Instruction Manual PD 30014 ADDENDUM 1: DISSOLVED OXYGEN & METER THEORYDissolved Oxygen (DO) refers to the volume of oxygen that is contained in water. There aretwo main sources of DO in water: from atmosphere and photosynthesis. Waves and tumblingwater mix air into the water where oxygen readily dissolves until saturation occurs. Oxygen isalso 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 thansaltwater does).3. Amount of DO decreases with decreasing atmospheric pressure (amount of DOabsorbed in water decreases as altitude increases).The chart below shows the solubility of DO in mg/L in water at various temperatures.Solubility of oxygen in water contact with water saturated air atstandard atmospheric pressure02468101214160 10 20 30 40 50 60Temperature °CSolubility mg/LFigure 46: DO Solubility in Water vs Temperature °C66
