Mine Site Rehabilitation Research Articles

MINERAL PRODUCTION AND ENVIRONMENTAL POLLUTION IN NIGERIA

This study empirically determined the effect of mineral production on environmental pollution in Nigeria from 1985 to 2022. The research utilised time series data obtained from the Central Bank of Nigeria (CBN) data bulletin and the World Development Indicators (WDI) of the World Bank. The data analysis methodologies utilised include descriptive statistical analysis, ADF Unit Root test, ARDL Bound Co-integration test, and ARDL methodology. The result of the ADF unit root test indicated the presence of a combination of stationary and non-stationary elements. That is a mixture of I(0) and I(1). Furthermore, the ARDL limits co-integration test has shown the presence of a long-term link between the variables. Finally, the ARDL estimation revealed that crude petroleum and natural gas production, likewise mining and quarrying had significant and positive implication on emission of CO2 in both long and short runs. Coal production had positively significant impact on CO2 emission in the long run but positively insignificant impact in the short run. In addition, metal ores positively and insignificantly impacted on CO2 emission in both the long and short runs. The study's results indicated that mineral mining in Nigeria resulted in a rise in environmental contamination. The report proposed that the Nigerian government should thoroughly evaluate and revise current environmental laws and regulations in order to effectively address the environmental consequences of mineral development. This should include establishing clear standards, guidelines, and permits for mining operations, waste management, pollution control, and rehabilitation of mining sites. KEYWORDS: Mineral Production, Environmental Pollution, CO2 Emission

Remote sensing reveals trends in vegetative recovery and land cover transformation post-reclamation at tar creek superfund site

The harmful effects of mining waste on human and ecosystem health make reclamation of former mine sites an environmental management priority. However, field-based monitoring of reclamation requires significant investments of time, labor, and money. Remote sensing offers a less expensive alternative to field-based monitoring, but work is still needed to determine which metrics can be reliably estimated using remote sensing techniques. This study uses remote sensing to examine over 20 years of reclamation efforts at Tar Creek Superfund Site and to assess revegetation after site restoration. Using the Normalized Difference Vegetation Index (NDVI), we quantify key factors affecting vegetation recovery and stability after reclamation across 123 surface mining waste cleanup locations within Tar Creek. Leveraging long-term imagery from Landsat and high-resolution PlanetScope imagery, we combine time series analysis of vegetation regrowth and landcover change detection for a comprehensive picture of recovery at each site. Across all reclamation sites, the average recovery duration was 3.5 years, and average recovery rate was 0.1 NDVI year−1. After vegetative growth had plateaued, reclaimed sites had an average NDVI of 0.70. All reclamation areas were converted from majority barren landcover to vegetated landcover classes after reclamation, and vegetative stability at reclamation sites was high (70% of reclaimed area saw continuous vegetative cover from 2017 to 2023). These results demonstrate a strong potential for multi-method remote sensing techniques in tracking and explaining vegetation recovery after reclamation and represent a cost-effective approach for real-time monitoring of reclamation progress and outcomes.

Tools to improve mine closure: 10 years of research in integration of environment in the mine life cycle

Abstract Mine closure can be approached by several points of view, from the technical, engineering, ecological, up to social and governance aspects. The definition of a good mine closure should cover most, if not all, of these aspects. This article provides a review of technical and engineering-oriented research work as a partial answer to the question ‘what is good mine closure’. The article presents a ten-year research program realized in the framework of a Canada Research Chair in integration of environment in the mine life cycle. Research projects aimed at better planning mine closure and mine site reclamation from the early stages of a mining project life cycle are exposed as possible steps to strive for optimal mine waste management. At the exploration stage, geo-environmental characterization and modeling are proposed as tools to improve mine waste management planification. During mine operations, environmental desulfurization is suggested as a method to reduce environmental risks associated with sulfidic tailings and waste rock. Indeed, research has shown that acid mine drainage and metal leaching can be significantly limited via desulfurization. At the closure stage, desulfurized tailings can be used to replace at least part of natural materials used for reclamation cover systems. Research work done on other types of mine waste, such as waste rock and water treatment sludge, also show good potential for their reuse as closure material. All these tools can be integrated into the mine life cycle to better plan for closure, which ultimately will make mine closure more sustainable.

