| 1. |
- Eriksson, Ann Kristin, et al.
(author)
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Evolution of phosphorus speciation with depth in an agricultural soil profile
- 2016
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In: Geoderma. - : Elsevier. - 0016-7061 .- 1872-6259. ; 280, s. 29-37
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Journal article (peer-reviewed)abstract
- With time, different soil-forming processes such as weathering, plant growth, accumulation of organic matter, and cultivation are likely to affect phosphorus (P) speciation. In this study, the depth distribution of P species was investigated for an agricultural clay soil, Lanna, Sweden. Small amounts of apatite-P was demonstrated in the topsoil whereas the speciation of Pat 70-100 cm depth consisted of approximately 86% apatite according to P K-edge XANES (X-ray absorption near-edge structure) spectroscopy. Because there were only minor differences in bulk mineralogy and texture, these variations in P speciation were interpreted as the result of apatite weathering of the topsoil. Speciation modeling on soil extracts supported this idea: hydroxyapatite was not thermodynamically stable in the top 50 cm of the soil. Apatite was enriched in the bulk soil relative to the clay fraction, as expected during apatite dissolution. Combined results from batch experiments, XANES spectroscopy and X-ray diffraction suggested chemical transformations of the topsoil as a result from accumulation of organic matter and airing from tillage followed by enhanced weathering of apatite, amphiboles, clay minerals, and iron oxides. This caused the formation of poorly crystalline secondary iron and aluminum (hydr)oxides in the topsoil, which retained part of the released P from apatite. Other P was incorporated into organic forms. Furthermore, the results also showed that short-term acidification below the current pH value (below 5.5 in the topsoil and 7.2 in the deeper subsoil) caused significant solubilization of P. This is attributed to two different mechanisms: the instability of Al-containing sorbents (e.g. Al hydroxides) at low pH (in the topsoil), and the acid-mediated dissolution of apatite (the subsoil).
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| 2. |
- Eriksson, Ann Kristin, et al.
(author)
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Phosphorus dynamics in Swedish agricultural soils as influenced by fertilization and mineralogical properties : Insights gained from batch experiments and XANES spectroscopy
- 2016
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In: Science of the Total Environment. - : Elsevier. - 0048-9697 .- 1879-1026. ; 566, s. 1410-1419
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Journal article (peer-reviewed)abstract
- The soil chemistry of phosphorus (P) is important for understanding the processes governing plant availability as well as the risk of environmental losses of P. The objective of this research was to investigate both the speciation and the pH-dependent solubility patterns of P in clayey agricultural soils in relation to soil mineralogy and fertilization history. The study focused on soil samples from six fields that were subjected to different P fertilization regimes for periods of 45 to 57 years. Soil P speciation was analyzed by P K-edge XANES spectroscopy and chemical fractionation, sorption isotherms were constructed, and dissolved P was measured as a function of pH. The XANES fitting results showed that organic P and P adsorbed to Fe and Al (hydr) oxides were common P constituents in all soils. Calciumphosphateswere identified in five of six soil samples. The XANES results also indicated an increase in P adsorbed to Al and to a lesser extent Fe (hydr) oxides as a result of fertilization. Moreover, the fluorescence intensity from the P K-edge XANES analysis was most strongly correlated with HCl-digestible P (r = 0.81***). Consistent with the XANES analysis, laboratory sorption isotherm models showed that the Freundlich sorption coefficient (K-F) was most closely related to oxalate-extractable Al. Greater proportions of Ca phosphate in two of the heavily fertilized soils in combination with enhanced PO4 solubilization upon sample acidification indicated neoformation of Ca-phosphate precipitates. The results for the unfertilized soil samples generally showed a minimum in dissolved PO4 between pH 6.5 and 7.5, with increases particularly at lower pH. This behavior can be explained either by the dissolution of Al-hydroxide-type sorbents or Ca phosphates at lower pH. In fertilized soils, there was no consistent trend in pH-dependent solubilization of P, with a complex relationship to solid-phase speciation. To conclude, inorganic P species changed most dynamically in agricultural clay soils over a period of several decades, and the role of pH in the solubilization of P depended mainly on P fertilization history and the content of reactive Ca phosphates.
