Acid-volatile Sulfide In Sediments Research Articles

Mercury concentrations in sediments and oysters in a temperate coastal zone: a comparison of farmed and wild varieties.

Oyster aquaculture has progressively increased to meet growing demands for seafood worldwide; however, its effects on methylmercury (MeHg) production in sediment and accumulation in oysters are largely unknown. In this study, total Hg (THg) and MeHg in sediments collected from aquaculture and reference sites and in farmed and wild oysters were measured and compared to explore potential factors that regulate MeHg production and bioaccumulation at the aquaculture sites. The results showed that the mean concentrations of THg and MeHg in varying sediment depths at the aquaculture site were 34 ± 4.1 ng g-1 and 16 ± 12 pg g-1, respectively. In comparison, the mean concentrations of THg and MeHg in sediments at the reference site were 25 ± 2.5 ng g-1 and 63 ± 28 pg g-1, respectively. While the MeHg/THg in the aquaculture sediments increased with organic carbon content, the slope of MeHg/THg versus organic carbon content was suppressed by high concentrations of dissolved sulfide in the pore water. Multiple parameters (total sulfur, total nitrogen and acid volatile sulfide in sediment, and dissolved sulfide in pore water) showed significant negative relationships with MeHg/THg in the sediment, and the total sulfur content in the sediment showed the highest inverse correlation factor with MeHg/THg (r = - 0.83). The mean concentrations of THg and MeHg in farmed oysters (mean weight 3.2 ± 1.5 g) were 36 ± 10 ng g-1 and 15 ± 6.7 ng g-1, respectively, while those in wild oysters (mean weight 0.92 ± 0.32 g) were 47 ± 9.9 ng g-1 and 15 ± 6.7 ng g-1, respectively. Concerning oysters of the same size range, THg and MeHg levels were higher in farmed oysters than in wild oysters despite the faster growth rate of farmed oysters, suggesting that the Hg content of food sources is more important than growth dilution rates in the control of Hg levels. The mean hazardous quotient for MeHg in farmed oyster was calculated as 0.044 ± 0.020, suggesting no expected health risk from farmed oyster consumption.

Sulfate reduction and alterability of sulfur species in sediments of an estuary with irregular hydrological regime

The irregular hydrological regime in Patos Lagoon estuary has been suggested as having a distinctive influence on sulfur speciation in sediments. We performed an investigation for different prolonged hydrological conditions focusing on the distribution of sulfides (acid volatile sulfide (AVS), chromium reducible sulfide (CRS), and Free-S2-) in sediment cores from salt marsh and non-vegetated shallow zone. Significant differences in sulfides content and distribution between the different hydrological periods were found. The predominance of more reducing conditions was observed during the freshwater period. It reflects a higher total reducible inorganic sulfur (TRIS) content in this period, with a great accumulation of AVS in sediments (> 100 mg kg-1). In the maximum salinity period, more oxidizing conditions prevailed, which significantly decreased the concentrations of metastable sulfides. The intense bioirrigation process exerts control over sulfide formation and distribution, which is as important as that exerted by the variations of the hydrological regime.

Uptake and trophic changes in polybrominated diphenyl ethers in the benthic marine food chain in southwestern British Columbia, Canada

We examined the physical and geochemical effects of sediment on the uptake of polybrominated diphenyl ethers (PBDEs) into marine sediment feeders and their transfer to higher trophic fauna. Sediment PBDEs increased with % total organic carbon (%TOC), organic carbon (OC) flux and grain size (%fines). Tissue PBDE variance was best explained ( R2 = 0.70) by sediment acid volatile sulfides (AVS), PBDEs, and organic lability and input, with the highest values near wastewater outfalls. Dry weight tissue/sediment PBDEs declined with increasing sediment PBDEs, resulting in tissue dilution (ratio <1) at >10 000 pg/g in harbours. Ratios also decreased with increasing %fines, resulting in regional differences. These patterns imply that high levels of fines and high sediment concentrations make PBDEs less bioavailable. Dry weight PBDEs increased >100× between background deposit feeders and predators (polychaetes, crabs, bottom fish, seal), but lipid normalized PBDEs barely increased (<1.3%), suggesting remarkably high uptake in low-lipid sediment feeders, and that PBDEs don’t accumulate at higher trophic levels, but lipid content does. Filter feeders had lower lipid-normalized PBDEs than deposit feeders, highlighting the importance of food resources in higher trophic fauna for bioaccumulation. The most profound congener change occurred with sediment uptake, with nona/deca-BDEs declining and tetra-hexa-BDEs increasing. Harbour sediment feeders had more deca-BDEs than other samples, suggesting PBDEs mostly pass unmodifed through them. Deca-BDEs persist patchily in all tissues, reflecting variable dependence on sediment/pelagic food.

