Development of soil water repellency in the course of isothermal drying and upon pH changes in two urban soils

Abstract

Abstract:The potential influence of pH on water repellency in soils has already been mentioned in some studies, but no clear correlation between these parameters has been found to date. In addition, although correlations of water content and water repellency have been found in numerous studies, the influence of drying and subsequent storage conditions on water repellency are still unclear. In this study, a series of samples showing water repellent and wettable conditions respectively at field moist states from two urban locations were compared regarding two main aspects: (i) the influence of artificial pH-changes on their wetting behaviour and (ii) sample wettability changes during drying for different drying temperatures. The assumption made in a study by Hurraß and Schaumann (2006) on the same sample site, that differences in wettability of closely neighboured samples from one sample location can be interrelated with differences in pH, was confirmed. However, in contrast to the assumption that rising pH will improve the wettability and decreasing pH will intensify water repellency, we found a maximum in water repellency at a pH above the initial pH. The results from drying samples at different temperatures confirmed the dependence of water repellency development on the drying temperature. Additionally, we could confirm the conclusion from previous studies that the water content alone cannot explain the water content-WDPT (water drop penetration time) relationship. The results from drying and pH changes show that some location specific factors, like the number of pH active functional groups, may be relevant for sample wettability. As additional mechanism, which may be partly antagonistic to the influence of the water content, we assume temperature-dependent conformational changes in SOM (Soil Organic Matter). It seems that aspects of these conformational changes may additionally be governed by pH in one of our two locations.

Hydro-physical processes and soil properties correlated with origin of soil hydrophobicity

“…Organic molecules consisting of long chain fatty acids are the major hydrophobic substances found in soils (CAMBRONERO et al, 2011). However, more research is needed to accurately characterize the chemically compounds that cause water repellency (BAYER & SCHAUMANN et al, 2007).…”

“…Sandy soils have a lower specifi c surface area, so a hydrophobic surface will push a greater proportion of particles than in the case of a silt clay soil or where the specifi c surface area is larger (TÄUMER et al, 2005;WOCHE et al, 2005). In addition, sandy soils also provide a better habitat for fungi than bacteria, due to the low particle surface area and pore size distribution, which is a poor habitat for bacteria (HALLET et al, 2003;BAYER & SCHAUMANN et al, 2007).…”

“…A recent study by Bayer & SCHAUMANN (2007) shifted the focus to other factors affecting water repellency towards the infl uence of drying conditions and soil pH. Both are frequently mentioned as potential drivers of hydrophobicity in the soil, but little data exists.…”

“…The local vegetation, depending on their chemical composition, may contribute to hydrophobic organic compounds, by deposition or decomposition (MATAIX-SOLERA et al, 2007). It may also be associated with other factors such as soil moisture conditioned by rain and drought (ROBINSON et al, 2010), the granulometric composition (WOCHE et al, 2005;KAWAMOTO et al, 2007;VOGELMANN et al, 2010), soil pH (BAYER & SCHAUMANN, 2007) and presence of some species of fungi WAHL et al, 2008) and burnings (MADSEN et al, 2011.…”

Occurrence and spatial pattern of water repellency in a beech forest subsoil

“…The opposite behaviour was observed for humic acid when the ambient pH was decreased (Terashima et al, 2004). Bayer and Schaumann (2007) investigated the effect of pH modifications on WR by adding different concentrations of aqueous NaOH and HNO 3 to water repellent and wettable soil with a field pH between 4.0 and 4.6. They found the maximum WR above the original pH, contradicting the assumption that increasing pH will always increase wettability.…”