Trace Metal Chemistry Research Articles

Declining metal availability in the Mesozoic seawater reflected in phytoplankton succession

Variable trace metal concentrations in the Precambrian ocean were closely linked to oxygen availability, although less is known about the drivers of seawater trace metal chemistry after the spread of complex life into the Phanerozoic eon. A major phytoplankton succession took place at the transition from the Palaeozoic to the Mesozoic era (~250 Myr ago), from an ocean dominated by the green Archaeplastida to secondary endosymbiotic algae with red-algal-derived plastids. Here, our comparative genomic analysis of 26 complete proteomes and metal domain analysis of additional 608 partially complete sequences of phytoplankton reveal that groups with different evolutionary history have distinct metal-binding proteins and contrasting metal acquisition strategies, adapted to differing availability of trace metals. The secondary-endosymbiont-bearing lineages are better adapted to well-oxygenated, nutrient-poor environments. This is supported by an enhanced thiol-based binding affinity of their transporters, coupled with minimized proteomic requirement for trace elements such as iron, copper and zinc at both protein and domain levels. Such different metal requirements across these lineages suggest a drastic decline in open-ocean trace metal concentrations at the inception of the Mesozoic, contributing to the shifts in phytoplankton communities that drove major changes in ocean chemical buffering.

Mineral-scale variation in the trace metal and sulfur isotope composition of pyrite: implications for metal and sulfur sources in mafic VMS deposits

The link between metal enrichment and the addition of a magmatic volatile phase in volcanogenic massive sulfide deposits and actively forming seafloor massive sulfide deposits remains poorly characterized. This is especially true when considering how metal, sulfur and fluid flux change with time. In this study, we combine in situ sulfur isotope (δ34S; n = 31) measurements with trace metal chemistry of pyrite (n = 143) from the Mala VMS deposit, Troodos, Cyprus. The aim of our study is to assess the links between volatile influx and metal enrichment and establish how, or indeed if, this is preserved at the scale of individual mineral grains. We classify pyrite based on texture into colloform, granular, disseminated and massive varieties. The trace metal content of different pyrite textures is highly variable and relates to fluid temperature and secondary reworking that are influenced by the location of the sample within the mound. The sulfur isotope composition of pyrite at Mala ranges from − 17.1 to 7.5‰ (n = 31), with a range of − 10.9 to 2.5‰ within a single pyrite crystal. This variation is attributed to changes in the relative proportion of sulfur sourced from (i) SO2 disproportionation, (ii) thermochemical sulfate reduction, (iii) the leaching of igneous sulfur/sulfide and (iv) bacterial sulfate reduction. Our data shows that there is no correlation between δ34S values and the concentration of volatile elements (Te, Se) and Au in pyrite at Mala indicating that remobilization of trace metals occurred within the mound.

Synchrotron x‐ray fluorescence analysis reveals diagenetic alteration of fossil melanosome trace metal chemistry

AbstractA key feature of the pigment melanin is its high binding affinity for trace metal ions. In modern vertebrates trace metals associated with melanosomes, melanin‐rich organelles, can show tissue‐specific and taxon‐specific distribution patterns. Such signals preserve in fossil melanosomes, informing on the anatomy and phylogenetic affinities of fossil vertebrates. Fossil and modern melanosomes, however, often differ in trace metal chemistry; in particular, melanosomes from fossil vertebrate eyes are depleted in Zn and enriched in Cu relative to their extant counterparts. Whether these chemical differences are biological or taphonomic in origin is unknown, limiting our ability to use melanosome trace metal chemistry to test palaeobiological hypotheses. Here, we use maturation experiments on eye melanosomes from extant vertebrates and synchrotron rapid scan‐x‐ray fluorescence analysis to show that thermal maturation can dramatically alter melanosome trace element chemistry. In particular, maturation of melanosomes in Cu‐rich solutions results in significant depletion of Zn, probably due to low pH and competition effects with Cu. These results confirm fossil melanosome chemistry is susceptible to alteration due to variations in local chemical conditions during diagenesis. Maturation experiments can provide essential data on melanosome chemical taphonomy required for accurate interpretations of preserved chemical signatures in fossils.

