scholarly journals Mobility of Iron-Cyanide Complexes in a Humic Topsoil under Varying Redox Conditions

2009 ◽  
Vol 2009 ◽  
pp. 1-6
Author(s):  
Thilo Rennert ◽  
Tim Mansfeldt
Keyword(s):  
Organic Matter ◽  
Soil Organic Matter ◽  
Redox Potential ◽  
Opposite Direction ◽  
Redox Conditions ◽  
Reductive Dissolution ◽  
Redox Processes ◽  
Iron Cyanide ◽  
Cyanide Complexes ◽  
Mn Oxides

The potentially toxic Fe-CN complexes ferricyanide,[FeIII(CN)6]3−, and ferrocyanide,[FeII(CN)6]4−, undergo a variety of redox processes in soil, which affect their mobility. We carried out microcosm experiments with suspensions of a humic topsoil (pH 5.3;Corg107 gkg-1) to which we added ferricyanide (20 mgl-1). We varied the redox potential (EH) from −280 to 580 mV by usingO2,N2and glucose. The decrease ofEHled to decreasing concentrations of Fe-CN complexes and partial reductive dissolution of (hydrous) Fe and Mn oxides. The dynamics of aqueous Fe-CN concentrations was characterized by decreasing concentrations when the pH rose and theEHdropped. We attribute these dependencies to adsorption on organic surfaces, for which such a pH/EHbehavior has been shown previously. Adsorption was reversible, because when the pH andEHchanged into the opposite direction, desorption occurred. This study demonstrates the possible impact of soil organic matter on the fate of Fe-CN complexes in soil.

The transformation and fate of silver nanoparticles in paddy soil: effects of soil organic matter and redox conditions

2017 ◽  
Vol 4 (4) ◽  
pp. 919-928 ◽  
Author(s):  
Min Li ◽  
Peng Wang ◽  
Fei Dang ◽  
Dong-Mei Zhou
Keyword(s):  
Silver Nanoparticles ◽  
Organic Matter ◽  
Soil Organic Matter ◽  
Paddy Soil ◽  
Redox Conditions ◽  
Soil P ◽  
Soil Effects

Soil OM and Eh have significant impacts on the transformation and dissolution of AgNPs in paddy soil.

Soil organic matter and phosphate sorption on natural and synthetic Fe oxides under in situ conditions

2020 ◽  
Author(s):  
Lydia Pohl ◽  
Kristof Dorau ◽  
Christopher Just ◽  
Carmen Höschen ◽  
Kristian Ufer ◽  
...  
Keyword(s):  
Organic Matter ◽  
Soil Organic Matter ◽  
Oxide Coating ◽  
Redox Status ◽  
Fe Oxide ◽  
Fe Oxides ◽  
Mn Oxide ◽  
Mn Oxides ◽  
Natural And Synthetic

