TY - JOUR

T1 - Quantitative analysis of liquid penetration kinetics and slaking of aggregates as related to solid-liquid interfacial properties

AU - Goebel, Marc O.

AU - Woche, Susanne K.

AU - Bachmann, Jörg

N1 - Funding Information: Financial support provided by the German Research Foundation DFG (Priority program 1315, BA 1359/9-2) for this study is greatly appreciated. We thank H. Flessa for providing the samples from the Rotthalmünster site and G.E. Schaumann for providing the samples from Chorin. Finally, we would like to thank two anonymous reviewers for their constructive comments and suggestions on an earlier version of the manuscript. Copyright: Copyright 2013 Elsevier B.V., All rights reserved.

PY - 2012/6/6

Y1 - 2012/6/6

N2 - Aggregate stability is frequently shown to be enhanced by strong soil water repellency, however, there is limited systematic evidence on this effect for moderately (subcritically) water repellent soils. This study aimed to investigate the specific effects of interfacial properties on the liquid penetration kinetics in relation to the stability of subcritically water repellent aggregates (4-6.3mm) from various arable and forest soils against breakdown by slaking. In contrast to many other studies, where aggregate stability was determined by wet sieving, we here assessed the stability by immersion of air-dry aggregates in water-ethanol solutions with surface tensions ranging from 30 to 70mNm-1. This approach allowed a highly sensitive discrimination of different stability levels and the determination of breakdown kinetics also for less stable aggregates. Interfacial properties were characterized in terms of contact angle measured on crushed aggregates, θc, and calculated for intact aggregates, θi, based on infiltration measurements with water and ethanol. Aggregate stability turned out to be higher in forest soils compared to arable soils with topsoil aggregates generally found to be more stable than subsoil aggregates. For water repellent aggregates, characterized by contact angles >40° and low water infiltration rates (<0.2mm3s-0.5), the fraction of disrupted aggregates after 30s of immersion was generally below 10%, whereas in case of the more wettable aggregates, characterized by contact angles <10° and higher infiltration rates (>0.25mm3s-0.5) more than 80% of the aggregates were disrupted. In accordance, we found a close relationship between aggregate stability and wettability with differences between θc and θi being generally small. In addition, aggregate stability turned out to be related to organic carbon content. However, correlation analysis revealed that both persistence of aggregate stability and kinetics of aggregate breakdown were more strongly affected by the contact angle, θc (r=0.90 and r=-0.83, respectively) and θi (r=0.89 and r=-0.76, respectively) than the organic carbon content (r=0.62 and -0.52, respectively), suggesting that stability was primarily controlled by aggregate interfacial properties. Calculation of liquid penetrativity as a function of surface tension and contact angle clearly demonstrated the importance of both solid and liquid interfacial properties in determining the stability of subcritically water repellent aggregates against slaking.

AB - Aggregate stability is frequently shown to be enhanced by strong soil water repellency, however, there is limited systematic evidence on this effect for moderately (subcritically) water repellent soils. This study aimed to investigate the specific effects of interfacial properties on the liquid penetration kinetics in relation to the stability of subcritically water repellent aggregates (4-6.3mm) from various arable and forest soils against breakdown by slaking. In contrast to many other studies, where aggregate stability was determined by wet sieving, we here assessed the stability by immersion of air-dry aggregates in water-ethanol solutions with surface tensions ranging from 30 to 70mNm-1. This approach allowed a highly sensitive discrimination of different stability levels and the determination of breakdown kinetics also for less stable aggregates. Interfacial properties were characterized in terms of contact angle measured on crushed aggregates, θc, and calculated for intact aggregates, θi, based on infiltration measurements with water and ethanol. Aggregate stability turned out to be higher in forest soils compared to arable soils with topsoil aggregates generally found to be more stable than subsoil aggregates. For water repellent aggregates, characterized by contact angles >40° and low water infiltration rates (<0.2mm3s-0.5), the fraction of disrupted aggregates after 30s of immersion was generally below 10%, whereas in case of the more wettable aggregates, characterized by contact angles <10° and higher infiltration rates (>0.25mm3s-0.5) more than 80% of the aggregates were disrupted. In accordance, we found a close relationship between aggregate stability and wettability with differences between θc and θi being generally small. In addition, aggregate stability turned out to be related to organic carbon content. However, correlation analysis revealed that both persistence of aggregate stability and kinetics of aggregate breakdown were more strongly affected by the contact angle, θc (r=0.90 and r=-0.83, respectively) and θi (r=0.89 and r=-0.76, respectively) than the organic carbon content (r=0.62 and -0.52, respectively), suggesting that stability was primarily controlled by aggregate interfacial properties. Calculation of liquid penetrativity as a function of surface tension and contact angle clearly demonstrated the importance of both solid and liquid interfacial properties in determining the stability of subcritically water repellent aggregates against slaking.

KW - Aggregate stability

KW - Contact angle

KW - Infiltration rate

KW - Repellency index

KW - Soil water repellency

KW - Surface tension

UR - http://www.scopus.com/inward/record.url?scp=84861213183&partnerID=8YFLogxK

U2 - 10.1016/j.jhydrol.2012.03.039

DO - 10.1016/j.jhydrol.2012.03.039

M3 - Article

AN - SCOPUS:84861213183

VL - 442-443

SP - 63

EP - 74

JO - Journal of hydrology

JF - Journal of hydrology

SN - 0022-1694

ER -