Everything's Elemental

One line on the directory board upstairs in the Phytotron Building reads "Jonathan Karr DEVIL." But instead of being fiery hot, the room it sends you to is remarkably cold. There a group of large, sleek machines hum and buzz as they process samples of soil, plants, water, and other material collected in scientific experiments around the world. These machines are the stars of Duke's new mass spectrometry lab, officially named "DEVIL" for Duke EnVironmental stable Isotope Laboratory. The chemical information they churn out is so precise that measurements differing by even a ten-thousandth of a percent are notable.

Mass spectrometry is used widely in science to determine the chemical makeup of anything from molecules to mammoths to meteors. The equipment in the Phytotron, however, is designed for the specific needs of ecologists and environmental scientists. "This facility," says Jonathan Karr, DEVIL's technical director, "specializes in measuring the ratios of different forms of just four elements--carbon, nitrogen, oxygen, and hydrogen--that are involved in biological and geological processes."

If you examine the chemistry of, say, nitrogen, you'll find that almost all the nitrogen on Earth is in a form known as N14. However, a small but predictable portion of it--around 0.37 percent--is a different, slightly heavier form called N15. The atoms of N15 are like those of N14, except they have an extra uncharged particle, an extra neutron. Called "stable isotopes," the two forms behave similarly but not identically in nature.

The differences between isotopes make possible two important types of research. One is the study of natural abundances of the four elements, such as bear expert Barrie Gilbert's research on fish-based N15 in the British Columbian rainforest. N15 is generally more common in the ocean (and thus in salmon) than it is on land; by finding it in soil and plants near where bears are taking salmon, Gilbert and his student can better understand the role of bears and fish in forest fertilization. A second type of study uses isotopes as tracers. You can introduce a known quantity of isotope into a process like plant growth or soil decay, and follow it through to learn where it goes and how long it stays.