<p>In redoximorphic soils, iron (Fe) and manganese (Mn) oxides undergo reduction with subsequent oxidation of their reduced counterparts (Fe<sup>2+</sup> and Mn<sup>2+</sup>) impacting nutrient sorption and the stability of soil organic matter (SOM). One tool to investigate the soil redox status is the indicator of reduction in soils (IRIS) method. Thereby, synthetic Fe and Mn oxides are coated onto polyvinyl chloride (PVC) bars, which are typically installed for an operator-defined period in the soil. After removal of the bars we studied organo-mineral associations, which have been formed under field conditions on the surface of the coated bars.</p><p>In this study, each one Mn and Fe oxide-coated redox bar were installed for 30 days in a Mollic Gleysol. A previous study revealed, that the Mn oxide coating facilitated a non-enzymatic redox reaction under anoxic conditions, while Fe<sup>2+</sup> from the soil solution is oxidized to Fe<sup>3+</sup> along the Mn oxide coating and Mn<sup>2+</sup> is removed from the PVC surface [1]. In consequence, in situ Fe oxides formed along the Mn oxide coatings and were further considered as ‘natural’ Fe oxides. This enables us to differentiate between sorption occurring onto the surfaces of ‘synthetic’ Fe oxides from the Fe bar versus ‘natural’ formed Fe oxides along the Mn bar. They were analysed by nanoscale secondary ion mass spectrometry (NanoSIMS) to study the distribution of Fe (<sup>56</sup>Fe<sup>16</sup>O<sup>−</sup>), SOM (<sup>12</sup>C<sup>14</sup>N<sup>−</sup>), and phosphorus (<sup>31</sup>P<sup>16</sup>O<sub>2</sub><sup>−</sup>). NanoSIMS is a spectromicroscopic technique offering a high lateral resolution of about 100 nm, while having a great sensitivity for light elements. In contrast to classic bulk analysis, it offers the possibility to examine the spatial distribution of SOM and phosphorous at the microscale within the intact organo-mineral matrix. </p><p>Image analysis of individual Fe oxide particles revealed a close association of Fe, SOM, and P resulting in coverage values up to 71% for synthetic and natural iron oxides. Furthermore, ion ratios between sorbent (<sup>56</sup>Fe<sup>16</sup>O<sup>−</sup>) and sorbate (<sup>12</sup>C<sup>14</sup>N<sup>−</sup>; <sup>31</sup>P<sup>16</sup>O<sub>2</sub><sup>−</sup>) were smaller along the natural oxides when compared with those for synthetic Fe oxides. We conclude that both natural and synthetic Fe oxides rapidly sequestered SOM and P (i.e., within 30 days) but that newly, natural formed Fe oxides sorbed more SOM and P than synthetic Fe oxides.</p><p> </p><p>[1] Dorau, K.; Eickmeier, M.; Mansfeldt, T. Comparison of Manganese and Iron Oxide-Coated Redox Bars for Characterization of the Redox Status in Wetland Soils. Wetlands 2016, 36, 133–144.</p>

scholarly journals Differential effects of redox conditions on the decomposition of litter and soil organic matter

2020 ◽  
Author(s):  
Yang Lin ◽  
Ashley N. Campbell ◽  
Amrita Bhattacharyya ◽  
Nicole DiDonato ◽  
Allison M. Thompson ◽  
...  
Keyword(s):  
Organic Matter ◽  
Soil Organic Matter ◽  
High Resolution Mass Spectrometry ◽  
Terrestrial Ecosystems ◽  
Plant Litter ◽  
Redox Conditions ◽  
Co2 Production ◽  
Luquillo Experimental Forest ◽  
Soil Redox ◽  
Extractable Organic Matter

Abstract. Soil redox conditions exert substantial influence on biogeochemical processes in terrestrial ecosystems. Humid tropical forest soils are often characterized by fluctuating redox dynamics, yet how these dynamics affect patterns in soil versus litter decomposition and associated CO2 fluxes is not well understood. We used a 13C-labeled litter addition to explicitly follow the decomposition of litter-derived vs. native soil-derived organic matter in response to four different soil redox regimes – static oxic or anoxic, and two oscillating treatments – in soil from the Luquillo Experimental Forest, Puerto Rico. We coupled this incubation experiment with high-resolution mass spectrometry to characterize the preferential decomposition of specific classes of organic molecules. CO2 production from litter and soil organic matter (SOM) showed distinctly different responses to redox manipulation. The cumulative production of SOM-derived CO2 was positively correlated with the length of soil exposure to an oxic headspace (r = 0.89, n = 20), whereas cumulative 13C-litter-derived CO2 production was not linked to oxygen availability. The CO2 production rate from litter was highest under static anoxic conditions in the first half of the incubation period, and later dropped to the lowest among all redox treatments. In the consistently anoxic soils, we observed the depletion of more oxidized water-extractable organic matter (especially amino sugars, carbohydrates, and proteins) over time, suggesting that under anaerobic conditions, microbes preferentially used more oxidized litter-derived compounds during the early stages of decomposition. Results from kinetic modeling showed that more frequent anoxic exposure limited the decomposition of a slow-cycling C pool, but not a fast-cycling pool. Overall, our results demonstrate that substrate source – freshly added litter vs. native organic matter – plays an important role in the redox sensitivity of organic matter decomposition. In soil environments that regularly experience redox fluctuations, anaerobic heterotrophs can be surprisingly effective in degrading fresh plant litter.

