Vance Almquist, Utah State University
Plants, Soils, and Climate
Fire induced soil water repellency has been characterized across a variety of soils and landscapes as being a cause of watershed degradation and surface water pollution. The repellency is due to the condensation of volatile polyaromatic hydrocarbons onto soil particles. Although repellency is known to reverse, in some locations the reversal takes months; whereas, in other locations it may take years. Little is known about the reversal mechanisms and how they lead to such a large range of reversal times. Access to untreated fired-affected sites, can be unpredictable and samples vary greatly from site to site. Therefore, a model compound that mimics fire-induced soil hydrophobicity is needed to be able to systematically investigate soil hydrophobilicty reversal mechanisms. Fluorene is a relatively non-toxic, hydrophobic polyaromatic hydrocarbon. The behavior of fluorene coated sand grains was investigated under laboratory conditions using quartz sand. Moreover, its fluorescent properties could be used to non-destructively monitor its degradation over time. In this context fluorene was studied as a possible model compound for the study of mechanisms involved in the reversal of fire-induced soil hydrophobilicy. The compound was subjected to conditions known to degrade or reverse water repellency including temperature, UV-light, and moisture content. Changes in hydrophobicity were monitored using the ethanol drop test and fluorescent imaging. Digital image processing techniques with the public domain software, ImageJ, produced by the National Institute of Health, were used to analyze the images and generate spatial maps of treatment effects on fluorene degradation and hyrdophobicity reversal. Our results indicate that the hydrophobic fluorene-coated sand layers were degraded by treatments such UV light known to reverse hydrophobicity in fire-affected soils, thus suggesting that fluorene may serve as a suitable model compound for producing hydrophobic layers on course grained material.