Low Sulfate Concentrations Research Articles

The Formation of Highly Positive δ34S Values in Late Devonian Mudstones: Microscale Analysis of Pyrite (δ34S) and Barite (δ34S, δ18O) in the Canol Formation (Selwyn Basin, Canada)

The sulfur isotope composition of pyrite in marine sedimentary rocks is often difficult to interpret due to a lack of precise isotopic constraints for coeval sulfate. This study examines pyrite and barite in the Late Devonian Canol Formation (Selwyn Basin, Canada), which provides an archive of δ34S and δ18O values during diagenesis. Scanning electron microscopy (SEM) has been combined with microscale secondary ion mass spectrometry (SIMS) analysis (n = 1,032) of pyrite (δ34S) and barite (δ34S and δ18O) on samples collected from nine stratigraphic sections of the Canol Formation. Two paragenetic stages of pyrite and barite formation have been distinguished, both replaced by barium carbonate and feldspar. The δ34Sbarite and δ18Obarite values from all sections overlap, between +37.1‰ and +67.9‰ (median = +45.7‰) and +8.8‰ and +23.9‰ (median = +20.0‰), respectively. Barite morphologies and isotopic values are consistent with precipitation from diagenetically modified porewater sulfate (sulfate resupply << sulfate depletion) during early diagenesis. The two pyrite generations (Py-1 and Py-2) preserve distinct textures and end-member isotopic records. There is a large offset from coeval Late Devonian seawater sulfate in the δ34Spyrite values of framboidal pyrite (-29.4‰ to -9.3‰), consistent with dissimilatory microbial sulfate reduction (MSR) during early diagenesis. The Py-2 is in textural equilibrium with barite generation 2 (Brt-2) and records a broad range of more positive δ34SPy-2 values (+9.4‰ to + 44.5‰). The distinctive highly positive δ34Spyrite values developed from sulfate limited conditions around the sulfate methane transition zone (SMTZ). We propose that a combination of factors, including low sulfate concentrations, MSR, and sulfate reduction coupled to anaerobic oxidation of methane (SR-AOM), led to the formation of highly positive δ34Spyrite and δ34Sbarite values in the Canol Formation. The presence of highly positive δ34Spyrite values in other Late Devonian sedimentary units indicate that diagenetic pyrite formation at the SMTZ may be a more general feature of other Lower Paleozoic basins.

A novel κ-carrageenan extracting process with calcium hydroxide and carbon dioxide

Traditional κ-carrageenan extraction method with alkaline (NaOH) has the problems of low yield, huge water consumption, and high sewage treatment cost. Thus, an efficient, water-saving, and eco-friendly κ-carrageenan extraction method was explored using Ca(OH)2 for boiling extract and CO2 for neutralization. The results showed that the quality of κ-carrageenan extracted by Ca(OH)2 (Ca-KC) was superior to that extracted by NaOH (Na-KC). The Fourier transform infrared spectroscopy result indicated that the absorption peak of Ca-KC at 1250 cm−1 weakened, whereas that at 931 cm−1 enhanced compared with those of the Na-KC. This result was consistent with the results of low sulfate content of Ca-KC and high content of 3,6-anhydro-d-galactose. Thermogravimetric analysis and differential scanning calorimetry analysis indicated that Ca-KC had a better thermal stability than Na-KC. The average molecular weight and molecular weight distribution of Ca-KC were not significantly different from those of Na-KC. Moreover, the gel strength and whiteness of Ca-KC increased, whereas its viscosity and transparency all decreased compared with those of the Na-KC. The yield of Ca-KC (36.2% ± 0.8%) was 40% higher than that of Na-KC (25.8% ± 0.7%), while material consumption significantly decreased and wastewater was avoided. Considering the above advantages, this new extraction method for κ-carrageenan extraction is a promising alternative to the traditional NaOH extraction method.