scholarly journals High-pH and anoxic conditions during soil organic matter extraction increases its electron-exchange capacity and ability to stimulate microbial Fe(III) reduction by electron shuttling

2020 ◽  
Vol 17 (3) ◽  
pp. 683-698 ◽  
Author(s):  
Yuge Bai ◽  
Edisson Subdiaga ◽  
Stefan B. Haderlein ◽  
Heike Knicker ◽  
Andreas Kappler
Keyword(s):  
Organic Matter ◽  
Soil Organic Matter ◽  
Organic Carbon ◽  
Exchange Capacity ◽  
Chemical Extraction ◽  
Redox Processes ◽  
Anoxic Conditions ◽  
Electron Shuttling ◽  
Redox Active ◽  
Water Extractable

Abstract. Soil organic matter (SOM) is redox-active, can be microbially reduced, and transfers electrons in an abiotic reaction to Fe(III) minerals, thus serving as an electron shuttle. The standard procedure to isolate organic matter (OM) from soil involves the use of alkaline and acidic solutions and the separation of humic acids (HAs) and fulvic acids (FAs). This process potentially leads to unwanted changes in SOM chemical and redox properties. To determine the effects of extraction conditions on the redox and electron-shuttling properties of SOM extracts, we prepared HA, FA, and water-extractable organic matter (OM) extracts, applying either a combination of 0.1 M NaOH and 6 M HCl or ultrapure water (pH 7), from soil samples collected from the subsoil (0–15 cm, A horizon, pH 6.5–6.8) in Schönbuch forest, Baden-Württemberg, Germany. Both chemical extractions (NaOH∕HCl) and water extractions were done in separate experiments under either oxic or anoxic conditions. Furthermore, we applied the NaOH∕HCl treatment to a subsample of the water-extractable OM to separate HA and FA from the water-extractable OM. When comparing the amount of carbon extracted from soil by different extraction methods, we found that FA and HA chemically extracted from the soil can make up to 34 %–40 % of the soil organic carbon pool while the water-extractable OM only represents 0.41 %–2.74 % of the total soil organic carbon. The higher extraction efficiency of the chemical extraction is probably due to the deprotonation of carboxyl and phenol functional groups under high pH. Anoxic extraction conditions also led to more extracted carbon. For water-extractable OM, 7 times more C was extracted under anoxic conditions compared to oxic conditions. This difference was probably due to the occurrence of microbial reduction and dissolution of Fe(III) minerals in the soil during the anoxic water extraction and thus the concomitant release of Fe(III) mineral-bound organic matter. To compare the redox activity of different SOM extracts, the electron-exchange capacity (EEC) of all extracted HA, FA, and water-extractable OM was analyzed and our results showed that, under anoxic extraction conditions, the HA chemically isolated from the water-extractable OM had 2 times higher EEC values compare to the water-extractable OM itself, suggesting the potential formation of redox-active aromatic functional groups during the extraction with NaOH under anoxic conditions by condensation reactions between amino acids, aldehydes, and hydroxyl- and catechol-containing molecules. We also performed a microbial Fe(III) reduction experiment with all extracts and found that higher EEC of extracts in turn resulted in a higher stimulation of microbial Fe(III) mineral reduction by electron shuttling, i.e., faster initial Fe(III) reduction rates, and in most cases also in higher reduction extents. Our findings suggest that OM extracted with water at neutral pH should be used to better reflect environmental SOM redox processes in lab experiments and that potential artefacts of the chemical extraction method and anoxic extraction condition need to be considered when evaluating and comparing abiotic and microbial SOM redox processes.

