Stockpiled Soils Research Articles

Migration patterns of heavy metals from solid waste stockpile soils by native plants for ecological restoration in arid and semi-arid regions of Northwest China

Ecological remediation with native plants is the main measure to control the pollution of solid waste in Northwest China. However, the heavy metal transport characteristics of these native plants are still unidentified. This study analyzed the distribution of 16 heavy metals in native plants in the desulfurization gypsum yard (DGY), the gangue yard (GY) and the fly ash yard (FAY). The results showed that the soil contained many heavy metals in high concentrations. For instance, As concentrations were comparable to the global soil background values, whereas Cr and Mn concentrations in the area were 2–3 times greater than the global soil background values. The content of heavy metals in the plant root system increased first, then decreased as the distance from the yard increased. Ni, Pb, and Cd migrated well in Artemisia frigida Willd and Artemisia sieversiana Ehrhart ex Willd, with A. sieversiana showing a particularly strong migration in GY. A. sieversiana, on the other hand, was more successful at migrating Cd at DGY and had a similar capability for Mg migration in all three locations. Festuca rubra L was potentially suitable for planting in GY for Ni removal. In conclusion, the migration patterns of different heavy metals were not alike for plants in the three landfills. The results provided a basis for plant selection for ecological restoration in arid and semi-arid regions.

Stockpiling disrupts the biological integrity of topsoil for ecological restoration

PurposeBiotic and abiotic properties of soils can hinder or facilitate ecological restoration, and management practices that impact edaphic factors can strongly influence plant growth and restoration outcomes. Salvaged topsoil is an invaluable resource for mine-site restoration, and a common practice is topsoil transfer from mined areas to restoration sites. However, direct transfer is often not feasible, necessitating storage in stockpiles. We evaluated the effects of topsoil stockpiling on plant performance across diverse ecosystems impacted by mining throughout Western Australia.MethodsWe conducted a bioassay experiment using a widespread native Acacia species to assess how topsoil storage might impact plant growth, physiology, and nodulation by N-fixing bacteria using soils from native reference vegetation and stockpiled soils from six mine sites across Western Australia.ResultsPlant responses varied across mine sites, but overall plants performed better in soils collected from native vegetation, exhibiting greater biomass, more root nodules, and higher water-use efficiency compared to those grown in stockpiled soils. Soil physiochemistry showed few and minor differences between native soils and stockpiles.ConclusionResults strongly suggest observed differences in plant performance were biotic in nature. This study highlights the negative effects of topsoil storage on the biological integrity of soil across diverse ecosystems, with important implications for mine-site restoration; our results show that topsoil management can strongly influence plant performance, and stockpiled soils are likely inferior to recently disturbed topsoil for restoration purposes. We also use this study to illustrate the utility of bioassays for assessing soil quality for ecological restoration.

How societal expectations, new digital tools, andthe COVID crisis are driving a step-change in human centric remediation.

How societal expectations, new digital tools, andthe COVID crisis are driving a step-change in human centric remediation.

Impact of soil stockpiling on ericoid mycorrhizal colonization and growth of velvetleaf blueberry (Vaccinium myrtilloides) and Labrador tea (Ledum groenlandicum)

Soil stockpiling is a common practice prior to the reclamation of surface mines. In this study, velvetleaf blueberry and Labrador tea plants were grown from seed in fresh soil, stockpiled soil (1 year), and autoclaved stockpiled soil (1 year) obtained from the Canadian boreal forest. After 7 months of growth, the root colonization intensity with ericoid mycorrhizal (ERM) fungi in both plants growing in stockpiled soil was lower compared to plants growing in the fresh soil. The diversity of ERM fungal species in roots also decreased due to soil stockpiling and Pezoloma ericae was absent from the plants growing in stockpiled soil. Changes in the ERM root colonization in plants growing in stockpiled soil were accompanied by decreases in root and shoot dry weights. Leaf chlorophyll, nitrogen, and phosphorus concentrations of velvetleaf blueberry were higher in fresh soil compared to 1‐year stockpiled soil. Plants grown in the autoclaved stockpiled soil became colonized by the thermotolerant ERM fungus Leohumicola verrucosa and showed higher root and shoot biomass compared to the nonautoclaved stockpiled soil. The results point to the importance of ERM fungi for growth of ericaceous plants, even under favorable environmental conditions and adequate fertilization, and suggest that reduced ERM colonization intensity and ERM fungal diversity in roots likely contributed to the negative effects of soil stockpiling on growth of velvetleaf blueberry and Labrador tea.

