ÐÓ°ÉÔ­´´

IS ACID RAIN yesterday’s scientific problem? The British government
thinks so. It is withdrawing its research funds and switching them to the
issue of the 1990s, the greenhouse effect. So too is the electricity industry,
which during much of the past decade spent millions of pounds trying to
show that it was not responsible for the disappearance of fish from remote
lakes and trees from highland hillsides.

The nation’s top young researchers are taking the hint. They are also
moving on. Take David Fowler at the Institute of Terrestrial Ecology in
Edinburgh. Having solved many of the riddles about why some clouds are acid
enough to fill your car battery while other clouds would barely turn a litmus
paper pink, he is now devising instruments to measure the greenhouse gases
that bubble out of soils.

Likewise Paul Whitehead at the Institute of Hydrology in Wallingford,
Oxfordshire. He is rejigging Magic, a statistical model of soil chemistry
and hydrology, to predict the effects of greenhouse warming rather than
acid fallout. In Norway, a large greenhouse built on a remote hillside to
demonstrate that streams lose their acidity when rainwater is intercepted
and cleaned up is also being redeployed. Now it is to investigate whether
trees will grow faster in an atmosphere rich in carbon dioxide.

Veterans of the ‘acid wars’ of the past decade meet in Glasgow in the
coming week for the fourth quinquennial conference on acid deposition. For
many of them it will be their last such conference. The sense of an era
passing arises in part because the research money is drying up. But it is
also because many of the big scientific issues identified a decade ago have
been resolved and because, in many of the places most vulnerable to its
effects, rain has lately become less acid.

One research project to shut up shop this year was the Surface Water
Acidification Programme (SWAP), a five-year study into acid rain’s pathways
through soils and streams that involved dozens of researchers from Britain,
Norway and Sweden. The programme, funded by the Central Electricity Generating
Board (CEGB) and British Coal, began in acrimony in 1984. It was launched
just as several European nations announced plans to clean up emissions of
acid sulphur from their power stations, and was widely seen in Scandinavia
as a device to postpone similar investment in Britain.

Moreover, there was bad feeling between Norwegian scientists and their
British counterparts, especially those who worked at the CEGB, who were
accused of using their resources to obscure the truth. One of the first
Scandinavian scientists to back SWAP was Lars Walloe, one of the organisers
of a pioneering study of Norway’s lakes. The study had established a strong
link between acid rain falling on hills in the south of the country, the
acidification of hundreds of lakes in those hills, and the disappearance
of fish. He encouraged many of his colleagues to accept SWAP funding to
continue their work. He says today: ‘I saw SWAP as a way to get non-CEGB
British scientists involved in the research. The trouble was that so far
as the British were concerned, any important observation made by a non-British
scientist must be confirmed by a Briton.’

One of the most important of SWAP’s findings was just how acid British
highland lakes had become. Some of the earliest research anywhere into acid
lakes and streams was carried out in Britain in the late 1950s, by scientists
such as John Mackareth, who blamed acid waters in upland tarns in the Lake
District on acid rain. But in the 1960s and 1970s, as Scandinavian concerns
grew, the British trail was lost.

Dick Wright, from the Norwegian Institute for Water Research, first
described the acidity of lakes in the Galloway Hills of southwest Scotland
after a visit in 1978. SWAP revived that research. It found that in Scotland,
Wales and the Lake District, there were many fishless acid lakes. And, as
in southern Norway, damage was greatest where acid fallout was most intense.

Many British scientists remained convinced that acid rain could be only
a minor factor in the acidity of freshwaters, however. Crucial in winning
over these waverers was what seemed a rather esoteric piece of research
on the fossil remains of diatoms in the sediments of lakes.

The various species of diatoms are extremely sensitive to freshwater
acidity. By dating successive layers of sediment in more than a dozen lakes,
and identifying the species of diatoms in them, Rick Battarbee, of University
College London, established the history of the acidity of the lakes. He
showed that, after many hundreds of years of stable pH, lakes suddenly began
to grow acidic after 1800. Moreover, at each lake, acidification began after
tiny particles of soot from burning coal first appeared in the sediments.

Politics and predictions

Hans Seip, a leading Norwegian researcher from the University of Oslo,
agrees that the new findings were important in influencing British scientific
and political opinion. But, he adds: ‘If you go back 10 years to our original
report, you will find that the main conclusions then and today do not differ
substantially.’ The main scientific gain, he believes, has been to quantify
the processes, especially in soils, that transfer acidity from rainfall
to rivers and lakes. This is of more than academic interest. New statistical
models can predict the likely effects of reducing acid fallout. The application
of those models to establish ‘critical loads’ of acid will be one of the
few areas of research to survive current cuts by the Department of the Environment.

