Assessment and monitoring of rehabilitation efforts by analysis of soil microbial communities as biological indicators of sustainability

Abstract

The disposal of solid waste material produced by mining activities can have vastly negative environmental impacts with regards to soil ecosystems. Global and South African legislation requires the mining company to rehabilitate the disturbed area in such a manner that sustainable ecosystem stability is achieved. Rehabilitation of co-disposed diamond tailings at Finsch mine (De Beers) entails the application of organic matter in the form of vermi-compost, organic and inorganic fertilizers, as well as different grass seed mixtures. Optimal amounts of chemical ameliorants were determined in a previous experimental trial prior to the current field study at the mine. The aim of this study was to evaluate the rehabilitation progress by analysis of soil microbial communities as biological indicators of sustainability. Soil quality can be determined by the analysis of physical, chemical and biological soil properties. Chemical analysis of the tailings material was done by 1 :2 water extract, as well as ammonium acetate extraction techniques. Enzymatic analysis (dehydrogenase, acid and alkaline phosphatase, f3-glucosidase and urease) as well as substrate induced respiration (SIR) was used to determine the soil microbial community function. Soil microbial community structure was evaluated by the analysis of specific microbial lipid biomarkers. The vegetation response towards the rehabilitation effort was evaluated by determination of subjective ratings for plant species frequency and density, and plant biomass. Plant vitality was determined by analysis of photosynthetic activity, which is known to be extremely sensitive towards environmental disturbance. In terms of overall enzymatic activity (dehydrogenase), the application of 90-tonlha vermi-compost in the experimental plots showed the best results. No statistically significant differences in SIR results were noted in the experimental plots. However, the plots treated with 60-tonslha vermi-compost showed the best results in terms of plant vitality and plant biomass. The determination of soil microbial community structure showed that fungal to bacterial ratios were increasing over time although actual ratio values are much less than one, and that overall bacterial population dominance is evident in the experimental plots.