Salt weathering of sandstone under dehydration and moisture absorption cycles: An experimental study on the sandstone from Dazu rock carvings

AbstractSalt crystallization and phase change in porous media cause significant deterioration of cultural heritage made of stones and bricks. In this study, laboratory experiments on salt weathering of sandstone from the Dazu rock carvings (DRC) in Chongqing, southwest China, were carried out by exposing them to cycles of temperature and humidity change. Mirabilite, the main component of the salts in DRC that readily undergoes phase change, was utilized for the study. Three groups of Dazu sandstone (DS) samples with high (2.4 mol/L), moderate (1.5 mol/L) and low concentrations (1.0 mol/L) of sodium sulphate were prepared; and two conditions, high‐temperature with low‐humidity and low‐temperature with high‐humidity, were designed to simulate the fluctuations of temperature and humidity in the Dazu area. After several cycles, the dehydration and moisture absorption of DS under these two conditions forces the phase change of sodium sulphate between thenardite (Na2SO4) and mirabilite (Na2SO4·10H2O), causing different levels of damage. A combination results of sample length, weight, microstructure, and mechanical property variations show that the damage effect of the thenardite formed during dehydration is more significant than that of mirabilite in moisture absorption. During these cycles, there is noticeable salt migration and the local concentration of salts is influenced by the microstructure of the stone and the distribution of clay minerals. Samples with high salt content show disintegration of the stone into powder, while those with moderate salt concentration show flaking and salt accumulation on the surface. These types of damage correspond with observations of natural weathering in the field. The experiment shows that no obvious damage takes place when the salt content is lower than 0.67%. These results contribute to a better understanding of the effects of salt weathering on sandstone and provide references for choosing correct prevention and protection measures for the world heritage site DRC.

Changes in sulfur cycling in a large lake during the Paleocene-Eocene Thermal Maximum and implications for lake deoxygenation

Understanding the biogeochemical effects of global warming on large lakes is central to managing aquatic resources. The Paleocene-Eocene Thermal Maximum (PETM) presents an excellent paleo-analog for potential impacts arising from current global warming. Here, we reconstructed dynamic redox changes in a large lake located in modern Central China during the PETM, using carbonate-associated sulfate sulfur and oxygen isotopes. Three major anoxic episodes (AE) associated with intensive microbial sulfate reduction (MSR) were identified, as indicated by higher sulfur and oxygen isotope compositions, and/or decreased sulfate contents. Thermal stratification in the lake was the likely main cause of the anoxia and associated changes in sulfur geochemical cycles. The first two AEs occurred during the initial stage of PETM. They are characterized by low sulfate and total organic carbon-minus-black carbon (TOC-BC) contents, suggestive of low biological productivity related to limited nutrient cycling in a stratified and anoxic water mass. The third AE occurred during the peak of the PETM. It was characterized by extremely low sulfate and high TOC-BC contents, possibly the product of increased near-surface productivity coupled with anoxia in the lower water column. An intensified hydrological cycle triggered by severe warming may have enhanced terrestrial nutrient fluxes to the lake, leading to increased surficial lake productivity. Upward expansion of the anoxic/sulfidic zone, however, may have suppressed the lake ecosystem by contracting its livable space. Our results suggest that current global warming could trigger similar ecological stress in large lakes.

Hydrocarbon seepage in the mid-Cretaceous greenhouse world: A new perspective from southern Tibet

