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Study the graph given below. Explain how is oxygen concentration affected in the river when sewage is discharged into it?


1. It causes high mortality rate among aquatic animals. The excessive nutrients facilitate algal growth causing algal bloom.

2. There is a decline in dissolved oxygen from the point of sewage discharge . It is because of biodegradation of organic matter in the receiving water body which consumes dissolved oxygen. It leads to fish mortality as well as other aquatic forms.