Dissolved Oxygen
Dissolved Oxygen
Definition: A measure of oxygen molecules dissolved in the water. These are not the bubbles in the water and are invisible to our eyes.
Why we monitor dissolved oxygen: Dissolved oxygen is essential for aquatic organisms. This is what fish and macroinvertebrates breathe through their gills underwater. If values get too low then organisms can die.
What influences dissolved oxygen: Water temperature has a large effect on dissolved oxygen. As water warms, the amount of dissolved oxygen water can hold decreases. Therefore, human actions that increase stream temperature (e.g. removing water or riparian trees that create shade) lead to lower dissolved oxygen levels. Aquatic plants also influence dissolved oxygen because the photosynthesis process releases oxygen into the water so dissolved oxygen concentrations often increase throughout a day. At night plants use oxygen but do not photosynthesize, so dissolved oxygen concentrations decrease until the sun comes up again.
The State of Utah has set minimum dissolved oxygen concentrations to protect fish and other aquatic animals. In addition, different species and different activities require different concentrations of oxygen. You can find the water quality standards as part of the Utah Administrative Code R 317-2.
For more information on dissolved oxygen visit our Dissolved Oxygen page.
For instructions on how to monitor dissolved oxygen select either the Chemets (Tier 1 method) or the LaMotte method above.
Tier 1
Steps |
Illustration |
Rinse the collection cup with stream water three times and then fill to 25 mL with water 15 cm below the surface | |
Place glass ampoule in cup and break tip under the water. Let ampoule fill with water
(30 seconds). |
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Mix the ampoule by turning it up and down several times. *DO NOT PLACE FINGERS ON OR NEAR BROKEN GLASS TIP* Wait 2 minutes. | |
With even light shining on the color comparator, place the test ampoule in front of the color standards. Place on both sides to determine the best color match. Record the concentration that the test ampule most closely matches. Do not choose a value in between two color samples. |
Stream Side Science dissolved oxygen instructions - great for laminating and using with a group.
Also, watch the instructional video below:
Tier 2
Aside from these steps, you will also need to record the barometric pressure right before or after monitoring your site.
Steps |
Illustration |
I. Collect Water Sample |
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II. Add the Reagents |
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NOTE: Make sure to wear gloves |
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NOTE: Now the sample has been "fixed" and contact between the sample and the atmosphere will not affect the results. If desired, samples may be held at this point and titrated up to 4 hours later. In this case, keep the sample cool (cooler with wet ice) until you are ready to continue. |
III. Titration |
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NOTE: You need to repeat these steps twice in order to meet our Quality Control standards by repeating a duplicate sample. | |
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NOTE: If air bubbles appear in the titrator barrel, free them by partly filling the barrel, then pump the titration solution back into the reagent container. Repeat until there are no more bubbles. |
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