| 1. |
- Adediran, Gbotemi A., et al.
(författare)
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Phosphorus in 2D : Spatially resolved P speciation in two Swedish forest soils as influenced by apatite weathering and podzolization
- 2020
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Ingår i: Geoderma. - : Elsevier BV. - 0016-7061 .- 1872-6259. ; 376
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Tidskriftsartikel (refereegranskat)abstract
- The cycling and long-term supply of phosphorus (P) in soils are of global environmental and agricultural concern. To advance the knowledge, a detailed understanding of both the vertical and lateral variation of P chemical speciation and retention mechanism(s) is required, a knowledge that is limited in postglacial forest soils. We combined the use of synchrotron X-ray fluorescence microscopy with multi-elemental co-localisation analysis and P K-edge XANES spectroscopy to reveal critical chemical and structural soil properties. We established a two-dimensional (2D) imagery of P retention and speciation at a microscale spatial resolution in two forest soil profiles formed in glaciofluvial and wave-washed sand. The abundance and speciation of P in the upper 40 cm was found to be influenced by soil weathering and podzolization, leading to spatial variability in P speciation on the microscale (< 200 pm) with P existing predominantly as organic P and as PO4 adsorbed to allophane and ferrihydrite, according to XANES spectroscopy. These species were mostly retained at sharp edges and in pore spaces within Al and Si-bearing particles. Despite the relatively young age ( < 15,000 years) of the soils, our results show primary mineral apatite to have weathered from the surface horizons. In the C horizon however, a large fraction of the P was in the form of apatite, which appeared as widely dispersed ( > 600 pm) hot spots of inclusions in aluminosilicates or as discrete micro-sized apatite grains. The subsoil apatite represents a pool of P that trees can potentially acquire and thus add to the biogeochemically active P pool in temperate forest soils.
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| 2. |
- Aullón Alcaine, Anna, et al.
(författare)
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Hydrogeochemical controls on the mobility of arsenic, fluoride and other geogenic co-contaminants in the shallow aquifers of northeastern La Pampa Province in Argentina
- 2020
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Ingår i: Science of the Total Environment. - : Elsevier. - 0048-9697 .- 1879-1026. ; 715
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Tidskriftsartikel (refereegranskat)abstract
- Elevated Arsenic (As) and Fluoride (F) concentrations in groundwater have been studied in the shallow aquifers of northeastern of La Pampa province, in the Chaco-Pampean plain, Argentina. The source of As and co-contaminants is mainly geogenic, from the weathering of volcanic ash and loess (rhyolitic glass) that erupted from the Andean volcanic range. In this study we have assessed the groundwater quality in two semi-arid areas of La Pampa. We have also identified the spatial distribution of As and co-contaminants in groundwater and determined the major factors controlling the mobilization of As in the shallow aquifers. The groundwater samples were circum-neutral to alkaline (7.4 to 92), oxidizing (Eh similar to 0.24 V) and characterized by high salinity (EC = 456-11,400 mu S/cm) and Na+-HCO3- water types in recharge areas. Carbonate concretions ("tosca") were abundant in the upper layers of the shallow aquifer. The concentration of total As (5.6 to 535 mu g/L) and F (0.5 to 14.2 mg/L) were heterogeneous and exceeded the recommended WHO Guidelines and the Argentine Standards for drinking water. The predominant As species were arsenate As(V) oxyanions, determined by thermodynamic calculations. Arsenic was positively correlated with bicarbonate (HCO3-), fluoride (F), boron (B) and vanadium (V), but negatively correlated with iron (Fe), aluminium (Al), and manganese (Mn), which were present in low concentrations. The highest amount of As in sediments was from the surface of the dry lake. The mechanisms for As mobilization are associated with multiple factors: geochemical reactions, hydrogeological characteristics of the local aquifer and climatic factors. Desorption of As(V) at high pH, and ion competition for adsorption sites are considered the principal mechanisms for As mobilization in the shallow aquifers. In addition, the long-term consumption of the groundwater could pose a threat for the health of the local community and low cost remediation techniques are required to improve the drinking water quality.
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| 3. |
- Baken, Stijn, et al.
(författare)
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The association between iron and carbon in freshwater colloids
- 2013
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Konferensbidrag (refereegranskat)abstract
- Iron and carbon are important constituents of natural colloids, which intimately links the fate of these two elements in riverine systems. Iron may strongly affect the binding of trace metals by organic matter, e.g. through competition for binding sites, which highlights the importance of a correct appreciation of the Fe speciation in surface waters. However, the chemistry of Fe and C in natural colloids is complex and depend on many factors including the pH, the Fe:C ratio, and the redox speciation of Fe [1-3]. Two areas with a contrasting Fe chemistry were studied: a lowland area with widespread seepage of iron-rich groundwater, and an upland peat area. Samples of ten oxic, well-mixed streams were subjected to cascade filtration using conventional filtration (1.2 µm, 0.45 µm, 0.1 µm) and cross-flow ultrafiltration (CFF; 5 kDa). The colloidal fraction, here operationally defined as between 0.45 µm and 5 kDa, was isolated by CFF and subsequently freeze-dried. The speciation of colloidal Fe was determined by EXAFS spectroscopy at the Fe K-edge (MAX-lab, Lund, Sweden). In the rivers draining upland peat, Fe and C were predominantly recovered in the fraction between 5 kDa and 0.1 µm. Conversely, in the rivers draining the lowland with extensive seepage of iron-rich groundwater, Fe was most abundant in the > 0.1 µm fraction, whereas C was predominantly present < 0.1 µm. The EXAFS data reveal that colloidal Fe speciation is different in both study areas. It exists as mononuclear Fe complexed by dissolved organic matter, as colloidal hydrous ferric oxides (likely stabilized by adsorbed organic matter), or as a mixture of these. The colloidal Fe concentrations show considerable seasonal variability. Overall, this study contributes to a better understanding of colloidal Fe speciation and of its interaction with organic C.
