TY - JOUR

T1 - Natural colloid mobilization and leaching in wettable and water repellent soil under saturated condition

AU - Sepehrnia, Nasrollah

AU - Fishkis, Olga

AU - Huwe, Bernd

AU - Bachmann, Jörg

N1 - Funding information: We thank Andreas Kolb and Michael Wachten for their helps with preparing staff and soil sampling, and the German Academic Exchange Service (DAAD) for partial financial support of this project. We appreciate the valuable manuscript reviews provided by Professor Mark Coyne from the University of Kentucky, USA Acknowledgements.

PY - 2018/9

Y1 - 2018/9

N2 - The coupled transport of pollutants that are adsorbed to colloidal particles has always been a major topic for environmental sciences due to many unfavorable effects on soils and groundwater. This laboratory column study was conducted under saturated moisture conditions to compare the hydrophobic character of the suspended and mobilized colloids in the percolates released from a wettable subsoil and a water repellent topsoil. Both soils with different organic matter content were analyzed for wettability changes before and after leaching using sessile drop contact angles as well as water and ethanol sorptivity curves, summarized as repellency index. Hydrophobicity of the effluent suspensions was assessed using the C18 adsorption method. Water repellency level of the repellent soil decreased after leaching but remained on a lower level of water repellency, while, the wettable soil remained wettable. The leached colloids from the repellent soil were predominantly hydrophilic and the percentage of the hydrophobic colloid fraction in the effluent did not systematically changed with time. Total colloid release depended on soil carbon stock but not on soil wettability. Our results suggest that due to the respective character of transported colloids a similar co-transport mechanism for pollutants may occur which does not depend explicitly on soil wettability of the releasing horizon, but could be more affected by total SOM content. Further studies with a wider range of soils are necessary to determine if the dominant hydrophilic character of leached colloids is typical. Due to the mostly hydrophilic colloid character we conclude also that changes in wettability status, i.e. of wettable subsoil horizons due to the leachate, may not necessarily occur very fast, even when the overlaying topsoil is a repellent soil horizon with a high organic matter content.

AB - The coupled transport of pollutants that are adsorbed to colloidal particles has always been a major topic for environmental sciences due to many unfavorable effects on soils and groundwater. This laboratory column study was conducted under saturated moisture conditions to compare the hydrophobic character of the suspended and mobilized colloids in the percolates released from a wettable subsoil and a water repellent topsoil. Both soils with different organic matter content were analyzed for wettability changes before and after leaching using sessile drop contact angles as well as water and ethanol sorptivity curves, summarized as repellency index. Hydrophobicity of the effluent suspensions was assessed using the C18 adsorption method. Water repellency level of the repellent soil decreased after leaching but remained on a lower level of water repellency, while, the wettable soil remained wettable. The leached colloids from the repellent soil were predominantly hydrophilic and the percentage of the hydrophobic colloid fraction in the effluent did not systematically changed with time. Total colloid release depended on soil carbon stock but not on soil wettability. Our results suggest that due to the respective character of transported colloids a similar co-transport mechanism for pollutants may occur which does not depend explicitly on soil wettability of the releasing horizon, but could be more affected by total SOM content. Further studies with a wider range of soils are necessary to determine if the dominant hydrophilic character of leached colloids is typical. Due to the mostly hydrophilic colloid character we conclude also that changes in wettability status, i.e. of wettable subsoil horizons due to the leachate, may not necessarily occur very fast, even when the overlaying topsoil is a repellent soil horizon with a high organic matter content.

KW - C18

KW - Hydrophobic colloids

KW - Repellency index

KW - Sessile drop

KW - Soil water repellency

UR - http://www.scopus.com/inward/record.url?scp=85051970348&partnerID=8YFLogxK

U2 - 10.1515/johh-2017-0058

DO - 10.1515/johh-2017-0058

M3 - Article

AN - SCOPUS:85051970348

VL - 66

SP - 271

EP - 278

JO - Journal of Hydrology and Hydromechanics

JF - Journal of Hydrology and Hydromechanics

SN - 0042-790X

IS - 3

ER -