Sulfidic Sediments Research Articles

Organic sulfur compositions and their relationships with iron sulfides in Antarctic lake sediments

本文利用有机硫硫同位素组成（δ³⁴S_org）及活性铁的黄铁矿化度（DOP）和硫化度（DOS）研究了南极阿德雷岛受企鹅活动影响的Y2湖和未受影响的菲尔德斯半岛燕鸥湖YO沉积物中有机硫的来源组成及其与铁硫化物的联系.结果表明，Y2沉积物1~15 cm较低的δ³⁴S_org指示有机质硫化形成的贫³⁴S成岩有机硫（S_diag）占比较高，其中在8~15 cm较高的DOS指示铁硫化物形成和有机质硫化同时发生，源于该层位高含量的活性铁供给.Y2剖面48~56 cm沉积物有机硫富集³⁴S显著，对应于企鹅数量高峰期，表明大量企鹅粪的外部输入使沉积物中富³⁴S的生物有机硫（S_bio）快速增加，并超过了内部硫转化过程中成岩有机硫的增加.YO沉积物在28 cm处δ³⁴S_org显著降低，主要是由于该层位硫酸盐异化还原强，有机质硫化形成的大量S_diag成为有机硫的主要成分，同位素质量平衡计算结果显示该层位S_diag占比高达95.4%；同时，28 cm处较高的DOP指示沉积物黄铁矿的形成与有机质硫化同时发生，主要源自沉积物中高硫酸盐还原强度产生了足够多的硫化氢前体.本研究表明，有机硫组分的来源转化与有机质、活性铁紧密耦合，对区域湖泊有机质成岩埋藏及潜在的气候环境效应具有重要的指示意义.;Sulfur isotope ratios of organic sulfur (δ³⁴S_org), degrees of pyritization (DOP) and sulfurization (DOS) in sediments were analyzed to reveal the organic sulfur compositions and their relationships with iron sulfides in a penguin-affected lake Y2 and a pristine Yanou Lake (YO) at Ardley Island and Fildes Peninsula, Antarctica, respectively. The depleted δ³⁴S_org values in Y2 sediments of 1-15 cm indicated a high proportion of ³⁴S-depleted diagenetic organic sulfur (S_diag) in total sulfur. Meanwhile, the high DOS in Y2 sediments of 8-15 cm indicated a concurrent sulfurization of iron and the organic matter, likely due to the high availability of active iron in this layer. The observed much enriched δ³⁴S_org in Y2 sediments of 48-56 cm corresponding to the period of high penguin populations, which indicated that large external inputs of penguin guanos result in a rapid increase in ³⁴S-enriched biological organic sulfur (S_bio) in the sediments, and exceeds the S_diag that from the internal sulfur transformations. The depleted δ³⁴S_org in YO sediment of 28 cm indicates a high proportion (95.4%) of ³⁴S-depleted S_diag which was from strong sulfurization of organic matter, corresponding to the strongest sulfate reduction in this layer. Meanwhile, the high DOP in YO sediment of 28 cm indicated a concurrent formation of pyrite sulfur and the sulfurization of organic matter in this layer, due to the high available precursors of hydrogen sulfide and/or intermediate species of sulfur from the sulfate reduction. Our study indicates that the components of organic sulfur are coupled tightly with organic matter and reactive iron and provides a direct implication for the depositions of organic matter and thus the potential climatic and environmental effects in regional aquatic ecosystems.

Spatiotemporal Variation of Surface Sediment Quality in the Xiamen Sea Area, China.

The study analyzes the survey data on the surface sediments in 355 stations in Xiamen Sea area during 2004-2006, 2007-2009, 2010-2013, and 2014-2016. The result finds that contents of TOC, sulfide, and oils in the surface sediments were generally low but showed significant spatial differences (p < 0.05) in most cases, with TOC in the West Sea area (WS) staying significantly higher than other sea areas. Xiamen Sea area suffered universal heavy metal pollution mainly from Cu and Zn for years in the WS, the Jiulong River Estuary (JE), and the East Sea area (ES), and the heavy metal pollution index (HPI) exhibited significant spatial differences across the four periods (p < 0.05). With the source of heavy metals in the WS being mainly related to human activities, Cu and Zn were related to the development of port shipping and Pb to aquaculture. The heavy metal pollution in JE was mainly related to the input of rivers emptying into the sea. The high Cu content in the ES was related to the direct discharge of massive domestic sewage into the sea at the time. From 2004 to 2016, the potential ecological risks of heavy metals in Xiamen Sea area stayed low.