The mid-Cretaceous greenhouse climate was induced by volcanic outgassing and the release of biogenic or thermogenic methane into the ocean-atmosphere system. During this period, major episodes of oceanic anoxic conditions enabled the large scale deposition of marine black shales rich in organic carbon, serving as a source for methane production. Studies on the anaerobic oxidation of methane, the key biogeochemical process at sites where methane is transported toward the seafloor, and its associated authigenic carbonates from mid-Cretaceous strata can contribute to elucidate such extreme climatic conditions. A total of nine layers of authigenic carbonates were recognized in the sequence of mid-Cretaceous inner shelf sedimentary rocks of the Qiangdong section, Gamba area, southern Tibet. In this study, we decipher the mode and causes of carbonate authigenesis by combining field observation, thin section petrography, mineralogy, and carbon and oxygen stable isotope geochemistry. The lowest obtained δ13Ccarb value of −30.5‰ is not low enough to exclude oil compounds as a carbon source, but since other evidence of oil seepage is lacking, methane is the most likely carbon source that was admixed to dissolved inorganic carbon to form authigenic carbonate. Typical seep carbonate phases including 13C depleted matrix micrite, clotted micrite, and banded and botryoidal cement as well as three types of authigenic pyrite comprising framboids, zoned aggregates with radial overgrowths surrounding a framboidal core, and euhedral pyrite crystals indicate the occurrence of methane seepage in the mid-Cretaceous depositional environments. In situ brecciation and subvertical tubular carbonates – the former reflecting rupture caused by local fluid overpressure and the latter interpreted as part of a plumping system – agree with widespread and vigorous seepage. Expanded shallow and deep-water anoxia in combination with low seawater sulfate concentration prior to the oceanic anoxic event 2 (OAE 2) event apparently caused an increased flux of organic matter to the methanogenic zone, stimulating methanogenesis and enabling a higher flux of methane toward the seafloor. In the water column, aerobic oxidation of methane would have enhanced oxygen depletion, thereby contributing to black shale deposition and providing a positive feedback to organic matter preservation and burial. Based on correlation with coeval authigenic carbonate deposits from the Tethyan continental margin, we conclude that organic matter accumulation and sea-level change were the main factors controlling carbonate authigenesis in the mid-Cretaceous.

Risk Assessment of Gypsum Amendment on Agricultural Fields: Effects of Sulfate on Riverine Biota.

Gypsum (CaSO4∙2H2O) amendment is a promising way of decreasing the phosphorus loading of arable lands, and thus preventing aquatic eutrophication. However, in freshwaters with low sulfate concentrations, gypsum‐released sulfate may pose a threat to the biota. To assess such risks, we performed a series of sulfate toxicity tests in the laboratory and conducted field surveys. These field surveys were associated with a large‐scale pilot exercise involving spreading gypsum on agricultural fields covering 18% of the Savijoki River (Finland) catchment area. The gypsum amendment in such fields resulted in approximately a four‐fold increase in the mean sulfate concentration for a 2‐month period, and a transient, early peak reaching approximately 220 mg/L. The sulfate concentration gradually decreased almost to the pregypsum level after 3 years. Laboratory experiments with Unio crassus mussels and gypsum‐spiked river water showed significant effects on foot movement activity, which was more intense with the highest sulfate concentration (1100 mg/L) than with the control. Survival of the glochidia after 24 and 48 h of exposure was not significantly affected by sulfate concentrations up to 1000 mg/L, nor was the length growth of the moss Fontinalis antipyretica affected. The field studies on benthic algal biomass accrual, mussel and fish density, and Salmo trutta embryo survival did not show gypsum amendment effects. Gypsum treatment did not raise the sulfate concentrations even to a level just close to critical for the biota studied. However, because the effects of sulfate are dependent on both the spatial and the temporal contexts, we advocate water quality and biota monitoring with proper temporal and spatial control in rivers within gypsum treatment areas. Environ Toxicol Chem 2022;41:108–121. © 2021 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Sulfate‐ and iron‐dependent anaerobic methane oxidation occurring side‐by‐side in freshwater lake sediment

AbstractAnaerobic oxidation of methane (AOM) is a potentially important methane sink in lake sediments, but the biogeochemistry and microbial ecology of this process are understudied. Potential electron acceptors for AOM include Fe(III) and sulfate; however, it is not clear to which extent low sulfate concentrations constrain the coupling of AOM to sulfate reduction, nor if Fe(III) reduction drives AOM directly or via a cryptic sulfur cycle. We investigated AOM pathways in the sediment of iron‐rich Danish Lake Ørn through anoxic sediment slurry incubations with additions of 13C‐labeled methane as a substrate, sulfate and Fe(III) as potential electron acceptors, and molybdate as an inhibitor of sulfate reduction. The experiments demonstrated the co‐occurrence of sulfate‐ and iron‐dependent modes of AOM, with the former supported by recycling of sulfate coupled to iron reduction. Quantitative PCR analysis demonstrated the abundance of archaea of the ANME‐2d clade (Ca. Methanoperedenaceae) as likely drivers of AOM. Our study demonstrates that sulfate‐dependent AOM can consume methane at sulfate concentrations typical for freshwater systems and emphasizes the importance of sulfur and iron cycling in the regulation of methane emission from freshwater sediments.

