page 21 of the UWP Educator’s Guide to Teaching Students About the Upper Uncompahgre River Watershed (also see contents, introduction & pdf link)
Dissolved Oxygen (mg/L or ppm): What is It?
Dissolved oxygen levels depend on many factors: whether water is flowing or still, whether there are rocks or other obstacles for water to flow over, how many plants are in the water, water temperature, ice cover, and depth. When water in creeks and rivers flows over rocks, oxygen can enter into the water.
Dissolved oxygen levels are higher in very cold water compared to very warm water. But if a lake or river has ice cover, oxygen is usually low because air from the atmosphere cannot get in. In the open water season, oxygen levels decrease the deeper you get in a lake.
Plants in the water take up carbon dioxide and release oxygen, just like they do on land. But if there are too many plants in the water, all of the oxygen will get used up by the bacteria that decompose them after they die.
Why Does It Matter?
Oxygen from the atmosphere dissolves in the water of rivers and lakes. Fish and other aquatic animals depend on this oxygen to breathe.
Dissolved oxygen is influenced by : water temperature, algae growth (e.g., chlorophyll ). Dissolved oxygen influences : the forms and toxicity of certain metals (e.g., dissolved metals) and concentrations of certain chemical constituents (e.g., sulphide and ammonia)
How is It Measured?
Testing dissolved oxygen (DO) in water is often measured using chemical analysis such as a titrimetric method.
Teachers: This is a big group demonstration and students will be provided the measurements for each of the four sites.
Source: https://datastream.org/en-ca/guidebook/dissolved-oxygen-do
