Post-Mining Restoration in Zambia : Screening native tree species for phytoremediation potential

Sammanfattning: Africa has a long history of mining, which has generated a large amount of wastes (tailings dams and overburden materials) that are hazardous for the environment and human health. Phytoremediation, which involves the use of plants and microorganisms to reduce the toxic effects of heavy metals in the soil environment, is considered an efficient, eco-friendly and cost-effective restoration method. However, little is known about Zambian native tree and shrub species that are suitable for phytoremediation. Thus, the main objective of the studies presented in this thesis was screening candidate tree species for phytoremediation of copper (Cu) mine wastelands. This was achieved first by reviewing the state of knowledge about restoration of mine wastelands in Africa, followed by characterization of mine wastes to get insights into the barriers to restoration, a survey of autochthonous colonization of tailings dams and analysing their biological traits, and finally testing the tolerance mechanism of selected candidate species to elevated Cu concentrations and the potential of biochar and poultry manure as amendments to boost survival and growth. The results showed that (1) research and application of post-mining landscape restoration in Africa is very limited focusing mainly on identifying herbaceous species suitable for phytoremediation; (2) Cu mine wastes were characterized by high soil compaction, poor macro-nutrient availability, high soil acidity, and toxic level of heavy metals, which are the main constraints for successful phytoremediation; (3) there was autochthonous colonization of tailings dams with a floristic composition distinct from nearby natural forests, and the main biological traits of species colonizing tailings dams were light-demanding (93%), moderately tolerant to elevated copper concentration (87%), suitable for erosion control (75%) endomycorrhizal (47%) and nitrogen-fixing (29%); (4) candidate species for phytoremediation tolerated high Cu concentration by excluding its uptake by roots; and (5) amendments of tailings dams substrate with biochar, poultry manure and their combination slightly boosted survival and growth of some selected species. As a whole, the pace of restoration research and practice after mining disturbance in Africa is slow and as mining activities are likely to increase, restoration of mine wastelands will become even more urgent. The know-how to restore those landscapes requires a more mainstreamed approach that can easily be implemented by the mining companies in order to make the mining sector “green”.