FW: current environmental concern is fertilizer falling from thesky

[Jane Sherry]

Title: FW: current environmental concern is fertilizer falling from the sky

It never rains but it pours

After acid rain and the greenhouse effect, the current
environmental concern is fertilizer falling from the sky. Simon
Hadlington reports on how excess nitrogen could change our
ecosystem

http://news.independent.co.uk/world/environment/story.jsp?story=3 <http://news.independent.co.uk/world/environment/story.jsp?story=3>
46638

28 October 2002

Hold on to your hats for the next global environment crisis:
we've had acid rain, the hole in the ozone layer and the
greenhouse effect. The new menace is an excessive accumulation of
compounds of nitrogen in the earth and in the air. In many parts
of the world fertilizer is, literally, falling from the sky. As
the Weather Girls might have sung: "It's raining N!"

Many of us are aware of the problem of nitrogen oxides from car
exhausts causing smog in cities. However, the subtle effects of
nitrogen compounds are less immediately visible. A gas called
nitrous oxide is accumulating in the upper atmosphere. It is 200
times more potent than carbon dioxide as a greenhouse gas, and
has been implicated in the thinning of the ozone layer. Ammonia
from animal waste dissolves in rain water and falls back to the
earth as fertilizer. This disrupts delicate plant communities
that thrive only in nitrogen-depleted environments. Other
compounds of nitrogen also cause rain to become acidic.

In an effort to understand the problem, the Natural Environment
Research Council, with the environment ministry DEFRA and the
Scottish Executive, has launched a £7m research programme called
Gane - "global nitrogen enrichment". The programme's scientific
co-ordinator is Professor Alan Davison, of the University of
Newcastle. "Nitrogen enrichment has been ignored for too long,"
he says. "It needs to be raised much higher up the agenda."

The key to the problem lies in the way that nitrogen is cycled
between its different chemical forms, and how man has radically
interfered with the natural balance.

As a gas, nitrogen makes up four-fifths of the atmosphere. It is
almost completely chemically unreactive in this form, but
compounds of nitrogen - nitrogen atoms chemically combined with
other atoms - are essential for life. There are two main ways by
which nitrogen in its gas form becomes chemically altered to make
it available to living organisms, a process called nitrogen
fixing. The first is by populations of microbes that inhabit the
soil and roots of leguminous plants. These convert atmospheric
nitrogen into amino acids, the building blocks of protein, which
are taken up by plants and incorporated into the food chain.
Naturally occurring nitrogen-fixing organisms are thought to
process 110 million tons of nitrogen a year. A further 10 million
tons is fixed by the action of lightning - a high-temperature
chemical process that forces atmospheric nitrogen to react with
oxygen.

This 120 tons of fixed nitrogen was, for millennia, sufficient to
keep the world's natural ecosystems supplied each year. Then man
came along. Early farmers discovered that crops would grow better
with manure spread on the land; that livestock thrived on certain
plants, such as clover; and that other plants, such as soybean
and other legumes, were rich in protein and nutritious.
Deliberate cultivation of these nitrogen-fixers started to tilt
the natural balance.

The big change came in Victorian times. In a speech to the
British Association for the Advancement of Science in 1898, the
scientist Sir William Crooke said: "England and all civilized
nations stand in deadly peril of not having enough to eat." There
was insufficient nitrogen fertilizer to grow the quantity of food
needed to satisfy demand. Man had to find ways of fixing
nitrogen. A few years later, the German chemist Fritz Haber
showed how it was possible to take nitrogen from the air and
react it with hydrogen to make ammonia, from which nitrates could
be produced. When his countryman Carl Bosch showed how to do this
on an industrial scale, the era of mass-produced artificial
fertilizers had begun.

Nowadays, around 80 million tons of nitrogen is fixed each year
as fertilizer. A further 30 million tons is fixed by cultivation
of legumes, notably soybean. Together, these have doubled the
quantity of nitrogen taken out of the air and made chemically
reactive. The final "big fixer" is the combustion of fossil fuels
in power stations and motor cars. The high temperatures cause the
nitrogen in the air to form a variety of oxide gases. These
account for a further 25 million tons of fixed nitrogen each
year.

"In other words, through our efforts we are more than doubling
the quantity of fixed nitrogen in the Earth and its atmosphere
than would be achieved if nature was left to its own devices,"
says Professor Davison. "The polluting aspects of nitrogen
oxides, the smogs in cities, are only a small part of the
problem. Huge areas are being affected in ways that are not so
obvious."

For a start, there is the production of nitrous oxide by microbes
in the soil. An excess of fixed nitrogen results in more nitrous
oxide being generated. This finds its way into the upper
atmosphere, where it is a potent greenhouse gas. "Nitrous oxide
is of great concern," says Davison. "The UK has obligations under
various agreements to reduce greenhouse gas emissions, so Gane
aims to provide DEFRA with the science to underpin policy
decisions."

Another problem is the precipitation of nitrogen compounds from
the air - it literally rains fertilizer. Ammonia is produced in
significant quantities from intensive animal production - pigs,
cattle and poultry. This enters the atmosphere, where it
dissolves and is precipitated in rain. An estimated 230,000 tons
of nitrogen in the form of ammonia is deposited on the UK in
rain. Around 150,000 tons of nitrogen oxides also come back to
earth in rainwater.

"It is difficult to give accurate figures, but most of England
gets somewhere between 15 and 30 kilograms of nitrogen per
hectare of land each year from the sky," says Davison. "Some
places might get as much as 60 kilos. If you consider that a
farmer growing wheat will add between 150 and 250 kilos of
nitrogen fertilizer over the same area, the quantities are very
significant."

The problem with this is the effect on wilderness areas that
have, otherwise, remained largely undisturbed by man. "If you
start to fertilize areas you will change the flora," says
Davison. "Some plants will take advantage of this - stinging
nettles and blackberries, for example - and begin to dominate at
the expense of others. By adding fertilizer to natural vegetation
you will almost certainly damage the biodiversity."

As well as its fertilizing effect, nitrates dissolved in
rainwater are acid. "Since we have managed to control acid rain
from sulphur, nitrogen in rain is the biggest acidifier," says
Professor Davison. "This results in soils and streams becoming
acid, which can have harmful ecological effects."

What can be done? Research programmes such as Gane are attempting
to fill the huge gaps in our knowledge of the "new" nitrogen
cycle. "When political decisions are being made, the
decision-makers need to have reliable science to hand," says
Davison. "We are trying to understand the underlying science of
the way that the environment is becoming enriched with nitrogen.
It is only recently that people have recognised this as an
important global issue. It is clear that there are difficult
scientific problems and political challenges ahead."

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