Understanding the isotopic composition of sedimentary sulfide: A multiple sulfur isotope diagenetic model for Aarhus Bay

Measurement of the multiple sulfur isotopes (³²S/³³S/³⁴S) enables the calibration of microbial biosignatures and provides a unique diagnosis of S-based metabolic processes: sulfate reduction, disproportionation, and sulfide oxidation. All three metabolisms carry distinct geochemical consequences for S cycling in modern systems, and are particularly powerful for paleoenvironmental interpretations if their respective contributions can be separated. To hone those interpretations and to further develop a quantitative context for understanding early diagenetic sulfur cycling, we constructed a multiple S isotope reactive transport model for the sediments of a geochemically well-characterized system (Aarhus Bay, Denmark). The model reconciles pore water and solid phase concentration profiles of the major species associated with Fe/S/C cycling, and uses multiple S isotope systematics to predict the isotope profiles of the major S species, including pore water sulfate, free sulfide and solid phase pyrite. We note that very large fractionations associated with sulfate reduction (³⁴ε_sr = 70‰) are required to reproduce the observed pore water profiles, and we reconcile these fractionations with low temperature theoretical predictions for isotope equilibrium fractionation. The minor sulfur isotope values (noted as Δ³³S) of sulfate increase at shallow depths within the Aarhus Bay core, and decrease when sulfate drops below 10 mM. Values (Δ³³S) for sulfide decrease nearly monotonically towards seawater sulfate values near the zone of sulfate depletion. Pyrite Δ³³S values are nearly uniform downcore (0.170 ± 0.010‰) despite a ∼10‰ enrichment in surface versus deep pyrite δ³⁴S values. Sulfate reduction is the most important process controlling S isotope pore water distributions, with modest contributions from oxidative S cycling. Further, microbial sulfate reduction demonstrates large fractionations typically not expected for shallow, organic rich (TOC ∼ 4%) continental margin systems.

Simultaneous control of sulfide and methane in sewers achieved by a physical approach targeting dominant active zone in sediments

Sewer sediments not only induce sewer blockages, but also contributes to significant sulfide and methane productions in gravity sewer systems. Chemical control of sulfide and methane production is extremely expensive. This study aims to propose a novel physical control approach—intermittent surface sediment flushing to synchronously address sediment-induced multiple issues. The proposed approach was established investigating the suppression and recovery characteristics of sulfidogenic and methanogenic activities of sediments including the in-situ activity analysis by using the diffusive gradients in thin films (DGT). The results showed that ∼70% of total sulfide and methane production in sediments was contributed by surface sediments (0–1.5 cm), which could be easily flushed away by a low shear stress (<0.1 N/m2). Surface sediment flushing resulted in an immediate reduction in sulfidogenic and methanogenic activities, which both required about one week to recover to 50% of the maximum. These novel insights hopefully provide a feasible approach, i.e., intermittent surface sediment flushing, to effectively reduce sulfide and methane production in sewers. Compared with chemical dosing methods, the proposed approach, which has no chemical input, greatly reduces operating cost and environment impact. Moreover, intermittent surface flushing is expected to keep sediment thickness within a certain range to alleviate sewer blockage.

Carbon assimilating fungi from surface ocean to subseafloor revealed by coupled phylogenetic and stable isotope analysis

Fungi are ubiquitous in the ocean and hypothesized to be important members of marine ecosystems, but their roles in the marine carbon cycle are poorly understood. Here, we use 13C DNA stable isotope probing coupled with phylogenetic analyses to investigate carbon assimilation within diverse communities of planktonic and benthic fungi in the Benguela Upwelling System (Namibia). Across the redox stratified water column and in the underlying sediments, assimilation of 13C-labeled carbon from diatom extracellular polymeric substances (13C-dEPS) by fungi correlated with the expression of fungal genes encoding carbohydrate-active enzymes. Phylogenetic analysis of genes from 13C-labeled metagenomes revealed saprotrophic lineages related to the facultative yeast Malassezia were the main fungal foragers of pelagic dEPS. In contrast, fungi living in the underlying sulfidic sediments assimilated more 13C-labeled carbon from chemosynthetic bacteria compared to dEPS. This coincided with a unique seafloor fungal community and dissolved organic matter composition compared to the water column, and a 100-fold increased fungal abundance within the subseafloor sulfide-nitrate transition zone. The subseafloor fungi feeding on 13C-labeled chemolithoautotrophs under anoxic conditions were affiliated with Chytridiomycota and Mucoromycota that encode cellulolytic and proteolytic enzymes, revealing polysaccharide and protein-degrading fungi that can anaerobically decompose chemosynthetic necromass. These subseafloor fungi, therefore, appear to be specialized in organic matter that is produced in the sediments. Our findings reveal that the phylogenetic diversity of fungi across redox stratified marine ecosystems translates into functionally relevant mechanisms helping to structure carbon flow from primary producers in marine microbiomes from the surface ocean to the subseafloor.

High Potential for Anaerobic Microbial Sulfur Oxidation in Oil Sands Tailings Ponds.

The biogenic production of toxic H2S gas in sulfate-rich oil sands tailings ponds is associated with strong environmental concerns. Beside precipitation into sulfide minerals and chemical re-oxidation, microbial sulfur oxidation may catalyze sulfide re-cycling but potentially contributes to acid rock drainage (ARD) generation. To evaluate the microbial potential for sulfur oxidation, we conducted a microcosm-based pilot study with tailings of an active pond. Incubations were performed under oxic and anoxic conditions, with and without KNO3 as an electron acceptor and thiosulfate as a common substrate for microbial sulfur oxidation. The highest potentials of sulfur oxidation occurred in oxic assays (1.21 mmol L−1 day−1). Under anoxic conditions, rates were significantly lower and dominated by chemical transformation (0.09 mmol L−1 day−1; p < 0.0001). The addition of KNO3 to anoxic incubations increased microbial thiosulfate oxidation 2.5-fold (0.23 mmol L−1 day−1; p = 0.0474), with complete transformation to SO42− coupled to NO3− consumption, pointing to the activity of sulfur-oxidizing bacteria (SOB) under nitrate-reducing conditions. Importantly, in the presence of KNO3, a decrease in sedimentary sulfides was associated with an increase in S0, which indicates the potential for microbially mediated oxidation of sulfide minerals and ARD generation. Furthermore, the comparative analysis of sediments from other anthropogenic aquatic habitats demonstrated high similarities with respect to viable SOB counts and corresponding activity rates.

Effects of sulfide availability on the metabolic activity and population dynamics of cable bacteria in freshwater sediment

Cable bacteria occur in many natural environments, and their electrogenic sulfide oxidation (e-SOx) may influence sediment biogeochemistry. The environmental factors determining the growth and diversity of cable bacteria are poorly known, especially in freshwater sediments. We conducted a laboratory incubation experiment, using freshwater sediments with different sulfide supply levels, to study how sulfide availability in sediment affects the metabolic activity and population dynamics of cable bacteria. A moderate increase in the sulfide availability in sediment significantly promoted metabolic activity and the proliferation of the cable bacteria population, as revealed by enhanced e-SOx intensity and increased bacteria abundance. In high-sulfide treatments there was a more significant increase in the population of cable bacteria in the deeper sediment layers, indicating that increased sulfide availability may expand the vertical scale impact of cable bacteria activities on sediment biogeochemistry. The relative proportions of co-existing species in the cable bacteria population also changed with sulfide supply levels, indicating that sulfide availability can be involved in determining the interspecies relationships of cable bacteria. Our findings provide new insight into the relationship between sediment sulfide availability and the growth, depth distribution, and species composition of cable bacteria, implying the consideration of regulating environmental sulfide availability as a potential management practice for the development of cable bacteria–based environmental biotechnologies.

Giant sulfur bacteria (Beggiatoaceae) from sediments underlying the Benguela upwelling system host diverse microbiomes.

