The first step in making soil from scratch: Add water.
“I am from Ukraine, so I know the perfect soils are from Ukraine,” says Katerina Dontsova.
Now, home is in the middle of the dusty Sonoran Desert.
“That’s why I have to make some from scratch,” she says, laughing.
Dontsova is a soil researcher at Biosphere 2’s Landscape Evolution Observatory (LEO) and is an associate research professor in the department of soil, water and environmental science at the University of Arizona.
LEO allows researchers like Dontsova to observe and measure how lifeless, mineral rock transforms into living landscapes. After only five years, they’re already witnessing soil formation.
LEO research will also contribute to the growing field of carbon capture and storage, she said. Burning fossil fuels for energy emits carbon dioxide (CO2), a greenhouse gas, which in excess causes rising global temperatures and climate change.
“It’s critical that we find some mechanisms to remove CO2 from the atmosphere,” Dontsova said, “and soils appear to be one of the best ways of doing this because they have two available mechanisms that allow carbon sequestration.”
Scientific disciplines involved at LEO span soil, water and environmental science; ecology and evolutionary biology; geoscience; hydrology; water resources; atmospheric science; and natural resources.
“To tackle the grand challenges and answer the big questions, you have to bring together disciplines to answer those questions,” said Kevin Bonine, education and outreach director of Biosphere 2.
The landscape observatory was built within the glass- and steel-framed section of Biosphere 2 originally used to grow crops during the ill-fated, sealed environment experiments of the early ’90s.
For LEO, crews filled three identical 100- by 36-foot tilted steel beds with 1 million pounds of meter-deep crushed volcanic rock, called basalt, excavated near Flagstaff. The project was completed in 2012 after five years of planning and construction, and about $7 million spent.
The basalt was crushed into grains large enough for water to flow, yet small enough to retain some moisture when gently “rained on” by sprinklers arching over each slope.
Almost 2,000 sensors buried within, situated on and hanging above the slopes monitor soil moisture, temperature, CO2 levels and more as they change over time.
Each slope sits on scales to weigh the system as water moves in and out.
“If you start with existing soil, it has legacy and history that you cannot know,” said Peter Troch, LEO’s principal investigator and science director for Biosphere 2.
But the basalt is simple and clean.
It lacks the diversity of materials found in natural soils, making it easier to see changes than in complex soil.
“Basaltic rocks have a lot of basic elements in them,” Dontsova said. “These elements tend to dissolve very fast when rained on,” and then react with other elements, minerals and biota in the soil.
As this process of dissolving and recombining continues, the basaltic sand of the slopes gets more complex and becomes a pool of nutrients for life to thrive on.
Lock it up
Atmospheric CO2 hitches a ride on raindrops, lands on the basaltic sand, then reacts with the elements from the dissolved basalt such as calcium, magnesium and iron. The reaction most commonly locks up carbon as bicarbonates, a chalky material that’s basically baking soda.
“You have carbon in the soil now rather than in the atmosphere,” Dontsova said.
Rainwater washes bicarbonates into rivers, which run into oceans where carbon, in it’s bicarbonate prison, can be stored for centuries or more, she said.
In the desert, there’s nowhere to go, so bicarbonates settle in the dirt and harden, forming caliches, the hardpan just under a layer of desert dirt.
At LEO, it’s washed downhill and into instruments that monitor water volume and composition.
After the very first rain, 11 pounds of CO2 were removed from one slope.
Soil also captures carbon in the form of organic material, the building blocks of life. Plants soak CO2 out of the air and use it to build their bodies.
The soil’s two natural carbon-capturing processes store four times as much carbon as the atmosphere.
“We always knew it was happening, but we’re now looking at the ways how it can be enhanced, how it can be used to remove CO2 from the atmosphere,” Dontsova said.
Applying the science
One of the most famous carbon capture and storage (CCS) facilities is at Sleipner, a natural-gas field in the North Sea off Norway. Since 1996, 1 million tons of CO2 has been injected annually into sedimentary rock deep under the ocean floor, physically trapping the CO2 with dense rocks.
But leakage is a risk.
The sedimentary rock does not contain elements that would chemically lock the carbon underground.
Increasingly, researchers are looking toward the benefits of injecting CO2 into basalt, just like the crushed rock at LEO.
The Pacific Northwest National Laboratory (PNNL) in Richland, Washington, originally discovered the quick conversion power of basalt and published what is the seminal paper on the subject in 2006, said Pete McGrail, a PNNL laboratory fellow.
He noted that many variables can influence the rate at which basalt absorbs CO2, including the varied chemical composition of basalts, the presence of microscopic life and the environmental pressure and temperature in which a reaction occurs.
PNNL has been running field experiments by pumping CO2 into basalt deep underground.
LEO operates under a different and less-extreme range of variables and on a scale that is somewhere between a typical lab and field studies. The knowledge harvested from LEO is shared within the growing field of carbon capture and sequestration, which includes PNNL.
Investigating basalt’s effectiveness under different conditions is an important piece of the puzzle, McGrail said, so that ultimately carbon capture via basalt can be implemented at an industrial scale.