Mine Site Rehabilitation Research Articles

Vulnerability of fish and macroinvertebrates to key threats in streams of the Kakadu region, northern Australia: assemblage dynamics, existing assessments and knowledge needs

By 2100, it is predicted that streams in the Kakadu region in Northern Australia will be transforming in their coastal floodplains to saline environments because of sea-level rise. Potential impacts need to be assessed, together with existing threats, to manage future change. The fish and macroinvertebrate assemblages of the streams in the region are well researched and were used as indicators to assess centennial-scale changes to freshwaters. Spatial and temporal patterns in assemblage dynamics were described using data from different habitat types, and used as a framework to review current knowledge and assemblage vulnerability for likely conditions ≥100 years from present-day. Twenty threats within three broad classes were identified (climate change, invasive species, decommissioning and rehabilitation of Ranger uranium mine). Seven threatening processes were ranked as high risk to catchment-scale distributions of fish and macroinvertebrate taxa, with six being associated with climate change and one with mine-site rehabilitation. Habitat connectivities and dependencies were identified as key ecological processes for both groups, with saltwater intrusion to coastal floodplains being identified as the major process that will alter assemblage dynamics and system energy flow. Risks posed by climate change highlighted priority research and monitoring needs for management and protection of upland freshwater-refuge habitats.

Development and testing of a model for simulating weathering and trace elements release from fixated scrubber sludge utilized in abandoned coal mine reclamation site

In this paper we present the first approximation to a fully coupled model for simulating chemical reactions between engineered coal combustion byproducts (specifically fixed scrubber sludge-FSS) and ambient groundwater. If FSS is placed at a mine site as a hydrologic barrier over pyritic refuse, it would interact with acidic mine water at the bottom and soil water at the top of the FSS. A coupled reactive transport model was developed for simulating reactions at the exposed edges of the FSS over long time frames. In our modeling, emphasis was placed on the release and fate of toxic trace elements such as arsenic, boron, barium, and zinc, which are commonly present in FSS. The parameters associated with dissolution of trace element hosts were calibrated and optimized using data from column leachate experiments on core samples extracted from a reclaimed abandoned mine land site in Indiana. In an effort to evaluate the leaching potential of these trace elements, reactive transport simulations were conducted and compared with historical chemistry data. The model successfully reproduced many characteristics observed in the field, such as initial rises in the concentrations of arsenic, boron, and zinc, following by continuous decline toward steady state by the end of simulation. Also, simulation results indicated that the weathering rate was slightly higher at the top of the FSS where it is in contact with ambient soil water than at the bottom of the FSS. While the preliminary modeling results are promising, comparisons between model calculations and historical data point to the fact that there must be other sources or mechanisms that accommodate rapid releasing of trace elements. Further model development will require explicit inclusion of mechanisms for sorption/desorption of the potentially toxic elements.

Flood hazard assessment and heavy metal distributions around Um Gheig mine area, Eastern Desert, Egypt

This study focuses on wadi Um Gheig and its associated Pb-Zn mine to quantify the possible dispersion pathways of heavy metals to the surrounding environment. The morphometric drainage system parameters were specified by ArcGIS 9.3. A total of 21 samples were collected and analyzed using XRF, XRD, ICP-OES and SEM. Different enrichment indices were applied to specify the degree and source of contaminations in the area upon transport mainly by flooding events. The wadi Um Gheig basin is characterized by dendritic to sub-dendritic drainage pattern with a moderate degree of hazardousness. Five groups of metal sources were identified by chemical and mineralogical patterns. Group I reflects the anthropogenic impact from the mine site by Pb, Zn, Cd, Ba, Sr, Mo, Sn, W, U, As, S, Cl, part of Mn and Fe, as well as from host rock minerals namely gypsum/anhydrite, calcite and dolomite. Group II covers the lithological background of the drainage system with schists, source of Cu, Co, Ni and Cr, part of Ti, and Fe, and granitoids represented by REE, Y, Nb, and Ta, and finally quartz from sands and sandstone acting as a dilutant. Group III comprises moderate to strong enrichment of heavy minerals from Group I and II. Moderate groundwater recharge promotes metal dissolution from the mine and continuous evaporation causes a slight enrichment due to capillary transport downstream (Group IV). Finally the sea water influence (Group V) enhances dilution of heavy metal carriers and enrichment due to efflorescence. The contamination factor, enrichment factor and the geoaccumulation index show a very strong contamination degree close to the mine site by Cd, Pb and Zn. Without suitable mine site rehabilitation strategies the Pb-Zn wastes along the Red Sea coast will suffer severe erosion, transport and contribute to the contamination of the sea environment.

