Global nitrogen: cycling out of control.

Abstract

Like the Earth’s water, nitrogen compounds cycle through the air, aquatic systems, and soil. But unlike water, these compounds are being injected into the environment in ever increasing quantities. In doing so, we are altering the global nitrogen cycle, causing possible grave impacts on biodiversity, global warming, water quality, human health, and even the rate of population growth in developing nations. In a world surrounded by nitrogen, you would think there’s always been plenty to go around and that perhaps a little more wouldn’t matter. But having enough of the right kind of nitrogen—reactive nitrogen that has been “fixed,” or converted from the nonreactive N2 form—determines such fundamentals of life as the extent of plant growth, which in turn determines to a large extent the dynamics of the world’s food supply. During the twentieth century, mankind has produced increasingly more reactive nitrogen, intentionally as fertilizer and unintentionally as a by-product of combusting fossil fuels. Although carbon dioxide may get more press, “the nitrogen cycle has been altered more than any other basic element cycle,” says John Aber, vice president for research and public service at the University of New Hampshire. And now, he says, humans are adding more reactive nitrogen to the global nitrogen cycle than all other sources combined. Yet, reactive nitrogen is hardly all bad. The use of nitrogen fertilizer is critical to feeding the world’s hungry, say researchers including University of Virginia environmental sciences professor James Galloway. The question, then, is how do we manage nitrogen responsibly?