Note: Safety goggles and aprons should be worn at all times during this lab activity.
Fresh water sample from a local stream or pond
1000 milliliter beaker or large container
3 500 milliliter beakers or jars to set up miniature water ecosystems
Dissecting microscope and hand lenses
Dissolved Oxygen test kit (Chemical)
Fish tank pump and tubing with a t-connection so the tubing can provide air to 2 beakers
Air regulator for beaker 2 or a paper clip
Working with a partner:
1. Take an approximate 1000 ml sample of the water sample from a local stream or pond.
2. Pour a portion of the sample into a petri dish and examine it under low power on the dissecting microscope or with a hand lens.
3. Provide a detailed description of the water sample. What types of organisms are found?
Are the organisms living?
4. Test the dissolved oxygen levels of the water sample.
Initial dissolved oxygen reading:
5. Separate the water sample into the three beakers or jars and label as follows:
Note: Beaker 2 should be receiving less air than beaker 3.
10. Place beakers 2 and 3 in an area where they will be undisturbed
for a 24 hour period and the air pump can remain plugged in and running.
11. Based on the initial levels of dissolved oxygen, hypothesize how the biodiversity of each water sample will change over the 24 hour period. Will the organisms increase or decrease? Make sure your hypothesis includes a statement about the dissolved oxygen levels.
12. After the 24 hour period, place a portion of each of the water samples
from beakers 1, 2 and 3 in a petri dish and examine it under low and high
power on a dissecting microscope. Provide a detailed description of each
sample. Record your description in the appropriate column in the data table.
13. Test the dissolved oxygen level of each sample and record the number in the appropriate column in the data table.
2. Write a short paragraph explaining how each water sample changed
based on the dissolved oxygen levels. What can you conclude about the dissolved
oxygen levels and biodiversity?
3. Research the effects of decreased levels of dissolved oxygen on aquatic plants and animals. Describe the causes of decreased oxygen levels and determine how these causes can be reduced or eliminated.