Effects of nitrate dosing on the migration of reduced sulfur in black odorous river sediment and the influencing factors

At present, nitrates were widely used to remediate sulfur-rich sediment in black odorous rivers. However, the optimal nitrate dosage and influencing factors during remediation have not been fully investigated. In this study, various nitrate dosages and possible influencing factors were investigated for their efficiency in treating sulfur-rich sediment. The results indicated that acceptable remedial efficiency (the percentage of acid volatile sulfide (AVS) oxidation and the residual ammonium production) can be achieved when 1.6 times the theoretical nitrate dosage is used. Large amounts of AVS cannot be oxidized if too little nitrate is used and will regenerate after several days of remediation. Conversely, high concentrations of ammonium will form if too much nitrate is used. The results of this study indicated that a rapid AVS oxidation rate will be achieved in higher temperatures; no significant treatment efficiency was found when temperatures were in the range of 15–35 °C. Organic matter slowed the rate of nitrate reduction but did not affect its remedial efficiency for AVS oxidation in sediment. A high concentration of ferrous iron primarily influenced nitrate treatment efficiency in the oxidation of AVS in sediment, simultaneously causing the production of a high ammonium concentration. This study once again proved that microbial mediation of the autotrophic sulfide-driven denitrification dominates AVS oxidation in sediment. This study indicated that a universal nitrate dosage calculation equation should be established, and that factors such as ferrous iron concentration should be considered in future remediation of black odorous rivers.

Effects of sediment resuspension on the oxidation of acid‐volatile sulfides and release of metals (iron, manganese, zinc) in Pescadero estuary (CA, USA)

Bar-built estuaries are unique ecosystems characterized by the presence of a sandbar barrier, which separates the estuary from the ocean for extended periods and can naturally reopen to the ocean with heavy rainfall and freshwater inflows. The physical effects associated with the transition from closed to open state, specifically water mixing and sediment resuspension, often indirectly worsen water quality conditions and are suspected to drive near-annual fish kills at the Pescadero estuary in northern California. The effects of sediment acid-volatile sulfide (AVS) oxidation, specifically oxygen depletion, acidification, and metal release, are believed to aggravate water conditions for fish but remain poorly understood. We performed slurry incubations containing sediment from 4 sites in the Pescadero estuary, representing a gradient from the Pacific Ocean to freshwater tributaries. We measured near-maximum rates of aqueous hydrogen sulfide oxidation, sediment AVS oxidation, sulfate production, and acidification, as well as near-maximum release rates of iron (Fe), manganese (Mn), and zinc (Zn) to the water column. We estimated AVS oxidation rates of 8 to 21 mmol S kg-1 d-1 , which were 3 orders of magnitude higher than aqueous hydrogen sulfide oxidation rates, 6 to 26 μmol S kg-1 d-1 . We suggest that aqueous hydrogen sulfide cannot be responsible for the observed kills because of low concentrations and minimal oxidative effects on pH and metal concentrations. However, the oxidative effects of AVS are potentially severe, decreasing pH to strongly acidic levels and releasing aqueous Fe, Mn, and Zn concentrations up to 11.2 mM, 0.46 mM, and 88 μM, respectively, indicating a potential role in worsening water conditions for fish in the Pescadero estuary. Environ Toxicol Chem 2018;37:993-1006. © 2017 SETAC.

