| Mining is the most profound human activities impacted on the natural ecological system now. There are large of lands been wasted by the mining. In these mining wasted land, ecological risks and environmental stresses are very prominent while the structure of ecosystem dissolved and the function degenerated. Land reclamation and ecosystem restoration of the wasteland educed by the mining have become an important and interest issue because the wasteland not only occupied the vast tillable lands but also caused serious environment pollution. After nearly a century of research and technology applications, the proportion of mining land reclamation has reached an average of55%to65%; meanwhile, it has reached85%in the United States, Britain, Australia and other mining giants. According to the ministry of land and resources statistics, the proportion of the mining area land reclamation in China has increased from2%in1988to around15%in2012. But now the mine land increases at an annual rate of33000to47000hm2for the mine reclamation speed far behind the damage in China. At a conservative estimate, there are1500mining areas have occupied or damaged land of2million hm2.The object of this study was the wasteland educed for more than40years in Xiangtan manganese mine which had mined for100years. The basic technical measures had determined for the mining area ecological restoration based on the forest ecology, landscape ecology and restoration ecology. Two native tree species was selected by pot experiment after analyzing the soil physical and chemical properties, the characteristics of settle existing plants, which photosynthetic characteristics had been analyzed. The forest conditions, soil characteristics and mineral biological cycle of the demonstration forest base in the mining wasteland had been analyzed. The result showed that:1. The soil texture of the wasteland is mainly coarse sandy or silt. The proportion of physical sand (1-0.01mm) in the soil is over85%, and physical clay (<0.01mm) is below15%. The total soil fertility index is lower in the wasteland than in the Chinese fir forestland. It is found that the main factors limiting soil fertility in the wasteland were percentage of sandy grain(1～0.01mm), soil organic matter content, soil concentrations of N and P. The groundwater in mining area is polluted seriously which high levels of in heavy metal and NH4+, NO3-, PO4-3, SiO2, addition to the pH value and dissolved oxygen is lower than the contrast. The concentration of Mn(52924.0mg/kg), Zn(396.70mg/kg), Cu(42.30mg/kg), Fe(29782.0mg/kg), Pb(354.10mg/kg), Cd(4.37mg/kg) and Ni(40.30mg/kg) in the wasteland are179,7,3,6,2,3,3and71times of those in the Hu’nan province land, respectively. In comparison with the mean values of soil heavy metal elements recorded in the control site, Hu’nan province and national level, the syntheses pollution indexes of the six6heavy metal elements(Mn, Cu, Pb, Zn, Cd and Ni) in the wasteland are13.82,75.72and98.05, respectively, which all exceeded the heave pollution standard. The potential ecological risk index of Mn, and Cd are2419.75and373.83respectively that indicate the environmental risk are at the highest level, as so as the heavy metal potential ecological comprehensive risk. On the individual element basis, the elements on Mn and Cd exceeded heave pollution standard. It is indicated that mining of Manganese result in serious environment pollution and tillable land degradation.2. There are53species settled in the mining area after40years of natural succession. They are belonging to28families with herbs36species,17kinds of trees and shrubs. It is indicated that the current local communities are dominated by perennial shrub and grass, which are at the primary stage of succession towards subtropical evergreen broadleaved forest. It is a must that ecological restoration needs to give preference to these native tree species which have certain resistance, fast growth, and high economic value and ecological benefits, through the analysis of the characteristics of settle existing plants. The plotted plant test results show that Koelreuteria paniculata Laxm is the preferred plant for the ecological restoration in the slag wasteland, which grows and adapts strongly in the slag wasteland.3. By using the slag wasteland soil in Xiangtan Manganese Mine, five different mixed soil treatments by which potted plant tests are conducted, five treatments are as follows:CK:100%untreated soil; W1:25%slag