Study the graph alongside and explain how oxygen concentration is affected in the river

cbse
natural-resources

#1

Study the graph alongside and explain how oxygen concentration is affected in the river when sewage is discharged into it.


#2

As per the graph, the concentration of dissolved oxygen gets dropped sharply on introduction of sewage in waterbody.
A large amount of ${{O}_{2}}$ is used by microorganisms in river to decompose the organic matter (sewage) thus reducing its concentration in water: