Dissolved Oxygen
Dissolved oxygen (DO) is a relative measure of the amount of oxygen that is dissolved in water. DO can be measured, regionally and non-invasively. Although water is composed of oxygen and hydrogen atoms, biological life in water depends upon molecules of oxygen that are dissolved in water. Oxygen is used by organisms in aerobic respiration, where energy is released by the combustion of sugar in the mitochondria. This form of oxygen can fit into the spaces between water molecules and is available to aquatic organisms. Fish, invertebrates, and other aquatic animals depend upon the oxygen dissolved in water. Without this oxygen, they would suffocate. Some organisms, such as salmon, mayflies, and trout, require high concentrations of oxygen in their water. Other organisms, such as catfish, midge fly larvae, and carp can survive with much less oxygen. The ecological quality of the water depends largely upon the amount of oxygen the water can hold.
The GLOBE Dissolved Oxygen Protocol measures the amount of molecular oxygen (O2) dissolved in water. It does not measure the amount of oxygen in the water molecule (H2O). Students often confuse the oxygen that is part of the water molecule (the O in H2O) with dissolved oxygen (O2). We call the amount of dissolved oxygen the water will hold (under specific conditions) the solubility of dissolved oxygen. Factors affecting the solubility of dissolved oxygen include water temperature, atmospheric pressure, and salinity. Cold water can dissolve more oxygen than warm water. For example, at 25˚ C, dissolved oxygen solubility is 8.3 mg/L, whereas at 4˚ C the solubility is 13.1 mg/L. As temperature goes up, water releases some of its oxygen into the air. oxygen (or other types of measurements), both a probe and meter are required. Sometimes the probe and meter are within one instrument and cannot be taken apart. Other instruments have probes that are separate from the meters and need to be connected to the meters in order to take the water measurements. Dissolved oxygen probes must be calibrated before use. Check with the probe manufacturer to be sure the probe stores the most recent calibration.
Dissolved Oxygen Kits: Dissolved oxygen test kits involve two parts – sample preservation (stabilization or fixing) and sample testing. Preservation involves the addition of a chemical to the sample that precipitates in the presence of dissolved oxygen, followed by the addition of a chemical that produces a colored solution. Testing involves adding drops of a titrant solution until the color disappears. The dissolved oxygen value is calculated from the volume of titrant added.
The GLOBE Dissolved Oxygen Protocol measures the amount of molecular oxygen (O2) dissolved in water. It does not measure the amount of oxygen in the water molecule (H2O). Students often confuse the oxygen that is part of the water molecule (the O in H2O) with dissolved oxygen (O2). We call the amount of dissolved oxygen the water will hold (under specific conditions) the solubility of dissolved oxygen. Factors affecting the solubility of dissolved oxygen include water temperature, atmospheric pressure, and salinity. Cold water can dissolve more oxygen than warm water. For example, at 25˚ C, dissolved oxygen solubility is 8.3 mg/L, whereas at 4˚ C the solubility is 13.1 mg/L. As temperature goes up, water releases some of its oxygen into the air. oxygen (or other types of measurements), both a probe and meter are required. Sometimes the probe and meter are within one instrument and cannot be taken apart. Other instruments have probes that are separate from the meters and need to be connected to the meters in order to take the water measurements. Dissolved oxygen probes must be calibrated before use. Check with the probe manufacturer to be sure the probe stores the most recent calibration.
Dissolved Oxygen Kits: Dissolved oxygen test kits involve two parts – sample preservation (stabilization or fixing) and sample testing. Preservation involves the addition of a chemical to the sample that precipitates in the presence of dissolved oxygen, followed by the addition of a chemical that produces a colored solution. Testing involves adding drops of a titrant solution until the color disappears. The dissolved oxygen value is calculated from the volume of titrant added.
