Question

In waterlogged soil, the concentration of which one of the following is high?

• A. Ethane
• B. Methane
• C. Carbon dioxide
• D. Carbon monoxide

Hint:

Submerged/waterlogged soils experience anaerobic reduction producing methane ($\text{CH}_4$), hydrogen sulfide ($\text{H}_2\text{S}$), and ferrous iron ($\text{Fe}^{2+}$).

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Waterlogging fills soil pore spaces with water, displacing gaseous oxygen and inducing severe anaerobic reducing conditions.

Step 2: Detailed Explanation:
Under prolonged submergence and low redox potential ($E_h < -150\text{--}-200\,\text{mV}$), strict anaerobic methanogenic archaea reduce organic acids and carbon dioxide to produce methane ($\text{CH}_4$, marsh gas):
\[\text{CO}_2 + 4\text{H}_2 \to \text{CH}_4 + 2\text{H}_2\text{O}\] Methane accumulates in high concentrations in submerged and waterlogged paddy soils.

Step 3: Final Answer:
Hence, methane concentration is high in waterlogged soils.