TY - JOUR

T1 - Capturing water repellency cessation time by means of characteristic time method

AU - Sepehrnia, Nasrollah

AU - Bachmann, Jörg

N1 - Funding Information: We thank the Alexander von Humboldt Foundation for financial support of this project and donating post-doctoral fellowship to the first author. We thank Susanne K. Woche, Hanna Böhme, and Martin Volkmann for their assistance with soil sampling, sample preparation, and laboratory analysis. The authors greatly appreciate Prof. Mark Coyne, University of Kentucky, USA for proofreading the draft of the article.

PY - 2022/12/1

Y1 - 2022/12/1

N2 - Persistence of water repellency is a significant physical key factor that governs water infiltration into unsaturated soil. We investigated water and ethanol infiltration using the characteristic time method (CTM), repellency index (RI), and the contact angle (CA) behavior for a comprehensive assessment on soil water repellency (SWR). We analyzed the impact of soil structure and thermal and wetting–drying treatments on water and ethanol infiltration. The first objective was to evaluate the CTM for water-repellent soils by partitioning characteristic and gravity infiltration behavior (Ichar and Igrav) and to evaluate parameters like infiltration beginning (tb) and gravity times (tchar and tgrav). The second objective was to characterize the CTM estimated water sorptivity (Sw), either as the Sww (the hydrophilic state water sorptivity) or the Swh (the hydrophobic state water sorptivity) to improve the calculation of water repellency cessation time (WRCT). Three soils with initial contact angles (CAi) of 18°, 60°, and 90° (20 °C ± 3 °C) were additionally heated to temperatures of 40 °C and 60 °C resulting in CAT40: of 23.6°, 56.4°, and 97.3° and CAT60 of 18.5°, 88.0°, and 126.6°. The wetted state CA was determined for a wetting- and a rewetting-infiltration cycle (CAwe and CArewe) under –2 cm tension, followed by air-drying and further CA measurements (CAair-dried). There was significant agreement (R2 > 0.95) between the Sw evaluated by CTM and the Swh, and excellent correspondence between tchar and the tb. The relations between Se, RI, CAwe, CArewe, CAair-dried, and WRCT clearly showed dynamics and reversibility of SWR and also its dependence on persistence, even for the air-dried 20 °C soil with small CAi. Persistence of SWR as characterized by the time components resulted in a long flow transition state (i.e., time development and respective changing relevance of capillary and gravity forces). Hence, missing experimental data has to be considered as the main barrier for modeling approaches. Further research is necessary to improve flexibility of the CTM code to reliably estimate Sw and Swh with respect to persistence of SWR.

AB - Persistence of water repellency is a significant physical key factor that governs water infiltration into unsaturated soil. We investigated water and ethanol infiltration using the characteristic time method (CTM), repellency index (RI), and the contact angle (CA) behavior for a comprehensive assessment on soil water repellency (SWR). We analyzed the impact of soil structure and thermal and wetting–drying treatments on water and ethanol infiltration. The first objective was to evaluate the CTM for water-repellent soils by partitioning characteristic and gravity infiltration behavior (Ichar and Igrav) and to evaluate parameters like infiltration beginning (tb) and gravity times (tchar and tgrav). The second objective was to characterize the CTM estimated water sorptivity (Sw), either as the Sww (the hydrophilic state water sorptivity) or the Swh (the hydrophobic state water sorptivity) to improve the calculation of water repellency cessation time (WRCT). Three soils with initial contact angles (CAi) of 18°, 60°, and 90° (20 °C ± 3 °C) were additionally heated to temperatures of 40 °C and 60 °C resulting in CAT40: of 23.6°, 56.4°, and 97.3° and CAT60 of 18.5°, 88.0°, and 126.6°. The wetted state CA was determined for a wetting- and a rewetting-infiltration cycle (CAwe and CArewe) under –2 cm tension, followed by air-drying and further CA measurements (CAair-dried). There was significant agreement (R2 > 0.95) between the Sw evaluated by CTM and the Swh, and excellent correspondence between tchar and the tb. The relations between Se, RI, CAwe, CArewe, CAair-dried, and WRCT clearly showed dynamics and reversibility of SWR and also its dependence on persistence, even for the air-dried 20 °C soil with small CAi. Persistence of SWR as characterized by the time components resulted in a long flow transition state (i.e., time development and respective changing relevance of capillary and gravity forces). Hence, missing experimental data has to be considered as the main barrier for modeling approaches. Further research is necessary to improve flexibility of the CTM code to reliably estimate Sw and Swh with respect to persistence of SWR.

KW - Capillary infiltration dynamics

KW - Characteristic time method

KW - Contact angle

KW - Molecular interfacial properties

KW - Persistence

KW - Water repellency breakdown

UR - http://www.scopus.com/inward/record.url?scp=85137182079&partnerID=8YFLogxK

U2 - 10.1016/j.geoderma.2022.116126

DO - 10.1016/j.geoderma.2022.116126

M3 - Article

AN - SCOPUS:85137182079

VL - 427

JO - GEODERMA

JF - GEODERMA

SN - 0016-7061

M1 - 116126

ER -