Clean forests prompt pollution rethink

Nitrogen in unpolluted streams is more organic. <br>© Nature <br>

South American streams call current nitrogen-cycle theory into question.

Pollution may have altered northern hemisphere forests dramatically. The surprise finding that clean forests use nitrogen differently to polluted ones emphasizes the effect that humans have on the planet’s nitrogen cycle1. It may even prompt a rethink of the way that this cycle works.

Humans have added vast amounts of nitrogen to the earth’s ecosystems. The element fertilizes plants. To understand what affect this has had already, and how the planet might fare in the future, we need to know how forests used nitrogen before this artificial influx began.

So Steven Perakis and Lars Hedin, ecologists at Cornell University, Ithaca, New York, searched the globe for an environment with as little nitrogen pollution as possible. They settled on 100 streams in temperate forests in Chile and Argentina, far from industry.

They found that more than three-quarters of the nitrogen in these streams is organic (combined with carbon). Nitrogen from pollution is overwhelmingly inorganic – chemically bound to oxygen, hydrogen or metals.

Over 70% of the nitrogen in woodland rivers in Europe and North America is in the form of inorganic nitrate. But in the 100 South American streams, nitrate was the least abundant form of the element, at only 5%.

So it looks as if northern nitrate is a legacy of human activity. “People have had an even greater effect than we thought,” says Perakis.

“It’s an amazingly powerful message,” says ecosystems researcher Knute Nadelhoffer of the Marine Biological Laboratory at Woods Hole, Massachusetts. “It changes the way we think about the nitrogen baseline in pristine environments.”

It’s a good reminder of how much pollution has altered northern ecosystems, comments Bridget Emmett, who studies nitrogen pollution at the Centre for Ecology and Hydrology in Bangor, Wales. “Whether the baseline in Chile is the same as the baseline would have been in northern systems is debatable,” she cautions.

Cycle path

Nitrogen makes up about 80% of the air, but only a few bacteria can turn the gas into a form that plants can use.

Over the past century, nitrate fertilizers and nitric oxides emitted from the burning of fossil fuels have roughly doubled the amount of nitrogen available to the biosphere. And farmers are still adding nitrogen to the land, particularly in developing countries.

Plants and microbes have taken up most of the slack. But large quantities of nitrogen are still washed into rivers and the sea, either because the element is not used or because it is released through death or leaf fall.

In many freshwater, estuarine and coastal environments, such as the Gulf of Mexico, this fertilization has changed the range of plants and animals that live there. Nitrogen-loving species swamp others more suited to poorer conditions (the same thing happens in a fertilized lawn). The extra nitrogen can also feed suffocating blooms of algae.

We need to think about nitrogen emissions in the same way that we consider the influence of sulphur on acid rain, or carbon on the climate, says Nadelhoffer.

“We have perturbed the nitrogen cycle much more than the carbon cycle,” he says. “Most forests are still retaining more nitrogen than they release. The question is how much they can retain and for how long.”

The theory that seeks to answer these questions currently hinges on nitrate. The new finding might force a rethink. “It seems that our models might be biased,” Perakis concludes.

References

  1. Perakis, S. S. & Hedin, L. O. Nitrogen loss from unpolluted South American forests mainly via dissolved organic compounds. Nature, 415, 416 – 419, (2002).

Media Contact

JOHN WHITFIELD © Nature News Service

Alle Nachrichten aus der Kategorie: Ecology, The Environment and Conservation

This complex theme deals primarily with interactions between organisms and the environmental factors that impact them, but to a greater extent between individual inanimate environmental factors.

innovations-report offers informative reports and articles on topics such as climate protection, landscape conservation, ecological systems, wildlife and nature parks and ecosystem efficiency and balance.

Zurück zur Startseite

Kommentare (0)

Schreib Kommentar

Neueste Beiträge

Scientists achieve higher precision weak force measurement between protons, neutrons

Through a one-of-a-kind experiment at the Department of Energy’s Oak Ridge National Laboratory, nuclear physicists have precisely measured the weak interaction between protons and neutrons. The result quantifies the weak…

High-performance single-atom catalysts for high-temperature fuel cells

Individual Pt atoms participate in catalytic reaction to faciitate the electrode process by up to 10 times. Single-atom Pt catalysts are stable at 700 degrees Celsius and expected to stimulate…

New method allows precise gene control by light

A novel optical switch makes it possible to precisely control the lifespan of genetic “copies”. These are used by the cell as building instructions for the production of proteins. The…

By continuing to use the site, you agree to the use of cookies. more information

The cookie settings on this website are set to "allow cookies" to give you the best browsing experience possible. If you continue to use this website without changing your cookie settings or you click "Accept" below then you are consenting to this.

Close