Experimental characterization of the impact of temperature and humidity on the breakdown of soil water repellency in sandy soils and composts

Abstract

Soil water repellency is a widespread phenomenon with the capacity to alter hydrological and geomorphological processes. Water repellency decays with time, and the consequences are only of concern during the timescale at which the water repellency persists. This study aimed to characterize the influence of temperature and humidity on the breakdown of water repellency. Apparent contact angle measurements were carried out on samples consisting of sand treated with stearic acid as well as naturally repellent dune sands and composts. Temperature and humidity were controlled using a cooled incubator and a purpose designed enclosed box in which humidity could be raised or lowered. Results showed the contact angle of the stearic‐acid‐treated sands decayed with time and that there was a significant increase with stearic acid concentration. For all samples, the decay in apparent contact angle could be described with a continuous breakdown model. The stearic‐acid‐treated sands showed a significant increase in contact angle with relative humidity at a temperature of 10 and 20 °C. These differences diminished with increasing temperature. Similar results were seen for the dune sands and composts. Despite the influence of temperature and humidity on contact angles, there was no significant change in the rate at which the contact angle decayed in any sample. Absolute humidity was found to provide a more relevant indicator than relative humidity when assessing the influence of humidity on repellency over a range of temperatures. The contact angle initially increased with absolute humidity before plateauing owing to the confounding effect of temperature. Copyright © 2014 John Wiley & Sons, Ltd.

Water Repellency Decreases Vapor Sorption of Clay Minerals

“…In natural soils, repellency often breaks down at high water contents (de Jonge et al, ), so the reduced ability to condense water vapor may represent a positive feedback by which hydrophobic conditions are maintained even in relatively humid conditions. This mechanism may also pertain to previous observations showing that air humidity and liquid solid‐water contact angles were positively correlated (i.e., greater contact angles were observed at higher air humidity; Whelan et al, ). Still, the Whelan et al () study observed this relationship for sand particles that had been treated with SA yet not in natural dune sand particles, meaning that these results could be artifacts arising from the use of pure minerals and hydrophobicity‐inducing chemicals.…”

“…This mechanism may also pertain to previous observations showing that air humidity and liquid solid‐water contact angles were positively correlated (i.e., greater contact angles were observed at higher air humidity; Whelan et al, ). Still, the Whelan et al () study observed this relationship for sand particles that had been treated with SA yet not in natural dune sand particles, meaning that these results could be artifacts arising from the use of pure minerals and hydrophobicity‐inducing chemicals. Similar caution may be warranted when extending the findings of the present study, which used model minerals, to natural soils.…”

Peer Review #2 of "Analyzing moisture-heat coupling in a wheat-soil system using data-driven vector autoregression model (v0.1)"

“…Because of complicated biological, physical and chemical processes like soil respiration, soil evaporation, plant transpiration and so on, soil temperature and moisture have a close dynamic relationship with each other. Therefore, in order to better control and predict the hydrothermal conditions of a wheat-soil system, models simulating soil moisture-heat coupling need to be established (Perez et al 2013;Whelan et al 2015).…”

Peer Review #1 of "Analyzing moisture-heat coupling in a wheat-soil system using data-driven vector autoregression model (v0.1)"

“…Because of complicated biological, physical and chemical processes like soil respiration, soil evaporation, plant transpiration and so on, soil temperature and moisture have a close dynamic relationship with each other. Therefore, in order to better control and predict the hydrothermal conditions of a wheat-soil system, models simulating soil moisture-heat coupling need to be established (Perez et al 2013;Whelan et al 2015).…”