Microbial Functional Capacity Is Preserved Within Engineered Soil Formulations Used In Mine Site Restoration

Mining of mineral resources produces substantial volumes of crushed rock based wastes that are characterised by poor physical structure and hydrology, unstable geochemistry and potentially toxic chemical conditions. Recycling of these substrates is desirable and can be achieved by blending waste with native soil to form a 'novel substrate' which may be used in future landscape restoration. However, these post-mining substrate based 'soils' are likely to contain significant abiotic constraints for both plant and microbial growth. Effective use of these novel substrates for ecosystem restoration will depend on the efficacy of stored topsoil as a potential microbial inoculum as well as the subsequent generation of key microbial soil functions originally apparent in local pristine sites. Here, using both marker gene and shotgun metagenome sequencing, we show that topsoil storage and the blending of soil and waste substrates to form planting substrates gives rise to variable bacterial and archaeal phylogenetic composition but a high degree of metabolic conservation at the community metagenome level. Our data indicates that whilst low phylogenetic conservation is apparent across substrate blends we observe high functional redundancy in relation to key soil microbial pathways, allowing the potential for functional recovery of key belowground pathways under targeted management

Chemico-mineralogical changes of ultramafic topsoil during stockpiling: implications for post-mining restoration

International audienceLateritic topsoils, which are usually removed and stored apart before mining operations take place, play an essential role in the success of post-mining restoration. They contain elements to recover chemical (organic matter, nutrients) and biological (seed and bud banks, microorganisms) fertility of the soil. Conserving topsoil fertility during storage time is essential for a successful use of topsoil during restoration. In this study, different chemico-mineralogical properties of a lateritic topsoil from the Goro nickel mine (New Caledonia) were monitored from its original in situ emplacement on the soil profile, immediately after its stockpiling and after 24 months of storage. Our analyses show that topsoil experienced noticeable changes immediately after storage, mostly produced by mixing of different soil profiles. Cation Exchange Capacities and concentrations of most elements did not vary even after 24 months of storage. However, a slight reduction of Ni, Cr, K, Na and of the C:N ratio, and an increase of Ca have been observed. Stockpiling has not affected negatively the chemical fertility of the topsoil, although biological parameters should be considered to have a complete view of stockpiling sustainability

Structural development of vegetation on rehabilitated North Stradbroke Island: Above/belowground feedback may facilitate alternative ecological outcomes

Introduction: This study depicts broad-scale revegetation patterns following sand mining on North Stradbroke Island, south-eastern Queensland, Australia. Methods: Based on an ecological timeline spanning 4-20 years post-rehabilitation, the structure of these ecosystems (n = 146) was assessed by distinguishing between periods of 'older' (pre-1995) and 'younger' (post-1995) rehabilitation practices. Results: The general rehabilitation outlook appeared promising, whereby an adequate forest composition and suitable levels of native biodiversity (consisting of mixed-eucalypt communities) were achieved across the majority of rehabilitated sites over a relatively short time. Still, older sites (n = 36) appeared to deviate relative to natural analogues as indicated by their lack of under-storey heath and simplified canopy composition now characterised by mono-dominant black sheoak (Allocasuarina littoralis) reaching up to 60% of the total tree density. These changes coincided with lower soil fertility parameters (e.g., total carbon, total nitrogen, and nutrient holding capacity) leading us to believe that altered growth conditions associated with the initial mining disturbance could have facilitated an opportunistic colonisation by this species. Once established, it is suspected that the black sheoak's above/belowground ecological behaviour (i.e., relating to its leaf-litter allelopathy and potential for soil-nitrogen fixation) further exacerbated its mono-dominant distribution by inhibiting the development of other native species. Conclusions: Although rehabilitation techniques on-site have undergone refinements to improve site management, our findings support that putative changes in edaphic conditions in combination with the competitive characteristics of some plant species can facilitate conditions leading to alternative ecological outcomes among rehabilitated ecosystems. Based on these outcomes, future studies would benefit from in depth spatio-temporal analyses to verify these mechanisms at finer investigative scales