Study On Forest Tree Species Selection And Soil Improvement Effect In Antimony Mine Restrict In Lengshuijiang City

With the rapid growth of global population and economic development, combined with the great increase of industrial standards, people get better and better life condition day by day. But the conflict between people and land has become a core problem during the whole sustainable development process for the increasingly deteriorating environment. Abandoned mining lands have made a great land waste and caused serious pollution problems, which has critically restricted the regional social-and-economic-development. As other heavy metals, we can not ignore the great impact on people's health from Sb.We arranged 3 trials, which were the study on heavy metal content, the selection of resistant plant materials in Antimony Mine Restrict, and influence of soil conditioners and lime on heavy metal forms and biological effectiveness of soil in Antimony Mine Restrict. We chose the representative sites in Antimony Mine Restrict in Lengshuijiang City to carry on trials. We studied on basic characteristics of physical and chemical properties of soil, fertility status, pollution condition, PH value, etc. Using variety of trees and plants as materials, we carried on trials to know the enrichment characteristics of Sb, As, Cd, Hg, Pb, Cu, Zn and others and biomass. We also researched on the relationship between the adopting of soil improvement measures (with soil conditioners and lime) and indicators of survival rate and biomass of tree species. Combined with the analysis of 6 forms of Sb, Cd and Hg 5 forms of As after improved, and the exploration of the improvement effects and the reason of afforestation survival, we integrated all technologies into the optimization model of vegetation resoration in Antimony Mine Restrict and demonstrated it. We got results as follows:1. Soil of Antimony Mine Restrict in Lengshuijiang City was weak acidity. There was a relatively high soil bulk density in 3 sites of Lianmeng, Changlongjie and Qilipu, and the soil bulk density of effective soil ranged from 1.33 to 1.6, higher than that of forest. Comprehensive soil fertility of Lianmeng and Changlongjie were poor and that of Qilipu was general. Soils of 3 sites were all rich in soil organic matter and available K but extremely lack of available P. Qilipu soil was rich in Alkali-hydro N which was just lack in Lianmeng and Changlongjie. The Antimony Mine Restrict in Lengshuijiang City was in the condition of serious Sb, As, Cd and Hg pollution and mild Zn-Pb-combined pollution, which had become the constraint factors of low survival rate of tree species in the Antimony Mine Restrict.2. We selected several tree species with relatively higher survival rate in the Antimony Mine Restrict seriously polluted by heavy metals, which were Brossonetia papyrifera, Ailanthus altissima, Koelreuteria paniculata Laxm, CatalpabungeiC. A. Mey, Ligustrun lucidum Ait and Zenia insignis Chun, all with higher survival rate of above 90%. The annual average height increment of Brossonetia papyrifera, Ailanthus altissima and Zenia insignis Chun were larger than 0.7m, and that of CatalpabungeiC. A. Mey and Ligustrun lucidum Ait were higher than 0.5m. The canopy density of 4a Brossonetia papyrifera was 0.75, which suggested that vegetation in Antimony Mine Restrict could be restored in a short peiriod by planting Brossonetia papyrifera. In this area, tree species of Alnus cremastogyne, Liquidambar formosana, Pinus massoniana, slash pine and fir had the worst performance and the bad planting effect of Alnus cremastogyne and Pinus massoniana lasted two years, with a survival rate of lower than 15% and a poor restoration effect.3. The measurement data of different plant organs indicated that 8 plants of Brossonetia papyrifera, Koelreuteria paniculata Laxm, Ailanthus altissima, Zenia insignis Chun, Ligustrun lucidum Ait, Rohinia pesudoacacia L., CatalpabungeiC. A. Mey and Boehmeria nivea (Linn.)Gaud. were determined as heavy metals enrichment plants. General law of heavy metal enrichment was leaf>stem>root. Respectively, laws of heavy metal enrichment of leaf, stem and root of all 8 plants were as follows: Ligustrun lucidum Ait>Brossonetia papyrifera, CatalpabungeiC. A. Mey>Boehmeria nivea (Linn.)Gaud.> Ailanthus altissima, Koelreuteria paniculata Laxm> Zenia insignis Chun>Rohinia pesudoacacia L.; Ligustrun lucidum Ait>Boehmeria nivea (Linn.)Gaud>Brossonetia papyrifera>Ailanthus altissima, Rohinia pesudoacacia L. >Koelreuteria paniculata Laxm>Zenia insignis Chun>CatalpabungeiC. A. Mey; Boehmeria nivea (Linn.)Gaud.>Ligustrun lucidum Ait>Rohinia pesudoacacia L., CatalpabungeiC. A. Mey>Zenia insignis Chun>Brossonetia papyrifera>Ailanthus altissima>Koelreuteria paniculata Laxm. By comprehensive analysis, we finally chose Ligustrun lucidum Ait, Brossonetia papyrifera, Boehmeria nivea (Linn.)Gaud. and Ailanthus altissima as restoration materials in areas polluted by heavy metals of Sb, Pb, Cd, Hg and As. They could restore vegetation effectively. 4. After the application of soil conditioners (with main content of CaCO3 and phosphate rock, larger than 60% proportion, PH=12), plants of CatalpabungeiC. A. Mey, Koelreuteria paniculata Laxm, fir, Rohinia pesudoacacia L.and Zenia insignis Chun got high survival rate between 84.5% and 88%. Plants of Zenia insignis Chun, Rohinia pesudoacacia L., Koelreuteria paniculata Laxm and CatalpabungeiC. A. Mey got large height increment between 62.44cm and 155.33cm. Plants applied with 200g/tree got the optimum growth, with an average survival rate of 89.2% in all 8 plants.5. Soil conditioners and lime could improve the PH value in the Antimony Mine Restrict. Slightly acidic soil could benefit plant growth. Applying soil conditioners and lime reduced the toxicity of soil and the biological effectiveness of Sb, As, Cd and Hg and was conducive to plant growth. That is the mechanism of increasing the survival rate of plants after the application of soil conditioners and lime.6. We could plant Brossonetia papyrifera, Koelreuteria paniculata Laxm, Ailanthus altissima, Zenia insignis Chun, Ligustrun lucidum Ait, Rohinia pesudoacacia L., CatalpabungeiC A. Mey and Boehmeria nivea (Linn.)Gaud. with the application of 200g/tree soil conditioner and lime and use the dimensionally configurated mode of "tree+herb" in accordance with conventional afforestation and tending model to recover vegetation in mine area and complete the ecological reconstruction environmentally. Even without out-soil, the forest canopy density could be larger than 0.75 in 4-6 years.