Role of the injected water salinity and ion concentrations on the oil recovery in carbonate reservoirs

Low salinity water flooding (LSWF) was initially considered using water with a low concentration of dissolved salts and was later extended to include modifying the ionic content of injected brines. This work investigates the effects of changing water salinity and composition along with the concentration of sulfate and iodide ions on oil recovery in carbonate reservoirs during the tertiary recovery stage. An experimental study was carried out using crude oil of 29°API, 8 core samples extracted from the Eocene carbonate reservoir (Egypt), and 6 different water salinities.The results showed additional oil recovery up to 5% of the original oil in place (OOIP) in the tertiary recovery stage with changing water salinity and water composition. Injection of high salinity (HS) and low salinity (LS) brines with high sulfate concentrations increased the incremental oil recovery by a value ranging from 1.7 to 3.8% of the OOIP. On the contrary, injection of HS and LS brines with low sulfate concentrations showed insignificant incremental oil recovery (less than 1% of the OOIP). Furthermore, injection of water with potassium iodide (KI) after injection of water with high sulfate brines showed additional oil recovery of about 1.7% of the OOIP. On the other hand, injection of water with KI after injection of water with low sulfate concentration showed insignificant incremental oil recovery (less than 0.4% of the OOIP).The concentration of sulfate in the injected water appeared to be key parameter to achieve effective waterflooding (WF) projects in carbonate reservoirs. Moreover, the results revealed that the multi-component ion exchange (MIE) mechanism seems to be the primary recovery mechanism for LSWF in carbonate reservoirs. The results and conclusions of this study can be used to develop guidelines for designing waterflooding projects in carbonate reservoirs with optimum salinity.

Predominant microbial iron reduction in sediment in early Cambrian sulfidic oceans

Microbial sulfate reduction (MSR) and microbial iron reduction (MIR) are two major anaerobic metabolic pathways, and account for the majority of anaerobic organic matter degradation in modern marine sediments. Because it is thermodynamically more favorable, the zone of porewater Fe2+ accumulation usually overlies the zone of porewater H2S accumulation in modern marine sediments. The sequence of redox reactions is collectively known as the ‘redox latter’, which has been used as a yardstick in reconstructing the marine redox landscape in Earth's history. To understand the redox profile in the early Cambrian oceans, here we analyzed syndepositional and diagenetic pyrite (FeS2) in carbonate concretions hosted in the black shale of the early Cambrian Shuijingtuo Formation in the Yangtze Block, South China. Syndepositional pyrite laminae, disseminated pyrite and diagenetic pyrite aggregates in the periphery of carbonate concretions have nearly identical sulfur isotope compositions, which cannot be resolved by quantitative reduction of seawater sulfate. Instead, a homogeneous H2S source from sulfidic (H2S-enriched) seawater might be the major sulfur source, and pyrite precipitation was sustained by H2S diffusion from sulfidic seawater. In addition, the homogeneous pyrite sulfur isotopes also imply negligible MSR in sediment porewater, reflecting low sulfate concentration in sulfidic seawater. On the other hand, the enrichment of Fe2+ in carbonate concretions implies deposition in ferruginous (Fe2+-enriched) porewater, resulting from active MIR that reduced detrital iron oxides to Fe2+. Thus, the early Cambrian sulfidic ocean might be characterized by extensive MSR in seawater and MIR in sediment porewater, which differs from the modern sulfidic ocean, such as the Black Sea, showing predominantly MSR in sediment. The development of such a reverse redox profile might be attributed to the terrestrial supply of particulate iron oxides that passed through the thermodynamically unstable sulfidic water column and low seawater sulfate concentration in sulfidic seawater that prohibited MSR in sediment. Finally, our study indicates that the redox profile might be diverse in the early Cambrian oceans.

Pretreatment Techniques and Green Extraction Technologies for Agar from Gracilaria lemaneiformis.

