The Pro20 Dissolved Oxygen Meter (Left), and the EcStik II Disssolved Oxygen Meter (Right)
Dissolved oxygen (DO) is an important indicator of water quality, as it is necessary for fish and other aquatic organisms to survive. Dissolved oxygen concentrations can be affected by the process of eutrophication, which is caused by nutrient pollution from within the watershed. Therefore, measuring dissolved oxygen concentrations in a water body can help indicate the health of the watershed. There are a number of sensors on the market that can be used in the field to evaluate dissolved oxygen content of water bodies.Â
One type of sensor is called a galvanic sensor, which uses a zinc and a silver anode, which are continuously polarized and therefore have no warm-up period (Dissolved Oxygen Measurement, 2019). An option for this type of meter is the Pro20 Dissolved Oxygen Meter from YSI. With the sensor, this goes for $930 and can measure from 0-50 mg/L DO.Â
Another type of meter is called the polarographic probe, which has a gold and silver anode, which require about 10 minutes to polarize before use but last longer than galvanic probes because they are not always on (Dissolved Oxygen Measurement, 2019). One such dissolved oxygen meter is called the Pocket Dissolved Oxygen Meter from Hach. This goes for $704 and its accuracy is ±0.4 mg/L of DO and can measure from 0-20 mg/L. Another option for polarographic meters is the Sension+ 5130 Portable Polarographic Dissolved Oxygen Probe from Hach. This option goes for $658, but requires a reader device to go with it, which go for over $1,000. Its accuracy is ±0.5 mg/L DO. One other option is the ExStik II Dissolved Oxygen Meter from Extech which goes for $277. Its accuracy is ±0.4 mg/L and measures from 0-20 mg/L DO.Â
Another type of sensor for DO concentration measurement is an optical sensor. These sensors are more accurate in the 0-200% DO range, require less frequent calibration, last longer, and are lower maintenance, but have a higher price tag as a result (Dissolved Oxygen Measurement, 2019). One example of an optical sensor is the Pro DSS sensor from YSI. This goes for $1,965 and allows for the measurement of many other parameters, such as pH, turbidity, total algae, or salinity, but these probes are sold separately. Its accuracy from 1-20 mg/L is ±0.1 mg/L.Â
The best sensor is going to depend on application. When accuracy is highly important, optical sensors will be the best option. These sensors last longer, which can help offset the high upfront cost when extended monitoring is required. When accuracy is less important, polarographic and galvanic sensors are good options as well. Deciding between these two comes down to how important readiness of the device is, since polarographic meters take about 10 minutes to polarize, and how important longevity is, since galvanic meters do not last as long as a consequence of their 'always on' state. There are many pocket versions available for these sensors which can help get quick measurements in the field.
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References
Dissolved Oxygen Measurement. (2019). YSI. https://www.ysi.com/parameters/dissolved-oxygen