Reduction Of Manganese Oxides Research Articles

Manganese reduction and associated microbial communities in Antarctic surface sediments

The polar regions are the fastest warming places on earth. Accelerated glacial melting causes increased supply of nutrients such as metal oxides (i.e., iron and manganese oxides) into the surrounding environment, such as the marine sediments of Potter Cove, King George Island/Isla 25 de Mayo (West Antarctic Peninsula). Microbial manganese oxide reduction and the associated microbial communities are poorly understood in Antarctic sediments. Here, we investigated this process by geochemical measurements of in situ sediment pore water and by slurry incubation experiments which were accompanied by 16S rRNA sequencing. Members of the genus Desulfuromusa were the main responder to manganese oxide and acetate amendment in the incubations. Other organisms identified in relation to manganese and/or acetate utilization included Desulfuromonas, Sva1033 (family of Desulfuromonadales) and unclassified Arcobacteraceae. Our data show that distinct members of Desulfuromonadales are most active in organotrophic manganese reduction, thus providing strong evidence of their relevance in manganese reduction in permanently cold Antarctic sediments.

Enhancing cadmium immobilization by AQDS-mediated dissimilatory reduction under coexisting conditions of iron and manganese oxides

The serious contamination of cadmium (Cd) in sediments has become an urgent environmental problem. Quinones mediated dissimilatory iron and manganese reduction widely occurs in sediments, this process may enhance Cd immobilization by promoting production of secondary minerals. Nevertheless, the enhancing effect of Cd immobilization is still poorly understood. Here, 9,10-anthraquinone-2,6-disulfonic acid (AQDS) was used to facilitate the microbial reduction of iron and manganese oxides by Geobacter metallireducens GS-15, and its effects on Cd species was investigated. Compared to goethite (FeOOH), microorganisms preferentially reduced birnessite (MnO2) due to more dramatic interfacial electron transfer between birnessite and AQDS. AQDS thus significantly enhanced microbial reduction of iron and manganese coexisted minerals as well as Cd2+ immobilization. After 80 days, an impressive 83% of reducible-Cd appeared in the FeOOH–MnO2-AQDS group, demonstrating the most effective Cd immobilization. Furthermore, XANES results suggested that AQDS promoted the increase of vivianite-Cd in secondary minerals in MnO2-AQDS and FeOOH–MnO2-AQDS groups. Based on the structural equation model, HCl-extracted Fe(II) indirectly affected the increase of reducible-Cd mainly through vivianite-Cd. The AQDS enhancement on microbial reduction of iron and manganese oxides promotes the recrystallization of secondary minerals and the immobilization of Cd, offering a promising strategy for the remediation of Cd-contaminated sediments.

Removal of hexavalent chromium in water by chitosan-modified Enteromorpha prolifera biochar loaded with iron-manganese oxides: Application performances and reaction mechanisms

This study successfully synthesized magnetic iron-manganese biochar (F1M3BC) and iron-manganese chitosan biochar (Chi-F1M3BC) using Enteromorpha prolifera (EP) as the raw material, aiming to efficiently remove hexavalent chromium (Cr(VI)) from water. Compared to F1M3BC, Chi-F1M3BC, after chitosan cross-linking encapsulation, exhibited significant advantages in terms of specific surface area, pH adaptability, and adsorption performance. The specific surface area of Chi-F1M3BC reached 101.47 m³/g, approximately double that of F1M3BC (52.89 m³/g), making it rich in reactive groups for Cr(VI) removal. The addition of chitosan elevated the pHpzc value of Chi-F1M3BC from 5.5 to 9, and the abundant active groups enabled it to efficiently remove Cr(VI) over a wider pH range. Under 30 °C conditions, 0.5 g/L of Chi-F1M3BC could completely remove 30 mg/L of Cr(VI) solution within 1 h. Adsorption isotherm and kinetic studies indicated that Chi-F1M3BC complied with the Langmuir model and pseudo-second-order kinetics. At 30 °C, the adsorption capacity of Chi-F1M3BC reached 104.5 mg/g, approximately twice that of F1M3BC (58.93 mg/g). Moreover, after five consecutive usage cycles, the removal efficiency of Cr(VI) by Chi-F1M3BC only slightly decreased by 3%, demonstrating its superior stable removal performance. Subsequent characterization and experimental investigations elucidated the elimination of Cr(VI) by Chi-F1M3BC, achieved through the synergistic interplay of ion exchange, electrostatic attraction involving surface hydroxyl and amino functional groups, chelation, and the reduction of iron and manganese oxides. In conclusion, the synthesized Chi-F1M3BC has demonstrated its efficiency and stable adaptability in removing Cr(VI), coupled with the additional benefit of utilizing waste Enteromorpha prolifera.