The relationship between zinc, its isotopes, and the major nutrients in the North-East Pacific

Trace metal micronutrients play key roles in photosynthesis by oceanic phytoplankton. Though they are required in much smaller amounts than the major nutrients (P, N, Si), their bioavailable forms are also present in the seawater solution at much lower levels. Relationships between the dissolved chemistry of the nutrient-type trace metals, their stable isotope variations, as well those of the major nutrients, have highlighted the importance of biological and physical processes in the Southern Ocean in controlling their oceanic biogeochemistry. However, the first-order Southern Ocean processes are overprinted by vertical cycling in other parts of the ocean, particularly upwelling regions remote from the Southern Ocean, with the North Pacific standing out in particular. Here we present new zinc (Zn) concentration and isotope, as well as major nutrient data for the NE Pacific, and couple these new data with a compilation of published data from across the region, with the objective of better understanding the impact of this important region on oceanic biogeochemical cycles.The new Zn isotope data for two stations along Line P (P04 and P26) show a large range in δ66Zn in the upper ocean (−0.4‰ up to >1‰), associated with a very small isotope fractionation but extreme depletion of the dissolved pool during photic zone biological uptake, and the regeneration of this cellular Zn at very shallow depths (50 m). Beneath this, the two profiles approach the δ66Zn value of +0.5‰, seen throughout the deep ocean, by about 500 m. The minimum δ66Zn resulting from regeneration is associated with very high Zn concentrations, particularly at the marginal P04 station where diatoms dominate the phytoplankton ecology. Combining the new data with published Zn and major nutrient concentrations from across the North Pacific emphasises the role of vertical biological cycling in controlling regional biogeochemistry in the North Pacific, resulting in the partial overprinting of biogeochemical signatures transported out of the Southern Ocean by the ocean circulation. Zinc isotope data document the uptake of this metal into diatoms and the co-regeneration of Zn with phosphate in the upper water column. Silica in contrast is regenerated at greater depth, resulting in a decoupling of the Zn–Si correlation that is set in the Southern Ocean and that dominates the Atlantic. Previous work has suggested that the decoupling of Zn and Si in the subarctic North Pacific results from removal of Zn (and other metals) to water column particulate sulphide. In our dataset, and in the compilation of data documenting relationships between Zn and the major nutrients across the North Pacific, this decoupling is clearly due to the different lengthscales of regeneration for organic matter (Zn and P) and diatom opal (Si).

Zinc association with surface-bound iron-hydroxides on cultured marine diatoms: A zinc stable isotope perspective

Abstract Uptake of trace metals by marine phytoplankton for metabolic use exerts a fundamental control on their marine geochemical distributions. Moreover, such trace metals limit primary productivity over large areas of the surface ocean. As such, an understanding of the mechanisms and extent of phytoplankton uptake are essential components of oceanic trace metal chemistry. Efforts to quantify intra-cellular quotas of phytoplankton are complicated by the presence of metals adsorbed to external surfaces, including surface-bound Fe-hydroxides, both in nature and in culturing experiments. In the relatively new discipline focused on oceanic metal isotopes, these surface-bound metal hydroxides may be of particular importance in that they could result in isotope signatures that complicate studies that seek to understand intra-cellular signatures related to metabolic uptake. In this contribution, we assess the extent to which heavy Zn isotopes are preferentially adsorbed to surface-bound Fe-hydroxides on marine diatoms. For this purpose, the marine diatom Thalassiosira oceanica has been cultured at low versus high inorganic Fe concentrations in the medium, while two further diatoms strains have been compared at elevated Fe levels. The formation of surface bound Fe-hydroxides at elevated Fe was further stimulated by reducing the trace metal buffering capacity of the experimental medium, lowering the concentration of the used organic chelator. We also investigate an alternative procedure for quantifying intra-cellular metal quotas, the analysis of the contents of deliberately lysed cells. In good agreement with previous work, we find that biomass associated Fe/P ratios represent a good proxy for the absolute quantity of Fe-precipitates on diatom surfaces. Zn sorption to these surface-bound Fe-hydroxides can drive bulk biomass δ 66Zn compositions up. On the other hand, the loss of heavy Zn from the experimental medium causes the biomass Δ66Zn, if referred to the starting medium, to be biased in the other direction, towards more negative values. To avoid any such complications, likely to occur at high Fe or low buffer capacities, we conclude that diatoms cultured at low Fe are most likely to record the Δ66Zn signatures of Zn uptake into the phytoplankton cell.

