Ecological engineering of iron ore tailings into useable soils for sustainable rehabilitation.

Ecological engineering of soil formation in tailings is an emerging technology toward sustainable rehabilitation of iron (Fe) ore tailings landscapes worldwide, which requires the formation of well-organized and stable soil aggregates in finely textured tailings. Here, we demonstrate an approach using microbial and rhizosphere processes to progressively drive aggregate formation and development in Fe ore tailings. The aggregates were initially formed through the agglomeration of mineral particles by organic cements derived from microbial decomposition of exogenous organic matter. The aggregate stability was consolidated by colloidal nanosized Fe(III)-Si minerals formed during Fe-bearing primary mineral weathering driven by rhizosphere biogeochemical processes of pioneer plants. From these findings, we proposed a conceptual model for progressive aggregate structure development in the tailings with Fe(III)-Si rich cements as core nuclei. This renewable resource dependent eco-engineering approach opens a sustainable pathway to achieve resilient tailings rehabilitation without resorting to excavating natural soil resources.

Native plant Maireana brevifolia drives prokaryotic microbial community development in alkaline Fe ore tailings under semi-arid climatic conditions.

Native pioneer plants of high environmental tolerance may be exploited as early colonisers in alkaline Fe-ore tailings to drive the development of functional prokaryotic microbial communities, which is one of the critical pedogenic processes leading to in situ soil formation in the tailings. The present study deployed high throughput Illumina Miseq sequencing, to characterise the diversity and potential functionality of prokaryotic microbial communities in the aged Fe-ore tailings and topsoils colonised by native plant species Maireana brevifolia at an Fe ore mine in Western Australia, in comparison with those in the tailings/topsoils without plants. The composition of prokaryotic microbial communities differed between the aged tailings (AT) and topsoil sites (TS). Aged tailings (AT1-AT3) contained more bacteria tolerant of alkaline/saline conditions (e.g., Alkalilimnicola sp.) and those related to Fe biogeochemical cycling (e.g., Acidiferrobacter sp., Aciditerrimonas sp.). In comparison, the prokaryotic microbial communities in the topsoil (TS) contained abundant bacteria related to N cycling (e.g., Rhizobium sp., Frankia sp.). The presence of M. brevifolia plants significantly increased the diversity of prokaryotic microbial communities in tailings and topsoil, particularly favouring the development of bacteria related to N cycling and OM degradations (e.g., Mesorhizobium sp. Paracoccus sp., Oxalicibacterium horti, and Microbacterium sp.). The variation of microbial community were mainly explained by pH, amorphous Fe, and total N, which were regulated by M. brevifolia colonisation. The beneficial roles of pioneer plants M. brevifolia in the development of prokaryotic microbial community in the alkaline Fe ore tailings may be integrated as a key factor when designing and scaling up the process of eco-engineering Fe-ore tailings into soil under semi-arid climatic conditions.

Correction to: Molecular diversity of arbuscular mycorrhizal fungal communities across the gradient of alkaline Fe ore tailings, revegetated waste rock to natural soil sites.

The authors thank the Australian Centre for Ecogenomics in the University of Queensland for conducting Illumina sequencing.

Molecular diversity of arbuscular mycorrhizal fungal communities across the gradient of alkaline Fe ore tailings, revegetated waste rock to natural soil sites.

Arbuscular mycorrhizal (AM) fungi are important to the establishment of native vegetation for mined land rehabilitation, particularly in semi-arid and infertile landscapes. However, the information has been scarce about the colonization of AM fungal community in alkaline magnetite Fe ore tailing sites (without toxic metal (loid) contamination). The present study has characterized the diversity of AM fungi across typical domains of a magnetite Fe ore mine located in 200 km south-east of Geraldton, Western Australia, by adopting high throughput Illumina Miseq sequencing. The investigated domains included two tailing sites without top soil covering (T1 and T2), a rehabilitated area of tailings with top soil covering (R1), a revegetated waste rock area (R2), and two native undisturbed soil sites (S1 and S2). The results indicated that the T1/T2 sites had different AM fungal community structure, compared with R1/R2 and S1/S2 sites. The dominant families were Glomeraceae, Claroideoglomeraceae, Archaeosporaceae, Ambisporaceae, and Paraglomeraceae, with Paraglomeraceae (more than 50%) as the most abundant in the T1/T2 and R1/R2 sites. At genus level, Ambispora spp. and Archaeospora spp. were rich in T1/T2 sites (> 10%), while Glomus spp. were preferably dominant in S1/S2 sites (> 10%). Furthermore, amorphous Fe and available P were found to explain the variations associated with AM fungal community composition, particularly the abundance of Archaeosporaceae and Glomeraceae. The study revealed the AM fungal community composition shift across the gradient of Fe ore mine sites, as well as the effects of revegetation on AM fungal community development. The findings indicate the possible restoration of AM fungal community in the tailings undergoing revegetation, and potential adoption of indigenous AM fungi to rapid phytostabilization of the Fe ore tailings under semi-arid climatic conditions.