Biogeochemical Cycling Of Metals Research Articles

Fungal biomineralization of toxic metals accelerates organic pollutant removal

Fungal biomineralization plays an important role in the biogeochemical cycling of metals in the environment and has been extensively explored for bioremediation and element biorecovery. However, the cellular and metabolic responses of fungi in the presence of toxic metals during biomineralization and their impact on organic matter transformations are unclear. This is an important question because co-contamination by toxic metals and organic pollutants is a common phenomenon in the natural environment. In this research, the biomineralization process and oxidative stress response of the geoactive soil fungus Aspergillus niger were investigated in the presence of toxic metals (Co, Cu, Mn, and Fe) and the azo dye orange II (AO II). We have found that the co-existence of toxic metals and AO II not only enhanced the fungal biomineralization of toxic metals but also accelerated the removal of AO II. We hypothesize that the fungus and in situ mycogenic biominerals (toxic metal oxalates) constituted a quasi-bioreactor, where the biominerals removed organic pollutants by catalyzing reactive oxygen species (ROS) generation resulting from oxidative stress. We have therefore demonstrated that a fungal/biomineral system can successfully achieve the goal of toxic metal immobilization and organic pollutant decomposition. Such findings inform the potential development of fungal-biomineral hybrid systems for mixed pollutant bioremediation as well as provide further understanding of fungal organic-inorganic pollutant transformations in the environment and their importance in biogeochemical cycles.

Heterogeneous Coprecipitation of Nanocrystals with Metals on Substrates.

ConspectusThe heterogeneous coprecipitation of nanocrystals with metals on substrates plays a significant role in both natural and engineered systems. Due to the small dimensions and thereby the large specific surface area, nanocrystal coprecipitation with metals, which is ubiquitous in natural settings, exerts drastic effects on the biogeochemical cycling of metals on the earth's crust. Meanwhile, the controlled synthesis of nanocrystals with metal doping to achieve tunable size/composition enables their broad applications as adsorbents and catalysts in many engineered settings. Despite their importance, complex interactions among aqueous ions/polymers, nanocrystals, substrates, and metals are far from being well-understood, leaving the controlling mechanisms for nanocrystal formation with metals on substrates uncovered.In this Account, we discuss our systematic investigation over the past 10 years of the heterogeneous formation of representative nanocrystals with metals on typical substrates. We chose Fe(OH)3 and BaSO4 as representative nanocrystals. Mechanisms for varied metal coprecipitation were also investigated for both types of nanocrystals (i.e., Fe, Al, Cr, Cu, and Pb)(OH)3 and (Ba, Sr)(SO4, SeO4, and SeO3)). Bare SiO2 and Al2O3, as well as those coated with varied organics, were selected as geologically or synthetically representative substrates. Through the integration of state-of-the-art nanoscale interfacial characterization techniques with theoretical calculations, the complex interactions during nanocrystal formation at interfaces were probed and the controlling mechanisms were identified.For BaSO4 and Fe(OH)3 formation on substrates, the local supersaturation levels near substrates were controlled by Ba2+ adsorption and the electrostatic attraction of Fe(OH)3 monomer/polymer to substrates, respectively. Meanwhile, substrate hydrophobicity controlled the interfacial energy for the nucleation of both nanocrystals on (in)organic substrates. Metal ions' (i.e., Cr/Al/Cu/Pb) hydrolysis constants and substrates' dielectric constants controlled metal ion adsorption onto substrates, which altered the surface charges of substrates, thus controlling heterogeneous Fe(OH)3 nanocrystal formation on substrates by electrostatic interactions. The sizes and compositions of heterogeneous (Fe, Cr)(OH)3 and (Ba, Sr)(SO4, SeO4, SeO3) formed on substrates were found to be distinct from those of homogeneous precipitates formed in solution. The substrate (de)protonation could alter the local solution's pH and the substrates' surface charge; substrates could also adsorb cations, affecting local Fe/Cr/Ba/Sr ion concentrations at solid-water interfaces, thus controlling the amount/size/composition of nanocrystals by tuning their nucleation/growth/deposition on substrates. From slightly supersaturated solution, homogeneous coprecipitates of microsized (Ba, Sr)(SO4, SeO4, SeO3) formed through growth, with little Sr/Se(VI) incorporation due to higher solubilities of SrSO4 and BaSeO4 over BaSO4. While cation enrichment near substrates made the local solution highly supersaturated, nanosized coprecipitates formed on substrates through nucleation, with more Sr/Se(VI) incorporation due to lower interfacial energies of SrSO4 and BaSeO4 over BaSO4. The new insights gained advanced our understanding of the biogeochemical cycling of varied elements at solid-water interfaces and of the controlled synthesis of functional nanocrystals.