CFD Modelling of Gas-Solid Reactions: Analysis of Iron and Manganese Oxides Reduction with Hydrogen

Metallurgical processes are characterized by a complex interplay of heat and mass transfer, momentum transfer, and reaction kinetics, and these interactions play a crucial role in reactor performance. Integrating chemistry and transport results in stiff and non-linear equations and longer time and length scales, which ultimately leads to a high computational expense. The current study employs the OpenFOAM solver based on a fictitious domain method to analyze gas-solid reactions in a porous medium using hydrogen as a reducing agent. The reduction of oxides with hydrogen involves the hierarchical phenomena that influence the reaction rates at various temporal and spatial scales; thus, multi-scale models are needed to bridge the length scale from micro-scale to macro-scale accurately. As a first step towards developing such capabilities, the current study analyses OpenFOAM reacting flow methods in cases related to hydrogen reduction of iron and manganese oxides. Since reduction of the oxides of interest with hydrogen requires significant modifications to the current industrial processes, this model can aid in the design and optimization. The model was verified against experimental data and the dynamic features of the porous medium observed as the reaction progresses is well captured by the model.

Reductive transformation of birnessite by low-molecular-weight organic acids

Soil biogeochemistry is intrinsically coupled to the redox cycling of iron and manganese. Oxidized manganese forms various (hydr)oxides that may reductively transform and dissolve, thereby serving as electron acceptors for microbial metabolisms. Furthermore, manganese oxides might reduce purely abiotically by oxidation of dissolved Mn2+ in a specific route of transformation from birnessite (MnIVO2) into metastable feitknechtite (β-MnIIIOOH) and stable manganite (γ-MnIIIOOH). In natural soil solutions, however, dissolved Mn2+ is not abundant and organic substances such as low-molecular-weight organic acids (LMWOA) may be oxidized and serve as an electron donor for manganese oxide reduction instead. We investigated whether LMWOA would impact the transformation of birnessite at a temperature of 290 ± 2 K under ambient pressure for up to 1200 d. We found that birnessite was reductively transformed into feitknechtite, which subsequently alters into the more stable manganite without releasing Mn2+ into the solution. Instead, LMWOA served as electron donors and were oxidized from lactate into pyruvate, acetate, oxalate, and finally, inorganic carbon. We conclude that the reductive transformation of short-range ordered minerals like birnessite by the abiotic oxidation of LMWOA is a critical process controlling the abundance of LMWOA in natural systems besides their microbial consumption. Our results further suggest that the reduction of MnIV oxides not necessarily results in their dissolution at neutral and alkaline pH but also forms more stable MnIII oxyhydroxides with less oxidative degradation potential for organic contaminants.

In Situ Construction of Manganese Oxide Photothermocatalysts for the Deep Removal of Toluene by Highly Utilizing Sunlight Energy.

The alternative use of electric energy by renewable energy to supply power for catalytic oxidation of pollutants is a sustainable technology, requiring a competent catalyst to realize efficient utilization of light and drive the catalytic reaction. Herein, in situ-synthesized manganese oxide heterostructure composites are developed through solvothermal reduction and subsequent calcination of amorphous manganese oxide (AMO). 95% of toluene conversion and 80% of CO2 mineralization were achieved over amorphous manganese oxide calcined at 250 °C (AMO-250) under light irradiation, and catalyst stability was maintained for at least 40 h. Highly utilization of light energy, uniformly dispersed nanoparticles, large specific surface area, improved metal reducibility, and oxygen desorption and migration ability at low temperature contribute to the good catalytic oxidation activity of AMO-250. Light activated more lattice oxygen to participate in the reaction via the Mars-van Krevelen (MvK) mechanism, and traditional e--h+ photocatalytic behavior exists over the AMO-250 heterostructure composite as an auxiliary degradation path. The reaction pathways of photothermocatalysis and thermocatalysis are close, except for the emergence of different copolymers, where light enhances the deep conversion of intermediates. A proof-of-concept study under natural sunlight has confirmed the feasibility of practical application in the photothermocatalytic degradation of pollutants.

