Environmental Engineering Reference
In-Depth Information
ecosystem to neutralize the incoming acid. This ability is known as its
buffering capacity
and it depends largely upon the amount of calcium or magnesium in the bedrock. Levels
of these minerals are generally low in much of the recently
Figure 2
The geography of acid rain.
glaciated areas of northern Europe, so lakes in that area have been particularly affected by
acid rain. Fish stocks have dropped dramatically, but other aquatic organisms have been
affected. The causes are complex. One factor is believed to be the release of aluminium as a
result of acid water reacting with heavy metal cations in the soil. Aluminium can affect fish
by obstructing their gills.
The other area of impact of acid rain is on vegetation. Acid rain will increase soil acidity,
decrease nutrient availability, mobilize toxic metals like aluminium and affect micro-
organisms. It is not surprising that it has been held responsible for many changes in the
terrestrial ecosystem. Perhaps the most drastic effect has been on forests. Monitoring of
forests in Europe since 1986 has shown evidence of increasing damage, especially to
deciduous species. The damage takes the form of thinning of the crown, the shedding of
leaves or needles and decreased resistance to disease, drought and frost. Pollution is not the
only factor involved but is believed to be important. In Britain, Poland and the Czech
Republic, it is suggested, more than 50 per cent of trees are showing signs of damage by way
of defoliation.
Efforts to combat the problem can be made at source or in the environment affected. Some
attempts have been made to reduce sulphur emissions at power stations, such as at Drax in
the United Kingdom. Unfortunately they cost money, which makes the electricity more
expensive to generate. Greater use is being made of natural gas as a source of energy, though
this has more to do with economics than with environmental considerations. Alternatively
soil or water acidity can be neutralized by adding lime. It has been argued that it is cheaper to
add lime than to adopt expensive systems of reducing sulphur emission
Some success has
