established in the lead-zinc tailing ecological restoration project site. Results obtained from the sample analysis showed that models IV and V appeared to be high efficient models characterized as high plant growth rates, large biomass production, high coverage percentage, large numbers of companion plant species, high stability in community composition, high amount of heavy metal accumulation, and high economic value of plant resource. The conducted engineering practice proves that the eco-economic plant community models and the eco-interception and purification system are effective in ecological restoration and control of the effect of soil erosion and heavy metal diffusion on regional water environment.(5) Analytical data further showed that the established ecological interception system using constructed wetland technology along the boundary between the lead-zinc tailing site and the adjacent rivulet was effective in control of soil erosion and heavy metal diffusion. All monitored water quality index of the effluent from the treatment system met Standard II of the "Surface Water Environment Quality Standard" (GB3838-2002).