Collaborative research: Enhancement of wind erosion by fire-induced water repellency

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The role of fires in enhancing wind erosion by changing the physical-chemical properties at the soil surface remains unexplored. In fact, fire-wind erosion feedbacks have never been studied before through the analysis of soil water repellency. This proposal investigates new fundamental soil processes ? i.e., fire-induced enhancement of soil erodibility ? and provides a new mechanistic framework for their explanation.Recent experimental evidence suggests that the erodibility of burned areas is significantly higher than that of adjacent bare unburned soil and that this difference significantly affects the redistribution of nutrient-rich soil particles across the landscape. To explain these experimental findings, this project will test the hypothesis that by affecting the strength of interparticle bonding forces, fire-induced water repellency enhances soil erodibility. It will be shown how the mechanisms causing the enhancement of post-fire soil erodibility are associated with fire-induced soil hydrophobicity. This central hypothesis will be tested through a set of laboratory, field, and modeling activities at scales ranging from the soil grain to field/landscape scale. Hydrophobicity and other relevant hydraulic and chemical properties of soils from burned and unburned areas at two field sites will be measured and compared. A field wind tunnel will be used to measure the threshold velocity for wind erosion on burned and unburned plots. Additional wind tunnel tests of the soils from the field sites as well as clean sands treated to make them hydrophobic will be conducted in the lab to directly test the effect hydrophobicity on erodibility by wind. A theoretical framework will be developed to explain changes in erodibility with hydrophobicity by changes in interparticle forces, and atomic force microscopy (AFM) will be used to further validate the theoretical framework measuring soil interparticle forces directly.Most of the existing studies on the effect of surface moisture on the threshold wind velocity has ignored the effect of soil water repellency. The impact of fires on soil erodibility has been traditionally confined to the obvious ability of fires to degrade the vegetation cover thereby depriving the soil surface of the sheltering effect of grass and shrub vegetation. This proposal recognizes the importance of fire-induced water repellency and its ability of rendering burned areas more erodible than adjacent bare (i.e., intercanopy) soil, with important effects on the redistribution of sediments and nutrients within the patchy landscapes typical of arid and semiarid regions. Broader Impacts: This project will involve the training of a Ph.D. student, and up to two high school science teachers in the methods of research and of presentation of research results. It will support education by integration into a course being developed by the PI, and provide a basis for collaboration between different groups working on similar questions. Members of underrepresented groups will be sought for inclusion in the research team. The results of the proposed research will be disseminated through publications in scholarly journals and conference presentations. Society will benefit from the improved understanding of processes controlling wind erosion, a widespread process affecting climate, agriculture, and human health.