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| 3. |
- Eriksson, Ann Kristin, et al.
(author)
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Phosphorus speciation of clay fractions from long-term fertility experiments in Sweden
- 2015
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In: Geoderma. - : Elsevier. - 0016-7061 .- 1872-6259. ; 241, s. 68-74
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Journal article (peer-reviewed)abstract
- Phosphorus (P) losses from agricultural soils constitute a main driver for eutrophication of the Baltic Sea. There is limited knowledge about sorption and release processes of P in these soils, especially concerning the effects of fertilization. In this study, P speciation of the clay fractions from six different soils in long-term fertility experiments in Sweden was investigated by P K-edge XANES spectroscopy. As expected, unfertilized soils had lower concentrations of acid-digestible P compared with fertilized soils. Based on best-fit standards that emerged from linear combination fitting (LCF) of XANES spectra, phosphate sorbed on iron (Fe) (hydr)oxides was a dominant P species in clay fractions from unfertilized soils containing more than 35 mmol kg(-1) of oxalate-extractable Fe. In contrast, P sorbed on aluminum (Al) (hydr)oxides predominated in soils with lower concentrations of oxalate-extractable Fe. A greater proportion of organically bound P was fit for soil samples containing >2% organic carbon. The soils included one calcareous soil for which a greater proportion of P was fit as apatite. After long-term fertilization, P had accumulated mainly as P adsorbed to Al (hydr) oxides according to the XANES analysis. Our research shows that P speciation in fertilized agricultural soils depended on the level of P buildup and on the soil properties.
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| 4. |
- Eveborn, David, et al.
(author)
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XANES Speciation of P in Environmental Samples : An Assessment of Filter Media for on-Site Wastewater Treatment
- 2009
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In: Environmental Science and Technology. - Washington, DC : American Chemical Society (ACS). - 0013-936X .- 1520-5851. ; 43:17, s. 6515-6521
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Journal article (peer-reviewed)abstract
- X-ray absorption near edge structure (XANES) spectroscopyis a useful technique for characterization of chemical speciesof phosphorus in complex environmental samples. To developand evaluate bed filters as sustainable on-site wastewater treatment solutions, our objective in this study was to determine the chemical forms of accumulated phosphorus in a selectionof promising filter materials: Filtralite P, Filtra P, Polonite, Absol, blast furnace slag, and wollastonite. Full-scale operational wastewater-treatment systems were sampled and in addition, filter samples collected from laboratory studies provided access to additional media and complementary samples.Phosphorus species were characterized using phosphorus K-edge XANES spectroscopy, complemented by X-ray powder diffraction (XRPD) and attenuated total reflectance Fouriertransform infrared spectroscopy (ATR-FTIR). No systematic differences could be seen in the results between laboratory and full-scale samples. All six filter media contained significant amounts of crystalline calcium phosphates. Some samples also contained amorphous calcium phosphate (>60 % of totalP in Absol). In Filtralite P and blast furnace slag, more than 35 % of the accumulated phosphorus was associated with Fe or Al. Both the power and shortcomings of XANES analysis for characterizing P species in these filter media are discussed.
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| 5. |
- Gustafsson, Jon Petter, 1964-, et al.