Vegetation change on mine sites in the most arid part of the Succulent Karoo Biome and their implications for mine closure

Restoring biodiversity is an important component of mine site rehabilitation. It needs to be evaluated regularly to assess success or failure of restoration methods and compliance with mine closure completion criteria. Yet vegetation dynamics in the driest part of the Succulent Karoo Biome are poorly understood. This study contributes to the question whether succession theory applies in this ecosystem by investigating 40 sites in a completely altered mining landscape and accompanying reference sites in the southern Namib within a 17-year time interval. Plant cover and species composition of the same site were compared between a field survey in 2005 and 2022. Multivariate analyses indicated that the importance of investigated environmental variables shifted between the survey periods, affecting the secondary vegetation on altered landforms as well as the undisturbed reference sites. This complicated the interpretation of perceived changes between the 2005 and 2022 surveys, making it difficult to detect successional trends. A drying of the general area is indicated which reduced species richness and cover overall and may have precipitated a change in habitat from stabilised to shifting dunes with concomitant changes to more sand-tolerant species in the southern part of the study area. These changes in both natural and secondary vegetation pose challenges when deciding on appropriate measures for restoration monitoring and setting completion criteria for mine closure.

Acidithiobacillus species drive the formation of ferric-silica cemented microstructure: Insights into early hardpan development for mine site rehabilitation

Hardpan-based profiles naturally formed under semi-arid climatic conditions have substantial potential in rehabilitating sulfidic tailings, resulting from their aggregation microstructure regulated by Fe-Si cements. Nevertheless, eco-engineered approaches for accelerating the formation of complex cementation structure remain unclear. The present study aims to investigate the microbial functions of extremophiles on mineral dissolution, oxidation, and aggregation (cementation) through a microcosm experiment containing pyrites and polysilicates, of which are dominant components in typical sulfidic tailings. Microspectroscopic analysis revealed that pyrite was rapidly dissolved and massive microbial corrosion pits were displayed on pyrite surfaces. Synchrotron-based X-ray absorption spectroscopy demonstrated that approximately 30 % pyrites were oxidized to jarosite-like (ca. 14 %) and ferrihydrite-like minerals (ca. 16 %) in talc group, leading to the formation of secondary Fe precipitates. The Si ions co-dissolved from polysilicates may be embedded into secondary Fe precipitates, while these clustered Fe-Si precipitates displayed distinct morphology (e.g., “circular” shaped in the talc group, “fine-grained” shaped in the chlorite group, and “donut” shaped in the muscovite group). Moreover, the precipitates could join together and act as cementing agents aggregating mineral particles together, forming macroaggregates in talc and chlorite groups. The present findings revealed critical microbial functions on accelerating mineral dissolution, oxidation, and aggregation of pyrite and various silicates, which provided the eco-engineered feasibility of hardpan-based technology for mine site rehabilitation.

Identifying biomass yield potential of tetra‐, hexa‐, and octoploid prairie cordgrass populations grown on marginal lands

AbstractAs the demand for renewable energy sources with reduced carbon emissions to the atmosphere increases, bioenergy crops remain an attractive alternative to fossil fuels. Another appeal of bioenergy crops is the potential utilization of marginal lands not suitable for food crops. Prairie cordgrass is a perennial warm‐season polyploid grass species that is considered a bioenergy crop that also exhibits a high tolerance for salinity and flooding. The ploidy level of prairie cordgrass has previously been suggested to correlate with agronomic traits. However, little is known about the agricultural performance of prairie cordgrass on marginal lands and if a correlation of ploidy level and stress tolerance exists. In this experiment, the productivity of tetra‐, hexa‐, and octoploids was investigated when grown on three different marginal sites, including waterlogged, saline, and low‐nutrient gravelly soils. Here, we found that prairie cordgrass populations annually produced dry biomass on a wet marginal site comparable to normal cropland. However, the productivity was remarkedly decreased at both a salt‐affected site and a limestone mine reclamation site. We were unable to conclude that different ploidy levels affected the biomass yield of prairie cordgrass grown under abiotic stress. However, there was a differential response of populations to various types of marginal sites. These results indicate potential genetic resources for developing breeding targets and identifying mechanisms of abiotic stress tolerance. Moreover, we highlight the need to generate diverse ploidy levels of prairie cordgrass in the same genetic backgrounds for future testing.

Delayed seeding and nutrient amendment seed enhancement technology: potential to improve sagebrush establishment?