Due to their lithotrophic metabolisms, morphological complexity and conspicuous appearance, members of the Beggiatoaceae have been extensively studied for more than 100 years. These bacteria are known to be primarily sulfur-oxidizing autotrophs that commonly occur in dense mats at redox interfaces. Their large size and the presence of a mucous sheath allows these cells to serve as sites of attachment for communities of other microorganisms. But little is known about their individual niche preferences and attached microbiomes, particularly in marine environments, due to a paucity of cultivars and their prevalence in habitats that are difficult to access and study. Therefore, in this study, we compare Beggiatoaceae strain composition, community composition, and geochemical profiles collected from sulfidic sediments at four marine stations off the coast of Namibia. To elucidate community members that were directly attached and enriched in both filamentous Beggiatoaceae, namely Ca. Marithioploca spp. and Ca. Maribeggiatoa spp., as well as non-filamentous Beggiatoaceae, Ca. Thiomargarita spp., the Beggiatoaceae were pooled by morphotype for community analysis. The Beggiatoaceae samples collected from a highly sulfidic site were enriched in strains of sulfur-oxidizing Campylobacterota, that may promote a more hospitable setting for the Beggiatoaceae, which are known to have a lower tolerance for high sulfide to oxygen ratios. We found just a few host-specific associations with the motile filamentous morphotypes. Conversely, we detected 123 host specific enrichments with non-motile chain forming Beggiatoaceae. Potential metabolisms of the enriched strains include fermentation of host sheath material, syntrophic exchange of H2 and acetate, inorganic sulfur metabolism, and nitrite oxidation. Surprisingly, we did not detect any enrichments of anaerobic ammonium oxidizing bacteria as previously suggested and postulate that less well-studied anaerobic ammonium oxidation pathways may be occurring instead.

Microbial Communities Involved in Methane, Sulfur, and Nitrogen Cycling in the Sediments of the Barents Sea.

A combination of physicochemical and radiotracer analysis, high-throughput sequencing of the 16S rRNA, and particulate methane monooxygenase subunit A (pmoA) genes was used to link a microbial community profile with methane, sulfur, and nitrogen cycling processes. The objects of study were surface sediments sampled at five stations in the northern part of the Barents Sea. The methane content in the upper layers (0–5 cm) ranged from 0.2 to 2.4 µM and increased with depth (16–19 cm) to 9.5 µM. The rate of methane oxidation in the oxic upper layers varied from 2 to 23 nmol CH4 L−1 day−1 and decreased to 0.3 nmol L−1 day−1 in the anoxic zone at a depth of 16–19 cm. Sulfate reduction rates were much higher, from 0.3 to 2.8 µmol L−1 day−1. In the surface sediments, ammonia-oxidizing Nitrosopumilaceae were abundant; the subsequent oxidation of nitrite to nitrate can be carried out by Nitrospira sp. Aerobic methane oxidation could be performed by uncultured deep-sea cluster 3 of gamma-proteobacterial methanotrophs. Undetectable low levels of methanogenesis were consistent with a near complete absence of methanogens. Anaerobic methane oxidation in the deeper sediments was likely performed by ANME-2a-2b and ANME-2c archaea in consortium with sulfate-reducing Desulfobacterota. Sulfide can be oxidized by nitrate-reducing Sulfurovum sp. Thus, the sulfur cycle was linked with the anaerobic oxidation of methane and the nitrogen cycle, which included the oxidation of ammonium to nitrate in the oxic zone and denitrification coupled to the oxidation of sulfide in the deeper sediments. Methane concentrations and rates of microbial biogeochemical processes in sediments in the northern part of the Barents Sea were noticeably higher than in oligotrophic areas of the Arctic Ocean, indicating that an increase in methane concentration significantly activates microbial processes.

Enhancing pollutant removal and electricity generation in Sediment Microbial Fuel Cell with nano zero-valent iron

A nano zero-valent iron (NZVI) was added into sediments to enhance the capacities of sediment microbial fuel cells (SMFCs) for pollutant removal and electricity generation. Open and closed circuits were applied to confirm the impact of NZVI on the pollutant removal performance of SMFCs. The operation of SMFCs in a closed circuit with 0.06% NZVI produced a current density of 340.8 mA/m 2 . Adding 0.6% NZVI to closed-circuit SMFCs reduced hydrogen sulfide from 12.5 mg/L to 0 mg/L. Moreover, adding NZVI to closed-circuit SMFCs reduced phosphate concentration from 49 mg/L to 11 mg/L. With the same amount of NZVI, the pollutant removal in a closed circuit was higher than that in an open circuit because of the electricity flow at SMFCs. In conclusion, addition of NZVI to SMFCs effectively enhanced the produced current density and reduced the concentrations of hydrogen sulfide and phosphate in sediments. • Addition of NZVI to the anode chamber enhanced electricity production in SMFCs. • The higher current density of 340.8 mA/m2 in SMFC with addition 0.06% of NZVI . • Addition of 0.6% of NZVI reduced phosphate and hydrogen sulfide in sediments. • Excessive NZVI reduces electricity production in SMFCs.

