Seeking answers from the ashes

Seeking answers from the ashes

Seeking answers from the ashes

January 20, 2022
RENO, NEV.

By Kelsey Fitzgerald

Above: A soil collection field site located within the perimeter of Dixie fire. November 18, 2021.

Credit: Vera Samburova.

DRI scientists study soil dynamics in the wake of Sierra Nevada wildfires

After a wildfire, soils in burned areas become temporarily water-repellent, resulting in increased risk of flooding and erosion in the months that follow. Scientists and land managers have never thoroughly understood why or how this happens – but when last summer’s Dixie, Tamarack, and Caldor fires burned through the Sierra Nevada in close proximity to DRI’s Reno campus, scientists Brad Sion, Ph.D., Vera Samburova, Ph.D., and Markus Berli, Ph.D., jumped into action. 

The team, led by Sion, obtained a Rapid Response Research grant from the National Science Foundation for a new project aimed at exploring the impacts of wildfires on physical and chemical properties of burned soils.

Brad Sion
vera samburova

Above, left: Brad Sion, Ph.D., Assistant Research Professor of Geomorphology, holds a frozen chunk of burned soil at a soil sample collection site  near Kirkwood in the wake of the Tamarack Fire.

Credit: Vera Samburova.

Above, right: Vera Samburova, Ph.D., inspects soils in a burned area near Frenchman Lake that was affected by the Beckwourth Complex Fire.

Credit: Brad Sion.

To collect soil samples before the burned areas were impacted by rain or snowfall, time was of the essence. In October, the team made several trips to nearby fire sites to collect soil samples and to conduct field measurements of soil water repellency.

Then, in late October, a major atmospheric river storm came through. The team’s next visit to the fire sites revealed a changed landscape – a real-world example of how wildfires and water repellent soils can impact ecosystems and infrastructure.

“When we first went out into the field, the sites were very dry and ash-covered,” said Samburova. “When we went back out after the atmospheric river storm, we saw lots of mudslides along the roads, and even dirt on top of the road in some places. The soil was very mushy at the surface, but bone dry within centimeters below. And a lot of water was staying on the surface. It was hard to walk on – very slippery.”

water droplet penetration test results
erosion and mudslides

Above, left: The results of a water droplet penetration test on burned soils at the Dixie fire show a high degree of soil water repellency.

Credit: Vera Samburova.

Above, right: After a late October atmospheric river storm passed through the region, researchers observed erosion and mudslides field sites at the Dixie fire. 

Credit: Vera Samburova.

An interdisciplinary approach

Although previous studies have examined impacts of fire on soils in a controlled laboratory setting, the new DRI study will be one of the first to investigate changes in soil properties and their interrelationships using samples collected directly from freshly burned forests. This work builds upon earlier research by co-investigators Samburova and Berli, which investigated the impacts of fire smoke on water repellency of sand samples.

The team, which includes experts from all three of DRI’s research divisions, is approaching their research questions from several angles. Sion is leading the effort to measure the hydraulic (water-related) and thermal (heat-related) properties of burned soils. Samburova is analyzing organic compounds found in the burned soil samples, and Berli is conducting tests to assess the degree of soil water repellency.

Together, their results will provide new insight into linkages between fire burn severity, changes in soil thermal and hydraulic properties, and more.

“Our goal is to understand from a basic science perspective, what the cause is for these various soil characteristics pre- and post- fire,” said Sion. “If we can look at different fire conditions and the soil conditions that result, then we can say something about how a soil may respond in the future, and eventually that information can be extrapolated to different landscape settings.”

At present, the researchers have completed sample collection and are analyzing samples in their respective laboratories in Reno and Las Vegas. They plan to return to their field sites next fall to see how the soil water repellency changes over time.

As climate warms and western wildfire activity increases, Sion and his colleagues believe that understanding how forest fires impact soil properties will continue to be a topic of growing importance.

“Climate change and wildfires are not problems that are unique to the Sierras,” Sion said. “Whether you’re in the Pacific Northwest, Canada, Alaska, or elsewhere, you’re seeing increases in fire activity. People are thinking about the landscape responses and what they mean.”

Diana Brown

Diana Brown, Staff Research Scientist of Geomorphology, analyzes samples in the Soil Characterization and Quaternary Pedology laboratory in Reno. The soil samples have been saturated with water and contain tensiometers and heat probes to analyze hydraulic and thermal properties of the soil.

