66 Algal bioremediation of mine waste tailings by application of moss protonema

Moss was discovered growing on mine waste tailings with high heavy metal content and low pH at the Badger State Mine near Butte, MT. It has been proposed that inoculation of plots with moss protonema, a stage of moss development, will produce a microbial mat. This process is fairly straightforward in mesic environments, but the aridity, acidity and high metal content of the tailings present some difficulty with the establishment of moss protonema or even algae. Consequently, a hydrophilic polymer and nutrients will be applied in addition to the protonema. This combination may assist in the retention of moisture to ensure the growth of the mature moss and other pioneer organisms. Soil from the mine tailings will be analyzed for evidence of cyanobacterial and other algal diversity. Benefits of cyanobacteria growth include their ability to fix nitrogen for use by other plants and production of photosynthates that leak organic carbon into the soil at a rate that can feed the heterotrophic microbes found in the microbial mat. The combination of algae, fungi, bacteria, protists and moss in a self‐sustaining microbial mat may help to stabilize the soil and create a hospitable environment for the colonization of vascular plants. Formation of a microbial mat in this xeric environment of mine waste tailings with the use of a hydrophilic polymer may be an ideal solution for the stabilization of mine wastes.     

Significance of microbial communities and interactions in safeguarding reactive mine tailings by ecological engineering

Pyritic mine tailings (mineral waste generated by metal mining) pose significant risk to the environment as point sources of acidic, metal-rich effluents (acid mine drainage [AMD]). While the accelerated oxidative dissolution of pyrite and other sulfide minerals in tailings by acidophilic chemolithotrophic prokaryotes has been widely reported, other acidophiles (heterotrophic bacteria that catalyze the dissimilatory reduction of iron and sulfur) can reverse the reactions involved in AMD genesis, and these have been implicated in the "natural attenuation" of mine waters. We have investigated whether by manipulating microbial communities in tailings (inoculating with iron- and sulfur-reducing acidophilic bacteria and phototrophic acidophilic microalgae) it is possible to mitigate the impact of the acid-generating and metal-mobilizing chemolithotrophic prokaryotes that are indigenous to tailing deposits. Sixty tailings mesocosms were set up, using five different microbial inoculation variants, and analyzed at regular intervals for changes in physicochemical and microbiological parameters for up to 1 year. Differences between treatment protocols were most apparent between tailings that had been inoculated with acidophilic algae in addition to aerobic and anaerobic heterotrophic bacteria and those that had been inoculated with only pyrite-oxidizing chemolithotrophs; these differences included higher pH values, lower redox potentials, and smaller concentrations of soluble copper and zinc. The results suggest that empirical ecological engineering of tailing lagoons to promote the growth and activities of iron- and sulfate-reducing bacteria could minimize their risk of AMD production and that the heterotrophic populations could be sustained by facilitating the growth of microalgae to provide continuous inputs of organic carbon.     

生物结皮对铜尾矿废弃地土壤微生物量及酶活性的影响

生物结皮是铜尾矿废弃地自然原生演替的最初阶段.本研究以铜陵杨山冲铜尾矿库和铜官山新铜尾矿库为对象,采用熏蒸浸提和化学分析法研究了两尾矿库不同类型生物结皮下土壤微生物量C、N及脱氢酶、过氧化氢酶、碱性磷酸酶和脲酶活性.结果表明：铜尾矿废弃地上的生物结皮能够显著提高表层尾矿中的微生物量和土壤酶活性,其中藻类结皮对土壤微生物量C、N的影响高于藓-藻混合结皮,藓类结皮的影响最小;随着土壤生物结皮类型的变化,土壤微生物区系也随之变化;各类生物结皮下表层尾矿中土壤酶活性无显著差异.相关分析表明,碱性磷酸酶活性与土壤微生物量、脱氢酶和脲酶活性呈显著正相关,但与土壤pH呈显著负相关.此外,藓类植物假根能够显著提高藓类结皮假根层的微生物量和酶活性.     

