| Exploitation of mineral resources can lead to many ecological and environmental consequences. Ecological restoration of mined lands is of great significance to both improvement of eco-environmental quality and regional sustainable economic development. Establishment of vegetation is one of the critical steps in achiving the goal of ecosystem restoration on mined lands. In recent years, restoration of vegetation on mined lands has progressed rapidly in China, but generally lacks long-term and systematic studies on the operating mechanisms; especially the well-established case studies and information are lacking on the vegetation dynamics following restoration practices. At the Shouyun Iron Ore Mine in suburb of Beijing, this dissertation investigated selective traits of vegetation, soil, and ecological stoichiometry on a tailings dam many years after treatments with three different methods. The objectives were to determine the effectiveness of vegetation establishment on sites with different treatments and to provide a case study for treatment of mined lands. Major results are as follows:(1) The site treated by combination of soil covering and application of vegetation carpet (designated as SC+VC) had significantly higher species richness and greater values of Shannon-Wiener index than the sites treated by either soil covering (designated as SC) alone or application of ecological vegetation carpet (designated as VC) alone. The VC site had a comparable plant abundance with the SC+VC site; whereas the SC site outperformed the VC and SC+VC sites in species evenness. Above-and belowground biomass and litter mass on the SC+VC site were higher than on the other two sites. The VC site did not differ with the SC site in the vegetational traits, albeit low soil fertility. It is suggested that application of vegetation carpet can be an alternative to introduction of topsoil for treatment of tailings dam with fine-structured substrate of ore sands. However, combination of topsoil treatment and application of vegetation carpet greatly increases vegetation coverage and plant biodiversity, and is therefore a much better approach for assisting vegetation establishment on the tailings dam of strip-mining operations.(2) The vegetation on the tailings dam sites treated during1997-2011was compared with undisturbed vegetation around the mining operation area. Species in the Poaceae, Legume and Compositae dominated the plant communities across all treatment sites, accounting for58%of total number of plant species. The plant abundance was greatest after one year of site treatment, and species richness was greatest after two years of site treatments, respectively. The value of Shannon-wiener index decreased with time after treatments on the tailings dam, but was not significantly different from the undisturbed vegetation nearby. Value pf Pielou index increased with site after site treatments until reaching maximu in the8th year after site treatments. The aboveground biomass decreased initially and then increased following site treatments. The belowground biomass consistently decreased with time following site treatments. Ground-surface litter mass increased with time following site treatments until reaching maximum and comparable level as the undisturbed sites surrounding in the6th year. These results indicate that the SC+VC treatment is most effective for facilitating vegetation establishment on tailings dam, resulting in rapid development of biodiversity and plant productivity comparable to the nearby undisturbed vegetation.(3) The seasonal variations of N and P in foliage and fine roots were studied in three dominant composites, including Artemisia scoparia Waldst. et Kit., A. annua L. and A. capillaries Thunb. The N and P concentrations of foliage and roots fluctuated seasonally in all the three composite plants. The foliar N and P concentrations increased in initial stage and then decreased until end of growth seasonl; whereas N and P concentrations in fine roots displayed opposite trend as of foliar N and P concentrations. Seasonal variations in foliar N:P ratio also contradicted that of foliar N and P concentrations, i.e. initial decrease followed by a trend of increase after the peak growth. Variations of N:P ratio in fine roots followed the trend of foliar N:P ratio except during the initial stage. Foliar N and P concentrations were significantly and positively related; whereas foliar P concentration and foliar N:P ratio were negatively related.(4) At community level, N and P concentrations in foliage and fine roots fluctuated across sites differing in the years of site treatments. The foliar N concentration decreased and then increased whereas P concentration increased and then decreased with years of site treatments. Foliar C:N ratio, C:P ratio and N:P ratio all increased with duration of restoration. Fine root N:P ratio varied greatly during the first four years after site treatmemt and then remained relatively steady thereafter. |
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