Death of a Pond

Prompt: A fairly large pond near where you live is “dying.” At one time the pond was a favorite spot for local people to swim and fish. It had a gravel bottom, and the water was clear. Now the pond is choked with small, floating plants called duckweed. The bottom is mucky, and very few fish can be found swimming in its waters. Locals want to answer the question, “What is the cause of the deterioration of our pond?”

Through some background research, it has been determined that the pond receives three main sources of runoff that are polluting the water. One source is a large vegetable farm (runoff contains fertilizer). The other sources are a bakery (runoff contains sugar) and a small factory (runoff contains slightly acidic wastewater). You have been asked to use any or all of the materials from the list below to develop a laboratory experiment that can be used to determine if any of these sources of runoff may be responsible for the conditions of the pond. You are to formulate a hypothesis, develop a procedure, and perform your experiment to collect data on the effect of each of the three sources of runoff on pondwater.

Materials: Small plastic cups goggles 25 mL Sugar water vinegar 125 mL Pond water 25 mL graduated cylinder Duckweed culture wax pencil or tape (labeling) 25 mL Liquid fertilizer paper towels Light source Inoculating loop(to transfer duckweed)

Planning the Investigation: Using any or all of the materials provided, your team should now plan an investigation to determine the effects that each of the three sources of runoff have on growth of duckweed in pond water. As duckweed grows, the population will increase in both the number of plants and the number of leaf parts called fronds. Use Figure 1 for identification of new frond growth. You will need to record the number of original fronds on the first day (Day 0) in order to collect data throughout this experiment. When designing your experiment and it’s time frame, plan on taking data through at least 4 days, not including today. Also be sure to include a control group for comparison to your experimental groups.

Figure 1

1 A. On the computer, create a document to print for each member of your team. Your lab document should include the following: Full names of each group member, the date, the name of the lab, the question, hypothesis, identification of the variables (DV and IV), as well as the control group, a detailed procedure, and a data table to fill in. Recalling what you have learned about the condition of the pond, form a hypothesis explaining which source of runoff has the greatest impact on duckweed growth. Be sure to use the following format: If…..then….because….

Example: If two brands of fertilizer are tested for their ability to produce bigger tomatoes, then Brand A will allow the plant to produce larger tomatoes than Brand B because Brand A’s ingredients contain more necessary nutrients for fruit production.

(you may use this space to you’re your hypothesis, or do it directly on the computer – but it must be on the computer before you begin your lab)______B. Now plan your procedure to test your hypothesis. 1. What is the dependent variable (that you will measure)? ______2. What is the independent variable (manipulated)? ______3. What will be your control group? ______4. Write a detailed description of the procedures you will follow using any or all the materials listed previously. Hints – you will take data for 5 days (Day 0 – 4), you will only need 20-25 mL of each runoff source, you may want to consider mixing the runoff with pond water (like in the real pond)… don’t put more than a total of 50 mL of combined liquid in any cup. ______C. In the space below your procedure, construct a data table to be used for recording your data each day starting with Day 0 (initial # of fronds) through Day 4.

2