Changes in water quality following opening and closure of a bar-built estuary (Pescadero, California)

Abstract Bar-built estuaries are coastal environments characterized by the partial closure of the estuary's mouth with a sandbar barrier for extended periods (closed state). Through natural events (rainfall) or anthropogenic influences, the sandbar is breached, reopening the estuary to the ocean. The transition from closed to open state often leads to extensive physical and chemical changes in the estuarine conditions, as water mixing and sediment resuspension are increased, which could result in the oxidation of sediment acid-volatile sulfides (AVS). We followed monthly changes in water's and sediment geochemical characteristics at thirty-two sites spanning the Pescadero Estuary over a one-year period. We showed that the transition from closed to open state leads to significant decreases in aqueous pH to circumneutral values and significant increases in aqueous hydrogen sulfide and iron concentrations to 10.6 μM and 59.1 μM, respectively, due to sediment AVS oxidation following sediment resuspension. Aqueous hydrogen sulfide concentrations observed in both closed and open states were significantly higher than the recommended thresholds for aquatic life. Moreover, mildly acidic water conditions in the open state were lower than the recommended limits for aquatic life. Our spatial analysis further highlighted that some parts of the estuary were more vulnerable to decreased water quality. Indeed, high sediment AVS contents (19–24 mmol kg− 1 ) were observed year-round at the River Confluence and Butano Creek regions, which implies a high potential for severe water acidification and metal release when the estuary transitions from closed to open state.

Reduced inorganic sulfur in sediments of the mariculture region of Sanggou Bay, China

AEI Aquaculture Environment Interactions Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections AEI 8:233-246 (2016) - DOI: https://doi.org/10.3354/aei00154 Theme Section: Integrated Multi-Trophic Aquaculture (IMTA) in Sanggou Bay, China Reduced inorganic sulfur in sediments of the mariculture region of Sanggou Bay, China Xuming Kang1, Sumei Liu1,2,*, Xiaoyan Ning1 1Key Laboratory of Marine Chemistry Theory and Technology MOE, Ocean University of China/ Qingdao Collaborative Innovation Center of Marine Science and Technology, Qingdao 266100, PR China 2Laboratory of Marine Ecology and Environmental Science, Qingdao National Laboratory for Marine Science and Technology, Qingdao, PR China *Corresponding author: sumeiliu@ouc.edu.cn ABSTRACT: Reduced inorganic sulfur (RIS) and organic matter (OM) in a mariculture region (Sanggou Bay, China; SGB) and at a reference station without mariculture were determined to assess the influence of mariculture on sulfide accumulation and the benthic environment. To this end, sediment acid-volatile sulfide (AVS), pyrite sulfur (pyrite-S), elemental sulfur (ES), OM, porosity, reactive iron, and pore water sulfate were measured. The results indicate that the concentration of RIS was negatively correlated with dissolved oxygen concentration. Principal component analysis showed that sulfide distribution was influenced by sediment porosity, OM, and reactive iron concentration. In addition, sulfide distribution was influenced by water current and water depth. More sulfide content accumulated at an oyster monoculture site than at a scallop/kelp polyculture site and a kelp monoculture site. We found no significant difference in ES concentration among the 3 mariculture types. While no significant influence on benthic OM accumulation was observed, except slightly enhanced reactivity of the OM (making it easily decomposable), mariculture activities in SGB significantly promoted sulfide accumulation compared to the reference station. However, there was no potential threat of toxic sulfide to the benthic biomass in SGB. KEY WORDS: Acid volatile sulfide · Pyrite-S · Elemental sulfur · Sediment · Mariculture · Sanggou Bay Full text in pdf format PreviousNextCite this article as: Kang X, Liu S, Ning X (2016) Reduced inorganic sulfur in sediments of the mariculture region of Sanggou Bay, China. Aquacult Environ Interact 8:233-246. https://doi.org/10.3354/aei00154 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in AEI Vol. 8. Online publication date: April 19, 2016 Print ISSN: 1869-215X; Online ISSN: 1869-7534 Copyright © 2016 Inter-Research.

Assessing the Sulfide Footprint of Mussel Farms with Sediment Profile Imagery: A New Zealand Trial.

