151
water must be pure and uncontaminated. Hence
drinking water reservoirs are best located in the
upland areas. Here, the hard rocks of the catchment area yield few salts to the water. If a lake is
used as a reservoir, it frequently results in a barren zone of bare earth or mud around the lake
shore. It is because water tends to be drawn off at
times where infl ow is low. This ‘drawdown’ kills
the vegetation and its associated animals of the
littoral zone.
6.10.1 Industrial Uses of Water
Industry needs water, often in very large quantities. Industry also causes signifi cant impact when
the water is put back as effl uent. Users of water
inevitably want to get rid of waste. Some of these
substances in the effl uents, e.g . insecticides, are
directly toxic to plants and animals. Most of them
have more insidious effects. Power stations and
factories use water for cooling. When this water
is re-discharged back to the lake, the lake water
gets warmed by a few degrees. This encourages
plant growth and speeds up the life cycle of
insects and plankton. It might help a species,
which could have died in winter, to fl ourish for
longer in the year. Further, it may allow a species
introduced from a warmer climate to grow and
breed, which would not have otherwise bred
under the normal temperature regime.
Notwithstanding the above, many industries,
e.g . logging and mining, wash huge quantities of
particulate matter into the lakes and rivers.
Further, silt has a devastating effect on the structure of the environment. Many wastes contain
toxic substances like heavy metals (Pb, Hg, As,
etc.). These often go into the living system
through food. These are retained in the body tissue and may reach toxic levels due to
bio-magnifi cation.
6.10.2 Sewage and Agricultural Uses
of Water
Intensive agriculture makes use of large quantities of pesticides to control insects and fungi.
This may reduce or spoil the yield of crops.
Artifi cial fertilisers are also used in modern
agriculture which are washed off the fi elds into
rivers and lakes. They contain both nitrogen and
phosphorus to stimulate the growth of plants.
Sewage is the other major source of fertilising
nutrient. Phenomenal growth of human population has increased lot of sewage in the waterbodies. Sewage also contains extra phosphorus
from detergents. It may also contain heavy metals and toxins. Thus, the natural waterbodies
become victims of eutrophication due to addition of excess nitrogen and phosphorus. This is
of great concern.
6.10.3 Lake Fisheries
In many parts of the world, people obtain their
source of protein from the freshwater (FW) fi sh.
At the end of 1970s, fi sh yield from FW contributed less than one quarter of the total global harvest of the aquatic species. This was commercial
fi shing for food and was quite separate from substantial fi shing and fi shing from sport. Strenuous
efforts have been made all over the world to
increase the size of total harvest. However, more
benefi ts are likely to come from intensively managed pond system (‘fi sh farming’). Here, much
yields per area of water are possible than from
natural lakes.
In Europe, the traditional role of lake as
sources of cheap food has gradually declined
over the centuries. It has now been almost
totally extinguished by pollution. Severe
decline in the lake fi sheries has also been found
in Japan, Russia, the USA, etc. Today, >50 % of
the total harvest of FW fi sh is, perhaps, obtained
from Asia. These are mostly from highly managed systems of aquaculture developed since
>2,000 years. In this connection, it may be said
that India and its adjoining neighbour
Bangladesh have been blessed with myriads of
precious FW lotic and lentic waterbodies spread
across the length and breadth of the countries.
These waterbodies had been potential reserves
of FW fi shes serving as answers for our diminishing protein supply and as sources of earning
6.10 Use and Abuse of Lakes
water must be pure and uncontaminated. Hence
drinking water reservoirs are best located in the
upland areas. Here, the hard rocks of the catchment area yield few salts to the water. If a lake is
used as a reservoir, it frequently results in a barren zone of bare earth or mud around the lake
shore. It is because water tends to be drawn off at
times where infl ow is low. This ‘drawdown’ kills
the vegetation and its associated animals of the
littoral zone.
6.10.1 Industrial Uses of Water
Industry needs water, often in very large quantities. Industry also causes signifi cant impact when
the water is put back as effl uent. Users of water
inevitably want to get rid of waste. Some of these
substances in the effl uents, e.g . insecticides, are
directly toxic to plants and animals. Most of them
have more insidious effects. Power stations and
factories use water for cooling. When this water
is re-discharged back to the lake, the lake water
gets warmed by a few degrees. This encourages
plant growth and speeds up the life cycle of
insects and plankton. It might help a species,
which could have died in winter, to fl ourish for
longer in the year. Further, it may allow a species
introduced from a warmer climate to grow and
breed, which would not have otherwise bred
under the normal temperature regime.
Notwithstanding the above, many industries,
e.g . logging and mining, wash huge quantities of
particulate matter into the lakes and rivers.
Further, silt has a devastating effect on the structure of the environment. Many wastes contain
toxic substances like heavy metals (Pb, Hg, As,
etc.). These often go into the living system
through food. These are retained in the body tissue and may reach toxic levels due to
bio-magnifi cation.
6.10.2 Sewage and Agricultural Uses
of Water
Intensive agriculture makes use of large quantities of pesticides to control insects and fungi.
This may reduce or spoil the yield of crops.
Artifi cial fertilisers are also used in modern
agriculture which are washed off the fi elds into
rivers and lakes. They contain both nitrogen and
phosphorus to stimulate the growth of plants.
Sewage is the other major source of fertilising
nutrient. Phenomenal growth of human population has increased lot of sewage in the waterbodies. Sewage also contains extra phosphorus
from detergents. It may also contain heavy metals and toxins. Thus, the natural waterbodies
become victims of eutrophication due to addition of excess nitrogen and phosphorus. This is
of great concern.
6.10.3 Lake Fisheries
In many parts of the world, people obtain their
source of protein from the freshwater (FW) fi sh.
At the end of 1970s, fi sh yield from FW contributed less than one quarter of the total global harvest of the aquatic species. This was commercial
fi shing for food and was quite separate from substantial fi shing and fi shing from sport. Strenuous
efforts have been made all over the world to
increase the size of total harvest. However, more
benefi ts are likely to come from intensively managed pond system (‘fi sh farming’). Here, much
yields per area of water are possible than from
natural lakes.
In Europe, the traditional role of lake as
sources of cheap food has gradually declined
over the centuries. It has now been almost
totally extinguished by pollution. Severe
decline in the lake fi sheries has also been found
in Japan, Russia, the USA, etc. Today, >50 % of
the total harvest of FW fi sh is, perhaps, obtained
from Asia. These are mostly from highly managed systems of aquaculture developed since
>2,000 years. In this connection, it may be said
that India and its adjoining neighbour
Bangladesh have been blessed with myriads of
precious FW lotic and lentic waterbodies spread
across the length and breadth of the countries.
These waterbodies had been potential reserves
of FW fi shes serving as answers for our diminishing protein supply and as sources of earning
6.10 Use and Abuse of Lakes