A water body characterized by nutrient rich water supports abundant growth of phytoplankton and other water plants on its surface. Over time, the water body gets filled with a large number of such plants and the process is called Eutrophication. In such water bodies, dissolved oxygen content is nil or very less.
In eutrophicated waler body, growth rate of phytoplankton is high because of:

Options

A. Light penetrating the lower surfaces of water body
B. Enrichment of nutrients in the water body
C. Less of dissolved oxygen in the water body.
D. Aquatic fauna flourishes well in eutrophicated water body.

Answer

To solve the question regarding the high growth rate of phytoplankton in eutrophicated water bodies, we can break it down into the following steps:

### Step-by-Step Solution:

1. **Understanding Eutrophication**:
- Eutrophication is a process where water bodies become enriched with nutrients, often due to runoff from fertilizers, sewage, or other sources. This leads to an increase in the growth of aquatic plants and phytoplankton.

2. **Identifying Key Factors**:
- The question mentions that the water body is characterized by nutrient-rich water. This is crucial because it directly influences the growth of phytoplankton.

3. **Analyzing Light Penetration**:
- The first option suggests that light penetrates the lower surface of the water body. However, in eutrophicated waters, the surface is often covered with dense plant growth, which blocks light from reaching deeper layers. Thus, this option is incorrect.

4. **Considering Nutrient Enrichment**:
- The second option states that the growth rate of phytoplankton is high due to the enrichment of nutrients in the water. This is a correct statement, as the abundance of nutrients such as nitrogen and phosphorus promotes rapid growth of phytoplankton.

5. **Evaluating Dissolved Oxygen Levels**:
- The third option mentions less dissolved oxygen in the water body. While it is true that eutrophication can lead to low oxygen levels due to decomposition of dead plants, this does not directly contribute to the growth of phytoplankton. Therefore, this option is incorrect.

6. **Assessing Aquatic Fauna**:
- The last option suggests that aquatic fauna flourish well in eutrophicated water bodies. However, the low oxygen levels typically associated with eutrophication can harm aquatic fauna, making this option incorrect as well.

7. **Conclusion**:
- Based on the analysis, the correct answer is that the growth rate of phytoplankton is high because of the enrichment of nutrients in the water bodies.

### Final Answer:
The growth rate of phytoplankton in eutrophicated water bodies is high because of the enrichment of nutrients in the water bodies.