Unit 1: Hydrologic Cycle

Unit 1 Learning Goals

By the end of this unit, students will be able to:

• Sketch a diagram of the hydrologic cycle. Explain based on observational evidence, how matter (a single water molecule) is stored or moved between a storehouse in the geosphere (lithosphere, atmosphere, hydrosphere) and biosphere
• Explain how the rock cycle interacts with the hydrologic cycle to create sedimentary rock.

Unit 1 Learning Objectives

In order to achieve these learning goals, students will work through the following learning objectives:

• Objective 1-1. Students will construct a model of the hydrologic cycle as an analogy for how water moves through and between Earth systems.
• Objective 1-2. Students will demonstrate the processes of evaporation, condensation, and precipitation.
• Objective 1-3. Students will collect and analyze data to identify soil and surface conditions that result in a higher volume of infiltration or runoff.
• Objective 1-4. Students will infer how human activity can affect the rate of infiltration and runoff in the local landscape and impact the quality of water readily available for human consumption.

This unit may be used as part of the Interactions between Water, Earth's Surface and Human Activity module, or the unit may be taught as a stand-alone or following a unit on the rock cycle. For those students who are unfamiliar with the primary components of the Earth system, a pre-unit reading is recommended. The reading called, The Earth Systems can be downloaded from the References and Resources section.

The curriculum is designed for students preparing to be elementary school teachers. The ideal class size is 24 students or fewer. Activities are designed to foster group collaboration as they work in small groups (ideally in groups of 3–4) with faculty acting as the facilitator. Unit 1 is designed to take two hours in a lab setting. It is not recommended for implementation in a large lecture class.

This unit offers a version of the activity that utilizes an energy diagram, which can be used to describe the way that energy is transformed and transferred during processes. Read more about the energy diagram and the benefits of its use.

The content in this unit aligns well with Science and Engineering Practices, Disciplinary Core Ideas and Crosscutting Concepts in the Next Generation Science Standards (NGSS):

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Handouts that guide students through the unit

• Student worksheet (Microsoft Word 2007 (.docx) 1.1MB Jan11 15)
• Student worksheet for the energy diagram version (Microsoft Word 2007 (.docx) 1.2MB Jan12 15) - Read more about the energy diagram

Students work in groups of three or four to read and answer questions on the worksheets. Once students have been guided to a particular point of understanding, they are asked to write down their thoughts and share them with the rest of the class. One effective way to do this is with small, portable whiteboards. This facilitated discussion is where much of the learning takes place or is solidified.

The role of the teacher is to facilitate, and to try to avoid directly providing answers. The worksheets are designed so that students can reach scientifically sound conclusions on their own. If they do not, the instructor/facilitator can guide the discussion to address any remaining misconceptions.

Initial ideas

To begin this unit, elicit students' initial ideas about Earth's water reservoirs with the following questions:

• If you viewed Earth from a satellite, you would observe that about 70% of the planet's surface is covered by water. Of the 70%, what percentage would you estimate is available for human consumption?
• At some point the water you consume at your house was held in a natural storehouse. Where do you think your drinking water comes from?
• Imagine that you are following the path of a water molecule as it moves between storehouses in the geosphere (lithosphere, atmosphere, hydrosphere) and biosphere. Sketch a diagram of what this path might look like (indicate the direction the molecule of water is moving with an arrow).

This can be done in class or as homework prior to class. Students should have time to write down their own ideas first, then share them in small groups and with the class.

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Part 1: Water, Water Everywhere

This is a demonstration that serves as a scaffold for student questions and discussion around water in terms of availability, and the impact of humans on the quality of Earth's water held in natural storehouses. Guided by a series of prompts read by one student and demonstrated by another, students observe a collection of containers ranging in size from a 5-gallon bucket of water (represents 100% of all the water) to a petri dish containing a drop of water (represents the percentage of of water that is held in the world's freshwater lakes and rivers). Each container represents a different type of natural storehouse for Earth's water. The percentage of water held in each storehouse is relative to the total amount of water on Earth. An emphasis is placed on the small percentage of freshwater that is available for human consumption and the impact of human activity on the quality of the water in a storehouse.

