Dissolved oxygen is important for life in waterways
Dissolved oxygen (D.O.) within streams or rivers is measured by WAV citizen stream monitors because oxygen is one of the most important needs of aquatic organisms.
By measuring concentrations of oxygen that are dissolved in the water, particularly when the concentrations are expected to be at their lowest, WAV monitors can assess how healthy the water quality is for aquatic organisms at their sampling site. Follow the link to find out how healthy a stream is.
Dissolved oxygen basics:
Oxygen enters the water in several ways. Like terrestrial plants, aquatic plants use the sun's energy for growth during photosynthesis. Since oxygen is a byproduct of photosynthesis, it is then available in the water for consumption by aquatic organisms. Oxygen also enters the water from the atmosphere through mixing as the water flows or due to wind or wave action.
What affects dissolved oxygen concentrations?
Aquatic plants and other living organisms use oxygen for respiration. Because plants are not producing oxygen during the night, but oxygen is still being used for respiration at that time, dissolved oxygen concentrations will be the lowest within a waterbody just before sunrise. The colder the water, the greater capacity it has to hold oxygen. (This is like soda or pop; the colder it is, the more gases can be dissolved in it. You have probably noticed that there are more bubbles of the gas, carbon dioxide, in the soda when it is colder than when it is warm.)
The atmospheric pressure effects the amount of oxygen dissolved in water. At higher elevations, less oxygen can be dissolved in water. At higher elevations, less oxygen can be dissolved in water.
The more turbid the water, the warmer it is, so less oxygen can be held in it. The more nutrients in the water, the greater opportunity for plant growth. With more plants, there will be more photosynthesis, but also more respiration. This means that dissolved oxygen concentrations may be very low in the morning, and very high in the afternoon.
How D.O. is monitored through WAV
The majority of WAV volunteers use Hach Dissolved Oxygen monitoring test kits (Model OX-2P) to monitor dissolved oxygen on a monthly basis between May and October. Some WAV monitors use a LaMotte kit to assess dissolved oxygen. Both of these kits use chemical reagents to mimic a more complicated in-lab method (Winkler titration) of monitoring dissolved oxygen in water. Some WAV monitors also use YSI 550a meters to assess dissolved oxygen. This was the standard method for WAV Level 2 monitors until 2015 at which time WAV reallocated funds within the program to support additional total phosphorus monitoring. WAV continues to support existing YSI 550a meters and will train local groups to use these meters if they are able to purchase their own.
How D.O. data are used
Point in time dissolved oxygen data are used to identify acute issues at a stream site. If volunteers measure dissolved oxygen levels of 4 mg/L or less, they should repeat the test. If they still find D.O. levels that low, they should call their local DNR biologist, county biologist or the DNR tip line (1-800-TIP-WDNR) immediately, as a severe health concern may exist for the biota in the stream. Local biologists are listed on the WAV website by county. >> View local DNR and county contacts