Natural Water Repellency Research Articles

Mass Stranding of Marine Birds Caused by a Surfactant-Producing Red Tide

In November-December 2007 a widespread seabird mortality event occurred in Monterey Bay, California, USA, coincident with a massive red tide caused by the dinoflagellate Akashiwo sanguinea. Affected birds had a slimy yellow-green material on their feathers, which were saturated with water, and they were severely hypothermic. We determined that foam containing surfactant-like proteins, derived from organic matter of the red tide, coated their feathers and neutralized natural water repellency and insulation. No evidence of exposure to petroleum or other oils or biotoxins were found. This is the first documented case of its kind, but previous similar events may have gone undetected. The frequency and amplitude of red tides have increased in Monterey Bay since 2004, suggesting that impacts on wintering marine birds may continue or increase.

Laboratory and outdoor water repellency and dimensional stability of southern pine sapwood treated with a waterborne water repellent made from resin acids

Abstract A major consumer concern regarding lumber in above-ground exposure such as decking is the poor dimensional stability that leads to warping, splitting, and checking. One method to increase dimensional stability is to treat lumber with a water repellent. A waterborne water repellent made from the resin acid abietic acid or a commercial source of resin acids, tall oil rosin or TOR, was tested using southern pine sapwood. In laboratory water-swelling tests, the waterborne abietic acid provided water repellency that was almost equivalent to that provided by wax, while no water repellency was observed with solventborne resin acid. Wood treated with waterborne TOR also provided good water repellency in laboratory tests and fair water repellency at up to 13 months of outdoor exposure, but the laboratory efficacy was partially reduced by a water leach. The dimensional stability (cupping and checking) and mold growth on TOR-treated lumber in above-ground exterior exposure was better than for untreated boards, but not as good as for wax-treated lumber. Analysis of the wood in southern pine tree trunks of 14 or 29 years of age of various diameters and sampled at the bottom, middle and top showed that the resin acid content in southern pine wood is quite variable. This may explain the wide variation in natural water repellency and decay resistance previously observed with untreated southern pine sapwood.

Water‐repellent soil and its relationship to granularity, surface roughness and hydrophobicity: a materials science view

SummaryConsiderable soil water repellency has been observed at a wide range of locations worldwide. The soil exhibiting water repellency is found within the upper part of the soil profile. The reduced rate of water infiltration into these soils leads to severe runoff erosion, and reduction of plant growth. Soil water repellency is promoted by drying of soil, and can be induced by fire or intense heating of soil containing hydrophobic organic matter. Recent studies outside soil science have shown how enhancement of the natural water repellency of materials, both porous and granular, by surface texture (i.e. surface roughness, pattern and morphology) into super‐hydrophobicity is possible. The similarities between these super‐hydrophobic materials and observed properties of water‐repellent soil are discussed from a non‐soil scientist, materials‐based perspective. A simple model is developed for a hydrophobic granular surface and it is shown that this can provide a mechanism for enhancement of soil water repellency through the relative size and spacing of grains and pores. The model provides a possible explanation for why soil water repellency should be more prevalent under dry conditions than wet. Consequences for water runoff, raindrop splash and soil erosion are discussed.

On the role of organic adlayers in the anomalous water sorptivity of Lépine limestone.

Sorptivity data are reported for the capillary absorption of water, ethanol, propan-2-ol, and n-heptane by the calcitic limestone Lépine (Lavoux à grain). The data confirm that the water sorptivity is anomalously low, an indication of partial wetting by water. Results are expressed in terms of a wetting index. The water sorptivity increases after heat treatment and chemical oxidation by hydrogen peroxide bleaching, while the sorptivity with organic liquids is unchanged. These treatments, therefore, increase the water wetting index. The results provide strong evidence that the presence of a natural organic adlayer is responsible for the anomalously low water sorptivity of this particular limestone. This natural water repellency effect may be exploited in developing chemical treatments to modify the water transport properties of stone.