The sagebrush steppe provides vital habitat across the western United States, but its range is declining. Wyoming big sagebrush (Artemesia tridentata Nutt. spp. wyomingensis Beetle & Young) is difficult to establish on restoration and reclamation sites, with low seedling survival due to drought, competition, and limited available nutrients. Incorporating seeds into seed enhancement technologies (SET) has potential to overcome barriers to establishment. Here, we tested the effects of a high phosphorus nutrient amendment using three application techniques (dust over bare seed, dispersed seed pellets, and clustered seed pellets) versus bare seed on sagebrush establishment on 5‐, 1‐, and 0‐year‐old mine reclamation sites. Regardless of seed technology, emergence was highest in the year 5 site, but survival was lowest, likely due to competition from established plants. Survival and growth were highest in the year 0 site, but emergence was lowest, likely due to poor soil stability. The year 1 site, where soil was stable and competition was low, produced the greatest number of surviving seedlings. Across all times since reclamation, pellets reduced emergence compared to dust and bare seed treatments. There was no clear evidence of any benefit of the SETs. These results highlight the challenges of delivering nutrient amendments in SETs and unresolved questions about the effectiveness of the amendment tested here. Seeding sagebrush 1 year after reclamation may be an additional way to improve restoration and reclamation success for this foundation species.

The role of intercultural differences and challenges faced in negotiating active mine sites'rehabilitation objectives from Africa to Europe

Analysing the challenges that govern an active mining project during negotiations, especially its rehabilitation, can give a better insight from a cross-cultural perspective. Despite the cultural variations distinguished by region or country, there can be common strategies in negotiating rehabilitation objectives of mine sites via specific negotiation strategies. This study investigates how intercultural differences influence the rehabilitation of active mine sites from Africa to Europe. The goal is to provide new insights into cultural differences regarding the communication process in negotiations, issue an unprecedented groundwork for research, and contribute to practitioners of cross-cultural business negotiations by better understanding the context. Through semi-structured interviews, primary data was collected from participants representing a multinational mining corporation based in Europe negotiating the rehabilitation of active mine sites in Cameroon and South Africa. The analysis employed a data reduction process, interpreting the collected data, connecting it to existing literature, and analysing the findings. The outcomes showed the significance of cultural dimensions to variables of international business negotiations. They indicated the attention that culturally diverse organisations must pay to them to increase their chances of succeeding in rehabilitating mine sites’ integration. African and European stakeholders demonstrated opposing negotiation styles that affect how they communicate, build their agreements, show their emotions, and are willing to take risks.

Consideration of First Nations’ cultural values in mine site rehabilitation by environmental professionals

Rehabilitation of mined land on First Nations’ country after mine closure must achieve particular criteria to be considered successful. Generally, these conditions are based on achieving a habitable condition that is more or less similar to analogue sites or to the pre–mining state. Rehabilitating a site to a habitable condition requires the restoration of cultural values, as well as environmental and economic values. This study investigates the extent to which First Nations’ cultural values are considered in mine rehabilitation in northern Australia. Interviews were conducted with environment professionals who had experience rehabilitating mine sites on First Nations’ land in the Northern Territory, Australia. The participants were asked about their experiences restoring First Nations’ cultural values to mined land. Thematic analysis found six main themes: “Values” (which need to be restored); “Planning” (of rehabilitation activities); “Impediments/barriers” (to successful rehabilitation); “Solutions” (to the barriers); “Traditional Owners” and “Principles”. This study shows that mining environmental professionals argue that, with suitable political and corporate support, many cultural values could be restored. However, it was generally agreed that government oversight and regulation in relation to reinstatement of First Nations’ cultural values needed to be improved. Several participants suggested that greater consideration should be given to closure plans generally, to financial means to carry out rehabilitation, and specifically to planning to identify and address the rehabilitation of First Nations’ cultural values prior to approval. Other findings were also that First Nations’ cultural values and environmental values are closely aligned, and that consultation and effective communication with Traditional Owners are the key to integrating awareness of First Nations’ cultural values into mine rehabilitation practices.

