The commonly observed enrichment of middle rare earth elements (MREE) in water sampled in acid mine drainage (AMD)-impacted areas was found to be the result of preferential release from the ...widespread mineral pyrite (FeS₂). Three different mining-impacted sites in Europe were sampled for water, and various pyrite samples were used in batch experiments with diluted sulphuric acid simulating AMD-impacted water with high sulphate concentration and high acidity. All water samples independent on their origin from groundwater, creek water or lake water as well as on the surrounding rock types showed MREE enrichment. Also the pyrite samples showed MREE enrichment in the respective acidic leachate but not always in their total contents indicating a process-controlled release. It is discussed that most probably complexation to sulphite (SO₃ ²⁻) or another intermediate S-species during pyrite oxidation is the reason for the MREE enrichment in the normalized REE patterns.
Natural Mn oxides are largely biogenic in origin, formed via the microbial oxidation of Mn(II). These minerals are extremely efficient scavengers of heavy metals, yet to date microbial Mn oxide ...precipitation and subsequent heavy metal sorption have received little attention in mining-impacted environments, where heavy metal concentrations are elevated but (bio)geochemical conditions are typically unfavourable for both abiotic and biogenic Mn oxide precipitation, featuring acidic pH and low organic carbon contents. Here we investigate the formation of Mn oxide (bio)geochemical barrier layers, and the immobilisation of heavy metals in these layers, in soil profiles from a former uranium mining site in Ronneburg, Germany. Detailed soil profiling shows the site has an acidic soil pH that varies from 4.7 to 5.1 and Eh values from 640 to 660mV. Using synchrotron X-ray diffraction and X-ray absorption spectroscopy, together with scanning electron microscopy and electron microprobe analysis, we find that the dominant Mn oxide present in the Mn oxide layers is a poorly crystalline hexagonal birnessite, akin to synthetic δ-MnO2, covering and cementing quartz grains. Using phylogenetic analysis based on 16S rDNA, we identify and characterise six strains of manganese oxidising bacteria (MOB) from the acidic Mn oxide layers which we subsequently culture to produce poorly crystalline hexagonal birnessite akin to that found at the study site. Specifically, we identify three Gram-positive spore-forming firmicutes affiliated to Bacillus safensis, Bacillus altitudinis and Brevibacillus reuszeri, which are able to oxidise Mn after initiating spore formation, two Gram-positive actinobacteria belonging to the genera Arthrobacter and Frondihabitans, and one Gram-negative proteobacteria belonging to the genus Sphingomonas. Geochemical thermodynamic speciation modelling indicates that the abiotic precipitation of Mn oxides in the Mn oxide layers is unfavourable and we suggest that the Mn oxides in the (bio)geochemical barriers at our study site are biogenically precipitated in an acidic soil environment. To our knowledge, this is the first report to identify the above six bacterial strains, and specifically identify spore-forming bacteria, as MOB in an acidic soil environment. We find that the poorly crystalline hexagonal birnessite precipitated in the Mn oxide layers efficiently immobilises Ba, Ni, Co, Cd, Zn and Ce, and as such we find that MOB and biogenically precipitated Mn oxides can exert a strong control on the fate and mobility of metals in mining-impacted environments.
•We investigate the origin of and metal retention on Mn oxides in Mn oxide layers at a mining-impacted site with acidic pH.•We identify Mn oxidising bacteria and precipitation of biogenic Mn oxides in the Mn oxide layers at acidic soil pH.•This is the first report to identify spore-forming bacteria as Mn oxidisers in an acidic environment.•The biogenic Mn oxide is poorly crystalline hexagonal birnessite.•The biogenic Mn oxide efficiently immobilises Ba, Ni, Co, Cd, Zn and Ce at acidic soil pH.
