Introduction

Water quality can be impaired by human actions. Water drips off rooftops, flows over parking lots, courses through our bodies, travels down the drain, and percolates through the soil of fields and forests. During its journey, water picks up such materials as agricultural and lawn chemicals, emissions of sulfur dioxide from coal-burning electric power plants, dishwashing detergents, gasoline from cars, and road salts—all of which have a profound influence on life in terrestrial and aquatic systems.

Sodium chloride is one of the most widely used de-icing products, working effectively at winter temperatures where other de-icing agents fail. However, this salt has an environmental cost as it runs off into vegetated areas and storm sewers that empty into streams. Sodium chloride is a major pollutant to our local waters throughout the winter and into spring.

In this lab you are to investigate the effects of salt in the form of sodium chloride on the germination of radish seeds. You will use five concentrations of salt, from no salt (the experimental control) to a relatively high concentration of salt.

Lab Directions

1. Generate a hypothesis regarding the effect various salt concentrations will have on the germination of radish seeds. Record your hypothesis in the Lab Response and briefly explain the reasoning/prior knowledge that led you to propose this hypothesis.
2. Prepare the five test solutions as described below using the same kind of water (tap or bottled drinking water or distilled water). Be sure to thoroughly mix the water with any added salt. Label and store each of the five test solutions in a separate covered container and away from sunlight (to reduce evaporation) until the end of the entire experiment.
   • Control: 250 ml or one cup of water
   • Very low salt concentration: 1.4 g salt/250 ml of water (≈ 1/4 tsp salt/1 cup water)
   • Low salt concentration: 2.8 g salt/250 ml of water (≈ 1/2 tsp salt/1 cup water)
   • Medium salt concentration: 4.3 g salt/250ml of water (≈ 3/4 tsp salt/1 cup water)
   • High salt concentration: 5.7 g salt/250 ml of water (≈ 1 teaspoon salt/1 cup water)
3. Set up the seed germination trays as follows:
   1. Line the five petri dishes you were provided (or some other plastic or glass dishes, but use the same type of dish for all five trays) with cotton (the round makeup cotton pads work well; use 2-3 pads to get a decent thickness for your cotton substrate).
   2. Label the trays: control, very low concentration, low concentration, medium concentration, and high concentration.
   3. Soak the cotton in each germination tray with the appropriate liquid (i.e., the cotton in the germination tray labeled “control” should be soaked with the water from the container labeled “control,” and so on).
   4. Place 50 radish seeds in each tray. Cover and place all germination trays in the same environment (somewhere dark and warm is ideal).
4. Upload a photo of your experimental setup on Day 1 to the Lab Response.
5. Observe the seeds over the next 7 days. Make sure that the cotton liners in the seed trays stay moist; if not, re-moisten with the appropriate liquid. The liner should not be too soggy because that will promote growth of mold; neither should it be too dry because the seeds will not germinate.
6. Document the seed germination. On each day of the experiment, count and record (in Table 18.1 on the Lab Response) the number of seeds that germinated in each tray. A seed is considered germinated when it shows evidence of root, stem, or leaf growth. Keep a rolling count—e.g., if on Day 3, 10 seeds germinated, you would record 10 as your count; if on Day 4 another 5 seeds germinated, you would record 15 as your count. Record any changes in the seeds (color, shape, texture, etc.) and when the changes occurred. Also record how much liquid was added to each experimental setup.
7. Upload a photo of your experimental setup on Day 7 (i.e., the last day of your experiment) to the Lab Response.
8. Calculate the daily percent germination rate of seeds for each seed germination tray and record in Table 18.2 on the Lab Response.
9. Generate and upload 2 graphs of your data to the Lab Response. You can use the graphs provided or generate your own. Be sure to label axes and provide a written summary below each graph.
   1. Plot a bar graph (Figure 18.2) of the total seed germination count (data reported for Day 7 from Table 18.1) for each salt treatment group (including the control). Plot Salt Treatment on the x-axis and Total Seed Germination on the y-axis. There will be 5 bars on this graph, one bar for each experimental group. Label each bar. Also provide a brief interpretation of your graph.
   2. Plot a line graph (Figure 18.3) showing the percent germination in each experimental set-up (control and salt treatments) over the days of the experiment (from Table 18.2). There will be 5 plot lines on this graph: one line for each experimental group over time. Label each line and/or provide a legend. Also provide a brief interpretation of your graph.
10. Answer the questions in the Lab Response.

Lab 18 Response: Investigating Salt Pollution

Hypothesis

State your hypothesis regarding the effect you expect salt to have on radish seed germination:

Briefly explain the reasoning/prior knowledge that led you to propose this hypothesis:

Photos

To receive credit for tables and figures, upload TWO photos of your experimental setup as follows:

• Photo of experimental setup on the first day—DAY 1
• Photo of experimental setup on the last day—DAY 7

Make sure all 5 seed germination trays are labeled and clearly visible in each photo.

Data Tables

Graphs

For Figure 18.2, plot the data from Table 18.1.

Brief interpretation of Figure 18.2:

For Figure 18.3, plot the data from Table 18.2.

Brief interpretation of Figure 18.3:

Questions

1. Was your hypothesis supported? Explain using your data.
2. Describe what a limiting factor is, and what is meant by the range of tolerance. Relate your experimental findings to these two concepts.
3. What are some impacts of salt pollution on ecosystems? Discuss at least two impacts.
4. Connect salt pollution to our daily lives:
   1. What are some ways in which we contribute to salt pollution either directly or indirectly? Identify and discuss at least two ways.
   2. Discuss some solutions for how to reduce salt pollution.