Lab 2: Pollution - The Overabundance of Nutrients

P urpose: To demonstrate the effects of excessive amounts of nutrients on the environment

Materials:

1. Total Count Easygel and special petri dishes
2. Sterile pipettes or droppers
3. Two small aquaria with identical contents, each containing one small goldfish
4. Goldfish food

Procedure and Comments:

1. Fill the two aquaria (A and B) with water, using identical procedure. Allow the water to stand overnight to equalize temperature and eliminate chlorine.
2. Place one small goldfish in each tank
3. In one to six hours following step two, sample the water for microorganisms as follows:
   a. Remove the cap from a bottle of Easygel and, using a sterile dropper, remove water from one tank (A) and deposit 0.5 mL (about 11 drops) into the still liquid medium in the bottle. Replace the lid, swirl the medium and water to give even distribution of the water and pour into a pretreated petri dish.
   b. Repeate the process with water from tank B.
   c. Place the inoculated sihes on a level table until the medium gels and then incubate inverted at room temperature (pick a warm spot in the room).
   d. Count the number of microbial colonies growing in each dish at about 48 hours.
4. Each day feed the goldfish as follows:
   a. Give the Tank A gold fish on as much food as it can eat in five minutes. Be sure that it cleans up all the food or remove remaining food from the tank.
   b. Give the Tank B goldfish twice as much food as it can clean up in five minutes. Leave remaing food in the tank.
5. Every two to three days observe and sample the water in each tank, following the procedure given in step #3. You may have to use fewer drops of water in each dish as time progresses in order to be able to count the colonies in each dish.
6. Translate your counts into microbes/mL of water and record.

	Time (in Days) from Tank Setup
	1	3	5	7	9	11
Fish A
Fish B

 

Questions:

1. Why do the microbial populations differ between A and B?
2. Is there a difference in the clarity of the water between A and B?
3. What causes the water to get cloudy?
4. What can be done to regain clarity in the water?
5. What is a bloom of microbes and what can cause it?
6. What effects might a high microbial count have on the fish or other organisms?
7. Can you translate your results into the form of a graph?

Return to Lab 1: The Prevalence of Microbes in the Environment
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