Sulfide-rich Sediments Research Articles

Sulfide-rich sediments remediation by slow-release calcium nitrate with low risk: Experiments in a continuous flow reactor

Nitrate-driven sulfide oxidation has been proven to be a cost-effective approach for controlling sediment odor. However, injecting liquid nitrate (LN) directly into sediment carries ecological risks of nitrate escape and release of pollutants into overlying water. In this study, slow-release nitrate granules (GN) were prepared and applied in a continuous flow reactor to assess the differences between GN and LN in sediment remediation and control of this ecological risk. The results showed that the GN slowly released calcium nitrate, resulting in a decrease in acid volatile sulfide (AVS) from an initial 1328 ± 42.7 mg/kg to 490 ± 341 and 212 ± 32.8 mg/kg in the upper (U) and deeper (D) layers of the sediment, respectively. No significant decrease in AVS concentrations was observed in the LN treatments. Compared with LN-D and -U, the NH4+-N production and PO43--P release doses were reduced by 29.5% and 52.0% for GN-D and 41.2% and 37.8% for GN-U, respectively. Taxonomic analysis showed that sulfide-driven denitrifiers such as Thiobacillus, Rhodanobacter, Sulfurimonas, and Pseudomonas became dominant in the GN treatments, which were 2.8–6.7, 27.0–201.8, 1.5–3.0, and 3.0–496 times that of the LN treatments, respectively. The abundance of sulfur oxidation genes (e.g., sat and aprB) and denitrifying genes (e.g., nirS and nosZ) were also upregulated to higher levels by GN. Moreover, the genes (e.g., nrfA) responsible for the isomerization of nitrate into ammonium were down-regulated by GN. The results showed that the slow-released calcium nitrate should be a promising way for in-situ remediation of sulfide-rich sediment.

Applying industrial side streams in the neutralization of acid generating sulfide-rich sediments – The impact on pH and leaching of harmful elements

Acid sulfate soils can cause severe environmental harm due to a low pH and mobilization of harmful elements. Acid sulfate soil material is formed when oxidation of sulfide minerals causes a drop in pH to <4.0 for mineral oil materials and <3.0 for organic soil materials or when the soil materials contain enough sulfide to potentially do so.Two dredged, acid sulfate soil materials from Finland were used in this laboratory study. Chemical analyses were performed to determine the pre-incubation characteristics of both fresh dredged sediment samples and oxidized samples after 23 weeks of incubation. Total element concentrations were determined after digestion in aqua regia by ICP-MS or ICP-OES. The leachable concentration of elements was determined by using the two-stage shaking test (method SFS-EN 12457-3). The leaching of harmful elements (Cd, Co, Ni, Mn, and Zn) was high in the acidified dredged spoil samples. Also, the leaching of S was high. The soluble concentration was dependent on total concentration, pH, and the mobility of the elements.During a 23-week oxidation period, the impact of various amounts of industrial side streams (alkaline ashes, industrial lime residues) as neutralizing agents on the acid-generating dredged sediments was investigated in the laboratory. Calcite was used as a reference material. pH measurements were carried out during the incubation period. The leaching of elements was determined with a modified method based on the SFS-EN 12457-2 standard before and after oxidation.The untreated dredged spoils and the samples treated with too low amounts of neutralizing agents, acidified to pH < 4 during the oxidation period. Thus, harmful elements were leached out. However, the 100 % theoretical calculated neutralization need was suitable to prevent acidification and thus the leaching of harmful substances from the neutralized acid-generating dredged spoils. However, the leaching of Mo increased at neutral pH values. The results showed that industrial side streams can be applicable for the neutralization of acid sulfate soil materials. However, the legislation must also be considered.

Risk control and assessment of sulfide-rich sediment remediation by controlled-release calcium nitrate

Nitrate stimulation is widely used in sediment remediation to eliminate sulfides, degrade organic pollutants and immobilize phosphorus. However, the environmental risks of nitrate escape and the subsequent release of pollutants (e.g. nitrite, ammonium and trace metals) to water bodies during its application has received less attention. In this study, controlled-release nitrate pellets (SedCaN pellets) were manufactured and applied at different sediment depths to examine their effectiveness in controlling the risk of nitrate escape and subsequent pollutant release. The germination of submerged plant was also analyzed to assess the ecological risks associated with the remediated sediment. The results showed that the SedCaN pellets slowly released calcium nitrate, which led to denitrifying sulfide oxidation, organic matter degradation and the immobilization of phosphorus as a calcium-bound species. Gas production by denitrification increased the sediment porosity (0.3–2.2%) and led to the concomitant release of nitrite, ammonium, and heavy metals, creating secondary risks. Application of the SedCaN pellets at depth decreased the nitrate escape and the secondary risks, presumably by means of a capping effect of the upper sediment. The release of nitrate, ammonium, Ni and Cu were partially limited by 91.6%, 19.0%, 61.6% and 57.4% when SedCaN pellets were incorporated into deeper sediments (7–9 cm). Moreover, the range of sulfide oxidation extended to the upper and lower sediments in the profile (column), while the sulfide oxidation efficiency reached 85.9–95.0%. Finally, increased germination of Bacopa monnieri (20.0–26%) demonstrated that in comparison to reference materials the ecological risks of the treated sediments was reduced and the habitat function of sediment was restored after nitrate-stimulating remediation. The results of this study provide valuable guidelines for nitrate-stimulating remediation of sulfide-rich (black-odor) sediments.

