Question

Which of the following statements regarding eutrophication are correct ?
(i) Eutrophication is the natural ageing of a lake by nutrient enrichment of its water.
(ii) Pollutants from human activities like effluents from the industries and homes can radically accelerate the aging process of a lake. This phenomenon is called as cultural or accelerated eutrophication.
(iii) The plant nutrients responsible for eutrophication are nitrates and phosphates.
(iv) These phosphates and nitrates accelerate the growth of algae, which utilise oxygen and may deoxygenate the water to kill the fish and other aquatic animals.

• A. (i) and (ii)
• B. (iii) and (iv)
• C. (i), (ii) and (iii)
• D. (i), (ii), (iii) and (iv)

Answer 1

The correct option is D (i), (ii), (iii) and (iv)

Eutrophication is when a body of water becomes overly enriched with minerals and nutrients that induce excessive growth of plants and algae. This process may result in oxygen depletion of the water body. One example is the "bloom" or great increase of phytoplankton in a water body as a response to increased levels of nutrients. Eutrophication is almost always induced by the discharge of nitrate or phosphate-containing detergents, fertilizers, or sewage into an aquatic system. Cultural eutrophication is the process that speeds up natural eutrophication because of human activity. Due to clearing of land and building of towns and cities, land runoff is accelerated and more nutrients such as phosphates and nitrate are supplied to lakes and rivers, and then to coastal estuaries and bays. Extra nutrients are also supplied by treatment plants, golf courses, and agricultural practices through the use of fertilizers. Human activities, including the ones previously listed, can be responsible for an increase in nutrients, therefore, cultural eutrophication is more pronounced in non-polar ecosystems which have higher levels of human activity.

So the correct option is '(i), (ii), (iii) and (iv)'.