ISSN:
1435-0661
Source:
Springer Online Journal Archives 1860-2000
Topics:
Geosciences
,
Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
Notes:
3 , goethite, and a subsoil low in organic C. These sorbents were equilibrated with increasing amounts of water-extractable NOM from the Oa horizon of a mor forest-floor layer and then extracted with solutions of different ionic strengths, pH, and concentrations of inorganic anions (Cl−, SO2− 4, H2PO− 4). Sorbed NOM was extracted after 24, 48, 72, and 120 h. We investigated structural and functional characteristics of the desorbed NOM by XAD-8 (macroporous resin) fractionation and by 13C-NMR spectroscopy. Desorption of NOM from minerals and soils was negligible (〈3%) under solution conditions similar to those during the sorption (hysteresis). It was not influenced by increasing concentrations of noncompeting inorganic anions such as Cl−. Increased concentrations (≤0.1 M) of competing anions like SO2− 4 or H2PO− 4 increased the NOM desorption. Though H2PO− 4 was most efficient in desorbing NOM, the extractability was only ≤60% at the highest H2PO− 4 concentration. The most significant desorption occurred when solution pH was raised. For goethite, NOM desorption reached a maximum at a pH above the point of zero charge (PZC) of the mineral. With increasing surface coverage of the sorbent by NOM, the proportion of desorbable NOM decreased for all extractants. Increased sorption hysteresis was also observed with an increasing time period between sorption and desorption. The desorption was more pronounced for NOM compounds that exhibit hydrophilic properties and have low contents of aromatic structures and carboxyl groups. The irreversible binding of NOM, especially of the lignin-derived portion, to soil minerals seems to result from its polyelectrolytic nature. This may favor the formation of multi-site coordinative bonds and effective shielding of the binding ligands by other parts of the sorbed
Type of Medium:
Electronic Resource
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