South SFV Today

The escalating prevalence of extensive, enduring wildfires in recent years can lead to alterations in soil chemistry, impacting water contamination, air quality, and plant growth. However, these changes are often inadequately monitored and seldom incorporated into post-fire recovery strategies or risk evaluations. This is according to a review study published on May 14 in Nature Reviews Earth & Environment.

The study was spearheaded by scientists from Stanford University and Colorado State University. They discovered that improved techniques are required to monitor modifications in soil and surrounding ecosystems. Enhanced monitoring could guide decisions regarding the treatment of drinking water sourced from burned areas, support reforestation efforts, and safeguard workers against toxins during cleanup, rebuilding, or revegetation processes.

“In our study, we mesh organic and inorganic chemistry together, whereas a lot of fire research will typically just consider one subject area,” stated soil biogeochemist Claudia Avila. She co-led the study with Alandra Lopez while both researchers were postdoctoral scholars at Stanford Doerr School of Sustainability under Professor Scott Fendorf.

“A better understanding of the molecular mechanisms in soil can help explain why drinking water from a forest fire-impacted watershed is suddenly more toxic or why a forest is not coming back,” added Thomas Borch, a senior author of the study and soil chemist at Colorado State University.

The review also highlights evidence suggesting that wildfires may release more carbon dioxide into the atmosphere than previously thought. Contrary to hopes that charcoal-like remnants known as black carbon would trap carbon dioxide for extended periods, recent findings indicate that this may not be the case. “Carbon that's gone through forest fires and becomes black carbon can actually turn more readily into carbon dioxide by microbes than previously thought,” explained Fendorf.

Wildfires can provide several benefits for ecosystems. Some fires can increase nitrogen levels in soils and enhance the water solubility of soil organic carbon—both crucial for regrowth. However, recovery is contingent on the presence of other chemicals. For instance, certain types of organic molecules formed in soil during fires are needed for many seeds to germinate. If these molecules, known as karrikins, are not produced in sufficient quantities due to local soil chemistry and fire conditions, revegetation may be stunted.

The review also revealed that wildfires can double the soil concentration of a group of toxic chemicals known as polycyclic aromatic hydrocarbons. These can induce chemical reactions that inhibit revegetation. This could explain why trees have struggled to reestablish after wildfires in vast areas of the Rocky Mountains.

Wildfires can also alter the chemical properties of inorganic materials such as metals within soils. Fire can transform these metals into dangerous forms that readily move through the environment, ending up in the air or nearby water. The scientists documented high levels of a hazardous form of metal chromium at wildfire sites resulting from heat-induced transformation of naturally occurring, benign forms of chromium.

Broader surveillance and modeling could inform strategies for protecting lives, property, and natural resources, as well as wildlife management decisions. “By identifying an area that has a high potential for chromium release, we can call for prescribed burns that are lower intensity and reduce the potential for high-intensity, toxin-releasing fires,” suggested Avila.

“If we can grasp the complexity of the intertwined processes happening both on the organic and inorganic side, then that helps give us the ability to predict outcomes for different fire, landscape, and geological conditions,” concluded Fendorf.