Phosphorus adsorption on iron-coated sand under reducing conditions.

Mitigation measures are needed to prevent large loads of phosphate originating in agriculture from reaching surface waters. Iron-coated sand (ICS) is a residual product from drinking water production. It has a high phosphate adsorption capacity and can be placed around tile drains, taking no extra space, which increases the farmers' acceptance. The main concern regarding the use of ICS filters below groundwater level is that limited oxygen supply and high organic matter concentrations may lead to the reduction and dissolution of iron (hydr)oxides present and the release of previously adsorbed phosphate. This study aimed to investigate phosphate adsorption on ICS at the onset of iron reduction. First, we investigated whether simultaneous metal reduction and phosphate adsorption were relevant at two field sites in the Netherlands that use ICS filters around tile drains. Second, the onset of microbially mediated reduction of ICS in drainage water was mimicked in complementary laboratory microcosm experiments by varying the intensity of reduction through controlling the oxygen availability and the concentration of degradable organic matter. After 3 yr, ICS filters in the field removed phosphorus under low redox conditions. Over 45 d, the microbial reduction of manganese and iron oxides did not lead to phosphate release, confirming field observations. Electron microscopy and X-ray absorption spectroscopy did not evince systematic structural or compositional changes; only under strongly reducing conditions did iron sulfides form in small percentages in the outer layer of the iron coating. Our results suggest that detrimental effects only become relevant after long periods of operation.

Organoclastic sulfate reduction in deep-buried sediments: Evidence from authigenic carbonates of the Gulf of Mexico

The fate of organic matter in deep-buried marine sediments determines the formation of hydrocarbon reservoirs, shapes the deep biosphere, and affects the global carbon cycle. Several geochemical processes such as silicate weathering, iron and manganese (hydr)oxide reduction, and sulfate reduction influence the remineralization of organic matter in buried sediments. However, little information on deep-seated organoclastic sulfate reduction is available and the involved geochemical processes are largely unknown. Here, authigenic carbonates recovered from Ship Shoal Block 296 (SS296) of the Gulf of Mexico, all dominated by low-magnesium calcite, were investigated to constrain organoclastic sulfate reduction in deep-buried sediments. The SS296 carbonates had been previously suggested to be of a deep origin and transported upward by salt diapirism. The presence of cone-in-cone textures in samples 3110R1 and 3110R2 as well as vitrinite reflectance values of 0.48% to 0.58% indicate carbonate formation at a relatively deep burial. Likewise, clumped isotope thermometry yielded formation temperatures from 45 °C to 53 °C for sample 3110R1, 60 °C for sample 3110R2, and 11 °C to 37 °C for sample 3110R3. In spite of formation at greater depth, the temperatures of samples 3110R1 and 3110R2 are still within the temperature range of microbial sulfate reduction, reflecting formation depths between 1 km and 2.7 km. The presence of framboidal pyrite and its relatively low δ34S values (−27.8‰ to +11.5‰) agree with the occurrence of microbial sulfate reduction during carbonate precipitation. The carbon isotopic composition of the carbonates (δ13C: −16.6‰ to −8.9‰) and enclosed organic matter (δ13Corg: −26.8‰ to −20.5‰) suggests that organic matter is the dominant carbon source of carbonate minerals. This study confirms that microbial sulfate reduction occurs in deep-buried sediments, driving the degradation of organic matter. Our findings suggest that organoclastic sulfate reduction might be common in deep-seated sedimentary environments, controlling the fate of organic matter in deep subsurface environments and affecting the global carbon cycle.