Microbial community structure and relationship with physicochemical properties of soil stockpiles in selected South African opencast coal mines

ABSTRACT At present, there is no comprehensive soil quality assessment practice for soil stockpiles in the South African coal mining industry. Soil microorganisms and enzymes are suitable indicators for soil quality monitoring. Therefore, this study investigated the microbial community and enzyme (beta-glucosidase and urease) activities in soil stockpiles of opencast coal mines in the coal-rich region of South Africa. Soil stockpiles of three opencast coal mines were sampled at depths of 0–20 cm (‘topsoil’) and >20 cm (‘subsoil’) across three seasons. Beta-glucosidase and urease activities were mostly higher in soil stockpiles than in unmined soils and were significantly influenced (P < 0.05) by the interaction of site and seasonal factors. However, analyses of PCR-denaturing gradient gel electrophoresis (PCR-DGGE) profiles of partial 16S rRNA gene and internally transcribed spacer 2 (ITS2) sequences revealed higher microbial diversity in unmined (reference) soils compared to soil stockpiles across all seasons. Redundancy analysis further revealed that microbial communities of topsoil were not significantly (P > 0.05) influenced by soil properties, whereas microbial communities of subsoils were significantly (P < 0.05) influenced by pH, organic carbon, total nitrogen and phosphorus contents. Furthermore, operational taxonomic units (OTUs) belonging to genera of known phytobeneficial species such as Azomonas, Aureobasidium, Phialocephala, Phoma and Sordariomycetes were detected in these soils. Overall, results suggest that the microbial community structure and diversity observed in stockpiles is impaired (compared to the unmined site), although variations in the microbial community structure of soil stockpiles across seasons are site-specific. The impaired microbial community of stockpiles may have negative implications on soil biological processes driven by microbes; especially those that are critical for nutrient cycling and ecosystem sustainability. More importantly, such alteration in soil biodiversity may impair post-mining land use capability of stockpile soils.

Growth Response of Aspen and Alder to Fresh and Stockpiled Reclamation Soils

Soil stockpiling is a common reclamation practice used in oil sands mining in the boreal forest region of Canada to conserve soil resources; but stockpiling may have detrimental effects on soil quality and plant growth. We examined growth response of trembling aspen (Populus tremuloides Michx.), a fast-growing early successional tree, and green alder (Alnus viridis (Chaix) DC. ssp crispa (Ait.) Turrill), a nitrogen-fixing shrub, to stockpiling and fertilization treatments on two reclamation soils (forest floor mineral mix (FFMM) and peat mineral mix (PMM)). Aspen and alder seeds were planted and their growth monitored for four months in the greenhouse. We found that unfertilized stockpiled FFMM supported significantly higher aspen and alder aboveground biomass than the other fresh and stockpiled soils. Phosphorus and potassium supply rates were highest in stockpiled FFMM and were positively correlated with aboveground plant biomass. There was no significant difference in aspen and alder aboveground biomasses between unfertilized fresh FFMM and PMM soils. Aspen grown in combination with nitrogen-fixing alder did not experience competition or facilitation except on fresh PMM, where aspen height declined. Fertilization increased both aspen and alder growth and eliminated differences in growth between soil types and stockpiling treatments. Our study showed that individual soil properties are more important for revegetation purposes than type of soil or stockpiling treatment.