Mineralogy and geochemistry of clastic sulfide ores from the Talgan VHMS deposit, South Urals, Russia: Signatures of diagenetic alteration

Diagenetically altered thin-layered sulfide ores from the Talgan volcanic-hosted massive sulfide deposit (South Urals) represent an intercalation of thin sulfide and hyaloclastite layers up to 3 and 0.5 cm thick. Their mineralogy and trace element, including rare earth elements (REE), and S, C and O isotopic geochemistry are considered in this work. They occur at the slopes of ore bodies and pinch outside them within hyaloclastites and their thickness increases towards the flanks of the ore bodies. The sulfide layers are mostly composed of authigenic pyrite, which forms zoned nodules, anhedral aggregates, euhedral crystals and pseudomorphs after pyrrhotite crystals. The pyrite nodules and anhedral aggregates host inclusions of authigenic chalcopyrite, sphalerite, galena, barite, cotunnite, native gold, stromeyerite, tellurobismutite and hessite. The trace element content of sulfide layers widely varies and depends on the amount of non-sulfide minerals (chlorite, illite, calcite, quartz, rutile, scheelite), which formed as a result of alteration of dacitic hyaloclastite components mixed with sulfide clasts. The sulfide layers are enriched in REEs (up to 561 ppm) due to the presence of REE-bearing minerals (bastnaesite, parisite, synchysite, galgenbergite, REE-bearing xenotime), which do not occur in massive sulfide ores. A narrow range of δ34S values of pyrite (1.41–3.27 ‰) from sulfide layers is explained by equilibrium or kinetic dissolution–precipitation processes of redeposition of sulfide ore clasts during diagenetic processes. The δ13C values of bulk samples of sulfide layers (–5.29 to –17.89 ‰) indicate that the authigenic carbonates formed from pore fluids circulated in former organic-rich hyaloclastite layers. The δ18O values of the same samples (+4.00 to + 8.36 ‰) are higher compared to seawater δ18O values due to diagenetic isotopic exchange between the hyaloclastitic components and pore fluids at elevated temperatures of burial process. The positive δ34S–Mn, δ13C–Mn, δ13C–As, δ13C–Sb, δ18O–Mn and δ18O–U correlations reflect organic matter consumption during the evolution of authigenic minerals. Data presented in this study helps to define the origin of diagenetically altered layered sulfide ores in volcanic-hosted massive sulfide deposits and are important for understanding diagenetic REE accumulations in sulfide-rich sediments of these deposits.

Geochemical Features of Redox-Sensitive Trace Metals in Sediments under Oxygen-Depleted Marine Environments

Organic- and sulfide-rich sediments have formed in oxygen-depleted environments throughout Earth’s history. The fact that they are generally enriched in redox-sensitive elements reflects the sedimentary environment at the time of deposition. Although the modern ocean is well oxidized, oxygen depletion occurs in certain areas such as restricted basins and high-productivity zones. We measured bulk chemical compositions (major and trace elements, total organic carbon, and total sulfur) of organic- and sulfide-rich sediments collected from eight areas having oxygen-depleted water to discuss relationships between geochemical features and sedimentary environments. Major elemental compositions generally show mixtures of terrigenous detritus and biogenic carbonate. Some redox-sensitive elements might be controlled by organic matter content, whereas others could be contained in sulfide minerals in sediments. In particular, Mo and U show a characteristic trend; areas with higher Mo and U—at least partially owing to a depositional process called the “particulate shuttle”—generally correspond to regions influenced by the open ocean. In contrast, areas with lower Mo and U are more restricted marine environments. This suggests that the degree of Mo and U enrichment reflects the geography in terms of proximity to the open ocean, or the degree of the supply of these elements from the open ocean.

