Dissolved Oxygen and Water Quality

Water is essential to life, and the quality of water is important for human health, aquatic life, and ecosystem balance. One important aspect of water quality is dissolved oxygen (DO), which is the amount of oxygen gas dissolved in water. In this article, we will discuss the significance of dissolved oxygen in water and how it affects water quality.

What is Dissolved Oxygen in Water?

Dissolved oxygen in water is the amount of oxygen that is present in the liquid form in water. It is measured in milligrams per liter (mg/L) or parts per million (ppm). Dissolved oxygen is essential for the survival of most aquatic species, including fish, invertebrates, and plants. It also plays a crucial role in maintaining the balance of the ecosystem.

DO Sources

DO in water can come from several sources, including:

  1. Atmospheric exchange: Oxygen from the air dissolves into water at the surface, especially when water is moving, such as in streams or rivers.
  2. Photosynthesis: Aquatic plants and algae release oxygen into the water through photosynthesis.
  3. Aeration: Mechanical or natural aeration, such as waterfalls or rapids, can increase the amount of DO in water.

Factors that Affect DO Levels in

  1. Temperature: As water temperature increases, its ability to hold dissolved oxygen decreases.
  2. Salinity: Higher salinity reduces the amount of DO in water.
  3. Water Movement: Moving water has a higher oxygen exchange rate than still water, and therefore, generally has higher DO levels.
  4. Organic Matter: Decay of organic matter, such as leaves, plants, and dead animals, consumes dissolved oxygen.

Importance of DO

  1. Aquatic Life: DO is essential for the survival of most aquatic species, and low DO levels can lead to fish kills and harm other aquatic life.
  2. Bacterial Decay: Dissolved oxygen is essential for the decomposition of organic matter by bacteria, which helps to maintain the balance of the ecosystem.
  3. Water Odor and Taste: Low DO levels can result in the growth of anaerobic bacteria, which produce unpleasant odors and tastes in water.

Maintaining DO Levels in Water

  1. Aeration: Increasing water movement and aeration can increase DO levels.
  2. Limiting Pollution: Controlling pollution from sources such as sewage and industrial waste can help maintain DO levels.
  3. Proper Land Use: Maintaining proper land use practices, such as reducing runoff from agricultural and urban areas, can help preserve DO levels in water.


DO is an important aspect of water quality, and its levels affect the health of aquatic life, the balance of the ecosystem, and the overall quality of water. By understanding the sources and factors that affect DO levels and implementing measures to maintain them, we can ensure clean, healthy water for the future.