Biological Mn oxidation is responsible for producing highly reactive and abundant Mn oxide phases in the environment that can mitigate metal contamination. However, little is known about Mn oxidation ...in low-pH environments, where metal contamination often is a problem as the result of mining activities. We isolated two Mn(II)-oxidizing bacteria (MOB) at pH 5.5 (Duganella isolate AB_14 and Albidiferax isolate TB-2) and nine strains at pH 7 from a former uranium mining site. Isolate TB-2 may contribute to Mn oxidation in the acidic Mn-rich subsoil, as a closely related clone represented 16% of the total community. All isolates oxidized Mn over a small pH range, and isolates from low-pH samples only oxidized Mn below pH 6. Two strains with different pH optima differed in their Fe requirements for Mn oxidation, suggesting that Mn oxidation by the strain found at neutral pH was linked to Fe oxidation. Isolates tolerated Ni, Cu, and Cd and produced Mn oxides with similarities to todorokite and birnessite, with the latter being present in subsurface layers where metal enrichment was associated with Mn oxides. This demonstrates that MOB can be involved in the formation of biogenic Mn oxides in both moderately acidic and neutral pH environments.
The West Eifel Volcanic Field comprises 98 maars, tuff rings, and scoria rings of volcanoes younger than 700 ka. Digital Terrain Models (DTMs) allow to automatically measure morphologic parameters of ...volcanic edifices such as slope angles, diameters, elevations, floor, and slope surface areas. Based on their morphological characteristics, we subdivided the West Eifel volcanoes into five morphometric groups which reflect different stages of erosion. Group I, II, and IV comprise clear ring-shaped structures. The difference between these groups is that a tephra ring is well preserved in Group I, partially preserved in Group II and absent in Group IV. The original shapes of Group III maars have been lost more substantially than in Groups I, II, or IV, but they nevertheless retain a negative shape (a depression) and have characteristic channel systems, which can be used as search criteria. Maar-diatremes of Group V are eroded down to their feeder pipes and form hills. In order to locate potential volcanic depressions that are likely to be maar volcanoes, we defined common search criteria such as circular negative landforms or particular drainage system patterns for all groups except the least well-preserved Group V. These criteria were taken as the basis for further processing of the DTM data. The first processing step consisted of constructing a residual relief calculated as the difference between a filtered (smoothed) topographic surface and the original DTM data. This identifies local topographic features. We propose a method for regulating the degree of smoothing which is based on filtering of local maxima according to their distance from a surface constructed from local minima. The previously defined search criteria for Groups I to IV such as specific ranges of curvature, slope, circularity, density of the drainage network were then applied to the residual relief in order to extract maar shapes. Not all criteria work equally well for all morphological groups. Combinations of multiple search criteria therefore yield the best results and efficiently identify most known maars. They also separate some probable new, hitherto unrecognized maars from a large number of other local depressions. We also compared the erosional state of maars to their absolute ages. Published estimates of erosion rates for maars in the French Massif Central suggest a general trend of erosion rates decreasing with time elapsed since eruption. However, this cannot explain the strongly varying ages for maars of the same morphometric group (i.e., similar preservation state) in the West Eifel Volcanic Field. The spatial distribution of the morphometric groups shows some regularity. For example, strongly eroded maars are concentrated in the Gerolstein area (where maar density is highest), whereas most well-preserved maars are located east of the Eifel North–South Depression (ENSD). Most maars affected by fluvial erosion lie near the Kyll and Kleine Kyll streams. These observations suggest differential recent uplift of the West Eifel Volcanic Field, with stronger uplift occurring west of the ENSD.
High levels of metals impede plant growth by affecting physiological processes. Siderophores are microbial Fe-chelators that, however, bind other metals. This study evaluated plant growth in a soil ...containing elevated levels of metals, including Al, Cu, Fe, Mn, Ni, and U, using
Streptomyces-derived cell-free supernatant containing siderophores and auxins. Cowpea plants in the soil were treated with the culture filtrate. Growth was measured and biochemical analyses such as chlorophyll contents, RNA and protein quantification, lipid membrane peroxidation, and anti-oxidative responses were conducted to evaluate oxidative stress in the plants. Liquid chromatography–mass spectrometry was used to simulate competition for siderophore binding, and metal content of plants was determined spectroscopically. Whereas the metals inhibited plant growth, addition of siderophores improved growth. There was evidence of lipid peroxidation, an enhanced superoxide dismutase activity, and lowered chlorophyll, RNA, protein, carotenoid and residual indole acetic acid contents, especially in control plants. Siderophore competition assays between Al and Fe, and Fe and Cu suggested that trivalent metals are more competitive for siderophore binding than divalent ones. Compared to control plants, higher amounts of metals were obtained in siderophore-treated plants. Siderophores were able to supply plants with Fe in the presence of levels of metals, mainly Al, Cu, Mn, Ni and U that otherwise inhibit Fe acquisition. This led to enhanced chlorophyll content, circumventing lipid peroxidation effects on leaves. Siderophores lowered the formation of free radicals, thereby protecting microbial auxins from degradation and enabling them to enhance plant growth which in turn resulted in augmented metal uptake.
