DISSOLVED OXYGEN

The measure of the amount of life-sustaining oxygen dissolved in the river water and, therefore, available to fish, invertebrates, and all other animals living in the river.

INSTRUCTIONS FOR USING KIT:

1. Collect a water sample in a BOD bottle by totally submerging the bottle in the water. Stopper the bottle tightly, using the stopper that comes with it. Make sure that no air bubbles are found in the bottle! If you collect your river water in a collecting bottle and fill the BOD bottle from that collecting bottle, be sure that you do not shake the collecting bottle so that air would get introduced into it! It is very important that the water in the bottle be an exact sample of the water in the river and that no air has been introduced either by shaking or by bubbles.

2. Add the contents of Hach powder pillows #1 (manganous sulfate) and #2 (alkaline iodide azide) to the BOD bottle. Shake vigorously to mix fully. Again, make sure that no air bubbles are introduced into the bottle. If oxygen is present in the water a brownish floc (precipitate) will form.

3. Let the sample stand for a while, until the precipitate settles halfway. Shake the bottle again to see if more floc forms, then wait for the precipitate to settle somewhat.

4. Add the contents of powder pillow #3 (sulfamic acid). As you shake it up, the floc will dissolve, and the water will turn yellow.

5. Fill the measuring tube with the yellow DO sample. Pour the contents into the square mixing bottle. Pour a second full measuring-tube full of the same sample into the mixing bottle.

6. Add the sodium thiosulfate titrant one drop at a time to the sample in the bottle. Swirl the sample after adding each drop! Count the number of drops you add. The sample's color becomes lighter with each drop. Stop when the sample turns from yellow to clear.

7. Divide the number of drops you have added to the sample by 2. This is equal to the dissolved oxygen concentration of the water in mg/l.

QUESTIONS TO THINK ABOUT:

Is your Dissolved Oxygen low (< 90% saturation) or high?

EFFECTS OF LOW DISSOLVED OXYGEN:

• Fish and other organisms suffocate
• Lowers the amount and diversity of aquatic life
• lowers the quality of the river

EFFECTS OF HIGH DISSOLVED OXYGEN:

• Many varieties of fish, such as trout
• Healthy and stable aquatic ecosystem

WHY EITHER CONDITION EXISTS:

A. River may have large amounts of organic wastes

• What are some organic wastes?
• Where do these wastes come from in your area?
• Is a sewage plant nearby? Stream vegetation?
• Are there farms or feedlots?
• Are there sewer overflows nearby?
• Check your Fecal Coliform test!

B. River may be in balance with organic wastes

• Is the river fast-flowing at this site?
• What is the surrounding area used for?
• If the DO is high, why do you think it is?

*IF YOU HAVE A PROBLEM AT YOUR SITE, HOW CAN YOU MAKE IT BETTER?

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