Strip mining rehabilitation by translocation in arid coastal Namaqualand, South Africa

[摘要] ENGLISH ABSTRACT: This study investigates the use of top-soiling, irrigation and translocating indigenous plants tofacilitate the cost-effective return of a mined landscape to its former land-use (small stockfarming) in an arid winter rainfall Succulent Karoo shrub land biome on the West Coast of SouthAfrica.Effects of topsoil stockpiling and subsoil mineral concentration on soil fertility and chemistrywere investigated, as soils are likely to determine rates of vegetation recovery on post-minedareas. Results of a radish bioassay show that stockpiling topsoil and mineral concentration subsoildecreased soil fertility. Mineral concentration decreased phosphorus, potassium, calcium,magnesium, carbon and nitrogen levels significantly relative to other soil treatments. Sodium infreshly deposited tailings was at potentially toxic levels and significantly higher than for all othersoil treatments. Spreading of stockpiled topsoil over tailings may ameliorate harsh conditionscreated by mineral separation.Translocation of plants from pre-mined to post-mined areas was carried out on a trial basis in aneffort to facilitate the return of natural vegetation and processes to strip-mined landscapes. Fivelocal indigenous plant species: Asparagus spp., Ruschia versicolor, Othonna cylindrica,Lampranthus suavissimus and Zygophyllum morgsana were planted into multi-species clumps ina replicated experiment. Variables examined in the translocation trial included the effects ofplant origin, soil treatment and/or irrigation on plant survival and establishment. The proportionof O. cylindrica transplants surviving for 15 months was greater than for other species. Wholeplants survived better than salvaged plants, and Asparagus spp., R. versicolor, L. suavissimusand 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-plantclumps were significantly larger than whole-plant clumps at planting, however, this effect wasnot observed after 12 months, indicating that whole-plant clumps grew faster than salvaged-plantclumps. The evergreen, leaf succulent shrubs O. cylindrica, L. suavissimus and R. versicolorappeared 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 beganwere compared for combinations of top-soiling, irrigation, plant translocation and unmodifiedtailings. Irrigation may reduce biodiversity and seedling densities. Over a 15-month period following back filling and topsoil spreading, sodium, potassium and calcium appeared to returnto levels observed for undisturbed soils. Magnesium remains at levels lower than in pre-minedsoil conditions. Soil conditions may be more conducive to plant establishment and rehabilitationafter back-filling of tailings and topsoil spreading. Electrical resistance increased over timeindicating a reduction of free salts and salinity on rehabilitation sites. Phosphorus did not returnto pre-disturbance levels, and carbon remained below pre-mining levels for at least 15 monthsafter rehabilitation began, remaining a potential limiting factor in rehabilitation.Each rehabilitation technique that a mine employs has costs and benefits, and it is increasinglyimportant that insights from ecology and economics are coupled if restoration efforts are going tosucceed. A review of valuation systems indicates that Discounted Cash Flow Techniques (DCF)are suitable for valuation of rehabilitation operations.

[发布机构] Stellenbosch University