What is Dissolved Oxygen
Dissolved oxygen measurement is the gaseous oxygen (O2) dissolved in a solution. Diffusion from the surrounding air by aeration (stream or wave movement) causes oxygen, to become dissolved oxygen in water. Dissolved oxygen also enters as a waste product of photosynthesis.
The dissolved oxygen measurement, should be performed as a grab sample in the field.
Oxygen in the water diffuses through the DO meter probe membrane at a rate proportional to oxygen's partial pressure. Probes of dissolved oxygen meters measure a current as oxygen arrives at the meter's internal cathode and then is presented, upon proper calibration, at the meter read-out.
Dissolved oxygen in water should not exceed 110 percent. Higher concentrations may be lethal to fish. Dissolved oxygen levels below 5.0 mg/l in water create stress on aquatic life. Dissolved oxygen measurements below 1-2 mg/l can result in fish kills.
Dissolved 02 in water is used in the decomposition of organic matter. Large amounts of organic matter in water reduces dissolved oxygen creating stress on the aquatic population.