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Melanie Mayes digs deep to explain soil's role in climate change

ORNL scientist Melanie Mayes conducts interdisciplinary research in carbon and nutrient cycling in soils. (Photo: Marsha Walton)

At Oak Ridge National Laboratory (ORNL) in Tennessee, soils scientist Melanie Mayes wants to understand the critical role soil plays in climate change.

"We have a really good idea about what's going on in the atmosphere; a pretty good idea what's going on in the ocean; and then the land is a mess!" she said.

Soil is a big carbon sink. Understanding how it gets there, and how much it can hold and release, is a process known as carbon cycling, and researchers like Mayes develop models to make predictions about our future climate.

Mayes says most current models ignore the fact that decomposition is actually performed by microbes. When animals and plants die, they release carbon-rich materials into the soil as they decay. Enzymes speed up the process, degrading the organic material, and releasing dissolved carbon molecules that microbes use as materials for new life. That process leads to the release of carbon dioxide.

So her models focus on the carbon dioxide-releasing activity of these microbes in the ground. 

"MEND is our model. This is the Microbial Enzyme Decomposition Model. We designed it here at ORNL several years ago. What we wanted to do was bring explicit microbes into the soil decomposition approach," she said.

The MEND model, based on the physiological functions of microbes, may help scientists understand how the world will be different if warming temperatures change existing rates of decomposition.

Temperature, moisture, and permafrost all affect decomposition rates. So for example, scientists must take into account that as temperatures increase, the decomposition process may change because microbes are likely to get less efficient (just like humans, who have to work harder to accomplish the same tasks if temperatures are hot and humid).

That provides insight about soil, because soil either stores or releases carbon based on how rapidly carbon-rich materials are breaking down. Studies using MEND have also taken into account times of the year when microbes are dormant.

Mayes says in some studies, the MEND model shows that after a few years, microbes may simply adjust to higher temperatures. She says it's also possible that other microbes might take over.

For her work on soil decomposition, Mayes was selected as an AAAS Fellow in 2014 "for distinguished contributions to the field of soil hydrogeology, using experimentation to improve models of biogeochemical processes relevant to contaminant transport and organic carbon cycling."

Mayes wasn't always focused on climate change. Her early work was on contaminant hydrogeology. "When I went to college, environmental contamination of groundwater was very, very important. So that was the career path that I chose," she said. Mayes spent time at the Hanford site, the nuclear production complex in Washington state.

There she studied the migration of radionuclides beneath the Hanford Tank Farms, with a goal of long-term management of huge quantities of multiple contaminants at the site.

Mayes says understanding the toxic contamination at Hanford was actually a helpful transition to her current focus on climate change, even though she is no longer dealing with nuclear materials.

"You are just thinking about how something moves through soil," she said.

And she says nothing is more important than tackling global climate change.   

"You have to look around and see what's needed, and apply your skills to that. And it has to be a conscious effort, where to put your emphasis, where to put your research. There are lots of things I could do, but I think this is really, really an important area to be in," she said.

Mayes believes it may take either a generational change or some devastating human impacts before the world truly starts to tackle the effects of climate change.

She's inspired by the outlook of young scientists at the University of Tennessee, where she holds a Joint Faculty Appointment with the Department of Earth and Planetary Sciences. Mayes has also mentored dozens of students and researchers, including young people from Historically Black Colleges and Universities and the Chinese Academy of Sciences.

"Many of them really want to do something that is important, that makes a difference. Climate science really hits that mark," adding, "a lot of younger people are like, 'of course, climate change is real,' and we can [and want] do something about it."


Marsha Walton

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