Effect of organic amendment on the physicochemical characteristics of tailing and root development of tree species, fifteen years after planting

Among mine wastes, tailings are known to have the largest environmental impact, as they have the high concentrations of trace elements and are susceptible to wind dispersal and water erosion. A tree plantation trial was installed at Kipushi tailing (Democratic Republic of the Congo) in order to mitigate the contaminant dispersal on the surrounding areas. Fifteen years later, the present study was conducted on the purpose of investigating the macronutrient and trace metal concentrations in amended holes and assessing the development of tree species through root behavior in the tailing (in soil profiles at the base of tree). Results show elevated available P, K, Ca and Mg concentration in the surface and amended layers which is higher than the unpolluted soil of the miombo woodland. Cu and Co concentration trended to increase in the rich OM layers (L1 and L3 amended), but Zn, Cd, Pb and As remained higher in tailings. Compared to the tailing layer, roots developed well in the amended layers (very abundant, all sizes and regular distribution), but few roots ranging from very fine to big from all the surviving species were able to go beyond the amended layers indicating the possibility of tree survival on the tailing over many years. Acacia polyacantha and Psidium guajava showed an abundant root development in the unamended tailing layers compared to other 8 tree species.
Therefore, species that are less sensitive to metal toxicity and soil compactness challenges need to be promoted for the phytostabilisation of tailings with fewer amendments and the top soil from the uncontaminated areas should be mixed with the organic amendments for the rehabilitation of larger areas.