Credit: DRI.

Funding for this study is provided by the National Science Foundation (award # 2154013). Additional DRI scientists participating in this project include Hans Moosmüller, Ph.D., Diana Brown, M.S., Chris Baish, M.S., Janelle Bustarde, Palina Bahdanovich, Shelby Inouye, Adam Hackbarth, Zimri Mena and Kendrick Seeber.

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About DRI

The Desert Research Institute (DRI) is a recognized world leader in basic and applied environmental research. Committed to scientific excellence and integrity, DRI faculty, students who work alongside them, and staff have developed scientific knowledge and innovative technologies in research projects around the globe. Since 1959, DRI’s research has advanced scientific knowledge on topics ranging from humans’ impact on the environment to the environment’s impact on humans. DRI’s impactful science and inspiring solutions support Nevada’s diverse economy, provide science-based educational opportunities, and inform policymakers, business leaders, and community members. With campuses in Las Vegas and Reno, DRI serves as the non-profit research arm of the Nevada System of Higher Education. For more information, please visit www.dri.edu.

New DRI Internship Program Focuses on Mentorship for Inclusion in STEM

New DRI Internship Program Focuses on Mentorship for Inclusion in STEM

New DRI Internship Program Focuses on Mentorship for Inclusion in STEM

Oct 26, 2021
RENO, NEV.

By Kelsey Fitzgerald

Internships
Career Development
STEM
Above: DRI Research Internship Immersion Program students Mary Andres (left) and John Cooper (right) work with faculty mentor Dr. Riccardo Panella in his laboratory on DRI’s Reno campus.
Credit: DRI.
Research immersion internships provide career-building opportunities for students from Nevada’s two-year colleges
From wildflower blooms to microplastics pollution, fourteen students from Nevada’s two-year colleges are spending this fall building career skills in exciting new directions.  The students are conducting hands-on research alongside DRI scientists in Reno and Las Vegas through DRI’s new Research Immersion Internship Program.

Although professional internship opportunities are fairly common in the sciences, many positions are aimed at students who are enrolled in four-year science degree programs. DRI’s new internship program takes a more inclusive approach, creating an opportunity specifically aimed at students from two-year colleges and welcoming those majoring in fields from outside of traditional scientific disciplines.

“Science and innovation thrive when people of diverse skillsets work together, because real-world problems are often very interdisciplinary,” said Internship Program Director Meghan Collins, M.S. “In addition to traditional scientific fields, drawing in students with interests in communications, business, public health, computing, and many other areas can bring new perspectives and new solutions to the table.”

Riccardo Panella and John Cooper in lab

DRI faculty mentor Riccardo Panella, Ph.D., (left) and student intern John Cooper (right) review calculations as part of an ongoing research project that tests a new therapeutic approach to treating metabolic disorders. Panella is an assistant research professor of cancer and genetics with the Center for Genomic Medicine at DRI; Cooper is a student at Truckee Meadows Community College. 

Credit: DRI.
DRI’s internship program began in September and runs for 16 weeks. Students have been placed in teams of two to four people, and are working under the direction of DRI faculty mentors from the Institute’s Reno and Las Vegas campuses on a variety of project themes.

One team of interns is working with Erick Bandala, Ph.D., assistant research professor of environmental science from DRI’s Las Vegas campus, to investigate water security in Native American communities of the Southwestern U.S. His team consists of three students from Nevada State College – two environmental studies majors and one math major.

“Many people in Native American communities lack access to running water in their homes and experience problems with water quality as well,” Bandala said. “We are exploring data that was collected by Tribes and water treatment facilities to learn about the scale of the problem and how it can be improved. I love the challenge and hope that my team will come out with helpful information. Water security is a very complicated issue, but the students that I am working with are very enthusiastic, and I am happy to be interacting with them.”

Other project themes for the program’s inaugural semester include documentation and analysis of wildflower superblooms (above-average bursts of blooming wildflowers) in the Western U.S., an investigation into the effects of wildfire on water repellency of soils, a study on how microplastic particles can be transported through the air, and a study investigating the effects of obesity on health challenges in mice.