Effects of Compost on Colonization of Roots of Plants Grown in Metalliferous Mine Tailings, as Examined by Fluorescence In Situ Hybridization

The relationship between compost amendment, plant biomass produced, and bacterial root colonization as measured by fluorescence in situ hybridization was examined following plant growth in mine tailings. Mine tailings can remain devoid of vegetation for decades after deposition due to a combination of factors that include heavy metal toxicity, low pH, poor substrate structure and water-holding capacity, and a severely impacted heterotrophic microbial community. Research has shown that plant establishment, a desired remedial objective to reduce eolian and water erosion of such tailings, is enhanced by organic matter amendment and is correlated with significant increases in rhizosphere populations of neutrophilic heterotrophic bacteria. Results show that for the acidic metalliferous tailings tested in this study, compost amendment was associated with significantly increased bacterial colonization of roots and increased production of plant biomass. In contrast, for a Vinton control soil, increased compost had no effect on root colonization and resulted only in increased plant biomass at high levels of compost amendment. These data suggest that the positive association between compost amendment and root colonization is important in the stressed mine tailings environment where root colonization may enhance both microbial and plant survival and growth.     

Artificial inoculation-perspectives in tailings phytostabilization

Intensive mining and processing activities worldwide resulted in the generation of huge amounts of waste (tailings), generally characterized as toxic, radioactive, and/or hazardous. The exposure potential and, hence, the risk posed by such wastes is enhanced by a general lack of vegetation. Phytostabilization has proven to be efficient in reducing this risk. However, establishing vegetation on tailing dumps may be expensive due to the intensive use of amendments and chemical fertilizers. In this article, investigations on artificial inoculation of mine tailings with bacterial strains as a means to improve the development of vegetative covers and reduce application cost by eliminating chemical fertilization are presented and discussed. The development of plants and microbial communities from tailings, as well as the impact of inoculation on metal uptake in plants, were studied. Experiments were carried out in greenhouse using two types of mine tailings (phosphogypsum and sulphidic tailings) from the Romanian Black Sea coast. Indigenous herbaceous plants were cultivated on tailings with the addition of chemical fertilizers versus bacterial inoculation. After a 6-month experimental period, excellent plant growth, which is associated with a rich microbial community, was observed in all inoculated treatments, in contrast with poor plant growth and microbiota from the chemical fertilization treatments alone. Additionally, artificial inoculation improved plant resistance to heavy metals by reducing the uptake of some toxic metals. Once a rich microbial community is established, inoculation may be discontinued. Based on these results, efficient and cost-effective phytostabilization schemes can be proposed.     

Chemistry and plant ecology of zinc-rich wastes dominated by blue-green algae

An account is given of the chemistry and vegetation of wet areas below the Elvins tailings pile in the Old Lead Belt of Missouri. Zinc in particular is present at highly elevated levels in the water (5.9–21.0 mg l^–1) and most sediments. The two most widespread plants are a blue-green alga,Plectonema gracillimum, and a moss,Dicranella sp. In wetter areas the latter exists predominantly as protonema.Plectonema and the protonema typically grow in very close association, although situations do occur where only one or the other is present. For instance, algal flocs in two permanent ponds consisted largely ofPlectonema and unicellular blue-green algae, with a few eukaryotic algae, but no protonema. Other dominants in the area areEleocharis sp.,Scirpus americanus andTypha latifolia. One seepage was studied in more detail; it showed marked changes in both chemistry and vegetation on passing from source to a site 15 m downstream. Aqueous Zn dropped from 21 to 8 mg l^–1. ThePlectonema-Dicranella protonema community predominated in the upper part, developing a laminated structure up to 3 cm thick (justifying recognition as a stromatolite). Further downstream a white crust including much hydrozincite and with a very high overall zinc content (c. 370 mg g^–1 Zn) was deposited over the green layer, making it endolithic in position, though probably not in origin. Still further downstream the green layer disappeared, leaving only a hard white crust. A discussion is included of the extent to which observed variations in the zinc content of water and sediments below the tailings pile are influenced by living and dead plants. An apparent diel cycle in aqueous zinc at some sites is of particular interest, as it was not matched by changes in Ca or Cd.     

