- Engage: Since students struggle with visualizing how groundwater works, this engagement is designed to improve their understanding of this type of water movement. There are several suggestions for engaging students to think about groundwawter:
- You can create a simple groundwater model by following the plans on this website: http://www.groundwater.org/kc/activity8.html .
- There is also a good visualization online through the MetEd website: https://www.meted.ucar.edu/index.php . You have to create an account, but it is free. Once on their website, look for the module titled “Understanding the Hydrological Cycle”. Within that module, there is a section on Groundwater that students can go through on their own time. There is also a wonderful module on “Watersheds”, which has a section on Water Quality that explains how contaminants move into groundwater.
- You can do a simple demonstration of water movement through “soil” – add food coloring to a small clear cup of dried rice. Students can see how the liquid moves.
- The powerpoint slides 1-9 provide background information on groundwater and images to support this lesson, but are optional.
- Explore: Hold up a pot of soil, and add water. Ask students to draw a diagram of what happens to the water that falls on the surface of the soil in the pot. Check for understanding by making sure students have labeled both evaporation and infiltration. Then, ask students to use a different colored pen to diagram what happens if salt water is added to the soil. Students should recognize that when the water evaporates, the salt is left behind. Ask students to pretend that the pot of soil is the ground, and ask them to imagine what happens when water is continuously added to the system. This is “groundwater”, which adds to stream flow. Ask students to think about what happens to the salt that is in groundwater – where does it go? Does it stay in the groundwater, or does it go into the stream?
- Hand out the “Salt Pollution & Groundwater” worksheets. Ask students to answer questions #1 and #2 after the demonstration.
- Explore: Remind students about the powerpoint slides from Lesson 2 which demonstrate what happens when you continue to add salt to a body of water. If you didn’t show these slides in Lesson 2, please do so now (slides 10-24).
- To demonstrate this idea, hold up a beaker of water (100 ml is plenty), measure the conductivity, and add a spoonful of salt. Ask for a volunteer to measure the conductivity again. Ask students to predict what they think will happen to the conductivity level as the water evaporates. Remind students to think about what happens to salt when salt water heats up – it stays behind. Then, ask students to think about what happens if plants are using water that has salt in it. Do the plants take up the salt?
- Explain: If you keep adding salt to water, some of the salt molecules will accumulate in the groundwater, and some will be discharged into the surrounding waterways. Students should recognize that the salt doesn’t leave the groundwater, ie it doesn’t evaporate or get used by vegetation. Instead, it will be discharged into the streams throughout the year, or stored in the groundwater.
- Explore: Students should now look at the sets of graphs provided of the Wappinger Creek. The first two graphs explore students’ understanding of scatterplots vs bar graphs, while the second set of graphs includes a bar graph with error bars. Students are asked to make a claim for each set of graphs; this should help them understand the benefits and limitations of each type of graph.
- Extend: AP students could be given the following challenge, to help them think about the input/outputs to the ecosystem:
The Town of Washington, where the Wappinger Creek is located, has been using thousands of pounds of salt every year on its roads. Scientists at the Cary Institute of Ecosystem Studies measured the amount of sodium chloride that came out of- or was “exported” from- the stream. Based on what went into the stream (the “inputs”) and what came out of the stream (the “outputs”), we can identify how much of the salt stayed in the ground water.
Kg of salt 1986
Kg salt 2005
Softeners, Deposition + Weathering
Total from known sources “INPUTS”
Total NaCl exported from stream “OUTPUTS”
Check for understanding with these questions:
- In 1986, the amount of salt that was an “INPUT” to the stream was greater than/less than the amount of salt that was exported (OUTPUT).
- Why didn’t all of the salt that was “input” end up leaving the stream in the “output”? Where do you think the extra salt went?
- In 2005, the amount of salt that was an input to the stream was greater than/less than the amount of salt that was exported.
- Why was the amount of the “OUTPUT” so much different in 2005? Hint: think about the diagram and the groundwater system.
Besides road salt, there are other sources of salt to our watersheds. Water softeners, runoff from sewage systems, deposition, and rock weathering are some other ways that salt can enter the ecosystem. When road salt is applied, it eventually dissolves into water and moves through the soil to groundwater or into surface water. Salt affects organisms even below lethal concentrations by altering the drifting of aquatic insects (drifting is a form of migration and movement). Another problem with creating consistently salty, unnatural conditions is the resulting ability of salt-tolerant invasive species to move into an area. Generally, zooplankton die at a concentration of 1000 mg/L, although students should note that salt accumulates over time, and the longer the organisms are in a high salt environment, the more toxic the effects.
- Evaluate: Students should complete the rest of the lab sheet. Pay attention to students’ ability to state a claim, provide adequate evidence, and connect the evidence and claim through reasoning.
- Final assignment: To help students bring together what they've learned about data and salt pollution, a final assignment is provided. Students are asked to critique a news article of their choice, paying attention to the claim, evidence, and reasoning in the article.