Acid Volatile Sulfide Research Articles

Effects of filling substrates on remediation performance and sulfur transformation of sulfate reducing packed-bed bioreactors treating acid mine drainage

The filling substrate is one of key factors influencing effectiveness of sulfate reducing packed-bed bioreactor (SRPB) treating acid mine drainage (AMD). The effects of four substrates (i.e. quartz sand, steel residue, biochar, and peanut shell) on remediation performance and sulfur transformation of SRPB treating AMD was studied. The results showed that steel residue and biochar improved sulfate reduction efficiency (61% and 49%) compared to quartz sand (32%), whereas peanut shell inhibited sulfate reduction efficiency (19%), attributed to its decomposition process leading to a severe accumulation of acetic acid. More amounts of sulfides generated in steel residue bioreactor were converted into acid volatile sulfide and elemental sulfur, resulting in a significant decrease in dissolved sulfide in the effluent. Metals (Fe, Al, Zn, Cd and Cr) except for Mn were effectively immobilized in the bioreactors, particularly for Al and Cd. Sulfate reducing bacteria and sulfide oxidizing bacteria lived symbiotically in all bioreactors which exhibited similar heterogeneity in microbial distribution and function, i.e. bacterial sulfate reduction mainly occurring in bottom-middle layers and photoautotrophic sulfide oxidation in upper layer close to outlet. The microbial response mechanism to various substrate environments was revealed through co-occurrence networks analysis. This study suggests that attention should be paid to the inhibitory effect of acetic acid accumulation on sulfate reduction when using sole lignocellulosic waste (peanut shell), and steel residue and biochar could be utilized as filling substances to promote sulfate reduction.

Mechanistic insights into Fe3O4-mediated inhibition of H2S gas production in sludge anaerobic digestion

The addition of iron-based conductive materials has been extensively validated as a highly effective approach to augment methane generation from anaerobic digestion (AD) process. In this work, it was additionally discovered that Fe3O4 notably suppressed the production of hazardous H2S gas during sludge AD. As the addition of Fe3O4 increased from 0 to 20 g/L, the accumulative H2S yields decreased by 89.2 % while the content of element sulfur and acid volatile sulfide (AVS) respectively increased by 55.0 % and 30.4 %. Mechanism analyses showed that the added Fe3O4 facilitated sludge conductive capacity, and boosted the efficiency of extracellular electron transfer, which accelerated the bioprocess of sulfide oxidation. Although Fe3O4 can chemically oxidize sulfide to elemental sulfur, microbial oxidation plays a major role in reducing H2S accumulation. Moreover, the released iron ions reacted with soluble sulfide, which promoted the chemical equilibrium of sulfide species from H2S to metal sulfide. Microbial analysis showed that some SRBs (i.e., Desulfomicrobium and Defluviicoccus) and SOB (i.e., Sulfuritalea) changed into keystone taxa (i.e., connectors and module hubs) in the reactor with Fe3O4 addition, showing that the functions of sulfate reduction and sulfur oxidation may play important roles in Fe3O4-present system. Fe3O4 presence also increased the content of functional genes encoding sulfide quinone reductase and flavocytochrome c sulfidedehydrogenase (e.g., Sqr and Fcc) that could oxidize sulfide to sulfur. The impact of other iron-based conductive material (i.e., zero-valent iron) was also verified, and the results showed that it could also significantly reduce H2S production. These findings provide new insights into the effect of iron-based conductive materials on anaerobic process, especially sulfur conversion.

Response of sulfate concentration to eutrophication on spatio-temporal scale in freshwater lakes

The dramatical increase of sulfur concentration in eutrophic lakes, especially sulfate (SO42−), has brought attention to the impact on the lake ecosystem; however, the mechanisms driving the intensification of eutrophication and the role of SO₄2− concentrations remain poorly understood. To assess the impact of eutrophication on SO42− dynamics in lakes, this study monitored SO42− concentrations in water and sediments across seven lakes with varying trophic statuses on a spatial scale, and in the eutrophic Lake Taihu over one year on a temporal scale, as well as a series of microcosms with different initial SO42− concentrations. Exogenous sulfur input is the primary driver of increased SO42− concentrations in lakes, the highest SO42− concentration in overlying water was 100 mg/L, as well as which reached 310.9 mg/L in sediment. The concurrent input of nutrients such as nitrogen and phosphorus exacerbated eutrophication, resulting in the destabilization of the sulfur cycle. Eutrophication promoted the SO42− concentration on the spatio-temporal scale, especially in sediment, and trophic lake index (TLI) showed a positive correlation with the SO42− in sediments (R2 = 0.99; 0.88). The SO42− concentration in water and TLI showed a nonlinear correlation on the temporal scale (R2 = 0.44), and showed a positive correlation on the spatial scale (R2 = 0.49). Microscopic experiments demonstrate that the anaerobic environment created by cyanobacteria decomposition induced sulfate reduction and significantly reduces SO42− concentrations. Concurrently, the anaerobic environment facilitates the coupling of iron reduction with sulfate reduction, leading to a substantial increase in Acid Volatile Sulfides (AVS) in the sediment. These findings reveal that eutrophication has a dual effect on the dynamic change of SO42− concentrations in overlying water, which is helpful to accurately evaluate and predict the change of SO42− concentrations in lakes.