Synoptic sampling and principal components analysis to identify sources of water and metals to an acid mine drainage stream

Combining the synoptic mass balance approach with principal components analysis (PCA) can be an effective method for discretising the chemistry of inflows and source areas in watersheds where contamination is diffuse in nature and/or complicated by groundwater interactions. This paper presents a field-scale study in which synoptic sampling and PCA are employed in a mineralized watershed (Lion Creek, Colorado, USA) under low flow conditions to (i) quantify the impacts of mining activity on stream water quality; (ii) quantify the spatial pattern of constituent loading; and (iii) identify inflow sources most responsible for observed changes in stream chemistry and constituent loading. Several of the constituents investigated (Al, Cd, Cu, Fe, Mn, Zn) fail to meet chronic aquatic life standards along most of the study reach. The spatial pattern of constituent loading suggests four primary sources of contamination under low flow conditions. Three of these sources are associated with acidic (pH <3.1) seeps that enter along the left bank of Lion Creek. Investigation of inflow water (trace metal and major ion) chemistry using PCA suggests a hydraulic connection between many of the left bank inflows and mine water in the Minnesota Mine shaft located to the north-east of the river channel. In addition, water chemistry data during a rainfall-runoff event suggests the spatial pattern of constituent loading may be modified during rainfall due to dissolution of efflorescent salts or erosion of streamside tailings. These data point to the complexity of contaminant mobilisation processes and constituent loading in mining-affected watersheds but the combined synoptic sampling and PCA approach enables a conceptual model of contaminant dynamics to be developed to inform remediation.

Trace Metal Distribution and Mobility in Soils after Silvicultural Thinning and Burning

Silvicultural thinning and burning are common management practices that are widely used to address ecosystem problems such as tree stocking and general forest health. However, high-severity fire has variable effects on soils, resulting in damages which are directly or indirectly reflected on the trace metal chemistry of the soil. This study was conducted to evaluate the trace metal variation at the Bankhead National Forest in Northern Alabama following the silvicultural thinning and burning. The experimental site had treatments consisting of two burning patterns and three levels of thinning as part of an overall treatment of three burning patterns and three levels of thinning applied to nine treatment plots to fit a completely randomized block design experiment. Four treatments sites were used for this study and samples were collected from soil profile pits excavated at representative plots within each treatment. The samples were analyzed for trace metals-As, Cu, Ni, Zn and Pb-using Perkin Elmer 2100 ICP-OES. Post treatment samples indicated that the trace metal concentrations generally decreased with soil depth. Copper, Ni, and Zn at the Pre-burn site gradually increased with depth to a maximum concentration at about 50 cm below the soil surface. Arsenic in the surface horizons increased by 156% in the burn-only sites, 54% in the thin-only treatment, 30% for the burn and thin treatments. Such differences were unlikely due to differences in the geochemistry of the parent material, but likely due to anthropogenic activities and possibly the forest management practices in question.

Reconstructing Early Industrial Contributions to Legacy Trace Metal Contamination in Southwestern Pennsylvania.