Materials for the demonstration:

• 5-gallon aquarium or 5-gallon bucket filled with water
• 24-oz. measuring cup, green food coloring, ice cube tray, dropper, petri dish
• Clear container (at least 8 ounces) filled with sand
• Laptop, projector, and overhead screen

Running the demonstration:

Prior to the start of class, fill the aquarium or bucket with water. At the start of class, ask for one student to be the demonstrator and another to be the narrator.

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Additional notes for the demonstration:

• It is important for the narrator to not only read the prompts but to provide some talking points to the class by asking the audience for clarification on what kind of reservoir the container represents in the natural environment.
• The demonstration can be useful as a visual for understanding where Earth's water is stored and how limited water is as a resource for human consumption. However, it does not address the concept of time. A discussion is needed to explain that the average length of time that water is stored in a storehouse can vary from days in the atmosphere to thousands of years deep underground.
• Ask students what they think the term "readily" available means by prompting them to com[are the difference between freshwater lakes and glaciers. Liquid water in a lake is readily available for human consumption versus glaciers where water is in a solid state.

After the demonstration, prompt students to answer the following questions, given on page 3 of their handout:

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• The table to the right lists the average percentage of water that is held in each type of storehouse. Of the 100% of water held in storage, what percentage is fresh?
• Of the percentage of freshwater held in storage, what percent is readily available for human consumption?
• How does this percentage compare to your initial ideas? (This is a metacognitive, reflective prompt, and students are encouraged to go back and look at what they wrote previously to compare.)
  

• Why is Earth called the blue planet?
• There has been a growing public awareness about the value and importance of water and water resources. How do you think the quality and quantity of the freshwater stored in a local reservoir might be affected by human activity?

After students have had a chance to answer these questions on their own, you can lead a short discussion in which they share their responses with the class.

Part 2: Following the Movement of Matter in the Hydrologic Cycle

The hydrologic cycle is a conceptual model that illustrates the flow of matter (water) as it moves between Earth systems by energy that is ultimately derived from the Sun. The movement of water can be grouped into three directions: 1) moisture moving into the atmosphere, 2) moisture moving through the atmosphere, and 3) moisture returning from the atmosphere to Earth.

Because of the interconnectedness of Earth's systems, a change in one system often results in a change in one or more of the other systems. In this activity, students conduct three mini investigations to model the movement, processes and phase changes that occur as matter is cycled through the hydrologic system on a local and regional scale. There are three physical model setups described below; students work through each of these investigations on their own in small groups, following the procedures on pages 4–11 of their handouts to collect, analyze, and interpret observational data.

A: Evapotranspiration, condensation, and precipitation

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Students create a bottle-model hydrologic system, shown on the right, as an analogy of how water is transferred between natural storehouses in the atmosphere, biosphere, geosphere, and hydrosphere by the processes of evapotranspiration, condensation, and precipitation.

Materials needed:

• 2-liter soda bottle
• Ring stand
• Stand and clip-on lamp
• Sand (use playground-type sands), enough to fill 1/3 of the bottle
• Ice (approx. 1 cup)
• Volumetric container (beaker, measuring cup, graduated cylinder, etc)
• Permanent marker, scissors, water
• Metric measuring cup (or other material able to measure in 100 ml increments)
  

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Tips on setting up the system

• Select clear 2-liter soda bottles because they provide easier viewing of the contents of the bottle-model system; remove any labels.
• Remove the bottom 1/3 of the plastic bottle. Turn the bottle upside down so the capped end is now the bottom and place the section of the bottle that has just been cut off on the top. The bottom will now act as the top to hold the ice and to keep air from escaping out the bottle-model system. Note: The best fit is between the matching top and bottom of the same bottle. A snug fit between the lid and bottle gets the system up and running much quicker than one where the system is losing warm air out the top.
• Place the light bulb at a height on the rod of the stand so it is aimed at the sand, not over the top of the ice. You want the temperature to heat up inside, not outside, of the bottle.
• Slowly pour approximately 200 milliliters of water into the system until the water level is just below the surface of the sand. Be careful not to flood the container with water.

