Rehabilitation of Organic Carbon and Microbial Community Structure and Functions in Cu-Pb-Zn Mine Tailings for in situ Engineering Technosols Fang You Bachelor of Natural Sciences Master of Sciences A thesis submitted for the degree of Doctor of Philosophy at The University of Queensland in 2015 Sustainable Mineral Institute Abstract Base metal mine tailings phytostabilisation has been severely hindered by the lack of growth media (soil and inert overburden), and associated hydrogeochemical instability, and phytotoxicity in the tailings. A new paradigm of in situ engineered pedogenesis of tailings into functional technosols has been proposed as a cost-effective and sustainable solution. This project aimed to understand critical factors and processes driving soil formation towards functional technosols in Cu-Pb-Zn tailings, which may be manipulated and stimulated by ecological engineering inputs (e.g., organic amendments, microbial inoculum, and pioneer plants). Native soil characteristics (under native plant communities located in subtropical, semi- arid Mount Isa region) have set the direction of technosols formation and justified the plant biomass-based organic amendment option, to couple with physiological traits (slow growth rates, low water and nutrient requirements) of native plant communities dominant in the investigated region. Both Cu-Pb-Zn tailings (TD5, TD7) from Mount Isa Mines and Cu-Mo- Au tailings from Ernest Henry Mine were used in this study, representing typical hydrogeochemical conditions of tailings. Organic carbon (OC) is recognised as an overall indicator of technosols formation in tailings. In a 2.5-year old column trial under field conditions with weathered (TD5) and fresh (TD7) Cu-Pb-Zn tailings, exogenous organic amendments (woodchips) rapidly built up OC content with 61.5-80.3 % OC physically protected in aggregates and organo-mineral complexes in the amended tailings, regardless of the mineral weathering stages. N-rich and surface charged organic compounds interacted with tailings minerals (e.g., Fe and Al (hydr-) oxides) to form organo-mineral complexes and aggregates, contributing significantly to OC stabilisation. Native plants (e.g., Acacia chisolmii, Triodia pungens) survived beyond the time of sampling in the TD5 in the field trial, but not in the TD7. Plant colonisation in TD5 further accelerated technosols formation in the amended tailings, significantly stimulating OC stabilisation, microbial biomass and functions. While the amended tailings were far from reaching the desired hydrogeochemical stability, the pioneer native plant species were proven to be critical to the colonisation of heterotrophic bacteria and associated biogeochemical processes. Organic matter properties (e.g., labile OC, C: N ratio) induced biogeochemical changes in the tailings with different directions. In a 6-month microcosm experiment, the weathered and neutral Cu-Pb-Zn tailings were amended with plant litter (Acacia chisolmii) and biochar. Although little improvement was observed for microbial diversity, the plant litter significantly i increased the labile OC and N, and microbial biomass and enzymatic activities in the amended tailings. Comparatively, bacterial communities more readily recolonised than the fungi in the tailings. The abundance of heterotrophic bacteria affiliated to Bacteroidetes and Proteobacteria stimulated in the plant litter amended tailings significantly. Interestingly, biochar enhanced the dominance of autotrophic bacteria, Thiohalobacter sp., with suppressed rehabilitation of heterotrophic bacteria, probably related to the lack of labile OC and N in the biochar. Combined plant litter and biochar further increased the microbial diversity and functions in the amended tailings. Topsoil underneath native plant communities rich in microbial inoculums may be used to rapidly prime microbial diversity in the amended tailings. In an 8-week microcosm experiment, the weathered and neutral Cu-Pb-Zn tailings were inoculated with native soils, which had been amended with sugarcane as the base treatment. The colonisation of heterotrophic bacteria and fungi were observed in the tailings-soil mix, strongly linkedto the microbial biomass and functions. Microbial biomass and enzymatic activities increased by 1.5-8 folds in the tailings-soil mix compared to the control, depending on soil addition rates. 25 % soil addition doubled the microbial diversity in the tailings-soil mix compared to the control. 