After wildfires, the soil in burnt areas often becomes water repellent, leading to increased post-rainfall erosion and flooding. This is a phenomenon that many scientists attribute to changes in soil chemistry due to smoke and heat. However, according to a new treatise from the Nevada Desert Institute (DRI), this post-fire water repellency can also be caused by wildfire smoke in the absence of heat.
In this pilot study, an exploratory study conducted prior to large-scale studies, a team of interdisciplinary scientists led by Dr. Vera Samburova, DRI Associate Research Professor of Atmospheric Sciences, sampled clean sand from Jeffrey’s burning smoke. Exposed. Next, we analyzed the pine needles and branches in the DRI’s combustion chamber and analyzed the time it took for the water droplets on the surface of the sand to be absorbed. This is a measure of water repellency.
The pilot study was the first study to investigate the effects of smoke and heat on the water repellency of sand and to incorporate analysis of cold smoke. In the experiment, sand was used instead of soil and Jeffrey pine, a common wilderness fire fuel in the western United States, was used as the fuel source for thorough cleaning and accurate analysis.
Water droplets placed on the surface of the sand sample were quickly absorbed before being exposed to the smoke of Jeffrey pine. However, after exposure to smoke, sand samples showed severe to extreme water repellency and, in some cases, retained water droplets on the soil surface for more than 50 minutes without soaking. It made little difference whether the sample was exposed to heat. And smoke, or just cold smoke.
“The classic explanation for water repellency from fire is that it is caused by smoke diffusing and settling in the soil under fairly high temperature conditions, but in our study, to make the sand hydrophobic. It shows that the smoke does not have to be hot. The presence of chemicals in the smoke is sufficient. ” “This is something we really need to investigate, as soil water repellency leads to increased flooding, erosion and surface runoff.”
This study was conducted by former DRI postdoctoral fellow Rose Shillito, Ph.D. (Currently US Army Corps of Engineers), Markus Berli, Ph.D. , And Teamrat Ghezzehei, Ph.D. Based on a previously published study by. At the University of California, Merced, researchers have developed an analytical model for associating soil water repellency with water infiltration.
“Our previous treatise focused on how fire alters soil properties from a hydrological point of view,” Berli said. “In my current research, I wanted to know more about the chemistry behind the process of soil becoming hydrophobic. Combining geochemistry and organic geochemistry with soil physics and hydrology, fire water repellency I understand the impact. About hydrology. “
The project team is currently working on a larger proposal to further investigate the questions raised in this study on the role of heat and smoke in the water repellency of fires. Above all, they want to know how long the water repellency of the soil will last after a fire and better understand the detailed processes and mechanisms by which cold smoke affects the soil.
It is important to fully understand the processes that lead to the water repellency of the soil caused by the fire. This is because managers need this information to accurately predict where the soil can become hydrophobic after a fire.
“We still don’t really understand the process that leads to the water repellency of the soil caused by this fire,” Berli said. “Depending on what we have found, the method of predicting water repellency from a fire can be different, which has a significant impact on how to predict and prevent floods and debris flows that occur after a fire. There is a possibility.”
“This study was a big step forward, but the importance of future research on how fires affect soil is highlighted, as wildfires affect thousands of square kilometers of land each year in the western United States. “I’m doing it,” added Sanbrois. “Some of our future goals are to know exactly how this soil water repellency occurs, where it occurs, and how long it lasts.”
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Vera Samburova et al, Effect of Biomass Combustion Emissions on Soil Water Repellent: Pilot Laboratory Study, fire (2021). DOI: 10.3390 / fire4020024
Provided by Desert Research Institute
Quote: Does cold wildfire smoke contribute to the water-repellent soil in the burnt area? (May 25, 2021) May 25, 2021 Obtained from https://phys.org/news/2021-05-cold-wildfire-contribute-repellent-soils.html
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Does cold wildfire smoke contribute to the water-repellent soil in the burnt area?
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