重庆溶溪锰矿区土壤重金属污染评价及植物吸收特征

对重庆溶溪锰矿尾渣堆积区土壤、优势植物以及周边农田土壤的重金属含量(Mn、Cd、Cu、Zn和Pb)进行测定分析,并以重庆市土壤背景值为评价标准,应用Hakanson潜在生态危害指数法对土壤中重金属的潜在生态危害进行了评价。结果表明:该锰矿尾渣堆积区土壤中Mn、Cd、Cu、Zn和Pb的平均含量分别为48382.5、3.91、79.97、131.23和80.68 mg/kg,受到Mn、Cd的严重污染,Mn为强或很强生态危害,Cd为极强生态危害,而Cu、Zn、Pb为轻微生态危害,各尾矿渣堆积区的综合潜在生态危害指数(RI)均远大于720,为极强生态危害。对优势植物重金属含量的分析显示,绝大部分植物地上部Mn、Cd含量都超出正常范围的上限值,而Cu、Zn和Pb含量基本都在正常范围内;根据植物对重金属的吸收特征,将植物分为三类:将重金属主要累积于地上部分的富集型,如垂序商陆(Phytolacca americana L.)和酸模叶蓼(Polygonum lapathifolium Linn.),适用于重金属复合污染土壤的植物修复;将重金属主要累积于根部的根部囤积型,如芒(Miscanthus sinensis Anderss.)和乌蕨(Stenoloma chusanum Ching);重金属含量较低的规避型,如黄花蒿(Artemisia annua L.)、长波叶山蚂蝗(Desmodium sequax Wall.)及钻形紫苑(Aster subulatus Michx.);后两种类型的植物可种植在重金属污染严重且使用价值相对较低的矿山废弃地上,同时规避型植物对于研究植物的重金属排斥机理具有重要价值。溶溪锰矿区周边农田土壤主要受到Cd的严重污染,Cd为很强或极强生态危害。     

Soil-covered strategy for ecological restoration alters the bacterial community structure and predictive energy metabolic functions in mine tailings profiles

Native soil amendment has been widely used to stabilize mine tailings and speed up the development of soil biogeochemical functions before revegetation; however, it remains poorly understood about the response of microbial communities to ecological restoration of mine tailings with soil-covered strategy. In this study, microbial communities along a 60-cm profile were investigated in mine tailings during ecological restoration of two revegetation strategies (directly revegetation and native soil covered) with different plant species. The mine tailings were covered by native soils as thick as 40 cm for more than 10 years, and the total nitrogen, total organic carbon, water content, and heavy metal (Fe, Cu, and Zn) contents in the 0–40 cm intervals of profiles were changed. In addition, increased microbial diversity and changed microbial community structure were also found in the 10–40 cm intervals of profiles in soil-covered area. Soil-covered strategy rather than plant species and soil depth was the main factor influencing the bacterial community, which explained the largest portion (29.96%) of the observed variation. Compared directly to revegetation, soil-covered strategy exhibited the higher relative abundance of Acidobacteria and Deltaproteobacteria and the lower relative abundance of Bacteroidetes, Gemmatimonadetes, Betaproteobacteria, and Gammaproteobacteria. PICRUSt analysis further demonstrated that soil-covered caused energy metabolic functional changes in carbon, nitrogen, and sulfur metabolism. Given all these, the soil-covered strategy may be used to fast-track the establishment of native microbial communities and is conducive to the rehabilitation of biogeochemical processes for establishing native plant species.

     

Mine tailing disposal sites: contamination problems,remedial options and phytocaps for sustainable remediation

