Question

What is Eutrophication? Mention the harmful effect of eutrophication?

Answer 1

Nutrients are very important in the aquatic system as may lives are sustaining there but when its accumulation starts then it becomes a problematic situation and needs to get rid of this.

Complete step by step answer:
Eutrophication is the process in which accumulation of nutrients occur in water bodies which causes the death of aquatic animals due to lack of oxygen in it. It is also called as the natural ageing of the lake.
Initially aquatic life flourish due to increase in nutrients availability but when nutrients become excess in amount then it becomes a life threatening event for aquatic animals.
What exactly happens in eutrophication?
Initially in the young lake, when water used to be cold and supporting very less life but as time passess amount of nutrients such as nitrogen, phosphorus start to increase and due to this, the number of aquatic organisms also increase and their organic remains begin to deposit in the bottom of the lake . As the century passed organic debris piles up and the lake grows shallower and warmer and now this lake is supporting warmer organisms in place of cold water organisms which once thrived.
And a time comes when lake is completely filled and becomes a piece of land and hence it is called natural ageing of land which takes thousands of year but due to human activity like discharge of industrial effluents into the lake exponentially increase the ageing process and this is called Cultural or Accelerated Eutrophication.

Additional information:
Eutrophication decreases the Dissolved Oxygen content and increases the BOD (Biological Oxygen Demand).
Dissolved oxygen is the measure of oxygen content of water bodies and this is very necessary for aquatic life as this is the only source of oxygen for them.
Dissolved oxygen is more in pure water but very less in polluted water.
BOD (Biological oxygen demand): it refers to the amount of oxygen consumed by microorganisms while they decompose the organic matter present in water bodies.
More is the BOD , more the water will be polluted.

Note:
one more similar term or phenomena is called Algal Bloom. In this phenomena , excessive amounts of nutrients cause the excessive growth of algae which impart some unpleasant odour from the lake.