by Naomi White, Science Teacher, Jefferson High School, LAUSD

STUDENT HANDOUT

Background and Information:

Turbidity is the amount of cloudiness in the water. If the water is turbid,less sunlight passes through. Since plants need sunlight forphotosynthesis, less photosynthesis takes place in turbid waters. This cutsdown the amount of oxygen in the water. Turbidity is not the only thingthat affects the amount of oxygen. Temperature, pH, plant life, bacteria,can all affect oxygen. Ecologists always measure the oxygen content of thewater, but since tests must be done at the water site, we will not conductthis important test. Instead we will test for turbidity with aturbidometer. Since they are extremely expensive, we will use a simpler,cheaper, but less accurate method.

Laboratory Procedure:

1. Fill one of the tubes with the water sample to the 50 ml mark.
2. Fill the second tube with tap water to the 50 ml mark.
3. Looking down into the tubes from the top, compare the black dots onthe bottom of the tube (if one cannot be seen, only fill each tube to the25 ml mark).
4. Using the eye dropper, add the standard turbidity reagent .5 ml ata time, until the dots appear the same. Record the amount of reagent used.
5. Use the turbidity test result chart to determine the JTU's.

Observations:

# of Measured Additions	Amount in ml	#of JTU's

Discussion Questions:

1. What is turbidity?
   
2. How does turbidity affect living things?
   
3. In what situations do you think that the turbidity test that you usedwould not be useful?
   
4. Why is oxygen content in water an important ecological factor?