Working in small groups, students will:

1. Fill the lid of the plastic bottle (previously the bottom section of the plastic bottle) with ice and place it securely back on top of the bottle. Be sure to push it down snugly to prevent any air from escaping.
2. Position the heat lamp so it is pointed at the sand and not at the ice.
3. Turn on the lamp and observe closely, looking for evidence that indicates some initial movement of water in the system

Answer the following questions (given on pages 5–6 in the student handout):

• What evidence did you observe to indicate the initial movement of water?
• What is the source of energy that moves the water through the bottle-model system?
• Explain in detail the processes and phase changes that occurred as water moved through the bottle-model hydrologic system. Start from when you turned on the lamp to where you observed evidence for the initial movement of water.
• As water moved through the bottle-model hydrologic system it was transferred between several storehouses. Identify the analog in the hydrologic system for each item in the bottle-model (sand, water, empty space, ice cubes) and the Earth system where the interaction occurs (atmosphere, hydrosphere, lithosphere and biosphere).

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Additional questions in the energy diagram version ask students to abstract the processes involved in this model to the transfer of energy in general. They answer two questions by filling in diagrams for the processes of evaporation and condensation, as shown below.

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Energy diagram from student handout for use in answering question 2-5 on student handout.

Provenance: Sue DeBari, Western Washington University.
Reuse: This item is offered under a Creative Commons Attribution-NonCommercial-ShareAlike license http://creativecommons.org/licenses/by-nc-sa/3.0/ You may reuse this item for non-commercial purposes as long as you provide attribution and offer any derivative works under a similar license.

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Energy diagram from student handout for use in answering question 2-6 on student handout.

Provenance: Sue DeBari, Western Washington University.
Reuse: This item is offered under a Creative Commons Attribution-NonCommercial-ShareAlike license http://creativecommons.org/licenses/by-nc-sa/3.0/ You may reuse this item for non-commercial purposes as long as you provide attribution and offer any derivative works under a similar license.

They also answer additional questions that connect these processes from what they see in the bottle-model system to what they see outdoors.

You may find that you need to remind students to think about the phase changes that occur as water goes from a liquid state (in the pore spaces between the sand grains) to a gas state (as water vapor rises to the underside of the lid) and back to a solid state as water droplets condense on the underside of the lid.

B: Transpiration

As energy from the sun heats the air surrounding plants, the plants transpire water vapor through their leaves. Environmental conditions such as soil moisture, wind, relative humidity, and light are important factors in determining the movement of water out of the plant and the ability to control water loss.

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Essential question to answer from this investigation: How does the amount of sunlight affect the rate of transpiration?

Students predict conditions that would create a greater volume of transpiration, then make observations of plants to confirm their predictions using the setup shown on the right.

Materials needed:

• Two identical potted broadleaf plants
• Two clear plastic bags
• Two twist ties or rubber bands

Note: For best results, this activity requires setup 24 hours ahead of time (the day before) for students to see evidence of any water that has evaporated from the leaves.

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Tips on setting up the system

• Use the same type and size of plants. Broadleaf plants make the best choices, such as Shefflera, often called Umbrella Tree. They are easy to care for and can be kept in an office or classroom in between uses for this class.
• For a few days prior to the activity, give the plants less water than they need.
• The day before implementing the activity, water each plant with an equal volume of water.
• Place one plant in a sunny window and one in a fairly dark area of the classroom. Tie a plastic bag tightly around the same number of leaves on each plant and seal tightly with a twist tie or a rubber band.

There are two questions in the student handout on page 7 associated with this setup. Be sure to ask students to write down their predictions before they make observations of the two plants.

• Prediction question: A plastic bag has been placed over a group of leaves on two identical plants. Both bags have been tied tightly to prevent air from escaping. The same volume of water has been added to each plant. One has been placed in a sunny window, the other in the shade for at least 24 hours. Predict which plant will have the greater amount of water evaporate from its leaves, and explain why.
• Observation question: Two plants have been placed in the classroom under those exact conditions. Describe any observational evidence that validates or nullifies your prediction.