Growing numbers and increased stocking of marine mussel farms make reliable techniques for environmental effect assessment a priority. Previously, we showed how the color intensity of soft sediment could be used to estimate its acid volatile sulfide (AVS) content, a product of the anaerobic microbial degradation of organic matter deposits. We then proposed to include assessments of the AVS farm footprint in marine farm monitoring, in particular, to investigate temporal changes in the extent of the seafloor area of elevated sediment AVS content. Such assessment requires accurate detection of the AVS footprint boundary. Here, we demonstrate how to detect this boundary with analyses of sediment color intensity. We analyzed 182 sediment profile images taken along three transects leading from approximately 50 m inside to 200 m outside a long-line mussel farm in New Zealand and found that the mean sediment color intensity inside the farm boundary was almost one third lower than that of the sediment distant from the farm. Segmented regression analysis of the combined color intensity data revealed a breakpoint in the trend of increasing grey values with increasing distance from the farm at 56 ± 13 m (± 95% confidence interval of the breakpoint) outside the mussel farm. Statistical analyses indicated that the extent of the color intensity footprint was a function of water column depth, as was shown visually using mapping methods; organic particles disperse further in a deeper seawater column. We conclude that for soft coastal sediments, our sampling and data analysis techniques may provide a rapid and reliable supplement to existing benthic surveys that assess environmental effects of mussel farms.

Ecological risk index for aquatic pollution control: a case study of coastal water bodies from the Rio de Janeiro State, southeastern Brazil

The Potential Ecological Risk Index (PERI) was proposed by Håkan- son in 1980 to be used as a diagnostic tool for water pollution. The aim of this study was to apply the PERI for tropical conditions, proposing modifications. The metal contamination of 15 areas, including five bays, from the coastal systems of the Rio de Janeiro State, Brazil, which pre- sent different pollution degrees and trophic status, was assessed. For environment sensitivity assessment through bioproduction estimation, the ratio of total phosphorus (in mg/g)/organic matter in sediment (in %) ×100 was used, instead of the correlation between total nitrogen and organic matter as used in the original index calculation. The results for environment sensitivity were correlated with the concentration of acid volatile sulfides in sediments and with chlorophyll-a of the water column, showing a compatible relationship between water trophic status and se- diment anoxia. The highest degree of contamination (DC) was found for the N-NW sector of the Guanabara bay (60.21 – classified as very high), followed by the Sepetiba bay stations, which showed DC values classified as moderate. The Ilha Grande bay and Paraty (Mamanguá) showed low DC values. The station of the Guanabara bay was the only one classified by the index as of very high ecological risk (PERI=697), followed by three stations classified as of moderate risk (Mouth of Guanabara bay; Garsas, Sepetiba bay; and Angra, Ribeira bay). All the other stations present low risk associated with metal exposure. As mercury is the metal of highest toxicity factor in the Håkanson formulation, a control test was applied to observe the relationship between PERI and mercury concentrations in fish and its bioconcentration factors, which are related to mercury bioavailability in the system. The results of the modified PERI were fully satisfactory for ranking areas of contamination. Keywords: coastal systems, toxic metals, trophic status, sediments, fish.

Acid volatile sulfide and simultaneously extracted metals in superficial sediments from Baihua Lake, China

The bioavailability of five divalent cationic heavy metals (Pb, Cd, Cu, Zn and Ni) in 10 superficial sediment samples from Baihua Lake was assessed based on the molar ratio of simultaneously extracted metals (SEMs) to acid volatile sulfide (AVS). Atomic absorption spectrometry (AAS) and X-ray powder diffraction (XRD) were used to determine the heavy metal concentrations and examine the mineralogy of the crystalline phases, respectively. The AVS loadings in sediments from Baihua Lake ranged from 64.30 to 350.08 μmol/g (dry weight). The corresponding SEM levels for the sampling sites varied from 1.770 to 14.660 μmol/g. The molar ratio of SEMs to AVS ranged from 0.014 to 0.084 with a mean value of 0.034. The XRD analysis also confirmed the presence of some metal sulfides in sediments from Baihua Lake. The SEMs/AVS ratios for all sampling sites were significantly lower than 1.0, indicating that AVS in the sediments was sufficient to bind the five heavy metals; thus, these heavy metals are currently not significantly bioavailable to benthic organisms. Comparing the SEMs results to published guideline values for metal toxicity to benthic organisms in sediments, however, suggests that Zn and Ni pose a risk at some sampling locations in Baihua Lake.

