Coal mine tailings: development after revegetation with salttolerant tree species

Coal mine tailings are often hostile media in which to grow plants. This paper reports selected physical and chemical properties of alkaline saline-sodic tailings 1.4 and 9.4 years after deposition in three experimental tailings storage facilities (TSFs). This study included the effects on the tailings of three moderately salt-tolerant tree species grown on their surfaces during the last 7.6 years of this period. Few changes occurred to the physical properties of the vegetated or unvegetated tailings over this period apart from strength increases associated with drying and settling. Chemical changes over this period included lower salinity (as EC), Na and S concentrations beneath the tree canopies which were associated with reduced site irradiance. No pedologically meaningful changes to properties reflecting soil organic matter or the concentrations of other elements were apparent. It is concluded that meaningful pedological development in these wastes is likely to require lengthy periods. The tailings materials of a seasonal wetland studied in one of the TSFs showed materials differences due to deposition of non-tailings materials eroded from upslope. Salinity was substantially reduced in the near-surface materials due to extensive leaching and lower C and N concentrations indicated a reduced organic matter content; further, the lower C:N ratio may indicate a different type of organic matter associated with the wetland vegetation present. It is concluded that for successful direct rehabilitation of tailings, careful evaluation is required of the physical, chemical and biological properties that potentially limit plant growth. The plant species to be initially established must be chosen for their tolerance of potentially growth limiting properties, particularly extremes of pH and salinity. Where tailings properties exceed tolerance limits of the species to be established or plant nutrient element supply limits growth, the materials may need to be ameliorated. In the field, particular attention to drainage of these fine-textured materials is critical to plant success. Pedological development of these fine-textured wastes is considered to require extended time periods, even under optimal conditions.