Chemistry of post-fire soil water repellency

About This Grant

With support from the Environmental Chemical Sciences (ECS) program in the Division of Chemistry, Professor Vera Samburova at the Nevada System of Higher Education, Desert Research Institute, will investigate the chemistry of soil organic compounds that contribute to the formation of fire-induced soil water repellency. Wildfires are known to cause the formation of water-repellent soil layers, primarily due to the presence of hydrophobic organic compounds. These water-repellent layers alter post-fire hydrological processes, reduce water infiltration and thus increase the risk of flooding, landslides, and debris flows. Despite recognition of these effects, the specific chemistry of the organic compounds responsible for fire-induced soil water repellency remains poorly understood. The proposed study aims to address this critical knowledge gap by identifying the organic compounds that contribute to soil water repellency in post-fire environments. The experiments and resulting data will offer insights into the chemistry of soils affected by wildfires, help improve post-fire soil assessments, and support efforts to reduce hydrological consequences of soil water repellency. This research project will help train the next generation of graduate students, providing them with expertise in environmental chemical sciences and it will also help to predict and mitigate fire impacts on communities and the environment in the Unites States. This project will explore how water-repellent soil layers form after wildfires by combining two key approaches: controlled laboratory experiments with heating in ovens and a combustion chamber, and the analysis of soil samples collected from recent wildfires in the western United States. During laboratory experiments, common organic compounds found in litter and soil, such as resin acids, alkanols, humic and fulvic acids, terpenes, carbohydrates, and lignins, will be loaded onto test sand and heated to specific temperatures to simulate wildfire-induced heating. These experiments will investigate how selected organic compounds chemically transform during heating and how these changes contribute to soil water repellency, which will be measured using contact angle and water drop penetration time techniques. The goal is to better understand how heat from fires transforms soil organics into water-repellent substances and what chemical functional groups are responsible for this process. A variety of advanced chemical analysis techniques, including nuclear magnetic resonance spectroscopy and high-resolution mass spectrometry will be used to identify and quantify relevant compounds and functional groups. The laboratory-generated results will be compared with results for real post-fire soils and the obtained data will be of the essence for future modeling, prediction, and mitigation of fire-induced water repellency. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.