Dissolved oxygen is the amount of oxygen gas dissolved into water. This test calculates the amount of oxygen dissolved in the water in parts per million. DO is important to the river because fish and other animals need a certain standard of oxygen to survive in the water. The standard for large fish like trout and salmon is 8 - 15 ppm. For smaller fish like buffalo, carp, and catfish the standard is 4 - 8 ppm. Nitrates and phosphates can remove dissolved oxygen. Also lower temperatures promote more dissolved oxygen.

Procedures:

1. To find the value of dissolved oxygen, fill the DO bottle with the water to be tested by allowing the water to overflow into the bottle for a few minutes. To avoid trapping in air bubbles, cap the bottle under the water with a quick thrust.

2. Clip open pillow 1 reagent powder and pillow 2 reagent powder and add them into the bottle. Cap the bottle with the stopper and shake vigorously to mix. A flocculent will be formed. If oxygen is present in the sample, the precipitate will be a brownish-orange color.

3. Allow the sample to stand until the floc has settled halfway in the bottle, leaving the upper half of the sample clear.

4. Clip open pillow 3 reagent powder. Remove the stopper from the bottle and pour in. Place the stopper back into position and then shake again to mix. The floc should disappear and a yellow color will develop if oxygen is present.

5. Fill the plastic measuring tube level full of the sample prepared in steps 1 through 4. Pour the sample into the square-mixing bottle.

6. Add Sodium Thiosulfate Standard Solution drop by drop to the mixing bottle, swirling to mix after each drop. Hold the dropper vertically above the bottle and count each drop as added.

7. Continue to add drops until the sample changes from yellow to colorless. (Note: Each drop used to bring about the color in step 6 is equal to one part per million (ppm) of dissolved oxygen.)