(author)
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A Probabilistic Approach to Phosphorus Speciation of Soils Using P K-edge XANES Spectroscopy with Linear Combination Fitting
- 2020
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In: Soil systems. - : MDPI. - 2571-8789. ; 4:2
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Journal article (peer-reviewed)abstract
- A common technique to quantitatively estimate P speciation in soil samples is to apply linear combination fitting (LCF) to normalized P K-edge X-ray absorption near-edge structure (XANES) spectra. Despite the rapid growth of such applications, the uncertainties of the fitted weights are still poorly known. Further, there are few reports to what extent the LCF standards represent unique end-members. Here, the co-variance between 34 standards was determined and their significance for LCF was discussed. We present a probabilistic approach for refining the calculation of LCF weights based on Latin hypercube sampling of normalized XANES spectra, where the contributions of energy calibration and normalization to fit uncertainty were considered. Many of the LCF standards, particularly within the same standard groups, were strongly correlated. This supports an approach in which the LCF standards are grouped. Moreover, adsorbed phytates and monetite were well described by other standards, which puts into question their use as end-members in LCF. Use of the probabilistic method resulted in uncertainties ranging from 2 to 11 percentage units. Uncertainties in the calibrated energy were important for the LCF weights, particularly for organic P, which changed with up to 2.7 percentage units per 0.01 eV error in energy. These results highlight the necessity of careful energy calibration and the use of frequent calibration checks. The probabilistic approach, in which at least 100 spectral variants are analyzed, improves our ability to identify the most likely P compounds present in a soil sample, and a procedure for this is suggested in the paper.
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| 6. |
- Olsson, Rickard, 1969-
(author)
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Surface reactions on mineral particles controlling the hydrolysis of glucose phosphates
- 2011
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Doctoral thesis (other academic/artistic)abstract
- Phosphorus (P) is an essential nutrient. A significant amount of soil P may be in the form of organophosphates. Due to the size of these compounds, hydrolysis is often required before P can be assimilated by organisms. Hydrolysis may be mediated by mineral surfaces, or catalyzed by extra cellular enzymes. Since both organophosphates and enzymes have a strong affinity for environmental particles, a study of the hydrolysis of organophosphates must focus on reactions at the water/particle interface. This thesis is a summary of four papers, discussing the adsorption, desorption, and abiotic and enzymatic hydrolysis of glucose-1-phosphate (G1P) and glucose-6-phosphate (G6P) in aqueous goethite suspensions. A new technique for simultaneous infrared and potentiometric titrations (SIPT) allowed in-situ measurements of the interfacial reactions. It was found that glucose phosphates form pH-dependent inner sphere complexes on goethite, which coordinate in a monodentate fashion, and are stabilized by hydrogen bonding. Desorption involves a change in speciation of the surface complexes, illustrating the difficulty in determining desorption rates for individual complexes. The surface mediated hydrolysis is primarily base catalyzed for G1P, and acid catalyzed for G6P. The difference is partly due to electronic factors, and partly to differences in glucose group/goethite interactions. Considerably more extensive is the hydrolysis catalyzed by an acid phosphatase (AcPase). The rate of the enzymatic hydrolysis are strongly dependent on the glucose phosphate surface coverage, showing that surface properties affect the adsorption mode of enzymes, and thus their catalytic activity. In solution, AcPase showed a greater specificity towards G6P, but this specificity was partly lost after adsorption onto goethite.
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| 7. |
- Sjöstedt, Carin, 1981-, et al.
(author)
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Iron speciation in soft-water lakes and soils as determined by EXAFS spectroscopy and geochemical modelling
- 2013
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In: Geochimica et Cosmochimica Acta. - : Elsevier BV. - 0016-7037 .- 1872-9533 .- 0046-564X. ; 105, s. 172-186
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Journal article (peer-reviewed)abstract
- Complexation of iron by organic matter can potentially compete with toxic metals for binding sites. Iron(III) forms both monomeric and di/trimeric complexes with fulvic and humic acids, but the nature and extent of complexation with natural organic matter samples from soft-water lakes has not been extensively studied. The aim of this study was to determine the coordination of iron in complexes with organic matter in two soft-water lakes and in the surrounding Oe soil horizons. Iron K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy was performed on particles and large colloids (>0.45. μm) collected by in-line pre-filtration, and on smaller colloids isolated both on an AGMP-1 anion-exchange column and by concentration using 1000. Da ultrafiltration. The results showed that iron(III) was mainly present in monomeric complexes with organic matter, both in the lake water smaller colloids and in the soil samples. Evidence for iron(III) (hydr)oxides was found for the lake particles, in the ultrafiltration retentates, and in some of the soils. Overall, the results suggest that complexation of iron(III) to organic matter prevents hydrolysis into polymeric forms. Strong complexation of iron(III) would lead to competition with other metals for organic-matter binding sites.
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