scholarly journals Differential effects of redox conditions on the decomposition of litter and soil organic matter

2020 ◽  
Author(s):  
Yang Lin ◽  
Ashley N. Campbell ◽  
Amrita Bhattacharyya ◽  
Nicole DiDonato ◽  
Allison M. Thompson ◽  
...  
Keyword(s):  
Organic Matter ◽  
Soil Organic Matter ◽  
High Resolution Mass Spectrometry ◽  
Terrestrial Ecosystems ◽  
Plant Litter ◽  
Redox Conditions ◽  
Luquillo Experimental Forest ◽  
Soil Redox ◽  
Slow Cycling ◽  
Extractable Organic Matter

AbstractSoil redox conditions exert substantial influence on biogeochemical processes in terrestrial ecosystems. Humid tropical forest soils are often characterized by fluctuating redox dynamics, yet how these dynamics affect patterns in soil versus litter decomposition and associated CO2 fluxes is not well understood. We used a 13C-labeled litter addition to explicitly follow the decomposition of litter-derived vs. native soil-derived organic matter in response to four different soil redox regimes—static oxic or anoxic, and two oscillating treatments—in soil from the Luquillo Experimental Forest, Puerto Rico. We coupled this incubation experiment with high-resolution mass spectrometry to characterize the preferential decomposition of specific classes of organic molecules. CO2 production from litter and soil organic matter (SOM) showed distinctly different responses to redox manipulation. The cumulative production of SOM-derived CO2 was positively correlated with the length of soil exposure to an oxic headspace (r = 0.89, n = 20), whereas cumulative 13C-litter-derived CO2 production was not linked to oxygen availability. The CO2 production rate from litter was highest under static anoxic conditions in the first half of the incubation period, and later dropped to the lowest among all redox treatments. In the consistently anoxic soils, we observed the depletion of more oxidized water-extractable organic matter (especially amino sugars, carbohydrates, and proteins) over time, suggesting that under anaerobic conditions, microbes preferentially used more oxidized litter-derived compounds during the early stages of decomposition. Results from kinetic modeling showed that more frequent anoxic exposure limited the decomposition of a slow-cycling C pool, but not a fast-cycling pool. Overall, our results demonstrate that substrate source—freshly added litter vs. native organic matter—plays an important role in the redox sensitivity of organic matter decomposition. In soil environments that regularly experience redox fluctuations, anaerobic heterotrophs can be surprisingly effective in degrading fresh plant litter.

Nickel and cadmium speciation in soils under long-term aerosol pollution

2021 ◽  
Author(s):  
Elena Fedorenko ◽  
Marina Burachevskaya ◽  
Victoria Severina ◽  
Anatoly Barakhov ◽  
Victoria Tsitsuashvili ◽  
...  
Keyword(s):  
Organic Matter ◽  
Soil Organic Matter ◽  
Power Plant ◽  
Power Plants ◽  
Emission Source ◽  
Anthropogenic Sources ◽  
Residual Fraction ◽  
Wide Range ◽  
Uncontaminated Soil ◽  
Mn Oxides

