Acid Volatile Sulfide Research Articles

Diagenetic Processes in Aquaculture Ponds Showing Metal Accumulation on Shrimp Gills

The gill is the organ by which many toxic metals are taken up by crustaceans. Iron is known to precipitate at its surface, a phenomenon recently observed in some tropical aquaculture ponds. The present study uses a field approach to understand better the environmental conditions and ecological processes involved in this deposit. Because shrimp are exposed to reduced products originating from organic waste accumulated in the sediment, spatial variation in pH, redox potential and concentrations of dissolved metals in pore water were investigated in these ponds. Total organic carbon, acid volatile sulfide and pyrite were also analyzed in the solid phase. Fe2+ in pore waters showed high spatial variability between ponds and within the same pond with concentrations up to 1,193 μmol l–1. Behaviors of Fe2+, Mn2+ and Co2+ in pore water were similar. Four geochemical environments were identified, based on their physico-chemical characteristics. Highest concentrations for Fe2+, Mn2+ and Co2+ in sediment pore water occurred in slightly acidic and suboxic conditions. When the sediment became anoxic, the H2S produced reacted with Fe2+ and/or Co2+ to form acid volatile sulfide and pyrite. When pH increased, the concentration of free H2S rose up to 736 μmol l–1. With neutral and suboxic conditions, dissolved metal concentrations could be controlled by their precipitation as oxides and hydroxides. The production of pyrite suggested the existence of a possible process of sediment acidification between two crop periods through the production of sulfuric acid. This acidification could increase with pond age and be the cause of the accumulation of reduced metal after 30 years of aquaculture activity.

Simultaneous PAHs degradation, odour mitigation and energy harvesting by sediment microbial fuel cell coupled with nitrate-induced biostimulation

The study investigates a bioremediation process of polycyclic aromatic hydrocarbons (PAHs) removal and odour mitigation combined with energy harvesting. Sediment microbial fuel cells (SMFCs) were constructed with the addition of nitrate in the sediment to simultaneously remove acid-volatile sulphide (AVS) and PAHs. With the combined nitrate-SMFC treatment, over 90% of the AVS was removed from the sediment in 6 weeks of the SMFC operation and a maximum of 94% of AVS removal efficiency was reached at Week 10. The highest removal efficiencies of phenanthrene, pyrene, and benzo[a]pyrene was 93%, 80%, and 69%, respectively. The maximum voltage attained for the combined nitrate-SMFC treatment was 341 mV. Illumina HiSeq sequencing revealed that the autotrophic denitrifiers Thiobacillus are the dominant genus. In electricity generation, both sulphide-oxidation and PAH-oxidation are the possible pathways. Besides, the addition of nitrate stimulated the growth of Pseudomonas which is responsible for the electricity generation and direct biodegradation of the PAHs, indicating a synergistic effect. The developed bioremediation process demonstrated the potential in the in-situ bioremediation process utilizing SMFC combined with nitrate-induced bioremediation.

Effects of intensive fish farming on sediments of a temperate bay characterised by polyculture and strong currents

Sansha Bay, facing the East China Sea, is characterised by high fish production (Pseudosciaena crocea, 91,000 t yr–1) and the polyculture of seaweeds (Saccharina japonica and Gracilaria lemaneiformis) and abalone (Haliotis discus hannai). To investigate the environmental effects of fish farming on sediments, surface (0–1 cm) sediments were collected from 41 stations grouped into four areas: fish, seaweed, and abalone farms and reference area. The physical and chemical parameters of these sediments were analysed. Nitrogen and phosphorus loadings from trash fish as feed were estimated to be 12,000 and 2,400 t yr–1, respectively, accounting for 90% and 86% of the total anthropogenic loading in Sansha Bay. However, no significant differences were observed in stable C and N isotope ratios, carbon-to-nitrogen ratio, total organic carbon, total nitrogen, total phosphorus, acid volatile sulfide, water content, and silt–clay fraction among the four areas (Kruskal–Wallis test, P > 0.05). Principal component and cluster analyses supported this conclusion, indicating that fish farming has no significant effect on the sediment. The amount of N removed by the cultured seaweed was estimated to be 288 t yr–1, accounting for only 2% of the N loaded from fish farming. The results suggested that the dispersion of fish farm-derived wastes were primarily facilitated by the topographic and hydrodynamic characteristics of Sansha Bay, such as its large depth (∼90 m), strong currents (1.4–1.9 m s–1), large tidal amplitude (5.4 m), and rapid exchange (<18 days) of a large volume of bay water (7.4 × 109 m3).