Early industrial trace metal loadings are poorly characterized but potentially substantial sources of trace metals to the landscape. The magnitude of legacy contamination in southwestern Pennsylvania, the cradle of North American fossil fuel industrialization, is reconstructed from trace metal concentrations in a sediment core with proxies including major and trace metal chemistry, bulk density, and magnetic susceptibility. Trace metal chemistry in this sediment record reflects 19th and 20th century land use and industry. In particular, early 19th century arsenic loadings to the lake are elevated from pesticides used by early European settlers at a lakeside tannery. Later, sediment barium concentrations rise, likely reflecting the onset of acidic mine drainage from coal operations. Twentieth century zinc, cadmium, and lead concentrations are dominated by emissions from the nearby, infamous Donora Zinc Works yet record both the opening of a nearby coal-fired power plant and amendments to the Clean Air Act. The impact of early industry is substantial and rivals more recent metal fluxes, resulting in a significant potential source of contaminated sediments. Thus, modern assessments of trace metal contamination cannot ignore early industrial inputs, as the potential remobilization of legacy contamination would impact ecosystem and human health.

Antarctic Palaeoclimate Reconstruction Using Ice Cores: Indian Initiatives during 2008-2016

Study of ice core proxy records provide one of the most direct and accurate method to study the Antarctic climate change beyond the instrumental limits. Understanding the Antarctic climate variability on millennial, centennial to decadal level is crucial to our knowledge on the role and response of Antarctic ice sheets to the global climate variability. The Indian ice core studies have made significant contributions to the understanding of Antarctic climate variability and the various factors involved. The proxy environmental parameters used include temporal variability of stable isotopes, trace metal chemistry, ionic composition, dust particulates, and microbial components that are indicators of environmental change in the coastal Antarctica. Ice core proxy based reconstruction revealed significant changes in Southern Hemispheric climate during the past several hundreds of years. The study also revealed the utility of shallow ice cores in reconstructing the past changes in major climatic modes like the El Nino Southern Oscillation (ENSO) and Southern Annular Mode (SAM).

The unique trace metal and mixed layer conditions of the Costa Rica upwelling dome support a distinct and dense community of Synechococcus

The Costa Rica Dome (CRD) is a wind‐driven upwelling feature in the eastern tropical Pacific that supports unusually high concentrations (&gt; 106 cells mL−1) of the picocyanobacteria Prochlorococcus and Synechococcus. To understand what causes this unusual phytoplankton bloom, we conducted a comprehensive survey of the hydrography, picophytoplankton population structure, and trace metal chemistry of the CRD and surrounding oligotrophic and equatorial upwelling waters. Based on size‐fractionated chlorophyll, picoplankton dominated phytoplankton biomass in the region, and the three water regimes sampled supported different assemblages of Prochlorococcus, Synechococcus, and eukaryotic picophytoplankton. Cobalt (Co), a required nutrient for cyanobacteria, was strongly complexed in surface waters and was at least twice as high in the photic zone of the CRD than in surrounding waters. In contrast, iron (Fe) and manganese (Mn) levels were comparable in and outside the CRD. Synechococcus clades II and CRD1 and Prochlorococcus ecotype eMIT9312 (high light II) were the dominant genotypes throughout the region, as assessed by quantitative polymerase chain reaction assays. The composition of less abundant Synechococcus clade subpopulations differed in and outside the CRD and within the CRD. Co, mixed layer depth, and temperature were the important drivers of both total Synechococcus abundance and cyanobacterial community composition. This supports a model whereby the combination of upwelled macronutrients, high concentrations of complexed Co, and Fe and Mn scarcity in the warm, shallow mixed layer of the CRD limit larger phytoplankton and induce dense concentrations of picocyanobacteria. Globally, we suggest that trace metals influence phytoplankton distributions at both the broad (cyanobacterial vs. eukaryotic) and the fine (ecotype‐level) taxonomic levels.