Selective extraction performance of Ni, Cu, Co, and Mn adopted by a coupled leaching of low-grade Ni-sulfide ore and polymetallic Mn-oxide ore in sulphuric acid solutions

The coupled leaching of ocean polymetallic nodule and low-grade nickel sulphide ore in sulphuric acid solution was investigated, especially in performance on selective extraction of Ni, Cu, Co, and Mn. This work can be divided into three parts. First, the advantageous selective metal extraction conditions, parallel to the optimal coupled leaching conditions, were measured by coupled leaching tests which adopted the Ni, Mn, Cu, Co, and Fe dissolution efficiency. Under the optimal conditions, the extraction ratios of Ni, Mn, Cu, Co, and Fe are 96.8%, 97.3%, 92.2%, 97.9%, and 28.9%, respectively. Second, electrochemical tests revealed that multi-metal simultaneous extraction from two ores depends on the reduction-oxidation dissolution of a corrosion cell of the nodule cathode and the sulphide ore anode. The results showed that acidity and Fe3+ ion affected dissolution of both ores significantly; high valence manganese oxide reduction takes precedence which is in control of the Ni, Mn, Cu, and Co dissolution of the nodule; Ni, Cu, and Co extraction from the nickel ore is a course of sulphide minerals oxidative conversion which significantly affected by Fe2+-containing sulphide oxidation. Third, the separation performance of iron substance in the solution was determined by the transformation of minerals phases of the leached residues, showing that Fe-bearing minerals dissolved to Fe3+ ion then precipitated as iron vitriol or oxide during the selectively coupled leaching. The selectively coupled leaching of low-grade multi-metallic sulphide ore and oxide ore mainly rests with the transformation of Fe-containing species in the system.

THERMODYNAMIC SIMULATION OF SILICOTHERMAL METHOD FOR PRODUCTION OF MEDIUM CARBON MANGANESE IN A CONVERTER

The widespread use of manganese in the production of steel somewhat limits its use in the deoxidation of low-carbon steel grades due to the use of manganese, mainly in the form of high-carbon ferromanganese. Thermodynamic modeling of equilibrium in a complex heterogeneous Mn-Si-Fe-P-O-C slag-metal-gas system was carried out for a detailed study of the behavior of metal and slag components for each period separately using the technology of silicothermal reduction of manganese oxides from slag in an envelope with bottom blast. An analysis of the calculated data showed a decrease in the silicon content from 16.05% in the starting material to 0.7 in the final ferromanganese. The carbon content decreases slightly from 1.72 to 1.28%. The manganese content increases from 67.25% in the starting material to 83.8% in the final ferromanganese. For phosphorus, an increase in content is observed in all periods. To achieve acceptable concentrations of phosphorus in the metal, it is necessary to use low-phosphorus initial charge materials. The results of theoretical studies indicate the prospects for further development of the technology for decarburization of high-carbon manganese melts using blowing with gaseous oxygen and treatment with slag melts of a certain composition.

Intensified interactions of triclosan and diclofenac mitigation and nitrogen removal in manganese oxide constructed wetlands

Pharmaceuticals and personal care products (PPCPs) have received increasing attention due to their potential threats to the environment and human health. To explore economic and effective methods to treat wastewater containing triclosan (TCS) and/or diclofenac (DCF), six lab-scale CWs using birnessite modified sand (B-CWs) or sand (C-CWs) as substrate were operated for one year. The removal efficiency of TCS and DCF are affected by seasonal and temperature changes. In summer, the mean removal efficiency of TCS and DCF reached 91.7% ± 2.5% (C-CWs) and 97.7% ± 1.4% (B-CWs), and 85.8% ± 10.1% (C-CWs) and 80.8% ± 9.5% (B-CWs), respectively. B-CWs showed a better removal performance than control groups in ammonium nitrogen and TCS removal, especially under low temperatures. Degradation of TCS and DCF promoted the simultaneous occurrence of denitrification coupled with Mn2+ oxidation. The mechanisms of birnessite sand enhanced nitrogen nutrients and PPCPs removal was proposed as, both ammonium oxidation and PPCPs degradation were promoted by manganese oxide reduction to Mn2+, intermediates of PPCPs promoted denitrification coupled to Mn2+ oxidation. Overall, we propose the addition of birnessite sand is an effective way to enhance the removal performance of both PPCPs and nitrogen nutrients in subsurface flow CWs.

