Question

Arrange the following consequences of submergence in the soil in the correct sequence:
(A). Depletion of soil oxygen,
(B). Accumulation of toxic substances like hydrogen sulfide,
(C). Loss of beneficial soil organisms,
(D). Increased soil pH in acidic soil

Choose the correct answer from the options given below:

• A. (A), (C), (B), (D)
• B. (A), (B), (C), (D)
• C. (B), (A), (D), (C)
• D. (C), (B), (D), (A)

Hint:

Remember that oxygen depletion is always the immediate trigger of all subsequent biochemical changes in flooded soils.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Soil submergence triggers a predictable sequence of chemical and biological changes as the environment transitions from aerobic to anaerobic.

Step 2: Detailed Explanation:
When a soil is flooded, the following sequence of events occurs:
1. (A) Depletion of soil oxygen: Dissolved oxygen is rapidly consumed by soil microbes within hours to a few days.
2. (C) Loss of beneficial soil organisms: The sudden lack of oxygen causes a decline in beneficial aerobic microorganisms and soil fauna.
3. (B) Accumulation of toxic substances: Anaerobic microbes begin using alternative electron acceptors. Eventually, sulfate-reducing bacteria produce hydrogen sulfide (\(\text{H}_2\text{S}\)), which accumulates to toxic levels.
4. (D) Increased soil pH in acidic soil: Anaerobic reduction processes consume hydrogen ions (\(\text{H}^+\)), causing the pH of acidic soils to rise toward neutrality (pH 7).
This logical progression corresponds to the sequence: (A), (C), (B), (D).

Step 3: Final Answer:
The correct chronological sequence is (A), (C), (B), (D).