Topsoil Stockpiling in Restoration: Impact of Storage Time on Plant Growth and Symbiotic Soil Biota

Addressing plant-soil relationships within restoration science may improve success and reduce costs. Here we assess the question of topsoil storage time: how does stockpile age impact plant biomass and soil microbial activity, particularly root symbionts such as rhizobia and arbuscular mycorrhizal fungi (AMF)? Working in Western Australia and in sandy soils, we grew a legume species <i>Acacia saligna</i> (Fabaceae) in one-, two-, three-, five- and ten-year-old stockpile soils under controlled glasshouse conditions. We assessed whether plant biomass, specific root length, and root diameter decreased with stockpile age. Further, we investigated how stockpile age affected the distribution and the number of effective nodules, nodule biomass and AMF colonization in roots. These above and belowground traits were chosen because they reflect the <i>A. saligna</i> response to growing in soils stockpiled for 1–10 years. We hypothesised that in older stockpiles there would be fewer rhizobial and AMF propagules which would constrain <i>A. saligna</i> growth, whereas in younger stockpiles there would be more rhizobial and AMF propagules, and <i>A. saligna</i> growth would be facilitated via these root symbionts. Using generalized linear mixed models, we found that total plant biomass was the lowest but AMF percent colonization was the highest when <i>A. saligna</i> was grown in ten-year-old soils, suggesting that AMF spores and hyphae are present in old stockpiles. Our results demonstrate that AMF communities may be initially disrupted by soil disturbance and storage, and then begin to re-establish between 5–10 years after stockpiling. However, other soil microbial communities, such as fungal pathogens that were not assessed in this study may have been responsible for decreased <i>A. saligna</i> biomass in older soils. Further research, particularly on other soil microbial communities, is needed to understand restoration success using stockpiled soil older than ten years.

The Impact of the Quality of Coal Mine Stockpile Soils on Sustainable Vegetation Growth and Productivity

Stockpiled soils are excavated from the ground during mining activities, and piled on the surface of the soil for rehabilitation purposes. These soils are often characterized by low organic matter (SOM) content, low fertility, and poor physical, chemical, and biological properties, limiting their capability for sustainable vegetation growth. The aim of the study was to evaluate the impact of stockpile soils of differing depth and quality on vegetation growth and productivity. Soils were collected at three different depths (surface, mid, and deep) as well as mixed (equal proportion of surface, mid and deep) from two stockpiles (named Stockpile 1: aged 10 and Stockpile 2: 20 years) at the coal mine near Witbank in the Mpumalanga province of South Africa. Soils were amended with different organic and inorganic fertilizer. A 2 × 4 × 5 factorial experiment in a completely randomized blocked design with four replications was established under greenhouse conditions. A grass species (Digiteria eriantha) was planted in the pots with unamended and amended soils under greenhouse conditions at 26–28 °C during the day and 16.5–18.5 °C at night. Mean values of plant height, plant cover, total fresh biomass (roots, stems and leaves), and total dry biomass were found to be higher in Stockpile 1 than in Stockpile 2 soils. Plants grown on soils with no amendments had lower mean values for major plant parameters studied. Soil amended with poultry manure and lime was found to have higher growth rate compared with soils with other soil amendments. Mixed soils had better vegetation growth than soil from other depths. Stockpiled soils in the study area cannot support vegetation growth without being amended, as evidenced by low grass growth and productivity in this study.

Soil thermal regime after fuel spill cleanup response in a continuous permafrost zone

ABSTRACTReleases of diesel fuel in the Arctic tundra are a common occurrence. Response to such releases in this region typically involves excavating the contaminated soil and backfilling the excavation with clean material. Owing to the lack of clean stockpiled native soils, coarse-grained soil (aggregate) used for the construction of roads and foundation pads may be the only backfill material available. Backfilling the excavated zone with soil that has different characteristics than the surrounding native soil, combined with the removal of natural vegetation, may drastically change the maximum thaw depth reached during the thawing season, altering the underlying permafrost condition. At the extreme, such measures in areas of ground ice can result in the creation of thermokarsting. We measured maximum thaw depths in aggregate backfill at a diesel spill site located in northwestern Alaska. Using an analytic solution, we investigated the reduction in maximum thaw depth by placing a relatively thin layer (0.5 m) of fine-grained native soil over the aggregate backfill. Such a practice reduces the maximum thaw depth by as much as 1.4 m over backfilling with aggregate only.