Preliminary study on the effect of Fenton oxidation on black odor river sediment

沉积物中有机质的削减是黑臭水体治理的关键.Fenton（Fe²⁺+H₂O₂）试剂在有机污染废水和土壤原位修复中的应用广泛且效果良好；Fenton试剂也能很好地去除黑臭水体中的色度和浊度，但其氧化沉积物有机质的研究未见报道.为探究Fenton试剂对黑臭水体沉积物的氧化效果，本研究通过室内模拟实验用Fenton氧化法对黑臭河道沉积物进行处理，考察氧化过程沉积物特征和性质的变化；分析覆水后沉积物中污染物的释放特征，并和H₂O₂体系（无Fe²⁺）进行比较.结果表明：Fenton体系显著提高了沉积物与上覆水的氧化还原电位，对黑臭河道沉积物中的有机质具有很强的氧化效率.在温度为28℃、H₂O₂为20% Q（Q为体系中沉积物有机质完全矿化的理论H₂O₂用量）和Fe²⁺：H₂O₂（摩尔比）为0.5：1时，反应1 d，酸挥发性硫化物去除率为70.13%，沉积物总有机碳减少了22.14%，总有机氮减少了87.60%，生成了较多的铵态氮和硝态氮；由于铁对磷的钝化，沉积物中溶解性反应磷含量大幅减少.H₂O₂体系的氧化速度较Fenton体系慢，覆水后对体系中的Eh提高不明显.值得注意的是，Fenton体系会降低上覆水的pH，释放较多的铵态氮.需要联合其他技术（如微生物法），强化水体中有机质和氨氮的降解，以取得理想的修复作用.;The reduction of organic matter in the sediment is key to solve the issue of black odor river. Fenton (Fe^{2 +} + H₂O₂) reagent is effectively in the treatment of organic contaminated water or soil. Fenton reagent has been also found to remove the coloration and turbidity of black odor water effectively. But the research on the treatment of organic matter in sediment by Fenton reagent has not been reported until now. In order to explore the oxidation effect of Fenton reagent on the sediment of black odor river, in this study, Fenton reagent was used to treat black odor river sediment. The changes of sediment characteristics were investigated during the oxidation process, also the release of pollutants from the sediment was analyzed. In addition, the treatment of the sediment by H₂O₂ system (without Fe^{2 +}) was compared with Fenton treatment. The results showed that under the condition of T=28℃, input (H₂O₂) =20%Q (Q is the theoretical dosage to mineralize completely organic carbon in sediment), the molar ratio of Fe²⁺ to H₂O₂=0.5∶1, the Fenton treatment significantly increased the redox potential of the sediment and overlying water, and had a strong oxidation efficiency for organic matter in black odor sediment. During Fenton treatment, the removal of acid volatile sulfide, total organic carbon, and total organic nitrogen were 70.13%, 22.14%, and 87.60%, respectively. A substantial amount of ammonium nitrogen and nitrate nitrogen were produced. Due to the presence of iron, the concentration of soluble reactive phosphorus in the sediment was greatly reduced. Compared to Fenton treatment, the oxidation rate of H₂O₂ system was slower, and the improvement of redox potential in the system was not obvious. The release of organic acids and ammonium nitrogen to the overlying water during the Fenton treatment should be paid attention to. It is suggested that the post-treatment of the overlying water, such as biological methods, should be used to obtain the ideal repair effect.