Mining practices and the absence of proper mine land reclamation has led to heavy metal contaminated sites with serious impact on the ecosystems and risk for human health. The origin of the contamination is often associated to mine tailing deposits because they are a source of the acid mine drainage (AMD). These areas are devoid of vegetation due to the harsh soil conditions that prevent the rooting of plant species. The remediation of these areas followed by revegetation is necessary to suppress the generation of the AMD and its negative effects on the ecosystems. Conventional remediation technologies for heavy metal contaminated sites are usually not applicable because of the high cost associated with chemicals and energy requirements, as well as the long treatment time to remediate large areas. In this study, the use of phytocapping for the remediation of mine tailing deposits and abandoned mine areas is reviewed. Phytocapping is cost effective, environmentally friendly and has multifunctional role against various problems of mine tailings: it provides erosion control, landscape rehabilitation, enhances the soil properties for further colonization of other more demanding vegetal species, reduces the leachability of metals downwards the groundwater, and favors the immobilization of metals forming less bioavailable species. The most critical step in phytocapping is the developing of the first vegetative cover because of the biotoxicity of the mine soil and mine tailings. Several amendment materials can be used to ameliorate soil conditions creating a favorable environment for the rooting of plants, as well as serving as a source of nutrients. Local plant species with fast growing are preferable because their adaptation to the soil and climate conditions favors their self-propagation.     

Pongamia pinnata inoculated with Bradyrhizobium liaoningense PZHK1 shows potential for phytoremediation of mine tailings

Mine tailings contain high concentrations of metal contaminants and only little nutrients, making the tailings barren for decades after the mining has been terminated. Effective phytoremediation of mine tailings calls for deep-rooted, metal accumulating, and soil fertility increasing plants with tolerance against harsh environmental conditions. We assessed the potential of the biofuel leguminous tree Pongamia pinnata inoculated with plant growth promoting rhizobia to remediate iron–vanadium–titanium oxide (V–Ti magnetite) mine tailing soil by pot experiment and in situ remediation test. A metal tolerant rhizobia strain PZHK1 was isolated from the tailing soil and identified as Bradyrhizobium liaoningense by phylogenetic analysis. Inoculation with PZHK1 increased the growth of P. pinnata both in V–Ti magnetite mine tailings and in Ni-contaminated soil. Furthermore, inoculation increased the metal accumulation capacity and superoxide dismutase activity of P. pinnata. The concentrations of Ni accumulated by inoculated plants were higher than the hyperaccumulator threshold. Inoculated P. pinnata accumulated high concentration of Fe, far exceeding the upper limit (1000 mg kg⁻¹) of Fe in plant tissue. In summary, P. pinnata–B. liaoningense PZHK1 symbiosis showed potential to be applied as an effective phytoremediation technology for mine tailings and to produce biofuel feedstock on the marginal land.

     

Phytotoxicity of tin mine waste and accumulation of involved heavy metals in common buckwheat (Fagopyrum esculentum Moench)

Extraction and processing of cassiterite (SnO₂) left large tailings with high concentrations of tin, tungsten, molybdenum and lithium. Information on the phytotoxicity of mine waste is important with regard to ecological hazards. Exposure studies help to identify plants useful for the stabilization of waste tips and the phytomining of metals. A greenhouse study was performed using a dilution series of mine waste and four crops, a halophytic and a metallophytic species to derive dose response curves. Based on effective doses for growth reductions, sensitivity increased in the following order: maize > common buckwheat > quinoa > garden bean. Element analyses in different species and compartments of common buckwheat grown in a mixture of standard soil and 25% of the mine waste showed that only low levels of the metals were taken up and that transfer to seed tissues was negligible. As indicated by soil metal levels prior to and after the experiment, only lithium and arsenic proved to be plant available and reached high levels in green tissues while seed levels were low. The experiment confirmed differences in the uptake of metals with regard to elements and species. Common buckwheat is a suited candidate for cultivation on metal polluted soils.     

Balancing positive and negative plant interactions: how mosses structure vascular plant communities

