Dissolved Oxygen

December 21st, 2018

Dissolved oxygen (DO) is the amount of oxygen (O2) dissolved in the water

Most aquatic organisms need a minimum of 3-5 mg/L to survive

dissolved oxygen levels frequently range from 2 to 14 mg/l

Oxygen is used to break down food to produce energy

Aquatic organisms need dissolved oxygen to live (respiration)

Decomposition is a type of respiration by bacteria, which uses oxygen to break down organic matter

Dissolved oxygen concentrations can be affected by many factors

  • Diffusion
  • Aeration
  • Photosynthesis
  • Respiration

Dissolved oxygen often reaches over 100% air saturation due to photosynthesis activity during the day.

In freshwater systems such as lakes, rivers and streams, dissolved oxygen concentrations will vary by season, location and water depth

Dissolved oxygen levels can range from less than 1 mg/L to more than 20 mg/L depending on how all of these factors interact

units of measure 

% Air Saturation



Electro-chemical Sensors

Optical Sensor

Galvanic – 

Zinc or lead anode, Silver cathode

In an electrolyte solution, the cathode and anode self polarize, producing an electric current. The Sensor measures this electric current.


Silver anode, gold or platinum cathode

detects changes in the electrical current caused by oxygen reduction


red light, blue light

Measures the interaction between oxygen and certain luminescent dyes

Measured effects are inversely proportional to the partial pressure of oxygen in the water

Interesting Fact

Dissolved oxygen values in water are often well over 100% air saturation due oxygen being produced by photosynthesis

Dissolved oxygen enters the water by diffusion from the air and through photosynthesis

The amount of oxygen that can dissolve in water depends on:

Water temperature



It is lost from the water through respiration and decomposition

Leave a Reply

Your email address will not be published. Required fields are marked *