Elevated nitrate simplifies microbial community compositions and interactions in sulfide-rich river sediments

Excessive nitrate in water systems is prevailing and a global risk of human health. Polluted river sediments are dominated by anaerobes and often the hotspot of denitrification. So far, little is known about the ecological effects of nitrate pollution on microbial dynamics, especially those in sulfide-rich sediments. Here we simulated a nitrate surge and monitored the microbial responses, as well as the changes of important environmental parameters in a sulfide-rich river sediment for a month. Our analysis of sediment microbial communities showed that elevated nitrate led to (i) a functional convergence at denitrification and sulfide oxidation, (ii) a taxonomic convergence at Proteobacteria, and (iii) a significant loss of biodiversity, community stability and other functions. Two chemolithotrophic denitrifiers Thiobacillus and Luteimonas were enriched after nitrate amendment, although the original communities were dominated by methanogens and syntrophic bacteria. Also, serial dilutions of sediment microbial communities found that Thiobacillus thiophilus dominated 18/30 communities because of its capability of simultaneous nitrate reduction and sulfide oxidation. Additionally, our network analysis indicated that keystone taxa seemed more likely to be native auxotrophs (e.g., syntrophic bacteria, methanogens) rather than dominant denitrifiers, possibly because of the extensive interspecific cross-feeding they estabilished, while environment perturbations probably disrupted that cross-feeding and simplified microbial interactions. This study advances our understanding of microbial community responses to nitrate pollution and possible mechanism in the sulfide-rich river sediment.

P.834 The effects of nicotinamide on the brain functional protein markers in prevention of diabetic neuropathy

There are several methods for studying metal-contaminated freshwater sediments, but more information is needed on which methods to include in ecological risk assessment. In this study, we compliment the traditional Sediment Quality Triad (SQT) approach – including information on chemistry, toxicity and ecological status – with studies on metal bioavailability and metal body residues in local organisms.We studied four mining-affected boreal lakes in Finland by conducting chemical analyses of sediment and water, toxicity tests (L. variegatus, V. fischeri, C. riparius, L. stagnalis), and analysis of benthic organism community structure. In addition, we studied the relationships between metal loading, toxicity, metal bioavailability, and metal body residues in the field-collected biota.Chemistry and benthic organism community structures show adverse effects in those lakes, where the metal concentrations are the highest. However, toxicity was connected to low sediment pH during the experiment, rather than to high metal concentrations. Toxicity was observed in 4 out of 6 toxicity tests including growth test with L. variegatus, bulk sediment test with V. fischeri, and the L. stagnalis toxicity test. The C. riparius test did not show toxicity. Metal body residues in biota were not high enough to induce adverse effects (0.1–4.1 mg Cu/kg fw, 0.01–0.3 mg Ni/kg fw, 2.9–26.7 mg Zn/kg fw and 0.01–0.7 mg As/kg fw).Chemical analyses, metal bioavailability assessment and benthic community structures survey revealed adverse effects in the sediments, where metal concentrations are highest (Lake SJ and Lake KS). Standard toxicity tests were not suitable for studying acid, sulfide-rich sediments and, therefore, benthic structure study and chemical analyses are believed to give more reliable results of the ecological status of these sediments.

The Sedimentary Carbon-Sulfur-Iron Interplay – A Lesson From East Anglian Salt Marsh Sediments

We explore the dynamics of the subsurface sulfur, iron and carbon cycles in salt marsh sediments from East Anglia, United Kingdom. We report measurements of pore fluid and sediment geochemistry, coupled with results from laboratory sediment incubation experiments, and develop a conceptual model to describe the influence of bioturbation on subsurface redox cycling. In the studied sediments the subsurface environment falls into two broadly defined geochemical patterns – iron-rich sediments or sulfide-rich sediments. Within each sediment type nearly identical pore fluid and solid phase geochemistry (in terms of concentrations of iron, sulfate, sulfide, dissolved inorganic carbon (DIC), and the sulfur and oxygen isotope compositions of sulfate) are observed in sediments that are hundreds of kilometers apart. Strictly iron-rich and strictly sulfide-rich sediments, despite their substantive geochemical differences, are observed within spatial distances of less than five meters. We suggest that this bistable system results from a series of feedback reactions that determine ultimately whether sediments will be sulfide-rich or iron-rich. We suggest that an oxidative cycle in the iron-rich sediment, driven by bioirrigation, allows rapid oxidation of organic matter, and that this irrigation impacts the sediment below the immediate physical depth of bioturbation. This oxidative cycle yields iron-rich sediments with low total organic carbon, dominated by microbial iron reduction and no methane production. In the absence of bioirrigation, sediments in the salt marsh become sulfide-rich with high methane concentrations. Our results suggest that the impact of bioirrigation not only drives recycling of sedimentary material but plays a key role in sedimentary interactions among iron, sulfur and carbon.