Student intern Mary Andres
Riccardo Panella and Mary Andres

Above, left: Student intern Mary Andres from Truckee Meadows Community College prepares reagents needed to analyze lipid profiles and hepatic enzymes in a study being conducted by DRI’s Center for Genomic Medicine. The results of these experiments will pave the way for a new generation of RNA-based therapies to treat metabolic disorders and prevent cancer progression.

Credit: DRI.

Above, right: DRI faculty mentor Riccardo Panella, Ph.D., (left) of the Center for Genomic Medicine and Truckee Meadows Community College student Mary Andres (right) use a bright light to view a sample in Panella’s laboratory in Reno. 

Credit: DRI.
This year’s cohort includes students from Nevada State College, Truckee Meadows Community College, Great Basin College, and the University of Nevada, Reno. Because many of the students are early in their college journeys, or come from fields outside of the sciences, the internship program provides stepping-stones to help them build the fundamental skills they need to succeed, including a month-long period of training prior to implementing their projects.

At the end of the semester, the student teams will deliver their project results and receive feedback from their faculty mentors. The end goal is to help foster the next generation of diverse scientists through mentorship, inclusion, and skill building.

“There are a lot of independent internships available to science majors, but not many  programs that prepare students to be successful working in the sciences in the real world – especially for students who are coming from two-year college programs or from outside of scientific disciplines,” Collins said. “This program aligns with some of DRI’s larger goals of improving diversity and inclusion at DRI and in the sciences as a whole, while also providing important stepping-stones for students to learn to navigate the culture of science.”

Student Intern John Cooper

Student Intern John Cooper from Truckee Meadows Community College prepares reagents in Riccardo Panella’s laboratory at DRI in Reno, as part of DRI’s new Research Internship Immersion Program.

Credit: DRI.

More Information:

For more information on DRI’s Research Immersion Internship Program, please visit: https://www.dri.edu/immersion/.

DRI faculty mentors for the Research Immersion Internship Program include Erick Bandala, Riccardo Panella, Eden Furtak-Cole, Markus Berli, Christine Albano, and Meghan Collins.

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About DRI

The Desert Research Institute (DRI) is a recognized world leader in basic and applied environmental research. Committed to scientific excellence and integrity, DRI faculty, students who work alongside them, and staff have developed scientific knowledge and innovative technologies in research projects around the globe. Since 1959, DRI’s research has advanced scientific knowledge on topics ranging from humans’ impact on the environment to the environment’s impact on humans. DRI’s impactful science and inspiring solutions support Nevada’s diverse economy, provide science-based educational opportunities, and inform policymakers, business leaders, and community members. With campuses in Las Vegas and Reno, DRI serves as the non-profit research arm of the Nevada System of Higher Education. For more information, please visit www.dri.edu.

Does Cold Wildfire Smoke Contribute to Water Repellent Soils in Burned Areas?

Does Cold Wildfire Smoke Contribute to Water Repellent Soils in Burned Areas?

Does Cold Wildfire Smoke Contribute to Water Repellent Soils in Burned Areas?

May 25, 2021
RENO, NEV.

By Kelsey Fitzgerald

Soil Science
Wildfires
Hydrology

Above: After a wildfire, soils in burned areas often become water repellent, leading to increased erosion and flooding after rainfall events. The hillside shown here burned in California’s Loyalton Fire during August 2020.

Credit: Kelsey Fitzgerald/DRI.

A new DRI pilot study finds severe water repellency in sand samples after treatment with both hot and cold smoke.

After a wildfire, soils in burned areas often become water repellent, leading to increased erosion and flooding after rainfall events – a phenomenon that many scientists have attributed to smoke and heat-induced changes in soil chemistry. But this post-fire water repellency may also be caused by wildfire smoke in the absence of heat, according to a new paper from the Desert Research Institute (DRI) in Nevada.

In this pilot study (exploratory research that takes place before a larger-scale study), an interdisciplinary team of scientists led by DRI Associate Research Professor of Atmospheric Science Vera Samburova, Ph.D., exposed samples of clean sand to smoke from burning Jeffrey pine needles and branches in DRI’s combustion chamber, then analyzed the time it took for water droplets placed on the sand surface to be absorbed – a measure of water repellency.

Natasha Sushenko processes samples in the Environmental Microbiology Lab at the Desert Research Institute during a COVID-19 wastewater monitoring study.

