Question

How do algal blooms affect the life in water bodies?

Answer 1

Hint: Algal bloom is defined as when there occurs rapid growth of algae on the surface of water due to which other organisms do not get oxygen. $\mathop O\nolimits_2 $ consumption by organisms and decomposition of organic matter are the factors which determine the amount of dissolved $\mathop O\nolimits_2 $ (DO) present in water. Higher the amount of organic waste increases the rate of decomposition and $\mathop O\nolimits_2 $, consumption, thereby causing a drop in DO content of water.

Complete answer:
Presence of large amounts of materials in water also causes excessive growth of planktonic (free-floating) algae, called algal bloom, which imparts a distinct colour to the water bodies. Algal bloom causes deterioration of the water quality and fish mortality. Some bloom-forming algae (e.g., Microcystis) are extremely toxic to human beings and animals. when formation of algal bloom takes place, it leads to Eutrophication of lakes.
Eutrophication: It is excessive growth of algae, plants and animals in water bodies due to the nutrient enrichment particularly with nitrogen and phosphorus. Eutrophication is both natural and accelerated.
Cultural or Accelerated Eutrophication
It is caused by human activities like effluents that are dissolving substances from the industries and homes, run-off of fertilizer that is chemicals -rich agriculture fields.
During the past century, lakes and oceans also in many parts of the earth have been severely eutrophied by sewage damaging particles and agricultural and industrial wastes.
The prime contaminants that damage the water are nitrates and phosphates, which act as plant nutrients. They cause excessive growth of algae, causing unsightly scum also called as foaming substance and unpleasant odours, and robbing the water of dissolved oxygen vital to other aquatic life.
At the same time other pollutants that are contamination substances flowing into a lake may poison whole populations of fish, and also cause death of them whose decomposing remains further deplete the water's dissolved oxygen content. In such a fashion, a lake can literally choke to death.
 Natural eutrophication: It is defined as the natural ageing due to nutrient enrichment of the water body. It is a slow process which may not be seen in human lifetime. A young water body has cold, clear water where there is no nutrient enrichment. Runoff and streams draining into it gradually add nutrients, especially nitrogen and phosphorus, which encourage growth of aquatic organisms.

Note:
Human beings have been deteriorating and damaging the water-bodies around the world by disposing of all kinds of waste generated from factories and other places. We always think and believe that water can take away everything not taking into consideration the fact that the water bodies are our lifeline as well as that of all other living organisms and are essential to all. Due to such activities of humans that are throwing waste in water, the ponds, lakes, streams, rivers, estuaries and oceans are becoming polluted in several parts of the world.