The chemical tests of water quality the National Park Service uses to monitor Little Cottonwood Creek include measurements of water temperature, dissolved oxygen, and pH. These tests indicate a variety of things about the health of the stream environment.

Temperature

Temperature directly affects many of the physical, biological, and chemical characteristics of a stream: the amount of oxygen that can be dissolved in water, the rate of photosynthesis, and the metabolic rate of other aquatic organisms. Aquatic organisms have adapted to survive within a certain range of water temperatures. Very high or low temperatures may exceed the tolerance limit for some aquatic life. Because warm water holds less oxygen than cool water, increasing temperature can negatively affect the whole aquatic ecosystem. Temperature also affects aquatic life's sensitivity to toxic wastes, parasites and disease. Fish become more vulnerable because they are in a weakened condition from lack of dissolved oxygen, or under stress from higher water temperature.

Dissolved Oxygen

Dissolved oxygen is essential for the maintenance of healthy lakes and rivers, since most aquatic plants and animals need a certain level of dissolved oxygen for survival. Waters with consistently high dissolved oxygen are healthy and stable aquatic ecosystems, capable of supporting many different kinds of organisms.

Much of the dissolved oxygen in water comes from the atmosphere. Waves on still water and tumbling water on fast-moving rivers mix atmospheric oxygen into the water. Algae and rooted aquatic plants also deliver oxygen to water through photosynthesis. In lakes, rooted plants are more abundant than in rivers. This results in a daily variance in dissolved oxygen levels due to photosynthesis. Dissolved oxygen levels are at their highest in the afternoon and lowest just before dawn, sometimes endangering fish life.

Water temperature, volume of water moving down a river, build-up of organic wastes, and fertilizers in runoff all affect the level of dissolved oxygen in a system. Depletions in dissolved oxygen can cause major shifts in the types of organisms present in a stream. Aquatic insects that are sensitive to low oxygen levels, such as mayfly nymphs and caddisfly larvae, will be replaced by creatures tolerant of these lower levels.

pH

The pH scale is a measure of the degree of acidity or alkalinity of a substance. Most aquatic organisms have adapted to life in water of a specific pH and may die if the pH shifts even slightly. Increased amounts of nitrogen oxides and sulfur dioxide, primarily from automobile and coal-fired power plant emissions, are converted to nitric and sulfuric acids in the atmosphere. These acids combine with moisture and fall to the earth as acid rain or snow. Acid rain has acidified thousands of lakes in the northern hemisphere to the point where they are devoid of life. (For more detail on this phenomenon, see Chapter 4 on Air Quality).

1. Before visiting the monument please contact the National Park Service for information on appropriate sites for this activity. One of our staff members will unlock the gate on the road in to north end of the monument, where the streams are located, and accompany your group to the monitoring location.

2. Split the class into small groups and assign each group a small reach of stream. Students then complete the "Survey of the Physical and Chemical Condition of a Stream" work sheet, rating characteristics of the upper banks, lower banks and channel bottom as poor, fair, good, or excellent. The lower bank is the intermittently submerged portion of the channel from the normal high water line to the water's edge during the summer low flow period. The upper bank extends from the break in the general slope of the surrounding land to the normal high water line. Terrestrial plants and animals normally inhabit this area. The same procedure can be repeated on a stream at home and the results compared.

3. Each group should also complete tests for temperature, dissolved oxygen, and pH and enter the results on the work sheet. The instructions for each of these tests are as follows:

Temperature Testing Procedure

1. Lower the thermometer four inches below the surface of the stream.
2. Keep the thermometer in the water until it reaches equilibrium (approximately two minutes).
3. Record the temperature in degrees centigrade.
4. Repeat the test once in the same location.
5. Record your results.

Dissolved Oxygen Testing Procedure (Using a Hach water testing kit)

It is important to sample away from the shore, and just below the surface of the water. Use an extended rod sampler with a wire basket, or collect your sample from a bridge. (There is no bridge available at the monument, but may be on your home stream.)

1. Remove the stopper and immerse the dissolved oxygen bottle beneath the surface.
2. Allow the water to flow over the bottle for a few minutes, and make sure no air bubbles are present when you take the bottle from the river. Add the contents of pillow #1 (Manganous sulphate powder) and insert the stopper, making sure no air is trapped inside. Shake vigorously to fully mix. If oxygen is present a brownish-orange precipitate will form. If air bubbles form after the first shake, discard the sample and begin again.
3. Allow the sample to stand until the precipitate settles halfway. When the top half clears, shake again and allow the sample to settle.
4. Add pillow #3 (sulfuric acid powder) to the sample and shake. The precipitate will dissolve and the water will turn yellow.
5. Pour the sample to the top of the measuring tube; pour the contents into the square mixing bottle. Repeat once.
6. While swirling the bottle, use the dropper to add the titrant to the prepared sample. Count the number of drops needed to change the sample from yellow to a clear solution. Each drop equals 0.5mg/l of dissolved oxygen. Record your results.

pH Sampling Procedure (Using a Hach water testing kit)

Collect the water sample away form the bank just below the surface of the stream. Measure the sample immediately, because changes in temperature can affect the pH value.

1. Rinse each test tube with the water sample.
2. Fill both viewing tubes with the water sample to the first line.
3. Add 6 drops of the Wide Range 4 pH indicator solution into one tube and swirl to mix. This is your prepared sample.
4. Place the tube of the prepared sample into the right opening of the comparator wheel. Place the other tube into the left opening.
5. Hold the wheel up to a light source and rotate the wheel until the color on the wheel matches the color of the prepared sample.
6. When the colors match, read the pH value of the sample through the window and record the value.