Question

Sewage from the nearby town was dumped into the sea. Which among the given conditions would happen in the above ecosystem after mixing of sewage into the water? i) Biochemical oxygen demand (BOD) of receiving water body increases. ii) Dissolved oxygen of receiving water body increases. iii) It will cause mortality among fish and other aquatic creatures iv) It will lead to nutrient enrichment of receiving waterbody. a) i, iii, iv b) i .ii ,iv c) ii, iii d) iii, i ​

Answer 1

Answer:

a that is 1 3 and4

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Answer 2

ii) Dissolved oxygen of receiving water body increases.

Biochemical oxygen demand (BOD) represents the amount of oxygen consumed by bacteria and other microorganisms while they decompose organic matter under aerobic (oxygen is present) conditions at a specified temperature.

Option (b) is Correct

When sewage, having biodegradable organic matter is released into the water body, microorganisms involved in the biodegradation of organic matter (in the receiving water body) consume a lot of oxygen to decompose the sewage and as a result, there would be a sharp decline in dissolved oxygen downstream from the point of sewage discharge and biological oxygen demand (BOD) would increase. The presence of sewage causes nutrient enrichment (a large amount of nutrients) in water which causes excessive growth of planktonic (free-floating) algae, called algal bloom. Algal bloom causes deterioration of water quality and fish mortality. Therefore, statements 1, 2 and 4 are correct.

Option (a) is Incorrect

This option is incorrect because statement 3 is false. Because draining of sewage in rivers will cause mortality (death) among fishes and other aquatic creatures.

Option (c) is Incorrect

This option is incorrect because statement 3 is false. Because draining of sewage in river will cause mortality (death) among fishes and other aquatic creatures.

Option (d) is Incorrect

This option is incorrect because statement 3 is false. Because draining of sewage in river will cause mortality (death) among fishes and other aquatic creatures.

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