Worsening wildfires have EMSL researchers looking for impact on soil, climate

Wildfires today burn twice as much tree cover worldwide as they did 20 years ago.

More than 22.9 million acres of tree cover were lost globally in 2021 due to wildfires compared to 11.9 million acres lost in 2003, according to figures from the World Resources Institute.

Increased greenhouse gases in the atmosphere have resulted in extreme temperatures and drought conditions worldwide, providing the perfect proving ground for fires that burn longer and span further.

Immediate impacts of these farther-reaching wildfires are easily visible to the naked eye: loss of ecosystems, destruction of homes and other structures, and worsening air quality due to wildfire smoke. But what about the impacts not seen with the naked eye? That is exactly what researchers at the Environmental Molecular Sciences Laboratory (EMSL) are trying to get to the bottom of.

Both EMSL users and staff scientists study some of Earth’s tiniest components—molecular compounds, chemical processes, microorganisms, and atmospheric particles that, combined, work together to form the world we see today.

Any increase in wildfires disrupts the natural rhythm of these systems, and as a result, stands to disrupt life on Earth. EMSL researchers aim to find out how, why, and possibly offer solutions to help preserve the planet amid and post wildfires.

Will microbial communities survive?

Steven Allison, a professor in the biological and environmental sciences at the University of California, Irvine, is studying the impact of wildfires on soil systems, and more specifically, the microbes that make life possible beneath our feet. He is partnering with EMSL as part of a Large-Scale Research project to conduct a variety of analyses on soil samples from a site in Southern California where wildfires are prevalent.

“For many years, our team has looked at the role of microbial community composition and diversity in regulating the carbon cycle and specifically how plant litter decays,” he said. “Once plants senesce and die, what’s the fate of that material and how do microbes on the surface soil affect that process of decomposition?”

Microbes, Allison said, support the recycling of decaying and dead plant materials by turning them into nutrients for growing plants to use. Microbes like bacteria and fungi are also vitally important in the capture and release of carbon, which is significant when studying atmospheric makeup and climate change.

The area where more information is needed, however, is how well microbial communities respond and repopulate when exposed to extreme events. Through their project, Allison said they are looking at whether disturbances like wildfires, nitrogen deposition, and drought affect microbes’ metabolism and their capacity to metabolize dead plant material.

Initially, the team was primarily looking at just nitrogen deposition and drought as stressors. But coincidentally, a wildfire destroyed one of their experiments in 2020.

“We decided to use it to our advantage,” Allison said. “Sure, the fire destroyed our experiment temporarily, but we used it as an opportunity to study the impact and legacy of that disturbance. We want to know the legacy of how perturbations like a fire impact the vital functioning of these microbes.”

Allison and his team are working with EMSL staff scientists to access a variety of instruments to probe soil and its microbes. They are using liquid chromatography-mass spectrometry to analyze microbial life history traits that will provide a good picture of the soluble compounds in their samples and their diversity. Gas chromatography-mass spectrometry will provide data on more volatile chemical compounds in their samples. Nuclear magnetic resonance helps to measure the amounts of different chemical constituents in their samples. Further, they are using X-ray computed tomography to provide a three-dimensional look at the structure of their soil samples.

“We really threw everything but the kitchen sink at this project that will allow us to compare each of the different techniques and pull together a much more complete picture of these processes and responses,” he said.

Allison said the team has already received a lot of great data from each of the techniques.

“I’m excited to continue the last remaining samples and put it all together,” he said.

Looking toward the future, Allison is interested in the longer-term microbial responses and their relation to climate change. They plan to continue their experiments, where they aim to eventually combine their data and build out models that will help predict microbial responses based on different conditions and environmental stressors. They are putting together a framework that includes multiple facets of soil biology, including microbial evolution, physiology, and ecology.

Allison said he and his team are interested in synthesizing the importance of evolution of genetic change.

“Are the microbes evolving at the same speed that climate change is occurring?” he asked. “Hopefully we can make sense of that, the ongoing change, and then put this all together in a predictive framework. It is very difficult to make accurate predictions, so really, that’s kind of the holy grail. But we can put our best knowledge into the models and refine them and they will get better and better.”

Brown clouds as stressors on atmosphere

When examining wildfires and their impact on the atmosphere, staff scientists at EMSL are especially interested in atmospheric particles that are not always visible to the naked eye.

Nurun Nahar Lata, a postdoctoral researcher at EMSL, works as part of a team of researchers in the Terrestrial-Atmospheric Processes Integrated Research Platform (IRP) to study a range of particulate matter, especially aerosol particles and compounds in the atmosphere. These aerosol particles affect cloud formation, cloud dynamics, precipitation, cycling of carbon and other relevant compounds, and more.

Depending on their composition, aerosols can either be hygroscopic (able to absorb moisture) or hydrophobic (unable to absorb moisture), which affects their ability to form clouds and ice in the atmosphere.

As part of a few active research projects, the EMSL team, led by IRP leader Swarup China, is examining the molecular makeup of aerosols in areas that have been affected by wildfires, how far those aerosols travel, how long they remain in the atmosphere, as well as how their makeup affects cloud and ice formation long term.

“Wildfire aerosols, in particular, have an adverse effect on the climate,” Lata said.

Different particles, she said, are emitted from wildfires stemming from the burning of plants and other materials. A range of carbon-based particles are released, including a special type of carbon called black carbon.

Black carbon particles absorb solar radiation, which contributes to temperature fluctuations that cause disruptions in atmospheric processes. They are also initially hydrophobic—they do not absorb moisture. This flux in temperature and disruption to moisture absorption leads to changes in weather patterns that interrupt many other processes on Earth. The crops that depend on regular rain during certain seasons, for example, may not receive their required precipitation for a standard crop yield.

A specific type of organic aerosol called tarball is also released during wildfires. Researchers have much to learn about how this type of aerosol is formed, its long-term impact on the atmosphere, as well as how long they remain and how far they travel. Tarball particles are spherical in nature, which is different from other types of aerosols.

“These particles are interesting to study because very little is known about the formation mechanism of tarball in the atmosphere and how they are affecting cloud formation or ice formation in the atmosphere,” Lata said.

Because not a lot is known about tarball particles, the EMSL team is also researching the differences in freshly emitted aerosols containing these particles compared to those that have aged.

“Initially when a fire starts, you see lot of black or light brownish smoke depending on temperature and other factors,” Lata said. “But after two to three weeks, that smoke turns into a different color. Those are aged aerosols.”

By learning about the differences and impacts of fresh aerosols compared to aged aerosols, important insights can be made not only about how they affect the atmosphere and cloud formation, but also how they stand to affect human health.

“The release of these aerosols is really difficult to control and contain,” Lata said. “But through research, we can develop additional preventative measures. One simple thing we can do now is plant more trees.”