A new pilot study by an interdisciplinary team from DRI exposed samples of clean sand to smoke from burning Jeffrey pine needles and branches, then analyzed the time it took for water droplets placed on the sand surface to be absorbed — a measure of water repellency. After exposure to smoke, water droplets sometimes remained on the sand surface for more than 50 minutes without soaking in.

Credit: Vera Samburova/DRI.

The full text of the paper, Effect of Biomass-Burning Emissions on Soil Water Repellent: A Pilot Laboratory Study, is available from Fire: https://www.mdpi.com/2571-6255/4/2/24

The pilot study investigated the effects of smoke and heat on water repellency of the sand and was the first study to also incorporate an analysis of cold smoke. In the experiments, sand was used in place of soil because it could be cleaned thoroughly and analyzed accurately, and Jeffrey pine for a fuel source because it represents a common wildland fire fuel in the Western U.S.

Before exposure to Jeffrey pine smoke, water droplets placed on the surface of the sand samples were quickly absorbed. But after exposure to smoke, the sand samples showed severe-to-extreme water repellency, in some cases retaining water droplets on the sand surface for more than 50 minutes without soaking in. It made little difference whether or not samples had been exposed to heat and smoke, or just cold smoke.

“The classic explanation for fire-induced water repellency is that it is caused as smoke diffuses under rather hot conditions and settles down into the soils, but our work shows that the smoke does not have to be hot to turn the sand hydrophobic — simply the presence of the chemical substances in the smoke is enough,” Samburova said. “This is something we really need to look deeper into because soil water repellency leads to increases in flooding, erosion, and surface runoff.”

Above, left: Jeffrey pine needles and sticks were used as a fuel source in the new DRI study because Jeffrey pine represents a common wildland fire fuel in the Western U.S.

Credit: Vera Samburova/DRI.

Above, right: Jeffrey pine needles and branches burn inside of the combustion chamber at DRI during a new study that investigated the effects of smoke and heat on water repellent of sand samples.

Credit: Vera Samburova/DRI.

This study built on previously published work by former DRI postdoctoral researcher Rose Shillito, Ph.D., (currently with the U.S. Army Corps of Engineers), Markus Berli, Ph.D., of DRI, and Teamrat Ghezzehei, Ph.D., of University of California, Merced, in which the researchers developed an analytical model for relating soil water repellency to infiltration of water.

“Our earlier paper focused on how fire changes the properties of soils, from a hydrology perspective,” Berli explained. “In our current study, we were interested in learning more about the chemistry behind the process of how soils come to be hydrophobic. We’re bringing together geochemistry and organic geochemistry with soil physics and hydrology to understand the impact of fire-induced water repellency on hydrology.”

The project team is now working on a larger proposal to further investigate questions touched on by this study about the roles of heat and smoke in fire-induced water repellency. Among other things, they would like to know how long soil water repellency lasts after a fire, and gain a better understanding of the detailed processes and mechanisms through which cold smoke affects the soil.

In her free time, Natasha enjoys hiking and being outside in beautiful areas like the Desolation Wilderness in California.

DRI’s combustion chamber, pictured here, is a specialized facility that has been designed and built for the open combustion of solid fuels under controlled conditions. In this experiment, it was used to expose samples of clean sand to Jeffrey pine smoke. 

Credit: Kelsey Fitzgerald/DRI.

Gaining a thorough understanding of the process that leads to fire-induced soil water repellency is important because land managers need this information in order to accurately predict where soils are likely to be hydrophobic after a fire, Berli explained.

“We still don’t really understand the processes that lead to this fire-induced soil water repellency,” Berli said. “Depending on what we find, the measures to predict fire-induced water repellency might be different, and this can have a significant impact on how we can predict and prevent flooding or debris flows that happen after a fire.”

“This study was one big step forward, but it highlights the importance of future research on how fires affect soil, because wildfires are affecting thousands and thousands of square kilometers of land each year in the Western U.S., ” Samburova added. “Some of our future goals are to find out how exactly this soil water repellent happens, where it happens and how long it lasts.”

Additional Information:

This study was made possible with support from DRI and the National Science Foundation. Study authors included Vera Samburova, Ph.D., Rose Shillito, Ph.D. (currently with U.S. Army Corps of Engineers), Markus Berli, Ph.D., Andrey Khlystov, Ph.D., and Hans Moosmüller, Ph.D., all from DRI.