Creek Dynamics Determine Pond Subsurface Geochemical Heterogeneity in East Anglian (UK) Salt Marshes

Salt marshes are complex systems comprising of ephemerally flooded, vegetated platforms hydraulically fed by tidal creeks. Where drainage is poor, formation of saline-water ponds can occur. Within East Anglian (UK) salt marshes, two types of sediment chemistries can be found beneath these ponds; iron-rich sediment, which is characterized by high ferrous iron concentration in subsurface porewaters (up to 2 mM in the upper 30 cm); and sulfide-rich sediment, which is characterized by high porewater sulfide concentrations (up to 8 mM). We present five years of push-core sampling to explore the geochemistry of the porewater in these two types of sediment. We suggest that when carbon is present in quantities sufficient to exhaust the oxygen and iron content within pond sediments, conditions favour the presence of sulfide-rich sediments. In contrast, in pond sediments where oxygen is present—primarily through bioirrigation—reduced iron can be reoxidised and thus recycled for further reduction, favouring the perpetuation of iron-rich sedimentary conditions. We find these pond sediments can alter significantly over an annual timescale. We carried out a drone survey, with ground-truthed measurements, to explore the spatial distribution of geochemistry in these ponds. Our results suggest a pond’s proximity to the creek partially determines the pond subsurface geochemistry with iron-rich ponds tending to be closer to large creeks relative to sulfide-rich ponds. We suggest differences in surface delivery of organic carbon, due to differences in the energy of the ebb flow, or the surface/ subsurface delivery of iron may control the distribution. This could be amplified if tidal inundations flush ponds closer to creeks more frequently, removing carbon and flushing with oxygen. These results suggest that anthropogenic creation of drainage ditches could shift the distribution of iron- and sulfide-rich ponds and thus have an impact on nutrient, trace metal and carbon cycling in salt marsh ecosystems.

A map-based comparison of chemical characteristics in the surface horizon of arable acid and non-acid sulfate soils in coastal areas of Finland

Reclamation of acid sulfate (AS) soils for agriculture causes severe environmental problems and may expose the human population to increased metal intake in some cases. This is due to drainage-induced oxidation of reduced sulfide-rich sediments, and subsequent acid formation and metal mobilization in the soil. Most of the mobilized elements are lost through leaching, but some metals may be transported upwards in the soil profile. In this study, we compared the concentrations of total N and C, electrical conductivity (EC), and easily available (AAAc/AAAcEDTA-extractable) Al, Cd, Cr, Cu, Fe, Ni, Pb, S, and Zn in the surface horizon (0–15 cm) of arable AS and non-AS soils, classified on a map basis (mb), in the whole coastal area of Finland covered by the Litorina Sea stage of the Baltic Sea. Our aim was to assess whether the surface horizon of AS soils poses a risk of increased metal bioavailability. The study was conducted by combining two regional-scale datasets, monitoring data on the chemical status of Finnish cultivated soils, and a probability map of occurrence of AS soils in coastal areas of Finland. Mean total N and C concentration was 40% and 56% higher, respectively, in fine-textured ASmb soils, and 20% and 18% higher, respectively, in clay ASmb soils, than in the corresponding non-ASmb soils, although in clay soils the differences were not statistically significant. Electrical conductivity and easily available S and Ni concentrations were significantly higher in ASmb soils than in non-ASmb soils (29%, 56%, and 106% higher, respectively, in fine soils; 72%, 61%, and 47% higher, respectively, in clay soils). Mean Fe, Cr, Cu, and Zn concentrations were higher in ASmb than non-ASmb soils, but the difference was statistically significant only for Zn in clay soils (63%) and Cr in fine soils (68%). Mean Al, Cd, and Pb concentrations did not differ between ASmb and non-ASmb soils. These results are consistent with earlier findings in more spatially restricted studies. Enrichment of easily available metals in the surface horizon of AS soils could affect the quality of crops grown on these soils, an issue requiring further study.

Ecotoxicity assessment of boreal lake sediments affected by metal mining: Sediment quality triad approach complemented with metal bioavailability and body residue studies

