Deep temperate lakes undergo circulation

Options

A. Once
B. Twice
C. Thrice
D. Four times.

Answer

### Step-by-Step Solution:

1. **Understand the Concept of Circulation in Lakes**:
- Circulation in lakes refers to the movement of water within the lake, which is essential for nutrient distribution and temperature regulation.

2. **Identify the Types of Circulation**:
- In deep temperate lakes, circulation is often referred to as "lake turnover." This process involves the mixing of water layers.

3. **Recognize the Layers of Water**:
- Lakes have different layers based on temperature and density:
- **Epilimnion**: The upper layer of the lake, which is warmer and has lower density.
- **Hypolimnion**: The deeper layer, which is colder and has higher density.

4. **Seasonal Changes Affecting Circulation**:
- In **summer**, the epilimnion is warmer and less dense, while the hypolimnion is colder and denser.
- In **winter**, the situation reverses: the epilimnion becomes colder and denser, while the hypolimnion remains warmer and less dense.

5. **Determine the Number of Circulations**:
- Due to the seasonal changes, deep temperate lakes undergo circulation twice a year: once in summer and once in winter. This results in two distinct turnover events.

6. **Conclusion**:
- Therefore, deep temperate lakes undergo circulation **two times** a year.

### Final Answer:
Deep temperate lakes undergo circulation **two times**.

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