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Study the graph given below and answer t...

Study the graph given below and answer the question that follow ?
(i) What is relationship between dissolved oxygen and biochemical oxygen Demand (BOD) ?
(ii) Mention their effect on aquatic life in the river.

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(i) As BOD refers to the amount of oxygen consumed if all the organic matter in one liter of water were oxidised by bacteria. Thus greater the BOD, lesser will be the dissolved oxygen in sewage discharge.
(ii) Effects on aquatic life
(a) It causes high mortality rate aquatic animals.
(b) The excessive nutrients facilitate algel growth causing algal bloom .
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