The full text of the paper, Effect of Biomass-Burning Emissions on Soil Water Repellency: A Pilot Laboratory Study, is available from Fire: https://www.mdpi.com/2571-6255/4/2/24

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About the Desert Research Institute
The Desert Research Institute (DRI) is a recognized world leader in basic and applied interdisciplinary research. Committed to scientific excellence and integrity, DRI faculty, students, and staff have developed scientific knowledge and innovative technologies in research projects around the globe. Since 1959, DRI’s research has advanced scientific knowledge, supported Nevada’s diversifying economy, provided science-based educational opportunities, and informed policy makers, business leaders, and community members. With campuses in Reno and Las Vegas, DRI serves as the non-profit research arm of the Nevada System of Higher Education. For more information, please visit www.dri.edu

What happens when rain falls on desert soils? An updated model provides answers

What happens when rain falls on desert soils? An updated model provides answers

What happens when rain falls on desert soils?

DEC. 14, 2020
LAS VEGAS, NEV.

Soils
Hydrology
Deserts

An updated model from DRI scientists in Las Vegas provides a new understanding of water movement in dry soils

Several years ago, while studying the environmental impacts of large-scale solar farms in the Nevada desert, Desert Research Institute (DRI) scientists Yuan Luo, Ph.D. and Markus Berli, Ph.D. became interested in one particular question: how does the presence of thousands of solar panels impact desert hydrology?

This question led to more questions. “How do solar panels change the way water hits the ground when it rains?” they asked. “Where does the water go? How much of the rain water  stays in the soil? How deep does it go into the soil?”

“To understand how solar panels impact desert hydrology, we basically needed a better understanding of how desert soils function hydraulically,” explained Luo, postdoctoral researcher with DRI’s Division of Hydrologic Sciences and lead author of a new study in Vadose Zone Journal.

DRI scientists Yuan Luo (left) and Markus Berli (right) inside of DRI's SEPHAS Lysimeter facility in Boulder City, Nev.

DRI scientists Yuan Luo (left) and Markus Berli (right) conducting research at DRI’s SEPHAS Lysimeter facility in Boulder City, Nev. November 2020.

Photograph by Ali Swallow/DRI.

The full text of the paper “Modeling near-surface water redistribution in a desert soil”, is available from Vadose Zone Journal: https://acsess.onlinelibrary.wiley.com/doi/10.1002/vzj2.20081

In the study, Luo, Berli, and colleagues Teamrat Ghezzehei, Ph.D. of the University of California, Merced, and Zhongbo Yu, Ph.D. of the University of Hohai, China, make important improvements to our understanding of how water moves through and gets stored in dry soils by refining an existing computer model.

The model, called HYDRUS-1D, simulates how water redistributes in a sandy desert soil based on precipitation and evaporation data. A first version of the model was developed by a previous DRI graduate student named Jelle Dijkema, but was not working well under conditions where soil moisture levels near the soil surface were very low.

To refine and expand the usefulness of Dijkema’s model, Luo analyzed data from DRI’s SEPHAS Lysimeter facility, located in Boulder City, Nev. Here, large, underground, soil-filled steel tanks have been installed over truck scales to allow researchers to study natural water gains and losses in a soil column under controlled conditions.

Above: Yuan Luo and Markus Berli of DRI’s Division of Hydrologic Sciences used data from DRI’s SEPHAS Lysimeter facility (shown here) to refine an existing model called HYDRUS-1D, which simulates how water moves through dry soils.

Photographs by Ali Swallow/DRI.

Using data from the lysimeters, Luo explored the use of several hydraulic equations to refine Dijkema’s model. The end result, which is described in the new paper, was an improved understanding and model of how moisture moves through and is stored in the upper layers of dry desert soils.

“The first version of the model had some shortcomings,” Luo explained. “It wasn’t working well for very dry soils with volumetric water content lower than 10 percent. The SEPHAS lysimeters provided us with really good data to help understand the phenomenon of how water moves through dry soils as a result of rainfall and evaporation.” 

In desert environments, understanding the movement of water through soils is helpful for a variety of practical uses, including soil restoration, erosion and dust management, and flood risk mitigation. For example, this model will be useful for desert restoration projects, where project managers need to know how much water will be available in the soil  for plants after a desert rainstorm, Berli said. It is also a key piece of the puzzle needed to help answer their original question about how solar farms impact desert hydrology.