Thresholds of irradiance for seagrass Posidonia oceanica meadow metabolism

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 466:69-79 (2012) - DOI: https://doi.org/10.3354/meps09928 Thresholds of irradiance for seagrass Posidonia oceanica meadow metabolism E. Gacia1,*, N. Marbà2, J. Cebrián3,4, R. Vaquer-Sunyer2, N. Garcias-Bonet2, C. M. Duarte2,5 1Biogeodynamics and Biodiversity Group, Centre d’Estudis Avançats de Blanes, Consejo Superior de Investigaciones Cientificas (CEAB-CSIC), Blanes 17300, Spain 2Department of Global Change Research, Mediterranean Institute for Advanced Studies (IMEDEA; UIB-CSIC), Miquel Marqués 21, Esporles 07190, Spain 3Dauphin Island Sea Lab, 101 Bienville Blvd, Dauphin Island, Alabama 36528, USA 4Department of Marine Sciences, University of South Alabama, Mobile, Alabama 36688, USA 5The UWA Oceans Institute, The University of Western Australia, 35 Stirling Highway, Crawley 6009, Western Australia, Australia *Email: gacia@ceab.csic.es ABSTRACT: Meadows of the endemic seagrass Posidonia oceanica are threatened in the Mediterranean due to a general deterioration of the light environment that becomes critical when light irradiance is insufficient to meet the carbon requirements of the system. Here, we conduct a 3 wk, in situ shading experiment (8 levels plus controls) to determine the threshold of irradiance for balanced metabolism in a shallow P. oceanica meadow and further assess the recovery of the system 1 wk later. Reduced light irradiance decreased the net community production of the meadow, which may turn negative (i.e. respiration exceeded gross community primary production) under 338 µE m−2 s−1. Shading throughout the experiment did not appear to cause sustained physiological damage to the system since values of net community production after the cessation of shading were similar to pre-experimental, ambient levels. Sediment acid volatile sulfide pools ranged between 0.002 and 0.058 mol m−2 across shading treatments, and the highest pools were observed in the most shaded sediments. At high light impairment, meristematic cell divisions were low, and carbohydrate content in young rhizomes decreased throughout the experiment. Eight days after the cessation of shading, reduced rhizome carbohydrate stores and elevated sediment sulfide levels still persisted in the previously intensively shaded areas. The present study provides evidence of resistance and resilience of the seagrass Posidonia oceanica to light impairment for short (3 wk) periods of time. Although the compensation irradiance of the system varied by ~2-fold, it provides a quantitative estimate of the irradiance threshold at which seagrass meadows may shift from being coastal carbon sinks to CO2 sources. KEY WORDS: Seagrass · Ecosystem · Production · Respiration · Compensation Irradiance · Mediterranean Full text in pdf format Supplementary material PreviousNextCite this article as: Gacia E, Marbà N, Cebrián J, Vaquer-Sunyer R, Garcias-Bonet N, Duarte CM (2012) Thresholds of irradiance for seagrass Posidonia oceanica meadow metabolism. Mar Ecol Prog Ser 466:69-79. https://doi.org/10.3354/meps09928 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 466. Online publication date: October 15, 2012 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2012 Inter-Research.

Impacts of mariculture practices on the temporal distribution of macrobenthos in Sandu Bay, South China

Sandu Bay is located in the East China Sea and is characterized by high-density fish farming and kelp culture. Despite this, little is known about the impacts of these different mariculture practices on the local environment. We investigated the temporal variation in macrobenthos and environmental conditions at three sites in the bay (fish farming site, kelp culture site, and a control site). We collected water and sediment samples during nine cruises between May 2009 and February 2010. The density of macrobenthos peaked at the fish farming site in July (655 ind./m2) whereas density did not fluctuate as widely at the other two sites. Biomass varied significantly at both the control and kelp culture sites, but had only a single peak at the fish farming site in June (21.90 g/m2). The dominant species varied throughout the study period at the control and kelp culture sites, whereas a single terebellid species (Lysilla pacifica) dominated the macrobenthos at the fish farming site. The diversity index H′ increased at the control site beginning in February then decreased after May, whereas H′ was low at the other sites in December. The mean dissolved oxygen level was highest at the control site (6.59 mg/L) and lowest at the fish farming site (5.54 mg/L). DO levels were lowest at all sites in summer (July and August). The sediment acid volatile sulfide content was higher at the fish farming site (1.46 mg/g dry weight) than those at the kelp culture and control sites (1.22 and 0.14 mg/g, respectively). Our results suggest that mariculture practices have a clear impact on the benthic environment/community in Sandu Bay.