There are several methods for studying metal-contaminated freshwater sediments, but more information is needed on which methods to include in ecological risk assessment. In this study, we compliment the traditional Sediment Quality Triad (SQT) approach – including information on chemistry, toxicity and ecological status – with studies on metal bioavailability and metal body residues in local organisms.We studied four mining-affected boreal lakes in Finland by conducting chemical analyses of sediment and water, toxicity tests (L. variegatus, V. fischeri, C. riparius, L. stagnalis), and analysis of benthic organism community structure. In addition, we studied the relationships between metal loading, toxicity, metal bioavailability, and metal body residues in the field-collected biota.Chemistry and benthic organism community structures show adverse effects in those lakes, where the metal concentrations are the highest. However, toxicity was connected to low sediment pH during the experiment, rather than to high metal concentrations. Toxicity was observed in 4 out of 6 toxicity tests including growth test with L. variegatus, bulk sediment test with V. fischeri, and the L. stagnalis toxicity test. The C. riparius test did not show toxicity. Metal body residues in biota were not high enough to induce adverse effects (0.1–4.1 mg Cu/kg fw, 0.01–0.3 mg Ni/kg fw, 2.9–26.7 mg Zn/kg fw and 0.01–0.7 mg As/kg fw).Chemical analyses, metal bioavailability assessment and benthic community structures survey revealed adverse effects in the sediments, where metal concentrations are highest (Lake SJ and Lake KS). Standard toxicity tests were not suitable for studying acid, sulfide-rich sediments and, therefore, benthic structure study and chemical analyses are believed to give more reliable results of the ecological status of these sediments.

First description of a new uncultured purple sulfur bacterium colonizing marine mangrove sediment in the Caribbean: Halochromatium-like PSB from Guadeloupe

Here, we report the first description of a marine purple sulfur bacterium (PSB) from sulfide-rich sediments of a marine mangrove in the Caribbean. TEM shows that this new isolate contains intracytoplasmic vesicular membrane systems (containing bacteriochlorophyll a) and larger internal sulfur granules, confirmed by EDXS analyses performed using ESEM. The sulfur distribution and mapping obtained for this PSB strain has allowed us to conclude that elemental sulfur is formed as an intermediate oxidation product and stored intracellularly. SEM shows that the bacterial cells are ovoid and extremely motile via lophotrichous flagella. Phylogenetic characterization, based on the analysis of 16S rDNA and functional gene pufM sequences, demonstrate that this strain belongs to the Chromatiaceae and may be a representative of a new species of the genus Halochromatium. Thus, reduced sediments of marine mangrove represent a sulfide-rich environment that sustains the development of Chromatiaceae, in addition to sulfur-oxidizing bacteria and cyanobacteria, as previously reported.

BLADE-SHAPED DIKES AND NICKEL SULFIDE DEPOSITS: A MODEL FOR THE EMPLACEMENT OF ORE-BEARING SMALL INTRUSIONS

Most of the world's major deposits of nickel and copper were formed as accumulations of magmatic sulfide liquid within small mafic-ultramafic intrusions. Ore-hosting intrusions exhibit a variety of forms but typically show greater horizontal than vertical extents, occurring as tube-shaped chonoliths, narrow elongate sills, boatshaped bodies, or sword blade-shaped dikes with originally horizontal principal axes. Sulfide accumulation at the downward termination of blade-shaped dikes is noted in a number of deposits worldwide. Based on evidence from continental dike swarms, Icelandic fissure eruptions, and active shield volcanoes, we suggest that these blade-shaped bodies formed by magma migration within vertical fractures that propagated laterally rather than vertically. Some examples, notably the bladed dikes of the South Raglan trend, have contact relationships indicating processes of active erosion, assimilation, and replacement of country rock. Where such dikes are injected into mixed volcanic-sedimentary sequences, thermal modeling of interaction with nonrefractory country rock predicts repeated formation and collapse of transient chilled margins against narrow zones of partially molten wall rock. Where the wall rock is sulfide-rich sediment, this generates a slurry of sulfide liquid, country-rock xenoliths, and chilled margin fragments that flows down the wall to accumulate at the bottom edge of the dike. This type of mixture is commonly seen as sulfide-matrix ore breccias in intrusion-hosted deposits. Widening of the conduit along zones of easily eroded country rock may result in a transition from a dike-like to a tubular chonolith geometry. Multiple magma pulses within the same magma conduit may give rise to complex superimpositions of ore zones, further complicated by formation of sulfide-silicate melting-infiltration fronts. Hence we argue that the bladed-dike geometry is an end-member type that commonly serves as a precursor form to a range of eventual geometric forms; recognition of this basic geometry provides general insights into the origins of other important deposits.