Occurrence and distribution of microplastics in long-term biosolid-applied rehabilitation land: An overlooked pathway for microplastic entry into terrestrial ecosystems in Australia

Wastewater treatment plants (WWTPs) efficiently eliminate over 98% of microplastics (MPs) from wastewater discharge, subsequently accumulating them in sludge. This sludge is frequently employed as fertilizer in agricultural practices or land rehabilitation. While there is significant research on biosolid application in agriculture, the discussion regarding its application in rehabilitating industrial zones and MPs contamination is limited. The current study investigates the abundance, distribution, and composition of MPs in rehabilitation land with long-term biosolid-application in Australia. Three minesite fields (designated 1–3), each with distinct biosolid application histories since 2011, 2012, and 2017, and a control field without any biosolid application history, were chosen for this study. The abundances of MPs in biosolid-applied fields 1–3 (6.04 ± 1.92 x 102 MP kg−1; 4.94 ± 0.73 x 102 MP kg−1; 2.48 ± 0.70 x 102 MP kg−1) were considerably higher compared to non-biosolid-applied field (0.70 ± 0.63 x 102 MP kg −1). This indicates that the application of biosolids significantly contributes to the presence of MPs in the soil. Moreover, the results suggest that with each successive application, the abundance of MPs increases. The abundance and size of MPs in both biosolid and non-biosolid soils decreased as the soil depth increased. Microbeads were dominant in soils where biosolids were applied (up to 61.9%), while fibres were dominant in non-biosolid soils (accounting for 85.7%). The distribution of plastic polymer types varied among fields and soil depths. Most MPs were microbeads of polyamide (PA), fragments of polyethylene (PE), foam of polystyrene (PS), and fibres of rayon. This research presents evidence that the extended utilization of biosolids results in elevated MP pollution in minesite rehabilitation land, highlighting a frequently overlooked origin of MP contamination in terrestrial settings. Additional evaluations needed to understand ecological risks of MPs in soil ecosystems affected by biosolid application.

Epigaeic invertebrate diversity of post‐mining revegetation evaluated by comparison with adjacent remnant woodlands

This study evaluated the validity of invertebrate diversity for evaluating the condition of minesite rehabilitation. Because the aim of rehabilitation of mined lands in this region is to establish a self‐sustaining ecosystem that resembles “bushland,” a variety of remnant woodlands in the vicinity of the minesite were selected as reference sites. Reference sites encompassed a range of soil types (alluvial, coarse‐textured, or clay) and understorey structural types (grassy, grass, and shrub or shrubby). Grassland sites (cleared woodlands) were also sampled to provide a negative control. Epigaeic invertebrates of three rehabilitation sites were compared with five reference sites and three grassland sites using pitfall traps over 6 years. Sites were sampled annually and the annual data within each of two time periods (T1: 2008–2010 and T2: 2011–2013) were pooled. Ants, beetles, and springtails were identified as morphospecies, providing site species richness and composition data. Springtail metrics of all three habitats, reference, rehabilitation, and grassland, resembled each other in T1 as well as T2, indicating that rehabilitation rapidly provided suitable conditions for this group. In contrast, the ant and beetle composition of rehabilitation sites differed significantly from that of reference sites in T1 but not T2, although only ants matched the expected negative control with grassland sites remaining distinct from reference sites in both time periods. Thus, ant assemblages of rehabilitation sites show a positive trajectory toward native woodlands and away from grasslands. These findings demonstrate that rehabilitation sites are developing diverse invertebrate assemblages comparable to local remnant woodlands in relatively short time frames.

Optimization of Soil-Sludge Mixtures by Compaction for Potential Use in Mine Site Reclamation

Studies have indicated the potential of mixtures of silty soil and sludge produced by active treatment of acid mine drainage for use in covers with capillary barrier effects for mine site reclamation. Very high water contents of sludge in the settling pond could negatively affect the required hydrogeotechnical properties of soil sludge mixtures with high sludge contents. The challenge is then to determine the optimum wet sludge content of soil-sludge mixtures with air entry values (AEV) and/or saturated hydraulic conductivity (ksat) required for use in mine site reclamation covers. This paper presents a method to determine the optimum wet sludge content βopt for obtaining the maximum dry density of compacted soil-sludge mixtures. Two types of soil (S1 and S2) and two types of sludge (A and W) were tested. It was observed that βopt can be determined when the initial water content of the soil used in the mixture is lower than the optimum water content determined from the Proctor curve of the soil alone (10 wt% and 6 wt% for soils S1 and S2, respectively) and that βopt does not change with increasing initial soil water content. Optimum wet sludge contents found were low (≈15 wt% and ≈7 wt% for mixtures containing soils S1 and S2, respectively) for the test conditions, indicting a limited quantity of reusable sludge in the mixtures. For all mixtures, the water content corresponding to βopt was close to the optimum water content of the soil alone. Results of soil water retention and saturated hydraulic conductivity (ksat) tests conducted on selected optimized mixtures indicated that the mixtures based on soils S1 and S2 have air entry values higher than 20 kPa and would be suitable for use in the moisture retention layer of covers with capillary barrier effects, while soil S2 and the derived mixtures exhibited ksat < 10−7 cm/s and would be potential materials for the low permeability layer in low saturated hydraulic conductivity covers.