Effects of pH variations caused by redox reactions and pH buffering capacity on Cd(II) speciation in paddy soils during submerging/draining alternation

Incubation experiments were conducted to investigate the influencing factors of pH variation in different paddy soils during submerging/draining alternation and the relationship between pH buffering capacity (pHBC) and Cd speciation in ten paddy soils developed from different parent materials (including 8 acid paddy soils and 2 alkaline paddy soils). The soil pHBC and the changes in soil pH, Eh, Fe2+, Mn2+, SO42- and Cd speciation were determined. The results showed that there was a significant positive correlation between cation exchange capacity (CEC) and pHBC of these paddy soils, indicating that soil CEC is a key factor affecting the pHBC of paddy soils. The contribution of Fe(III) oxide reduction to H+ consumption is far greater than the reduction of Mn(IV)/Mn(III) oxides and SO42- during the submerging. For example, the contribution of the reduction of manganese oxides, SO42- and iron oxides to H+ consumption in the paddy soils from Anthrosol at 15 d submerging was 1.2%, 11.6% and 87.2%, respectively. This confirms that the reduction of Fe(III) oxides plays a leading role in increasing soil pH. Importantly, we noticed that during submerging, soil pH was increased and resulted in the content of available Cd in soils being reduced. This was due to the transformation of Cd to less active forms. Also, there was a significant positive correlation between the change rate of available Cd, the percentage of acid extractable Cd and pH variation. This suggests that the variation in soil pH was responsible for the transformation of Cd speciation. In addition, the change rate of available Cd and the percentage of acid extractable Cd concentration were significantly negatively correlated with soil pHBC. The soil with higher pHBC experienced less pH change, and thus the change rate of available Cd and the percentage of acid extractable Cd concentration were less for the soil. The results of this study can provide a basis for the remediation of Cd-contaminated acidic paddy soils.

Enhanced performance of Pt-based diesel oxidation catalyst via defective MnOx: The role of Pt/MnOx interface

To strengthen the interface effect of Pt with MnOx, manganese oxides with different defective concentration were obtained via removing oxygen under reduction treatment. The excellent performance on the Pt-based oxidation catalyst with optimum reduction temperature is 250 °C, and it's the light-off temperature of CO, C3H6 and NO are 170 °C, 180 °C and 185 °C, respectively, and the highest NO maximum conversion of 76%. The defect on MnOx could induce the adsorption of Pt2+ to produce the higher platinum dispersion and more active oxygen species. The abundant oxygen vacancies on manganese manganite would transfer to the subsurface, reducing the Mn valence and affecting the electronic effect of Pt with MnOx. Meanwhile, the existence of interfacial structure induces the shrinkage of platinum cell with the reduction of lattice parameter, because of the doping of Mn ion. The strong interaction of Pt with MnOx could promote the reduction of manganese oxides at the lower temperature. The interface of Pt-MnOx could accelerate the oxygen mobility and facilitate the formation of more bridged nitrates and chelating nitrates. Due to the interfacial structure of Pt with MnOx, the low temperature catalytic performance and high NO conversion of catalyst are remarkably improved.

Biological manganese-dependent sulfide oxidation impacts elemental gradients in redox-stratified systems: indications from the Black Sea water column

The reduction of manganese oxide with sulfide in aquatic redox-stratified systems was previously considered to be mainly chemical, but recent isolation of the Black Sea isolate Candidatus Sulfurimonas marisnigri strain SoZ1 suggests an important role for biological catalyzation. Here we provide evidence from laboratory experiments, field data, and modeling that the latter process has a strong impact on redox zonation in the Black Sea. High relative abundances of Sulfurimonas spp. across the redoxcline in the central western gyre of the Black Sea coincided with the high-level expression of both the sulfide:quinone oxidoreductase gene (sqr, up to 93% expressed by Sulfurimonas spp.) and other sulfur oxidation genes. The cell-specific rate of manganese-coupled sulfide oxidation by Ca. S. marisnigri SoZ1 determined experimentally was combined with the in situ abundance of Sulfurimonas spp. in a one-dimensional numerical model to calculate the vertical sulfide distribution. Abiotic sulfide oxidation was too slow to counterbalance the sulfide flux from euxinic water. We conclude that microbially catalyzed Mn-dependent sulfide oxidation influences the element cycles of Mn, S, C, and N and therefore the prevalence of other functional groups of prokaryotes (e.g., anammox bacteria) in a sulfide-free, anoxic redox zone.

