Study: ‘safe’ nitrogen levels unsafe for wildflowers

By John Upton

When we think about air pollution, it’s easy to imagine airborne chemicals that kill or stunt wildlife by infiltrating tissues and disrupting cellular processes. But that is not the case with nitrogen pollution.

Nitrogen pollution is released from vehicle exhausts and power plant smoke stacks, which liberate the long-dormant compounds from tainted fossil fuels. Nitrogen is a fertilizer — plants lap it up — and farmers and gardeners have a habit of using too much of the stuff, causing it to spill into waterways and over nearby habitats.

Illustrated by Perry Shirley.
Illustrated by Perry Shirley.

When airborne nitrogen pollution fertilizes nutrient poor ecosystems, such as the rocky, serpentine soils of inland California, the native plant species that long ago adapted to the difficult growing conditions can be quickly edged out by weeds. It’s a typical case of environmental havoc helping generalist species displace specialists.

Governments are aware of the hazards of nitrogen pollution and they set limits that are considered safe. But scientists who studied wildflower populations growing within so-called safe limits of nitrogen pollution discovered major impacts on the native flowers.

“We studied many grasslands along the natural gradient of pollution across Europe,” Manchester Metropolitan University Professor Nancy Dise, one of the authors of the study, which was published in December in the Proceedings of the National Academy of Sciences, told The Ecologist. “We found that at even relatively clean sites, low levels of pollution had an effect on the abundance of some plant species.”

The scientists say their findings highlight the need for governments to review pollution rules and to vigorously protect areas that have not yet been tainted.

“Our results highlight the importance of protecting currently unpolluted areas from new pollution sources,” they wrote in their paper. “We cannot rule out ecological impacts from even relatively small increases in reactive N deposition.”