Hydrogeological Properties of Till Amended with Green Liquor Dregs (GLD): Recycling of an Industrial Residue for Reclamation of Acid Generating Mine Sites

The oxidation of sulfide minerals in mine wastes is a possible threat to the environment as it might have potential to generate acid rock drainage (ARD). A common method to reduce ARD is to apply a dry cover on the mine waste deposit. Considering the massive amounts of mine waste produced in Sweden (104-million-ton in year 2018) there is a great need for suitable dry cover materials. Using non-hazardous industrial residues in the dry cover would be beneficial for both the mining industry and the providing industry as stricter waste management legislation incentivizes them to develop their waste management strategies. The objective of this study was to investigate if an addition of Green Liquor Dregs (GLD), a residue from pulp production, can decrease the hydraulic conductivity and increase the water retention capacity (WRC) of three different tills, with the purpose of improving the performance of a dry cover material on a mine waste deposit. Another objective was to investigate how the hydraulic conductivity and WRC are affected by the contents of fines and clays in the tills. The study concludes that the water retention capacity of the tills improves with GLD addition, however, the hydraulic conductivity did not decrease enough to reach the in Sweden required < 10−8 m/s. Even though, GLD could still successfully be used in the reclamation of mine sites as the high WRC can be seen as the most important factor in deterring acid rock drainage by keeping the sealing layer close to saturation. This study further indicates that there are other factors than the particle size distribution of the materials that controls the hydraulic conductivity of the mixtures, such as initial water content, dry density, and compaction effort.

Post-Mining Multi-Hazard Assessment for Sustainable Development

Today, most mines (coal, iron, and others) in Europe are already closed due to economic, environmental, and societal issues. Therefore, post-mining risk assessment and management remain crucial for mining authorities, policymakers, and planners. In the post-mining period, several hazards are likely to affect the surface areas in the closed mining sites. The impact of closed mines can lead to potentially damaging changes in surface and/or underground water flow, as well as the development of surface instabilities that can affect people or infrastructure, sometimes dangerously. The assessment of the different hazards must consider the interaction between the mining hazards and other risks (natural and technological). Thus, land use planning, particularly the rehabilitation of former mining sites, requires better tools to apprehend the multiplicity of hazards and their constraints. The paper presents a methodology considering the interactions between hazards around closed mines. After recalling the advantages of this multi-hazard analysis, the work consisted of, almost exhaustively, describing the three prominent families of hazards: mining, natural, and technological. Then, the possible interactions between hazards were described according to their nature (trigger or aggravating), their category (technical or regulatory), and their typology (dependent or independent). Finally, an attempt was proposed to evaluate the type and intensity of interactions between hazards. The multi-hazard assessment methodology was applied to a coal mine and showed the complexity and the utility of such a risk assessment analysis to improve risk management in closed mines.

Arbuscular mycorrhizal fungi regulate plant mineral nutrient uptake and partitioning in iron ore tailings undergoing eco-engineered pedogenesis