Assessment of Photovoltaic Potentials at Abandoned Mine Reclamation Sites in Korea using Renewable Energy Resource Maps

Assessment of Photovoltaic Potentials at Abandoned Mine Reclamation Sites in Korea using Renewable Energy Resource Maps

A standard for design life and durability for engineered mine wastes structures

Within Australia, and arguably more widely, there is a dearth of mine site rehabilitation that has been validated as successful against agreed objectives and targets. One reason for this is the absence of accepted design life and durability standards, applied during the planning and design of major mine wastes landforms such as tailings storage facilities and waste rock dumps, against which performance can be assessed. The themes of design life and durability have been applied in other engineering disciplines such as construction, manufacturing, and transport infrastructure. Therefore, the template exists; albeit its application to mine wastes landforms is more complex, given the uniqueness of each mine site and the materials available for landform construction. Given the poor rehabilitation performance of the industry to date, an increasingly informed and sceptical public may no longer accept assurances that structures will be risk free for periods of 1000 years or more. In view of this, the industry and the regulator must present realistic expectations and be clear about, and have mechanisms in place to manage, residual risks. This paper aims to address this question and provides a framework around which standards that account for different levels of risk can be developed for design life and durability for engineered mine wastes structures.

Complexities with extractive industries regulation on the African continent: What has ‘best practice’ legislation delivered in South Africa?

The legal framework for mine closure and rehabilitation of new and former mine sites in South Africa, including legacy abandoned sites, is comprehensive. This paper discusses legislative provisions for mine site rehabilitation and closure in South Africa with reference to established international expectations. Overall, while the South African legislative framework for mine closure and rehabilitation generally conforms with international expectations for best practice, the system is extremely complex and unwieldy. Many individual laws, regulations, and guidelines and their corresponding ministries applicable to mine closure planning and management in South Africa has created a complicated inter-connected raft of provisions and expectations. It is an open question whether the most recent amendments (December 2014), have untangled or rather added to the complexities. This historical complexity along with identified governance capacity constraints (financial, technical and experience based) likely explains why implementation of the legislative framework has fallen short of mine closure expectations and mandates. As South Africa is a jurisdiction on the African continent with much experience in mining, there are many lessons that are applicable to emerging countries in the region who wish to attract the benefits of the extractives industries and minimize their potential negative consequences.

Early landscape evolution — A field and modelling assessment for a post-mining landform

Data from field plots describing how new surfaces evolve in the first few years post-construction are scarce in the literature. Here we examine sediment output from four similar 30m by 30m plots on a rehabilitated mine site over a six year period. Field measurements from the trial plots found that there is an initial high pulse of sediment over the first three years which rapidly reduces to rates similar to that expected for a natural or undisturbed surface. At 6years the sediment output is equivalent to that expected from the surrounding undisturbed landscape. This plot data was compared to predictions from a calibrated landscape evolution model. The landscape evolution model used two sets of parameters, one derived from bare waste rock and one derived from an older vegetated surface. The simulations using bare waste parameters produced sediment output that matched the plot data in the first few years while the vegetated parameters produced sediment output which compared well with the field plot data at times >3years. The results demonstrate that when correctly calibrated the landscape evolution model is able to reliably predict sediment output from these field plots. These results suggest that there is the potential to employ the bare waste rock dump parameters for the first 3–4years then switch to vegetated parameters for the longer term modelling. Both the field plots and landscape evolution model simulations displayed considerable annual variability in total load. This variability is the result of different surface structure from imposed surface roughness (ripping by a bulldozer) and their unique topographic structure. Both initial DEM and model parameters have a large influence on predicted sediment load. The results here support the reliability of the model at the sub-metre grid scale.

