Understanding Dissolved Oxygen in Water Bodies

Dissolved Oxygen (D.O.) is crucial for aquatic life. However, oxygen is constantly being consumed in water bodies, primarily by microorganisms that decompose organic matter. This process is called de-oxygenation.

The Process of De-oxygenation

De-oxygenation refers to the depletion of dissolved oxygen in a water body. This often happens when there is an excess of organic pollutants. Microorganisms like bacteria use dissolved oxygen during the aerobic decomposition of these pollutants, leading to a decrease in the D.O. level. If de-oxygenation is severe, it can harm or kill aquatic organisms.

Counterbalancing Oxygen Consumption: Re-oxygenation

To maintain a healthy level of dissolved oxygen, water bodies naturally receive oxygen from the atmosphere. This process counteracts the consumption of D.O. due to de-oxygenation. The transfer of oxygen from the air into the water occurs through diffusion and surface agitation (like wind and waves). This vital process of replenishing the dissolved oxygen in water from the atmosphere is specifically known as re-oxygenation.

Analyzing the Given Options

Let's look at the provided options in the context of the question:

• De-oxygenation: This is the process where dissolved oxygen is consumed, not replenished. So, this option is incorrect.
• Re-oxygenation: This is the process where oxygen is added back into the water, often from the atmosphere, counteracting de-oxygenation. This matches the description in the question.
• Self-purification: This is a broader term that encompasses all natural processes by which a polluted water body recovers. Re-oxygenation is one of the key processes involved in self-purification, but self-purification itself is not just the atmospheric oxygen supply.
• Dilution: This involves mixing polluted water with cleaner water, which reduces the concentration of pollutants but does not necessarily involve the transfer of oxygen from the atmosphere to the water body itself as the primary counterbalancing mechanism against de-oxygenation.

Conclusion

The question specifically asks for the process where the atmosphere supplies oxygen to counterbalance D.O. consumption due to de-oxygenation. Based on the definitions, this process is precisely termed re-oxygenation.