Excess available K and Fe in Fe-ore tailings with organic matter and water-deficiencies may restrain plant colonization and growth, which hinders the formation of eco-engineered soil from these tailings for sustainable and cost-effective mine site rehabilitation. Arbuscular mycorrhizal (AM) fungi are widely demonstrated to assist plant growth under various unfavorable environments. However, it is still unclear whether AM symbiosis in tailings amended with different types of plant biomass, and under different water conditions could overcome the surplus K and Fe stress for plants in Fe ore tailings, and if so, by what mechanisms. Here, host plants (Sorghum spp. Hybrid cv. Silk) either colonized or non-colonized by the AM fungi (Glomus spp.), were cultivated in Lucerne hay- (C: N ratio of 18, LH) or Sugarcane mulch- (C: N ratio of 78, SM) amended Fe-ore tailings under well-watered (55% water holding capacity (WHC) of tailings) or water-deficient (30% WHC of tailings) conditions. Mycorrhizal colonization, plant growth, and mineral elemental uptake and partitioning were examined. The results indicated that AM fungal colonization improved plant growth in tailings amended with plant biomass under water deficient conditions. AM fungal colonization enhanced plant mineral element uptake, especially P, both in the LH- and SM-amended tailings regardless of water condition. Additionally, AM symbiosis development restrained the translocation of excess elements (i.e., K and Fe) from roots to shoots, thereby relieving their phytotoxicity. AM roles in phosphorus uptake, and excess elemental partitioning were greater in tailings with LH amendment than those with SM amendment. Water deficiency weakened AM fungal colonization and functions in terms of mineral element uptake and partitioning. These findings have highlighted the vital role AM fungi played in regulating plant growth and nutrition status in Fe-ore tailings technosols, providing the basis for involvement of AM fungi in the eco-engineered pedogenesis of iron ore tailings.

Study of certain technical aspects of the rehabilitation of bauxite mining sites operated at the Sangarédi mine (Parawi deposit, Compagnie des Bauxites de Guinée mining concession; CBG)

The fatal consequences of open-cast mining are first and foremost the considerable degradation of the earth's surface. Soil disturbed during mining operations must be rehabilitated in line with the progress of the extraction work, to promote environmental protection. Restored areas contribute to the oxygen balance, rainfall and soil regeneration. The aim of this work is to highlight the development techniques used in areas affected by mining operations. To carry out this research work, we used technical restoration, which consists of rehabilitating disturbed soils with a view to their subsequent use for the needs of the population, and biological restoration, which consists of implementing appropriate measures to protect the environment and allow flora and fauna to flourish. This includes creating a fertile layer after logging, developing nurseries and seedlings, transplanting and protecting wooded areas. For forest and fruit restoration in our study area, we have planned: 395,760 cashew seedlings because of their resistance to unfavorable climatic conditions and 168,375 acacia seedlings for firewood, charcoal, furniture and construction. Mine rehabilitation is a more complex discipline, involving the use of native plants to mimic the natural ecosystem, rather than simple revegetation actions. In general, complete reclamation is impossible, but careful restoration and rehabilitation can create a favorable ecosystem.

Effects of Land Reclamation on Soil Bacterial Community and Potential Functions in Bauxite Mining Area.

Studying the characteristics of microorganisms in mine reclamation sites can provide a scientific reference basis for mine land reclamation. Soils in the plough layer (0-20 cm) of the bauxite mine plots in Pingguo city, Guangxi Zhuang Autonomous Region, China, with different reclamation years were used as the research objects. The community structure of soil bacteria was analyzed with high-throughput sequencing technology. The results show the following: (1) Reclamation significantly increased the contents of soil nutrients (p < 0.05). (2) The relative abundances of Proteobacteria were high (22.90~41.56%) in all plots, and reclamation significantly reduced the relative abundances of Firmicutes (3.42-10.77%) compared to that in the control plot (24.74%) (p < 0.05). The relative abundances of α-proteobacteria generally increased while the reclamation year increased. The relative abundances of α-proteobacteria and γ-proteobacteria showed significant positive correlations with soil carbon, nitrogen, and phosphorus nutrients (p < 0.01). The relative abundance of Acidobacteria Group 6 showed significant positive correlations with soil exchangeable Ca and Mg (p < 0.01). (3) Bacterial co-occurrence network showed more Copresence interactions in all plots (50.81-58.39%). The reclaimed plots had more nodes, higher modularity, and longer characteristic path length than the control plot, and the keystone taxa changed in different plots. (4) The chemoheterotrophy and aerobic chemoheterotrophy were the most abundant functional groups in all plots (35.66-48.26%), while reclamation reduced the relative abundance of fermentation groups (1.75-11.21%). The above findings indicated that reclamation improved soil nutrients, changed the bacterial community structure and potential functions, and accelerated the microbial stabilization of the reclaimed soil.