Decarbonisation of steel mill gases in an energy-neutral chemical looping process

The iron and steel industry is the largest industrial carbon dioxide emitter. More than 70% of their emissions originate from conventional combustion of steel mill gases. In this work, a strategy for carbon capture from the steel mill gases is laid out, using a combination of emerging technologies employing oxygen carrying nickel oxide, carbon dioxide accepting calcium oxide, and dioxygen uncoupling manganese(III) oxide. The process combination was simulated and analysed using Aspen Plus. By applying the proposed strategy, up to 85% of carbon dioxide emitted from the combustion of blast furnace gas and coke oven gas can be captured and compressed for storage or utilisation without external heat and electricity supply. The chemical energy in the steel mill gases is used for the reduction of nickel oxide to nickel and the exothermic capture of carbon dioxide by calcium oxide to form calcium carbonate. Auto-thermal conditions for the energy-intensive carbon dioxide release by the endothermic decomposition of calcium carbonate at 1173 K are achieved by combining it with the exothermic oxidation of nickel by dioxygen, thereby regenerating nickel oxide and calcium oxide for another cycle while efficiently using the chemical energy stored in the steel mill gases. The dioxygen necessary for nickel oxidation to nickel oxide is produced by using a fraction of the product carbon dioxide stream at 1173 K for the endothermic manganese(III) oxide reduction to manganese(II,III) oxide, operated between 1100 and 1140 K, making use of the sensible heat of the carbon dioxide product stream and shifting the equilibrium towards dioxygen uncoupling of manganese(III) oxide. Air is used to re-oxidise manganese(II,III) oxide to manganese(III) oxide and complete the process cycle. Self-sufficiency of electrical power for carbon dioxide compression is obtained by recovering high temperature heat and converting it into electricity via high pressure steam in a steam turbine assembly. A proof of concept is obtained in a laboratory scale fixed bed reactor and the effect of operating conditions is experimentally explored.

Development of a new cored wire based on silica manganese gas-cleaning dust

The paper describes the possibility of using cored wire for wear­resistant hardfacing containing waste (dust of gas­cleaners) from the production of silica manganese and aluminum. Hardfacing was carried out using a submerged welding tractor made of silica manganese slag produced by the West Siberian Electrometallurgical Plant. The wear rate on the samples was determined on 2070 CMT­1 machine. The method for it is based on change in the sample mass during the disc – pad test. Chemical composition of the deposited metal was determined by X­ray fluorescence method on XRF­1800 spectrometer and by the atomic emission method on DFS­71 spectrometer. The hardness of the deposited layers was measured using METH­DO hardness tester. Evaluation of the quantity of nonmetallic inclusions was made according to GOST 1778 – 70 using an OLYMPUS GX­51 optical microscope. The coefficient of manganese recovery was found at different ratios of components. This coefficient is associated with the reduction of manganese oxide from manganese­containing flux (due to the carbon contained in the cored wire). With a significant excess of carbon in the cored wire from manganese­containing flux, recovery of manganese exceeds 100 %. The process of manganese recovery was determined by filling coefficient of the cored wire, amount of the carbon­containing material in the charge, and carbon content in the electric­arc coating itself. The deposited metal contains non­deformable silicates and point oxides. Contamination by oxide nonmetallic inclusions of the deposited metal is small. The presence of these non­metallic inclusions does not significantly affect the operational characteristics of the deposited layer.

EXTRACTION OF MANGANESE FROM MANGANESE ORES BY ELECTROCHEMICAL LEACHING

The basis of the traditional technology of hydrometallurgical processing of manganese ore is the process of ore roasting. The results obtained in this article make it possible to exclude the roasting process and directly leach the crushed ore under the action of an electric current. The process of electrochemical leaching includes two simultaneous operations: reduction of hard-soluble higher manganese oxides (pyrolusite - MnO2, vernadite - MnO2- nH2O) in an acid medium and transition of reduced manganese into an aqueous solution. The main part of the reduction process of higher manganese oxides proceeds in the Fe2+ ↔ Fe3+ catalytic system, the remaining part proceeds at the cathode under stirring. The degree of influence of iron (III) ions was determined. During studies on the transfer of manganese into solution from manganese ore by electrochemical leaching, the influence of L:S: ratio, sulfuric acid concentration, and cathodic current density on the degree of manganese extraction were studied. As a result of electrochemical leaching studies in the presence of the catalyst system, Fe2+ ↔ Fe3+ under optimal electrolysis parameters the degree of manganese extraction was 99%.