The siderophore-producing ability of nickel-resistant
Streptomyces acidiscabies
E13 and the role of the elicited siderophores in promoting plant growth under iron and nickel stress are described. ...Siderophore assays indicated that S. acidiscabies E13 can produce siderophores. Electrospray ionization mass spectrometry (ESI-MS) revealed that the bacterium simultaneously produces 3 different hydroxamate siderophores. ESI-MS showed that in addition to iron, all 3 siderophores can bind nickel. In vitro plant growth tests were conducted with cowpea (
Vigna unguiculata
) in the presence and absence of the elicited siderophores. Culture filtrates containing hydroxamate siderophores significantly increased cowpea height and biomass, irrespective of the iron status of the plants, under nickel stress. The presence of reduced iron was found to be high in siderophore-containing treatments in the presence of nickel. Measurements of iron and nickel contents of cowpea roots and shoots indicated that the siderophore-mediated plant growth promotion reported here involves the simultaneous inhibition of nickel uptake and solubilization and supply of iron to plants. We conclude that hydroxamate siderophores contained in culture filtrates of S. acidiscabies E13 promoted cowpea growth under nickel contamination by binding iron and nickel, thus playing a dual role of sourcing iron for plant use and protecting against nickel toxicity.
A site in the former uranium mining area of Eastern Thuringia near Ronneburg was investigated with regard to effects of acid mine drainage (AMD) on reactive transport and bioattenuation. Processes ...involved in this attenuation might include physico-chemical reactions in reactive transport as well as activities of microorganisms for bioattenuation. In order to test the influence of the soil microbes, a mapping was carried out including both hydrogeochemical and microbiological parameters.
Mapping of contamination was performed along the banks of a creek in a 900
m stretch in 50
m steps by hydrogeochemical analysis of water extracts of soil samples, while general microbial activity was scored by examining soil respiration. The soil samples with high heavy metal load did show low soil respiration as a parameter for microbial activity and plating revealed minimal counts for spore producing bacteria at these contaminated locations. Actinobacteria strains isolated from adjacent locations revealed high levels of resistance as well as high numbers of resistant strains. Specific responses in actinobacteria were investigated after isolation from each of the 18 measuring points along the creek. Specific adaptation strategies and high yields of (intra)cellular heavy metal retention could be seen. Several strategies for coping with the high heavy metal contents are further discussed and genes for proteins expressed specifically under high nickel concentration were identified by two-dimensional gel electrophoresis.
Differentiating between regularly seasonal, irregular and event-based clastic sedimentation is difficult if sedimentation structures resemble and dating methods are imprecise. In this study - clastic ...light and dark laminae from lava-dammed Paleolake Alf in the Late Pleistocene in the Quaternary West Eifel Volcanic Field are analyzed to clarify how they formed and if they are of annual origin and comparable to assumed periglacial varves from neighboring Lake Holzmaar. Therefore, a multiproxy approach is applied combining sediment thin section analysis which focuses on composition and structure with 14C dates. The results are compared to recently-formed annually-laminated clastic sediments of, e.g., the High Canadian Arctic. Observed sedimentation structures reveal sediment delivery by over- and interflows and deposition from suspension forming two characteristic microfacies: Type I graded laminae and Type II laminae with graded sublayers. Additionally, erosional bases and event deposits indicate episodic underflows. Thus, lamination is potentially seasonal but is significantly veiled by extreme runoff causing erosion and resuspension processes or a mixed water body preventing sediment delivery into the lake basin. However, sedimentation processes between watershed and lake could be reconstructed by comparing recent and paleosediment structures.
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