50 % soil addition achieved a respiratory quotient, and C and N cycling processes similar to those of the native soil. Again, Proteobacteria and Bacteroidetes significantly stimulated in the tailings-soil mix. Stresses including EC (thus S) and total heavy metals (Pb, Zn) had negatively impacts on microbial community. Biogeochemical changes were investigated in fresh Cu-Mo-Au tailings (containing low levels of reactive minerals with stable hydrogeochemistry) in response to organic amendments (i.e., sugarcane and biochar) and introduction of native grass (Iseilema vaginiflorum) and leguminous shrub (Acacia chisholmii). Microbial diversity were 2-4 folds in all the amended/revegetated tailings compared to the control. Microbial biomass and enzymatic activities in sugarcane amended and revegetated tailings significantly increased by 4-25 folds, with stimulated abundance of Bacteroidetes and the dominance of heterotrophic bacteria (e.g., Algoriphagus sp. Sphingopyxis sp., Sediminibacterium sp., Planctomyces sp.), enhancing plants growth. Again, biochar stimulated the dominance of autotrophic bacteria (e.g., Thermithiobacillus sp. Acidiferrobacter sp.) in the amended tailings. Furthermore, biochar contributed to Cu immobility, considerably reducing Cu uptake by plant roots from the tailings. The introduced pioneer plants effectively involved in rehabilitating microbial community structure and functions, particularly in the sugarcane amended tailings with low levels of reactive minerals and relative stable hydrogeochemistry. ii In comparison, the presence of pioneer native plants seemed to be not critical to the development of microbial communities in the tailings amended with labile organic matter (e.g., sugarcane residue), unlike the Cu-Pb-Zn tailings (TD5) after long-term weathering. In summary, engineering technosols with desired biogeochemical capacity in hydrogeochemically stable Cu-Pb-Zn tailings must be consistent with the physiological characteristics of native plant communities specific to local edaphic and climatic conditions. Technosols formation from the tailings can be initiated and accelerated by plant biomass- based organic amendments coupled with the soil inoculation and the introduction of tolerant pioneer native plants. iii Declaration by author This thesis is composed of my original work, and contains no material previously published or written by another person except where due reference has been made in the text. I have clearly stated the contribution by others to jointly-authored works that I have included in my thesis. I have clearly stated the contribution of others to my thesis as a whole, including statistical assistance, survey design, data analysis, significant technical procedures, professional editorial advice, and any other original research work used or reported in my thesis. The content of my thesis is the result of work I have carried out since the commencement of my research higher degree candidature and does not include a substantial part of work that has been submitted to qualify for the award of any other degree or diploma in any university or other tertiary institution. I have clearly stated which parts of my thesis, if any, have been submitted to qualify for another award. I acknowledge that an electronic copy of my thesis must be lodged with the University Library and, subject to the policy and procedures of The University of Queensland, the thesis be made available for research and study in accordance with the Copyright Act 1968 unless a period of embargo has been approved by the Dean of the Graduate School. I acknowledge that copyright of all material contained in my thesis resides with the copyright holder(s) of that material. Where appropriate I have obtained copyright permission from the copyright holder to reproduce material in this thesis. iv Publications during candidature Peer-reviewed, published journal papers F You, R Dalal, L Huang. Biochemical characteristics in root zone associated with Acacia and Spinifex to sustain on infertile soil in semiarid northwest Queensland, Australia. Accepted by Soil Research on 18 Aug. 2015 X Li, F You, P Bond, L Huang (2015). Establishing microbial diversity and functions in weathered and neutral Cu–Pb–Zn tailings with native soil addition. Geoderma. 247-248, 108-116. F You, R Dalal, D. Mulligan, L Huang (2015). Quantitative measurement of organic carbon in mine wastes: Methods comparison for inorganic carbon removal and organic carbon recovery. Communications in Soil Science and Plant Analysis. 46 (sup1), 375-389. X Li, F You, L Huang, E Strounina, M Edraki (2013). Dynamics in leachate chemistry of Cu- Au tailings in response to biochar and woodchip amendments: a column leaching study. Environmental Sciences Europe. 25 (1):32. Published conference abstract and oral paper F You, R Dalal, D Mulligan, L Huang (2013). Microbial Biomass and Activities in Response to Nutrition and Toxicity Factors in Amended Base Metal Mine Tailings. ASA, CSSA, and SSSA International Annual Meetings, Tampa, Florida, USA. 3-6 November. v Publications