Effects of heating and post-heating equilibration times on soil water repellency

Abstract

The effects of variation in heating temperature T (50–300°C), heating duration (20–60 min), and post-heating equilibration times (24–168 h at 20°C and 50% relative humidity) on the wettability, as measured by the Critical Surface Tension (CST) method, of 4 initially water repellent soils from Canada, Portugal, and the UK are reported. All soils show an increase in water repellency following heating at temperatures in the range of 50 to 150°C, followed by a considerable decline after heating to 200–250°C, and, except for one soil, the eradication of repellency after heating to 300°C. For two soils with a comparatively high organic carbon content and fine texture, water repellency levels were also affected by the length of the post-heating equilibration period. The results demonstrate that (i) the common practice of heating samples to 105°C does not provide a viable standard procedure for the measurement of water repellency as it may alter repellency to different degrees, and (ii) where heat treatment is required, a post-heating equilibration time of 24 h is not necessarily sufficient for sample repellency levels to adjust to atmospheric laboratory conditions; therefore it is advisable to prolong equilibration to at least one week prior to measurement.

Temperature influences water sorptivity of soil aggregates

“…Haplic Cambisol and Gleyic Mollic Cambisol). Taking into account that the water sorptivity is inversely proportional to water repellency/contact angle (Bartoli and Dousset, 2011), our findings are in agreement with the findings of Doerr et al (2005). They showed for initially water repellent soils with soil organic carbon contents between 0.4% and 6.8% that exposure to temperatures from 20 to 200°C tended to increase soil water repellency (SWR), followed by a decline in SWR at exposure to 250°C and destruction of SWR at 300°C.…”

Water repellency of air-dried and sieved samples from limestone soils in central Portugal collected before and after prescribed fire

“…In the Mediterranean climate zone, SWR has been reported for pine forest (Santos et al 2013), eucalyptus forest (Doerr et al 2005;Prats et al 2012), deciduous forest (Jordán et al 2008), Californian chaparral (Hubbert et al 2006), and, more recently, also Mediterranean shrublands (Arcenegui et al 2008;Gimeno-García et al 2011). SWR of Mediterranean shrublands, however, has been studied more extensively for soils derived from acidic parent material in subhumid conditions (Martínez- Zavala and Jordán-López 2009;Stoof et al 2011) than for soils overlying carbonated bedrock (sedimentary rocks composed primarily of carbonate materials).…”

Biological and chemical factors controlling the patchy distribution of soil water repellency among plant species in a Mediterranean semiarid forest

“…For measuring WR, approximately 15 g of soil per sample was placed on separate 50-mm diameter plastic dishes and exposed to a controlled laboratory atmosphere (20°C,~50% relative humidity) for one week to eliminate potential effects of any variations in preceding atmospheric humidity on soil WR and in accordance with the findings of Doerr et al (2005a). The persistence of WR was measured by the Water Drop Penetration Time (WDPT) test (Wessel, 1988).…”