Synergistic effect of Ca(NO3)2 - CaO2 on the improvement of sediment microecology: Transformation of sulfur and ferrous iron, and improvement mechanism

The synergy of Ca(NO3)2 and CaO2 can effectively reduce the risks of secondary pollution caused by nitrate escape and release. However, the timing and suitable dosage of Ca(NO3)2 and CaO2 during the synergistic interaction have not been fully investigated. In this work, we separated acid volatile sulfides (AVS) oxidation and ferrous iron oxidation by controlling the dosage of Ca(NO3)2. Results indicated that at a low RN/1.6S2−ratio, there was an obvious competitive relationship between AVS oxidation and ferrous iron oxidation, and sulfide was oxidized prior to ferrous iron. More efficient AVS and ferrous iron oxidation was achieved using Ca(NO3)2 to oxidize AVS and CaO2 to oxidize ferrous iron. After the treatment with Ca(NO3)2 and CaO2, the anaerobic reduction environment of the sediment was modified, and the metabolic pathways dominated by sulfate respiration and methanogenic metabolism in the sediment were gradually converted to nitrate-reduction and dissimilatory iron reduction. The synergy of Ca(NO3)2 and CaO2 could reduce 99.61 % CH4 compared with control check and could reduce 81.66 % N2O compared with adding Ca(NO3)2 only. Furthermore, the biodegradability of organic matter was improved due to the transformation of stubborn organic matter. These results provide valuable guidance for applying Ca(NO3)2 and CaO2 in sediment remediation.

Distribution and response of electroactive microorganisms to freshwater river pollution

Electroactive microorganisms (EAMs) play a vital role in biogeochemical cycles by facilitating extracellular electron transfer. They demonstrate remarkable adaptability to river sediments that are characterized by pollution and poor water quality, significantly contributing to the sustainability of river ecosystems. However, the distribution and diversity of EAMs remain poorly understood. In this study, 16S rRNA gene high-throughput sequencing and real-time fluorescence quantitative PCR were used to assess EAMs in 160 samples collected from eight rivers within the Pearl River Delta of Southern China. The results indicated that specialized EAMs communities in polluted sediments exhibited variations in response to water quality and sediment depth. Compared to clean sediment, polluted sediments showed a 4.5% increase in the relative abundances of EAMs communities (59 genera), with 45- and 17-times higher abundances of Geobacter and cable bacteria. Additionally, the abundance of cable bacteria decreased with increasing sediment depth in polluted sediments, while the abundance of L. varians GY32 exhibited an opposite trend. Finally, the abundances of Geobacter, cable bacteria, and L. varians GY32 were positively correlated with the abundance of filamentous microorganisms (FMs) across all samples, with stronger interactions in polluted sediments. These findings suggest that EAMs demonstrate heightened sensitivity to polluted environments, particularly at the genus (species) level, and exhibit strong adaptability to conditions characterized by high levels of acid volatile sulfide, low dissolved oxygen, and elevated nitrate nitrogen. Therefore, environmental factors could be manipulated to optimize the growth and efficiency of EAMs for environmental engineering and natural restoration applications.

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.

Sediment microbial fuel cell with biochar-modified cathode for remediation of black-odorous water sediments and analysis of microbial community

Sediment microbial fuel cells (SMFCs) generate electricity through microbial degradation of organic matter in sediments, and the cathode catalyst used for the oxygen reduction reaction is a key factor affecting the performance of SMFCs. To improve power production in SMFCs and remediate black-odorous water sediments, this study modifies the cathode carbon felt of the SMFC system with Enteromorpha prolifera (EP) biochar with high N and P content. The study demonstrated that the SMFC system with the modified cathode carbon felt (C-800℃/CF) exhibited superior power generation capabilities, achieving a maximum power density of 219.44 mW·m−2. Over 25 days of operation, the anode biofilm effectively degraded around 78.15% of total organic carbon, 79.55% of acid volatile sulfide, 74.78% of total nitrogen, 80.58% of ammonia nitrogen, and 77.46% of total phosphorus in the sediment. In addition, microbial community analysis showed that functional bacteria Thiobacillus, Acidaminobacter, Sulfurimonas, Bacteroidetes_vadinHA17, and Sideroxydans were the dominant genera in the anode biofilm.