Heavy metal removal and acid mine drainage neutralization with bioremediation approach

Mining Industry can improve the national economic situation; however, it also can damage the environment, mainly because of its wastewater that contains heavy metal and acidic solid compounds. When exposed to free air, sulfide minerals can be naturally oxidized and create acid mine drainage (AMD), a highly acidic waste that can mobilize heavy metals towards the environment. This literature study will discuss practical and sustainable biological processing to remove AAT. Sulfate Reducing Bacteria (SRB) were isolated from AMD polluted soil and grown inside an AMD-containing batch reactor. The environmental conditions (temperature, AMD concentration, SRB concentration, and contact time) were controlled during this research. The implementation of pH sampling was conducted every day, and the heavy metal final result was measured with an Inductive Coupled Plasma Optical Spectrophotometry or ICP-OES. SRB produced Hbiogenic2S that reacts with heavy metal and creates metal sulfide sediment. The remediation process by SRB will create biogenic alkalinity as an SRB side product that plays a significant role in neutralizing acidic water. Remediation is also influenced by organic compounds such as animal waste, rice, hay, or coconut husks. In this research, SRB plays a significant role as biosorbent that utilizes organic compounds as electron sources. The iron removal efficiency in AMD reached 96% and occurred on a contact time of 144 hours. To reach similar efficiency removal on a pilot scale, we planned AMD bioremediation on a tube-shaped reactor with 7.3m3 with 3.5 m height and 0.88 of each reactor radiuses. This bioremediation study has provided an alternative solution for environmental management quality due to AAT pollution in water and groundwater around mining areas.

Rapid, concurrent formation of organic sulfur and iron sulfides during experimental sulfurization of sinking marine particles.

Organic matter (OM) sulfurization can enhance the preservation and sequestration of carbon in anoxic sediments, and it has been observed in sinking marine particles from marine O2-deficient zones. The magnitude of this effect on carbon burial remains unclear, however, because the transformations that occur when sinking particles encounter sulfidic conditions remain undescribed. Here, we briefly expose sinking marine particles from the eastern tropical North Pacific O2-deficient zone to environmentally relevant sulfidic conditions (20°C, 0.5 mM [poly]sulfide, two days) and then characterize the resulting solid-phase organic and inorganic products in detail. During these experiments, the abundance of organic sulfur in both hydrolyzable and hydrolysis-resistant solids roughly triples, indicating extensive OM sulfurization. Lipids also sulfurize on this timescale, albeit less extensively. In all three pools, OM sulfurization produces organic monosulfides, thiols, and disulfides. Hydrolyzable sulfurization products appear within ≤ 200-μm regions of relatively homogenous composition that are suggestive of sulfurized extracellular polymeric substances (EPS). Concurrently, reactions with particulate iron oxyhydroxides generate low and fairly uniform concentrations of iron sulfide (FeS) within these same EPS-like materials. Iron oxyhydroxides were not fully consumed during the experiment, which demonstrates that organic materials can be competitive with reactive iron for sulfide. These experiments support the hypothesis that sinking, OM- and EPS-rich particles in a sulfidic water mass can sulfurize within days, potentially contributing to enhanced sedimentary carbon sequestration. Additionally, sulfur-isotope and chemical records of organic S and iron sulfides in sediments have the potential to incorporate signals from water column processes.

Iron and sulfur speciation and cycling in the sediments of marine systems located in arid environments: the northern Red Sea

The high fluxes of iron minerals associated with aeolian dry deposition may result in an anomalously high reactive iron content and the rapid reoxidation of hydrogen sulfide in sediments. This will prevent the formation of pyrite and result in a ‘cryptic’ sulfur cycle. We studied the cycling of iron and sulfur in deep water (&gt;800 m water depth) sediments of the Red Sea and its northern extension, the Gulf of Aqaba. We found that the reactive iron content in the surface sediments of the Gulf of Aqaba and the Red Sea is high, whereas the amount of sulfur-bound iron is very low and decreases with the water depth. The presence of trace amounts of pyrite and zero-valent sulfur, as well as the isotopic compositions of sulfate and pyrite, which are consistent with sulfate reduction under substrate-limiting conditions, suggest that cryptic sulfur cycling is likely to be a result of the rapid reoxidation of hydrogen sulfide rather than the suppression of microbial sulfate reduction. The low amount of reactive iron and high organic carbon content in the sediments of the Shaban Deep, which are overlain by hypersaline hydrothermal brines, result in a non-cryptic sulfur cycle characterized by the preservation of pyrite in the sediments. Supplementary material: Data for sulfur speciation, iron speciation and sulfur isotope composition are available at https://doi.org/10.6084/m9.figshare.c.5508155 Thematic collection: This article is part of the Sulfur in the Earth system collection available at: https://www.lyellcollection.org/cc/sulfur-in-the-earth-system

