Nitrogen, Like Carbon, Also Leaving Footprint

May 15, 2008 -- People are getting increasingly savvy about their carbon footprint -- the ways in which carbon from fossil fuels or plants is converted into carbon dioxide, and how that CO2 in turn is taken up by the land and ocean.

Now, researchers argue, it's time we started watching our nitrogen footprint, too.

Through fertilizer use and fossil fuel-burning, humans are loading the environment with reactive forms of nitrogen that researchers say cause smog, acid rain, coastal dead zones, climate change and a growing ozone hole.

That's quite a list. But there is good news.

As two teams of scientists publishing papers in this week's issue of Science point out, the nitrogen problem is much easier to solve than the carbon one.

"Everyone is concerned with the carbon balance and increasingly with the availability of food," said study co-author Alan Townsend, of the University of Colorado at Boulder. "But those get straight to the nitrogen cycle issue."

"The biofuels explosion is intimately linked to the nitrogen cycle," he added. "Some of the main biofuels being looked at today are nitrogen-intensive crops."

Reactive nitrogen creation increased more than tenfold, from 16.5 million tons per year in 1860 to 172 million tons in 1995, the authors report. Most of this is attributable to fertilizer use.

Since the early 1900s when Fritz Haber and Carl Bosch figured out how to mimic microorganisms' ability to take inert nitrogen molecules from the air and make them into reactive forms of ammonia and nitrate that plants can use, humans have been able to supply nitrogen to soil at will -- and grow a lot more crops.

By 2005, output grew to 206 million tons, the team reports, driven by 20 and 26 percent increases in grain and meat production, respectively, since 1995.