Mobility of arsenic and environmentally significant elements in mine tailings following liming

ABSTRACTRemediation of a legacy tin-tailings site in northeast Tasmania, Australia was carried out by statutory authorities. This study evaluated the fate of As and other deleterious trace metals Cd, Cu, Fe and Zn (among others) following the application of lime and fertiliser. Arsenic concentrations in the tailings ranged from 86 mg/kg to 0.26 wt%. Surface application of lime resulted in a 100-fold reduction in dissolved As concentrations in on-site surface waters; from an average of 196 µg/L prior to lime addition, to between 2.0 and 7.4 µg/L post-amendment. The concentration of other deleterious elements, however, varied between dry and wet cycles. The concentrations of Cd, Cu and Zn in surface waters were high and similar to pre-remediation levels during dry conditions (0.4, 13.5 and 6.1 mg/L, respectively), and only below freshwater ecosystem protection values during wet conditions. Bioaccumulation of Cd was observed in the naturally occurring coloniser, Juncus pallidus, with 4–5 times more Cd in the above-ground biomass relative to the tailings. Ferric arsenate (scorodite) was the dominant source of As identified in the tailings mineralogy. Hydrous ferric oxides and Fe-bearing cassiterite were also identified as hosting As. The pH increase in the surface lime-amended tailings was inferred to result in precipitation of observed hydrous ferric oxides, hematite and goethite, providing high-surface area for adsorption of arsenate onto positively charged surfaces. Jarosite was observed in both the surface lime-amended and subsurface non-amended tailings and suggests a continued supply of acidity to the pore waters despite the application of lime. Leaching experiments showed that As was more mobile in the lime-dosed tailings than in subsurface non-amended tailings, likely owing to desorption in alkaline pH conditions. By contrast, the mobility of Cd, Cu and Zn in the surface lime-amended tailings was reduced by at least two orders of magnitude compared with subsurface non-amended tailings. Evaluation of the applied rehabilitation strategy highlights the limits of a single chemical remediation approach to a polymetallic (including metalloids) waste with complex mineralogy and large seasonal fluctuations. Rehabilitation of metalliferous mine sites requires a complete understanding of all environmentally significant elements and their pathways into local receptors.

Selective coal mine overburden treatment with topsoil and compost to optimise pasture or native vegetation establishment

Overburden at a coal mine in the Hunter Valley, New South Wales, was stored in a flat-topped artificial mound with 14-degree side slopes. Topsoil was scarce, dispersive and readily eroded. A split-plot factorial experiment applied an enhanced municipal solid waste compost at 0, 60 or 100 t ha−1 to untreated overburden or to overburden covered with 0.1 m of topsoil. Two seeding treatments, of trees and shrubs or of pasture species, were applied to two 0.5-ha replicates of each surface treatment. Substrate physical and chemical properties and vegetation attributes were assessed 2.5 years later. Compost application to both topsoil and overburden significantly increased total N, P, Cu and Zn, soluble K, Ca and Mg, and significantly reduced soluble Na and pH. Mean tree density, size and total canopy cover were significantly greater with compost applied at 60 t ha−1 to overburden than with all other treatments, especially those on topsoil where tree growth was inhibited by undesired species. Compost application to overburden and topsoil at 100 t ha−1 significantly increased biomass of desired pasture species and significantly reduced undesired species cover compared with unamended topsoil and the extent of bare ground compared with unamended overburden. Successful development of woody species on overburden and pastures on both overburden and topsoil treated with compost provides opportunities for new combinations of landscape design, surface preparation and plant species introductions to increase the stability of final landforms, the effectiveness of resource use, and the delivery of commercial and biodiversity benefits from mine site rehabilitation.