Investigation of Capitella spp. symbionts in the context of varying anthropic pressures: First occurrence of a transient advantageous epibiosis with the giant bacteria Thiomargarita sp. to survive seasonal increases of sulfides in sediments

Capitella spp. is considered as an important ecological indicator of eutrophication due to its high densities in organic-rich, reduced, and sometimes polluted coastal ecosystems. We investigated whether such ability to cope with adverse ecological contexts might be a response to the microorganisms these worms are associated with. In populations from the French Atlantic coast (Roscoff, Brittany), we observed an epibiotic association covering the tegument of 20–30% specimens from an anthropized site while individuals from a reference, non-anthropized site were devoid of any visible epibionts. Using RNAseq, molecular and microscopic analyses, we described and compared the microbial communities associated with the epibiotic versus the non-epibiotic specimens at both locations. Interestingly, data showed that the epibiosis is characterized by sulfur-oxidizing bacteria among which the giant bacterium Thiomargarita sp., to date only described in deep sea habitats. Survey of Capitella combined with the geochemical analysis of their sediment revealed that epibiotic specimens are always found in muds with the highest concentration of sulfides, mostly during the summer. Concomitantly, tolerance tests demonstrated that the acquisition of epibionts increased survival against toxic level of sulfides. Overall, the present data highlight for the first time a peculiar plastic adaptation to seasonal variations of the habitat based on a transcient epibiosis allowing a coastal species to survive temporary harsher conditions.

Cu and Ni Isotope Variations of Country Rock-Hosted Massive Sulfides Located Near Midcontinent Rift Intrusions

Abstract Previous Cu isotope work has documented a clear disparity between δ65Cu values of sheet-style (–0.5 to 0.5‰) and conduit-style (0.5–2.0‰) intrusions associated with the Midcontinent rift system. The application of metal isotopes to the study of magmatic Ni-Cu-platinum group element (PGE) deposits is in an early stage, and very little is known regarding isotope distributions and mechanisms of fractionation at high temperatures. In order to resolve the previously mentioned Cu isotope disparity, to determine metal sources for the intrusions, and to assess sources of high-temperature metal isotope fractionation, we have measured Cu and Ni isotope ratios from a suite of exceptionally well characterized Ni-Cu-PGE massive sulfides that occur in sedimentary country rocks near intrusions within the Midcontinent rift system in Michigan and Minnesota. Previous mineralogic and S, Pb, and Os isotope measurements indicate that the massive sulfides are of magmatic origin and provide a framework for the interpretation of the Cu and Ni isotope data in terms of magmatic processes, including assimilation of Proterozoic country rocks. Copper and Ni isotope ratios were determined for massive sulfides as well as local sedimentary sulfides, and these results were compared with available Cu and Ni isotope results of magmatic and sedimentary sulfides in the Midcontinent Rift and elsewhere. Nickel isotope ratios of the sulfides have been modeled in terms of the effects of variable silicate/sulfide ratios, or R-factors (the mass ratio of silicate magma to sulfide magma), crustal contamination, and olivine fractional crystallization. The near-zero and slightly negative δ60Ni values of country rock-hosted magmatic sulfides (–0.45 to 0.17‰) near Tamarack and Eagle can be explained by minor degrees of crustal contamination of a mantle-derived melt at variable R-factors. Igneous-sourced, Cu-poor sulfides from below the Partridge River intrusion generally have lower δ60Ni values (−0.77 to –0.52‰) that require substantially more contamination from a low δ60Ni source, similar to some of the local sedimentary rocks. Copper isotope ratios of country rock-hosted massive sulfides near Eagle and Tamarack are lower than those reported by previous workers and are mostly about 0‰, similar to those expected for unaltered mantle. Tamarack samples require very little crustal contamination to explain their isotope ratios, whereas Eagle samples require no contamination from local sedimentary rocks to explain their Cu isotope compositions. Copper isotope ratios of samples beneath the Partridge River intrusion are similar to those from previous analyses of igneous-hosted sulfides, supporting their origin from a magmatic sulfide liquid. The low δ65Cu values (–1.14 to 0.25‰) from samples below the Partridge River intrusion cannot be explained by contamination from the Virginia and Thomson Formations, which are characterized by mostly positive δ65Cu values (–0.33 to 3.12‰), unless a lighter reservoir remains to be discovered in the local Proterozoic rocks. We suggest these values may have been produced by a combination of incomplete sulfide melting during partial melt generation and fractionation related to sulfide segregation at variable R-factors.

