Question

Eutrophication is caused by
(a) Sewage and detergents
(b) Petrochemical and fertilizer plant effluents
(c) NO-13 and SO-24 present in acid rains
(d) Mine effluents

Answer 1

Hint: Eutrophication is caused by domestic or municipal water waste. It is the water waste produced by a community. The other pollutant is a surfactant or maybe a mixture of surfactants. It is used for its cleansing properties in dilute solutions.

Complete answer:
Sewage and detergents are the main causative agents of eutrophication. When the water of a lake undergoes natural ageing by nutrient enrichment, this process is known as ‘eutrophication.’ The water of a young lake is cold and clear and supports little life. However, the streams draining into the lake, with time introduce a number of nutrients into it. Added nutrients such as nitrogen and phosphorus encourage the growth of aquatic organisms. With the increase in the fertility of the lake, the inhabiting plants and animal life thrive and this results in the deposition of abundant organic matter at the bottom of the lake. Overtime as silt and organic debris accumulate continuously, the depth of the lake decreases and water becomes warmer.
Some water organisms thrive in warm water at the cost of inhabitant cold water organisms. Marsh plants also begin to fill in the lake basin. Ultimately, the lake gets filled up with large masses of floating plants (bog) and turns into land. Based on different factors like climate and size of the lake, the natural ageing of a lake may take place over thousands of years. However, man’s activities like effluents, detergents from industries and sewage from homes accelerate the ageing process i.e. the eutrophication of a lake. The phenomenon of rapid ageing of lakes artificially by means of various man made factors has also been called ‘cultural’ or ‘accelerated eutrophication.’
So, the correct answer is ‘Sewage and detergents.’

Note: -The prime contaminants in eutrophication are nitrates and phosphates from sewage and detergents. They support the excess growth of algae resulting in unpleasant odours and an unsightly scum.
-After sewage and detergents, runoff from mines also acts as a pivotal factor in eutrophication.
-Petrochemicals and fertilizers serve as a source of phosphorus, contributing to the phenomenon.