Effect of cementitious amendment on the hydrogeological behavior of a surface paste tailings’ disposal

Abstract Surface paste disposal (SPD) can be considered as an effective alternative technique for mine waste management. The technique consists of first removing upstream water (by thickening and/or filtration) from tailings, then depositing them at the surface in a paste-like state. These techniques allow for the recycling of water, limit risks related to the failure of dikes, and favor progressive mine site rehabilitation. However, there are, thus far, only a few studies on the environmental behavior of tailings deposited using the SPD technique. To evaluate the hydrogeological and geochemical behaviors of a sulphidic tailings’ deposit simulating the SPD method, a laboratory study was performed using a physical model. Paste tailings were prepared and deposited inside the physical model in nine layers. In the first stage, only the first two bottom layers were amended with cement (2 % w/w of PC10 Portland cement). The physical model was then subjected to wetting and drying cycles, and the water collected after each flush was analysed for chemistry and its volume was measured. At the end of the 27th cycle, a tenth layer of cemented tailings was deposited on the top of the tailings’ stack. Testing was performed for 34 cycles, and then, the model was dismantled and the collected samples were analysed through a multidisciplinary fine characterisation. The results of this investigation showed that the volume of collected water at the bottom of the physical model varied over the test’s duration. This could be due to seasonal variations in the temperature and moisture of the laboratory. The cemented layer deposited on the top of the physical model appears to play the role of protecting against underlying layers from evaporation. Finally, diffuse oxidation that progressed along the preferential pathway was observed.

Study on Eco-friendly Use of Coal Ash at Mine Reclamation Sites

Study on Eco-friendly Use of Coal Ash at Mine Reclamation Sites

Influence of freeze–thaw cycles on the performance of covers with capillary barrier effects made of crushed rock–bentonite mixtures to control oxygen migration

In temperate climates, covers with capillary barrier effects (CCBEs) are being used successfully to prevent oxygen fluxes from reaching covered potentially acid mine drainage (AMD) generating mine tailings. In northern climates, the more attractive option for mine site reclamation is insulation covers, which are designed to keep reactive materials frozen. This article suggests that CCBEs can simultaneously control oxygen migration and mine waste temperature to inhibit AMD generation. However, in northern conditions, where natural fine-grained materials needed for the CCBE moisture-retaining layer are not always available, soil–bentonite mixtures could be used instead. This laboratory study assessed — using instrumented columns — the effects of freeze–thaw cycles on the performance of three CCBEs made with crushed rock–bentonite mixtures. An oxygen diffusion test was developed to determine the effective diffusion coefficient of oxygen (De) and its sensitivity to freeze–thaw cycles. The results show good initial performance for the saturated CCBEs. However, the tested CCBEs are significantly affected by freeze–thaw cycles and have limited oxygen-limiting ability.

Preliminary geotechnical assessment of the potential use of mixtures of soil and acid mine drainage neutralization sludge as materials for the moisture retention layer of covers with capillary barrier effects

Lime treatment of acid mine drainage (AMD) generates sludge that is commonly stored in ponds for dewatering. The use of soil-aged sludge-based mixtures for mine site rehabilitation can allow the emptying of existing basins, thus extending their storage capacity, reducing the volume of the borrow soil pit required for mine site rehabilitation, and consequently reducing the mine footprint. The authors investigated the geotechnical properties of silty soil–sludge mixtures (SSMs) as possible components of covers with capillary barrier effects (CCBEs) to prevent AMD generation from mine waste. SSMs with β values of 10%, 15%, 20%, and 25% sludge (β = wet sludge mass / wet soil mass) were studied. Two water contents were considered for each of the mixture components: 175% and 200% for the sludge and 7.5% and 12.5% for the soil. Results indicate that saturated hydraulic conductivity (ksat) values were in the range of 10−5cm/s for the soil and SSMs at void ratios ranging from 0.28 to 0.53, with values decreasing slightly when β was increased from 0% to 25%. The air-entry value (AEV) increased from 20 kPa for the soil alone to 35 kPa for the SSM with β = 25%. These values of ksatand AEV are comparable to those of materials used in the moisture retention layers of existing efficient CCBEs. However, the volumetric shrinkage increased from about 2% for the soil alone to values ranging between 24% and 32% for the SSM with β = 25%, depending on the initial water contents of the components. Tools are provided to estimate to which extent the use of sludge in SSMs can reduce the volume of borrow natural soil required for a moisture retention layer of a CCBE.