Our understanding of positive and negative plant interactions is primarily based on vascular plants, as is the prediction that facilitative effects dominate in harsh environments. It remains unclear whether this understanding is also applicable to moss–vascular plant interactions, which are likely to be influential in low-temperature environments with extensive moss ground cover such as boreal forest and arctic tundra. In a field experiment in high-arctic tundra, we investigated positive and negative impacts of the moss layer on vascular plants. Ramets of the shrub Salix polaris, herb Bistorta vivipara, grass Alopecurus borealis and rush Luzula confusa were transplanted into plots manipulated to contain bare soil, shallow moss (3 cm) and deep moss (6 cm) and harvested after three growing seasons. The moss layer had both positive and negative impacts upon vascular plant growth, the relative extent of which varied among vascular plant species. Deep moss cover reduced soil temperature and nitrogen availability, and this was reflected in reduced graminoid productivity. Shrub and herb biomass were greatest in shallow moss, where soil moisture also appeared to be highest. The relative importance of the mechanisms by which moss may influence vascular plants, through effects on soil temperature, moisture and nitrogen availability, was investigated in a phytotron growth experiment. Soil temperature, and not nutrient availability, determined Alopecurus growth, whereas Salix only responded to increased temperature if soil nitrogen was also increased. We propose a conceptual model showing the relative importance of positive and negative influences of the moss mat on vascular plants along a gradient of moss depth and illustrate species-specific outcomes. Our findings suggest that, through their strong influence on the soil environment, mat-forming mosses structure the composition of vascular plant communities. Thus, for plant interaction theory to be widely applicable to extreme environments such as the Arctic, growth forms other than vascular plants should be considered.     

实验室条件下两种生物土壤结皮对荒漠植物种子萌发的影响

生物土壤结皮广泛分布在干旱、半干旱区,深刻影响着土壤表层特性,进而对植物种子散布、萌发和定居产生极大的影响。到目前为止,生物土壤结皮与植物关系的研究很少见到,并且这些有限的研究所得出的结论存在着争议。研究了不同年龄的两种生物土壤结皮（苔藓结皮和藻类结皮）对油蒿（Artemisia ordosica）和雾冰藜（Bassia dasyphylla）种子萌发的影响,同时也研究了这两种结皮在失去活性前后对油蒿、雾冰藜和小画眉草（Eragrostis poaeoides）种子萌发的影响。苔藓和藻类结皮的出现对油蒿和雾冰藜种子的萌发均有显著的促进作用,而结皮年龄对植物种子的萌发没有显著的差异。对于不同的植物种,结皮类型和活性对种子的萌发具有不同的作用。雾冰藜在两种结皮上的萌发有显著的差异而油蒿和小画眉草在两种结皮上的萌发没有显著差异。活藻类显著地增加了三种植物的种子萌发,活苔藓仅增加了油蒿和雾冰藜种子萌发量而对小画眉草种子的萌发没有作用,研究表明,生物土壤结皮对一些植物种子萌发具有明显的促进作用。     

Microbial communities from weathered outcrops of a sulfide-rich ultramafic intrusion,and implications for mine waste management

The Duluth Complex (DC) contains sulfide-rich magmatic intrusions that represent one of the largest known economic deposits of copper, nickel, and platinum group elements. Previous work showed that microbial communities associated with experimentally-weathered DC waste rock and tailings were dominated by uncultivated taxa and organisms not typically associated with mine waste. However, those experiments were designed for kinetic testing and do not necessarily represent the conditions expected for long-term environmental weathering. We used 16S rRNA gene methods to characterize the microbial communities present on the surfaces of naturally-weathered and historically disturbed outcrops of DC material. Rock surfaces were dominated by diverse uncultured Ktedonobacteria, Acetobacteria, and Actinobacteria, with abundant algae and other phototrophs. These communities were distinct from microbial assemblages from experimentally-weathered DC rocks, suggesting different energy and nutrient resources in environmental samples. Sulfide mineral incubations performed with and without algae showed that photosynthetic microorganisms could have an inhibitory effect on autotrophic populations, resulting in slightly lower sulfate release and differences in dominant microorganisms. The microbial assemblages from these weathered outcrops show how communities develop during weathering of sulfide-rich DC rocks and represent baseline data that could evaluate the effectiveness of future reclamation of waste produced by large-scale mining operations.     