Origin, distribution and hydrogeochemical controls on methane occurrences in shallow aquifers, southwestern Ontario, Canada

Natural gas reservoirs in organic-rich shales in the Appalachian and Michigan basins in the United States are currently being produced via hydraulic fracturing. Stratigraphically-equivalent shales occur in the Canadian portion of the basins in southwestern Ontario with anecdotal evidence of gas shows, yet there has been no commercial shale gas production to date. To provide baseline data in the case of future environmental issues related to hydraulic fracturing and shale gas production, such as leakage of natural gas, saline water, and/or hydraulic fracturing fluids, and to evaluate hydrogeochemical controls on natural gas accumulations in shallow groundwater in general, this study investigates the origin and distribution of natural gas and brine in shallow aquifers across southwestern Ontario. An extensive geochemical database of major ion and trace metal chemistry and methane concentrations of 1010 groundwater samples from shallow, domestic wells in bedrock and overburden aquifers throughout southwestern Ontario was utilized. In addition, select wells (n=36) were resampled for detailed dissolved gas composition, δ13C of CH4, C2, C3, and CO2, and δD of CH4. Dissolved gases in groundwater from bedrock and overburden wells were composed primarily of CH4 (29.7–98.6mol% of total gas volume), N2 (0.8–66.2mol%), Ar+O2 (0.2–3.4mol%), and CO2 (0–1.2mol%). Ethane was detected, but only in low concentrations (<0.041mol%), and no other higher chain hydrocarbons were present, except for one well in overburden overlying the Dundee Formation, which contained 0.81mol% ethane and 0.21mol% propane. The highest methane concentrations (30 to >100 in situ % saturation) were found in bedrock wells completed in the Upper Devonian Kettle Point Formation, Middle Devonian Hamilton Group and Dundee Formation, and in surficial aquifers overlying these organic-rich shale-bearing formations, indicating that bedrock geology is the primary control on methane occurrences. A few (n=40) samples showed Na–Cl–Br evidence of brine mixing with dilute groundwater, however only one of these samples contained high (>60 in situ % saturation) CH4. The relatively low δ13C values of CH4 (−89.9‰ to −57.3‰), covariance of δD values of CH4 and H2O, positive correlation between δ13C values of CH4 and CO2, and lack of higher chain hydrocarbons (C3+) in all but one dissolved gas sample indicates that the methane in groundwater throughout the study area is primarily microbial in origin. The presence or absence of alternative electron acceptors (e.g. dissolved oxygen, Fe, NO3, SO4), in addition to organic substrates, controls the occurrence of microbial CH4 in shallow aquifers. Microbial methane has likely been accumulating in the study area, since at least the Late Pleistocene to the present, as indicated by the co-variance and range of δD values of CH4 (−314‰ to −263‰) and associated groundwater (−19‰ to −6‰ δD-H2O).

Trace metal chemistry in the pristine freshwater Lake Hauroko, Fiordland, New Zealand

The south-western region of the South Island of New Zealand is remote from human activities and is thought to be minimally affected by anthropogenic contaminants, making it a good candidate for understanding the geochemistry of pristine systems, and for providing baseline concentrations for trace elements and other chemical parameters. We have determined the inorganic and physical characteristics of a remote mountain lake (Lake Hauroko) in this region. The lake exhibits oligotrophic character and major ion concentrations and total alkalinity are very constant throughout summer and winter as well as with depth. Because of the low ionic strength, trace metal concentrations were measured directly on acidified samples by Quadrupole ICP-MS. Concentrations are low throughout, averaging (in ngl−1) for Mn 102.9, Fe 4570, Co 5.31, Ni 98.6, Cu 247.8, Zn 140.7, Cd 1.23 and Pb 24.85. We have compared these results with other lakes in New Zealand, with freshwater systems in Europe and North America as well as with the temperate stream model of Meybeck (1987). These comparisons confirm the very pristine character of this lake, making it an ideal natural laboratory for the study of natural biogeochemical cycles of trace element and nutrients at temperate latitudes.

Characterization of a High Affinity Phytochelatin Synthase from The Cd-Utilizing Marine Diatom Thalassiosira pseudonana.

