Soil Quality Evaluation And Phytoremediation Design For Tailing Pond Area Of Lead And Zinc Mine In Tang Jia Town,Han Yuan County

The research object of this paper is the lead-zinc tailing reservoir area in Tangjia town,Hanyuan county.First of all,through the way of field investigation,sampling collected plant samples of soil and natural settled in the study area,analyzed the research in the natural settlement of the existing situation of plant community,and not in the same way is analyzed through the indoor experiment to determine the soil physical and chemical properties,heavy metal content distribution characteristics and the uptake of metals by plants,soil pollution to delimit the partition and screening plant species,on the basis of the study area for phytoremediation design,hope to improve the seriousness of the pollution in the study area,and for the purpose of the tailings of phytoremediation is designed to provide basic data and research data.The research contents are as follows:(1)There are relatively few natural resident plant species in the study area,of plant a total of 24,37 genera,40 species,annual herb 9,7 kinds of perennial herbaceous plants,shrubs 10,5 trees,ferns,5 kinds,1 kind of vines,shrubs or deciduous trees,3 species are mainly composed of compositae and leguminosae plants,leguminous plants accounted for 15.4% of total species,compositae accounted for 12.8% of total species.With the increasing years of ladder formation in the study area,the change index of dominance of settled species is increasing,the morphological distribution of settled plants is not uniform,and the morphological species of settled plants is also increasing.In the diversity index,the richness index(Ma),the dominance index(D)and the diversity index(H)all increased with the increase of recovery time.With the progress of stage succession,vegetation was gradually formed in a diversified and stable direction.(2)The overall soil pollution in the study area was extremely serious.The average contents of Pb,Zn,Cd and As were 110.64 times,24.95 times,209.24 times and 16.34 times higher than the soil background value in Sichuan province,and the surrounding soil contents were 65.93 times,8.26 times,103.04 times and 5.38 times higher than the soil background value in Sichuan province.Four kinds of heavy metals on the space distribution of present east and northeast within maximum,regional and local small area appeared peak,local not unified,irregular distribution,the characteristics of the four kinds of heavy metals on the overall spatial distribution with the loss of the ladder,content was lower,and diminishing roughly from northeast to southwest,top-down,the characteristics of diminishing from right to left.Considering the spatial distribution characteristics of heavy metals in the soil and the soil pollution evaluation results,the relative pollution zones of the soil pollution in the region were made,with A heavy pollution zone,B medium pollution zone and C light pollution zone.(3)In the rhizosphere soil of the plants in the study area,Cd was the most seriously polluted,followed by Pb,and then Zn.The average values of Pb,Zn,Cd and As were 3079.2876 mg/kg,1899.9224 mg/kg,14.9823 mg/kg and 156.8363 mg/kg,The highest content of heavy metal in plants was Zn,with an average value of 392.08 mg/kg,and the range of variation ranged from 13.83 to 2479.33 mg/kg.The second is Pb,with an average value of 99.50 mg/kg,with a range of 4.38?671.23 mg/kg.Followed by As and Cd.The highest content of heavy metal in the plants near the tailings pond is also Zn,with an average value of 246.99mg/kg,with a range of 58.42?1118.91 mg/kg.The second is Pb,with an average value of about 86.57 mg/kg,with a range of about 1.18?542.81 mg/kg.Followed by As and Cd.(4)The plants in the study area have strong heavy metal transport capacity and poor enrichment capacity,and have good tolerance to Pb and Zn,and the absorption of Zn is stronger than that of Pb.The average contents of Pb and Zn in the plants in this tailings mining area were 2.08?2.38 times and 1.54?2.45 times higher than the normal heavy metal content of plants,but they did not meet the standards of super-enriched plants(1000 mg/kg).Plant absorption of Cd and As is not obvious,only a few plants than the plant normal absorption of heavy metals.Based on the analysis of plant enrichment and transport capacity,the author selected Eriophorum comosum,Phragmites australis(Cav.)Trin,Incarvillea arguta,Pteris cretica L.var.nervosa(Thunb.)Ching et S.H.Wu and Nephrolepis auriculata(L.)Trimen as the pioneer plant group to improve the community structure and soil physical and chemical properties of the tailings pond.Leptodermis Pilosa Diels,Lespedeza bicolor Turcz and Coriaria nepalensis Wall are relatively enriched plants in the tailings pond,and serve as the local key restoration plant group.Campylotropis macrocarpa,Itea yunnanensis Franch and Vitex negundo L.var.cannabifolia can improve the community structure of tailing pond vegetation as a supplementary group of transitional phytoremediation community.(5)Design partition,mainly based on the soil,the soil heavy metal pollution degree partition space distribution rule and 10 parallel slant ladder terrain,combined with the front three factors in the design of the original three soil pollution area A,B,C,divided into A,B,C three design partition,A zone includes two steps,1,2 B area contains 3,4,5,6,17,five ladder,area C contains three steps 8,9,10.The two steps in zone a are close to the pollution source,no plants exist,and the ecological environment is bad.Due to the selection of local natural settlement plants in this design,there is no suitable plant for the design,waiting for the next step of research on introduction and domestication of the corresponding heavy metal super-enrichment plants and the improvement of soil quality to be suitable for plant growth.Since the 10 th step is close to the pollution source and at the top of the feasible design area,the pollution level is high,so the remediation plant design of the 10 th step is completed and applied to each step of the b and c design zones,the maximum effect of existing natural settlement plant restoration can be achieved.(6)In combination with the plants' ability to deal with heavy metals and the construction of plant community structure,the phytoremediation design takes the plants in the key restoration group as a group,plants are planted at a horizontal interval of 6m,and the first row is planted along the top of the horizontal ladder.The complementary group of transitional restoration plant community constructed a group with a horizontal interval of 6m and a vertical interval of 6m,interplanting the fourth row with the first row.Pioneer group as a community,the vertical interval of 4m,crisscross planting three rows of the horizontal interval of 2m,supplement group according to the effect of each group of each row of each step to supplement,the purpose is to build a suitable plant community,community structure configuration mainly adopts "arbor + shrub + herb",the combination of high and low is tie-in,various plants mixed design patterns.On this basis,the vegetation design should conform to the site conditions of the mining area and the natural succession law of the vegetation,and make the ecological environment of the mining area develop steadily towards a better direction.