DNRA was limited by sulfide and nrfA abundance in sediments of Xiamen Bay where heterotrophic sulfide-producing genus (Pelobacter) prevailed among DNRA bacteria

DNRA was limited by sulfide and nrfA abundance in sediments of Xiamen Bay where heterotrophic sulfide-producing genus (Pelobacter) prevailed among DNRA bacteria

Effects of elevated sulfate in eutrophic waters on the internal phosphate release under oxic conditions across the sediment-water interface

Eutrophication in freshwater environments may be enhanced by the elevation of sulfate in waters, through the release of internal phosphorus (P) from anoxic sediments. However, the influence of increasing but modest sulfate concentrations (less than 3000 μM) on P release under oxic conditions across the sediment-water interface (SWI) in eutrophic freshwater is poorly understood. In this study, the profiles of P, iron (Fe), sulfur (S) and physicochemical parameters were measured in a simulated lacustrine system with varying concentrations of sulfate (970–2600 μM) in overlying water. The results indicated that elevated concentrations of sulfate increased the soluble reactive P in overlying waters under oxic conditions across the SWI. A 100 μM increase of sulfate was found to induce a 0.128 mgm−2d−1 increase of P flux from surface sediments into overlying waters under oxic conditions. Higher sulfate concentrations in the overlying waters increased the concentrations of labile S(-II) in the deep sediments, due to sulfate penetration and subsequent reduction to S(-II). We also found the fluxes of labile Fe (10.34 to 18.33 mgm−2d−1) and P (2.70 to 1.33 mgm−2d−1) from deep to surface sediment were both positive and greater than the corresponding fluxes (Fe, 2.2 to 3.51 and P, 2.6 to 0.39 mgm−2d−1, respectively) from surface sediment to the overlying water, suggesting that reduction of P-bearing Fe(III)(oxyhydr)oxides in deep anoxic sediment acted as a major source of internal P release. In addition, the upward flux of Fe(II) was significantly lower under higher sulfate conditions, indicating that the Fe(II) flux could be mitigated by formation of Fe(II) sulfides in the deep sediment. Under these conditions, less Fe(II) from deep sediments could be re-oxidized and combine with P in the surface, oxic sediment, thereby reducing the retention capacity for P and leading to higher release of internal P to the water column.

Enhancing the retention of phosphorus through bacterial oxidation of iron or sulfide in the eutrophic sediments of Lake Taihu

Microbial activity can enhance the sequestration of phosphorus (P) in sediments, but little is known about the mechanisms behind it. In this study, sediment cores were sampled from the most eutrophic Meiliang Bay of Lake Taihu, and three treatments were set up in a laboratory incubation experiment, involving (a) the non-treated sediment cores, (b) inoculation, and (c) sterilization. The dissolved and labile iron (Fe) and P were obtained by high-resolution dialysis and the diffusive gradients in thin films (DGT) technique, respectively. AgI-based DGT was used for measuring the 2D distribution of labile sulfide. The bacterial community was investigated using a scanning electron microscope and 16S rRNA high throughput sequencing technique. The results showed that sterilization reduced the capacity of sediment to immobilize P, and that the critical sediment depth layer for microbial P sequestration was 0–10 mm. In addition, sterilization or inoculation significantly changes the structure of bacterial communities. Fe or S oxidation under micro-aerobic or anaerobic conditions played an important role in bacterial retention of P in the sediments. Nitrate-reducing coupling Fe(II)-oxidizing bacteria (Acidovorax) in the inoculated sediment and electrogenic sulfur-oxidizing bacteria (Candidatus Electronema) in the non-treated sediment were identified as the key bacterial genera responsible for the retention of P in sediments. This implies that bacterial communities could quickly establish the ability for negative feedback regulation by inoculation once the function and structure of indigenous sediment bacteria are seriously impaired, although this needs further validation in the field.

