What’s Monitored


 

Dissolved Oxygen: How healthy is a stream?

WAV citizen stream monitors are interested in learning both the quantity of dissolved oxygen in the water and how close the water's dissolved oxygen levels are to equilibrium at the specific temperature and air pressure where a sample is collected.

Dissolved oxygen (D.O.) is measured in milligrams per liter (mg/L). Different aquatic organisms require different amounts of dissolved oxygen. Trout and stoneflies, for example, need high dissolved oxygen concentrations for survival. They prefer dissolved oxygen to be at least 6 mg/L, but can likely withstand short time periods during which dissolved oxygen concentrations are slightly lower. Warm-water fish such as bass and bluegills do not need oxygen concentrations to be quite as high as trout and stoneflies. They can survive in water with dissolved oxygen concentrations of 5 mg/L. Other organisms, such as bloodworms, leeches, and carp, can survive in water with limited dissolved oxygen concentrations. Some of these tolerant organisms have even been found to be able to survive for a day or two without any oxygen at all!

Citizen stream monitors can determine how close the D.O. concentrations are to equilibrium by determining some of the basic information about D.O. that were mentioned above. Monitors measure the temperature of the water at the same time as measuring dissolved oxygen concentrations. Then they determine the percent saturation of dissolved oxygen at their sampling site by using a conversion chart that accounts for the effects of elevation on D.O. saturation levels.

The chart (from The Field Manual for Water Quality Monitoring by Mitchell and Stapp) that WAV monitors use is available to be viewed as a pdf file (26 K). View chart>>

The percent saturation is determined by lining up a straight edge between the measured temperature and the measured dissolved oxygen concentrations; the percent saturation is located where the straight edge crosses the percent saturation line.

 

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