Effects of Plow-Tillage on Preventing and Controlling the Black Water Events in Shallow Lakes

The high organic loading sediment in the areas of algal accumulation are the primary cause of frequent occurrence of black water in the western Chao Lake. Through an algal accumulation experiment, plow-tillage based on resuspension characteristics and its effect on lake sediment was assessed using a large device capable of simulating lake-winds and sediment resuspension. The dynamics of overlying water coloration, ρ(Fe²⁺), ρ(S2-) in the process of black water induction, the key physicochemical characteristics of newly formed water–sediment interface, and iron and sulfur variations in interstitial-water and their response to plow-tillage were examined. The results showed that plow-tillage depth significantly influenced black-water formation; a 15 cm plow-tillage depth helped in controlling black-water. When black water occurred in other plow-tillage controls, i.e., (2, 5, and 10 cm), along with blank-treatments during day 8 to 14, typical overlying water characteristics [ρ(Fe²⁺) and ρ(S2-)] of the plow-tillage 15 cm treatments were 68.6%, 79.5%, 48.1%, 46.7%, and 51.3%; and 75.2%, 65.7%, 57.1%, 74.5%, and 75.0%, respectively, in comparison to that of the other plow-tillage controls and blank-treatments. Further analysis of the bottom-water and bottom-sediments revealed that the 15 cm plow-tillage depth treatment significantly enhanced the tolerance of the fresh water–sediment interface to algal accumulation and anoxic environments. Through the black water induction simulation, the dissolved oxygen concentration, redox potential, and pH of the bottom-water and at the interface were observably much higher than those in the black-water groups. However, ρ(ΣH₂S) was significantly lower than that of other treatments. The ρ(Fe²⁺) in the surface-sediment water was 0.54 mg/L, which corresponds only 25.3–33.7% that of the black-water groups. Fe²⁺ accounted for 25.2% of the total iron, being considerably lower than ~40.0% of the black-water groups. The concentration of acid-volatile sulfides was 0.51 µg/g, which corresponds only 14.6–17.2% that of the black-water groups. Overall, plow-tillage helped to physically improve sediment in areas of algal accumulation. Plow-tillage could help turn surface-sediment overloaded with organic pollutants to the lower-layer, blocking material migration and supply of contaminated surface-sediment, and controlling anaerobic microbial activity. It could prevent the formation of black water-generating substances in the water column where algae accumulate and die, effectively preventing the occurrence of black water.

Ammonia and chromate interaction explains unresolved Hyalella azteca mortality in Flanders’ sediment bioassays

Agricultural, industrial and household chemicals are emitted in large rivers along populated areas, transported by water and deposited in sediments, posing (eco)toxicological risks. Sediments have received less attention than surface waters, likely because of the intrinsic complexity of interactions between sediment constituents complicating correct framing of exposures. Sadly, thorough assessment of the in situ behavior of sediment constituents in bioassays is often not practical.Alternatively, we related physicochemical properties of sediments from field testing to results from bioassays. The case study covers Flemish sediment (incl. Scheldt and Meuse) and mortality of Hyalella azteca, a sensitive bio-indicator. Though variable across Flanders’ main water bodies, heavy metals and ammoniacal nitrogen dominate the observed toxicity according to toxic unit (TU) assessments. Depending on the water body we explain between 50 and 90% of the variance in the observed H. azteca mortality, substantially more than previous ecotoxicity studies. We attribute the remaining variance to potential incoherently documented biophysicochemical sediment properties and concentrations of non-target biocides, testing conditions/set-ups and/or species variabilities.We discuss the relative influence of heavy metals/metaloxides, nitrogen (e.g. fertilizer), polycyclic aromatics and organochlorides. We highlight both direct and indirect mortality mechanisms. We note potential synergetic mixture effects between ammoniacal nitrogen and chromium. Such synergy may be phenomenological of ‘standard’ aerobic bioassays, and prove a complementary method alongside the ‘acid-volatile sulfide test’ to more effectively link concentration to toxicity. Future study ought to include variation in biophysicochemical properties between sampling locations and batch bioassays. Our approach enables water managers to interpret their monitoring data by converting sediment concentrations to H. azteca mortality and prioritize substances that contribute most.

Dynamic sulfur-iron cycle promoted phosphorus mobilization in sediments driven by the algae decomposition.