Phytochelatin synthase (PC synthase) is the enzyme that catalyzes the production of phytochelatins, peptides of the structure (γ-Glu-Cys)n -Gly, where n=2-11, from the sulfhydryl-containing tripeptide glutathione, in response to elevated metal exposure. Biochemical utilization of Cd in the marine diatom Thalassiosira weissfloggi, as well as unusually high ratios of PC to Cd in some Thalassiosira species including T. pseudonana Hasle et Heimdal, motivated the characterization of T. pseudonana PC synthase 1 (TpPCS1). This enzyme is the product of one of three genes in the T. pseudonana genome predicted to encode for a PC synthase based on its homology to canonical PC synthases previously examined. TpPCS1 was cloned, expressed in Escherichia coli and purified under both aerobic and anaerobic conditions. TpPCS1 exhibits several characteristics that set it distinctly apart from the well-studied PC synthase, Arabidopsis thaliana PCS1 (AtPCS1). It is extremely sensitive to oxidation, which suppresses activity, and it is readily inhibited by the addition of Cd in the absence of thiolate ligands. TpPCS1 also has significantly greater affinity for one of its key substrates, the bis-glutathionato-Cd complex. TpPCS1 kinetics is best described by a ternary complex model, as opposed to the ping-pong model used to describe AtPCS1 kinetics. The findings indicate that although the function of TpPCS1 is synonymous to that of AtPCS1, its divergent biochemistry suggests adaptation of this enzyme to the distinct trace metal chemistry of the marine environment and the unique physiological needs of T. pseudonana.

Influence of ocean warming and acidification on trace metal biogeochemistry

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 470:191-205 (2012) - DOI: https://doi.org/10.3354/meps10082 Influence of ocean warming and acidification on trace metal biogeochemistry Linn J. Hoffmann1,2,*, Eike Breitbarth1,2, Philip W. Boyd3, Keith A. Hunter1 1Department of Chemistry, University of Otago, PO Box 56, Dunedin 9054, New Zealand 2GEOMAR Helmholtz Centre for Ocean Research Kiel, Düsternbrooker Weg 20, 24105 Kiel, Germany 3National Institute of Water and Atmosphere Centre of Chemical and Physical Oceanography, Department of Chemistry, University of Otago, PO Box 56, Dunedin 9054, New Zealand *Email: lhoffmann@geomar.de ABSTRACT: Rising atmospheric CO2 concentrations will have profound effects on atmospheric and hydrographic processes, which will ultimately modify the supple and chemistry of trace metals in the ocean. In addition to an increase in sea surface temperatures, higher CO2 results in a decrease in seawater pH, known as ocean acidification, with implications for inorganic trace metal chemistry. Furthermore, direct or indirect effects of ocean acidification and ocean warming on marine biota will affect trace metal biogeochemistry via alteration of biological trace metal uptake rates and metal binding to organic ligands. We still lack a holistic understanding of the impacts of decreasing seawater pH and rising temperatures on different trace metals and marine biota, which complicates projections into the future. Here, we outline how ocean acidification and ocean warming will influence the inputs and cycling of Fe and other biologically relevant trace metals globally and regionally in high and low latitudes of the future ocean; we discuss uncertainties and highlight essential future research fields. KEY WORDS: Ocean acidification · Ocean warming · Trace metals Full text in pdf format PreviousNextCite this article as: Hoffmann LJ, Breitbarth E, Boyd PW, Hunter KA (2012) Influence of ocean warming and acidification on trace metal biogeochemistry. Mar Ecol Prog Ser 470:191-205. https://doi.org/10.3354/meps10082 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 470. Online publication date: December 06, 2012 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2012 Inter-Research.

