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Air Pollution Fallout Means 'You Drink What You Drive'

Air Pollution Fallout Means 'You Drink What You Drive'

(October 8, 2001)

Nitrogen in air pollution filters through the trees and into the ground water of our local forests and wilderness areas, said researchers at the University of California, Riverside and the USDA Forest Service, Forest Fire Laboratory in Riverside.

'The rates of nitrogen absorption here in the LA area are among the highest in the world,' said Thomas Meixner, assistant professor of hydrology and water resources at UCR. He and Mark Fenn, a scientist affiliated with the Forest Fire Laboratory, have measured nitrates in 22 mountain streams in the local area, including the San Gorgonio and the Cucamonga wilderness areas.

In some cases, the stream water contained up to six parts per million, more than half of the federal drinking water standard of 10 parts per million. 'Forests that are normally highly nitrogen-deficient are now nitrogen-enriched, analogous to an overfertilized agricultural field,' Fenn said.

The two Riverside researchers will present their research at the Second International Nitrogen Conference on Science and Policy, Sunday, Oct. 14 through Thursday, Oct. 18 near Washington, D.C. The conference looks at how increases in nitrogen have changed the world, from global warming to polluted drinking water.

Excess nitrogen in the environment comes from the combustion of fossil fuels, increased demand for animal protein in human diets, increased use of synthetic nitrogen fertilizers, and widespread planting of nitrogen-fixing legumes. Over time, excess nitrogen has built up in the environment.

The local mountains act as a catch basin for smog, augmented by ammonia vapor rising from cow manure on dairy lands. The problem here in the Los Angeles basin is comparable to the mountains downwind of Mexico City, which has a serious photochemical air pollution problem, Fenn said.

At a high-pollution study site near Crestline, Fenn's colleagues at the Forest Fire Laboratory noted changes in the root system of Ponderosa pine trees; and an unusual attack by the fruit tree leafroller insect on California Black Oak tree populations. Both, he said, could stem from rising nitrogen levels.

'People usually think of Southern California smog problems as a function of all the cars here, and that is, of course the main source,' Fenn said. 'In other words, 'You drink what you drive.' But in the forests of the San Bernardino mountains, ammonia rising from agricultural operations is another important source of nitrogen.

'We found a similar situation in the southern Sierra Nevada, which receives agricultural emissions from the Central Valley.' If the Chino dairies move to the north over the next couple of decades, Fenn said, nitrogen emissions may rise in the water of the Sierra Nevada, a source of drinking water for the entire state.

UCR's Meixner said that the semi-arid climate of Southern California handles nitrogen deposits differently than more humid areas. 'Here, we don't have acid rain, as much as we have acid fog, or acid dust,' he said. Nitrogen research done in humid areas simply doesn't always apply. 'Here it rains for three months and then doesn't rain for nine,' Meixner said. 'We have to find our own solutions.'

The University of California, Riverside ( is a doctoral research university, a living laboratory for groundbreaking exploration of issues critical to Inland Southern California, the state and communities around the world. Reflecting California's diverse culture, UCR's enrollment has exceeded 21,000 students. The campus opened a medical school in 2013 and has reached the heart of the Coachella Valley by way of the UCR Palm Desert Center. The campus has an annual statewide economic impact of more than $1 billion.

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