Direct evidence of the algae bloom in eutrophic freshwater lakes on sulfur cycle and the subsequent iron oxide reduction and the iron oxides-bound phosphate (Fe-P) release in sediments is lacking. In this study, microcosms experiment was carried out to investigate the dynamic variations of S, Fe and P species in the water column and sediments as well as the sulfate reducing bacteria (SRB) abundance variation in the sediments during algae decomposition. The sulfate reduction was stimulated by the algae decomposition, which resulted in dramatic sulfate decline, sulfide increase and SRB growth. In addition, large amounts of acid volatile sulfide (AVS), pyrite sulfur (Pyrite-S) and elemental sulfur (S0) accumulated in the sediment. In particular, the contents of sedimentary Fe(II) and Pyrite-S in surface sediments continuously accumulated until the end of the experiment. Moreover, the terminal Fe-P content reduced by 35.4% compared with the initial concentration at high algae density group. These results suggested the irreversible reduction of iron oxides and revealed iron chemical reduction mediated by sulfide during algae decomposition. In addition, the connection of sulfur-iron cycle and the significant promotion of Fe-P mobilization in sediments was established, which should be paid more attention in the eutrophic freshwater ecosystems.

Enhanced anaerobic digestion with the addition of chelator-nickel complexes to improve nickel bioavailability

Nickel (Ni) is one of the most essential trace elements in the anaerobic digestion system. In this study, green chelating agent Ethylenediamine-N, N′-disuccinic acid (EDDS), common chelating agents with low biodegradability nitrilotriacetic acid (NTA) and ethylenediaminetetraacetic acid (EDTA) were respectively used as ligands of Ni (II) to inspect the feasibility of enhancing methane production and reducing Ni dosage. In practice, continuous stirred-tank reactors (37 °C, 120 rpm) were operated with a mixture of pig manure and food waste as the substrate, and were supplied with extra Ni in the form of Ni (II) (0, 2.5, and 5.0 mg/L) or chelator‑nickel (EDDS-Ni, NTA-Ni and EDTA-Ni) complexes (2.5 mg/L). The results showed that compared with that of adding Ni (2.5 mg/L) individually, the methane production increased of 23.34%, 31.26% and 16.07% with the addition of EDDS-Ni, NTA-Ni and EDTA-Ni complexes (2.5 mg/L), respectively. Accompanying with that, the EDDS-Ni and NTA-Ni supplementations both significantly increased the F430 concentration of 28% and 36% on the day of peak methane production (day five). The BCR sequential extraction analysis indicated that the sum of Ni in water soluble and exchangeable fractions after digestion were increased of 43.28%, 39.41%, and 24.29%, respectively. Further, the acid-volatile sulfide (AVS) and the simultaneously extracted nickels (SEMNi) content in sediments confirmed that the chelator‑nickel improved Ni bioavailability due to dissolution of nickel ions from their sulfides. This study demonstrated that the addition of chelator-Ni complexes was a practicable method to enhance methane production and reduced Ni dosage.

Abundant sediment organic matter potentially facilitates chemical iron reduction and surface water blackness in a Chinese deep lake.

Black bloom has become an increasingly severe environmental and ecological problem in lots of lakes. Ferrous monosulfide (FeS), which is closely related to chemical iron reduction (CIR), is considered the major cause for black water in shallow lakes, but few studies focus on the effect of organic matters (OM) content on iron and sulfate reduction and its contribution to the black bloom in deep lakes. Here, in Lake Fuxian, a Chinese deep lake which has also suffered from black bloom, FeS was identified responsible for the surface water blackness by using multiple microscopy and element analyses. Dissolved oxygen (DO) penetrated 1.6-4.2mm in all sediment sites, further indicating FeS formed in the sediments instead of the permanently oxic water column. Geochemical characteristics revealed by diffusive gradients in thin films (DGT) showed that DGT-Fe2+ concentration was 57.6-1919.4 times higher than the DGT-S2- concentration and both were positively correlated with DGT-PO43-. Combining DGT profiles and anaerobic OM remineralization rate according to bag incubation, iron reduction is more effective than sulfate reduction although the two processes coexisted. Moreover, correlation of DGT-Fe2+ and DGT-PO43- was better than that of DGT-PO43- and DGT-S2- at OM-depleted sites but opposite at OM-rich sites. In addition, total organic carbon (TOC) was significantly positively related to acid volatile sulfide (AVS). We therefore conclude that abundant OM potentially exacerbate chemical iron reduction and further lead to surface water blackness. Our study revealed the mechanisms behind the black bloom and gives credence to the management strategy of reducing OM loading to protect water quality in deep lakes.

