Water repellency of volcanic ash soils from Ecuadorian paramo: effect of water content and characteristics of hydrophobic organic matter

• Published in: European journal of soil science Vol. 55; no. 3; pp. 487 - 496
• Main Authors: Poulenard, J, Michel, J.C, Bartoli, F, Portal, J.M, Podwojewski, P
• Format: Journal Article
• Language: English
• Published: Oxford, UK; Malden, USA Blackwell Publishing Ltd/Inc 01-09-2004; Blackwell Science; Wiley
• Subjects: adsorption isotherms; Agricultural sciences; Agronomy. Soil science and plant productions; altitude; Andisols; Biological and medical sciences; capillarity; Chemical, physicochemical, biochemical and biological properties; drying; Earth sciences; Earth, ocean, space; Exact sciences and technology; Fundamental and applied biological sciences. Psychology; grasslands; high-altitude grasslands; hydrophobicity; landforms; Life Sciences; Organic matter; paramo; Physical properties; Physics, chemistry, biochemistry and biology of agricultural and forest soils; soil drying; soil organic matter; Soil science; Soil study; soil water content; Soils; sorption isotherms; Surficial geology; volcanic ash soils; Water and solute dynamics; water contact angle; water repellent soils; Ecuador; South America; experimental studies; physical properties; soil moisture; Water repellent; Property of soil; Andisols; Hydrophobicity; Paramo; Tropical soil; Soil water properties; Volcanic soils; physicochemical properties; organic materials; water content; Soil science; soils
• ISSN: 1351-0754; 1365-2389
• DOI: 10.1111/j.1365-2389.2004.00625.x

Summary
Water repellency of volcanic ash soils from the Ecuadorian páramo was studied by a combination of extraction and analysis of water‐repellent products, Molarity Ethanol Droplet values, water contact‐angle measurements by capillary rise, and N2 adsorption isotherms. The undried samples studied are hydrophilic, but exhibit water repellency after moderate drying (48 hours at 30°C). The advancing water contact‐angle measured by capillary rise varies from 78° to 89°. These water contact‐angles decrease strongly after extraction of organic materials by an isopropanol–water mixture. Elemental analysis, infrared spectra and gas chromatography‐mass spectrometry analyses were used to characterize the extracts. The results show that long‐chain fatty acids and more complex non‐polar alkyl components (waxes) are the main water‐repellent materials. The deposition of such extracted materials onto hydrophilic sand leads to the rapid increase of water contact‐angle until values close to those measured on the soil samples are achieved. Assuming a coating of the mineral surface by organic hydrophobic products and using Cassie's law, the water contact‐angle of extracted materials was computed. The values ranged from 100° to 157°. Nitrogen specific surface areas of the soils studied were very small, indicating a low adsorbent–adsorbate interaction on hydrophobic surfaces. These results partially validate the hypothesis of water‐repellent materials that occur as coatings at least after a drying process.