The two models used in the SWAP research are Magic, an American model
adapted by the Institute of Hydrology, and a Norwegian model, BIM. Both
are based on an analysis of soil processes and how rainwater flows through
soils on the way to streams. The models take into account the chemistry
of the soils and the extent to which constituents of acid rain (acid, sulphate
and nitrate) have accumulated. The models offer strong hope that reduced
emissions from power stations will allow a return of fish to lakes. They
helped to persuade the British government, after four years of argument,
to agree to an EC directive requiring it to make cuts of around 60 per cent
in sulphur emissions from power plants by 1993.

The evidence of the models is now increasingly being borne out by events
in the real world. Since 1970, the year when acid emissions reached a peak
in Britain, the fallout of acid in rainfall over much of Scotland has halved.
So far, this has produced a 30-per-cent reduction in the acidity of some
lakes. The pH of the water in Round Loch in Galloway, one of the most thoroughly
investigated lochs, rose above 5 during the summer of 1988, probably for
the first time since the pH fell from a pre-industrial 5.5 to around 4.8
after 1850.

A similar improvement has yet to appear in Wales, where acid fallout
shows no similar decline. Nor are there signs of improvement yet in southern
Norway, where fish remain virtually extinct across several counties. Here
a reduction in fallout of sulphuric acid in rainfall has been balanced by
an increase in fallout of nitric acid, mostly derived from car exhausts.
In much of Europe (though not yet Britain), nitric acid is now the dominant
form of acid rain.

Despite the sharp reduction in acid fallout over Scotland, fish are
not likely to return to the lochs just yet. At three out of six Scottish
lochs investigated for SWAP, the Magic model predicts that even a further
decrease of 70 per cent in acid deposition will not return the surface water
to its natural acidity. At two, Round Loch and Loch Doilet, the water would
remain too acid to sustain fish. Similarly for Welsh streams, Magic predicts
that ‘even a 60-per-cent reduction in deposition would give only a modest
improvement at most acid sites’.

At Birkenes in southern Norway, a 30-per-cent reduction would not be
enough to halt the continued acidification of soils, the models predict.
A reduction of 60 per cent would improve streams but even a 90-per-cent
reduction would not guarantee the survival of fish brought in to restock
the streams.

If the British scientists from the CEGB (now mostly employed by its
successor National Power) are back on friendly terms with their Scandinavian
counterparts, the same cannot be said of their relations with many German
scientists. Scientific sniping continues over the reasons for the strange
death of Europe’s trees.

The science of forests and acid rain is at least a decade behind the
fish story. First signs of decline were spotted in the late 1970s by German
investigators, notably Bernhardt Ulrich of the University of Gottingen.
Ulrich found widespread changes in the chemistry of forest soils and he
predicted that many of the trees would become sick. In the early 1980s,
that is exactly what happened. The resulting panic spurred Germany and then
the European Community to demand draconian cuts in emissions of sulphur
dioxide from power stations.

A recent study of data on Europe’s forests by the International Institute
for Applied Systems Analysis speculated that the loss of timber to acid
rain could be about 16 per cent of Europe’s potential harvest, with a value
measured in billions of pounds. The need to act is clear. Nonetheless, there
remains a lively scientific debate about whether air pollution damages trees,
either directly by attacking leaves and needles, or indirectly by acidifying
soils. Nor is it clear how important other stresses on trees, such as disease
or the weather, are for the German tree sickness, or Waldsterben.

Since 1985 many German forests have shown modest recovery. But this
came too soon to be attributed to cleaner air and has revived suggestions
that acid rain was never to blame for the tree sickness. Sharp exchanges
on these issues surfaced recently in papers by Ulrich and by British researchers,
including Richard Skeffington from National Power and Mike Roberts, late
of the CEGB and now in charge of the Institute of Terrestrial Ecology at
Monks Wood. The British researchers suggest that the recovery in German
forests is permanent. Ulrich insists that it is a temporary remission in
what is in fact an irreversible decline of both the trees and the forest
soils.

Ulrich’s original studies were of the soil chemistry of the Solling
Forest, downwind of the industrial Ruhr. He showed that magnesium, a key
nutrient that is naturally in short supply in many German soils, had decreased
in forest soils. Moreover, the water seeping out into streams contained
large amounts of sulphate and nitrate from acid rain. Similar changes, says
Ulrich today, ‘have now been measured at over 100 sites’ throughout Germany.

Initially, Ulrich claimed that these changes were liberating toxic aluminium
in soils: trees were taking up the aluminium through their roots, and this
was the prime cause of the sudden yellowing of needles. Ulrich has had a
hard time demonstrating this, however, and today accepts that most of the
yellowing is probably the direct result of a shortage of magnesium.