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| 4. |
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| 5. |
- Biswas, Ashis, et al.
(författare)
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Estimating the role of competing ions on the arsenic mobilization processes in the aquifers of Bengal Basin by surface complexation modeling
- 2013
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Konferensbidrag (refereegranskat)abstract
- This study investigates the relative roles of the different competing ions on the arsenic (As) mobilization in the sedimentary aquifers of Bengal basin by surface complexation modeling of the temporal varaibility of As in shallow (<50 m) groundwater. Two sets of piezometers (2×5 = 10), installed at the two sites with relatively contrasting dissolved As concentration in groundwater, were monitored bi-weekly for As and other hydrogeochemical parameters over a period of 20 months. The estimation of the standard deviation (SD) for As(III) reflects strong temporal variation (SD ≥10 μg/L) in all the piezometers of two sites over the monitoring period. Particularly, the variation is more prominent in the shallowest part of the aquifer, where the site specific cyclic trends are evident. While, As(V) shows significant temporal variation in the piezometers of high As site only and no specific trend is reflected in the variation.Two different surface complexation models (SCMs), developed for ferrihydrite and goethite have been explored to account for the observed temporal variation in As(III) and As(V) concentrations. The SCM for ferrihydrite has provided the better estimation for both As(III) and As(V) variations.Among the different competing ions, PO43- appears as the major competitor of As(III) and As(V) adsorption onto ferrihydrite and the competition ability decreases in the order PO43- >> Fe(II) > H4SiO4 = HCO3-. It is further revealed that a small decrease in pH significantly increases the concentration of As(III) and decreases the As(V) concentration and vice versa. The present study suggests that the reductive dissolution of Fe oxyhydroxides alone cannot explain the observed high As concentration in groundwater of the sedimentary aquifers. Perhaps, the reductive dissolution of Fe oxyhydroxides followed by competitive sorption reactions with the aquifer sediment is the processes conducive for As enrichment in the groundwater of Bengal basin.
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| 6. |
- Biswas, Ashis, et al.
(författare)
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Surface complexation modeling of temporal variability of arsenic in groundwater : Estimating the role of competing ions in the mobilization processes
- 2013
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Konferensbidrag (refereegranskat)abstract
- This study investigates the relative roles of different competing ions on the mobilization of arsenic (As) by surface complexation modeling of As rich groundwater in the aquifer of Bengal Basin. Two sets of piezometers, installed at different depths of the shallow aquifer (<50 m), have been monitored for As and other relevant hydrogeochemical parameters over a period of 20 months. The potentiality of two different surface complexation models (SCM), developed for ferrihydrite and goethite has been explored to account for the observed temporal variation in As(III) and As(V) concentration in groundwater. The SCM for ferrihydrite appears as the better predictor for the observed variation in both As(III) and As(V) concentration. It is estimated that among the competing ions PO43- is the major competitor of As(III) and As(V) adsorption into Fe oxyhydroxide and competing ability of the ions decreases as PO43- >> Fe(II) > H4SiO4 = HCO3-. The result of sensitivity test indicates that the competition of PO43- with As for the adsorption sites might already reach nearly to the stage of maxima. It is also shown that a slight increase or decrease in pH can have overwhelming effect on the mobility of As(III) and As(V) by changing their concentration oppositely. It appears that only the reductive dissolution of Fe oxyhydroxide cannot explain the observed high As concentration in the groundwater of Bengal Basin. In absence of potential competition for the adsorption sites, As released due to reductive dissolution of Fe oxyhydroxide would have been re-adsorbed into the residual Fe phases. This study suggests that the reductive dissolution of Fe oxyhydroxide followed by competitive ion exchange with the aquifer sediment is the processes conducive for As enrichment in groundwater of the sedimentary aquifers.
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| 7. |
- Braun, Sabina, et al.
