river pollution
It seems that almost every day there is another story about
pollution of one form or another, in the food we eat, the water we drink and
the air we breathe. Very often our own actions lead to that pollution and in
many cases we can do something about it. These notes explain how you can
investigate pollution and advise on positive action to improve our rivers.
Polluting the rivers
Over 97% of all the water on Earth is salty and most of the
remaining 3% is frozen in the polar ice-caps. The atmosphere, rivers, lakes and
underground stores hold less than 1% of all the fresh water and this tiny
amount has to provide the fresh water needed to support the Earth's population.
It is estimated that, with the expected increase in population, there will be a
200% increase in world water needs by the year 2000. Fresh water is a precious
resource and the increasing pollution of our rivers and lakes is a cause for
alarm.
Investigating river pollution
Most fresh water pollution is caused by the addition of organic
material which is mainly sewage but can be food waste or farm effluent.
Bacteria and other micro-organisms feed on organic matter and large populations
quickly develop using up much of the oxygen dissolved in the water. Normally
oxygen is present in high quantities but even a small drop in the level can
have a harmful effect on the river animals. Animals can be listed according to
their ability to tolerate low levels of oxygen. In the following list animals
which indicate a high level of dissolved oxygen are at the beginning while
animals indicating a low level of oxygen are at the end: stone-fly nymphs,
mayfly nymphs, freshwater shrimps, freshwater hog lice, blood worms, tubifex
worms and rat-tailed maggots.
Sampling technique
Choose a place on a river bank which is safe to work from and
where there is reasonable access to the water. Push your net through the weeds
at the edge of the river and collect any animals hiding there. If the water is
shallow you could stand in the river and place your net on the bottom with the
opening pointing upstream allowing the current to wash the animals into the
net. Tip the catch into a white dish and identify the animals.
If you find only blood worms, tubifex worms or rat-tailed
maggots it would suggest that there is little oxygen in the water and that
pollution is occurring. If this is the case write to your regional Water
Authority informing them of your investigation giving details of where you
sampled and what you think might be the possible source of pollution.
Signs of pollution
If you see dead fish floating on the river or notice that the
water is discoloured and smelly any one of the following forms of pollution may
be the cause:
- fertilisers
- industrial waste
- oil
- warm water
All incidents of river pollution should be reported to the
Pollution Control officer at the Water Authority giving as much detail as you
can: date, time, exact place and precisely what you saw.
a) Fertilisers
If large amounts of fertiliser or farm waste drain into a river
the concentration of nitrate and phosphate in the water increases considerably.
Algae use these substances to grow and multiply rapidly turning the water
green. This massive growth of algae, called eutrophication, leads to pollution.
When the algae die they are broken down by the action of the bacteria which
quickly multiply, using up all the oxygen in the water which leads to the death
of many animals.
b) Industrial Waste
Chemical waste products from industrial processes are sometimes
accidentally discharged into rivers. Examples of such pollutants include
cyanide, zinc, lead, copper, cadmin and mercury. These substances may enter the
water in such high concentrations that fish and other animals are killed
immediately. Sometimes the pollutants enter a food chain and accumulate until
they reach toxic levels, eventually killing birds, fish and mammals.
Occasionally poisonous substances are deliberately dumped into
rivers and if you see this so-called 'fly-tipping' going on take the
registration number of the vehicle and if possible the name of the firm. Report
the matter to the police who will then take it further.
c) Oil Pollution
If oil enters a slow-moving river it forms a rainbow-coloured
film over the entire surface preventing oxygen from entering the water. On
larger stretches of water the oil contaminates the feathers of water birds and
when they preen the oil enters the gut and kills them.
d) Warm Water
Industry often uses water for cooling processes, sometimes
discharging large quantities of warm water back into rivers. Raising the
temperature of the water lowers the level of dissolved oxygen and upsets the
balance of life in the water.
Warning
When sampling polluted water simple precautions must be taken to avoid getting infected. Packed lunches should be eaten before visiting the river or after washing carefully in a supply of clean water. Rubber gloves should be worn and all the equipment should be thoroughly washed at the end of the investigatio
When sampling polluted water simple precautions must be taken to avoid getting infected. Packed lunches should be eaten before visiting the river or after washing carefully in a supply of clean water. Rubber gloves should be worn and all the equipment should be thoroughly washed at the end of the investigatio
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