Burning questions: The mysteries of pyrogenic carbon and the effects of prescribed fire on soil

When you think of a forest on fire, you aren’t usually thinking about what’s happening in the soil- but graduate student Ali Moss is. The Spencer Research Grant winner and Warnell School of Forestry and Natural Resources student’s research investigates the relationship between prescribed fire and carbon cycling, specifically studying an organic material known as pyrogenic carbon. This form of organic carbon appears when soil interacts with fire, and Moss intends to learn its secrets.

Soils are beautiful! Moss examines soils collected immediately after the prescribed burn in April 2021. In the background, pyrogenic carbon from burned grasses and litter blankets the soil surface.

“One of the big areas of mystery is that pyrogenic carbon is present in rivers, and is travelling from rivers to the ocean,” Moss said, “but we don’t really understand the details of how it moves from soil to waterways, and we don’t really understand how it becomes dissolved.” Pyrogenic carbon tends to persist in soil longer than unburned organic matter. Researchers originally thought that this was because microbes couldn’t break down pyrogenic carbon, but this since been disputed.

“We know that pyrogenic carbon is harder for microorganisms to decompose than regular organic matter,” Moss explained. “But it’s always a mistake to underestimate microorganisms, because they can do, like, anything.” Moving forward, Moss hopes to characterize dissolved pyrogenic carbon in South Georgia forests managed with prescribed fire, and figure out how it makes its way into water.

There are several moving parts to this research: Moss and their team pull soil cores to get a profile of organic matter at different soil depths. Then, to investigate the connections between carbon in the soil and in the water, they pull water samples directly from the soil using lysimeters. They also do extractions of soil in water in order to test and compare two different methods for studying dissolved pyrogenic carbon in soil.

A field of lysimeters installed in the burned stand of forest immediately after the prescribed fire, April 2021. A lysimeter is a device used to measure evapotranspiration by recording the amount of water percolating through soil.

Another major question is simply how long pyrogenic carbon can last in the soil after a burn. “Because pyrogenic carbon hangs out in the soil longer, it might be an important carbon sink,” Moss said, explaining how carbon, pulled from the atmosphere by plants, may remain sequestered in the soil longer after it has been exposed to fire. “Some pyrogenic carbon does hang out in the soils for millennia, but most of it is probably cycling out within decades or centuries. So what are the controls on this? How can we get a better idea of what kind of sink pyrogenic carbon is and how would we quantify that?”

The experiment is currently underway near Tifton, Georgia and compares two stands of longleaf pine trees, one of which is not managed with fire, and one where Moss and their team performed a prescribed fire back in April of 2021. Prescribed fire is a forestry management technique that involves strategic burning. The practice brings a lot of known environmental benefits that are still being explored—and Moss is a big fan. “I think prescribed fire is awesome.” Moss said. “Getting to participate in prescribed fire I felt was really cool…It’s a really powerful tool.”

The prescribed fire in April 2021, shortly after ignition: a backing fire crawls through the understory with low intensity.

Part of her interest in the project stems from this enthusiasm for prescribed fire. “Despite its importance as a land management tool,” Moss said in their Spencer Research Grant proposal, “prescribed fire science remains underfunded compared to wildfire science, resulting in many knowledge gaps.”

Moss hopes her research may one day help inform forest managers how to regulate carbon through fire. “I love to talk to people about prescribed fires and spread the word about how awesome prescribed fire is.”

Ali Moss in March 2021, assessing fuel composition before the prescribed fire.

Moss’s research is funded by the Warnell School of Forestry and Natural Resources as well as a 2022 Spencer Research Grant. The grant is an annual award given to graduate students studying freshwater resource management and conservation. It is named for the late John Kyle Spencer, an Odum graduate student who was passionate about freshwater research. Moss’s project reflects a love for ecological science and conservation-focused management techniques.

Photos provided by Ali Moss. Story by Olivia Allen.