Pioneer Studies on Metagenomic Evaluation of Diversity of Microbial Community in Banded Iron Formation (BIF) from Iron Ore Mining Belt of Goa, India

Goa is situated in the northwestern part of the Western Dharwar Craton (WDC) which is Asia’s major metallogenic province. The iron ore of Goa is associated with greenstone and occurs as bands, reefs, and lenses of Banded Hematite Quartzite (BHQ) and Banded Magnetite Quartzite (BMQ) none of these are explored for geo-microbiological dimensions, such as detection of microbioform Gold. The presence of metalliferous WDC in Goa affords sampling of auriferous materials from mining area having hitherto BHQ at latitude 15°29′54″ N and longitude 74° 03′44″ E) and BMQ at latitude 15°24′12″ N and longitude 74° 09′31″ E were collected, surface sterilized and drilled with a sterile driller to get the endolithic material under sterile conditions and sent for metagenomic analysis using Oxford nanopore sequencing. Both the samples showed the presence of microorganisms with Archea, such as Haloferax, Nitrososphaera, and Eubacteria, i.e., Bacillus, Ralstonia, Cupriavidus, Burkholderia, and Acetobacter. The traditional model of Banded Iron Deposition assumes precipitation by the oxidation of hydrothermal Fe (II), either via abiotic oxidation or biotic oxidation through chemo lithotrophic Eubacteria, such as cyanobacteria which produce oxygen. This paper reports the diversity and the presumptive role of these microorganisms in the biogeochemical cycling of metals, such as Fe, Mn, and gold (Au).

Trace metal complexation with dissolved organic matter stresses microbial metabolisms and triggers community shifts: The intercorrelations

The response of microorganisms to heavy metal-dissolved organic matter (Me-DOM) complexation is critical for the microbial-mediated coupled biogeochemical cycling of metals and DOM. This study investigated the impact of typical metals [As, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, and Zn (at an environmentally-relevant concentration of 200 ppb)], model DOM substrates [humic acids (HA) and bovine serum albumin (BSA)], and their complexation on riverine microbial DOM metabolisms. DOM biodegradability decreased after the metal complexation (especially Co, Cr, and Mn for HA and Ni for BSA). While microbial transformation of humics and proteins was observed, components with lower aromaticity and hydrophobicity were accumulated during the cultivation. The substrate difference and metal speciation changed community compositions and resulted in distinctive community member networks, which accounted for the varied metabolic DOM patterns. The correlations indicated that rather than metal uptakes, Me-DOM complexation and community shifts controlled microbial DOM metabolisms. Microbial BSA metabolisms were less correlated to the key genera identified by network analysis or community diversity. Instead, they were sensitive to metal speciation, which may be attributed to the complicated utilization and production of proteins and their essential roles in detoxification. The constructed correlations among metals (Me-DOM complexes), DOM metabolisms, and community shifts provide strong implications for the biogeochemical function of Me-DOM complexes and highlight the effect of metal speciation on microbial protein metabolisms even at trace concentrations.

