EUTECH INSTRUMENTS DO 6, Instruction Manual, Page: 68 / 76

Instruction Manual DO 6
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14 ADDITIONAL INFORMATION
14.1 Dissolved Oxygen
14.1.1 General Information
Dissolved Oxygen (DO) refers to the volume of oxygen that is contained in
water. There are two main sources of DO in water: from atmosphere and
photosynthesis. Waves and tumbling water mix air into the water where oxygen
readily dissolves until saturation occurs. Oxygen is also produced by aquatic
plants and algae as a by-product of photosynthesis.
The amount of DO that can be held by water depends on 3 factors: water
temperature, salinity, and atmospheric pressure.
1) Amount of DO increases with decreasing temperature (colder water holds
more oxygen);
2) Amount of DO increases with decreasing salinity (freshwater holds more
oxygen than saltwater does);
3) Amount of DO decreases with decreasing atmospheric pressure (amount
of DO absorbed in water decreases as altitude increases).