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Environment

Ecosystems are overdosing on nitrogen, study finds

Humans activities are overloading ecosystems with nitrogen, a study has found, polluting water systems and possibly contributing to climate change - but age-old sustainable practices could wind back the damage.

File photo of decaying fish floating on the surface of the water

Excess nitrogen is poisoning water systems worldwide

Nitrogen is essential to plant life and makes up more than three quarters of the Earth's atmosphere – but there can be too much of a good thing.

A rise in fossil fuel-burning and an increase in nitrogen-producing industrial and agricultural activities are leading to excess levels of the element in the environment, according to a study just published in the journal Science.

Researchers Donald Canfield, Alex Glazer and Paul Falkowski – of the University of Southern Denmark, the University of California, Berkeley and Rutgers University respectively – found that excess nitrogen is polluting fresh waters and coastal zones and may contribute to climate change, but that ecological damage could be reduced through the adoption of centuries-old sustainable practices.

"It has a tremendous impact on both aquatic ecosystems and the atmosphere," Falkowski told Deutsche Welle.

Side effects

Shadow of a farmer holding a scythe over a pile of grain

Much of the problem can be traced to increased use of fertilizers in the last 50 years

Excess accumulation of nitrogen in the environment is believed to contribute to a range of environmental problems including 'dead zones' in water ways, acid rain, smog, climate change and ozone depletion.

Falkowski said nitrogen pollution could be found around to world, from the Baltic Sea to the Gulf of Mexico and the South China Sea. "It is coupled to agriculture. Most countries in the world simply make a calculation that it is too expensive to reduce the nitrogen loading to rivers," he said.

The study centered on how human activities are influencing the nitrogen cycle and 'nitrogen fixation' – the process by which elemental nitrogen in the atmosphere is transformed into the nitrogen sources needed to create the building blocks of life.

For billions of years, that cycle has been regulated by volcanic and later microbial processes – but at the start of the 20th century, human contributions to the nitrogen cycle began to skyrocket, the researchers found.

Sudden impact

"No phenomenon has probably impacted the nitrogen cycle more than human inputs of nitrogen into the cycle in the last 2.5 billion years," Falkowski said. "Human activities currently contribute twice as much terrestrial nitrogen fixation as natural sources."

Much of the rise in human contributions can be explained by an 800 percent jump in use of nitrogen fertilizers between 1960 and 2000.

Even when used correctly these fertilizers contribute extra nitrogen to the environment, but when applied inefficiently, the nitrogen they contain is more likely to wash out and pollute nearby water ways.

Excess nitrogen in the environment may also lead to the release of nitrogen oxide – a greenhouse gas more potent than carbon dioxide.

Falkowski said that, over time, the nitrogen cycle would likely stabilize.

However, with global population expected to pass the seven-billion mark by 2012, a growing demand for food could also end up driving greater fertilizer use.

The Science paper's authors argue that unless sustainable farming practices are adopted now, damage to the nitrogen cycle could persist for decades.

A Pakistani girl holds a dish while lining up to get a ration of rice during a donated food distribution

Population growth is likely to increase demand for food and fertilizers

Rethinking traditional farming

Simple solutions could include optimizing the timing and amounts of fertilizer applications, and using traditional breeding techniques to boost the ability of crops like wheat, barley and rye to absorb nitrogen efficiently, the researchers wrote.

In Europe, according to European agriculture union COPA-COGECA, farmers have already been responding to the problem with a 20 percent cut in fertilizer-use between 2003 and 2008.

"There's only so far we can reduce fertilizer use before it starts to affect yield and food security, which will be of growing concern in the future because food demand around the world is expected to double by 2050," COPA-COGECA spokesperson Amanda Cheesley said.

Cheesley said that reducing fertilizer use any further is now a matter of innovating to produce varieties of crops that demand less fertilizer.

Rutgers' Falkowski said that fertilizer application practices in Europe are generally better than in most parts of the world. "However, new types of [timed-release] fertilizers would probably be more practical in the short term relative to developing new crop varieties that require less fertilizer," he said.

Author: Sophie Tarr
Editor: Nathan Witkop

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