In the Breath of the Forest

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by Neil Caudle

asically, it’s a radio-antenna tower made of rods held together with Z-shaped, quarter-inch metal braces," he says. "And the weather is hot—one hundred degrees in the canopy, ninety-nine percent relative humidity. So you’re soaking wet. And you start climbing this tower, and by fifty feet you’re wondering why you didn’t just stay home watching TV or, better yet, go for a swim in Key Largo.

"Then at a hundred feet you’re still below the forest canopy, but you’re up there with the climbing vines and the bird noises, and it’s still hot, and you’re dripping and you’re thirsty, and your arms are tired. And the metal is dimpled and rough, so when you need to rest your hands you are hugging the Zs and the metal nicks and scrapes your arms. So you have to make this decision. And in my case, the decision was, 'I’m the group leader, and if I don’t do this now, I might not ever do this.'

"So I did. And then, when I got to a hundred and fifty feet, all of a sudden I felt a cool breeze, and I popped up to the top of that tower. I stayed for three-and-a-half hours and got sunburned. I could see the Tapajos River, fifteen kilometers away. There was no sound, no jet contrails. I had macaws flying around me. Once you’re above them, they don’t notice you any more. So they fly along below you, chattering away."

He is back in Chapel Hill now, but Christopher Martens still hasn’t really come down from that perch in the clouds. As he describes the spectacular rivers and animals and trees, describes his fearless team and their adventures in Amazonia, you can feel the rain forest spreading steamy and green all around him. And, to make things just perfect, more perfect than he’d ever dared to hope, the instruments work. Every 15 minutes, 24 hours a day, the data come boiling out of those pressure cookers and align themselves into beautiful, meaningful valleys and peaks.

n the door of his office, Martens has taped a sample printout—a series of colored lines, each color corresponding to an altitude. "What you see," Martens says, tracing lines with his finger, "is a buildup in radon that begins during the nighttime, when everything is more still than usual—unless there’s a storm, of course. So there’s an inversion layer that forms over the canopy—it’s called a nocturnal inversion—and it basically caps the forest and makes everything quiet. The air becomes stagnant. The radon doesn’t escape. So it builds up until morning, when the sun comes up and starts heating the top of the canopy. At first you see the radon drop at the upper elevations because the heat has to work its way down. And then, all of a sudden as the sun reaches down in the forest, there’s a flushing. Ventilation starts, and the radon drops."

Martens had known to expect this pattern of nighttime buildup and daytime venting. But during the late afternoon, the levels were building again. That was a surprise.

"What we’ve learned," he says, "is that on most days there’s a second really stagnant-air period in these tropical rain forests that I don’t think has been fully understood. We believe that it happens at the end of hot, steamy days when the hot canopy begins giving heat back to the cooling atmosphere. It’s hot, but the air is stagnant, so there’s a lack of turbulence, and you’ll sometimes see a radon level higher than the nocturnal ones. This is the first time, to my knowledge, that this has ever been measured this way."

Ultimately, the goal of the radon work is what Martens calls a "gas exchange coefficient," a factor that could be multiplied by the concentration of any gas to yield the exchange rate of that gas. Having such a coefficient would be a fundamental step toward learning how rain forests affect greenhouse gases.

In the meanwhile, the project’s first step—to set up an accurate, reliable system for continuously measuring radon in air as it moves through the rain forest—has been a resounding success. So Martens and his team are celebrating, but just a little. They know that the technical issues will grow more complex as they begin working with other scientists to factor the radon data into numerical models. "Once you meet your initial goals people get all excited," Martens says, smiling. "They want you to become more sophisticated."

One research group in the LBA project wants him to take his instruments to higher altitudes, using airplanes to collect the samples. Other groups would like to use the radon data to corroborate their studies of how gases travel and mix in random eddies of air sampling of various gases. These groups are taking "eddy correlation flux measurements," which employ the rapid sampling of gas concentrations and a numerical model to estimate rates of exchange.

"We can cross-check and corroborate those kinds of measurements because we use a totally different approach," Martens says. "So if a big jet of air that’s low in radon comes in from outside and flushes the canopy with low-radon air, we’ll see it. Because we’re independent of the other models."

or Martens, though, the next logical level of sophistication involves sorting out what happens at ground zero—on the rain forest floor. Having spent a good portion of his career studying "biogeochemical cycling," which, among other things, involves learning how gases enter the atmosphere from decaying organic matter in coastal sediments and muds, Martens is at home on soggy ground. Using several of the "fluxometers," the crock-potted radon detector invented at Carolina, the team will measure the rate at which radon escapes the soil and how that rate varies with such things as rainfall and soil hydrology. Martens’ plans for Brazil also include a study of methane, perhaps the most pernicious of greenhouse gases. By detecting the isotopic signatures of methane produced by rapidly decaying organic matter, Martens hopes to help calculate how much methane the rain forest yields.

And so, as he outlines this work from his office in Venable Hall, constantly harking back to something he’s learned on the coast of North Carolina or the tundra of Alaska or the slopes of northern Quebec, it seems as though Martens has seized his career by its various roots and planted it right in the heart of Brazil. The radon is the same, the methane is the same, and the physics are the same. But now there are jaguars and bushmaster snakes. There are harpy eagles that swoop down and pick off monkeys from the canopy’s top.

He knows that Mary Menton can take care of herself, so he won’t say he’s worried about her. But he can’t help thinking his way through the checklist of hazards. The nearest hospital is hours away, so she will just have to watch out for 10-foot bushmaster snakes, one of which has already crossed her path. And when her truck goes up to its headlights in muddy water, so deep that the engine needs a snorkel to suck air into its carburetor, she will just have to find the right gear and drive on. She will have to learn how to go back to sleep, at four in the morning, when the howler monkey troops come prowling through the forest, loud as a raucous political rally.

Yes, there is help with the work. Two Brazilian students are already on-site, and one of them has a new driver’s license. The quarters are decent, and there’s a reasonably liveable outpost a few miles away. So the basics are covered. The team is in place. And the hardware is pulling some mighty fine numbers right out of the air.

And Chris Martens will be there as soon as he can.

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