Actinorhizal Alder Phytostabilization Alters Microbial Community Dynamics in Gold Mine Waste Rock from Northern Quebec: A Greenhouse Study.

Phytotechnologies are rapidly replacing conventional ex-situ remediation techniques as they have the added benefit of restoring aesthetic value, important in the reclamation of mine sites. Alders are pioneer species that can tolerate and proliferate in nutrient-poor, contaminated environments, largely due to symbiotic root associations with the N2-fixing bacteria, Frankia and ectomycorrhizal (ECM) fungi. In this study, we investigated the growth of two Frankia-inoculated (actinorhizal) alder species, A. crispa and A. glutinosa, in gold mine waste rock from northern Quebec. Alder species had similar survival rates and positively impacted soil quality and physico-chemical properties in similar ways, restoring soil pH to neutrality and reducing extractable metals up to two-fold, while not hyperaccumulating them into above-ground plant biomass. A. glutinosa outperformed A. crispa in terms of growth, as estimated by the seedling volume index (SVI), and root length. Pyrosequencing of the bacterial 16S rRNA gene for bacteria and the ribosomal internal transcribed spacer (ITS) region for fungi provided a comprehensive, direct characterization of microbial communities in gold mine waste rock and fine tailings. Plant- and treatment-specific shifts in soil microbial community compositions were observed in planted mine residues. Shannon diversity and the abundance of microbes involved in key ecosystem processes such as contaminant degradation (Sphingomonas, Sphingobium and Pseudomonas), metal sequestration (Brevundimonas and Caulobacter) and N2-fixation (Azotobacter, Mesorhizobium, Rhizobium and Pseudomonas) increased over time, i.e., as plants established in mine waste rock. Acetate mineralization and most probable number (MPN) assays showed that revegetation positively stimulated both bulk and rhizosphere communities, increasing microbial density (biomass increase of 2 orders of magnitude) and mineralization (five-fold). Genomic techniques proved useful in investigating tripartite (plant-bacteria-fungi) interactions during phytostabilization, contributing to our knowledge in this field of study.

Genomics to assist mine reclamation: a review

Mine reclamation succeeds when healthy, self‐sustaining ecosystems develop on previously mined lands. Regulations require reclamation of ecosystem services; however, there are few specified targets, and those that are presented are vague. Sequencing genomic DNA and transcribed RNA from environmental samples may provide critical supportive information for attempts to recreate ecosystem functions from the ground up on disturbed lands. In this review, we highlight the use of genomics to meet mine closure goals, to enhance ecosystem development, and to optimize ecosystem services inherent in self‐sustaining reclaimed ecosystems. We address the development of environmental genomics—sequencing and analysis of environmentally derived DNA—to characterize microbial communities on mine sites. We then provide four areas where genomics has proven instrumental for informing management and assisting in reclamation of mine sites in the form of bioreactors, passive treatment systems, novel gene discovery, and DNA barcoding. Finally, we describe how recently developed techniques have transferable value to mine reclamation and provide evidence for future applications of genomics and the necessary steps to integrate these data into comprehensive management of mined sites.

Valorization of Phosphate Waste Rocks and Sludge from the Moroccan Phosphate Mines: Challenges and Perspectives