Redoksimorfne značajke kao pokazatelji režima vlaženja tla

Soil water regime, as one of the key components of soil fertility, refers to the quantity, retention, and movement of soil water. Rather than through expensive and/or time-consuming measurements, it can be assessed from the field-observable morphological properties in the soil profile. Excessively wetted soils have a specific morphology, and are therefore often referred to as hydromorphic. Their morphology is caused by various soil redoximorphic features (RMFs), resulting from the reduction, translocation, and oxidation of iron and manganese oxides. Hydromorphic soils largely comprise Gleysols and Stagnosols (along with Gleyic Fluvisols) that are excessively wetted by groundwater, precipitation and/or flooded water. Their morphology is often described/analyzed with different terms/criteria in line with their global distribution. This complicates the comparison and classification of such soils and thus their use or reclamation. This review paper describes and compares common RMFs and explains their formation. It then proposes the revised Croatian terms for these features, which are in line with the terms used in the international soil classification systems of WRB and/or Soil Taxonomy. Furthermore, the criteria/rules used for diagnosing RMFs when classifying hydromorphic soils are critically reviewed. Finally, it is shown that a methodologically sound RMFs description can provide a quick insight into the crucial soil water regime parameters, such as location and duration of soil saturation, the origin of the excess soil water, recentness of excessive soil wetting, etc. However, depending on the research objectives and/or actual soil conditions, field soil description cannot always fully replace continuous field monitoring of the soil water regime and/or laboratory and micromorphological soil analyses.

Distribution and sources of fatty acids in surface sediments of mangrove ecosystems in the Northern Kerala Coast, India

Fatty acids and bulk geochemical proxies were employed to understand the sources and transformation of sedimentary organic matter from surface sediments of major five mangrove systems in the northern Kerala coast. Texture, tidal rhythm and the proximity to the south eastern Arabian Sea were the main factors influencing distribution and accumulation of the organic matter in these systems. A total of 118 fatty acids were quantified and grouped into short-chain (SCFA), long-chain (LCFA), monounsaturated (MUFA), polyunsaturated (PUFA) and branched-chain (BrFA) fatty acids, hydroxy fatty acids, cyclic fatty acids, and dicarboxylic acids. The distribution of fatty acid groups was in the order SCFA > BrFA > MUFA > LCFA > PUFA. Total fatty acids (TFA) concentration exhibited profound seasonal variations and ranged from 6.25 to 580.49 μg/g (pre-monsoon > post-monsoon > monsoon except in Kadalundi which follows the reverse order). The sedimentary fatty acids in the study region reveal a wide spectrum of inputs from terrestrial, planktonic (preponderance of diatom followed by dinoflagellates along with brown algae, cyanobacteria, red algae) and bacterial sources (e.g., Desulfobulbus-type bacteria, sulfur-reducing bacteria, Sulfur-oxidizing bacteria). Significant concentrations of bacterial fatty acids suggest the functioning of an effective microbial loop and various biogeochemical pathways operating in these sediments (sulfate reduction, iron and manganese oxide reduction, etc.).

Abiotic soil properties affecting interpretation of IRIS sensors in tidal and freshwater soils

AbstractIndicator of Reduction in Soils (IRIS) films are visual sensors used to document weakly or moderately reducing conditions in soils based on the reduction and removal of brown manganese (Mn) oxide or orange iron (Fe) oxide paints, respectively, from underlying white polyvinyl chloride (PVC) films. Paint removal is largely assumed to result from anaerobic microbial reduction using metal oxides on the PVC films as electron acceptors. If true, IRIS films could indicate conditions favorable to other biogeochemical processes that occur at similar redox potentials to those facilitating paint removal. Our objective here was to assess the effects of selected abiotic soil properties on IRIS film paint removal to determine whether removal can accurately be attributed to biotic processes alone. Through field deployments and laboratory incubation experiments using IRIS films, we investigated relative sulfide concentration and dissolved organic matter as two abiotic factors potentially capable of removing paint from Mn IRIS films. Our results showed that abundance of reactive soluble sulfides cause rapid and extensive abiotic paint removal from Mn films, whereas ambient concentrations of dissolved organic matter in freshwater wetland porewater does not drive abiotic removal. Furthermore, we found that the visible formation of black iron monosulfides on Fe films can be used to detect sulfide concentrations that will remove paint from Mn films. This study suggests that whereas some abiotic soil properties (e.g., sulfide concentration) can cause paint removal, IRIS films may be a viable tool to approximate biotic process rates where abiotic paint removal can be ruled out.