Nitrate pollution is tied to crumbling bedrock (AP)
arne at snowcrest.net
Thu Oct 22 07:38:23 EST 1998
Dear fellow news-groupies. Thought you'd find this interesting....
Nitrate pollution is tied to crumbling bedrock
5.34 a.m. ET (935 GMT) October 22, 1998
By Joseph B. Verrengia, Associated Press
(AP) There may be a natural explanation for all those nitrates in wells and reservoirs.
Researchers working in a central California watershed have determined for the first time that high levels of nitrates are released as crumbly bedrock weathers year after year. Sloppy farming and factory pollution take a lot of the public blame for nitrate pollution.
Nitrogen compounds that leach into waterways and aquifers are linked to environmental damage and serious illnesses. In high concentrations, nitrates can cause miscarriages and "blue baby syndrome,'' in which an infant's red blood cells are unable to carry sufficient oxygen.
The pollution taints drinking water around the world, including many communities in the United States.
Until now, the contamination has been blamed on overuse of fertilizer and releases of untreated livestock manure, as well as timber clear-cutting and factory emissions that contribute to acid rain.
But exposed rock deposits around the world contain as much as 20 percent of the planet's total nitrogen, the researchers calculated, and geology might be a significant contributor in some places.
Their report was published in today's issue of the journal Nature.
"It appears that the early rains flush out the nitrogen that weathers from the rock during the summer,'' said biogeochemist JoAnn Holloway of the University of California, Davis. "Even small areas of these rocks can have a profound influence on water quality.''
Other researchers said that farming and industry still represent a threat to drinking water, and even natural contamination must be treated if the nitrate levels exceed public health standards.
"Humans have created the problem by building reservoirs that act like a pool for these nitrates to concentrate,'' said Lloyd Walker, a biological resources engineer at Colorado State University. "In a natural environment, these nitrates would flush right through.''
In the study, UC-Davis researchers sampled the water in 35 streams in the 600-square-mile Mokelumne River watershed in the Sierra Nevada southeast of Sacramento.
They were seeking to pinpoint the source of elevated nitrate levels in downstream reservoirs. The nitrates have caused large-scale algae blooms and fish kills, though levels were within federal health standards.
Holloway and others ruled out several culprits before concluding the contamination has geological origins. Laboratory tests showed that the nitrate is a form of naturally occurring nitrogen rather than isotopes of nitrogen from feedlots and fertilizer.
Near the mountain resort of Kirkwood, nitrate levels in the water were much lower than in the downstream reservoirs. The hard granite bedrock there contains much less nitrogen and it weathers slowly, Holloway said.
However, the bedrock changes to slate and other sedimentary deposits in lower elevations near the foothills town of Jackson, Calif. The soft bedrock there formed from nitrogen-rich organic materials hundreds of millions of years ago.
The study was funded by the California Department of Forestry. The researchers ruled out timber clear-cutting as a nitrate source because water samples from logged areas showed low nitrate levels.
Planting trees may help reverse the contamination.
"Oak trees have deep root systems that can draw up the nitrogen,'' said co-author Randy Dahlgren of Cal-Davis.
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