Post‐fire runoff and erosion from simulated rainfall on small plots, Colorado Front Range

AbstractAn Erratum has been published for this article in Hydrological Processes 16(5) 2002, 1131–1133. Wildfires in the Colorado Front Range can trigger dramatic increases in runoff and erosion. A better understanding of the causes of these increases is needed to predict the effects of future wildfires, estimate runoff and erosion risks from prescribed fires, and design effective post‐fire rehabilitation treatments. The objective of this project was to determine whether runoff and sediment yields were significantly related to the site variables of burn severity, percent cover, soil water repellency, soil moisture, time since burning, and slope. To eliminate the variability due to natural rainfall events, we applied an artificial storm of approximately 80 mm h−1 on 26 1 m2 plots in the summer and fall of 2000. The plots were distributed among a June 2000 wildfire, a November 1999 prescribed fire, and a July 1994 wildfire.For 23 of the 26 plots the ratio of runoff to rainfall exceeded 50%. Nearly all sites exhibited strong natural or fire‐induced water repellency, so the runoff ratios were only 15–30% larger for the high‐severity plots in the two more recent fires than for the unburned or low‐severity plots. The two high‐severity plots in the 1994 wildfire had very low runoff ratios, and this probably was due to the high soil moisture conditions at the time of the simulated rainfall and the resulting reduction in the natural water repellency. Sediment yields from the high‐severity sites in the two more recent fires were 10–26 times greater than the unburned and low‐severity plots. The plots burned at high severity in 1994 yielded only slightly more sediment than the unburned plots. Percent ground cover explained 81% of the variability in sediment yields, and the sediment yields from the plots in the 1994 wildfire are consistent with the observed recovery in percent ground cover. Copyright © 2001 John Wiley & Sons, Ltd.

Development and application of a new sessile drop contact angle method to assess soil water repellency

Existing methods for determining the contact angle as a measure of the water repellency of soils are either indirect, or cumbersome and time-consuming. Our objective was to develop a new method that is simpler than the existing procedures like the capillary rise method and that still yields accurate and reproducible results. To this end, we applied the so-called sessile drop method. To obtain the needed plane sample surface and to reduce geometrical effects, a single layer of air-dry soil particles is sprinkled on double-sided adhesive tape. Eight droplets of deionized water are placed carefully on this horizontal particle layer. Immediately after sample preparation, the contact angle at the three-phase boundary was measured with a goniometer-fitted microscope. In order to test the new method, contact angle measurements were carried out with wettable soil material that was hydrophobized, and with soils showing a wide range of natural water repellency. Both wettable silt and sand were made hydrophobic with Dimethyldichlorosilane and diluted with untreated soil to obtain a defined variation in the solid surface tension. Contact angle measurements showed a nonlinear decrease with increasing amounts of wettable particles in the 40–90° contact angle domain. Generally, the contact angle decrease was predictable and could be described with an empirical model. For volcanic ash soils showing a wide range of repellency, the contact angles of different, narrowly sieved soils fractions (<20μm, 20–38μm, 38–63μm, and 63–100μm) were within the range of 25–110°. The impact of the different sieved soil fractions on the contact angles was found to be small. Measurements performed with independent replicates showed good reproducibility across the whole range of contact angles.

Contribution of Some Soil Fungi to Natural and Heat‐Induced Water Repellency in Sand

Eight species of fungi isolated from a water repellent soil were incubated for varying periods of time in silica sand. In their latter stages of growth, two of the fungi, Aspergillus sydowi and Penicillium nigricans, caused limited water repellency in the sand. All the fungal sand cultures exhibited water repellency when heated briefly at temperatures between 200C and 400C. The times required to produce and destroy water repellency in the sand cultures at the various temperatures were similar to those required by the natural soil from which the fungi were isolated. The fungal sand cultures and natural water repellent soils were extracted with either water, methanol, acetone, or ethyl ether. The methanol and water extractions destroyed the natural water repellency of the A. sydowi and P. nigricans cultures. Methanol and water extractions also destroyed the water repellency of the heated sand cultures if the extractions were made before the heat treatments; however, if the extractions were made after the sand cultures had been heated, the water repellency of the samples was not affected. Wettable silica sand treated with the methanol extracts of the sand cultures exhibited water repellency when heated. Both the heat-induced and natural water repellency of the soil was not affected by any of the solvent extractions, but wettable sand treated with each of the extracts was made water repellent by heat. A variety of known organic substances was applied to wettable silica sand and the water repellency of the treated sand determined before and after heating. Amines were the only class of substances tested that caused water repellency in sand before heating. A variety of substances, however, caused heat-induced water repellency in the sand. The heating conditions required to cause water repellency were similar to those required by fungal sand cultures and natural water repellent soil. The primary conclusion of the study was that heat-induced water repellency may be a universal property of soils rather than property specific to a limited number of soils.