Synergistic use of soil microbes and plants to facilitate rehabilitation on gold tailings materials
The rehabilitation of mine tailings put emphasis on the physical/chemical characteristics of tailings storage facilities (TSF) and approaches to alleviate these adverse conditions to ensure plant cover. Minimal attention is given to soil biological properties, both during and after mining operations. This research will exemplify the importance of soil microbial activity as part of rehabilitation specifications and assessment criteria. A combination of chemical, physical and microbiological properties were identified as the major rehabilitation constraints, i.e., pH of 1.7, net acid lime requirement of 300t/ha; low soil enzymatic activity and compost requirement of 65t/ha are amongst the worst. The soil enzymatic activity of the different gold TSFs varied greatly. The enzymatic activity was greater in the voluntarily established grass rhizospheres, with barren TSFs having the lowest enzymatic activity. The low β-glucosidase, urease, dehydrogenase (DHA), acid and alkaline phosphatase enzymatic activities observed at these gold TSFs indicates poor soil quality and soil fertility (insufficient biodegradable organic matter and limited nutrient cycling). A negative association exists between salinity (EC) and DHA (ANOVA r-0.868; p<0.05) at the New Machavie TSFs. Salination is an abiotic soil factor, considered hazardous to soil fertility and consequently affect vegetation establishment. In order to integrate the microbiological components into rehabilitation plans, the synergistic use of soil microbes and plants to facilitate the rehabilitation of various gold TSFs was investigated. This research phase was conducted with the purpose of determining the influence of various bio-stimulants on different mother crop species (Brassicaceae members) survivability and growth in deleterious environments. It was anticipated that the synergistic use of bio-stimulants and mother crop species would improve vegetation establishment and revegetation efficiency. Results indicated that both bio-stimulants and mother crops stimulated soil rhizosphere DHA. Tailings from New Machavie geel TSF with canola/carbohydrates treatment possessing the highest DHA increase (857 INF μg/g/2h), and all un-treated tailings the lowest. Various bio-stimulants significantly increased the mother crop species germination and survival rate (ANOVA p<0.005). Results also indicate that rehabilitation is substrate specific, i.e., certain bio-stimulants and different mother crop species performed better on different gold tailings. In conclusion, the study gains novel insights into the use of soil enzymatic activity as a rehabilitation monitoring and assessment criteria indicator. The study also highlights the importance of integrating microbial properties into rehabilitation specifications. Biological factors are vital for soil quality to establish sustainable soil-plant systems.