Tracing sulfate recycling in the hypersaline Pétrola Lake (SE Spain): A combined isotopic and microbiological approach

Sulfur (S) plays a significant role in saline environments, and sulfate (SO42−) is an important component of the biogeochemical S-cycle since it acts as the main electron acceptor in anoxic sediments. The purpose of this paper is to evaluate the fate of S, its origin, and processes affecting sulfate outcome in the hypersaline Pétrola Lake in the Castilla-La Mancha region (High Segura Basin, SE Spain). The lake is the terminal discharge zone of an endorheic basin with considerable anthropogenic pressures. Anthropogenic activities (mainly agricultural inputs and wastewater discharge), together with bedrock leaching of sulfate and sulfide-rich sediments, increase dissolved SO42− in surface and groundwater up to 123,000mg/L. The source and fate of sulfate in this environment was investigated coupling hydrochemistry, including hydrogen sulfide (H2S) microprofiles, isotopic analyses (δ34S, δ18OSO4, δ2HH2O, δ18OH2O, and tritium), mineralogical determinations, and molecular biology tools (16S rDNA amplification and sequencing). The origin of dissolved SO42− in water is related to pyrite oxidation from Lower Cretaceous sediments, and secondary gypsum dissolution. Under the lake, dissolved SO42− decreases with depth, controlled by three main processes: (1) seasonal evaporation cycles, (2) hydrodynamic instability caused by the different density-driven groundwater flow, and (3) sulfate-reduction processes, i.e. dissimilatory bacterial sulfate reduction (BSR). These processes control the continuous recycling of sulfur in the system. Lake water and groundwater are in hydraulic connection, and a density-driven flow (DDF) is able to transport reactive organic matter and dissolved SO42− towards the underlying aquifer. Hydrochemical evolution in depth, H2S production (up to 0.024nmol/cm3·s) and the presence of sulfate-reducing bacteria suggest the existence of BSR processes. However, isotope techniques are insufficient to elucidate BSR processes since their isotopic effect is masked by low isotope fractionation and high SO42− concentrations. The pattern here described may be found in other saline basins worldwide.

First description of a new uncultured epsilon sulfur bacterium colonizing marine mangrove sediment in the Caribbean: Thiovulum sp. strain karukerense.

Here, the first description is reported of an epsilon sulfur-oxidizing bacterium from sulfide-rich sediments of marine mangrove in the Caribbean. By transition electron microscopy it was shown that this new strain contains intracytoplasmic large internal sulfur granules, which was confirmed by energy-dispersive X-ray spectroscopy analyses performed using an environmental scanning electron microscope. The sulfur distribution obtained for this sulfur-oxidizing bacterial strain allowed us to conclude that elemental sulfur is formed as an intermediate oxidation product and stored intracellularly. By conventional scanning electron microscopy it was shown that the bacterial cells are ovoid and extremely motile by lophotrichous flagella. Phylogenetic analyses based on partial sequence of the 16S rRNA gene confirmed that the bacterial strain belongs to the Thiovulum cluster and could be a representative of a new species in this poorly studied genus of sulfur-oxidizing free-living bacteria. Thus, reduced sediment of marine mangrove represents a sulfide-rich environment sustaining development of both gamma and epsilon sulfur-oxidizing Proteobacteria.

Fauna and habitat types driven by turbidity currents in the lobe complex of the Congo deep-sea fan

This study characterizes the habitats and megafaunal community of the Congo distal lobe complex driven by turbidity currents through the use of remotely operated vehicle (ROV) still imagery transects covering distances in the order of kilometers. In this sedimentary, abyssal area about 5000m deep and 750km offshore from western Africa, large quantities of deposited organic material supplied by the Congo River canyon and channel support aggregations of large sized foraminifers (Bathysiphon sp.) and vesicomyid clams (Christineconcha regab, Abyssogena southwardae) often associated with methane cold seeps, as well as opportunistic deep-sea scavengers. Additionally, bacterial mats, assumed to be formed by large sulfur-oxidizing filamentous bacteria (Beggiatoa type), and black patches of presumably reduced sediment were seen which are, together with sulfur-oxidizing symbiont- bearing vesicomyids, indicators of sulfide-rich sediments. Habitat and faunal distribution were analyzed in relation to the microtopography obtained with the ROV multibeam echosounder, at three sites from the entrance of the lobe complex where the channel is still deep, to the main, flatter area of turbidite deposition. Specific characteristics of the system influence animal distributions: both the forams and the vesicomyid clams tended to avoid the channels characterized by high-speed currents, and are therefore preferentially located along channel flanks affected by sliding, and on levees formed by channel overspill. Foram fields are found in flat areas and form large fields, whereas the vesicomyids have a patchy distribution and appear to show a preference for regions of local topographical relief such as slide scars or collapsed blocks of sediments, which likely facilitate sulfide exhumation. The colonization of sulfide rich sediments by vesicomyids is limited, but nonetheless was seen to occur in the main deposition area where they have to cope with very high sedimentation rates (up to 20cm/yr) and frequent turbidity currents. Other biological adaptations to the local conditions likely determine the presence and survival of animals in the system: large agglutinated forams are known to be adept at quickly colonizing disturbed sediment and capitalizing on abundant but irregular food sources, and vesicomyid clams have a mobile lifestyle that enables them to maintain their population in the ever changing landscape of sulfide-rich sediment outcrops. Turbiditic systems appear to be intermediate between other energy rich habitats sustaining chemosynthesis in the deep sea, being locally less stable in terms of energy supply than cold seeps, limiting the number of cold-seep specialists able to colonize, but constituting a longer lived habitat than food falls. Turbidite fans therefore represent distinct deep sea habitats that contribute to sustaining populations of both chemosynthesis-based and opportunistic taxa in the deep-sea.

