WHAT IS DISSOLVED OXYGEN?
The oxygen that makes aquatic life possible does not form bubbles, nor is it the oxygen that is part of the H2O water molecule. It is a separate O2 molecule that is dissolved in the water and invisible to our eyes.
WHY CARE ABOUT DISSOLVED OXYGEN?
All terrestrial and aquatic animals need oxygen to survive. Many aquatic macroinvertebrate species depend on oxygen-rich water. Without sufficient oxygen they may disappear. Even a small change in dissolved oxygen concentration can affect the composition of aquatic communities. Many fish require a certain dissolved oxygen range in order to survive
- Minimum dissolved oxygen concentration for warmwater fish: 5.5 mg/L
- Minimum dissolved oxygen concentration for coldwater fish: 6.5 mg/L
NATURAL FACTORS INFLUENCING DISSOLVED OXYGEN
- Aquatic life- animals living in water use up dissolved oxygen. Bacteria take up oxygen as they decompose materials. Dissolved oxygen levels drop in a water body that contains a lot of dead, decomposing material.
- Elevation- the amount of oxygen in elevation increases. Since streams get much of their oxygen from the atmosphere, streams at higher elevations will generally have less oxygen.
- Salinity (saltiness)- Salty water holds less oxygen than fresh water.
- Temperature- cold water holds more dissolved oxygen than warm water.
- Turbulence- more turbulence creates more opportunities for oxygen to enter streams.
- Vegetation- riparian vegetation directly affects dissolved oxygen by releasing oxygen into the water during photosynthesis. It indirectly affects dissolved oxygen concentrations because vegetation shading a stream may decrease water temperatures, and as temperature decreases dissolved, oxygen increases.
HUMAN FACTORS INFLUENCING DISSOLVED OXYGEN
- Clearing Land (e.g., construction, logging)-may send excess organic matter into streams. Organic matter is decomposed by microorganisms, which use up oxygen in the process. Therefore, if there is a lot of organic waste in the stream, the microorganims use more oxygen than can be replaced in the stream.
- Destruction of riparian areas (e.g., development or overgrazing) decreases the amount of shade and increases the water temperature. Warmer water holds less DO (Dissolved Oxygen) than colder water.
HOW DO WE MEASURE DISSOLVED OXYGEN?
Utah Water Watch- Learn how volunteers across the state measure Dissolved Oxygen. Select the Tier 1 tab for basic/classroom-friendly procedures, or select the Tier 2 tab for more advanced procedures.
Stream Side Science- Explore different lesson plans involving Dissolved Oxygen and see how they apply to the different core curriculums for grades k-12.