<p>Coal mining and burning are major anthropogenic sources of atmospheric particles and heavy metals (HMs) (Wang et al., 2011).Coal dust contains a wide range of metal including Ni and Cd. Sequential extractions are the most used methods to estimate the mobility of metals closely related to bioavailability. The classic sequential extraction methods by Tessier (Tessier et al., 1979) are the most popular method of HMs. The aim of this work was to study the speciation of Ni and Cd in soils under anthropogenic contamination with combustion products from the Novocherkassk power plant (NPP).</p><p>The monitoring plots were arranged along predominant wind direction at 1.6 and 15 km from the emission source. The studied soils are represented by Haplic Chernozem. The properties of the soil were: pH - 7.3-7.4; 28.6-30.9% of silt, the content of organic carbon is 3.0-3.7%; carbonates - 0.3%; content of nonsilicate Fe – 3.8-3.9%; CEC – 35-37 cmol kg<sup>–1</sup>. Areas located within 4 km from the power plants are subjected to the highest ecological disturbances; and a zone almost free from contamination is located beyond 15 km (Minkina et al., 2013).</p><p>It was found that the total content of Ni (39.0 mg kg<sup>–1</sup>) and Cd (0.1 mg kg<sup>–1</sup>) in the unpolluted soil far away from NPP (at 15 km) matching the background metal content in Haplic Chernozem was almost four times lower (145 mg kg<sup>–1</sup> and 3.8 mg kg<sup>–1</sup> accordingly) than in the soil located under the influence of aerosol emissions (at 1.6 km). In an uncontaminated soil occurring far from the emission source, 62–64% of total Ni and Cd fractions are concentrated in the residual fraction characterizing the metal bond with silicates. The following distribution of Ni among the fractions in the uncontaminated soil is noted: residual fraction > bound to organic matter > bound to Fe-Mn oxides > bound to carbonates > exchangeable. In uncontaminated soil, the following fractional distribution of Cd is observed: residual fraction> bound to Fe-Mn oxides > bound to organic matter > bound to carbonates > exchangeable.</p><p>Metals accumulate in the soil occurring near the power plant (at 1.6 km), which increases the total contents of Ni and Cd and their mobile (exchangeable and carbonate-bound) compounds in 18 and 33 times accordingly. With increasing pollution, the share of the residual fraction decreases (up to 42-47%) and the amount of the most mobile HM compounds increases. The high mobility in soils is established for Cd (exchangeable fraction was 9%). An increase in the Ni and Cd content in the soil increases its adsorption on the surface of Fe oxides (up to 20% and 27% accordingly). The role of soil organic matter in the absorption of Ni (up to 15%) is also noticeable.</p><p>Thus, the largest contributions to the adsorption and retention of metals are made by silicates, as well as nonsilicate Fe compounds for Cd and soil organic matter and nonsilicate Fe for Ni.</p><p>This work was supported by the Russian Science Foundation, project no. 19-74-00085</p>

scholarly journals Effects of extraction conditions on the redox properties of soil organic matter (SOM) and its ability to stimulate microbial iron(III) mineral reduction by electron shuttling

2019 ◽  
Author(s):  
Yuge Bai ◽  
Edisson Subdiaga ◽  
Stefan B. Haderlein ◽  
Heike Knicker ◽  
Andreas Kappler
Keyword(s):  
Organic Matter ◽  
Soil Organic Matter ◽  
Microbial Reduction ◽  
Redox Properties ◽  
Chemical Extraction ◽  
Redox Processes ◽  
Soil Extraction ◽  
Electron Shuttling ◽  
Neutral Ph ◽  
Redox Active

Abstract. Soil organic matter (SOM), including humic substances (HS), is redox-active, can be microbially reduced, and transfers electrons in an abiotic reaction to Fe(III) minerals thus serving as electron shuttle. The standard procedure to extract HS from soil and separate them into humic acids (HA) and fulvic acids (FA) involves alkaline and acidic solutions potentially leading to unwanted changes in SOM chemical and redox properties. To determine the effects of extraction conditions on the redox and electron shuttling properties of SOM extracts, we prepared HS and SOM extracts from a forest soil applying either a combination of 0.1 M NaOH and 6 M HCl, or water (pH 7). Both chemical extractions (NaOH / HCl) and water extractions were done in separate setups under either oxic or anoxic conditions. Furthermore, we applied the NaOH / HCl treatment to a subsample of the water-extracted-SOM. We found that soil extraction with NaOH lead to ca. 100 times more extracted C and the extracted HS had 2–3 times higher electron exchange capacities (EEC) than SOM extracted by water. For water-extracted SOM, anoxic extraction conditions lead to about 7 times more extracted C and 1.5 times higher EEC than under oxic extraction conditions. This difference was probably due to the occurrence of microbial reduction and dissolution of Fe(III) minerals in the soil during the water extraction at neutral pH and the concomitant release of Fe(III) mineral-bound organic matter. NaOH / HCl treatment of the water-extracted SOM lead to 2 times higher EEC values in the HA isolated from the SOM compared to the water-extracted SOM itself, suggesting the chemical treatment with NaOH and HCl caused changes of redox-active functional groups of the extracted organic compounds. Higher EEC of extracts in turn resulted in a higher stimulation of microbial Fe(III) mineral reduction by electron shuttling, i.e. faster initial Fe(III) reduction rates, and in most cases also in higher reduction extents. Our findings suggest that SOM extracted with water at neutral pH should be used to better reflect environmental SOM redox processes in lab experiments and that potential artefacts of the chemical extraction method and anoxic extraction condition need to be considered when evaluating and comparing abiotic and microbial SOM redox processes.