Cold-seep-like macrofaunal communities in organic- and sulfide-rich sediments of the Congo deep-sea fan

Methane-rich fluids arising from organic matter diagenesis in deep sediment layers sustain chemosynthesis-based ecosystems along continental margins. This type of cold seep develops on pockmarks along the Congo margin, where fluids migrate from deep-buried paleo-channels of the Congo River, acting as reservoirs. Similar ecosystems based on shallow methane production occur in the terminal lobes of the present-day Congo deep-sea fan, which is supplied by huge quantities of primarily terrestrial material carried by turbiditic currents along the 800km channel, and deposited at depths of up to nearly 5000m. In this paper, we explore the effect of this carbon enrichment of deep-sea sediments on benthic macrofauna, along the prograding lobes fed by the current active channel, and on older lobes receiving less turbiditic inputs. Macrofaunal communities were sampled using either USNEL cores on the channel levees, or ROV blade cores in the chemosynthesis-based habitats patchily distributed in the active lobe complex.The exceptionally high organic content of the surface sediment in the active lobe complex was correlated with unusual densities of macrofauna for this depth, enhanced by a factor 7–8, compared with those of the older, abandoned lobe, whose sediment carbon content is still higher than in Angola Basin at same depth. Macrofaunal communities, dominated by cossurid polychaetes and tanaids were also more closely related to those colonizing low-flow cold seeps than those of typical deep-sea sediment. In reduced sediments, microbial mats and vesicomyid bivalve beds displayed macrofaunal community patterns that were similar to their cold-seep counterparts, with high densities, low diversity and dominance of sulfide-tolerant polychaetes and gastropods in the most sulfidic habitats. In addition, diversity was higher in vesicomyid bivalve beds, which appeared to bio-irrigate the upper sediment layers. High beta-diversity is underscored by the variability of geochemical gradients in vesicomyid assemblages, and by the vesicomyid population characteristics that vary in density, size and composition. By modifying the sediment geochemistry differently according to their morphology and physiology, the different vesicomyid species play an important role structuring macrofauna composition and vertical distribution. Dynamics of turbiditic deposits at a longer temporal scale (thousands of years) and their spatial distribution in the lobe area also resulted in high heterogeneity of the “cold-seep-like communities”. Dynamics of chemosynthetic habitats and associated macrofauna in the active lobe area resembled those previously observed at the Regab pockmark along the Congo margin and rapid succession is expected to cope with high physical disturbance by frequent turbiditic events and huge sedimentation rates. Finally, we propose a model of the temporal evolution of these peculiar habitats and communities on longer timescales in response to changes in distributary channels within the lobe complex.

Can the hemoglobin characteristics of vesicomyid clam species influence their distribution in deep-sea sulfide-rich sediments? A case study in the Angola Basin

Vesicomyids live in endosymbiosis with sulfur-oxidizing bacteria and therefore need hydrogen sulfide to survive. They can nevertheless live in a wide range of sulfide and oxygen levels and depths, which may explain the exceptional diversity of this clam family in deep-sea habitats. In the Gulf of Guinea, nine species of vesicomyid clams are known to live in cold-seep areas with pockmarks from 600 to 3200m deep, as well as in the organic-rich sediments of the Congo deep-sea fan at 5000m deep. Our previous study showed that two species living in a giant pockmark have different oxygen carriers, suggesting different adaptations to hypoxia. Here, we studied the hemoglobin structure and oxygen affinity in three other species, Calyptogena valdiviae, Elenaconcha guiness and Abyssogena southwardae to determine whether the characteristics of their oxygen carriers contribute to their distribution in sulfide-rich sediments at a regional scale. Documenting pairwise species associations in various proportions, we give a semi-quantitative account of their local distribution and oxygen and sulfide measurements at seven sites. Mass spectrometry showed that each vesicomyid species has four intracellular monomeric hemoglobin molecules of 15–16kDa, all differing in their molecular mass. As expected, the monomers showed no cooperativity in oxygen binding. Their oxygen affinities were very high (below 1Torr), but differed significantly. C. valdiviae had the highest affinity and was dominant in the Harp pockmark, the site with the lowest oxygen content (half the value of fully oxygenated water). A. southwardae dominated in the Congo Lobe area, the site with the deepest sulfides. We discuss how hemoglobin may favor an active, vertical distribution of vesicomyids in sulfide-rich sediments.