Multibiomarker responses and bioaccumulation of fipronil in Prochilodus lineatus exposed to spiked sediments: Oxidative stress and antioxidant defenses

Fipronil is a current use pesticide, widely used in many crops, commonly adsorbed to sediments of aquatic environments. The purpose of this study was to evaluate the biomarker responses and fipronil distribution pattern in different matrixes (fish, sediment and water) after juveniles P. lineatus exposure at two environmental concentrations (5.5 and 82 μg kg‐−1) of fipronil-spiked sediments. The levels of oxidized proteins (PO), lipid peroxidation (LPO), and enzymatic activity of superoxide dismutase (SOD), reduced glutathione content (GSH), antioxidant capacity against peroxyls (ACAP) and acetylcholinesterase (AChE) were evaluated in liver, gills and brain. Concentrations of fipronil and its metabolites (f. desulfinyl, f sulphpHide and f. sulfone) were quantified by GC-ECD. F. desulfinyl was the major metabolite found in all matrixes, followed by f. sulphide in sediments, while f. sulfone was mainly accumulated in fish. Fipronil promoted oxidative stress in P. lineatus, as evidenced by the increases in LPO and PO levels and the decrease brain AChE activity. Fish exposed at both concentrations showed significant decrease in antioxidant capacity. Alterations in the antioxidant defenses system was evidenced in all organs. These results suggest that the occurrence of fipronil in aquatic environments can generate oxidative stress at different levels in P. lineatus, showing that this species is highly sensitive to the deleterious effects of fipronil and metabolites.

Cobalt concentration in a sulfidic sea and mobilization during orogenesis: Implications for targeting epigenetic sediment-hosted Cu-Co deposits

The origin of sediment-hosted copper-cobalt deposits (SCDs) within metamorphic terranes remains contentious, particularly in regard to the timing of mineralization relative to basin evolution. Here, we link the timing of Cu-Co mineralization in the Zhongtiao Mountains district, central China, to basin closure during development of the Trans-North China Orogen. Metamorphic apatite from meta-evaporite has a U-Pb age (1844 ± 25 Ma) within error of a Re-Os age for molybdenite from Cu- and Co-bearing veins (1819 ± 10 Ma), implying that mineralization and metamorphism were coincident. In situ trace element and Fe-S isotope analyses of deformed sedimentary pyrite (Py I) and younger euhedral metamorphic pyrite (Py II) in pyritic graphite schist indicate that Co was mobilized from Py I via fluid-mediated dissolution and reprecipitation. In the graphite schist, representing a sulfidic shale metamorphosed at upper greenschist facies conditions, relic Py I has high δ34S values (22.9 ± 0.4‰, n = 10) and δ56Fe values (0.90 ± 0.16‰, n = 8). These values are consistent with bacterial sulfate reduction and pyrite formation in a Paleoproterozoic sulfidic sea (i.e., after the first great oxygenation event). In addition, Py I has unusually high Co contents (0.8–3.0 wt.%), suggesting that transition metals, including Co and Ni, were originally concentrated in sedimentary pyrite in an evaporative setting. The evaporitic setting is supported by the presence of sylvite in sulfidic schists and adjacent scapolitic calc-silicates. Younger Co-poor Py II has slightly lower δ34S values (21.4 ± 0.2‰, n = 19) and higher δ56Fe values (1.61 ± 0.15‰, n = 9), supporting the hypothesis that Co was released from sedimentary sulfide during dissolution and reprecipitation. The great variability of δ34S (14.8 to 22.9‰) and δ56Fe (0.13 to 2.30‰) in hydrothermal pyrite (Py III) associated with Cu-Co mineralization suggests that an external Cu-rich oxidizing fluid was involved in the ore-forming process.Copper and Co in this type of deposit are typically both considered to be derived from fertile basement rocks. This study, however, highlights another potential source for the Co, with its enrichment in a sulfidic sea along an evaporative margin and its upgrading through mobilization during orogenesis that leads to formation of a relatively high-temperature group of SCDs. Tectonometamorphic processes causing such Co enrichments took place during the Paleoproterozoic and Neoproterozoic oxygenation events, implying that the most prospective targets for Co resources are concentrated in ca. 2.2–2.0 Ga and 0.9–0.7 Ga deformed passive margin marine sequences.