NEET 2016 Biology question

A river with an inflow of domestic sewage rich in organic waste may result in:

(1)Drying of the river very soon due to algal bloom.
(2)Increased population of aquatic food web organisms.
(3)An increased production of fish due to biodegradable nutrients.
(4)Death of fish due to lack of oxygen.Correct

Answer: (4)

Solution

Sewage rich in organic matter is decomposed by aerobic microbes that multiply rapidly and consume the dissolved oxygen of the water, so the biochemical oxygen demand (BOD) rises and the dissolved oxygen (DO) falls; fish and other aquatic animals die from lack of oxygen (NCERT,

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Question ID VK-092012