Study On Plant Adaptability And Environmental Benefit About Ecological Restoration Of Manganese Tailings

Abstract:Abandoned tailings are the most common metal mining wastelands, which are difficult to restore, containing large amounts of toxic and hazardous substances. Due to the poor physical structure, lacking of nutrients and high concentrations of heavy metals, plants are difficult to grow on abandoned tailings. The bare tailings usually affect the surrounding residents, pollute farmlands, and increase metal contents in groundwater and crops, as wind erosion and water erosion. Therefore, currently the environmental treatment and ecological restoration of abandoned tailings has become one of the most urgent task to realize the sustainable development strategies of mining industry.In this paper, based on systematically ecological investigation of Xiangtan Manganese tailing, research of the plant adaptability was carried out by analyzing the physical properties, nutrient status and metal element contents of tailing sand; Research center of the tailing was established, with the investigation of plant species using plot method; besides, surface runoff field and dust collection instrument were used to monitor surface runoff and dust emission, to assess the environmental benefits of ecological restoration of the tailing. Results are as follows:(1)The poor physical properties, which restrict plants’growth, are the main limiting factors to revegetate manganese tailings. The physical and chemical properties of tailing sand are significant different from normal soils, as the poor physical construction, low nutrient contents and high toxicity of metals, which may be the key limiting factors influencing the vegetation reconstruction and ecological restoration of the tailing.(2) The key of vegetaion reconstruction of manganese tailing is to improve micro environment of bare tailings, providing basic growth econditions for pioneer species. In the conditions of bare tailings, tolerant plants were hard to grow, whether using seed propagation or inoculating plant growth promotion bacteria. However, when the surface of the tailing was covered soils and the seed propagation of tolerant herb plants was used, plant growth was well, with vegetation coverage over98%. (3) After the ecological restoration of the manganese tailing, plant diversity was increased. The ecological restoration could accelerate pioneer species colonization, and increase species diversity; the index of species evenness of vegetation restored zone was the highest, while earth covered zone came second and bare tailing zones came last; Cynodon dactylon (Linn.) Pers. has the importance value of33.92%and44.88%in earth covered zone and vegetation restored zone respectively, which makes it the pioneer plant in tailing revegetation; under different recovery modes, plants in bare tailing zones showed the highest absorption capacity of heavy metals, while the earth covered zone came second and vegetation restored zone came last.(4) Cynodon dactylon (Linn.) Pers. is the most tolerant plant, and could be used as the pioneer plant of vegetation restoration. Despite its limited adsorption ability of heavy metals, it can improve the regional environment and promote the function restoration of degraded ecosystem in a short time.(5) Raising dust can be controlled effectively by vegetation reconstruction, resulting that94.64%of dust emission can be reduced, compared to the bare tailing zone. Volume of surface runoff in vegetation restored zone was far less than the earth covered zone and bare tailing zone, and meanwhile the soil covered zone had the maximum runoff. Suspended matter concentration of surface runoff and soil erosion amount per unit area of earth covered zone were higher than vegetation restored zone while lower than the bare tailing zone.By carrying the research of plant adaptability, analyzing the plant diversity, dust control, surface runoff control and heavy metal contents in surface runoff of different restoration modes, it is proved that ecological restoration in bare tailing can apparently control the relocation of heavy metals and reduce surface runoff and dust emission, while earth covering didn’t work effectively in controlling heavy metal pollution. Therefore, the study can provide scientific basis and practical reference for the engineering projects of closing tailings and ecological restoration of mining tailings.