Risk based land management requires focus beyond the target contaminants—A case study involving weathered hydrocarbon contaminated soils

Irrespective of the nature of contamination, the use of total contaminant loading as a measure of risk together with conservative policy guidance is proving major stumbling block towards remediation of contaminated sites. The objective of this study was to investigate the use of risk based approach to manage contaminated sites at field scale. This study recognizes the presence of weathered hydrocarbon compounds in long-term total petroleum hydrocarbon (TPH) contaminated soils and that such compounds may not pose risk to local receptors. A multispecies ecotoxicological assessment was used to determine the potential risk from weathered hydrocarbons to the surrounding environment. The ecotoxicity of soil residual TPHs was evaluated using earthworm, water-flea, two native and two non-native Australian plants, and soil microbial activity. Plant germination was 100% in all soils but post germination, seedlings except Ryegrass failed to establish. Earthworm toxicity studies found that there was a negative impact on earthworm reproduction and mortality. Further investigation of the poor plant growth and earthworm mortality revealed that it was due to the elevated salinity that developed due to surface evaporation of the saturated calcium sulphate and not residual soil TPHs. Toxicity assessment of the soil leachate on the aquatic environment showed no effect on the survival of water-flea even though the TPH concentrations in the first year leachate were as high as 1.6 mg TPH L−1. The study concluded that the residual TPHs in soils had little impact on a range of environmental receptors. Assessment of the residual TPH ecotoxicity was complicated by the elevated salinity of stockpile soils which impacted on the earthworm and phytotoxicity assessments. Therefore results of this study suggest that it is paramount to focus beyond target contaminants while implementing risk-based management approach. Indicators for risk based assessment are considered critical for regulatory decision making. The results of this study provide a valuable input in to the risk based management of contaminated sites.

Drastic Disturbance of Salt-Affected Soils in a Semi-Arid Cool Desert Shrubland

Disturbing soils in arid regions can mix subsurface materials with surface soils salvaged for reclamation. Pre-disturbance assessment of soils can minimize impacts of disturbance, and better understanding of drastic disturbance in arid soils will improve reclamation success. Reclaimed well pads have undergone stockpiled soil respreading, tillage, and seeding after drilling is complete. Soil texture and chemical properties were analyzed at 0–15 cm depth in saline and sodic soils from eight paired undisturbed and recently reclaimed sites in the Great Divide Basin of Wyoming. Soil organic matter and structural properties were analyzed in additional samples from two of the paired sites (one sodic, one saline-sodic). Paired difference analysis across the eight well pads indicated that disturbed/reclaimed soils had higher electrical conductivity (EC) than undisturbed soils (12.2 and 3.0 dS m−1, respectively) and higher sodium adsorption ratios (SAR) (26.1 and 1.3, respectively). Analysis of variance of soil organic C (SOC), total N, and soil structural properties indicate that disturbed soils had nearly one-third less total N and two-thirds less SOC than undisturbed soils, and over 65 times more >9.5 mm dry aggregates by weight, representing predominance of large clods in disturbed soils on both sites. Disturbed soils contained significantly smaller proportions of smaller dry aggregate fractions (<53 µm, 53–250 µm, and 250 µm–1 mm) than undisturbed soils, and saturated hydraulic conductivity (Ksat) was about 25% of that in undisturbed soils. Disturbed soils exhibited lower organic materials, higher salt contents, altered soil structure, and low potential for eventually supporting successful native plant communities.

Advanced mine restoration protocols facilitate early recovery of soil microbial biomass, activity and functional diversity