Late Archean euxinic conditions before the rise of atmospheric oxygen

Life on Earth is thought to have coevolved with the chemistry of the oceans and atmosphere, and the shift from an anoxic to an oxic world across the Archean-Proterozoic boundary represents a fundamental step in this process. In order to understand the relative influence of biological and geological factors on this transition, we must constrain key variables in seawater chemistry before the Great Oxidation Event (ca. 2500 Ma). We present a multielement (C-S-Fe-Mo) biogeochemical study of ca. 2662 Ma shales from the Hamersley Province in Western Australia. Our data reveal a sustained episode of Fe-limited pyrite formation under an anoxic and sulfidic (euxinic) water column. This is the oldest known occurrence of euxinia in Earth9s history and challenges the paradigm of persistently Fe-rich Archean oceans. Bulk trace metal chemistry and preservation of strong mass-independent S isotope fractionations in sedimentary pyrites indicate that ocean euxinia was possible prior to oxidative weathering, suggesting that sulfidic waters may have been common throughout the Archean Eon. C-S-Fe systematics suggest that oxygenic photosynthesis was the primary source of organic carbon in the basin, and the absence of Mo enrichments highlights a potential link between inefficient nitrogen fixation and the delayed arrival of the Great Oxidation Event.

Consequences of Unwanted Local Reducing Conditions in Biomass-Fired Boilers on Chemistry and Operation: A Thermodynamic Evaluation

The case studies investigated are focusing on uncontrolled local reducing conditions and their effects on alkali and trace metal chemistry in biomass-fired boilers. The chemical trends obtained by thermodynamic equilibrium were interpreted in terms of practical outcomes for thermal systems. There is a lack of knowledge concerning the fate of Na and K in reducing atmospheres. This study shows the following: (1) Corrosion is expected to be more severe at reducing than oxidizing conditions; however, the corrosive species and therewith the corrosion mechanisms are changing with the oxygen levels. The main corrosive species under pyrolytic conditions are Na2S (s), NaCl (g), and KCl (g), while the main corrosive species at mildly reducing conditions are H2S (g), NaCl (g), and KCl (g). Under oxidizing conditions, alkali chlorides are the main alkali species involved in corrosion. (2) Some chemical elements have stable chemistries; i.e., their speciation and/or phase distribution are little affected by oxygen lev...

Sources of aerosol nitrate to the Gulf of Aqaba: Evidence from δ 15N and δ 18O of nitrate and trace metal chemistry

The nitrogen (N) and oxygen (O) isotopic composition (δ 15N and δ 18O) of water soluble aerosol nitrate was measured in aerosol samples collected in Eilat, Israel, from August 2003 to November 2004. During this period δ 15N values ranged from − 6.9‰ to + 1.9‰ and δ 18O from + 65.1‰ to + 84.9‰ and exhibited strong seasonal variability with higher average δ 15N values observed in the summer and higher δ 18O values in the winter. Nitrate isotopic composition was compared with bulk chemical composition and extractable ion and trace metals on co-collected samples linking nitrate isotopic composition to various sources of aerosols to this region. Atmospheric processes impacting the isotopic signatures of nitrate were also considered. Based on back trajectory analyses, the majority of NO 3 − came from air masses originating over the Mediterranean Sea (34%), Western Europe (20%) and the local Negev desert (19%), which contain a larger anthropogenic imprint compared to southern and eastern air masses which are dominated by mineral dust. The potential role of reactive mineral dust aerosols as a regulator of NO 3 − isotopic composition is considered; however, based on factor analysis, neither δ 15N nor δ 18O were associated with mineral dust components (such as Fe or Al), but rather with anthropogenic indicators such as Cu, Cd, P and Pb. Seasonality in primary NO x cycling reactions driven by seasonal changes in solar radiation, relative humidity and temperature also influence the observed isotopic signatures. The isotope data, together with trace element analysis, suggests that seasonal variations in both δ 15N NO3 and δ 18O NO3 are related to both NO x source and transport processes as well as NO x chemical reactions in the atmosphere. The flux-weighted δ 15N of aerosol NO 3 − in this area averaged − 2.6‰ making aerosol deposition a substantial contributor of low δ 15N nitrogen to the oligotrophic waters of the Gulf of Aqaba. Thus, while the flux of atmospheric N to oligotrophic marine systems is smaller than the upward flux of NO 3 − from deep water, it nonetheless represents an important source of new N having a low δ 15N. Further, if this low δ 15N signature is not considered, it could interfere with N-fixation estimates based on isotopic composition of dissolved nitrate or particulate organic nitrogen. Thus, atmospheric deposition should be constrained for accurate estimates of marine N-fixation when based on δ 15N in the ocean. Indeed, in the Gulf of Aqaba, low upper water δ 15N NO3 values could be related to inputs of atmospheric NO 3 − as well as N-fixation.

