What greenhouse gas is released from large hydro reservoirs due to submerged vegetation decomposition?

• A. Coal mining releases methane.
• B. Ozone depletion.
• C. Nitrous oxide.
• D. Methane is released from submerged vegetation decomposition in large hydro reservoirs.

Answer: (D)

Methane is produced when submerged vegetation and other organic matter in a newly flooded large hydro reservoir decomposes under anaerobic conditions. Microbes break down this material without oxygen, releasing methane that can bubble up from sediments or diffuse into the water and escape to the atmosphere. This makes hydro reservoirs a source of methane, a greenhouse gas with a much higher short-term warming potential than carbon dioxide. The other options don’t describe this specific process: methane is the gas tied to the decomposition of submerged vegetation; ozone depletion is not a greenhouse gas; while nitrous oxide is a greenhouse gas, it’s produced mainly in soils and other environments rather than from submerged vegetation in reservoirs; coal mining releases methane as well, but not from submerged vegetation decomposition in large hydro reservoirs.