Many ecosystem restoration programmes can take over 15 years to achieve ecosystem functioning comparable to that of an unmodified ecosystem, therefore a reliable shorter-term method of assessing and monitoring ecosystem recovery is needed to ensure that recovery is following an appropriate trajectory. Soil microbes respond to environmental change relatively quickly, and shifts in microbial communities can reflect the current status of their environment. As well as potentially acting as ‘indicator communities’, microbes play an integral role in restoring ecosystem functions. On an active opencast mine on New Zealand's West Coast, three main restoration methods are used, differing in cost and restoration effort. They range from most expensive (1) vegetation direct transfer (VDT), to (2) biosolids-amended stockpiles that are spread and replanted, and (3) untreated stockpiles that are spread and replanted. We assessed the impacts of these methods on soil microbial communities by measuring microbial biomass, dehydrogenase activity, community level physiological profile (CLPP) and functional diversity as measured by carbon substrate utilisation, where restored sites were 5 years old or less. These measures were compared to an unmodified reference ecosystem in the same location. Microbial activity and biomass were highest in pristine habitats, followed by VDT and biosolids-amended soils, then untreated stockpile soil. When compared to all other treatments untreated stockpiled soils had significantly different CLPPs and significantly reduced microbial biomass and activity; microbial biomass was an order of magnitude lower than in pristine soils. Functional diversity and richness did not differ between pristine, VDT and biosolids-amended soils, but were higher than in untreated stockpiled soils. CLPPs did not differ between pristine habitat soil and VDT soil but biosolids-amended and untreated stockpiled soils were significantly different to pristine soil. This study has shown that soil microbial communities are a valuable tool to assess restoration progress, and that ecosystem restoration can begin in a relatively short time following investment in appropriate restoration strategy, ultimately benefiting recolonisation by plants and animals.

Accumulation and composition of total organic carbon in reclaimed coal mine lands

AbstractReclaimed coal mine lands have the potential to sequester atmospheric carbon (C); however, limited information exists for the western USA coalfields. This study was carried out on two chronosequences (BA‐C3 grasses and DJ‐shrubs) of reclaimed sites at two surface coal mines to determine the effects of vegetation, soil texture, and lignin content on soil total organic carbon (TOC) accumulations. In the BA chronosequence, TOC increased over 26 years at an average rate of 0·52 Mg C ha−1 yr−1 in the 0–30 cm depth and was significantly correlated with clay content. Comparison between &lt; 1 and 16‐year‐old stockpile soils indicated TOC content did not differ significantly. In the DJ chronosequence, TOC content in the 0–30 cm depth declined from 31·3 Mg ha−1 in 5‐year‐old soils to 23·4 Mg ha−1 in 16‐year‐old soils. The C:N ratios suggested that some (up to 2·0 per cent) of the TOC was potentially derived from coal particles in these reclaimed soils. Soil total N (TN) contents followed a similar trend as TOC with TOC and TN concentrations strongly correlated. Lignin contents in TOC of all reclaimed soils and topsoil stockpiles (TSs) were higher than that of nearby undisturbed soils, indicating the recalcitrant nature of TOC in reclaimed soils and/or possibly the slow recovery of lignin degrading organism. Results indicated that TOC accumulations in DJ were largely controlled by its composition, particular lignin content. In BA sites TOC accumulation was strongly influenced by both clay and lignin contents. Copyright © 2008 John Wiley &amp; Sons, Ltd.

English

Soil organic matter (OM) is drastically reduced by various processes (erosion, leaching, decomposition, dilution through soil horizon mixing etc.) typically associated with topsoil salvage prior to surface mining activities. Of these processes, loss of physical protection of OM through the breaking up of soil aggregation can result in up to 65% of soil carbon (C) reductions. Objectives of this research were to monitor soil aggregate size distribution and associated C throughout short-term stockpiling and subsequent utilization of topsoil for reclamation. Soil samples were collected from the top 5 cm of a stockpile over a 3 year period (<1, 1.5, 3 yrs) and an adjacent undisturbed, native site. Surface stockpile soils were then tracked to a temporary location following stockpile removal and sampled again. Samples were analyzed for aggregate size distribution, fractions, associated C, and OM turnover with 13 C natural abundance. Macroaggregation increased and microaggregation decreased after 3 yrs of storage, indicating recovery of aggregation in 3 yrs. Following the second removal, macroaggregate proportions decreased and silt and clay fractions were greater than that observed in the native site soils. The second disturbance resulted in greater destruction of aggregate structure than the initial disturbance during topsoil salvage. Carbon increased significantly between <1 and 1.5 yrs in both aggregate size classes. Macro- and microaggregate light fraction (LF) C decreased with storage time as this material was available for utilization by microbes. Aggregate δ 13 C values indicated up to 65% new C associated with aggregate structure. Topsoil storage was beneficial for aggregation and associated C in the surface layers only where plant roots and microbial communities are active; however, the second movement of the topsoil resulted in loss of soil aggregation without impact to soil C.

