Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Clean forests prompt pollution rethink

24.01.2002


Nitrogen in unpolluted streams is more organic.
© Nature


Agriculture has added to the natural nitrogen cycle.
© Photodisc


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).


JOHN WHITFIELD | © Nature News Service
Further information:
http://www.nature.com/nsu/020121/020121-10.html

More articles from Ecology, The Environment and Conservation:

nachricht Dispersal of Fish Eggs by Water Birds – Just a Myth?
19.02.2018 | Universität Basel

nachricht Removing fossil fuel subsidies will not reduce CO2 emissions as much as hoped
08.02.2018 | International Institute for Applied Systems Analysis (IIASA)

All articles from Ecology, The Environment and Conservation >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: In best circles: First integrated circuit from self-assembled polymer

For the first time, a team of researchers at the Max-Planck Institute (MPI) for Polymer Research in Mainz, Germany, has succeeded in making an integrated circuit (IC) from just a monolayer of a semiconducting polymer via a bottom-up, self-assembly approach.

In the self-assembly process, the semiconducting polymer arranges itself into an ordered monolayer in a transistor. The transistors are binary switches used...

Im Focus: Demonstration of a single molecule piezoelectric effect

Breakthrough provides a new concept of the design of molecular motors, sensors and electricity generators at nanoscale

Researchers from the Institute of Organic Chemistry and Biochemistry of the CAS (IOCB Prague), Institute of Physics of the CAS (IP CAS) and Palacký University...

Im Focus: Hybrid optics bring color imaging using ultrathin metalenses into focus

For photographers and scientists, lenses are lifesavers. They reflect and refract light, making possible the imaging systems that drive discovery through the microscope and preserve history through cameras.

But today's glass-based lenses are bulky and resist miniaturization. Next-generation technologies, such as ultrathin cameras or tiny microscopes, require...

Im Focus: Stem cell divisions in the adult brain seen for the first time

Scientists from the University of Zurich have succeeded for the first time in tracking individual stem cells and their neuronal progeny over months within the intact adult brain. This study sheds light on how new neurons are produced throughout life.

The generation of new nerve cells was once thought to taper off at the end of embryonic development. However, recent research has shown that the adult brain...

Im Focus: Interference as a new method for cooling quantum devices

Theoretical physicists propose to use negative interference to control heat flow in quantum devices. Study published in Physical Review Letters

Quantum computer parts are sensitive and need to be cooled to very low temperatures. Their tiny size makes them particularly susceptible to a temperature...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

2nd International Conference on High Temperature Shape Memory Alloys (HTSMAs)

15.02.2018 | Event News

Aachen DC Grid Summit 2018

13.02.2018 | Event News

How Global Climate Policy Can Learn from the Energy Transition

12.02.2018 | Event News

 
Latest News

Contacting the molecular world through graphene nanoribbons

19.02.2018 | Materials Sciences

When Proteins Shake Hands

19.02.2018 | Materials Sciences

Cells communicate in a dynamic code

19.02.2018 | Life Sciences

VideoLinks
Science & Research
Overview of more VideoLinks >>>