Optimizing the alkali treatment process alone without tracking the changes of algae and agar quality with each pretreatment process will not achieve the optimal agar yield and final quality. In this study, we monitored the changes of the morphology and weight of algae with each treatment process, and comprehensively analyzed the effects of each pretreatment process on the quality of agar by combining the changes of the physicochemical properties of agar. In conventional alkali-extraction technology, alkali treatment (7%, w/v) alone significantly reduced the weight of algae (52%), but hindered the dissolution of algae, resulting in a lower yield (4%). Acidification could solve the problem of algal hardening after alkali treatment to improve the yield (12%). In enzymatic extraction technology, agar with high purity cannot be obtained by enzyme treatment alone, but low gel strength (405 g/cm2) and high sulfate content (3.4%) can be obtained by subsequent acidification and bleaching. In enzyme-assisted extraction technology, enzyme damage to the surface fiber of algae promoted the penetration of low-concentration alkali (3%, w/v), which ensured a high desulfurization efficiency and a low gel degradation rate, thus improving yield (24.7%) and gel strength (706 g/cm2), which has the potential to replace the traditional alkali-extraction technology.

Dynamic interplay of biogeochemical C, S and Ba cycles in response to the Shuram oxygenation event

Compared with Phanerozoic strata, sulfate minerals are relatively rare in the Precambrian record; this is probably due to the lower concentrations of sulfate in dominantly anoxic oceans. Here, we present a compilation of sulfate minerals that are stratigraphically associated with the Ediacaran Shuram excursion (SE) – the largest negative δ 13 C excursion in Earth history. We evaluated 15 SE sections, all of which reveal the presence of sulfate minerals and/or enriched carbonate-associated sulfate concentrations, suggesting a rise in the sulfate reservoir. Notably, where data are available, the SE also reveals considerable enrichments in [Ba] relative to pre- and post-SE intervals. We propose that elevated seawater sulfate concentrations during the SE may have facilitated authigenesis of sulfate minerals. At the same time, the rise in Ba concentrations in shelf environments further facilitated barite deposition. A larger sulfate reservoir would stimulate microbial sulfate reduction and anaerobic oxidation of organic matter (including methane), contributing to the genesis of the SE. The existence of sulfate minerals throughout the SE suggests that oxidant pools were not depleted at that time, which challenges previous modelling results. Our study highlights the dynamic interplay of biogeochemical C, S and Ba cycles in response to the Shuram oxygenation event. Supplementary material: SEM and EDS data and figures S1-S4 and tables S1-S3 are available at: https://doi.org/10.6084/m9.figshare.c.5602560 Thematic collection: This article is part of the ‘Sulfur in the Earth system’ collection available at: https://www.lyellcollection.org/cc/sulfur-in-the-earth-system

Diversity and Activity of Sulfate-Reducing Prokaryotes in Kamchatka Hot Springs.

Microbial communities of the Kamchatka Peninsula terrestrial hot springs were studied using radioisotopic and cultural approaches, as well as by the amplification and sequencing of dsrB and 16S rRNA genes fragments. Radioisotopic experiments with 35S-labeled sulfate showed that microbial communities of the Kamchatka hot springs are actively reducing sulfate. Both the cultivation experiments and the results of dsrB and 16S rRNA genes fragments analyses indicated the presence of microorganisms participating in the reductive part of the sulfur cycle. It was found that sulfate-reducing prokaryotes (SRP) belonging to Desulfobacterota, Nitrospirota and Firmicutes phyla inhabited neutral and slightly acidic hot springs, while bacteria of phylum Thermodesulofobiota preferred moderately acidic hot springs. In high-temperature acidic springs sulfate reduction was mediated by archaea of the phylum Crenarchaeota, chemoorganoheterotrophic representatives of genus Vulcanisaeta being the most probable candidates. The 16S rRNA taxonomic profiling showed that in most of the studied communities SRP was present only as a minor component. Only in one microbial community, the representatives of genus Vulcanisaeta comprised a significant group. Thus, in spite of comparatively low sulfate concentrations in terrestrial hot springs of the Kamchatka, phylogenetically and metabolically diverse groups of sulfate-reducing prokaryotes are operating there coupling carbon and sulfur cycles in these habitats.

