Choose the correct representation of effect of sewage discharge on important characteristics of a river.

Options

A.
B.
C.
D.

Answer

To solve the question regarding the correct representation of the effect of sewage discharge on important characteristics of a river, we can follow these steps:

### Step-by-Step Solution:

1. **Identify Important Characteristics of a River**:
- The two main characteristics affected by sewage discharge are:
- Biological Oxygen Demand (BOD)
- Dissolved Oxygen (DO)

2. **Understand Biological Oxygen Demand (BOD)**:
- BOD measures the amount of oxygen required by microorganisms to decompose organic matter in water.
- An increase in organic matter (like sewage) leads to an increase in BOD.

3. **Understand Dissolved Oxygen (DO)**:
- DO refers to the amount of oxygen available in water for aquatic organisms.
- When sewage is discharged, the organic matter consumes oxygen, leading to a decrease in DO.

4. **Analyze the Effect of Sewage Discharge**:
- Initially, when sewage is discharged into the river:
- BOD increases due to the decomposition of organic matter.
- DO decreases because the oxygen is being consumed by microorganisms.

5. **Observe the Trends Over Time**:
- After the initial discharge:
- BOD may eventually decrease as the organic matter is broken down.
- DO may increase again as the microbial population stabilizes and the organic matter is depleted.

6. **Choose the Correct Representation**:
- The correct graph should show:
- An initial increase in BOD followed by a decrease.
- An initial decrease in DO followed by an increase.
- This pattern reflects the changes in oxygen levels and microbial activity after sewage discharge.

7. **Evaluate Other Options**:
- Review the other options provided in the question to confirm that they do not accurately represent the described trends.

### Conclusion:
The first option is the correct representation of the effect of sewage discharge on the important characteristics of a river, showing the initial increase in BOD and decrease in DO, followed by subsequent changes.