Which of the following statements regarding eutrophication are correct ?
(i) Eutrophication is the natural ageing of a lake by nutrient enrichment of its water.
(ii) Pollutants from human activities like effluents from the industries and homes can radically accelerate the aging process of a lake. This phenomenon is called as cultural or accelerated eutrophication.
(iii) The plant nutrients responsible for eutrophication are nitrates and phosphates.
(iv) These phosphates and nitrates accelerate the growth of algae, which utilise oxygen and may deoxygenate the water to kill the fish and other aquatic animals.

Options

A. (i) and (ii)
B. (iii) and (iv)
C. (i), (ii) and (iii)
D. (i), (ii), (iii) and (iv)

Answer

To determine which statements regarding eutrophication are correct, we will analyze each statement one by one.

### Step-by-Step Solution:

1. **Understanding Eutrophication**:
- Eutrophication refers to the process where water bodies, such as lakes, become enriched with nutrients (mainly nitrates and phosphates), leading to excessive growth of algae and other aquatic plants.

**Hint**: Remember that eutrophication is primarily caused by nutrient enrichment in water bodies.

2. **Evaluating Statement (i)**:
- Statement (i) claims that "Eutrophication is the natural ageing of a lake by nutrient enrichment of its water."
- This statement is correct. Eutrophication can occur naturally over time as lakes age, but it can also be accelerated by human activities.

**Hint**: Consider the difference between natural processes and those accelerated by human influence.

3. **Evaluating Statement (ii)**:
- Statement (ii) states that "Pollutants from human activities like effluents from the industries and homes can radically accelerate the aging process of a lake. This phenomenon is called as cultural or accelerated eutrophication."
- This statement is also correct. Human activities, such as the discharge of sewage and fertilizers, significantly speed up the eutrophication process.

**Hint**: Think about how human activities impact natural processes.

4. **Evaluating Statement (iii)**:
- Statement (iii) mentions that "The plant nutrients responsible for eutrophication are nitrates and phosphates."
- This statement is correct. Nitrates and phosphates are the primary nutrients that contribute to eutrophication.

**Hint**: Recall the key nutrients that lead to algal blooms.

5. **Evaluating Statement (iv)**:
- Statement (iv) states that "These phosphates and nitrates accelerate the growth of algae, which utilise oxygen and may deoxygenate the water to kill the fish and other aquatic animals."
- This statement is correct. The rapid growth of algae (algal blooms) can lead to oxygen depletion in the water, harming aquatic life.

**Hint**: Consider the consequences of algal blooms on oxygen levels in water bodies.

### Conclusion:
All four statements regarding eutrophication are correct. Therefore, the answer is that statements (i), (ii), (iii), and (iv) are all true.

### Final Answer:
All statements (i), (ii), (iii), and (iv) regarding eutrophication are correct.