Chemical recovery of a fish farm in Jinju Bay of South Korea after cessation of long-term fish farming

The development of aquaculture technology has led to significant increases in aquaculture production, which has deteriorated the coastal environment. This study is the first to conduct sedimentary environment recovery monitoring of an aquaculture environment using chemical indicators in a fallow fish farm in South Korea. The total organic carbon concentration in the surface sediments (≤2 cm) decreased to the control level within 1 year; the acid volatile sulfide concentration was not recovered for 3 years and 10 months. Nutrient and sulfide concentrations were high in deep sediments (≤15 cm) because of continuous fish farming for over 20 years and accumulation of organic matter beneath the cages. Complete chemical recovery of this study area may take a longer time than previously anticipated. Overall, this study provides significant insights for implementing coastal management plans and estimating adequate fallowing periods during long-term fish farming.

Distribution of acid-volatile sulfides and simultaneously extracted metals in Guanabara Bay: combination of anthropogenic, sedimentological, and geochemical processes.

Coastal sedimentary systems are affected by continental and marine metal pollutant inputs associated with different hydrodynamic characteristics and geochemical processes. These include the formation of acid-volatile sulfides (AVS) within sediments, which affects metal bioavailability and associated aquatic biota toxicity risks. Physicochemical changes in these environments in the face of extreme natural or man-made environmental influences can dramatically alter metal bioavailability and toxicity through metal binding and immobilization as insoluble sulfides. Surface sediments from Guanabara Bay, river mouths, and two mangrove areas were collected, and AVS and simultaneously extracted metals Cd, Cu, Fe, Mn, Ni, Pb, and Zn and ΣSEM were determined to assess sediment quality. A severe eutrophication history favored AVS concentrations exceeding or close to the sum-SEM concentrations, demonstrating that AVS play an important role in making trace metals unavailable for assimilation by living organisms, mitigating the risks of contamination for the local biota. This eutrophication-driven sulfide accumulation may attenuate the sediment toxicity in sites heavily polluted by metals, while some fewer eutrophic sites became more exposed to metals in excess to AVS.

Response of microbial communities to exogenous nitrate nitrogen input in black and odorous sediment

Since nitrate nitrogen (NO3−-N) input has proved an effective approach for the treatment of black and odorous river waterbody, it was controversial whether the total nitrogen concentration standard should be raised when the effluent from the sewage treatment plant is discharged into the polluted river. To reveal the effect of exogenous nitrate (NO3−-N) on black odorous waterbody, sediments with different features from contaminated rivers were collected, and the changes of physical and chemical characteristics and microbial community structure in sediments before and after the addition of exogenous NO3−-N were investigated. The results showed that after the input of NO3−-N, reducing substances such as acid volatile sulfide (AVS) in the sediment decreased by 80 % on average, ferrous (Fe2+) decreased by 50 %, yet the changing trend of ammonia nitrogen (NH4+-N) in some sediment samples increased while others decreased. High-throughput sequencing results showed that the abundance of Thiobacillus at most sites increased significantly, becoming the dominant genus in the sediment, and the abundance of functional genes in the metabolome increased, such as soxA, soxX, soxY, soxZ. Network analysis showed that sediment microorganisms evolved from a single sulfur oxidation ecological function to diverse ecological functions, such as nitrogen cycle nirB, nirD, nirK, nosZ, and aerobic decomposition. In summary, inputting an appropriate amount of exogenous NO3−-N is beneficial for restoring and maintaining the oxidation states of river sediment ecosystems.

Invasion mechanism of Spartina alterniflora by regulating soil sulfur and iron cycling and microbial composition in the Jiuduansha Wetland.