Sedimentary phosphate mines produce millions of tons of waste rocks during their open-pit mining. In addition, during ore phosphate beneficiation, fluorapatite is separated from associated gangue minerals by a combination of successive mineral processing steps that involve crushing / screening, washing, and flotation. These operations generate large volume of tailings (called phosphate sludge) that are deposited in large surface ponds and waste rocks stockpiled within the mining site. The potential reuse of these phosphate mine by-products (waste rocks and sludge) has been investigated in the last 10 years.The first investigated option consisted in using the alkaline waste rocks (APW) to control the acid mine drainage (AMD). Indeed, these alkaline mine wastes contain significant quantities of calcite (46 wt%) and dolomite (16 wt%) that help in neutralizing the acidity generated by the wastes from the closed Kettara mine, located near Marrakech, Morocco. The addition of 15 wt% APW to the coarse Kettara tailings produced leachates with significantly lower acidity and metal loads in comparison to the un-amended control sample. Secondly, the efficiency of APW was assessed in the laboratory as an alternative alkaline material for passive AMD water treatment. In semi-arid climate, the oxic passive treatment has been proven to be the most suitable. The pH of the water and its quality were significantly improved. As a third option, the hydrogeotechnical characterization of original and screened phosphate limestone waste rocks as well as the phosphate sludge showed their suitability for use as a component of store-and-release (SR) covers for industrial mine site reclamation. Lab tests (columns) and field tests (instrumented columns and experimental cells) showed that water infiltration can be controlled, even for extreme rainfall events (150mm/day), by 1 m thick of a SR cover made with APW. Further research is currently being investigated around the recycling and valorization of phosphate sludge from phosphate mines as ceramics. Furthermore, the overburden of the phosphates sedimentary basins are mainly composed of marls; limestones blocks; silex bed; silex nodule; marls and clays; silicified limestone; which have a significant reuse potential as marble-mosaic floor, mortars and concrete, and natural stone products slabs for floors and stairs.

Microbially Accelerated Carbonate Mineral Precipitation as a Strategy for in Situ Carbon Sequestration and Rehabilitation of Asbestos Mine Sites.

A microbially accelerated process for the precipitation of carbonate minerals was implemented in a sample of serpentinite mine tailings collected from the abandoned Woodsreef Asbestos Mine in New South Wales, Australia as a strategy to sequester atmospheric CO2 while also stabilizing the tailings. Tailings were leached using sulfuric acid in reaction columns and subsequently inoculated with an alkalinity-generating cyanobacteria-dominated microbial consortium that was enriched from pit waters at the Woodsreef Mine. Leaching conditions that dissolved 14% of the magnesium from the serpentinite tailings while maintaining circumneutral pH (1800 ppm, pH 6.3) were employed in the experiment. The mineralogy, water chemistry, and microbial colonization of the columns were characterized following the experiment. Micro-X-ray diffraction was used to identify carbonate precipitates as dypingite [Mg5(CO3)4(OH)2·5H2O] and hydromagnesite [Mg5(CO3)4(OH)2·4H2O] with minor nesquehonite (MgCO3·3H2O). Scanning electron microscopy revealed that carbonate mineral precipitates form directly on the filamentous cyanobacteria. These findings demonstrate the ability of these organisms to generate localized supersaturating microenvironments of high concentrations of adsorbed magnesium and photosynthetically generated carbonate ions while also acting as nucleation sites for carbonate precipitation. This study is the first step toward implementing in situ carbon sequestration in serpentinite mine tailings via microbial carbonate precipitation reactions.

An Economic Framework for Evaluating the Benefits and Costs of Biosolids Management Options

Agencies responsible for wastewater treatment have choices regarding how they manage their treatment process residuals. They can consider them waste products requiring suitable disposal (e.g., liquids managed as wastewater effluent, and sludges directed to traditional landfills), or as potential resources with significant “beneficial use” potential. For example, effluent can be rendered into reclaimed water, and solids can be used beneficially as a soil amendment in land applications and mine site reclamation, tapped as a renewable bio-fuel for energy production, or applied in other beneficial manners. Beneficial use options for biosolids management can generate important benefits to the utility and the community it serves. However, in some instances these beneficial use options also may have the potential to impose additional costs and/or risks. These benefits, costs, and potential risks generally accrue not only to the wastewater agency alone, but also to society as a whole (including the environment). As stewards of the environment and public trust, wastewater agencies need to consider the full range of benefits and costs associated with their activities. This means that they need to take into account all the impacts - good, bad, and uncertain - that their activities may impose on the broader community. Likewise, utilities cannot in good faith focus exclusively on the direct financial impacts on their agency alone. Instead, utilities also need to take account of the “externalities” their activities bestow (or impose) on the broader community: they need to think beyond the fence. This report describes the approaches, methods, and tools available to help utilities take a broad perspective and develop benefit-cost comparisons of their biosolids management options. This is designed to help agencies understand why it is important to conduct such analyses and why it is important to adopt a broad social accounting perspective when doing so. This report also provides tools and guidance to help utilities conduct such BCAs or related forms of Business Case Evaluation (BCE), including the Triple Bottom Line (TBL) approach. This title belongs to WERF Research Report Series ISBN: 9781843397830 (Print) ISBN: 9781780403762 (eBook)

