Question

Define the following terms:
(i) Eutrophication
(ii) Biomagnification

Answer 1

(i) Eutrophication:
It refers to the nutrient enrichment of water bodies, leading to a lack of oxygen and the deadening of life supporting environment. Usually, a rapid increase in the nutrient status of water bodies occurs, owing to both natural factors as well as human activity. It may be caused by the run – off of artificial fertilisers from agricultural lands, or by the input of sewage or animal wastes. The increased nutrient content of water bodies causes excess growth of algae. This algal bloom covers the surface of water, secretes toxins and reduces its oxygen content. Oxygen deficiency may cause death of aquatic animals.

(ii) Biomagnification:
Biological magnification is the increase in the concentration of a substance present inside tissues as it transfers from one trophic level to another in the food chain. Effluents from industries contain toxic chemicals that may contaminate the water used for agriculture. These chemicals are absorbed by crops through the soil. As the herbivores feed on these crops, chemicals enter their body. The herbivores pass on these chemicals to the carnivores, and so on. However, the toxic effect observed will be much higher in carnivores than herbivores. This is because of biomagnification. These toxic substances cannot be decomposed or degraded. Therefore, their concentration keeps on increasing as we move to higher trophic levels.