Question

Which of the following can directly cause eutrophication in lakes?
A. Sewage waste
B. Acidic precipitation
C. Agriculture runoff
D. Sulfur rich effluent from thermal power plant
E. Municipal waste water
Choose the correct answer from the options given below:

• A. A, C and D only
• B. B, D and E only
• C. B, C and D only
• D. A, C and E only

Hint:

Remember: Eutrophication is driven by excess Nitrogen ($\text{N}$) and Phosphorus ($\text{P}$).
Look for agricultural runoff (fertilizers) and domestic sewage/wastewater (detergents and excreta).
Acid rain and sulfur effluents cause lake acidification, not eutrophication.

Answer 1

The Correct Option is D

Concept:
Eutrophication refers to the accelerated nutrient enrichment of aquatic systems, primarily by nitrogen ($\text{N}$) and phosphorus ($\text{P}$).
This influx stimulates rapid blooms of algae and cyanobacteria, which subsequently decompose, depleting dissolved oxygen and causing fish kills.

Step 1: Detailed Examination of Potential Sources:
- A. Sewage waste: Untreated domestic sewage is rich in organic nitrogen, urea, proteins, and phosphates from human excreta and detergents. Its discharge directly enriches aquatic systems, driving rapid eutrophication.
- B. Acidic precipitation: Acid rain contains sulphuric and nitric acids resulting from $\text{SO}_2$ and $\text{NO}_x$ emissions. It lowers the pH of lakes and leaches toxic aluminium ions, causing lake acidification rather than nutrient enrichment.
- C. Agriculture runoff: Farmland runoff carries dissolved inorganic fertilizers (synthetic urea, ammonium nitrate, and superphosphates). These are primary drivers of cultural eutrophication in surface water bodies worldwide.
- D. Sulfur-rich effluent from thermal power plants: Discharges sulphates, heavy metals, and warm cooling water (thermal pollution). It does not provide the limiting nitrogen and phosphorus nutrients required to stimulate algal blooms.
- E. Municipal waste water: Municipal wastewater contains greywater loaded with synthetic detergents, surfactants, and phosphates, directly adding nutrients to receiving water bodies.

Step 2: Synthesizing the Direct Drivers:
The sources that directly supply limiting plant nutrients (N and P) and trigger algal blooms are:
- Sewage waste (A)
- Agriculture runoff (C)
- Municipal waste water (E)
Items B and D contribute to acidification and industrial chemical pollution rather than eutrophication.
Final Answer:
The sources that directly cause eutrophication are A, C, and E only, corresponding to option (D).