Chemical Speciation of Antarctic Atmospheric Depositions

Both inorganic and organic complexation of metal cations in clouds or rainwater is essential to describe the global biogeochemical cycles of metals, because complexation can increase metal solubility and stabilize some of their oxidation states. Within a Project of the National Research Program in the Antarctica, atmospheric depositions were collected during the Antarctic summer 2017–2018 in eight sampling sites. The main ionic components occurring in water extracts of these atmospheric depositions were quantified, and a chemical model was applied, in order to identify the main species occurring in the samples. The speciation study showed that most cations were present as aquoions, except for Fe, which occurred predominantly in hydrolytic forms. The model allowed us to foresee the effect of an increase in the concentration levels of all the solution components, by simulating what could happen when the original particles act as cloud condensation nuclei. The role of inorganic anions as complexing agents becomes important when increasing total concentrations of all the solutes by a factor >100 compared to the water extracts, while the presence of organic acids acquires significance for samples having organic acid concentration higher than 10−5 mol L−1. Moreover, it was possible to pinpoint the formation constants that mostly affect the chemical system, and to gain insight into the behavior of metals in wet depositions, which is fundamental knowledge in atmospheric photochemistry studies and in the modeling of the biogeochemical cycles of metal cations.

Climate influence on zinc isotope variations in a loess–paleosol sequence of the Chinese Loess Plateau

Zinc (Zn) is an essential micronutrient, and its isotopes are increasingly applied to understand trace metal biogeochemical cycling. Atmospheric deposition from anthropogenic or natural origins can perturbate the nutrient supply globally. However, our understanding on Zn isotope variations in natural mineral dust and during dust–climate interaction is still rare. This study presents Zn isotope data and leaching experiments with ammonium acetate buffering solution (pH = 5) on a loess–paleosol profile (S0–L3) from the Yimaguan section in the central Chinese Loess Plateau. The loess–paleosol sequence records the contributions from Asian mineral dust accumulation and chemical weathering, and the response to glacial–interglacial climate changes. Bulk loess–paleosol samples display limited Zn/Al (3.5 × 10-4 – 4.5 × 10-4) and δ66Zn variations (0.17–0.30‰). The mean δ66Zn of paleosol (0.19 ± 0.01‰, 2SD/√n, n = 11) is slightly lower than that of loess (0.24 ± 0.01‰, 2SD/√n, n = 13). Correlations with magnetic susceptibility and grain size distribution suggest that bulk δ66Zn variations between loess and paleosol are not sensitive to glacial–interglacial source fluctuations or wind sorting, but could result from loess pedogenesis.The leachable Zn fractions have high δ66Zn values (0.80–1.29‰) and display good positive correlations with Ca, Sr, Mg, Fe and Mn (r > 0.7), suggesting that carbonates are enriched in heavy Zn isotopes. Although Zn contents in carbonates are low (<3%) and dissolution of carbonates alone cannot explain the bulk Zn/Al variations (∼7% of Zn loss), significant carbonate weathering and biotic activities during loess pedogenesis could modify soil conditions (pH) and provide dissolved bicarbonate ions and organic ligands, which may facilitate the transport of heavy Zn isotopes by soil liquids. Conversely, the bulk δ66Zn of loess developed during glacial times were not modified by the low degree of chemical weathering, and thus the mean value of 0.24‰ for loess can be regarded as the average composition of the upper continental crust.

Bioprospecting of Extremophilic Microorganisms to Address Environmental Pollution.

Geothermal springs are rich in various metal ions due to the interaction between rock and water that takes place in the deep aquifer. Moreover, due to seasonality variation in pH and temperature, fluctuation in element composition is periodically observed within these extreme environments, influencing the environmental microbial communities. Extremophilic microorganisms that thrive in volcanic thermal vents have developed resistance mechanisms to handle several metal ions present in the environment, thus taking part to complex metal biogeochemical cycles. Moreover, extremophiles and their products have found an extensive foothold in the market, and this holds true especially for their enzymes. In this context, their characterization is functional to the development of biosystems and bioprocesses for environmental monitoring and bioremediation. To date, the isolation and cultivation under laboratory conditions of extremophilic microorganisms still represent a bottleneck for fully exploiting their biotechnological potential. This work describes a streamlined protocol for the isolation of thermophilic microorganisms from hot springs as well as their genotypical and phenotypical identification through the following steps: (1) Sampling of microorganisms from geothermal sites ("Pisciarelli", a volcanic area of Campi Flegrei in Naples, Italy); (2) Isolation of heavy metal resistant microorganisms; (3) Identification of microbial isolates; (4) Phenotypical characterization of the isolates. The methodologies described in this work might be generally applied also for the isolation of microorganisms from other extreme environments.

Ferrihydrite Reduction by Photosynthetic Synechocystis sp. PCC 6803 and Its Correlation With Electricity Generation.

Microbial extracellular electron transfer (EET) to solid-state electron acceptors such as anodes and metal oxides, which was originally identified in dissimilatory metal-reducing bacteria, is a key process in microbial electricity generation and the biogeochemical cycling of metals. Although it is now known that photosynthetic microorganisms can also generate (photo)currents via EET, which has attracted much interest in the field of biophotovoltaics, little is known about the reduction of metal (hydr)oxides via photosynthetic microbial EET. The present work quantitatively assessed the reduction of ferrihydrite in conjunction with the EET of the photosynthetic microbe Synechocystis sp. PCC 6803. Microbial reduction of ferrihydrite was found to be initiated in response to light but proceeded at higher rates when exogenous glucose was added, even under dark conditions. These results indicate that current generation from Synechocystis cells does not always need light irradiation. The qualitative trends exhibited by the ferrihydrite reduction rates under various conditions showed significant correlation with those of the microbial currents. Notably, the maximum concentration of Fe(II) generated by the cyanobacterial cells under dark conditions in the presence of glucose was comparable to the levels observed in the photic layers of Fe-rich microbial mats.

Role of Protein in Fungal Biomineralization of Copper Carbonate Nanoparticles

Biomineralization processes are of key importance in the biogeochemical cycling of metals and other elements by microorganisms, and several studies have highlighted the potential applications of nanoparticle synthesis via biomineralization. The roles played by proteins in the transformation and biologically induced biomineralization of metals by microorganisms is not well understood, despite the interactions of protein and nanoparticles at mineral interfaces attracting much interest in various emerging fields for novel biomaterial synthesis. Here, we have elucidated the association and involvement of fungal proteins in the formation of biogenic copper carbonate nanoparticles (CuNPs) using a carbonate-enriched biomass-free ureolytic fungal culture supernatant. Proteomic analysis was conducted that identified the major proteins present in the culture supernatant. Of the proteins identified, triosephosphate isomerase (TPI) exhibited a strong affinity to the CuNPs, and the impact of purified TPI on CuNP formation was studied in detail. The combined use of scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM) confirmed that TPI played an important role in controlling the morphology and structure of the nanomaterials. Fourier transform infrared spectroscopy (FTIR) was applied to examine conformational changes of the proteins to further clarity the interaction mechanisms with CuNPs during biomineralization. Such analyses revealed unfolding of proteins on the mineral surface and an increase in β sheets within the protein structure. These results extend understanding of how microbial systems can influence biomineral formation through protein secretion, the mechanisms involved in formation of complex protein/inorganic systems, and provide useful guidelines for the synthesis of inorganic-protein based nanomaterials.

Volcanic ash inputs enhance the deep-sea seabed metal-biogeochemical cycle: A case study in the Yap Trench, western Pacific Ocean

Although volcanic ash deposition into oceans has been a frequent phenomenon for much of geologic history, the potential effects on deep-sea seabed metal-biogeochemical cycles remain enigmatic. In this study, we analyzed mineral compositions, microbial communities, and metal-related functional genes in a sediment core with volcanic ash layers from the Yap Trench in the western Pacific Ocean. The mineralogical analysis showed that volcanic activity introduced large amounts of Fe-rich igneous minerals, such as olivine, pyroxene, hornblende, grossularite, and biotite, into the trench seabed sedimentary environments. Furthermore, some differentiation in microbial communities was observed and potential Fe-metabolizing bacteria (such as Pseudomonas, Alteromonas, Marinobacter, Halomonas, Pseudoalteromonas, and Erythrobacter) were dominant in the volcanic ash layers. Moreover, compared with the background sediment metagenome, the volcanic ash metagenomes were enriched in pathways for siderophore synthesis and uptake, and metal resistant functional genes. These results suggest that volcanic ash can lead to changes in trench-sediment-based microbial communities and stimulate microbial Fe acquisition and other metal-related metabolism. In response, microorganisms could promote decomposition of the metal-rich volcanic minerals and metal release rates from them, subsequently enhancing the deep-sea metal-biogeochemical cycle.

Biomineralization of Cu2S Nanoparticles by Geobacter sulfurreducens.

Biomineralization of Cu has been shown to control contaminant dynamics and transport in soils. However, very little is known about the role that subsurface microorganisms may play in the biogeochemical cycling of Cu. In this study, we investigate the bioreduction of Cu(II) by the subsurface metal-reducing bacterium Geobacter sulfurreducens Rapid removal of Cu from solution was observed in cell suspensions of G. sulfurreducens when Cu(II) was supplied, while transmission electron microscopy (TEM) analyses showed the formation of electron-dense nanoparticles associated with the cell surface. Energy-dispersive X-ray spectroscopy (EDX) point analysis and EDX spectrum image maps revealed that the nanoparticles are rich in both Cu and S. This finding was confirmed by X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) analyses, which identified the nanoparticles as Cu2S. Biomineralization of CuxS nanoparticles in soils has been reported to enhance the colloidal transport of a number of contaminants, including Pb, Cd, and Hg. However, formation of these CuxS nanoparticles has only been observed under sulfate-reducing conditions and could not be repeated using isolates of implicated organisms. As G. sulfurreducens is unable to respire sulfate, and no reducible sulfur was supplied to the cells, these data suggest a novel mechanism for the biomineralization of Cu2S under anoxic conditions. The implications of these findings for the biogeochemical cycling of Cu and other metals as well as the green production of Cu catalysts are discussed.IMPORTANCE Dissimilatory metal-reducing bacteria are ubiquitous in soils and aquifers and are known to utilize a wide range of metals as terminal electron acceptors. These transformations play an important role in the biogeochemical cycling of metals in pristine and contaminated environments and can be harnessed for bioremediation and metal bioprocessing purposes. However, relatively little is known about their interactions with Cu. As a trace element that becomes toxic in excess, Cu can adversely affect soil biota and fertility. In addition, biomineralization of Cu nanoparticles has been reported to enhance the mobilization of other toxic metals. Here, we demonstrate that when supplied with acetate under anoxic conditions, the model metal-reducing bacterium Geobacter sulfurreducens can transform soluble Cu(II) to Cu2S nanoparticles. This study provides new insights into Cu biomineralization by microorganisms and suggests that contaminant mobilization enhanced by Cu biomineralization could be facilitated by Geobacter species and related organisms.

Biogeochemical cycling of heavy metals in lake sediments: impact of multispecies diffusion and electrostatic effects

Fate and transport of heavy metals is controlled by the biogeochemical processes in the environment. Reactive transport modeling is particularly important for capturing the complex interplay between the microbial community dynamics and redox-stratified environments. The focus of this study is to investigate the impacts of (i) multicomponent diffusion (MCD) and (ii) electrical double layer (EDL) on reactive diffusive transport of heavy metals at Lake Coeur d’Alene (LCdA) sediments. The solute benthic fluxes at LCdA sediments are controlled by diffusion, and therefore, the biogeochemical model is focused purely on diffusive transport. In diffusive transport-dominated multicomponent systems, species-specific multicomponent diffusion (i.e., Nernst-Planck representation of diffusion) and the explicit treatment of electrostatic effects can play an important role on the overall dynamics of biogeochemical cycling of metals in the system. The results of this study demonstrate that the use of single uniform diffusion coefficient for all species in purely diffusion-dominated sediments may underestimate the mobility of heavy metals undergoing complex reaction network. This outcome is further signified when explicit treatment of EDL effects is considered in addition to MCD. The simulation results also illustrate the importance of aqueous metal (bi)sulfide complexes, especially when MCD and EDL effects are implemented in reactive transport simulations, impacting the solubility and dynamics of heavy metals in diffusion-dominated systems. The competitive effects of Fe-reducing bacteria FRB and sulfate reducing bacteria SRB activities on pH and overall biogeochemical processes are also demonstrated with multispecies diffusion and explicit treatment of electrostatic effects in the system.

Geomicrobial Investigations of Colored Outer Coatings from an Ethiopian Rock Art Gallery

The open rock shelter of Yabelo in Ethiopia hosts diverse Holocene paintings of great cultural importance. The paintings are characterized by the presence of different mineral coatings, whose features have not been studied yet. Our goal was to understand whether different rock samples from the Yabelo paintings collected in close proximity may reveal coatings with different minerology and biology. Thus, elemental analyses combined with microscopic and molecular investigations were performed on two coatings, one whitish (sample 1) and one reddish (sample 2). Although both samples were dominated by heterotrophic bacteria, the two coatings showed distinct mineralogical and microbiological characteristics. Sample 1 contained higher amounts of Ca and P than sample 2, which was likely related to the presence of organic matter. Sample 1 hosted bacterial genera that are potentially involved in biomineralization processes, metal redox cycles and metal resistance. In contrast, sample 2 showed mainly pathogenic and commensal bacteria that are characteristic of animal and human microbiota, and other microorganisms that are involved in nitrogen and metal biogeochemical cycles. Overall, our results indicated that the bacterial communities were particular to the coating mineralogy, suggesting a potential role of the biological components in the crust genesis.

Trace metal and nutrient dynamics across broad biogeochemical gradients in the Indian and Pacific sectors of the Southern Ocean

The Southern Ocean is the largest high-nutrient low-chlorophyll environment in the global ocean, and represents an important source of intermediate and deep waters to lower latitudes. Constraining Southern Ocean trace metal biogeochemical cycling is therefore important not just for understanding biological productivity and carbon cycling regionally, but also for understanding trace metal distributions throughout the lower latitude oceans. We present dissolved Fe, Ni, Cu, Zn, Cd, Pb and macronutrient concentrations in the Indian and Pacific sectors of the Southern Ocean from the Antarctic Circumnavigation Expedition (austral summer 2016-17), which included the first opportunities to study trace metal cycling at the Mertz Glacier Polynya and the Balleny Islands, as well as two meridional cross-frontal transects. Dissolved Ni, Cu, Zn, Cd and macronutrient concentrations show similar or greater variability latitudinally within surface waters than vertically through the water column, reflecting the combined influence of circulation and biological drawdown in shaping the distributions of nutrient-type elements in the Southern Ocean. Slopes of Cu-Si(OH)4 and Cd-PO4 increase from the Polar Frontal Zone to south of the Southern ACC Boundary (Cu-Si(OH)4) and from the Subantarctic Zone to the Antarctic Zone (Cd-PO4). Latitudinal differences are also observed for Ni-Si(OH)4 and Zn-PO4, with distinct Subantarctic Zone trends relative to those south of the Polar Front. Similarities between our Zn-Si(OH)4 and Cd-PO4 correlations and global compilations reflect the importance of exported Southern Ocean waters in setting these metal-macronutrient couples globally. Distinct Ni-macronutrient correlations are observed in this dataset relative to the global ocean, which supports a distinct cycling of Ni in the Southern Ocean compared to other basins. Concentrations of Pb are among the lowest observed in the global ocean; however, a local maximum is seen along the density level corresponding with Antarctic Intermediate Water. Concentrations within this isopycnal decrease with increasing latitude, which can be explained by decreasing atmospheric Pb input to more recently subducted waters.Substantial biological uptake of metals and macronutrients is observed at the Mertz Glacier Polynya. Here, inferred metal:macronutrient uptake ratios are comparable to those found in the Amundsen Sea Polynya, in Southern Ocean phytoplankton, and to metal-macronutrient correlations in our data set as a whole, highlighting the potential of Southern Ocean polynyas as natural systems for trace metal uptake and export studies. The Balleny Islands are a source of Fe to surface waters and the islands also appear to influence distributions of Zn, Cu and macronutrients, which may reflect the combined impact of Fe supply on biological uptake, mixing, and scavenging in deeper waters. The Kerguelen Plateau is also a source of Fe, as previously identified. Throughout our dataset, the ferricline is found deeper than the nitricline, in agreement with existing data and indicating that Fe is less easily entrained into the surface ocean than NO3. Additionally, Fe:NO3 ratios in most samples throughout the water column are Fe-limiting (<0.01 mmol mol−1). Therefore deep mixing, identified previously as the main Fe source to much of the Southern Ocean, would ultimately act to maintain Fe limitation.

Accumulation of metals and changes in composition of freshwater lake organic sediments during the Holocene

The distribution of metals in the strata of sediments deposited in the freshwater environment formed during the Holocene in the territory of Latvia has been studied rather insufficiently. Considering the large volume of accumulated organic matter in sediments, studies on the content of metallic elements in sediments can help to determine the peculiarities of the metal accumulation process in limnic systems and the biogeochemical cycling of metals. Lake Pilvelis, which is located in the eastern part of Latvia (the northern part of Europe), was selected as the main study site. Lake Pilvelis is a small lake of a glacial origin, and >90% of its depression is filled with organic-rich sediments. The development stages of Lake Pilvelis since circa 10,000 cal BP are described in detail via reconstruction of the Holocene palaeoenvironmental conditions using multi-proxy sedimentary records. The elemental composition and content of metallic elements in sapropel are analysed with the main objectives of characterising the accumulation rate of metals in the full profile of sapropel and determining the anthropogenic impact depending on the evolution of the lake and the genesis of sediment organic matter. The correlation among the components characterising sediments such as sapropel and metallic elements revealed that the elemental distribution could be divided into three main groups according to the content of the elements associated with organic compounds (e.g., for Zn and Mn) and mineral compounds (for Ni, Co, Cr, K, Fe, Mg, and Cu). Ni and Co are partly associated with mineral compounds and partly associated with carbonates. A principal component analysis revealed the main factors indicating the origin of metallic elements and the accumulation tendencies of metals in sediment layers: the input of the mineral matter, the characteristics of organic matter, and human impact. The content of metallic elements in sapropel from Lake Pilvelis is mainly affected by the composition of mineral matter, not by the size of the particles.

Chemical and microphysical properties of wind-blown dust near an actively retreating glacier in Yukon, Canada

AbstractAirborne mineral aerosols emitted in high-latitude regions can impact radiative forcing, biogeochemical cycling of metals, and local air quality. The impact of dust emissions in these regio...

Cd isotopes trace periodic (bio)geochemical metal cycling at the verge of the Cambrian animal evolution

Abstract Cadmium (Cd) isotopes are an emerging proxy for biological controlled metal and nutrient cycling in the modern oceans, but its potential as a geochemical proxy in ancient environments is still uncertain yet. Sequential leaching experiments of organic matter (OM)-rich shales from the early Cambrian Niutitang Formation (Fm.) were performed in order to understand the cycling of bioessential metals short after the Cambrian animal evolution. Carbonate, OM, sulphide and silicate leachates of OM-rich shales show an overall Cd isotope variation of 6 e112Cd/110Cd (e112Cd) units, indicating preferential incorporation of light Cd isotopes in the order sulphide > OM > carbonate > silicate. Carbonate leachates not only show negative correlations of e112Cd with bulk-rock total organic carbon (TOC) and δ13Corg but also show co-variations with redox-sensitive elements and bioessential metal concentrations, indicating a combined redox and primary productivity evolution of the early Cambrian Nanhua Basin on the Yangtze. Together with increased Cd/Zn ratios and decreasing total organic carbon (TOC) and redox-sensitive elements (RSE) concentrations in the upper Niutitang, this argues for an increase in essential metal availability for primary producers. Coinciding with the transition from a highly unstable ecosystem shortly after the Precambrian/Cambrian boundary to a more habitable environment increased nutrient uptake, oxygen availability and enhanced dissolved organic carbon (DOC) recycling match with the diversification of early metazoan fossil findings at the studied local. Our findings demonstrate that Cd isotopes in combination with trace metals can be used to infer changes in biogeochemical metal cycling in paleoenvironments and further allow establishing Cd isotope systematics as a reliable paleoproductivity proxy in the search for Earth’s earliest phototrophic life.

Moss facilitating mercury, lead and cadmium enhanced accumulation in organic soils over glacial erratic at Mt. Gongga, China

Moss is usually as an initial colonizer in alpine glacier retreated regions. We hypothesized that moss can significantly facilitate the toxic metals accumulation in alpine ecosystems based on its strong ability of absorption and the role in soil development. Hence, we investigated the trace element pool sizes and enrichment factors, especially for mercury (Hg) by using the Hg isotopic compositions to determine the source contributions in a moss-dominated ecosystem over glacial erratic in Eastern Tibetan Plateau. Results show that Hg, lead (Pb) and cadmium (Cd) are highly enriched in organic soils. Specifically, Cd concentration is 5–20 times higher than the safety limit of the acid soil (pH ≤ 5.5) in China. Atmospheric depositions dominantly contribute to the Pb and Cd sources in organic soils, and followed by the moraine particles influences. The lowering pH in organic soils increasing with glacial retreated time results in the desorption of Cd in organic soils. Atmospheric Hg0 uptake by moss predominantly contributes to the Hg sources in organic soils. The average Pb accumulation rate over last 125-year is about 5.6 ± 1.0 mg m−2 yr−1, and for Cd is 0.4 ± 0.1 mg m−2 yr−1, and for Hg0 is 27.6 ± 3.2 μg m−2 yr−1. These elevated accumulation rates are caused by the high moss biomass and elevated atmospheric Hg, Pb and Cd pollution levels in China and neighbouring regions. Our study indicates that the moss not only as the bioindicator, but also plays an important role in the hazardous metal biogeochemical cycling in alpine regions.

Dynamic Regulation of Extracellular Superoxide Production by the Coccolithophore Emiliania huxleyi (CCMP 374).

In marine waters, ubiquitous reactive oxygen species (ROS) drive biogeochemical cycling of metals and carbon. Marine phytoplankton produce the ROS superoxide (O2−) extracellularly and can be a dominant source of O2− in natural aquatic systems. However, the cellular regulation, biological functioning, and broader ecological impacts of extracellular O2− production by marine phytoplankton remain mysterious. Here, we explored the regulation and potential roles of extracellular O2− production by a noncalcifying strain of the cosmopolitan coccolithophorid Emiliania huxleyi, a key species of marine phytoplankton that has not been examined for extracellular O2− production previously. Cell-normalized extracellular O2− production was the highest under presumably low-stress conditions during active proliferation and inversely related to cell density during exponential growth phase. Removal of extracellular O2− through addition of the O2− scavenger superoxide dismutase (SOD), however, increased growth rates, growth yields, cell biovolume, and photosynthetic efficiency (Fv/Fm) indicating an overall physiological improvement. Thus, the presence of extracellular O2− does not directly stimulate E. huxleyi proliferation, as previously suggested for other phytoplankton, bacteria, fungi, and protists. Extracellular O2− production decreased in the dark, suggesting a connection with photosynthetic processes. Taken together, the tight regulation of this stress independent production of extracellular O2− by E. huxleyi suggests that it could be involved in fundamental photophysiological processes.

Metal transfer budgets in a Mediterranean marine environment subjected to natural and anthropogenic inputs: case of the Mejerda River Delta (Gulf of Tunis, northern Tunisia).

Deltaic sediments are important for biogeochemical metal cycling since they are hotspots for metal inputs. In addition, they are potential sites for diagenetic processes leading to either the burial of inorganic contaminants or their release. Diffusive fluxes of certain metals (Fe, Mn, Pb, Zn, Cu and Cd) in the sediments of the Mejerda River Delta (MRD) (Gulf of Tunis, Tunisia) were quantified by modeling the available concentration profiles in the pore water. The metals' burial and sedimentation fluxes were also calculated using both the asymptotic concentrations of available metal profiles and sediment trap results. These fluxes were assembled with the exchange fluxes at the sediment-water interface in order to develop complete metal transfer budgets. The results showed that budgets of Cu and Zn are almost neutral. The sediment appears to be a good trap for iron since its average burial flux at the three studied stations is about 332.6gm-2year-1. Organic matter degradation, carbonate dissolution, and oxyhydroxide reduction are the main mechanisms which accelerate the release of metals associated with the suspended particle matter once they reach the pore water in the seabed.