Structure and reactivity of zinc sulfide precipitates formed in the presence of sulfate-reducing bacteria

The biologically mediated formation of metal sulfide precipitates in anoxic sediments represents a potentially important mechanism for the sequestration of toxic metals. Current knowledge of the structure and reactivity of these biogenic metal sulfides is scarce, limiting the ability to effectively assess contaminant sequestration in, and remobilization from, these solids. In this study, SO4-reducing bacteria (Desulfovibrio sp.) were grown for 5 days in a high-SO4, minimal metal media amended with Zn at either 30 or 300 micromolar. Zinc speciation in the reactor solids was determined using X-ray absorption spectroscopy, and the results compared to spectra of known metal sulfide mineral phases and freshly formed metal sulfides synthesized through purely chemical processes. Biogenically mediated Zn sulfides showed significantly more short range crystallographic order than the abiotically prepared amorphous precipitates. The presence of dissolved Fe2+ at similar concentrations did not affect the nature of the Zn precipitates formed. The biogenic ZnS solids were also more resistant to re-oxidation than the chemical precipitates but more soluble than sphalerite mineral samples. These results suggest that Zn sulfides formed in anaerobic sediments are likely to be more resistant to re-oxidation than would be expected based on dissolution of Fe sulfides and/or sediment acid volatile sulfides.

Dynamics of Reactive Sulfide and its Control on Metal Bioavailability and Toxicity in Metal-Polluted Sediments from Lake Taihu, China

This study was conducted to elucidate the vertical and seasonal distribution of acid-volatile sulfide (AVS) and simultaneously extracted metals (SEM) in sediment cores of metal-polluted areas of Lake Taihu, China. The concentrations of AVS in sediments were more dynamic than the SEM values, which were higher in warmer seasons. Two types of AVS profiles were identified in the studied area. Generally, the AVS levels increased at a certain depth (6-18 cm), below which they decreased, except for two sites during summer. Very high concentrations of AVS were observed at these two sites during summer, and its concentrations decreased almost exponentially with increased depth. The higher content of AVS near surface sediments in summer at these two sites was attributed to a high input of organic matter resulting from dead algal deposits. The SEM contents decreased with depth and remained almost constant with season. Metal toxicity in the sediment cores was assessed on the basis of three models: ΣSEM - AVS, ΣSEM/AVS, and ΣSEM - AVS/f(OC), and the results showed that toxicity occurred in the surface sediment interval (0-1 cm) at one site during winter.

Rates of Hexavalent Chromium Reduction in Anoxic Estuarine Sediments: pH Effects and the Role of Acid Volatile Sulfides

Rates of Cr(VI) reduction were assessed in batch kinetic experiments using dilute suspensions of anoxic sediments collected from the Baltimore Harbor. Rapid and complete Cr(VI) reduction occurred on the time scale of minutes (pseudo-first-order rate constants ranged from 0.01 to 0.40 min(-1) for 1.0 g/L sediment suspensions at pH 7.0) via reaction with mineral surfaces. The reaction rate was first-order with respect to Cr(VI) concentration and proportional to the concentration of sediment acid volatile sulfides (AVS). AVS-normalized rates of Cr(VI) reduction decreased by approximately 2 orders of magnitude as the suspension pH increased from 5.0 to 8.2. The AVS-normalized rate constant was linearly correlated with the fraction of total dissolved Cr(VI) in the protonated HCrO(4)(-) form at a given pH (f(HCrO(4))((-))). The following rate law was found to describe all the experimental data: d[Cr(VI)]/dt = -k[AVS]f(HCrO(4))((-))[Cr(VI)](T), where the AVS- and pH-independent rate constant k = 3.14(+/-0.75) x 10(4) M(-1) min(-1). The results of this study suggest the importance of reactions between Cr(VI) and solid phase AVS constituents in controlling Cr(VI) fate in anoxic estuarine sediments, and indicate that Cr(VI) is unlikely to be a toxicological stressor in AVS-containing sediments.

Geochemistry of Iron, Sulfur and Related Heavy Metals in Metal-Polluted Taihu Lake Sediments

To understand the geochemical characteristics of iron and sulfur and the extent of iron-sulfide minerals influencing heavy metal behaviour in metal-polluted sediments of Taihu Lake, two sites, in Meiliang Bay (ML) and Wuli Lake (WL), were selected to study the fractionation of iron, sulfur and related heavy metals. There were relatively high concentrations of Fe 2+ and low concentrations of total S 2− in porewaters, indicating that conditions in these sediments favored iron reduction. The concentrations of acid volatile sulfides in sediments were 1.9–9.6 μmol g −1 at ML and 1.0–11.7 μmol g −1 at WL, both in the range of values detected in unpolluted lakes. Pyrite-S was 10.2–49.4 μmol g −1 at ML and 10.3– 33.0 μmol g −1 at WL, accounting for more than 69% of the reduced inorganic sulfur at both sites. The low degree of sulphidization (< 14%) and pyritization (< 10%) indicate that sulfate may be the limiting factor for pyrite formation. The extractability of Mn, Cu, Pb, Zn, Ni, and Cr in sediments all suggest that sulfides are not the major binding phase for these metals during early diagenesis. Sulfur may play a modest role in the geochemistry of iron and traced metals in the sediments.

Development of a new method for sulfide determination by vapor generator–inductively coupled plasma–mass spectrometry

A new sensitive methodology for the determination of total reduced sulfur species in natural waters and acid volatile sulfides in sediments at low levels (μg L − 1 ) is described. Reduced sulfur species were separated from the water matrix in the form of H 2S after reaction with hydrochloric acid in a commercial vapor generator coupled to an inductively coupled plasma quadrupole mass spectrometer (VG–ICP–QMS) equipped with a reaction cell. The method avoided the effect of polyatomic isobaric interferences at m/z 32 caused by 16O 16O + and 14N 18O + through the elimination of the aqueous matrix, a source of oxygen. By introducing a mixture of helium and hydrogen gases into the octopole reaction cell, a series of ion-molecule reactions were induced to reduce the interfering polyatomic species. Operating conditions of the octopole reaction cell system and the analyzer were optimized to get the best signal to background ratio for 32S; a full factorial 2 3 experimental design was developed in order to evaluate which variables had a significant effect and a simplex methodology was applied to find the optimum conditions for the variables. The new method was evaluated by comparison to the standard potentiometric method. The analytical methodology developed was applied to the analysis of reduced sulfur species in natural waters and acid volatile sulfides in sea sediments.

Effects of acid‐volatile sulfide on metal bioavailability and toxicity to midge (Chironomus tentans) larvae in black shale sediments

Metal bioavailability and toxicity to aquatic organisms are greatly affected by variables such as pH, hardness, organic matter, and sediment acid-volatile sulfide (AVS). Sediment AVS, which reduces metal bioavailability and toxicity by binding and immobilizing metals as insoluble sulfides, has been studied intensely in recent years. Few studies, however, have determined the spatial variability of AVS and its interaction with simultaneously extracted metals (SEM) in sediments containing elevated concentrations of metals resulting from natural geochemical processes, such as weathering of black shales. We collected four sediment samples from each of four headwater bedrock streams in northcentral Arkansa (USA; three black shale-draining streams and one limestone-draining stream). We conducted 10-d acute whole-sediment toxicity tests using the midge Chironomus tentans and performed analyses for AVS, total metals, SEMs, and organic carbon. Most of the sediments from shale-draining streams had similar total metal and SEM concentrations but considerable differences in organic carbon and AVS. Zinc was the leading contributor to the SEM molar sum, averaging between 68 and 74%, whereas lead and cadmium contributed less than 3%. The AVS concentration was very low in all but two samples from one of the shale streams, and the sum of the SEM concentrations was in molar excess of AVS for all shale stream sediments. No significant differences in mean AVS concentrations between sediments collected from shale-draining or limestone-draining sites were noted (p > 0.05). Midge survival and growth in black shale-derived sediments were significantly less (p < 0.001) than that of limestone-derived sediments. On the whole, either SEM alone or SEM-AVS explained the total variation in midge survival and growth about equally well. However, survival and growth were significantly greater (p < 0.05) in the two sediment samples that contained measurable AVS compared with the two sediments from the same stream that contained negligible AVS.

