Phosphorus in sequentially extracted fen peat soils: A K‐edge X‐ray absorption near‐edge structure (XANES) spectroscopy study |
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Authors: | Jens Kruse Peter Leinweber |
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Affiliation: | University of Rostock, Faculty of Agricultural and Environmental Sciences, Institute for Land Use, Justus‐von‐Liebig Weg 6, 18059 Rostock, Germany |
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Abstract: | The speciation of phosphorus (P) in native and degraded peat soils is an analytical challenge, and synchrotron‐based P K‐edge X‐ray absorption near‐edge structure (XANES) is a suitable method to gain information on P species in soils and organic materials. The objective of the present study was to test if P K‐edge XANES reflected differences in P fractions in fen peat due to sequential extraction and peat degradation. We investigated each one top‐ and subsoil sample of a Fibric Histosol, which differed in the degree of humification (H8 vs. H5) and concentration of total P (Pt) (1944 mg kg–1 vs. 436 mg kg–1). In the topsoil, residual P, H2SO4‐P, and NaOH‐P accounted for roughly the same proportions of Pt (≈30%). In the subsoil, residual P (64% of Pt) was more abundant than NaOH‐P (21% of Pt) and H2SO4‐P (10% of Pt). Among many different P reference standards, the P XANES spectra reflected differences in mineral P more distinctive than in organic P compounds. Phosphorus XANES spectra of the residues after each sequential extraction step all showed a prominent white‐line peak at around 2152 eV. Stepwise removal of resin‐P, NaHCO3‐P, and NaOH‐P were reflected mainly by the peak intensity but scarcely by distinct spectral features. Extraction with H2SO4 led to the disappearance of spectral features of Ca and Mg phosphates which is a first direct hint to these compounds in the peat. In conclusion, a combined sequential fractionation and spectroscopic (31P NMR, P K‐ and L‐edge XANES with linear‐combination fits) approach is proposed to overcome limitations of the present study and gain more insight into the P species in peat soils. |
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Keywords: | synchrotron XANES P K‐edge Hedley fractionation phosphorus histosol fen peat |
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