Tuesday, May 12, 2009

Thermal Pollution


Thermal Pollution may be defined as 'the excessive raising or lowering of water temperature above or below normal seasonal ranges in streams,lakes, or estuaries or oceans as the result of discharge of hot or cold effluents into such water'.

Sources of Thermal Pollution

Thermal pollution may be caused by four major sources.They are:

a. Water as a cooling agent,
b. Soil erosion,
c. Deforestation of shorelines, and
d. Run-off from hot paved surfaces.

a.Water as a cooling agent:It is the major source of thermal pollution of water in most part of the world.The use of water as a cooling agent in power plants and factories and industrial facilities causes thermal pollution.

b. Soil erosion:Soil erosion makes the water muddy,which in turn increases the absorption of light, thus increasing the water temperature.

c. Deforestation of shorelines:This contributes to the problem of thermal pollution in two ways.First the plant roots hold soil particles together.Hence the deforestation results erosion of soil particles.Secondly, vegetation provides shade to the water surface.Deforestation increases the amount of light hitting the water surface,thereby raising the water temperature.

d. Run-off on hot surface:Storm water runoff on warmed urban surfaces,such as streets,sidewalks and parking lots causes raising of the temperature water that flows on the surface

Effects of Thermal Pollution

Thermal Pollution increased the temperature of water considerably.This increase in temperature causes the following effects.

1.Change in water properties:Temperature affects physical,biological and chemical parameters in a water body

2.Disturbed Ecosystem:
Most aquatic organisms have adapted to survive within a range of water temperatures.Some organisms like trout and stonefly nymphs prefer cooler water,while others such as carp and dragonfly nymphs thrive under warmer conditions.As the temperature of river or lake increases,cool water species will be replaced by warm organisms.Few organisms can survive in temperatures of extreme heat or cold.

3.Reduced dissolved oxgen:
The addition of heat reduces the water's ability to hold dissolved gases,including the oxygen required for aquatic life.If the water temperature in greater than 95 degree fahernheit.,the dissolved oxygen content may be too low to support some species.

4.Increased bacterial growth:
Warmer water allows bacterial populations to increase and thrive and algae blooms may occur.

5.Photosynthesis:
The rate of photosynthesis by algae and larger aquatic plants is also affected by thermal pollution.

6.Thermal shock:
When a power plant first opens or shut down for repair,fish and other organisms adapted to a particular temperature range can be killed by the abrupt change in water temperature.This is called as thermal shock.

7.Increase in toxicity:
The rising temperature increases toxicity of the chemicals present in water causes massive morality of fishes.

Control of Thermal Pollution

Following are some of the preventive measures of thermal pollution.

a)Temperature of water can be reduced by taking the water to wet or dry cooling towers which are being used to pre cool that water before discharge tranfers the heat from the water to the atmosphere.

b)Discharging the heated water into shallow ponds or canal,allowing it to cool,and reusing it as cooling water.

c)The thermal discharge from an industry can also be used in heating homes,building or other such structures.This is achieved by circulating the hot water through pipes in the structures.

d)Water with temperature can be successfully used in aquaculture.

e)The heated water can also be used in agriculture,especially for frost protection during the cold seasons.

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