Dissolved oxygen (DO) is a measure of the quantity of free oxygen molecules in water. The concentration of DO is an important indicator of the health of an aquatic ecosystem because oxygen is essential for almost all forms of life. Oxygen is necessary for respiration and for some chemical reactions. Ongoing low dissolved oxygen in a water body will harm most aquatic life, because there will not be enough to sustain life.
Conversely, too much oxygen in water (supersaturated) can also be dangerous. Dissolved oxygen in water comes from two main sources: the atmosphere and photosynthesis. The concentration of DO is affected by numerous variables, including water temperature (colder water holds more oxygen than warmer water), salinity (freshwater holds more oxygen than saltwater) and atmospheric pressure (the amount of DO absorbed in water decreases as altitude increases).
DO is measured using a dissolved oxygen meter (or DO meter). The best method is to take the measurement in the field at the same time each day, because DO concentrations can vary throughout a 24 hour period. Dissolved oxygen testing equipment usually allows oxygen concentrations to be measured in both milligrams per litre (mg/)l and percentage saturation (% sat), which allows direct comparison between results from sites with different salinity and temperature values.
Aquaread's dissolved oxygen meter can measure in both formats. The AquaPlus Optical DO measurement system works on the principle of Dynamic Luminescence Quenching. Short bursts of blue light are emitted to increase the energy levels of a chemical known as a luminophore, causing the molecules to enter an excited state. This elicits molecules in the luminophore to emit red light, or photons. If oxygen molecules collide with the luminophore the red photons will be quenched or delayed.
Dynamic quenching is when the collision of the excited luminophore and the oxygen causes the energy to be transferred to the oxygen, preventing the luminophore from emitting light. By measuring the delay of the returned red photons with respect to the blue excitation, it is possible to determine the level of DO present. The optical dissolved oxygen meter comes as standard with all Aquaread Aquaprobes, as it’s one of the most commonly measured parameters during water monitoring.
The parameter is capable of measuring dissolved oxygen in water in the range of 0 – 500% or 0 – 50 mg/l. Our DO meter is multifunctional because it also measures electrical conductivity of the water, which means that the sensor automatically compensates for salinity. Dissolved oxygen is measured at the end of the electrode by the components behind the removable cap, and electrical conductivity (EC) is measured on the side of the electrode by the four stainless steel contacts.