Biochar-impacted sulfur cycling affects methylmercury phytoavailability in soils under different redox conditions

Recently, there has been increasing interest in reducing methylmercury (MeHg) phytoavailability using biochar, although the underlying mechanisms are not fully understood. By combining lab-scale batch incubation with pot and field validations, we demonstrate that biochar-impacted sulfur cycling in soils and MeHg-soil binding play key roles in controlling MeHg phytoavailability. (1) Under anoxic conditions, biochar-associated sulfate and biochar-facilitated microbial sulfate reduction enhanced the production of reduced inorganic sulfur species as acid-volatile sulfide (AVS) in soils by 122%, facilitating MeHg binding with soils and thus reducing MeHg phytoavailability. (2) In contrast, under oxic conditions, the reduced inorganic sulfur was oxidized (resulting in a 68–91% decrease in AVS), which released soil-bound MeHg and increased MeHg phytoavailability. The proposed mechanisms could explain the distinct effects of biochar amendment on MeHg bioaccumulation observed under anoxic (10–88% lower in rice grains) and oxic conditions (48–84% higher in wheat grains). Our results dispute the commonly held assumption that reduced MeHg phytoavailability under biochar amendment can be primarily attributed to MeHg-biochar binding. Therefore, the potential increased risk of MeHg in oxic soils following biochar amendment should be evaluated in more detail.

Bioelectricity generation and remediation of contaminated intertidal zone of Yamaguchi Bay, Japan

This study explores the use of sediment microbial fuel cells (SMFCs) to generate a safe, stable, and efficient supply of bioelectricity to sensors and simultaneously improve sediment quality. Supplying energy to geoenvironmental monitoring sensors remains a challenge as traditional batteries and solar cells are limited by the need to recharge and the erratic weather condition, respectively. Four different sediments from the Yamaguchi bay located in south part of the Honshu island, Japan were experimented on. The acid volatile sulfide (AVS) was the main source of contamination in the intertidal zone and was, hence, used as an indicator for possible bioremediation. Various factors have been studied for its effect on voltage generation. Voltage generation was dependent on the microbes in and grain size distribution of the sediment. It was found that voltage values showed almost twice when two anodes were used instead of a single anode. As the temperature reached optimum temperature of the enzymes of the Geobacteria, the increased activity lead to higher voltage. SMFC was effective in reducing the AVS value of the sediment. SMFCs in the field exhibited greater voltage generation compared to SMFCs of the same size in the laboratory. A positive correlation between voltage generation and AVS reduction was demonstrated.

Risk assessment for sediment associated heavy metals using sediment quality guidelines modified by sediment properties.

Sediment quality guidelines (SQGs) are a fundamental component of sediment quality assessment framework, frequently used in the first tier of assessment to predict the potential risks of contaminants in sediment. A recognized weakness of SQGs concerns the bioavailability of sediment contaminants, which may vary considerably with different physical-chemical properties. To better evaluate the ecological risks and predict the toxicity of the heavy metals (Cd, Cu, Ni, Pb, Zn) in the sediments of Haihe River of China, the risk quotients derived from total metal concentrations and SQG values were modified using multiple linear regressions with sediment properties, i.e. total organic carbon (TOC), acid-volatile sulfide (AVS), and particle size distribution (PSD). Then, the sediment toxicity was tested with the benthic organisms of chironomids and tubificids, and the relationships between the observed toxicity with the modified risk quotients were investigated. We found that the risk quotient modified with TOC and AVS displayed significantly improved relationship with the toxicity (p<0.001) compared to the original risk quotient without modification (p=0.062-0.074>0.05). Risk assessment indicated that although the heavy metals in the sediments of Haihe River of China are at a relatively low level, potential ecological risks caused by Ni and Zn still exist in some area, especially in the lower reaches along the estuary. The results indicated that the risk quotient and SQG values modified with sediment properties are promising for risk assessment of the metal contaminants in sediments.