Spartina alterniflora, an invasive plant widely distributed in China's coastal regions, has had a significant impact on the stability of wetland ecosystems and elemental biogeochemical cycles. The invasion of S. alterniflora has been found to lead to the accumulation of sulfides in the soil. The cycling of sulfur and iron in the soil is closely interconnected. Coastal estuarine wetlands are influenced by both freshwater in rivers and seawater tides, as well as the frequent variations in redox conditions caused by tidal fluctuations, which makes the cycling of sulfur and iron in the soil invaded by S. alterniflora more intricate. In this study, field surveys and laboratory experiments were conducted to explore the effects of S. alterniflora invasion and hydrological changes on the cycling of sulfur and iron as well as related functional microorganisms in the soil. The invasion of S. alterniflora showed an increase in soil reduced inorganic sulfur (RIS) components in both high and low marshes of Jiuduansha wetland, with higher content observed in summer and autumn. The tidal simulation experiments revealed abundant sulfate in seawater tidal conditions could promote the formation of acid volatile sulfides (AVS) in the soil of low marshes invaded by S. alterniflora and ensuring the continuous increase in AVS content. Diffusive gradients in-thin-films (DGT) technology indicated the existence of high-concentration soluble S2- enrichment zones in the soil of low marshes invaded by S. alterniflora, which may be related to S. alterniflora root exudates. Tidal action increased the relative abundance of sulfur-reducing bacteria (SRB) in the soil of low marshes, and under the influence of seawater tidal action, SRB exhibited higher relative abundance. However, S. alterniflora might inhibit the activity of iron-reducing bacteria (FeRB) in the soil of low marshes. In conclusion, S. alterniflora may enhance the sulfate reduction rate and promote the formation of free sulfides in tidal salt marsh ecosystems by releasing root exudates that stimulate the activity of SRB, while concurrently inhibiting the activity of FeRB and reducing their competition with SRB. This effect is particularly pronounced in low marshes under seawater tidal conditions. Thus, S. alterniflora is capable of rapidly invading tidal salt marshes by utilizing sulfides effectively.

Distribution characteristic and risk assessment of acid volatile sulfide and heavy metals in sulfate-rich reservoir sediment

Distribution characteristic and risk assessment of acid volatile sulfide and heavy metals in sulfate-rich reservoir sediment

Rape Straw Biochar Application Enhances Cadmium Immobilization by Promoting Formation of Sulfide and Poorly Crystallized Fe Oxide in Paddy Soils

The mechanisms of rape straw biochar that affect the fixation of cadmium (Cd) in paddy soil by influencing redox of iron and sulfur are unclear. Several anaerobic incubation experiments were carried out using Cd-contaminated paddy soils (LY and ZZ). Rape straw biochar at pyrolysis temperatures of 450 °C (LRSB) and 800 °C (HRSB) was selected as the soil remediation agent. The electron exchange capacity and electrical conductivity were higher in HRSB than those in LRSB. The lower pe + pH in HRSB enhanced Fe oxide reduction, with a maximum increase in Fe2+ of 46.0% in ZZ. Compared to treatment without biochar (CK), the poorly crystallized Fe oxide (Feo) in HRSB increased by 16.8% in ZZ. This induced Cd bound to Fe, and Mn oxides fraction (Fe-Mn Cd) increased by 42.5%. The SO42−-S content in LRSB was 4.6 times that of HRSB. LRSB addition increased acid-volatile sulfide by 46.4% and 48.9% in LY and ZZ soils, respectively, compared to CK. This resulted in an increase in sulfide’s contribution to Cd fixation, with values rising from 24.2% to 37.8% in LY and 19.1% to 29.8% in ZZ. Overall, LRSB reduced Cd mobility by forming more sulfide, while HRSB increased Fe-Mn Cd by increasing Feo.

Mussel Shells from Marine Aquaculture Act like Ecosystem Engineers: Legacy Effects on Benthic Communities

Ecosystem engineers are organisms that cause changes in the physical state of biotic and abiotic structures that modulate the availability of resources to other species, thus affecting biochemical cycles. Molluscs, especially bivalves such as mussels, are widespread in coastal environments and they are excellent ecosystem engineers because of the durability of their shells, which add complexity and heterogeneity to benthic environments. The presence of mussel farms favours the accumulation of shells in benthic environments and may influence surrounding bare sediments, with potential legacy effects on benthic communities. We studied the effects of the accumulation of mussel shells at finfish farms and mussel farms by experimentally comparing bare sediment and sediment with fragmented shells in terms of the abundance of the most relevant faunal groups, specifically polychaete families as well as physical–chemical variables in sediment water samples, specifically organic matter (OM), redox potential, and acid-volatile sulphides (AVS) NH4+ and PO43−. The experiment was replicated under two environmental conditions over a period of 35 days: eutrophic muddy sediments and oligotrophic sandy sediments. The OM and AVS values were significantly higher in the eutrophic sediment with mussel shells. Only NH4+ was positively affected by the mussel shells in the oligotrophic conditions. Differences between the two environments were observed, and the effect of the mussel shells on the polychaete assemblages was more significant in the oligotrophic conditions. Mussel shell accumulations affected the structure of benthic assemblages by modifying their heterogeneity and complexity, which suggests that the presence of mussel farms above bare sediment may affect ecosystem functioning. Aquaculture has potentially negative or positive effects that must be addressed on a large scale, considering the increased input of organic matter and also the simultaneous presence of mussel shell waste, both of which alter the surrounding environment. This is particularly important in oligotrophic sandy sediment.

