The largest source, however, is agriculture
Human-made nitrogen now affects even isolated waterways, presaging a world where humanity drives the natural cycle of this vital nutrient.
Scientists have recently found humanity’s nitrogen footprint on watersheds once thought to be isolated and pristine, indicating our impact on the world is more widespread than previously imagined.
These findings show that natural nitrogen equilibriums have shifted drastically and are now driven largely by human factors. This world awash in nitrogen can have devastating effects on health, ecology and the climate.
Nitrogen is an important element to all life as we know it. However, its various forms are not equal in how they affect the environment. Nitrous oxide, for example, is an especially potent greenhouse gas. According to U.S. EPA, it is 300 times more powerful than carbon dioxide at trapping heat, and it can stay in the atmosphere 300 years.
Meanwhile, nitrogen gas, which makes up close to 80 percent of the air we breathe, is relatively inert. Other forms, like nitrates, form aerosols in the atmosphere that can seed clouds, which generally have a net cooling effect on the climate.
Nitrates, nitrites and nitrous oxide can arise naturally, or they can come from human activities. Many of these compounds are byproducts of combustion, whether in cars and trucks or factories and power plants. The largest source, however, is agriculture. As the world’s population surges toward 7 billion people, many see nitrogen fertilizers as the only way to increase crop yields enough to feed a hungry planet.
But what’s really surprising is the scale of these impacts. According to a report published last month in the journal Science, researchers found that human activities produce more reactive nitrogen than all of nature combined.
“Almost certainly, more new fixed nitrogen and utilizable nitrogen is produced by the sum total of human activity than by the sum total of natural processes,” said Alexander Wolfe, a professor of Earth sciences at the University of Alberta, who co-authored the paper. “It turns out the nitrogen cycle is more pervasively controlled by humanity” than previously thought.
A big component is liquid fertilizer
Fixed nitrogen refers to nitrogen that is taken from the air and turned into more reactive forms like ammonia, either by bacteria or by man-made techniques. Humanity’s impacts, however, are so vast that nitrogen compounds from combustion and agriculture have found their way into lake beds isolated from farms, roads and suburban neighborhoods.
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