Metagenomic Analysis of Biochemical Passive Reactors During Acid Mine Drainage Bioremediation Reveals Key Co-selected Metabolic Functions.

Acid mine drainage (AMD) is the major pollutant generated by the mining industry, and it is characterized by low pH and high concentration of metals and sulfate. The use of biochemical passive reactors (BPRs) is a promising strategy for its bioremediation. To date, there are various studies describing the taxonomical composition of BPR microbial communities, generally consisting of an assemblage of sulfate-reducing organisms inside Deltaproteobacteria, and a diverse set of anaerobic (ligno)cellulolytic bacteria; however, insights about its functional metagenomic content are still scarce. In previous studies, a laboratory-scale AMD bioremediation using biochemical passive reactors was designed and performed, tracking operation parameters, chemical composition, and changes, together with taxonomic composition of the microbiomes harbored in these systems. In order to reveal the main functional content of these communities, we used shotgun metagenomics analyses to explore genes of higher relative frequencies and their inferred functions during the AMD bioremediation from three BPRs representing the main microbiome compositions detected in the system. Remarkably, genes encoding for two-component regulatory systems and ABC transporters related to metal and inorganic ions, cellulose degradation enzymes, dicarboxylic acid production, and sulfite reduction complex were all detected at increased frequency. Our results evidenced that higher taxonomic diversity of the microbiome was arising together with a functional redundancy of the specific metabolic roles, indicating its co-selection and suggesting that its enrichment on BPRs may be implicated in the cumulative efficiency of these systems.

Pore-Scale Oil Connectivity and Displacement by Controlled-Ionic-Composition Waterflooding Using Synchrotron X-Ray Microtomography

Summary Controlled-ionic-composition waterflooding is an economic and effective method to improve oil recovery in carbonate oil reservoirs. Recent studies show controlling the salinity and ionic composition of injection water can alter the wettability of carbonate mineral surfaces. The pore-scale oil connectivity and displacement by controlled-ionic-composition waterflooding in heterogeneous carbonate reservoirs, especially at the early stage, is still unclear. The goal of this study is to examine the role of ion concentrations and types in the oil displacement efficiency and investigate the impact of the waterflooding on the pore-scale oil displacement using the national synchrotron facility. A carbonate rock sample was flooded with synthetic high-salinity water and other water solutions with different sulfate concentrations. The waterflooding processes were visualized with synchrotron X-ray microtomography to follow the evolution of pore-scale oil/brine interactions at typical field flow rates. Experimental results show that the water with lower sulfate concentration and higher salinity did not change the wettability of the pore surfaces. Higher sulfate ion concentrations in the water, in contrast, altered the wettability of carbonate pore surfaces from oil-wet to neutral-wet within the first few minutes of waterflooding. Novel insight was gained on the ability of water with high-sulfate concentration to displace oil in the small pores and through abundant oil channels, which could consequently lead to higher oil recovery from the carbonate rock.

Sulfate-Controlled Heterogeneous CaCO3 Nucleation and Its Non-linear Interfacial Energy Evolution.

Unveiling the effects of an environmental abundant anion "sulfate" on the formation of calcium carbonate (CaCO3) is essential to understand the formation mechanisms of biominerals like corals and brachiopod shells, as well as the scale formation in desalination systems. However, it was experimentally challenging to elucidate the sulfate-CaCO3 interactions at the explicit first step of CaCO3 formation: nucleation. In addition, there is limited quantitative information on the precise control of nucleation kinetics. Here, heterogeneous CaCO3 nucleation is monitored in real time as a function of sulfate concentrations (0-10 mM Na2SO4) using synchrotron-based grazing incidence X-ray scattering techniques. The results showed that sulfate can be incorporated in the nuclei, resulting in a nearly 90% decrease in the CaCO3 nucleation rate, causing a 120% increase in the CaCO3 nucleus size, and inhibiting the vaterite-to-calcite phase transformation. Moreover, this work quantitatively relates sulfate concentrations to the effective interfacial energies of CaCO3 and finds a non-linear trend, suggesting that CaCO3 heterogeneous nucleation is more sensitive at a low sulfate concentration. This study can be readily extended to study other additives and obtain quantitative relationships between additive concentrations and CaCO3 interfacial energies, a key step toward achieving natural and engineered controls on CaCO3 nucleation.