Bioavailability Assessment of Metals from the Coastal Sediments of Tropical Estuaries Based on Acid-Volatile Sulfide and Simultaneously Extracted Metals

Bioavailability assessment is important for evaluating the risks to the local biota, and the combined use of several ecological risk indices in eutrophic environments allows the best analysis of the local reality for decision-making. The relationship between acid volatile sulfide (AVS) concentrations and simultaneously extracted metals (SEM) allows us to infer the metal holding capacity of sediment, with the objective of evaluating the potential bioavailability of trace metals (Cd, Cu, Ni, Pb, and Zn) using ecological risk indices, such as the ΣSEM/AVS model and Adverse Effect Index (AEI), in surface sediments from Guanabara Bay and Sepetiba Bay, Brazil. AVS was determined using a colorimetric method and SEM with ICP-OES. In general, almost all sampling in Sepetiba Bay showed ΣSEM/AVS ratio values above 1. However, all results for the ΣSEM/AVS ratio found for the Guanabara Bay sediments were <1 for both estuaries. After normalization by organic carbon content, a possible toxicity risk for biota was found in Sepetiba Bay. However, the AEI in Guanabara Bay was above 1 for all metals in most samples, also indicating a risk to the biota.

Improving toxicity prediction of metal-contaminated sediments by incorporating sediment properties

For the purpose of sediment quality assessment, the prediction of toxicity risk-levels for aquatic organisms based on simple environmental measurements is desirable. One commonly used approach is the comparison of total contaminant concentrations with corresponding water and sediment quality guideline values, serving as a Line of Evidence (LoE) based on chemistry-toxicity effects relationships. However, the accuracy of toxicity predictions can be improved by considering the factors that modify contaminant bioavailability. In this study we used paired chemistry-ecotoxicity data sets for sediments to evaluate the improvement in toxicity risk predictions using bioavailability-modified guidelines. The sediments were predominantly contaminated with metals, and measurements of sediment particle size, total organic carbon (TOC) and acid volatile sulfide (AVS) were used to modify hazard quotients (HQ). To further assess the predictive efficacy of the bioavailability-modified guideline models, sediments with differing contamination levels were tested for toxicity to a benthic amphipod's reproduction. To account for differences between laboratory exposure and field exposure scenarios, where the latter creates greater dilution, both static-renewal and flow-through test procedures were employed, and flow-through resulted in lower dissolved metal concentrations in the overlying waters. We also investigated how lower AVS concentration by oxidation modified the toxicity. This study reaffirmed that consideration of factors that influence contaminant bioavailability improves toxicity risk predictions, however the improvements may be modest. The sediment particle size data had the greatest influence on the modified HQ, indicating that higher percentage of fine particle size (<63 μm) contributed most to a lower predicted toxicity. The comparison of the static-renewal and flow-through test results continue to raise important questions about the relevance of static or static-renewal toxicity test results for risk assessment decisions, as both these test designs may cause unrealistically high contributions of dissolved metals in overlying waters to toxicity. Overall, this study underscores the value of incorporating outcomes from simple and routine sediment analysis (e.g., particle size, TOC, and consideration of AVS) to enhance the predictive efficacy of toxicity risk assessments in the context of sediment quality risk assessment.

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.