金属尾矿库生物土壤结皮的类型及物种组成

为对金属尾矿库生物土壤结皮进行研究, 2016年对湖北省黄石市的两个废弃尾矿库开展了生物土壤结皮调查,并采用空间代替时间的方法来研究结皮发育演替过程中的物种组成及变化。结皮中蓝藻、真菌和苔藓的绝对丰度分别为(0.63—2.01)×108、(0.19—1.53)×108和(0.08—3.34)×107 copies/g DW soil,随着结皮的演替蓝藻和真菌丰度降低,苔藓的丰度增加。从微生物组成来看,从两个尾矿库的生物土壤结皮中共分析出41门的物种,其中变形菌门、蓝藻门、放线菌门、拟杆菌门、绿弯菌门、疣微菌门、酸杆菌门、浮霉菌门、芽单胞菌门及热微菌门是主要组分,它们在不同结皮中累计丰度均达到90%以上。金属尾矿库中的生物土壤结皮物种组成及其变化规律与荒漠化地区类似,蓝藻在其中具有不可替代的作用。研究表明生物土壤结皮在金属尾矿库中广泛分布,同时可以起到增加尾矿库土壤养分的作用,可广泛应用于金属尾矿库的生态修复。     

铜尾矿废弃地生物土壤结皮固氮微生物多样性

生物土壤结皮能够有效提高矿业废弃地有机质和氮的积累,促进植被的恢复.本研究基于固氮微生物的nifH基因多样性,以铜陵铜尾矿废弃地3种类型的生物土壤结皮(藻结皮、藓结皮和藻-藓混合结皮)为对象,利用变性梯度凝胶电泳(DGGE)技术研究生物土壤结皮中固氮微生物的多样性以及废弃地植物群落发育对其产生的影响.结果表明： 尾矿库裸地表面的藻结皮的固氮微生物多样性最高,其次为维管植物群落下的藻-藓混合结皮,苔藓结皮的固氮蓝藻多样性最低;随着维管植物群落高度和盖度的增加,固氮微生物多样性降低,铜尾矿废弃地的pH、水分、有机质、养分含量(氮和磷)以及有效态和总重金属浓度对固氮微生物多样性的影响均不显著.测序和系统发育分析表明,废弃地结皮中固氮微生物以蓝藻为主,主要为不具有异形胞的丝状蓝藻.
     

A field study of constructed wetlands for preventing and treating acid mine drainage

The formation of acid mine drainage (AMD) from mine tailings is a severe environmental problem associated with tailings impoundments. The study evaluated the ability of wetlands built on tailings impoundments to prevent AMD formation and to treat already formed AMD, with special emphasis on the role of wetland plants in the remediation process. Four small-scale surface-flow wetlands of different designs, containing either mine tailings or sand, an inflow of AMD or unpolluted water, and with or without emergent plants (Phragmites australis, Carex rostrata, and Eriophorum angustifolium), were constructed at the Kristineberg mine tailings impoundment in northern Sweden in 2004. Water samples were collected every month in 2006 at inflow and outflow in order to analyse metals, sulphate, pH, and redox potential. At the end of 2006, plant and sediment samples were collected to enable the analysis of metal concentrations. The concentrations of Fe, Zn, Cd, and sulphate and pH did not change after passage through the wetlands treating AMD. However, the Cu concentration decreased by 36–57%, with the decrease higher in the presence than in the absence of plants. The study of AMD prevention indicated that metal concentrations in impoundment water tend to decrease as the water passes through the wetland. However, sulphate concentrations increase and the pH decreases in the water, suggesting sulphide oxidation of the mine tailings. On the other hand, wetland plants increased the pH, decreased the redox potential, and increased the metal concentrations in the substrate, despite the fact that metal uptake in the studied wetland plants accounted for only 0.002–2.9% of the annual metal loading into the wetlands, suggesting that plants promote metal sedimentation and adsorption. Emergent plants and the wetlands constructed in this study were thus inadequate to treat the very harsh AMD at the Kristineberg mine site.     