Assessing the carbon sequestration potential of poplar and black locust short rotation coppices on mine reclamation sites in Eastern Germany – Model development and application

In the temperate zone short rotation coppice systems for the production of woody biomass (SRC) have gained great interest as they offer a pathway to both sustainable bioenergy production and the potential sequestration of CO2 within the biomass and the soil. This study used the carbon model SHORTCAR to assess the carbon cycle of a poplar (Populus suaveolens Fisch. x Populus trichocarpa Torr. et Gray cv. Androscoggin) and a black locust (Robinia pseudoacacia L.) SRC. The model was calibrated using data from established SRC plantations on reclaimed mine sites in northeast Germany and validated through the determination of uncertainty ranges of selected model parameters and a sensitivity analysis. In addition to a ‘reference scenario’, representing the actual site conditions, 7 hypothetical scenarios, which varied in climate conditions, rotation intervals, runtimes, and initial soil organic carbon (SOC) stocks, were defined for each species. Estimates of carbon accumulation within the biomass, the litter layer, and the soil were compared to field data and previously published results. The model was sensitive to annual stem growth and initial soil organic carbon stocks. In the reference scenario net biome production for SRC on reclaimed sites in Lusatia, Germany amounted to 64.5 Mg C ha−1 for R. pseudoacacia and 8.9 Mg C ha−1 for poplar, over a period of 36 years. These results suggest a considerable potential of SRC for carbon sequestration at least on marginal sites.

Nitrogen recovery in planted seedlings, competing vegetation, and soil in response to fertilization on a boreal mine reclamation site

Field fertilization during reforestation often yields variable results, particularly on harsh restoration sites. An improved understanding of the recovery of applied nitrogen (N) under different fertilization practices should aid in developing more effective fertilizer prescriptions. We evaluated field establishment of white spruce (Picea glauca (Moench) Voss) and trembling aspen (Populus tremuloides Michx.) seedlings as well as N recovery within planted seedlings, soil, and competing vegetation on a mine reclamation site in the oil sands region of northern Alberta in response to immediately available fertilizer (IAF) and polymer-coated controlled-release fertilizer (CRF) applications. 15N-enriched urea was applied as IAF and as a polymer-coated CRF (20gNseedling−1 and 4gNseedling−1, respectively) to each species. Seedling survival, growth, and nutritional status, along with occurrence of competing vegetation and plant and soil 15N recovery were quantified after the first field season. Seedlings receiving CRF exhibited increased diameter and organ dry mass relative to the IAF and control treatments. Both IAF and CRF promoted comparable increases in seedling N status, and fertilizer type did not influence within-seedling 15N allocation. Neither IAF nor CRF affected vegetation cover or dry mass. Recovery of fertilizer-derived 15N was low, with much of the recovered 15N remaining in soils and only small amounts observed in seedlings and competing vegetation for both fertilizer treatments. Findings indicate that directed root zone application of CRF promotes first-year seedling growth and nutritional responses similar to or better than those induced by broadcast IAF applications, but at substantially lower N application rates. Our results suggest that a shift from broadcast IAF to targeted soil applications of CRF may produce similar or improved early seedling growth and nutrient uptake on reclamation sites, while greatly reducing overall quantities of N applied during the regeneration phase, much of which appears to be lost from the site of application regardless of fertilizer type.