IS ACID RAIN A THING OF THE PAST
26 August 1997
There seems to be no end to the air pollution problems in our cities, as the
recent smog alerts show. Hospitals are reporting higher numbers of respiratory
disease, children, the elderly and the sick are especially at risk. Municipal authorities
are urging motorists to leave their cars at home and use public transport. Though
voicing concern about this situation, the United Nations Economic Commission for
Europe (UN/ECE) is, nevertheless, sounding a more optimistic note about the future,
as it prepares to take further responsive action and its measures to curb sulphur
emissions are beginning to pay off.
Lake Storgama is a little known lake tucked away in southern Norway. As
there is little human activity in the area, long-range air pollution is the main
contributor to pollutant concentrations in the lake. This makes it the ideal location
for scientific research into acid atmospheric deposition. And the scientific
community is rejoicing as its long-term trend analyses show that since 1980 a 50%
drop in the sulphate concentration in precipitation has led to a spectacular
improvement in the lake's quality: its sulphate concentration is down by one third;
alkalinity has risen by more than 60%, which is a good sign.
Acid atmospheric deposition -- better known as 'acid rain' -- has attracted
much public attention in the past 25 years. It is a potent mixture of sulphur and
nitrogen compounds and other pollutants that originates from the burning of fossil
fuels and from road traffic. Acid rain travels long distances and when it eventually
comes down it damages surface water, groundwater and forest soils, particularly
in vulnerable areas.
However, since acid rain first hit the headlines scientists have learned more
about its effects, especially the acidification of lakes and rivers. Their research led
the United Nations Economic Commission for Europe (UN/ECE) to draw up
international measures to combat air pollution. This international cooperation now
seems to be yielding results. During the past 10 years emission reduction
measures in Europe and North America have resulted in a 50% fall in atmospheric
sulphur deposition. Nitrogen deposition, on the other hand, has remained virtually
constant, the main culprit being road traffic.
But has this had an impact on acidified lakes and streams? To find out, the
International Cooperative Programme on Assessment and Monitoring of
Acidification of Rivers and Lakes, established in 1985 under the UN/ECE
Convention on Long-range Transboundary Air Pollution, has used its extensive
database to analyse the trends in surface water chemistry and biology over the
past decade. It has just released its findingsThe Nine Year Report: Acidification of Surface Water in Europe and North America -
Long-term Developments (1980s and 1990s), prepared by the Programme's Coordinating
Centre, the Norwegian Institute for Water Research (NIVA). to coincide with the meeting of the
Convention's Working Group on Effects in Geneva (27-29 August 1997).
Its analyses show that sulphate concentrations are falling at nearly all its
monitoring sites, and that, in general, this decline has accelerated since 1990.
Lower sulphur deposition has helped water chemistry to improve and invertebrate
fauna to recover at many monitoring sites.
The changes in sulphate concentrations also cause changes in the
concentration of other constituents in the water. Alkalinity is a measure of water
quality. Generally speaking, high values are a good sign; low values point to acid-sensitive or acidified water. So an increase in alkalinity indicates that the water
quality is improving and recovering from acidification. In the Nordic countries
(Finland, Sweden, Norway), alkalinity fell in the 1980s leading to more
acidification, but it has increased in the 1990s, helping lakes and streams to
recover. At many other European sites (e.g. in Central Europe, Italy, Germany,
Netherlands, Denmark) alkalinity started to increase back in the 1980s, and the
rate of increase has accelerated in the 1990s. The remaining regions (Adirondacks
and Quebec, Midwestern North America, United Kingdom) show either no recovery
or further acidification, despite falling sulphate concentrations.
The concentration of nitrogen in surface waters rose nearly everywhere in
the 1980s, but these increases have come to a halt in the 1990s [(See
graph)]. It therefore seems likely that phenomena other than nitrogen
deposition (e.g. climate change) are responsible for the changes in water
quality in the 1990s. Future monitoring will tell.