Algal blooms in a lake

Options

A. Leads to oxygen depletion
B. Kills fishes and other organisms
C. Increase carbon dioxide level
D. All

Answer

**Step-by-Step Solution:**

1. **Understanding Algal Blooms**: Algal blooms refer to a rapid increase in the population of algae in freshwater systems, often due to nutrient enrichment in the water body.

2. **Causes of Algal Blooms**: The excessive nutrients, particularly nitrogen and phosphorus, lead to a phenomenon known as eutrophication, which triggers the growth of algae.

3. **Effects on Oxygen Levels**: As algae grow, they consume dissolved oxygen in the water. This leads to a decrease in oxygen concentration, which is critical for the survival of aquatic organisms.

4. **Impact on Aquatic Life**: The depletion of oxygen can result in the death of fish and other organisms that rely on oxygen for their survival.

5. **Increase in Carbon Dioxide**: The process of algal growth and subsequent decay can also lead to an increase in carbon dioxide levels in the water, further affecting the aquatic ecosystem.

6. **Conclusion**: Given the effects of algal blooms, all the provided options are correct:
- They lead to oxygen depletion.
- They kill fish and other organisms.
- They increase carbon dioxide levels.

Therefore, the correct answer is "all of the above."

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