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
ppm
mg/L
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.
Polarographic
Silver anode, gold or platinum cathode
detects changes in the electrical current caused by oxygen reduction
Optical
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
Salinity
Altitude
It is lost from the water through respiration and decomposition
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