C: Infiltration and Runoff

When precipitation reaches the ground as rain or snow, it will evaporate, infiltrate into the soil, or continue downslope as runoff. There are many variables that can affect the outcome of each condition like the type of soil, the amount of ground cover, the available pore space, and the slope of the terrain. In the following activity, students test the variables of soil type and slope using stream trays. Each group simulates the process of infiltration and runoff as precipitation occurs as rain on a hillside.

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Essential question to answer from this investigation: How do soil conditions determine whether precipitation will infiltrate the soil or continue downslope as runoff? How does the slope influence infiltration and runoff?

Materials needed (letters correspond with diagram of setup on the right):

• A. Tray, with pencil holes punched through the bottom and mesh screen covering the holes
• B. Sediment
  • ~3 cups per tray of soil type 1: Fine sand + clay mixture (make sure there is enough clay to impede infiltration)
  • ~3 cups per tray of soil type 2: Medium to coarse sand
• C. 1" block of wood
• D. 1/2" block of wood
• E. Infiltration catch pan (make sure this is below the holes punched in A.)
• F. Runoff catch basin or bucket
• Not shown:
  • Graduated cylinder for measuring runoff and infiltration (at least 500 ml)
  • 500-ml plastic cup with holes to dispense the water as rain
  • Stopwatch

Note: Before running the first test, check that the infiltration catch pan (E) is located directly under the holes that have been drilled through the bottom of the tray. Also, half the class should test soil type 1, the other half should test soil type 2.

Keys to success: Do not start with over-saturated sediment. If the sediment became over-saturated, students could not identify patterns in the data. If this activity is used in consecutive labs, the data will start to show a higher volume of runoff for both soil types at the beginning of the first run instead of a gradual change over time.

Students follow the procedure on page 9 of their handout, fill in the data table on page 10, and answer the questions on page 11.

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Procedure

1. Shape the soil mixture into a wedge. Lightly pat down the surface. If the ground surface is compacted, this will impede the infiltration of rainwater.
2. Place the ½-inch block under the tray on the side with the thickest part of the wedge.
3. Place a finger over the hole in the bottom of the 500-ml plastic container (which in this model is a cloud) and fill it to the top with "rainwater."
4. Hold the container over the end of the elevated side of the tray, and start the timer as soon as you release your finger from over the hole. Move the container continuously from side to side across the crest of the hillside until the container is empty. Try to keep the rate of movement and the height above the tray consistent.
5. The moment you observe the rainwater runoff entering the freshwater reservoir (catch basin in the sink), stop the timer and record the time on the table below. Continue to empty any remaining rainwater over the surface of the hillside.
6. Wait until the rainwater stops flowing into the reservoir before measuring the volume of runoff. Record the data on the table below. Important: Be sure you are entering the data in the table that corresponds to the soil conditions (type 1 or type 2) and slope (1 or 1-1/2" height) you are testing.
7. Carefully slide the catch pan beneath the hillside and measure the volume of rainwater that has infiltrated down to the water table (shallow pan). Record the data on the table below.
8. Remove the ½ inch block and replace with the 1-inch block. Make sure to re-mix the sediment and gently smooth the surface of the soil before you run the second test. Repeat steps 1–7.
9. After your group finishes collecting data, enter the group average on the class data collection table (use an overhead transparency or whiteboard) so it can be shared with the rest of the class.

Summarizing Questions

After completing parts 1 and 2, ask students to consider what they have learned by answering the questions on page 12 of their handout. The two questions are:

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1. Imagine that you are a water molecule on a journey through the hydrologic cycle. Identify the process that is occurring at each numbered location on the diagram.
2. Begin with the source of energy that ultimately drives the hydrologic cycle. At each numbered location, explain the process and or phase change that occurs as matter (water) moves through one complete cycle in the hydrologic system. (You might prompt students to look back at their initial ideas to see how their response compares to what they thought at the beginning of the unit.)
   

Optional Homework

Unit 1 homework handout for students (Microsoft Word 2007 (.docx) 107kB Jan11 15)

This assignment gives students the opportunity to examine and apply what they learned in class to their everyday lives. Students are prompted to explore the source and quality of the water in their home county and write a short paper summarizing what they have found. If you have access to a computer lab and time permits, this assignment could be completed in class allowing for a rich discussion about the local environment and sharing with peers about resources and information they learned.

All of this material can fit into one class session that is 2–3 hours long, or it can be divided up into shorter, 50-minute segments.

Part 2

Preparing materials ahead of time is important. If there are multiple labs during the day, it may be necessary to replace the two soil mixtures in the infiltration and runoff experiment or it will be difficult to see a difference in rates.

Provide as many bottle model and stream tray setups as possible. Ideally, students should be working in groups of 2–4, with no more than four people per group.

Formative assessment occurs via the following:

• Facilitator listening in on group discussions of specific prompts to make sure that students are on the right track/holding productive conversations
• Facilitator listening in on class discussions of specific prompts
• Quality of individual student answers to specific prompts in the activity sheet

Note: Assessable objectives are in normal font, and the writing/discussion prompts that assess those objectives are in italics:

Objective 1-1. Construct a model of the hydrologic cycle as an analogy for how water transfers through and between Earth systems.

Part 2, Question 2-4. As water moved through the bottle-model system, it was transferred between several reservoirs. Identify the analog in the hydrologic cycle for each item in the model-bottle system and in which Earth system it is found (atmosphere, biosphere, geosphere or hydrosphere).

Objective 1-2. Demonstrate the processes of evaporation, condensation, and precipitation.

Part 2, Question 2-3.Explain in detail the processes and phase changes that occurred as water moved through the bottle-model system. Start from when you turned on the lamp to where you observed evidence for the initial movement of water.

Objective 1-3. Collect and analyze data to identify soil and surface conditions that result in a higher volume of infiltration or runoff.

Part 2, Question 2-7. Underline the combination of surface soil and slope conditions that resulted in the most infiltration of rainwater: (1) Steep slope and type 1 soil, (2) Steep slope and type 2 soil, (3) Gentle slope and type 1 soil or (4) Gentle slope and type 2 soil. Explain where in the data you collected there is evidence to support your answers.

Part 2, Question 2-8. Underline the condition that resulted in the greatest amount of surface runoff: (1) Gradual slope, (2) Infiltration rate exceeds the rate of rainfall, (3) Surface soil has reached saturation (all the pore spaces between the grains are filled with water) or (4) permeability of the surface soil. Explain where in the data you collected there is evidence to support your answers.

Objective 1-4. Infer how human activity can affect the rate of infiltration and runoff in the local landscape and impact the quality of water readily available for human consumption.

Part 1, Question 1-4. There has been a growing public awareness about the value and importance of water and water resources. How do you think the quality and quantity of the freshwater stored in a local reservoir might be affected by human activity?

Part 2, Question 2-9. Apply your understanding of infiltration and runoff to explain how human activity might affect the rate of water infiltration and runoff where the university you attend is located.

Unit 1 Summative assessment occurs via the following:

Written answers to the summarizing questions:

Q1. Imagine that you are a water molecule on a journey through the hydrologic cycle. Identify the process that is occurring at each circled number on the diagram.

Q2. Begin with the source of energy that ultimately drives the hydrologic cycle and explain the process that transfers matter (water) at each circled number on the diagram. Include an explanation of each phase change that occurs during one complete cycle.

Rubric and key for summarizing questions Q1 and Q2 can be downloaded here:

• Unit 1 Summative Assessment Rubric -- private instructor-only file
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  Unit 1 Summative Assessment Rubric

  
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• The Earth Systems: from USGS
• Satellite image of Earth: The Blue Marble from NASA Goddard Space Flight
• The Blue Planet, a movie from NOAA
• All the Water in the World activity from US EPA