Characterizing sediment acid volatile sulfide concentrations in European streams

Sediment acid volatile sulfide (AVS) concentrations were measured in wadeable streams of a wide variety of ecoregions of western Europe (84 sites in 10 countries and nine ecoregions) to better understand spatial distribution and ecoregion relationships. Acid volatile sulfide has been shown to be a major factor controlling the bioavailability and toxicity of many common trace metals, such as Cd, Cu, Ni, Pb, and Zn. Sediment characteristics varied widely. The ratio of the sum of the simultaneously extracted metals (SEM) to AVS ranged from 0.03 to 486.59. The sigmaSEM-AVS ranged from -40.02 to 17.71 micromol/g. On a regional scale, sediment characteristics such as dominant parent soil material showed significant trends in AVS distribution and variation by ecoregion. Total Fe and Mn were correlated weakly with SEM concentrations. Three AVS model approaches (i.e., the SEM:AVS ratio, SEM-AVS difference, and carbon normalization) were compared at threshold exceedance levels of SEM/AVS > 9, SEM-AVS > 2, and SEM-AVS/foc > 150 micromol/g organic carbon (OC). Only 4.76% of the sediments exceeded all three AVS thresholds; 22.6% of the sediments exceeded two models; and 13% of the sediments exceeded one model only. Using the SEM:AVS, SEM-AVS, and fraction of organic carbon models, and including site-specific data and regional soil characteristics, ecoregions 1 (Portugal), 3 (Italy), 4 (Switzerland), and 9 (Belgium/Germany) had the highest potential metals toxicity; ecoregions 13 and 8 (Belgium/France) showed the lowest potential toxicity. However, because AVS can vary widely spatially and temporally, these data should not be considered as representative of the sampled ecoregions. The general relationship between AVS levels and sediment characteristics provides some predictive capability for wadeable streams in the European ecoregions.

Seasonal patterns of pore-water nutrients, benthic chlorophyll a and sedimentary AVS in a macrobenthos-rich tidal flat

Monthly field investigations were carried out at controlled low-tide in an estuarine intertidal sandflat of the Seto Inland Sea (Japan) between January 1995 and April 1996. We assessed the spatial and temporal distribution of pore-water nutrient [NH4+-N, (NO3− + NO2−)-N, PO43−-P and Si(OH)4-Si], chlorophyll a (chl a) and acid-volatile sulphide (AVS) concentrations in the uppermost 0–10 cm sediment horizon, and evaluated their relationships with macrobenthic assemblages. Monthly hydrological data, nutrient and chl a concentrations in low-tide creek water adjacent to the flat were used as a complementary environmental characterisation of the study area. All different pore-water nutrients showed a 10 to > 30-fold variability between different layers and periods. NH4+-N, PO43−-P and Si(OH)4-Si concentrations were lowest in winter, progressively increased throughout spring and summer, and were highest between September and October, with a major increase at intermediate (4–8 cm) layers. In contrast, (NO3− + NO2−)-N concentrations, correlated positively with chl a, peaked in winter and sharply decreased with depth in all different seasons and in most occasions. Depth-integrated NH4+-N, PO43−-P and Si(OH)4-Si pools were correlated positively with biogenic nutrient flux calculated from the nutrient excretion rates of dominant bivalves Ruditapes philippinarum and Musculista senhousia. These relationships indicated rapid removal pathways of P, Si and N (i.e., every 0.1, 0.24 and 0.34 day, respectively), implying highly dynamic sediments. Based on the mass balance P = F + I, biogenic production (P) vs. diffusive flux (F) estimates suggested a predominant contribution of animal bioirrigation (I) to the upward flux of nutrients. AVS concentrations, correlated negatively with both (NO3− + NO2−)-N and chl a, showed a progressive increase from late summer throughout winter, subsequent to that of NH4+-N, PO43−-P and Si(OH)4-Si. The results indicate that in our study area the spatial and temporal distribution of pore-water nutrients, chl a and AVS in sediments are strongly interlinked and suggest that the metabolic processes (e.g., excretion, bio-deposition) and behavioural activities (e.g., particle mixing, bioirrigation) of abundant macrobenthos play an important role in the year-round biogeochemical processes occurring on this flat.