Soil Seed Bank as an Input of Seed Source in Revegetation of Lead / Zinc Mine Tailings

The goal of the present study was to assess a soil seed bank as an input seed source for revegetating lead/zinc (Pb/Zn) mine tailings. The seed bank source was abandoned farmland, whose top 10‐cm layer of topsoil contained 6,850 ± 377 seeds/m² from 41 species. The seeds in the soil were principally distributed in the upper 0–2 cm, which held 75.8% of total seeds and 92.7% of species composition. The top 2‐cm layer of topsoil may be sufficient to serve the purpose of providing a seed source for revegetation on derelict lands, including mined lands. Four different thicknesses of topsoil (1, 2, 4, and 8 cm, redistributed from the total 0–10‐cm layer from the farmland) were field‐tested on the Pb/Zn mine tailings. There was no significant difference in seedling density among the 4 thickness treatments. Many seeds in the treatments with more than 1‐cm of topsoil were unable to emerge from the deeper layer. Seedlings in plots with topsoil of 1‐, 2‐ and 4‐cm failed to establish within 1 year due to the extremely high acidity (pH 2.39 to 2.76). A shallow layer of topsoil cannot neutralize the sulfuric acid generated from oxidation of pyrites in the tailings. For establishment of seedlings on metalliferous lands, an insulating layer such as subsoil, building rubble, or domestic refuse is necessary before covering with valuable topsoil. The woody legume Leucaena leucocephala grown on the tailings with a topsoil cover of 8‐cm was the most dominant species. Lead was accumulated in root, branch, stem bark, and xylem, which accounted for more than 80% of the total metal concentration in the plant. This portion of Pb will reside in the plant for a long period, while the smaller portion of Pb in the leaf (about 15%) could be returned to the environment as litter during growth. Woody plants may have an advantage in metal‐phyto‐remediation over herbaceous plants.     

Arctic mosses govern below-ground environment and ecosystem processes

Mosses dominate many northern ecosystems and their presence is integral to soil thermal and hydrological regimes which, in turn, dictate important ecological processes. Drivers, such as climate change and increasing herbivore pressure, affect the moss layer thus, assessment of the functional role of mosses in determining soil characteristics is essential. Field manipulations conducted in high arctic Spitsbergen (78° N), creating shallow (3 cm), intermediate (6 cm) and deep (12 cm) moss layers over the soil surface, had an immediate impact on soil temperature in terms of both average temperatures and amplitude of fluctuations. In soil under deep moss, temperature was substantially lower and organic layer thaw occurred 4 weeks later than in other treatment plots; the growing season for vascular plants was thereby reduced by 40%. Soil moisture was also reduced under deep moss, reflecting the influence of local heterogeneity in moss depth, over and above the landscape-scale topographic control of soil moisture. Data from field and laboratory experiments show that moss-mediated effects on the soil environment influenced microbial biomass and activity, resulting in warmer and wetter soil under thinner moss layers containing more plant-available nitrogen. In arctic ecosystems, which are limited by soil temperature, growing season length and nutrient availability, spatial and temporal variation in the depth of the moss layer has significant repercussions for ecosystem function. Evidence from our mesic tundra site shows that any disturbance causing reduction in the depth of the moss layer will alleviate temperature and moisture constraints and therefore profoundly influence a wide range of ecosystem processes, including nutrient cycling and energy transfer.     

Phytoremediation of mine tailings in temperate and arid environments

Phytoremediation is an emerging technology for the remediation of mine tailings, a global problem for which conventional remediation technologies are costly. There are two approaches to phytoremediation of mine tailings, phytoextraction and phytostabilization. Phytoextraction involves translocation of heavy metals from mine tailings to the plant shoot biomass followed by plant harvest, while phytostabilization focuses on establishing a vegetative cap that does not shoot accumulate metals but rather immobilizes metals within the tailings. Phytoextraction is currently limited by low rates of metal removal which is a combination of low biomass production and insufficiently high metal uptake into plant tissue. Phytostabilization is currently limited by a lack of knowledge of the minimum amendments required (e.g., compost, irrigation) to support long-term plant establishment. This review addresses both strategies within the context of two specific climate types: temperate and arid. In temperate environments, mine tailings are a source of metal leachates and acid mine drainage that contaminate nearby waterways. Mine tailings in arid regions are subject to eolian dispersion and water erosion. Examples of phytoremediation within each of these environments are discussed. Current research suggests that phytoextraction, due to high implementation costs and long time frames, will be limited to sites that have high land values and for which metal removal is required. Phytostabilization, due to lower costs and easier implementation, will be a more commonly used approach. Complete restoration of mining sites is an unlikely outcome for either approach.