What pollution kills more aquatic life than the BP oil spill and causes up to 300 times more global warming per ton than carbon dioxide?
Nitrogen compounds from agricultural fertilizers, farm effluent and poorly treated sewage.
A study published last week in the Proceedings of the National Academy of Sciences revealed that nitrogen pollution in rivers and streams is being converted by microbes into nitrous oxide, a gas that contributes both to global warming and to destruction of the ozone layer that protects the Earth’s surface from deadly ultraviolet rays.
The concentration of nitrous oxide in the atmosphere has grown 20 percent over the past century. The compound is 300 times more potent than CO2 as a greenhouse gas.
The new report points the finger at “nitrogen-enriched urbanized and agricultural watersheds, highlighting the importance of managing nitrogen before it reaches open water,” said Henry Gholz, program director for the National Science Foundation’s Division of Environmental Biology. “This new global emission estimate is startling.”
Adding urgency to the new findings is a study published in Science magazine just two months ago, which reported that human agricultural and industrial activity is overwhelming the environment with nitrogen.
“Altogether, human activities currently contribute twice as much terrestrial nitrogen fixation as natural sources, and provide around 45 percent of the total biological useful nitrogen produced annually on Earth,” said Paul Falkowski, a Rutgers University scientist and a member of the research team.
A major culprit is the 800 percent increase in nitrogen fertilizer from 1960 to 2000. Some 60 percent of that fertilizer never gets absorbed by plants. Much of it filters down into ground water or is washed away into rivers, where it flows into lakes and bays.
Last month, a major report on “Corporate Agribusiness and America’s Waterways,” by Environment America, also blamed giant agribusinesses that produce megatons of nitrogen-rich waste from enormous animal feedlots.
Each year, more than half a billion chickens are raised on the Delmarva Peninsula along Chesapeake Bay. They leave behind more than a billion pounds of poop. “When nutrients from chicken manure find their way into the bay, they contribute to the algae blooms that leave only 12 percent of the Chesapeake Bay with adequate levels of dissolved oxygen during the summer months,” the report notes.
Nitrogen fertilizer has also been implicated as a major contributor to the giant “dead zone” that appears each year in the Gulf of Mexico as vast quantities of algae bloom and subsequently decompose, sucking oxygen out of the water and suffocating life over thousands of square miles each year.
The dead zone has grown 20 percent since 1985 as agricultural and livestock waste from the Midwest pours out the mouth of the Mississippi River in ever greater quantities. “The growth of these dead zones is an ecological time bomb,” said Donald Scavia, an environmental scientist at the University of Michigan.
After decades of awareness of these problems, the Environmental Protection Agency is now taking steps in some areas to recommend tougher initiatives to reduce runoff of nitrogen-rich fertilizer, animal waste and sewage. Some of the remedies are likely to be expensive—and have come under predictable attack. But Chris Watts, an environmental expert at Actio Corportion, notes that farmers could help the environment and save money by cutting back on their use of fertilizer with no reduction at all in crop yields. That sounds like a good place to begin a long-overdue cleanup program.