Nitrogen Overdose

0 Comments | Oakland Tribune, Aug 12, 2007 | by Suzanne Bohan

With fertilizer literally falling from the sky, plants -- many of them invasive weeds -- get turbocharged from nitrogen, altering natural habitats by driving out native plants and the animals that rely on them.

California is at particular risk for this disruption, and the Bay Area is designated as one of the nation's "hot spots" for nitrogen- induced ecological shifts. Weiss estimates that in some Bay Area regions, auto emissions deliver up to 20 pounds per acre a year of nitrogen -- about half the amount typically used on lawns.

And of the 225 plant species in California listed as threatened or endangered by the federal and state government, 101 are exposed to levels of nitrogen suspected of causing ecological disruption, according to a May 2006 California Energy Commission study prepared by Weiss.

The nitrogen also alters bodies of water by inducing algae growth. At Lake Tahoe, for example, algae growth is contributing to the steady loss of clarity in the lake's famously clear waters.

"We've actually found that about 55 percent of the nitrogen that gets into the lake comes from the air," said John Reuter, acting associate director of the University of California, Davis Tahoe Environmental Research Center. "So the sky is literally falling for that."

Excess nitrogen also harms human health -- through contaminated water, air pollutants and by its role in spreading mosquito-borne diseases like West Nile disease by increasing algal food sources in water, according to a 2003 study on human health and excess nitrogen.

'Drive-by extinction'

Edgewood Park, located next to Interstate 280 in southern San Mateo County, is becoming a classic example within scientific circles of nitrogen's disruptive ecological effects.

Cars whizzing by on I-280 leave in their wake a trail of nitrogen. Plants absorb it, while some nitrogen also settles and accumulates in the nutrient-poor soil at Edgewood.

That extra dose of nitrogen enabled Italian rye grass, an aggressive nonnative, to drive out plantain, a favorite food of the bay checkerspot butterfly.

In 2002, nine years after the land was set aside as a preserve, the threatened butterfly disappeared from the area. This spring, after mowing down the rye grass, Weiss and others re-introduced the butterfly to the park.

Weiss believes a similar process is under way at Antioch Dunes National Wildlife Refuge, a

55-acre parcel in Antioch that's the last of the ancient San Joaquin River dune system. Invasive grasses have overtaken the sandy dunes, driving out a buckwheat plant native to the area. The Lange's Metalmark butterfly, which makes its only home in the dunes, feeds on the buckwheat, and the insect's numbers are rapidly declining. Two endangered wildflowers, the Antioch Dunes evening primrose and Contra Costa wallflower, are also struggling against the onslaught of invasive grass.

This list goes on: In the Mohave and Sonoran deserts, scientists believe that nitrogen deposition explains the spread of nonnative grasses. These grasses fuel fires that are devastating to a desert ecosystem poorly equipped to regenerate after a blaze, according to a 2003 study on nitrogen deposition in the western United States.