Trace metal enrichment in sugarcane soils due to the long-term application of fertilisers, North Queensland, Australia: geochemical and Pb, Sr, and U isotopic compositions

This study aimed to determine whether &gt;80 years of fertiliser application has led to recognisable changes in the trace metal (Cd, Cu, Mo, Ni, Pb, Sr, Th, U, Zn) chemistry of topsoils (0–0.10 m) from sugarcane land, northern Queensland, Australia. The metal concentrations of commercial nitrogen (N) and potassium (K) fertilisers currently used in northern Queensland were generally lower than those of phosphate fertilisers and fertiliser blends. Composite topsoil samples (0–0.10 m depth) taken from canelands had higher median Cd, Mo, Pb, Sr, Th, U, and Zn concentrations than topsoils from forested areas of the catchment. Niobium, Ta, and Ti were confirmed as refractory immobile elements and used as reference elements for the evaluation of trace metal enrichments. Bivariate plots of trace metal/immobile element ratios verified that Cd, Mo, Pb, Sr, Th, U, and Zn are enriched in sugarcane soils compared with background forest soils. Isotopic ratios for Pb, Sr, and U highlight that fertilisers, cane soils, and forest soils have isotopically distinct compositions. Phosphate fertilisers currently used in the agricultural industry possess the most radiogenic 87Sr/86Sr, 234U/238U, 207Pb/206Pb, and 208Pb/206Pb ratios. Background forest soils have the highest 87Sr/86Sr, 207Pb/206Pb, and 208Pb/206Pb and lowest 234U/238U ratios. By contrast, cane soils exhibit 207Pb/206Pb and 208Pb/206Pb ratios that appear on a mixing line between the isotopically distinct background soils and phosphate fertilisers. Also, cane soils possess 234U/238U ratios similar to phosphate fertilisers. Thus, the application of phosphate fertilisers to canelands has resulted in higher Cd, Mo, Pb, Sr, Th, U, and Zn concentrations and more radiogenic Pb, Sr, and U isotope ratios in cane soils. Trace metal ratios and the Pb, Sr, and U isotopic composition of topsoils and fertilisers are useful tools to recognise fertiliser-derived trace metals in agricultural landscapes.

Pore water trace metal chemistry in polluted sediments of a tropical estuary of SE Brazil

Pore water trace metal chemistry in polluted sediments of a tropical estuary of SE Brazil

Air quality and trace metal chemistry of different size fractions of aerosols in N–NW India—implications for source diversity

Three different size fractions of aerosols free fall (FF), suspended particulate matter (SPM) and particles less than 10 μm (PM 10) as well as surface sediments were collected from four different locations situated along a dust transport path of nearly 600 km in NW India starting from Bikaner in the Thar to Garhmuktesar through Jhunjhunu and Delhi and were studied for their heavy-metal chemistry. NW India is characterized by hot arid to semiarid climate with prevailing S–SW winds causing dust storms in summer and low intensity N–NW winds during winter months. The aerosol load in the atmosphere increased to several orders of magnitude for all size ranges (FF=21 g m −2 day −1; SPM=10,702 μg m −3 and PM 10=2907 μg m −3) during the summer dust storm period compared to national air quality standards as well as to the aerosol load in winter. Aerosol sources are dominantly crustal with a significant anthropogenic contribution during the winter. We also note multiplicity of sources for the heavy metals studied here. Sr, V and Cr are dominantly crustal. Ba and Pb are added largely by fossil fuel burning; Cu, Ni and Zn are contributed by various industries. Anthropogenically added heavy metals show maximum enrichment relative to the upper continental crustal component in finer fractions and especially in winter. We suggest that the aerosol loading in the atmosphere and its heavy-metal chemistry is strongly influenced by the climatic regime and the presence of desert and industrialization in this area.