Dissolved Oxygen and Simple Monitoring

Aquatic organisms need dissolved oxygen for respiration, so DO is an important water-quality indicator. More biodegradable organic waste → more microbial decomposition → greater oxygen consumption → lower DO Low DO can stress aquatic organisms. DO = dissolved molecular O₂ (not the O in H₂O).

Fish need oxygen too, but they obtain oxygen dissolved in water. If pollution causes microorganisms to use too much oxygen, the amount left for aquatic organisms decreases.

DO reflects the balance between oxygen entering or being produced in water and oxygen being consumed by respiration and chemical processes. Organic pollution can increase microbial respiration and lower DO.

Dissolved oxygen is controlled by interacting physical, chemical and biological processes: temperature, atmospheric exchange, photosynthesis, respiration, organic-matter decomposition and water movement. Therefore DO should be interpreted together with other water-quality measurements.

DO = dissolved oxygen · Aquatic organisms require oxygen · Organic decomposition consumes oxygen · Heavy organic pollution can lower DO · Low DO can stress aquatic organisms · Appearance alone cannot establish water quality · Monitoring should use several measurements