Microbiology of soils at opencast coal sites. I. Short‐and long‐term transformations in stockpiled soils

SUMMARYThe microbiology of soils subjected to stripping and stockpiling at opencast mine sites was investigated using a combination of and biomass fumigation plate‐count techniques. Mounds varied in age from a few weeks to 11 years, and soils included both mineral and organic variants. Results showed that after an initial stimulation of bacteria, microbial populations declined in stockpiles. Numbers of viable fungal propagules, and to a lesser extent actinomycetes, declined with depth in mounds, particularly below about 1 m, and this trend was accentuated with increased time of storage. However, stockpiled soils were highly variable in terms of microbiological status and displayed considerable lateral as well as vertical heterogeneity.

Determination of the activity of soil microbial populations in stored and restored soils at opencast coal sites

Soils at opencast coal mine sites which had been stockpiled in storage mounds, and soils which were taken from land that had subsequently been restored, were subjected to tests aimed at assessing the activity of indigenous microbial populations. Within stockpiles. the total biomass (measured as total bacteria and fungal hyphae) was variable, but often similar to that of unburied soil: however, most bacteria appeared to be non-viable (in that the proportion able to form colonies on solid media declined significantly within the mound), and a high percentage of surviving bacteria were capable of forming endospores. Vital fungal biomass. measured by PDA staining, was also low in buried soils compared to surface soil. It was concluded that much of the biomass in stockpiled soils was dead and that much of the surviving microflora existed in inactive forms. On restoration, platable soil bacteria increased dramatically and incidence of endospore-formers decreased, particularly in the early stages. The pattern was that of a typical flush of decomposition and tended to subside with time. Modifications to techniques used to evaluate total bacteria (by SEM) and vital fungal hyphae are described.

Acacias respond to additions of phosphorus and to inoculation with VA mycorrhizal fungi in soils stockpiled during mineral sand mining

Three pot experiments were conducted to test the hypothesis that the growth ofAcacia spp. in stockpiled soil from two mineral sand mines, could be increased by the addition of phosphorus (P) or inoculation with VA mycorrhizal fungi. In soils from North Stradbroke Island, the dry weight of shoots ofAcacia concurrens was increased by P and by VA mycorrhizal fungi in tailings sand, while in less adsorptive topsoil dry weight was only increased at low levels of applied P. WhenA. concurrens was grown in a layer of topsoil placed over tailings sand, shoot dry weight increased, in response to inoculation with VA mycorrhizal fungi banded between the soil layers.

Effect of topsoil storage on microbial activity, primary production and decomposition potential

The effects of disturbing (cultivating) and stockpiling prairie grassland topsoil on microbial activity, microbial biomass C, plant production and decomposition potentials were studied by measuring CO2 efflux from unamended and glucose amended soil in the laboratory and by conducting a pot and litter bag study in the greenhouse. Stockpiling appeared to have very little effect on soil respiratory activity, but did reduce the microbial biomass C levels. Throughout the 3 year study the microbial biomass C in the surface soil of the stockpile was less than that in the undisturbed soil, while the biomass C in soil at the bottom of the stockpile was at no time significantly different from that in the undisturbed soil. The reduction in microbial biomass C in the surface soil immediately after stockpiling was attributed to a decrease in the soil organic C levels caused by a slight dilution of the topsoil with subsurface mineral soil, and the exposure of the stockpile surface to extreme environmental conditions. Soils from all depths of the stockpile responded more slowly to the addition of glucose than soil from the undisturbed and cultivated treatments even when no differences in biomass were detected between the undisturbed and stockpiled soils. It is postulated that the rapidity with which the soil microbial biomass responds to glucose additions may be a sensitive indicator of stress on the soil biological components. The reduction in biomass after storage for 1 year had no adverse effects on the decomposition or primary production potential of the stored soil. Rather, shoot production by fall rye was stimulated in the stored topsoil, presumably a result of better N nutrition.