Effects of Acid Rain

The most important effects are: damage to freshwater aquatic life, damage
of vegetation and damage to buildings and material.
a) Damage to aquatic life: - The main impact of fresh water
acidification is a reduction in diversity and populations of fresh water species.
The effect on soil and rock will depend upon the in situ capacity called
‘buffering capacity’ to neutralize the acids. The soil organisms are killed in
acid rain where soils have limited buffering capacity. The acidic leaf litter in
forest areas adds to the nutrient leaching effects of acid rain. This scavenging
from cloud increases the amount of pollution deposited. Trees are quite
effective in intercepting the air borne pollutants than other types of upland
vegetation.
In the areas of high acid deposition and poor buffering in the lakes, a
PH less than 5 has become common. At PH 5, fish life and frogs begin to
disappear. By PH 4, 5, virtually all aquatic life has gone. Acid rain releases
metals particularly aluminium-from the soil, which can build up in lake water
to levels that are toxic to fish and other organisms. A decline in fish and
amphibian population will affect the food chain of birds and mammals that
depend on them for food.
b) Damage to Trees and Plants
For some years there has been concern about the apparent deterioration of
trees and other vegetation. It is not easy to establish the cause of damage:
pollution, drought, frost, pests and forst management methods can all affect
tree health. SO2 has a direct toxic effect on trees and in parts of central
Europe for example where SO2 levels are very high, extensive areas of forest
have been damaged or destroyed.
Acid deposition may combine with other factors to affect tree health; for
instance by making trees more susceptible to attack by pests, or by
acidifying soils which may cause loss of essential nutrients such as
magnesium, thus impairing tree growth. Nitrogen and sulphur are both plant
nutrients and deposition can upset the balance of natural plant communities
by encouraging the growth of other plant species. Secondary pollutants like
ozone are also known to exacerbate the effects of acid deposition.
c) Damage to Buildings and Materials
All historic buildings suffer damage and decay with time. Natural weathering
causes some of this but there is no doubt that air pollution, particularly SO2,
also plays an important part. SO2 penetrated porous stones such as
limestone and is converted to calcium sulphate, which causes gradual
crumbling. Most building damage happens in urban areas where there are
many SO2 emitters (domestic chimneys, factories and heating plant). The
introduction of the Clean Air Acts and the replacement of coal fires by gas
and electricity has greatly reduced sulphur dioxide levels in urban areas.
Other materials badly affected by pollutant gases include marble, stained
glass, most metals and paint. Poorly set or fractured concrete may also allow
sulphates to penetrate and corrode the steel reinforcement inside.