Question

Organic nutrients in water bodies promote -
A. Growth of natural population of aquatic bacteria
B. Biological Oxygen Demand
C. Eutrophication
Choose the most appropriate answer from the options given below:

• A. A only
• B. B only
• C. C only
• D. All A, B and C

Hint:

Nutrients $\rightarrow$ Algae/Bacteria $\rightarrow$ Decay $\rightarrow$ Oxygen loss (BOD) $\rightarrow$ Death of fish (Eutrophication).
This is a standard "cause-and-effect" chain in environmental science.

Answer 1

The Correct Option is D

Step 1: Understanding the Question:
The question asks about the cascading environmental effects of adding organic matter and nutrients to a water ecosystem.
Detailed Explanation:

• Bacterial Growth (Statement A):
When organic matter (sewage, agricultural runoff) enters water, it provides a source of carbon and energy for heterotrophic bacteria. This leads to a rapid "explosion" or growth of the natural bacterial population.

• Biological Oxygen Demand (Statement B):
As these bacteria decompose the organic matter, they consume dissolved oxygen through respiration.
BOD (Biological Oxygen Demand) is a measure of how much oxygen is required by these microbes to break down the organic load. High organic nutrients = High microbial activity = High BOD.

• Eutrophication (Statement C):
Inorganic nutrients (N and P) often accompany organic loads. These stimulate excessive growth of algae (algal blooms).
When the algae die, they further increase the organic load, continuing the cycle of oxygen depletion and leading to the overall degradation of the water body known as eutrophication.

• Conclusion:
All three statements describe linked stages of water pollution resulting from nutrient enrichment.

Step 2: Final Answer:
Organic nutrients promote bacterial growth, increase BOD, and ultimately lead to eutrophication.