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Write the causes of algal bloom and how it affects the quality of water?

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Hint: An algal bloom can be defined as rapid increase in the population of algae in marine water or freshwater bodies.

Complete Answer:
Algae are small microscopic organisms which are found in water bodies and have the ability to conduct the process of photosynthesis. When there is a rapid growth of the algae in the water body, it is known as an algal bloom.

Algal blooms are caused due to the following reasons,
1) If the water body has excess nutrients , especially phosphorus, then higher growth of algae is seen in the water body.
2) If the water body is stagnant or stable it can lead to thermal stratification which supports the growth of algal bloom
3) If there is intermittent high-intensity light and can promote growth of blue green algae.
4) If the temperature of water is around 25 degrees, then it is the optimal temperature for growth of blue green algae. Also at this temperature, other types of algae won't grow as their optimal temperature is around 12-15 degree celsius.

The harmful effect of algal blooms are,
1) The algal blooms also release harmful toxins which cause an adverse effect on the marine population living in the water body which would in turn harm humans and animals if the water is consumed.
2) They cause discolouration of water which in turn causes an increase in BOD (Biological Oxygen Demand).
3) If the BOD increases, then it would result in the water body not being favourable for survival for the fishes and other marine organisms and plants living in the body. This would lead to death of the fishes and other marine organisms and plants.
4) As the nutrient levels increase, the water is unfit for human consumption.

Note: In order to identify an algal bloom, one can look for discoloration of the water body or scum like appearance on the water body.
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