Addition of phosphate and nitrates /fertiliser into water and that water ultimately draining into lake firstly affects

Options

A. growth of aquatic organisms in lake
B. eutrophication of lake
C. the environment of lake
D. organic remains deposited on the lake bottom

Answer

### Step-by-Step Solution:

1. **Understanding the Problem**: The question asks about the effects of adding phosphates and nitrates (fertilizers) into water bodies that eventually drain into lakes.

2. **Identifying the Initial Impact**: When phosphates and nitrates enter the lake, they increase the nutrient levels in the water. This nutrient enrichment leads to a phenomenon known as eutrophication.

3. **Eutrophication Process**: Eutrophication is characterized by excessive growth of algae and aquatic plants due to the high nutrient levels. This can lead to algal blooms, which can cover the surface of the water.

4. **Consequences of Algal Blooms**: As the algae grow and eventually die, they decompose. This decomposition process consumes a significant amount of oxygen in the water, leading to hypoxic (low oxygen) conditions.

5. **Effects on Aquatic Life**: The decrease in oxygen levels can result in the death of fish and other aquatic organisms that rely on oxygen for survival. This shift in the ecosystem can also lead to changes in species composition, favoring those that can tolerate lower oxygen levels.

6. **Long-term Changes**: Over time, the lake's environment may change significantly, transitioning from a freshwater aquatic ecosystem to a more terrestrial ecosystem as sediments and organic matter accumulate at the bottom. This process can lead to the lake eventually becoming a marsh or dry land.

7. **Conclusion**: The addition of phosphates and nitrates into water bodies primarily affects the aquatic ecosystem by initiating eutrophication, which leads to oxygen depletion and significant changes in the lake's environment.

### Final Answer:
The addition of phosphates and nitrates into water bodies primarily affects the aquatic ecosystem by initiating eutrophication, leading to oxygen depletion and significant changes in the lake's environment.

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