“The model is very technical, but all of this technical stuff is just a mathematical way to describe how rainwater moves in the soil once the water hits the soil,” Berli said. “In the bigger picture, this study was motivated by the very practical question of what happens to rainwater when falling on solar farms with thousands and thousands of solar panels in the desert – but to answer questions like that, sometimes you have to dig deep and answer more fundamental questions first.”

Yuan Luo near a lysimeter tank at DRI's SEPHAS Lysimeter facility in boulder city, nevada

DRI scientist Yuan Luo standes near a weighing lysimeter at DRI’s SEPHAS Lysimeter facility in Boulder City, Nev. November 2020.

Photograph by Ali Swallow/DRI.

“In the bigger picture, this study was motivated by the very practical question of what happens to rainwater when falling on solar farms with thousands and thousands of solar panels in the desert – but to answer questions like that, sometimes you have to dig deep and answer more fundamental questions first.”

Additional Information:

This study was funded by the DRI Foundation Innovative Research Program, the National Science Foundation, and the U.S. Army Corps of Engineers. Rose Shillito, Ph.D. (DRI/ACOE) and Nicole Damon (DRI) also contributed to the success of this project.

The full text of the paper “Modeling near-surface water redistribution in a desert soil”, is available from Vadose Zone Journal: https://acsess.onlinelibrary.wiley.com/doi/10.1002/vzj2.20081  

To learn more about DRI’s SEPHAS Lysimeter facility, please visit: https://www.dri.edu/sephas/lysimeters/

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The Desert Research Institute (DRI) is a recognized world leader in basic and applied interdisciplinary research. Committed to scientific excellence and integrity, DRI faculty, students, and staff have developed scientific knowledge and innovative technologies in research projects around the globe. Since 1959, DRI’s research has advanced scientific knowledge, supported Nevada’s diversifying economy, provided science-based educational opportunities, and informed policy makers, business leaders, and community members. With campuses in Reno and Las Vegas, DRI serves as the non-profit research arm of the Nevada System of Higher Education. For more information, please visit  www.dri.edu.

Researchers Markus Berli and Yuan Luo near a sign for the Desert Research Institute

DRI scientists Markus Berli and Yuan Luo. November 2020.

Photograph by Ali Swallow/DRI.

Low-severity wildfires impact soils more than previously believed

Low-severity wildfires impact soils more than previously believed

Above: In semi-arid ecosystems such as the Humboldt-Toiyabe National Forest near Las Vegas, which burned as part of the Carpenter 1 fire during July and August 2013, fuel is limited and fires tend to be short lived and low in peak temperature. New research shows that these fires are more harmful to soils than they initially appear. This photo was taken on January 6, 2015 – approximately 18 months after the wildfire. Credit: Teamrat Ghezzehei, UCM.


New research shows negative effects of fire on soil structure and organic matter

Las Vegas, NV (August 28, 2018): Low-severity wildland fires and prescribed burns have long been presumed by scientists and resource managers to be harmless to soils, but this may not be the case, new research shows.

According to two new studies by a team from the University of California, Merced (UCM) and the Desert Research Institute (DRI), low-severity burns – in which fire moves quickly and soil temperature does not exceed 250oC (482oF) – cause damage to soil structure and organic matter in ways that are not immediately apparent after a fire.

“When you have a high-severity fire, you burn off the organic matter from the soil and the impact is immediate,” said Teamrat Ghezzehei, Ph.D., principal investigator of the two studies and Associate Professor of Environmental Soil Physics at UCM. “In a low-severity fire, the organic matter doesn’t burn off, and there is no visible destruction right away. But the burning weakens the soil structure, and unless you come back at a later time and carefully look at the soil, you wouldn’t notice the damage.”

DRI researcher Markus Berli, Ph.D., Associate Research Professor of Environmental Science, became interested in studying this phenomenon while visiting a burned area near Ely, Nev. in 2009, where he made the unexpected observation that a prescribed, low-severity fire had resulted in soil structure damage in the burned area. He and several colleagues from DRI conducted a follow-up study on another controlled burn in the area, and found that soil structure that appeared to be fine immediately after a fire but deteriorated over the weeks and months that followed. Berli then teamed up with Ghezzehei and a team from UCM that included graduate student Mathew Jian, and Associate Professor Asmeret Asefaw Berhe, Ph.D., to further investigate.

Researcher examines soils in a burned area near Las Vegas.