wasteland soil+75%untreated soil; W2:50%slag wasteland soil+50%untreated soil; W3:75%slag wasteland soil+25%untreated soil; W4:100%slag wasteland soil. Survival rate and height growth rate of Koelreuteria paniculata Laxm are lower than those of Elaeocarpus decipens. height growth rate of Koelreuteria paniculata Laxm each treatment (exceptW3) is higher than that in fall; the average diameter growth in order is W3>W4>CK>W2> W1,W1and W2are less than the contrast, while W3and W4are larger than the contrast. It means that low concentration inhibits diameter growth, while high concentration promotes it. Elaeocarpus decipens grow fast and well, height growth rate in summer is far higher than that in autumn. The average diameter growth in order is CK> W2> W1> W3> W4, all are lower than the contrast, heavy metal treatments in the soil inhibits diameter growth, and with the increase in the concentration of heavy metal, the inhibitory effect gets more obvious.4. Focused on net photo synthetic rate (Pn) of the two species in Summer and Autumn, the results showed that the average net photosynthetic rate (Pn) of both two species in summer are higher than in fall, and the relationship among all treatments (W1、W2、W3、W4) of the average net photosynthetic rate (Pn) has changed in autumn. For Koelreuteria paniculata Laxm, the average value of (Pn) of W3is the largest, W1is the minimum, While in autumn, the average value of (Pn) of W2is the largest, W3is the minimum. For Elaeocarpus decipens, the average value of (Pn) of W2is the maximum, while W4is the minimum in Summer; the average value of (Pn) of W1is the largest,while W4is the minimum in Autumn.5. For Koelreuteria paniculata Laxm Relevances among Pn and heavy metals Mn、Cu、Zn、Pb、Ni、Co、Cd contents in soil all fail to meet the significant level, while Relevances among Pn and Pb、Cd contents in soil reach negative significant level of Elaeocarpus decipens. Relevances among Pn and N、Chlorophyll content in leaves reach significant negative level,while Pn among Zn and Mn contents in leaves of Koelreuteria paniculata Laxm reach positive significant level; For Elaeocarpus decipens, among Pn and N、P、K、Mg、Ca、Fe、Mn、Zn and Chlorophyll in leaves all fail to meet the significant level.6. In the selection of0.67ha demonstration base in the mining wasteland, there are planted by1440Koelreuteria paniculata Laxm and720Elaeocarpus decipens while press2line Koelreuteria paniculata Laxm,1line Elaeocarpus decipens for the ecological restoration experiment. The stand biomass increased by1192.48kg/hm2in a year. Under the extreme habitat condition of mufu, Koelreuteria paniculata Laxm and Elaeocarpus decipens have preliminarily showed strong adaptability, high patience, and great production potential. It is indicated the mixed forest is appropriate, that can be used as a restoration mean in mining area to improve ecological environment. Main heavy metals are accumulated in the branches, leaves (the accumulation of leaves alone accounts for70.7%), and roots, the accumulation of heavy metals (only4.45%) in the mainly used trunk is very lower. It is very outstanding to avoid heavy metal spread in the environment for using timber and conducive to forestry production in the ecological restoration area.7. Of stand growth environmental conditions, the mineral elements content of forest distribution and biological cycle characteristics are analyzed, and the results show that the forest has high utilization of elements, the return amount is much, cycle time is short. It is conducive to maintaining forest productivity. Five years after ecological restoration, soil organic matter, nutrient element content and moisture content are increases, with soil alkaline weakening. The organic matter in rhizosphere soil of Koelreuteria paniculata Laxm and Elaeocarpus decipens reach106.793g/kg and45.50g/kg, respectively. Those of non-rhizosphere soil in the stand reach37.875g/kg. They are more than18.86g/kg of controlled soil out of the stand. Contents of main polluting element as Mn, Ni, Cd, decline of70%or more, and those of Cu decreased40%. It is concluded that ecological restoration has obviously improved the soil chemical properties and decline heavy metal contents. In the restoration area, soil nutrient condition and ecological environment has improved, basically achieved the mining wasteland ecological restoration research and demonstration purposes. |
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