In this short activity, students look at real stream data from Pennsylvania to see how salt from winter storms affects water quality. The goal is to help them connect their earlier lab work with what’s happening in actual local waterways.

Begin by showing students the conductivity graph from Vine Creek in Bala Cynwyd, PA on the Monitor My Watershed website. Set the date range to January 21 to February 21, 2025. Use the handout so students can follow along. Have students look at the graph and notice two key things: a fairly steady baseline during dry winter days and big spikes in early February. Let them know these spikes happened right after snowstorms.

Ask:

• What do you notice about the shape of the graph?
• When do the spikes happen, and what might be causing them?
• Why would this matter for fish, plants, or people using this water?

What Is Conductivity?

Conductivity measures how easily electricity can pass through water. Pure water cannot conduct electricity well, but streams do because they contain dissolved particles called ions. Ions are naturally occurring but can increase or decrease because of pollution.

Scientists measure conductivity in microsiemens per centimeter (μS/cm) to check stream health and test for pollution. If you have one available, show students a conductivity meter. How far apart are the electrodes—the metal points at the bottom? They are usually 1 cm apart. The meter passes electricity between the electrodes to measure the conductivity of the water.

Briefly explain that specific conductance increases as more dissolved substances (like road salt) enter the water. After a winter storm, snow and ice mix with road salt, melt, and run off paved surfaces into nearby streams, increasing the conductivity of the water.

This quick look at real data helps students connect what they’ve already learned to the bigger picture. That same salt that lowers the freezing point of water shows up in our streams and can be tracked through changes in water chemistry. It’s a powerful way to bring the unit’s essential question into focus: How can we balance winter safety with the health of our watershed?

In this investigation, students analyze real storm event data to determine how winter weather and road salt affect stream chemistry. Using site photos, watershed and land cover maps, weather data, and graphs showing stream height and specific conductance, students look for patterns that help explain what is happening in the stream during a storm event and how salt may be moving from roads into the water.

This activity scaffolds students’ data analysis skills. Students work in small groups while the teacher guides the class through the analysis section by section using the Storm Event Data worksheet and the Storm Event Data Teacher Guide. The Storm Event Investigation worksheet structures the analysis using the following sequence: Notice and Wonder → Read the Data → Look for Patterns → Think About the Watershed → Explain What Is Happening in the Stream → Scientific Explanation.

Part 1: Notice and Wonder

Begin by displaying the Storm Event Data for the class. Have students familiarize themselves with the maps and think about what they can tell us. Have students carefully examine the weather data, stream height graph, and conductivity graph before attempting to interpret them. At this stage, the goal is observation, not explanation. Invite students to share what they notice, encouraging them to describe patterns, shapes, spikes, or changes over time.

Then ask students what they wonder. Questions often include:

• Why do some lines spike suddenly?
• What might cause the stream height to increase?
• Why would conductivity change after a storm?

Record several student observations and questions on the board. This discussion helps students begin thinking like scientists by separating observation from explanation.

Part 2: Read the Data

Guide students through the first set of questions together. At this stage, students focus on extracting information directly from the graphs and data tables. Take your time and help students locate key features such as: dates on the x-axis, units on the y-axis, weather events in the data table, and peaks in stream height and conductivity. This is an opportunity to teach graph literacy and use the weather page to think about how we turn data in tables into graphs.

Ask students to identify when rainfall occurred, when stream height increased, and when conductivity levels changed. This step helps students build confidence reading environmental data before moving into deeper interpretation.

Part 3: Look for Patterns

Next, students look for relationships between the different data sets. Prompt them to compare the weather data with the stream height and conductivity graphs.

Ask questions such as:

• What happened to stream height after the rain?
• What happened to conductivity levels after the rain?
• Did the patterns occur at the same time or at different times?

Students should begin noticing that rainfall increases stream height and may influence conductivity levels. Emphasize that scientists often look for patterns across multiple data sources to understand environmental events.

Part 4: Think About the Watershed

Now ask students to connect the patterns in the data to what they know about watersheds and runoff. Students should consider how rain or snowmelt moves across land surfaces and carries dissolved materials into streams. Prompt them to think about how land cover influences this movement—applying ideas from earlier lessons on runoff, infiltration, and land use.

Questions may include:

• How might rain change the height of a stream?
• How could water move salt from roads and parking lots into nearby streams?
• How might forests, grass, roads, and parking lots affect how water and salt move through the watershed?

Part 5: Explain What Is Happening in the Stream

After students have examined the patterns, ask them to construct an explanation using Claim, Evidence, and Reasoning (CER). Students develop a claim describing what they think happened in the stream during the storm event. They then use specific evidence from the graphs or weather data to support their claim.

Encourage students to cite at least two pieces of evidence from the data—for example, a spike in stream height following rainfall or a change in conductivity during the same time period. Students should then explain how their evidence supports their claim by connecting rainfall, runoff, and watershed processes.

Part 6: Scientific Explanation

Finally, students synthesize their thinking using the sentence frame provided in the worksheet. This structure helps students translate their CER thinking into a clear scientific explanation. Remind students that environmental explanations often involve multiple interacting factors, such as weather events, land cover, and human activities like road salt application.

Ask them to work through the Storm Event Investigation worksheet together. As groups work, circulate and listen to their discussions. Encourage students to support their ideas by pointing to specific evidence in the data.

Whole Class Discussion

Bring the class back together and invite groups to share their explanations and the evidence they used. Students will likely find that at Walnut Creek, a snowstorm followed by melting led to salt runoff, and spikes in specific conductance match the rise in stream height.

Use the comparison of specific conductance and stream height graphs to highlight an important idea: graphs may look similar, but the story behind them can be very different depending on weather events, land cover, and human activity within the watershed. Scientists must use both data and context to understand what is happening in natural systems. The goal of this discussion is not for students to arrive at perfect answers—the purpose is to help students practice interpreting real data and explaining their thinking using evidence.