Researcher Markus Berli from the Desert Research Institute examines the soils at a burned area in the Humboldt-Toiyabe National Forest near Las Vegas on January 6, 2015, approximately 18 months after the area burned in the Carpenter 1 fire of 2013. Credit: Teamrat Ghezzehei, UCM.

Soil consists of large and small mineral particles (gravel, sand, silt, and clay) which are bound together by organic matter, water and other materials to form aggregates. When soil aggregates are exposed to severe fires, the organic matter burns, altering the physical structure of the soil and increasing the risk of erosion in burned areas. In low-severity burn areas where organic matter doesn’t experience significant losses, the team wondered if the soil structure was being degraded by another process, such as by the boiling of water held within soil aggregates?

In a study published in AGU Geophysical Research Letters in May 2018, the UCM-DRI team investigated this question, using soil samples from an unburned forest area in Mariposa County, Calif. and from unburned shrubland in Clark County, Nev. to analyze the impacts of low-severity fires on soil structure. They heated soil aggregates to temperatures that simulated the conditions of a low-severity fire (175oC/347oF) over a 15-minute period, then looked for changes in the soil’s internal pore pressure and tensile strength (the force required to pull the aggregate apart).

During the experiment, they observed that pore pressure within the soil aggregates rose to a peak as water boiled and vaporized, then dropped as the bonds in the soil aggregates broke and vapor escaped. Tensile strength measurements showed that the wetter soil aggregates had been weakened more than drier soil samples during this process.

“Our results show that the heat produced by low-severity fires is actually enough to do damage to soil structure, and that the damage is worse if the soils are wet,” Berli explained. “This is important information for resource managers because it implies that prescribed burns and other fires that occur during wetter times of year may be more harmful to soils than fires that occur during dry times.”Next, the research team wondered what the impact of this structural degradation was on the organic matter that the soil structure normally protects. Soil organic matter consists primarily of microbes and decomposing plant tissue, and contributes to the overall stability and water-holding capacity of soils.

In a second study that was published in Frontiers in Environmental Science in late July, the UCM-DRI research team conducted simulated burn experiments to weaken the structure of the soil aggregates, and tested the soils for changes in quality and quantity of several types of organic matter over a 70-day period.

They found that heating of soils led to the release of organic carbon into the atmosphere as CO2 during the weeks and months after the fire, and again found that the highest levels of degradation occurred in soils that were moist. This loss of organic carbon is important for several reasons, Ghezzehei explained.

“The loss of organic matter from soil to the atmosphere directly contributes to climate change, because that carbon is released as CO2,” Ghezzehei said. “Organic matter that is lost due to fires is also the most important reserve of nutrients for soil micro-organisms, and it is the glue that holds soil aggregates together. Once you lose the structure, there are a lot of other things that happen. For example, infiltration becomes slower, you get more runoff, you have erosion.”

Researcher collects soil samples in burned area near Las Vegas.

Researcher Rose Shillito from DRI collects soil samples in a burned area in the Humboldt-Toiyabe National Forest near Las Vegas on January 6, 2015, approximately 18 months after the area burned in the Carpenter 1 fire of 2013. Credit: Teamrat Ghezzehei, UCM.

Although the research team’s findings showed several detrimental effects of fire on soils, low-severity wildfires and prescribed burns are known to benefit ecosystems in other ways — recycling nutrients back into the soil and getting rid of overgrown vegetation, for example. It is not yet clear whether the negative impacts on soil associated with these low-severity fires outweigh the positives, Berli says, but the team hopes that their research results will help to inform land managers as they manage wildfires and plan prescribed burns.

“There is very little fuel in arid and semi-arid areas, and thus fires tend to be short lived and relatively low in peak temperature,” Ghezzehei said. “In contrast to the hot fires and that burn for days and weeks that we see in the news, these seem to be benign and we usually treat them as such. Our work shows that low-severity fires are not as harmless as they may appear.”

The study, “Soil Structural Degradation During Low‐Severity Burns,” was published on May 31, 2018 in the journal AGU Geophysical Research Letters and is available here: https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2018GL078053.

The study, “Vulnerability of Physically Protected Soil Organic Carbon to Loss Under Low Severity Fires,” was published July 19, 2018 in the journal Frontiers in Environmental Science, and is available here: https://www.frontiersin.org/articles/10.3389/fenvs.2018.00066/full.

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