While the yellowing of needles is not the only symptom of sick trees
in Germany and other European countries, it is the most distinctive and
widespread. It is also the only one, to date, for which a single mechanism
(magnesium deficiency) is widely accepted. So the debate about what causes
this deficiency has become central to the wider argument about Waldsterben.

Skeffington offers a list of reasons why magnesium disappears from the
soils. Plantation forestry, he says, removes large amounts of magnesium
from the forest ecosystem when trees are harvested. And while sulphates
and nitrates in acid rain may, as Ulrich insists, play some part in the
process, by washing magnesium from the soil, Skeffington believes that droughts
are the key.

Hot dry summers, such as those experienced in Germany between 1981 and
1984, slow the release of magnesium from forest litter into the soil. They
also stunted the growth of roots, so that trees were less able to take up
what little magnesium was still in soils. The end of the drought came in
1985. This, Skeffington says, ‘explains the reversal of (the) decline since
1985′. The headlines following this assertion were inevitable. ‘How hot
summers brought us stripped pines: ÐÓ°ÉÔ­´´s now believe a dramatic loss
of conifer needles . . . may have been caused by the weather, rather than
pollution,’ said The Independent.

When Ulrich mentioned the likely role of the weather in a letter to
Nature last year, the CEGB scientists pounced, congratulating him on his
belated ‘acceptance . . . of the importance of short-term climatic fluctuations’.
This was extremely unfair because Ulrich had argued since the early 1980s
that drought could trigger decline. At an international conference in 1982
he accurately predicted that: ‘After the next warm, dry years, the forest
damage will drastically increase.’ So his ‘acceptance’ was hardly new. It
was central to his argument.

The real difference is that while the Britons choose to identify droughts
as the prime cause of Waldsterben, Ulrich says that something much more
fundamental and long-lasting is going wrong below ground. ‘Soil acidification,’
he says, ‘is the key predisposing factor’ for the damage to forests across
central Europe. He argues that acid, sulphates and nitrates have accumulated
in forest soils since the Industrial Revolution. They are, he says, the
main force driving nutrients from the soil and damaging the growth of roots.

Ulrich sees three phases in the decline of a forest. In the first, which
may take many decades, the chemistry of the soil undergoes profound but
probably unnoticed change. In the second, the acidification of the soils
causes damage to roots, which often become extremely shallow. In the final
stage, some extra stress, such as disease or drought, frost damage or a
stormy night, pushes the tree into decline.

Starved of nutrients, the trees will lose leaves or needles, and so
the ability to photosynthesise. This causes a further decline in roots,
and reduces the tree’s ability to take up nutrients. Despite the apparent
modest recovery in the nation’s forests during the late 1980s, says Ulrich,
60 to 80 per cent of Germany’s forest soils remain in the second phase of
decline, ever vulnerable to the next long, hot summer. More than that, he
says, the soils’ store of nutrients ‘is too low to cover the needs of the
next forest generation’. Once the current crop of trees is harvested, no
new crop will grow until the pollution abates and soils recover.

The global impact of acid rain

Like the scientists investigating acid lakes, Ulrich has calculated
how much emissions of acid pollutants need to be reduced if forest soils
are to recover. He concludes that ‘a rapid reduction of emissions by 60
to 76 per cent (of 1982 levels) is necessary’, with cuts of at least 80
per cent in the long term. His predictions of ‘critical loads’ of pollution
that forest soils will tolerate are strikingly similar to those being made
for soils in Scotland and Scandinavia which are causing the acidification
of streams and lakes.

While some acid rain researchers have moved on to study the larger ‘global’
processes behind the greenhouse effect, others are finding a global dimension
to the study of acid rain itself. Most obviously, acid rain is showing up
well away from its traditional heartlands of Europe and North America. Acid
pollution in the coal-mining provinces of southwest China now approaches
levels in the more polluted parts of the US. Smaller acid zones have been
uncovered in Brazil and Venezuela, South Africa and Australia.

But the impact of acid rain on the planet may greatly exceed the sum
of these regional parts. David Schindler from the Canadian government’s
Freshwater Laboratory warns that acidification could be reducing the planet’s
biodiversity. Discussion of the disappearance of species ‘usually evokes
images of burning tropical rainforests in the Third World,’ he says. ‘I
believe that acid precipitation has had just as large an effect on the ecology
of the planet. It has caused catastrophic depletion of species and disruption
of key ecosystem processes in . . . the world’s most affluent and ecologically
aware nations.’ These areas, largely still in temperate lands, have far
fewer species than tropical regions and their ecosystems are more vulnerable
to disruption from the loss of a few species.