scholarly journals Seasonal dynamics of iron and phosphorus in reservoir sediments in Eucalyptus plantation region

2021 ◽  
Vol 10 (1) ◽  
Author(s):  
Eyram Norgbey ◽  
Yiping Li ◽  
Ya Zhu ◽  
Amechi S. Nwankwegu ◽  
Robert Bofah-Buah ◽  
...  
Keyword(s):  
Organic Matter ◽  
Sediment Concentration ◽  
Redox Conditions ◽  
Eucalyptus Plantation ◽  
Reservoir Sediments ◽  
Planar Optode ◽  
Labile P ◽  
Direct And Indirect Impacts ◽  
Indirect Impacts ◽  
Mn Oxides

Abstract Background Iron (Fe) and phosphorus (P) dynamics in sediments have direct and indirect impacts on water quality. However, the mobility of P and Fe in reservoir sediments in Eucalyptus plantation region remains unclear. This study examined P and Fe pollution in sediments in a Eucalyptus plantation region using the novel planar optode, the ZrO-Chelex DGT, and the DIFS model. Results Direct in situ investigations showed that the levels of labile P and Fe were smaller in the Eucalyptus species-dominated sediments (X2) compared to sediments without Eucalyptus species (X1). The mean concentration of labile P and Fe decreased by 25% and 42% from X1 to X2. The decrement was insignificant (p = 0.20) in the surface sediment concentration for labile P. The significant disparity for DGT-Fe (Fe2+) (p = 0.03) observed in the surface sediments could be attributed to the Eucalyptus species’ elevated organic matter (tannins) concentration at X2, which reacted and consumed labile Fe. For both regions, the maximum concentration of labile P and Fe occurred in November (autumn). The reductive decomposition of Fe/Mn oxides was recognized as the main driver for their high P efflux in July and November. Low concentration of labile P and Fe was observed in December (winter) due to the adsorption of Fe/Mn oxides. The concentration of labile Fe synchronizes uniformly with that of labile P in both sediments indicating the existence of a coupling relationship (r > 0.8, p < 0.01) in both regions. The positive diffusion fluxes in both regions suggested that the sediments release labile P and Fe. The fluxes of labile P and Fe in both regions were substantially higher (p < 0.05) in the summer (anoxic period) than winter (aerobic period), indicating that hypoxia and redox conditions influenced the seasonal efflux of labile P and Fe. From the DIFS model, the replenishment ability of reactive P was higher during the anoxic period (R = 0.7, k1 = 79.4 day− 1, k-1 = 0.2 day− 1) than the aerobic period (R = 0.4, k1 = 14.2 day− 1, k-1 = 0.1 day− 1), suggesting that oxygen inhibited the efflux of P in the sediments. Conclusion Our results indicated that hypoxia, Eucalyptus species (organic matter (tannins)), and redox conditions influenced the seasonal mobility of sediment labile P and Fe. Our findings provided an insight into the mobility of labile P and Fe in Eucalyptus-dominated sediments and, moreover, serves as a reference for developing future studies on Eucalyptus-dominated sediments.

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