Laura Naslund, sitting in a canoe on a pond, smiles while taking emissions data.

A Day in the Life of a Pond: Measuring Small-Reservoir Emissions to Inform Infrastructure Decisions

By 7:45 a.m. on Tuesday, June 21, Laura Naslund had already spent over an hour in a canoe on a little pond on the east side of Athens, Georgia. Naslund, a graduate student in the Odum School of Ecology and a 2022 Spencer Grant recipient, was finishing up the first field sampling event of her new research project. She’d started work early on Monday morning, and was still paddling a canoe out to measure gas emissions all over the pond 24 hours later.

“The idea is to understand the times, places and pathways that are most important for emissions,” Naslund said over a quick breakfast, “and then apply that information to a later study at more sites which examines the drivers of the differences in emissions between sites.” 

There are 364 reservoirs in Athens-Clarke County, but only 23 of them are listed in the National Inventory of Dams, leaving hundreds of smaller reservoirs that receive far less attention from freshwater research and management alike.

Laura Naslund and volunteer assistant Ally Whiteis paddle a canoe across a small pond for field sampling.
Laura Naslund and volunteer assistant Ally Whiteis paddle a canoe across a small pond for sampling, around the 2-hour mark of the 24-hour field sampling.

Naslund believes these small reservoirs may have a much larger impact on inland water systems than we currently recognize. She hopes to expand our understanding of freshwater reservoir emissions by focusing research attention on the small ponds of Athens. The end goal of Naslund’s research is to help inform infrastructure decisions regarding which of these dams have the greatest environmental impact and which may be highest priority for removal.

“Particularly as we are about to have the largest infrastructure investment probably in my lifetime, I think now’s a good time to start thinking about how we can use ecological knowledge to inform where and what kind of infrastructure we have,” she explained. “And this project, I think, is a little bit unique among that body of work in that it’s focused on the end of an infrastructure life cycle.”

Naslund is particularly dedicated to accurate field testing: data collection for this research will involve sampling all over each test reservoir for over 24 hours at each event. These methods were designed to get the most accurate possible understanding of where, when and how gases are emitted throughout a day.

Laura Naslund paddles a canoe across a wollfia-covered pond.
Laura Naslund paddles a canoe across a wollfia-covered pond, around the 6-hour mark of her 24-hour field sampling.

“I think researchers have thought about spatial variation a lot, we’ve thought about seasonal variation a lot, but we’ve though less about the variation in emissions that happens over the course of a single day,” Naslund explained. By focusing on variation at a daily scale, Naslund hopes to collect emissions data that more accurately represents the natural history and spatial heterogeneity of a system.

It’s strenuous work to sample for 30 hours at a time, but Naslund doesn’t mind camping out. “The places that I’m working in are beautiful. So that always helps!”

She also acknowledged that she could not do this research alone. Her team of volunteer assistants included professors, undergraduates, and fellow graduate students, who came in shifts throughout the 30-hour sampling. “It’s been really great to collaborate with people, to show them new techniques, and to learn from them,” Naslund said.

Ally Whiteis, Odum undergraduate, paddles a canoe on a wolffia-covered pond.
Ally Whiteis, Odum undergraduate, paddling a field canoe.
Olivia Allen, Odum undergraduate, sitting behind Laura Naslund in a field canoe and recording data.
Olivia Allen, Odum undergraduate, recording data.

Naslund’s research is funded by the Network for Engineering With Nature, a collaboration between UGA and the US Army Corps of Engineers, along with a grant from the Odum School of Ecology and a 2022 Spencer Grant from the River Basin Center. The Spencer Grants are annual awards given to graduate students studying freshwater management and conservation. The grant is named for the late John Kyle Spencer, an Odum graduate student who was passionate about freshwater research. Research like Naslund’s is a reflection of this passion for freshwater science and cooperation among environmental researchers.

Photos and story by Olivia Allen