The Effects of Nutrients on a Mini-Pond Ecosystem


Materials

8 4 L Glass Jugs 4 50 mL Graduated Cylinders
Glass Containers 4 100 mL Graduated Cylinders
4 Funnels 1 1000 mL Graduated Cylinder
4 Stirring Rods 8-24-8 Garden Fertilizer
Pond Water Water Test Kits: Nitrate & Phosphate
Tap Water Dissecting Microscope

Procedure

1. Fill 8 4 L glass jugs with 4 L of tap water and place them in a sunny location for a few days to allow the chlorine to escape.

2. Fill another container with tap water and place it with the glass jugs. This will allow chlorine to escape, and insure a supply of chlorine-free water for use in the experiment. Keeping the container with the jugs will assure that the water temperature is the same as the temperature of the water in the jugs.

3 . Inoculate each of the 4 L jugs with 150 mL of pond water that has been obtained from the water's edge. This creates mini-ponds that are as much alike as possible.

4. Choose an ordinary garden fertilizer such as 8-24-8. The fertilizer chosen should not contain any coloring agent. Make a fertilizer solution by adding 3 tablespoons of the fertilizer to 4 L of water. Do not use metal containers for mixing or storing the fertilizer solution. This fertilizer solution is referred to as the stock solution. A stock solution is the original solution from which other solutions are made. A supply of stock solution should always be available for use in the experiment.

5. Label each jug with a number; beginning with number 1.

6. Prepare the mini-ponds as outlined in the chart below.


Jug Number Stock Solution Water Jug Number Stock Solution Water
1 0 mL 14 mL 5 8 mL 6 mL
2 2 mL 12 mL 6 10 mL 4 mL
3 4 mL 10 mL 7 12 mL 2 mL
4 6 mL 8 mL 8 14 mL 0 mL

8. The doses of stock solution and chlorine-free water described in the chart will be added to the mini-ponds each week. To make this job easier, label each jug with the proper amounts of each liquid to be added. Then you need only refer to the "recipe" on the jug.


Observations

At the same time of each day note the following changes in the mini-ponds. Record the results in a table such as that shown below.

1. Look through each mini-pond toward the light. Note the color observed. Describe the color as: clear, green, gray, rust, brown, tan, yellow, blue, colorless with particles.

If two of the mini-ponds are the same color but there is a difference in the intensity or depth of the color, record the lightest color with a + sign. Increase the number of + signs as the depth of the color increases. For example: light green = green+ darker green = green++ and darkest green = green+++

2. Place a printed sheet of paper directly behind each mini-pond and attempt to read the print. Record the turbidity (cloudiness) of each mini-pond as follows:

clear print can be easily read
Slightly cloudy print can be read, but appears fuzzy
Cloudy print can be seen, but not read
Very cloudy print can barely be seen
Opaque print can not be seen

After definite changes in color and turbidity have been noted make the following observations:

1. Take samples from each mini-pond. Use a separate pipette for each "pond." Use the nitrate and phosphate test kits to determine the amount of phosphates and nitrates in the water. Follow the directions included with the kit.

2. Pour the mini-pond into a white-bottomed tray for study of the organisms. Use the dissecting microscope as needed to aid in the identification of the organisms. Identify the type of organisms seen using the references available. Record the name of each type of organism observed. Record the number as indicated: A 1-9, B 10-99, C 100 or more

3. After all observations are recorded. Complete the analysis of the results.


Date       Nutrient Tests
Jug # Color Intensity of color Turbidity Phosphate Nitrate
1          
2          
3          
4          
5          
6          
7          
8          


Analysis

1. In which jug was the color intensity the greatest?

2. In which jug was the turbidity the greatest?

3. Which jug had the greatest variety of organisms?

4. How did the increase in nutrients affect the algal growth?

5. How did the increase in nutrients affect the variety of organisms in the mini-pond?

6. Which jug had the best nutrient level for a healthy ecosystem?

7 . Would you consider any of the mini-ponds polluted? If so, which one(s)? Explain.

8. What other factors may have affected the populations of macroinvertebrates?

9. Why was a different amount of water added to each mini-pond?

10. Why were phosphate and nitrate chosen as the two nutrients in this investigation?