January 15, 2010

Nitrogen threat in earth growing

Last year, reactive nitrogen was identified as one of nine key global pollution threats and second worst in terms of having already exceeded a maximum “planetary boundary,” according to a study reported in the journal Nature.

“Nitrogen plays a tremendously important role in feeding the world’s peoples, so that’s a very positive benefit for humanity,” says James Galloway, a professor of environmental science at the University of Virginia, Charlottesville, and a leading nitrogen researcher. “The problem is how to maximize nitrogen’s benefits while diminishing its negatives – especially waste.”

Africa is one of a few places in the world where wider use of nitrogen fertilizers makes sense to help feed the population, many researchers agree. In the US, however, as much as 40 percent of reactive nitrogen is wasted – washing off farm fields into rivers, lakes, and the ocean, where oxygen-depleted “dead zones” are growing in number and size worldwide.
The situation is even worse in China, which uses about twice as much nitrogen fertilizer as the US to yield about the same amount of crops. As much as three-quarters of all nitrogen used to grow rice in China may be wasted, says Vaclav Smil, a nitrogen expert at the University of Manitoba in Winnipeg.
Vehicle exhaust, power-plant exhaust, and large-animal feeding operations are all sources of nitrogen emissions. Rising energy needs have meant more nitrogen oxides (NOx) – implicated in smog, acid rain, and global warming – emitted from fossil-fueled power plants.
Most nitrogen doesn’t stay in the atmosphere the way carbon dioxide from fossil fuel does, but precipitates out within a few days. Ammonia – a mixture of hydrogen and nitrogen – becomes ammonium when mixed with water and acts like fertilizer when it falls to the ground in rain.


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