Microbially-driven sulfur cycling microbial communities in different mangrove sediments

Microbially-driven sulfur cycling is a vital biogeochemical process in the sulfur-rich mangrove ecosystem. It is critical to evaluate the potential impact of sulfur transformation in mangrove ecosystems. To reveal the diversity, composition, and structure of sulfur-oxidizing bacteria (SOB) and sulfate-reducing bacteria (SRB) and underlying mechanisms, we analyzed the physicochemical properties and sediment microbial communities from an introduced mangrove species (Sonneratia apetala), a native mangrove species (Kandelia obovata) and the mudflat in Hanjiang River Estuary in Guangdong (23.27°N, 116.52°E), China. The results indicated that SOB was dominated by autotrophic Thiohalophilus and chemoautotrophy Chromatium in S. apetala and K. obovata, respectively, while Desulfatibacillum was the dominant genus of SRB in K. obovata sediments. Also, the redundancy analysis indicated that temperature, redox potential (ORP), and SO42− were the significant factors influencing the sulfur cycling microbial communities with elemental sulfur (ES) as the key factor driver for SOB and total carbon (TC) for SRB in mangrove sediments. Additionally, the morphological transformation of ES, acid volatile sulfide (AVS) and SO42− explained the variation of sulfur cycling microbial communities under sulfur-rich conditions, and we found mangrove species-specific dominant Thiohalobacter, Chromatium and Desulfatibacillum, which could well use ES and SO42−, thus promoting the sulfur cycling in mangrove sediments. Meanwhile, the change of nutrient substances (TN, TC) explained why SOB were more susceptible to environmental changes than SRB. Sulfate reducing bacteria produces sulfide in anoxic sediments at depth that then migrate upward, toward fewer reducing conditions, where it’s oxidized by sulfur oxidizing bacteria. This study indicates the high ability of SOB and SRB in ES, SO42−,S2− and S2− generation and transformation in sulfur-rich mangrove ecosystems, and provides novel insights into sulfur cycling in other wetland ecosystems from a microbial perspective.

Metal-sulfide dynamics in a constructed wetland in the Southeastern United States

The Tritium Processing Facility at the Savannah River Site releases effluent containing copper (Cu), zinc (Zn), and lead (Pb) to the H-02 constructed wetland for remediation before the final release. Sediment cores were collected in the wetland cells in both summer and winter. Concentrations of total metals in all sediment layers and acid-volatile sulfide (AVS) and simultaneously extracted metals (SEM) in surface sediments were determined. Total metal concentrations suggested most metals removed from surface water were retained by the organic-rich flocculent in the top sediment layers instead of being transported to the deeper sulfide mineral layers. The seasonal difference of AVS and SEM indicated a season-related sulfur cycle and metal removal process in the wetland cells. SEM-Zn was the major contributor to total SEM. Metals accumulating in surface sediments were mainly sequestered in AVS and SEM extractable phases including metal-sulfides and organic matter complexes. The general SEM/AVS ratio was > 1, demonstrating the metals associated with sediments were potentially mobile and/or bioavailable, which becomes a concern for the long-term sustainability of the constructed wetland. The disturbance event in the sediment triggered the release of total metals, which were mostly in particulate form and were not bioavailable. Due to the high levels of reduced ion (Fe) in the sediment, the released particulate metals were likely to form metal-scavenging particulate Fe3+ oxyhydroxides under oxic conditions.

Sulfur transformation in sulfur autotrophic denitrification using thiosulfate as electron donor.

Thiosulfate is frequently used as an energy source and electron donor in autotrophic denitrification (AD) for removing nitrate from wastewater. However, transforming pathways of S2O32- in this process is unclear. Herein, the aim of this study is to explore possible transforming pathways of sulfur compounds in thiosulfate-based AD process. After measuring the variation of NO3-, NO2-, and various sulfur compounds such as S0, SO42-, S2O32-, acid volatile sulfide (AVS), and S2- in the presence and absence of S2O32-, the variation process of S2O32- and the contribution of various sulfur compounds were analyzed. The results indicated that S0, AVS, and S2- were the intermediate products when S2O32- was applied as an electron donor. All S2O32-, S0, AVS, and S2- could act as electron donors in the nitrate removal process with the final products of SO42-. The utilization priority of these four sulfur sources was presumed in the following order: S2->S2O32->AVS≈S0. Furthermore, sulfur transformation and balance in nitrate removal process was also investigated. This suggests the transforming pathways of sulfur compounds in denitrification process. Nitrogen removal and sulfur conversion process are dependent on the presence of microorganisms in the sludge.

