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Poster communications

Contrasted distribution of colloidal and true dissolved phosphorus in shallow groundwaters from a small, lowland agricultural

Abstract : Colloids (1~1000 nm) are major phosphorus (P) carrier phases in agricultural soils. Most studies developed so far on the role of colloids in P transport have however focused on laboratory extracted colloids with only little attention being paid to natural soil solutions. Here, we monitored P speciation in natural soil solutions along two transects in a small, agricultural catchment located in Western France, during one hydrological year. We compared the P speciation in these solutions (<0.45 µm) with that of P in lab solutions (NaCl 0.001 M) obtained from the same soil samples, using different speciation techniques, including ultrafiltration combined with inductively coupled plasma mass spectrometry (UF-ICP-MS) and XANES spectroscopy. XANES data evidenced no difference in terms of P speciation between lab extracted colloids and bulk soil samples, however revealing a strong enrichment of P in extracted colloids, thereby confirming the role of colloids as a major P carrier phase in agricultural soils. In natural soil solutions, total dissolved P concentrations (TDP) were similar in transect K and G, while molybdate reactive dissolved P (MRDP) was nearly 10 times higher in transect G than in Transect K. UF-ICP-MS data showed that the natural and lab extracted colloids consisted of a homogeneous mixture of Fe(Al)-oxides and organic matter, despite strong spatial variations of colloidal P proportion in natural waters (from 25 to 70%). Overall, transect G waters showed high proportions of truly-dissolved MRDP (up to 65%), waters in Transect K being richer in colloidal P and truly-dissolved organic P (OP). Lab extractions, however, did not reveal the same difference in P speciation, all the extracts being dominated by colloidal P and MRDP in roughly the same proportions. So far, the cause of this difference is not clearly identified. Though confirming the important role of colloids as a major P carrier phase in agricultural soils, this study indicates that natural soil solutions and lab extracts may yield different results regarding P speciation in soils, and that care should be exercised in extrapolating lab data to field situation.
Document type :
Poster communications
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https://hal-insu.archives-ouvertes.fr/insu-01242053
Contributor : Isabelle Dubigeon <>
Submitted on : Friday, December 11, 2015 - 1:38:57 PM
Last modification on : Wednesday, September 23, 2020 - 9:28:03 AM

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  • HAL Id : insu-01242053, version 1

Citation

Sen Gu, Gérard Gruau, Rémi Dupas, Camille Rivard, Chantal Gascuel-Odoux, et al.. Contrasted distribution of colloidal and true dissolved phosphorus in shallow groundwaters from a small, lowland agricultural. AGU Fall Meeting 2015, Dec 2015, San Francisco, United States. pp.H11F-1406, 2015. ⟨insu-01242053⟩

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