Dissolved Oxygen

In-depth explanation of Dissolved Oxygen

Dissolved oxygen is oxygen gas dissolved in water, and it is essential for fish, invertebrates and aerobic bacteria. Its solubility decreases as temperature rises and as salinity increases, so warm water holds less oxygen. Water saturated with air at 25 C holds about 8 mg per L. Organic pollution and algal decay reduce dissolved oxygen by increasing consumption, while thermal discharge lowers solubility. Measurements are made by the Winkler titration method or with electrochemical probes. Most fish species need at least about 5 mg per L for healthy survival.

Going deeper: Dissolved Oxygen

Key ideas: Oxygen dissolves in water following Henry law, about 9 mg per liter at 20 C and 14.6 at 0 C in saturated fresh water; solubility drops with higher temperature and salinity. Most fish need above 5 mg per liter, below 2 is hypoxic. Measured by Winkler titration or probe. Stream aeration and photosynthesis raise it.

Common mistakes and connections: Mistake: thinking warm water holds more gas like it holds more solute; gases are less soluble when hot, so thermal pollution lowers oxygen while raising metabolic demand. Deep lakes can stratify and go anoxic. Links to gas solubility, BOD and eutrophication.

Visualization of Dissolved Oxygen

Oxygen solubility in fresh water falls as temperature rises, so thermal pollution leaves less oxygen for fish. The interactive lesson shows this as a live animation or chart.

Worked example and use case

Water saturated with air at 25 C holds about 8 mg per L, and fish become stressed as levels fall below about 5 mg per L.

Where Dissolved Oxygen fits in Biochemistry, Environment & Industry

Dissolved Oxygen is topic 82 of 127 in Biochemistry, Environment & Industry.

Related topics

• Water PollutionBeginner
• EutrophicationIntermediate
• Biochemical Oxygen DemandAdvanced
• Heavy Metal PollutionIntermediate
• PesticidesIntermediate
• BioaccumulationAdvanced

Browse all 127 topics in Biochemistry, Environment & Industry