Effect of multivalent cations, temperature and aging on soil organic matter interfacial properties

Abstract

Environmental context The supramolecular structure and resulting physicochemical properties of soil organic matter (SOM) significantly control storage and buffer functions of soils, e.g. for nutrients, organic molecules and water. Multivalent cations, able to form complexes, are suggested to form inter- and intramolecular cross-links in SOM. At present, specific effects of the valence and type of cation on SOM properties are incompletely understood. We investigated changes in SOM interfacial properties, its ability to release mobile colloids in aqueous solutions and its sorption affinity towards organic chemicals in dependence on cation–SOM interactions, temperature and aging time. Abstract The present study aims to improve our understanding on the effect of multivalent cations, temperature treatment and isothermal aging time on interfacial soil organic matter (SOM) properties as major factors that modify its supramolecular structures. A sandy topsoil (LW) and a peat soil (SP) were enriched with Na, Ca or Al, or desalinated in a batch experiment, treated at 25, 40, 60 and 105°C and aged at constant temperature and humidity (20°C, 31% relative humidity). After aging for different periods, contact angles (CAs), sorption properties towards xenobiotics and properties of water dispersible colloids were determined. With increasing valence of the dominant cations fewer and larger colloids were observed, probably attributable to cation cross-links or enhanced aggregation caused by reduced surface charge. Al-enrichment of LW resulted in more abundant or more accessible sorption sites for hydrophobic xenobiotics. But in contrast to expectations, hydrophilic sorption as well as wettability was not significantly affected by the type of adsorbed cation. Increasing the temperature had a major effect on surface properties resulting in rising surface hydrophobisation with increasing solid–water CAs, decreasing surface O/C ratio and decreasing sorption of hydrophilic substances; whereas systematic temperature effects on water dispersible colloids and on hydrophobic sorption were not detected. Aging was found to increase the initial CA of the 25°C treatment and to increase the sorption of phenanthrene to LW for all treatment temperatures. We conclude that aging of SOM is a process that changes surface properties and approaches a new equilibrium state after a disturbance. The aging process may be significantly accelerated for samples treated at elevated temperatures.

Considerations on cross‐linking by bivalent cations in soil organic matter with low exchange capacity

“…By this procedure, we aimed to remove as many as possible cations from the sample. The resin was used in a number of studies before (Kunhi Mouvenchery et al, 2013;Schaumann et al, 2013b;Diehl et al, 2014a;2014b). In preliminary experiments on a peat (Kunhi Mouvenchery et al, 2013), no relevant release of organic carbon from the resin was observed.…”

Soil water repellency changes with depth and relationship to physical properties within wettable and repellent soil profiles

“…Persistence and severity of soil water repellency can be extremely variable and this has been extensively studied to compare impacts of different land uses, fire and vegetation (Beatty and Smith, 2014;Jordán et al, 2011;Lichner et al, 2012Lichner et al, , 2013 on surface spatial variability (Diehl et al, 2014;Doerr et al, 2007;Orfánus et al, 2008). Depth dependent changes of SWR have been also investigated (Dekker et al, 2001), but studies on the variation of the extent and persistence of SWR and its relevance to hydrophysical properties throughout the soil profile are limited.…”

Occurrence and spatial pattern of water repellency in a beech forest subsoil

“…However, in case of more complex systems such as unfractionated soil, corresponding effects could not be clearly verified. In a recent study by Diehl et al (2014) -treated samples could not be reproduced. On the other hand, in a study by Woche et al (2005), analyzing several arable and forest soils ranging from pH 3.0 to 6.8, a significant inverse correlation between CA and pH was found which is in agreement with the general tendency found for the topsoils of this study.…”

“…Šolc et al (2015) further showed that decreasing concentration of hydroxyl groups leads to increasing hydrophobicity and larger CA in the same way as predicted by the FT-IR study by Ellerbrock et al (2005) for more complex soil particle surfaces. Diehl et al (2014) showed preliminary results to relate surface elemental composition in the interface of about 1 nm depth with WR using X-ray photoelectron spectroscopy (XPS). Results show that the element ratio of O to C was related to WR, hence the chemical composition of the thin interface governs particle wettability.…”