Algal bloom is caused by

Options

A. Availability of excess nutrients
B. Lack of nutrients
C. Increase in non - biodergradable pollutants
D. Decreased BOD

Answer

**Step-by-Step Solution:**

1. **Understanding Algal Bloom**:
- Algal bloom refers to the rapid increase in the population of algae in a water body, which can lead to discoloration of the water. The color can vary based on the type of algae present.

2. **Causes of Algal Bloom**:
- The primary cause of algal bloom is the availability of excess nutrients, particularly nitrogen and phosphorus. These nutrients often come from agricultural runoff, where fertilizers are used extensively.

3. **Impact of Nutrients**:
- When fertilizers enter the water body, they increase the nutrient levels, which promotes the rapid growth of algae. This can lead to dense algal mats that block sunlight from penetrating the water.

4. **Consequences of Algal Bloom**:
- As algae grow excessively, they can deplete oxygen levels in the water, leading to hypoxic conditions. This can result in the death of aquatic organisms that rely on oxygen for survival.

5. **Evaluating Options**:
- **Option 1: Availability of excess nutrients** - This is correct as it directly leads to algal bloom.
- **Option 2: Lack of nutrients** - This is incorrect because a lack of nutrients would inhibit algal growth.
- **Option 3: Increase in non-biodegradable pollutants** - This is also incorrect as these pollutants do not promote algal growth.
- **Option 4: Decrease in BOD** - This is incorrect because a decrease in BOD indicates less organic matter, which does not contribute to algal growth.

6. **Conclusion**:
- The correct answer to the question "Algal bloom is caused by" is **Option 1: Availability of excess nutrients**.

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