Composition and hydrophobic properties of organic matter in the densimetric fractions of soils from the Subpolar Urals

Natural colloid mobilization and leaching in wettable and water repellent soil under saturated condition

“…Total turbidity of the suspensions was significantly increased at these selected sampling points. Dymov et al (2015) also found that the hydrophobic property (in term of CA) for the upper mineral horizons of four studied soils were largely determined by the contents of free and occluded organic matter fractions. On the other hand, the data of 3, 4, 6 and 6.75 PVs for wettable soil (Fig.…”

“…Summarizing, at present information regarding the hydrophobity/hydrophilicity status of the suspended colloids in leachates drained to the subsurface media is scarce. Therefore, following the findings and conclusions published by Fishkis et al (2015) and Dymov et al (2015Dymov et al ( , 2017, we have the following hypothesis: i) the total amount of colloids that can be released from the soil matrix depends on soil wettability (either hydrophobic or hydrophilic), ii) colloids released from a repellent topsoil are more hydrophobic than those detached from the respective underlying wettable subsoil, because, topsoil is more influenced by higher rate of hydrophobic organic matters (Bachmann et al, 2016;Fishkis et al, 2015;Fröberg et al, 2003;Goebel et al, 2005Goebel et al, , 2011, iii) the relative amount of the hydrophobic colloids is increased by time and depended on soil carbon stock and wettability, and iv) the leached colloids may contribute differently to changes of subsoil wettability by time due to the specific hydrophilic or hydrophobic character of the colloids which is determined by the emitting soil horizon. The objectives of this study are correspondingly focused on the wetting properties of the soil and leachates: i) Comparison of the hydrophobicity status of the suspended colloids in leachates from a repellent topsoil and the respective underlying wettable subsoil under saturated conditions, ii) Evaluation of the relative amount of hydrophobic colloids from the wettable and repellent soils with leaching time, and, iii) Investigation of soil water repellency persistency in term of repellency index (RI) and contact angle (CA) changes before and after leaching.…”

“…They suggested that this could be associated partly with the composition of the horizon-specific SOM composition, but also partly due to the migration of hydrophobic components from upper soil layers with soil water transport. If the results including the CA (Table 1) and the amount of hydrophobic colloids for the wettable soil are compared with Dymov et al (2015Dymov et al ( , 2017 and Laegdsmand et al (2005), it might be assumed that the hydrophobic components in the leachate samples at 0.1 PV and 0.5 PV are likely originated from the release of larger occluded colloidal organic matter particles which were originally covered with a hydrophilic coating before the detachment from the solid interface. Experimental evidence also suggests that hydrophilic and hydrophobic components are packed side-by-side on the particle surface forming a chemically composite surface on the molecular scale (Tschapek, 1976).…”

“…Ritsema and Dekker (1998) found by using 3D-visualizations of water content and water repellency pattern that the dissolution of hydrophobic substances proceeded along flow paths which were formed by instability-driven fingered flow which rendered the soil within the pathways more wettable than the surrounding soil. In contrast, Dymov et al (2015Dymov et al ( , 2017 concluded that transport of hydrophobic components in water solutions might be the reason for an increase of subsoil water repellency.…”