The Influence of Root Exudate Flavonoids on Sulfur Species Distribution in Mangrove Sediments Polluted with Cadmium

To evaluate the influence of flavonoids on the biogeochemistry of sulfur in mangrove sediments polluted with Cd, Avicennia marina individuals were cultivated in rhizoboxes under different concentrations of Cd and flavonoid. The reduced inorganic sulfur concentrations in the rhizosphere and non-rhizosphere sediments were examined. According to the results, acid-volatile sulfide concentrations in non-rhizosphere sediments were from 12.77 ± 1.01 to 19.21 ± 0.05 umol/g (DW) and significantly higher than those in rhizosphere, and flavonoids increased acid-volatile sulfide concentrations under Cd stress. High Eh (from 103.00 ± 3.21 to 197.33 ± 14.74 mV) and Cd stress in the rhizosphere led to more elemental sulfur formation, and flavonoid applications significantly increased elemental sulfur in both rhizosphere and non-rhizosphere sediments. Chromium-reducible sulfur from the non-rhizosphere was the source of the Chromium-reducible sulfur in the rhizosphere sediments, in addition to acid-volatile sulfide and elemental sulfur in both rhizosphere and non-rhizosphere sediments. In the rhizosphere with high Eh microenvironments, acid-volatile sulfide could be converted into Chromium-reducible sulfur effectively, while its conversion efficiency was significantly lower in non-rhizosphere. In addition, flavonoid applications reduced acid-volatile sulfide to Chromium-reducible sulfur conversion efficiency. In conclusion, flavonoid treatments in mangrove rhizosphere sediments polluted with Cd increased reduced inorganic sulfur concentrations and influenced sulfur biogeochemistry significantly.

Spatial and vertical distribution, composition profiles, sources, and ecological risk assessment of polycyclic aromatic hydrocarbon residues in the sediments of an urban tributary: A case study of the Songgang River, Shenzhen, China

In this study, the Songgang River (SR) was selected as a typical tributary that is heavily polluted by rapid urbanization and industrialization. The polycyclic aromatic hydrocarbon (PAH) distribution at five representative sampling sites from different urban functional areas was studied. The chemical and physical properties and spatial and vertical distribution of PAHs in sediments were investigated. PAH source identification and the ecological risks of the sediments were evaluated. The results suggested that the industrial zone and dense residential and commercial areas were the most contaminated areas of the SR, as the chemical and physical properties of total organic carbon content in sediments was the highest at the dense residential and commercial areas (0.1–4.5%); however, the acid volatile sulfide, total nitrogen, and total phosphorus contents were the highest in the industrial zone, with ranges of 700.0–1618.4 mg/kg dw, 22.4–3543.9 mg/kg dw, and 82.3–4550.7 mg/kg dw, respectively. The spatial distribution of residual PAHs in the sediment cores showed a wide variation among different urban functional areas, and the vertical characterization (0–300 cm) depicted a significant decreasing trend with depth and with an abrupt increase at 180 cm. The concentration of ∑16 PAHs ranged from 208.7 to 7709.8 ng/g dw, with the highest concentrations obtained in the industrial zone. The low molecular weight-PAHs (153–6720 ng/g dw) were predominant in the sediments. Furthermore, there were combined sources (biomass burning: 40.3%; fossil fuel combustion: 25.5%; mixed source: 21.5%; oil pollution: 12.7%) and a long term accumulation effect, with anthropogenic activities and industrial pollution as the major contributing sources. The concentrations of Nap, Acy, Ace, Flu, and Ant exceeded the lower limit of the sediment quality criteria, and higher toxic equivalent concentration values of the total carcinogenic PAHs were observed nearby the midstream of the SR, which may cause adverse biological effects and implies a need for regular monitoring.

