Humic acid, dextran, and valeric acid representing macromolecules similar to compounds prevailing in treated wastewater
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SOILS, SEC 1 • SOIL ORGANIC MATTER DYNAMICS AND NUTRIENT CYCLING • RESEARCH ARTICLE
Humic acid, dextran, and valeric acid representing macromolecules similar to compounds prevailing in treated wastewater induce soil hydrophobicity Shai Tolkin 1 & Yona Chen 1 & Jorge Tarchitzky 1 Received: 5 December 2019 / Accepted: 28 May 2020 # Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Purpose Organic compounds originating from treated wastewater and soil texture have been reported to be the dominant factors influencing soil hydrophobicity. It is the aim of this investigation to elaborate the role of humic acid, dextran, and valeric acid, representing dissolved organic matter, polysaccharides, and fatty acids, respectively, as well as imitating their activity in inducing soil sub-critical water repellency induced by treated wastewater irrigation. Materials and methods The relationships between three model compounds imitating fractions of dissolved organic matter commonly found in treated wastewater, soil texture in relation to water repellency, were investigated. Three types of organic molecules, five soil mixtures with different specific surface areas, and three different organic compounds, as well as a mixture of the three, were tested. Results and discussion After 14–15 of wetting and drying cycles, low levels (sub-critical hydrophobicity) of water repellency developed in all soil mixtures were subjected to applications of several solutions of organic compounds, in comparison with a freshwater control. The highest degree of water repellency was exhibited by the soil with the lowest clay content (lowest specific surface area) and it decreased with increasing clay content (increasing specific surface area). Conclusions The order of intensity of sub-critical water repellency levels induced by the organic compounds was consistent, yet independent of soil texture. However, soil texture exhibited large influence on soil hydrophobicity in response to the various organic chemicals. Humic acid, the closest in structure to organic matter prevailing in treated wastewater, exhibited the largest effect in inducing soil hydrophobicity. Keywords Soil wettability . Polysaccharides . Humic acid . Water drop penetration time (WDPT)
1 Introduction At a global level, water resources are expected to be sufficient for food production until 2050, although many regions in the world will most likely face substantial water scarcity. Agriculture is the largest user of water resources, often accounting for 70% or more of water withdrawals from natural Responsible editor: Xilong Wang * Yona Chen [email protected] 1
Department of Soil and Water Sciences, Robert H. Smith Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, P.O. Box 12, 76100 Rehovot, Israel
sources (FAO and WWC 2015). The trend of rural population movement to cities is substantively increasing the volumes of wastewater, which are imposing serious environmental problems. Treated wastewater is the most readily available sourc
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