A lake has been polluted by sewage. Compared with unpolluted water, the water in this lake will have

Options

A. fewer bacteria
B. more fish
C. more nitrogen compounds
D. more oxygen

Answer

**Step-by-Step Solution:**

1. **Understanding Sewage Pollution:**
- Sewage is a mixture of waste from households, industries, and agricultural runoff. When it enters a lake, it introduces a variety of organic and inorganic pollutants.

2. **Impact on Organic Content:**
- The introduction of sewage increases the organic content in the lake. This organic matter serves as food for microorganisms, leading to an increase in their population.

3. **Decomposition Process:**
- Microorganisms such as bacteria and fungi break down the organic matter through a process called decomposition. This process requires oxygen, which is dissolved in the water.

4. **Oxygen Consumption:**
- As bacteria and other microorganisms decompose the organic material, they consume dissolved oxygen from the water. This leads to a decrease in the levels of dissolved oxygen available for aquatic life.

5. **Effects on Aquatic Life:**
- With the decrease in dissolved oxygen, aquatic organisms such as fish and other aquatic life struggle to survive. Fish and other organisms require a certain level of dissolved oxygen to thrive.

6. **Increase in Nitrogen Compounds:**
- Sewage often contains nitrogenous compounds (like ammonia and nitrates) which can lead to further problems such as eutrophication, where excessive nutrients promote algal blooms.

7. **Conclusion:**
- Compared to unpolluted water, the water in the polluted lake will have higher levels of nitrogen compounds, lower levels of dissolved oxygen, and an increased number of microorganisms.

**Final Answer:**
The water in the polluted lake will have more nitrogen compounds and less dissolved oxygen compared to unpolluted water.

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