(författare)
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Assessing the ability of soil tests to estimate labile phosphorus in agricultural soils : Evidence from isotopic exchange
- 2019
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Ingår i: Geoderma. - : Elsevier. - 0016-7061 .- 1872-6259. ; 337, s. 350-358
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Tidskriftsartikel (refereegranskat)abstract
- Efficient phosphorus (P) fertilization strategies are essential for intensive crop production with minimal negative environmental impacts. A key factor in sustainable P use is assessment of the plant available soil P pool using soil P tests. This study determined isotopically exchangeable P after six days of reaction with 33PO4 (P-E (6 d)) to determine how accurately two commonly used P tests, Olsen and AL (acid ammonium acetate lactate) can quantify the amount of labile P. Soil samples were taken from both highly P-amended and unamended plots at six sites within the Swedish long-term soil fertility experiments. According to P K-edge XANES spectroscopy, the P speciation was dominated by Al-bound P and organic P, with additional contributions from Fe-bound P and Ca phosphates in most soils. The results showed that the AL test overestimated P-E (6 d) by a factor of 1.70 on average. In contrast, the Olsen test underestimated P-E (6 d), with the mean ratios of P-Olsen to P-E (6 d) being 0.52 for high-P and 0.19 for low-P soils. The 33P/31P ratio in the Olsen extract of a 33PO4 spiked soil was closer to that of a 0.005 mol L−1 CaCl2 soil extract than the corresponding ratio in the AL extract, suggesting that AL extraction solubilized more non-labile P. In conclusion, the AL and Olsen methods are not suitable for direct quantification of the isotopically exchangeable soil P pool after 6 days of equilibration. However, based on the results, Olsen may be superior to AL for classification of soil P status, due to its even performance for calcareous and non-calcareous soils and lower extraction of non-labile P.
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| 8. |
- Braun, Sabina, et al.
(författare)
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Phosphorus desorption and isotope exchange kinetics in agricultural soils
- 2020
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Ingår i: Soil use and management. - : Wiley. - 0266-0032 .- 1475-2743.
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Tidskriftsartikel (refereegranskat)abstract
- To improve phosphorus (P) fertilization and environmental assessments, a better understanding of release kinetics of solid-phase P to soil solution is needed. In this study, Fe (hydr)oxide-coated filter papers (Fh papers), isotopic exchange kinetics (IEK) and chemical extractions were used to assess the sizes of fast and slowly desorbing P pools in the soils of six long-term Swedish field experiments. The P desorption data from the Fh-paper extraction of soil (20 days of continual P removal) were fitted with the Lookman two-compartment desorption model, which estimates the pools of fast (Q1) and slowly (Q2) desorbing P, and their desorption rates k1 and k2. The amounts of isotope-exchangeable P (E) were calculated (E1min to E>3 months) and compared with Q1 and Q2. The strongest relationship was found between E1 min and Q1 (r2 =.87, p <.01). There was also an inverse relationship between the IEK parameter n (the rate of exchange) and k1 (r2 =.52, p <.01) and k2 (r2 =.52, p <.01), suggesting that a soil with a high value of n desorbs less P per time unit. The relationships between these results show that they deliver similar information, but both methods are hard to implement in routine analysis. However, Olsen-extractable P was similar in magnitude to Q1 (P-Olsen = 1.1 × Q1 + 2.3, r2 =.96), n and k1 were related to P-Olsen/P-CaCl2, while k2 was related to P-oxalate/P-Olsen. Therefore, these extractions can be used to estimate the sizes and desorption rates of the different P pools, which could be important for assessments of plant availability and leaching.
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| 9. |
- Campos Pereira, H., et al.
(författare)
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Sorption of perfluoroalkyl substances (PFASs) to an organic soil horizon – Effect of cation composition and pH
- 2018
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Ingår i: Chemosphere. - : Elsevier. - 0045-6535 .- 1879-1298. ; 207, s. 183-191
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Tidskriftsartikel (refereegranskat)abstract
- Accurate prediction of the sorption of perfluoroalkyl substances (PFASs) in soils is essential for environmental risk assessment. We investigated the effect of solution pH and calculated soil organic matter (SOM) net charge on the sorption of 14 PFASs onto an organic soil as a function of pH and added concentrations of Al3+, Ca2+ and Na+. Often, the organic C-normalized partitioning coefficients (KOC) showed a negative relationship to both pH (Δlog KOC/ΔpH = −0.32 ± 0.11 log units) and the SOM bulk net negative charge (Δlog KOC = −1.41 ± 0.40 per log unit molc g−1). Moreover, perfluorosulfonic acids (PFSAs) sorbed more strongly than perfluorocarboxylic acids (PFCAs) and the PFAS sorption increased with increasing perfluorocarbon chain length with 0.60 and 0.83 log KOC units per CF2 moiety for C3–C10 PFCAs and C4, C6, and C8 PFSAs, respectively. The effects of cation treatment and SOM bulk net charge were evident for many PFASs with low to moderate sorption (C5–C8 PFCAs and C6 PFSA). However for the most strongly sorbing and most long-chained PFASs (C9–C11 and C13 PFCAs, C8 PFSA and perfluorooctane sulfonamide (FOSA)), smaller effects of cations were seen, and instead sorption was more strongly related to the pH value. This suggests that the most long-chained PFASs, similar to other hydrophobic organic compounds, are preferentially sorbed to the highly condensed domains of the humin fraction, while shorter-chained PFASs are bound to a larger extent to humic and fulvic acid, where cation effects are significant.
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| 10. |
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