Response to substrate limitation by a marine sulfate-reducing bacterium.

Sulfate-reducing microorganisms (SRM) in subsurface sediments live under constant substrate and energy limitation, yet little is known about how they adapt to this mode of life. We combined controlled chemostat cultivation and transcriptomics to examine how the marine sulfate reducer, Desulfobacterium autotrophicum, copes with substrate (sulfate or lactate) limitation. The half-saturation uptake constant (Km) for lactate was 1.2 µM, which is the first value reported for a marine SRM, while the Km for sulfate was 3 µM. The measured residual lactate concentration in our experiments matched values observed in situ in marine sediments, supporting a key role of SRM in the control of lactate concentrations. Lactate limitation resulted in complete lactate oxidation via the Wood-Ljungdahl pathway and differential overexpression of genes involved in uptake and metabolism of amino acids as an alternative carbon source. D. autotrophicum switched to incomplete lactate oxidation, rerouting carbon metabolism in response to sulfate limitation. The estimated free energy was significantly lower during sulfate limitation (-28 to -33 kJ mol-1 sulfate), suggesting that the observed metabolic switch is under thermodynamic control. Furthermore, we detected the upregulation of putative sulfate transporters involved in either high or low affinity uptake in response to low or high sulfate concentration.

Remediation of atmospheric sulfur and ammonia by wetland plants: development of a study method

In the context of S and N pollutant remediation, this study aimed to develop a methodology to test the ability of wetland plants to reduce atmospheric pollution by S and N. A methodology using 34S and 15N-labeled Sinapsis alba compost and five species (trap plants) used to fix volatile compounds was developed. 18.66% of 34S and 40.63% of 15N produced by Sinapsis alba compost, equivalent to 67 mg of S and 1611 mg of N, were recovered in trap plants, a negligible proportion of the labeling was found in the culture substrate. 34S and 15N atom% excess were two to ten times higher in leaves than in roots. Agrostis stolonifera, Symphytum officinale, and Lythrum salicaria were more efficient to use atmospheric inorganic sources of S and N than Mentha aquatica and Carex riparia. A low concentration of sulfate in the leaf laminas, a high specific leaf area, and a low leaf dry mass content could represent trait patterns that explain higher abilities to fix pollutants. This study confirms that plants can be used to remediate inorganic atmospheric pollution and highlights the importance of plant screening for this environmental function. Novelty statement The removal efficiency of botanical biofiltration is well-documented for Volatile Organic pollutants, but little is known concerning Volatile Inorganic pollutants, such as SO2 and NH3 which can also constitute plant nutrients. We developed a methodology based on the use of 34S and 15N-labeled mustard compost to study the ability of wetland plant species to fix volatile N and S pollutants. This methodology was effective as 19% of 34S and 41% of 15N lost by mustard compost were recovered in trap plants. Among the species used as “trap plants” Agrostis stolonifera, Symphytum officinale, and Lythrum salicaria appeared more efficient to use atmospheric inorganic sources of S and N than Mentha aquatica and Carex riparia.

Limnological Conditions and Photosynthetic Pigments in Clearwater Lakes of the Volga-Vyatka Karst Province

The features of summer stratification and vertical distribution of photosynthetic pigments (chlorophylls and bacteriochlorophylls) in five karst lakes in the Middle Volga region (Republics of Tatarstan and Mari-El) are studied. The water of the investigated lakes has low color and sulfate concentration and low-to-medium total dissolved salts content. Anoxic conditions develop in the hypolimnion in all lakes after the establishment of summer thermal stratification. Reduced iron and sulfur compounds are found in the anaerobic zones of most lakes. In these lakes, deep maxima of chlorophyll and bacteriochlorophylls are formed, indicating the presence of biomass maxima of microbial plankton, consisting of both oxygenic and anoxygenic phototrophs. The presented data demonstrate also a wide variety of features of both chemical stratification and vertical distribution of phototrophic organisms in the studied lakes, which are probably associated with differences in the limnological characteristics of lakes, their water composition, and the history of their existence.

