Why does the oxygen concentration in the water decrease when sewae is discharged into a river?

Why does the oxygen concentration in the water decrease when sewage is dicharged into a river?

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

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

Explain the change that can be observed in the characterstics of river water when sewage is discharged into it and a few weeks after the discharge with respect to (i) level of dissolved oxygen (ii) Population of fresh water organisms.

Explain the change that can be observed in the characterstics of river water when sewage is discharged into it and a few weeks after the discharge with respect to (i) level of dissolved oxygen (ii) Population of fresh water organisms.

Why does the concentration of OH^(-) ions in pure water increase with rise in temperature ? Does this increase make pure water alkaline ? Explain.

At high oxygen concentration, the rate of photosynthesis decreases due to

At high oxygen concentration, the rate of photosynthesis decreases due to