Question

In a village in Karnataka, people started cultivating crops all around a lake which was always filled with water. They added fertilisers to their field in order to enhance the yield. Soon they discovered that the waterbody was completely covered with green floating plants and fishes started dying in large numbers.

Analyse the situation and give reasons for excessive growth of plants and death of fish in the lake.

Answer 1

People added excessive fertilisers in their fields which leached down to the lake during rains. Since phosphates and nitrates are the main constituents of fertilisers, the lake became abundant in these ions. These ions led to excessive plant growth in lake, thereby, cutting off oxygen supply for the fishes living in it. So, due to insufficient availability of dissolved oxygen and nutrients fishes started dying in large numbers.