Evaluating the performance of anaerobic moving bed bioreactor and upflow anaerobic hybrid reactor for treating textile desizing wastewater

Performance and kinetic analysis of anaerobic moving bed bioreactor (AnMBBR) and upflow anaerobic hybrid reactor (UAHR) were investigated for the treatment of synthetic textile desizing wastewater (TDW) under organic loading rate (OLR) of 0.6–12 kgCOD/m3/day at thermophilic temperature (55 °C). The effects of increase in temperature (from 35 to 55 °C) on anaerobic treatment efficiency were studied. In the kinetic study for COD removal, first order substrate removal, Grau second order and modified Stover-Kincannon models were applied. By increasing temperature from 35 °C to 55 °C, COD removal, volumetric biogas production and methane content were increased 1.22, 2.58 and 1.08 times in AnMBBR. Whilst in the case of UAHR the increment for the aforementioned parameters were 1.10, 2.51 and 1.10 times, respectively. By increasing OLR from 0.6 to 6 kgCOD/m3/day, above 60% and 70% COD removal was observed, while the biogas increased from 0.12 to 0.97 L/L.day and 0.13–1.22 L/L.day for AnMBBR and UAHR, respectively. Up to an optimum OLR (6 and 8 kgCOD/m3/day for AnMBBR and UAHR) volumetric biogas production was also increased, simultaneously. Grau second order and modified Stover-Kincannon were found to be the best fit models (R2 =0.99). Biogas production and methane content in biogas were comparatively better in the case of real textile desizing wastewater due to lower sulfate concentration in the feed.

Relative risk of groundwater-quality degradation near California (USA) oil fields estimated from 3H, 14C, and 4He

Relative risks of groundwater-quality degradation near selected California oil fields are estimated by examining spatial and temporal patterns in chemical and isotopic data in the context of groundwater-age categories defined by tritium and carbon-14. In the Coastal basins, western San Joaquin Valley (SJV), and eastern SJV; 82, 76, and 0% of samples are premodern (pre-1953 recharge), respectively; and 3, 0, and 31% are modern (recharged during or after 1953), respectively. Carbon-14 and helium-4 data indicate most premodern samples are 1000 to 10,000 (33%) or >10,000 (50%) years old. Organic chemicals that could be associated with deeper hydrocarbon reservoirs (e.g. thermogenic gases and benzene) occur most frequently in premodern groundwater, suggesting premodern groundwater has a higher risk of degradation from upward migration of hydrocarbons than modern and mixed-age groundwater. Low sulfate concentrations in some premodern groundwater containing high thermogenic-methane concentrations (>28 mg/L) indicate methane attenuation associated with sulfate reduction can be limited in premodern groundwater. The more common occurrence of manufactured compounds, like tetrachloroethene, in modern and mixed-age groundwater than in premodern groundwater indicates modern and mixed-age groundwater has a higher risk of degradation from land-surface sources than premodern groundwater. Time-series data for chloride in groundwater affected by disposal of oil-field water in unlined ponds indicate some modern and mixed-age groundwater are susceptible to chemical migration within 2–3 km of surface sources. Timescales for diluting chloride concentrations in groundwater with fresh recharge once disposal ponds are decommissioned are shorter in mixed-age groundwater with large fractions of modern water (9–14 years in one example) than in mixed-age groundwater with large fractions of premodern water (no evidence of dilution after 12 years of monitoring in one example). The presence of predominantly premodern groundwater in the Coastal basins and western SJV indicates these areas have relatively high risk from upward migration of hydrocarbons, reduced methane attenuation capacity, and long dilution times, whereas predominantly modern- and mixed-age groundwater in the eastern SJV indicates this area has relatively high risk from chemical migration from land-surface sources and subsequent extensive spreading. Age-based characterizations of relative risk could inform the design of groundwater-monitoring programs near oil fields in terms of the spatial distribution of monitoring points relative to source areas and monitoring frequency and duration.