Development of a Dredging Sensitivity Index, applied to an industrialized coastal environment in Brazil

Ports link world commerce via maritime routes, and dredging services are essential to establish and maintain these connections. However, one question is critical when dredging is being considered: where are the best places to do it? To try to answer this question, a Dredging Sensitivity Index (DSI) was developed as a management tool to be used in project planning steps. In order to diminish environmental damages and quality-of-life losses, DSI provides alternatives by identifying sensitivity areas. This new methodology quantifies impacts caused by the sediment removal step and points out favorable areas to dredge, with a simple map. Parameters such as fine-grain content (% < 63 μm), Acid Volatile Sulfides (AVS), Shannon-Wiener Index and fisheries, among others, were used to calculate the DSI. Formulas were used to weight and aggregate both, the parameters and the DSI itself. Sepetiba Bay was chosen to apply this methodology because of its relevant economic and environmental aspects. The methodology was applied to dredging situations, but it can be used to indicate areas for dredged material disposal, with a few modifications in the DSI formulas. A DSI map was a final result of this methodology, and showed that the northern portion of the bay, close to the littoral is a more sensitive area, where dredging should be avoided, or carried out very carefully. DSI is a very useful tool for reducing damages from dredging services, it contributes with zonation and it provides alternatives to decision-makers who manage these areas.

In situ high-resolution measurement of phosphorus, iron and sulfur by diffusive gradients in thin films in sediments of black-odorous rivers in the Pearl River Delta region, South China

The cycling of phosphorus (P), iron (Fe) and sulfur (S) in sediments has been previously investigated, but its impacts on the formation of black-odorous waterbodies remains unclear. Here, high-resolution (i.e., 2 mm for P and Fe, and 0.042 mm for S of 2D presentation) simultaneous measurements of P, Fe, and S profiles in river sediments based on the diffusive gradients in thin-films (DGT) technique were conducted in the Pearl River Delta region, South China. Similar distribution trends and significant positive correlations (R = 0.67–0.93, p < 0.01) were observed between Fe and P. Considering the high diffusion fluxes of Fe and P together, it revealed that P release was promoted by the Fe reduction. The two-dimensional labile S profiles showed that their concentrations in sediments were higher by factors of 1.6–20 than those in overlying water. The minor diffusion fluxes of S and the accumulation of acid volatile sulfide indicated that S2− combining with Fe2+ occurred prior to diffusion. Furthermore, the formation mechanisms of black-odorous waterbodies were explored: (i) oxygen depletion by COD and NH4+‒N and large amounts of sulfate input were the main exogenous driving factors. (ii) Reduction of Fe and S to form ferrous sulfide accompanied with P release in sediments were the dominant endogenous causes. These observations together with mechanism analysis can provide a basis for the governance of black-odorous rivers.

Fish growth enhances microbial sulfur cycling in aquaculture pond sediments.

SummaryMicrobial sulfate reduction and sulfur oxidation are vital processes to enhance organic matter degradation in sediments. However, the diversity and composition of sulfate‐reducing bacteria (SRB) and sulfur‐oxidizing bacteria (SOB) and their environmental driving factors are still poorly understood in aquaculture ponds, which received mounting of organic matter. In this study, bacterial communities, SRB and SOB from sediments of aquaculture ponds with different sizes of grass carp (Ctenopharyngodon idellus) were analysed using high‐throughput sequencing and quantitative real‐time PCR (qPCR). The results indicated that microbial communities in aquaculture pond sediments of large juvenile fish showed the highest richness and abundance of SRB and SOB, potentially further enhancing microbial sulfur cycling. Specifically, SRB were dominated by Desulfobulbus and Desulfovibrio, whereas SOB were dominated by Dechloromonas and Leptothrix. Although large juvenile fish ponds had relatively lower concentrations of sulfur compounds (i.e. total sulfur, acid‐volatile sulfide and elemental sulfur) than those of larval fish ponds, more abundant SRB and SOB were found in the large juvenile fish ponds. Further redundancy analysis (RDA) and linear regression indicated that sulfur compounds and sediment suspension are the major environmental factors shaping the abundance and community structure of SRB and SOB in aquaculture pond sediments. Findings of this study expand our current understanding of microbial driving sulfur cycling in aquaculture ecosystems and also provide novel insights for ecological and green aquaculture managements.