Environmental implications of the use of sulfidic back-bay sediments for dune reconstruction — Lessons learned post Hurricane Sandy

Some barrier-island dunes damaged or destroyed by Hurricane Sandy's storm surges in October 2012 have been reconstructed using sediments dredged from back bays. These sand-, clay-, and iron sulfide-rich sediments were used to make berm-like cores for the reconstructed dunes, which were then covered by beach sand. In November 2013, we sampled and analyzed partially weathered materials collected from the cores of reconstructed dunes. There are generally low levels of metal toxicants in the reconstructed dune materials. However oxidation of reactive iron sulfides by percolating rainwater produces acid-sulfate pore waters, which evaporate during dry periods to produce efflorescent gypsum and sodium jarosite salts. The results suggest use of sulfidic sediments in dune reconstruction has both drawbacks (e.g., potential to generate acid runoff from dune cores following rainfall, enhanced corrosion of steel bulwarks) and possible benefits (e.g., efflorescent salts may enhance structural integrity).

Early Cambrian Black Shale-Hosted Mo-Ni and V Mineralization on the Rifted Margin of the Yangtze Platform, China: Reconnaissance Chromium Isotope Data and a Refined Metallogenic Model

The transgressive basal unit of the Early Cambrian black-shale sequence along the rifted margin of the southeastern Yangtze platform hosts a wide spectrum of marine sedimentary rocks distributed over more than a length of 1,000 km. A few-centimeter-thick sulfide-rich black shale units have spectacular metal tenors (Mo and Ni in the percent range, PGE + Au around 1 ppm) and consist of submillimeter-scale laminated sulfide and carbonaceous material and centimeter-sized pebble-like rip-up clasts of Mo-S-C compounds, pyrite, and Ni-rich polymetallic sulfides in carbonaceous and phosphate-rich matrix. The δ 53/52 Cr authigenic values of Mo-Ni sulfide-rich black shale samples from the Zunyi mining district (Guizhou province), as well as from the Sancha district (Hunan province), 400 km northeast, have a mean of 0.96 ± 0.22‰ ( n = 8), while V-rich black shale from both districts has a mean of 1.34 ± 0.46‰ ( n = 5). These data indicate significantly positively fractionated values compared to igneous silicate Earth. The Cr isotope values of the studied shales compare with recent findings of positively fractionated δ 53/52 Cr values in Late Neoproterozoic-Phanerozoic marine carbonates and shale/mudstones and attest for the operation of an intensified oxidative surface Cr cycle from at least around ~0.75 Gyr ago. We propose that the major change in Cr cycling around the Precambrian-Cambrian boundary was caused by a significant rise of atmospheric oxygen levels. The Cr isotope data confirm earlier conclusions from Mo and Os isotopes, which indicate a seawater metal source with ultimate metal supply by oxidative weathering of continental crust. In particular, covariation trends of Re-Os and of platinum-group elements display a distinct seawater signature, and a degree of metal enrichment which is an extension of the normal black shale pattern. The Mo-Ni sulfide-rich black shale units are probably produced by winnowing of subaquatic hardground deposited under euxinic conditions. The same stratigraphic level also hosts anoxic/suboxic V-rich black shale (V in illite) and huge phosphorite deposits in oxic/suboxic settings, bedded barite, as well as 10s of meter-thick sapropelic alginite (combustible shale). We show that the extreme metal enrichment of the Mo-Ni sulfide-rich black shale can be understood as a combination of redox cycling and bottom-water/sediment-interface scavenging under euxinic conditions (Mo, noble metals), and of oxidation (remineralization) of organic matter settling from the photic zone, with sulfide fixation of Ni and other biophile elements under denitrifying and sulfate-reducing conditions. High biological activity (as in coastal upwelling settings with high nutrient supply), very low clastic accumulation rate (as in protected basins), and low organic matter deposition (high rate of remineralization) in stratified oxic-suboxic-euxinic basins are requirements for advanced metal enrichment in black shales. A special bathymetric condition of slope deposition with intrabasinal olistostrome-like mass movement and gravitational winnowing explains both the peculiar ore textures and the further metal enrichment to ore grade in the Early Cambrian rock units on the Yangtze platform. The Mo-Ni sulfide-rich sediments can be regarded as the euxinic variant of the marine hydrogenous ore deposit spectrum, where ferromanganese nodules/crusts represent the oxic variant of extreme fractionation from seawater.