water.
4. In a certain region, industrial effluent rich in organic matter was discharged into a
river. The graph given below indicates the effect of this discharge on biological oxygen
demand as the river proceeds forward.
Dissolved oxygen
BOD
20
15
Amount of substance (mg/L)
B
Direction on river
a. Analyse the graph and establish a relation between the two parameters. How will the
phenomenon affect aquatic life?
b. At what point is the effluent discharged? Give reason.
c. At which of the points will aquatic life be most affected? Where will it be least affected
and why?
Answers
Answer:
Answer
Rich growth of the microorganism in the lakes consumes most of the dissolved oxygen. This condition is known as Eutrophication.
The excessive plant nutrients intensify eutrophication.
The impurity of water due to organic matter is measured in terms of biological oxygen demand. It is the demand for oxygen to decompose organic waste in litre of water. So where the BOD is high means the water is polluted and the organic matter is high. It shows that the sewage increase in biochemical oxygen demands of water as it has a lot of organic material.
So, the correct option is 'Peak A- Sharp increase in BOD, the disappearance of clean water organisms, Peak B- Increase in dissolved oxygen, the reappearance of clean water organisms
Explanation: