DRI Scientist Contributes to New Research on Toxic Mercury Deposition in Forests

DRI Scientist Contributes to New Research on Toxic Mercury Deposition in Forests

DRI Research Highlight

Mercury is deposited from the atmosphere into forests worldwide in greater quantities than previously thought, according to new research in the journal PNAS led by former Desert Research Institute (DRI) scientist Daniel Obrist (currently with University of Massachusets, Lowell) and a team that included Hans Moosmüller of DRI in Reno. Moosmüller contributed analytical tools for the measurement of mercury fluxes in this study, and also participated in writing the paper. The full news release from UMass Lowell is below.

The full study, Previously unaccounted atmospheric mercury deposition in a midlatitude deciduous forest, is available from PNAS.

Study Shows Forests Play Grater Role in Depositing Toxic Mercury Across the Globe

Reposted from UMass Lowell

LOWELL, Mass. – Researchers led by a UMass Lowell environmental science professor say mercury measurements in a Massachusetts forest indicate the toxic element is deposited in forests across the globe in much greater quantities than previously understood.

The team’s results underscore concern for the health and well-being of people, wildlife and waterways, according to Prof. Daniel Obrist, as mercury accumulating in forests ultimately runs off into streams and rivers, ending up in lakes and oceans.

Mercury is a highly toxic pollutant that threatens fish, birds, mammals and humans. Hundreds of tons of it are released into the atmosphere each year by coal-burning power plants, as well as through gold mining and other industrial processes, and the pollutant is distributed by winds and currents across the globe. Long-term exposure to mercury, or consuming food containing high levels of the pollutant, can lead to reproductive, immune, neurological and cardiovascular problems, according to Obrist, chair of UMass Lowell’s Department of Environmental, Earth and Atmospheric Sciences.

Forests constitute the world’s most abundant, productive and widespread ecosystems on land, according to Obrist, who said the study is the first that examines a full picture of how mercury in the atmosphere is deposited at any rural forest in the world, including the deposition of mercury in its gaseous form, which most previous studies do not address.

“Trees take up gaseous mercury from the atmosphere through their leaves and as plants shed their leaves or die off, they basically transfer that atmospheric mercury to the ecosystems,” he said.

The results of the project, which is supported by a three-year, $873,000 grant from the National Science Foundation (NSF), were published this week in an issue of the Proceedings of the National Academy of Sciences. UMass Lowell student Eric Roy, a double-major in meteorology and mathematics from Lowell, is among the study’s co-authors.

For the past 16 months, the team has measured how mercury in the atmosphere gets deposited at Harvard Forest in Petersham, a nearly 4,000-acre site that includes hardwood deciduous broadleaf trees such as red oak and red maple that shed their leaves every year. A set of measurement systems placed at various heights on the forest’s 100-foot-tall research tower assessed the site’s gaseous mercury deposition from the tree canopy to the forest floor.

“Seventy-six percent of the mercury deposition at this forest comes from gaseous atmospheric mercury. It’s five times greater than mercury deposited by rain and snow and three times greater than mercury that gets deposited through litterfall, which is mercury transferred by leaves falling to the ground and which has previously been used by other researchers as a proxy for estimating gaseous mercury deposition in forests,” Obrist said.

“Our study suggests that mercury loading in forests has been underestimated by a factor of about two and that forests worldwide may be a much larger global absorber and collector of gaseous mercury than currently assumed. This larger-than-anticipated accumulation may explain surprisingly high mercury levels observed in soils across rural forests,” he said.

Plants seem to dominate as a source of mercury on land, accounting for 54 to 94 percent of the deposits in soils across North America. The total global amount of mercury deposited to land currently is estimated at about 1,500 to 1,800 metric tons per year, but it may be more than double if other forests show similar levels of deposition, according to Obrist.

The researchers are continuing their work at a second forest in Howland in northern Maine. Howland Forest, a nearly 600-acre research site full of evergreens that retain their leaves year-round, offers a distinctly different habitat than the deciduous forest in Petersham. Assessing both forests will allow researchers to examine differences in mercury accumulation between different forest types, Obrist said.

The work is providing a hands-on research experience for Roy, a UMass Lowell Honors College student who was invited to become a member of the university’s Immersive Scholar program in 2019. The initiative enables first-year students with outstanding academic credentials to participate in lab work and research right from the start of their academic studies.

“It’s really exciting to be a co-author,” Roy said. “This study allowed us to quantify how much mercury is being accumulated in this type of forest. Modelers can use these results to improve their understanding of how mercury cycles through the environment on a global scale and how that might change in the future.”

Roy helped analyze the data collected in the field.

“Eric’s contributions to the study are tremendous. It’s not very common for an undergrad to play such an important role in a major, federally funded research project,” Obrist said. “His work is really impressive and he has become more and more active in data analysis and doing complex flux calculations and data processing. He really earned himself second author position in the paper in the Proceedings of the National Academy of Sciences.”

Other contributors to the study include Asst. Prof. Róisín Commane of Columbia University; students and postdoctoral researchers from UMass Lowell and Columbia University; and collaborators from Harvard University; the Desert Research Institute in Reno, Nevada; and the Northwest Institute of Eco-Environment and Resources and the University of the Chinese Academy of Sciences in Lanzhou. Additional research support was provided by the U.S. Department of Energy.

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UMass Lowell is a national research university offering its more than 18,000 students bachelor’s, master’s and doctoral degrees in business, education, engineering, fine arts, health, humanities, sciences and social sciences. UMass Lowell delivers high-quality educational programs and personal attention from leading faculty and staff, all of which prepare graduates to be leaders in their communities and around the globe. www.uml.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