Bridging soil biogeochemistry and microbial communities (archaea and bacteria) in tropical seagrass meadows

IntroductionSeagrass meadows are among the most valuable ecosystems, providing numerous ecosystem services and functions. Despite its importance, there is a lack of knowledge about soil’s biogeochemical process variability, which can control microbiological communities. Thus, this study aimed to evaluate whether seagrass meadows in different geo-environments exhibit varying Fe and sulfate reduction intensities, shaping distinct archaea and bacteria communities.MethodsSoil samples were collected in seagrass meadows under contrasting climatic, geological, vegetational and hydrological settings along the Brazilian coast (e.g., Semiarid Coast - SC, Southeastern Granitic Coast – GC, and Southern Quaternary Coast - QC). The soils were characterized by particle size, pH, redox potential (Eh), total organic C and total N content, acid-volatile sulfides (AVS), and simultaneously extracted Fe. Furthermore, a solid-phase Fe fractionation was performed to characterize the decomposition pathways in these soils, and the shifts in the microbial community along this spatial variation were analyzed using denaturing gradient gel electrophoresis.ResultsThe studied soils presented a sandy texture (values ranging from 74 ± 11.8 to 80.5 ± 6.4%) caused by energetic hydrodynamic conditions. The pH values were circumneutral, while redox conditions presented significant distinction among the studied sites, ranging from anoxic to oxic (values ranging from -63 to +334 mV). The degree of pyritization (DOP) ranged from&amp;lt; 10% to values higher than 80%, highly influenced by rhizospheric oxidation, and higher AVS content was recorded for sites with lower DOP (i.e., GC and QC).DiscussionsThus, biogeochemical processes in the seagrass soils present a wide variation in response to the geo-environmental settings. Plants influence the soil’s geochemical and microbiological communities, retaining fine particles, promoting rhizosphere oxidation, and inducing anoxic conditions controlling the Fe and S forms. Moreover, the same plant species can result in distinct soil conditions and microbial communities due to geoenvironmental settings.

Influence of submarine topography and sediment environment on microbial assemblages in a coastal lagoon in northeastern Japan

The relationships among eutrophication, anoxia, and microbial distribution were investigated for Nagatsura-Ura Lagoon on the northeastern Pacific coast of Japan. In September 2017, the bottom environment in a small area of the inner part of the lagoon (which has a basin-shaped bottom topology) was eutrophic and anoxic, with high carbon, nitrogen, phosphate, acid-volatile sulfide, and low dissolved oxygen and oxidation-reduction potential. Dissolved oxygen levels improved during the winter. Bacillariophyta (diatoms) were the main organic component according to pigment analysis and next-generation sequencing of nucleic acids in seawater samples. Phylum Proteobacteria was dominant among the bacterial flora in the sediment but the proportions of Class Epsilon-proteobacteria and Chlorobium (a green sulfur-utilizing bacterium) were high in the inner part of the lagoon compared to other stations, and these groups were also present in winter. Apparently groups able to thrive in both anoxic and aerobic conditions were predominant in the inner part of the lagoon.

Rape straw biochar enhanced Cd immobilization in flooded paddy soil by promoting Fe and sulfur transformation

Cd is normally associated with sulfide and Fe oxides in flooded paddy soil. The mechanisms of biochar enhanced Cd immobilization by promoting Fe transformation and sulfide formation are unclear. Rape straw biochar (RSB) pyrolyzed at 450 °C (LB) and 800 °C (HB) was added to Cd-contaminated paddy soil at 1% (LB1, HB1) and 2% (LB2, HB2) doses. The results showed that Fe/Mn oxide–Cd (Fe/Mn–Cd) and free Fe oxide (Fed) concentrations decreased in the first 12 days and then rose, while Fe2+ in pore water (W–Fe2+) tended to rise first and then fall. The electron transfer rate of soil in the HB2 treatment was 4.9-fold higher than that in the treatment without biochar (CK). Fe oxide reduction was enhanced by RSB, with a maximum increase in W–Fe2+ by 62.1% in HB2 on Day 12. The negative correlation between W–Fe2+ and Fed showed that Fe2+ promoted the reformatted of seconded Fe minerals after Day 12, and the Fed in the HB2 treatments increased by 31.5% in this period. RSB addition also promoted the reformation of poorly crystallized Fe oxide (Feo) by increasing soil pH, which increased by 17.2% and 15.1% on average in the LB2 and HB2 treatments, respectively, compared to CK. Compared to Day 7, the increased rate of Fe/Mn–Cd on Day 30 in RSB was approximately twice that of CK. Compared to the molybdate group, the maximum decrease in CaCl2–Cd was 29.1% in LB2 on Day 12. LB2 increased SO42− and acid-volatile sulfide concentrations by 6.9- and 4.1-fold, respectively, compared to CK. These results suggested that RSB, particularly HB, promoted more Cd adsorption in Fe minerals by increasing Fe hydroxylation and recrystallization processes. LB increased the contribution of sulfide to Cd immobility.