Soil ammonium (NH4+) toxicity thresholds for restoration grass species

Ionic rare earth mining has resulted in large amounts of bare soils, and revegetation success plays an important role in mine site rehabilitation and environmental management. However, the mining soils still maintain high NH4+ concentrations that inhibit plant growth and NH4+ toxicity thresholds for restoration plants have not been established. Here we investigated the NH4+ toxicological effects and provided toxicity thresholds for grasses (Lolium perenne L. and Medicago sativa L.) commonly used in restoration. The results show that high NH4+ concentration not only reduces the plant biomass and soluble sugars in leaves but also increases the H2O2 and MDA content, and SOD, POD, and GPX activities in roots. The SOD activities and root biomass can be adopted as the most NH4+ sensitive biomarkers. Six ecotoxicological endpoints (root biomass, soluble sugars, proline, H2O2, MDA, and GSH) of ryegrass, eight ecotoxicological endpoints (root biomass, soluble sugars, proline, MDA, SOD, POD, GPX, and GSH) of alfalfa were selected to determine the threshold concentrations. The toxicity thresholds of NH4+ concentrations were proposed as 171.9 (EC5), 207.8 (EC10), 286.6 (EC25), 382.3 (EC50) mg kg−1 for ryegrass and 171.9 (EC5), 193.2 (EC10), 234.7 (EC25), 289.6 (EC50) mg kg−1 for alfalfa. The toxicity thresholds and the relation between plant physiological indicators and NH4+ concentrations can be used to assess the suitability of the investigated plants for ecological restoration strategies.

Effect of spatial variation of spoil material properties on slope displacements under rapid drawndown of pit lakes

In many European countries, lignite or brown coal is used as a fuel source in steam-electric power generation. Upon completion of mining activities, a reclamation plan is imperative to ensure environmental and social prosperity of local areas. Abandoned mine pits are often reclaimed by creating a pit lake. Reclamation of large lignite open pit mine sites may use large amounts of previous overburden materials or “spoils” to create the slopes of the pit lake. Spoils are anthropogenic materials with large spatial variation in properties, hence, considering mean values of shear strength and hydraulic parameters to assess stability and seasonal displacements will not fully simulate actual field conditions. This paper considers the effect of spatial variation on slope stability and ground movements during rapid drawdown events (a critical case) using coupled flow-deformation 2D finite element analyses, incorporating unsaturated soil suctions above the phreatic surface. Effects of heterogeneity and randomness of spoils on the response of the slope are considered through random field modelling and the Monte-Carlo simulation technique. Four lognormally distributed random variables (spoil cohesion, friction angle, void ratio, and permeability coefficient) are examined. The effect of spatial variability of spoils is shown to be important; a significant number of the random field analyses resulted in larger displacements compared to a benchmark deterministic analysis adopting uniform mean parameter values.

Resolving ecosystem complexity in ecological risk assessment for mine site rehabilitation.

Ecological Risk Assessments (ERAs) are important tools for supporting evidence-based decision making. However, most ERA frameworks rarely consider complex ecological feedbacks, which limit their capacity to evaluate risks at community and ecosystem levels of organisation. We used qualitative mathematical modelling to add additional perspectives to previously conducted ERAs for the rehabilitation of the Ranger uranium mine (Northern Territory, Australia) and support an assessment of the cumulative risks from the mine site. Using expert elicitation workshops, separate qualitative models and scenarios were developed for aquatic and terrestrial systems. The models developed in the workshops were used to construct Bayes Nets that predicted whole-of-ecosystem outcomes after components were perturbed. The terrestrial model considered the effect of fire and weeds on established native vegetation that will be important for the successful rehabilitation of Ranger. It predicted that a combined intervention that suppresses both weeds and fire intensity gave similar response predictions as for weed control alone, except for lower levels of certainty to tall grasses and fire intensity in models with immature trees or tall grasses. However, this had ambiguous predictions for short grasses and forbs, and tall grasses in models representing mature vegetation. The aquatic model considered the effects of magnesium (Mg), a key solute in current and predicted mine runoff and groundwater egress, which is known to adversely affect many aquatic species. The aquatic models provided support that attached algae and phytoplankton assemblages are the key trophic base for food webs. It predicted that shifts in phytoplankton abundance arising from increase in Mg to receiving waters, may result in cascading effects through the food-chain. The qualitative modelling approach was flexible and capable of modelling both gradual (i.e. decadal) processes in the mine-site restoration and the comparatively more rapid (seasonal) processes of the aquatic ecosystem. The modelling also provides a useful decision tool for identifying important ecosystem sub-systems for further research efforts.