Browsing by Author "Mahood, Kirsten"
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- ItemStrip mining rehabilitation by translocation in arid coastal Namaqualand, South Africa(Stellenbosch : Stellenbosch University, 2003-03) Mahood, Kirsten; Milton, S. J.; Halbich, T.; Stellenbosch University. Faculty of AgriSciences. Dept. of Conservation Ecology and Entomology.ENGLISH ABSTRACT: This study investigates the use of top-soiling, irrigation and translocating indigenous plants to facilitate the cost-effective return of a mined landscape to its former land-use (small stock farming) in an arid winter rainfall Succulent Karoo shrub land biome on the West Coast of South Africa. Effects of topsoil stockpiling and subsoil mineral concentration on soil fertility and chemistry were investigated, as soils are likely to determine rates of vegetation recovery on post-mined areas. Results of a radish bioassay show that stockpiling topsoil and mineral concentration subsoil decreased soil fertility. Mineral concentration decreased phosphorus, potassium, calcium, magnesium, carbon and nitrogen levels significantly relative to other soil treatments. Sodium in freshly deposited tailings was at potentially toxic levels and significantly higher than for all other soil treatments. Spreading of stockpiled topsoil over tailings may ameliorate harsh conditions created by mineral separation. Translocation of plants from pre-mined to post-mined areas was carried out on a trial basis in an effort to facilitate the return of natural vegetation and processes to strip-mined landscapes. Five local indigenous plant species: Asparagus spp., Ruschia versicolor, Othonna cylindrica, Lampranthus suavissimus and Zygophyllum morgsana were planted into multi-species clumps in a replicated experiment. Variables examined in the translocation trial included the effects of plant origin, soil treatment and/or irrigation on plant survival and establishment. The proportion of O. cylindrica transplants surviving for 15 months was greater than for other species. Whole plants survived better than salvaged plants, and Asparagus spp., R. versicolor, L. suavissimus and Z. morgsana survived better on stockpiled topsoil spread over tailings than on tailings alone. Irrigation had no consistent effect across species and treatment replicates. Salvaged-plant clumps were significantly larger than whole-plant clumps at planting, however, this effect was not observed after 12 months, indicating that whole-plant clumps grew faster than salvaged-plant clumps. The evergreen, leaf succulent shrubs O. cylindrica, L. suavissimus and R. versicolor appeared to be most suitable for large-scale translocation at Namakwa Sands. The return of biodiversity and changes in soil quality 15 months after translocation trials began were compared for combinations of top-soiling, irrigation, plant translocation and unmodified tailings. Irrigation may reduce biodiversity and seedling densities. Over a 15-month period following back filling and topsoil spreading, sodium, potassium and calcium appeared to return to levels observed for undisturbed soils. Magnesium remains at levels lower than in pre-mined soil conditions. Soil conditions may be more conducive to plant establishment and rehabilitation after back-filling of tailings and topsoil spreading. Electrical resistance increased over time indicating a reduction of free salts and salinity on rehabilitation sites. Phosphorus did not return to pre-disturbance levels, and carbon remained below pre-mining levels for at least 15 months after rehabilitation began, remaining a potential limiting factor in rehabilitation. Each rehabilitation technique that a mine employs has costs and benefits, and it is increasingly important that insights from ecology and economics are coupled if restoration efforts are going to succeed. A review of valuation systems indicates that Discounted Cash Flow Techniques (DCF) are suitable for valuation of rehabilitation operations.