According to Schindler, acid rain may have made many ecosystems, perhaps
including Europe’s forests, much more vulnerable to climatic change caused
by the greenhouse effect: ‘Greenhouse warming may enhance the effects of
acid precipitation on boreal lakes and streams (in Canada and Scandinavia).
If greenhouse droughts cause water tables to fall, then a sudden rainstorm
could release many years of accumulated sulphuric acid in a single deadly
acid pulse.’ Work in Britain at the Institute of Hydrology is reaching a
similar conclusion.

ÐÓ°ÉÔ­´´s investigating the greenhouse effect are also concerned about
whether the fallout of large amounts of nitrogen in acid rain could trigger
the natural formation of greenhouse gases in soils. Jerry Melillo from the
Woods Hole Marine Biological Laboratory, in Massachusetts, estimates that
air pollution deposits 18 million tonnes of nitrogen in the temperate northern
hemisphere, and that this fallout increases the natural emissions of nitrous
oxide, a significant greenhouse gas, from soils. Nitrogen may also reduce
the ability of soils to consume methane, the most important greenhouse gas
after carbon dioxide. A reduction in the soil ‘sink’ for methane may have
contributed to the doubling of atmospheric concentrations of methane since
pre-industrial times.

More hopefully, acid rain could damp down the greenhouse effect through
nitrogen fallout over the oceans. James Galloway, from the University of
Virginia in the US, believes that this fallout could increase biological
activity in the oceans which, in turn, could allow the oceans to absorb
more of the carbon dioxide in the atmosphere.

Another line of thought is inspired by studies of trace gases. The British
scientist James Lovelock found that plankton give off sulphurous particles
called dimethyl sulphide that can act as ‘seeds’ for the formation of clouds
that shade and cool the planet. Tom Wigley, from the Climatic Research Unit
at the University of East Anglia, suggests that sulphate in acid rain may
act in the same way. He suggests that the spread of acid pollution in the
past 40 years could have contributed to the slight cooling of the northern
hemisphere before the sudden warming of the 1980s, and may have ‘significantly
offset the temperature changes that have resulted from the greenhouse effect’.

* * *

Smog on a summer’s day – a new acid problem

SOME of the same pollutants that cause the acid rains that damage remote
lochs and forests are also responsible for a modern version of the age-old
smog.

Unlike the old smoky peasoupers of the 1950s, modern smogs are summer
events and driven by the action of sunlight on a range of pollutants, some
of them acid and most of them emerging from the exhaust pipes of motor vehicles.
Modern photochemical smogs regularly afflict southern European cities such
as Athens, Naples and Milan, and periodically reach critical levels further
north. Last summer and this, London has experienced levels of ozone, the
prime constituent of photochemical smog, not seen since the long hot summers
of 1975 and 1976.

There is growing evidence that smog aggravates respiratory complaints,
including asthma and hay fever. In Greece, the death rate rises when the
nefos descends on Athens.

While photochemical smogs are not, strictly speaking, acid events, some
of the same pollutants cause both smogs and acid rain, and there is evidence
that smogs catalyse the formation of acid and vice versa. Two groups of
pollutants combine to create urban smogs. One is the various oxides of nitrogen
from cars and other fossil fuel burners. These are being brought under control
as part of EC efforts to curb acid rain. The other is a wide range of volatile
organic compounds (VOCs), given off as vapours from petrol stations, oil
refineries, chemical works and from all manner of industrial and household
solvents.

As emissions of nitrogen oxides are reduced, these VOCs will emerge
as the critical factor in controlling urban smogs.

Current emissions of VOCs in the EC amount to 7.5 million tonnes. Britain’s
contribution alone is estimated at almost 2 million tonnes. Britain’s Harwell
Laboratory has identified 10 ‘priority’ VOCs including toluene, ethylene,
propylene and various butanes and benzenes. Despite the problems in bringing
such a diverse group of chemicals under control, both the EC and the UN
Economic Commission for Europe, agreed that the effort must be made. At
the UNECE’s environment conference, held in Bergen in May this year, most
European nations agreed in a ministerial declaration to the drafting of
a protocol to control VOCs.

A series of long, hot summers across Europe, which is increasingly likely
to occur as global warming gathers pace, would catapult ozone smogs to the
forefront of public concern.

Ozone at ground level is a significant greenhouse gas itself, contributing
to global warming by trapping heat. It is still a small component in the
overall greenhouse effect, but current estimates suggest that the concentration
of ozone in the northern hemisphere may have doubled in the past century,
probably as a result of air pollution.

Fred Pearce writes about the environment. He is the author of Penguin
Special: Acid Rain, 1987.