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Under Where? Underground Water and Its Contribution to Streams

When snow melts or rain falls, some of the water runs off into streams or rivers. Most of the water, however, goes down into the soil. The water that stays close to the soil's surface flows laterally and down hillsides. Scientists in this study wanted to know how much this soil water, compared to other sources of water, contribute to stream flow in certain areas. They also wanted to know how levels of snowfall affect groundwater's contribution to stream flow.

Under Where? Underground Water and Its Contribution to Streams

Meet the Scientists

Fengjing Liu

Hydrologist

Carolyn Hunsaker

Ecologist

Roger Bales

Engineer | Environmental Scientist

What Kinds of Scientists Did This Research?

Ecologist: This scientist studies the relationship of living things with their living and nonliving environment.
Environmental engineering scientist: This scientist combines biological, chemical, and physical sciences with the field of engineering to protect and restore the natural environment.
Hydrologist: This scientist studies the distribution, movement, and quality of Earth’s waters

Thinking About Science

Chemistry is a useful science tool. Environmental scientists can use chemistry to discover how water flows in an ecosystem. In this study, the scientists wanted to understand how much water in a particular stream began as rainfall or snowfall. They also wanted to know what percentage of the stream’s flow came from various locations.

The scientists knew that atoms of the same element can have different atomic weights. Different atomic weights are like a signature that helps scientists identify the atom. The scientists also knew that atoms can gain or lose electrons, resulting in a positive or negative charge. This gain or loss creates different chemical compounds, such as calcium or fluoride. These chemical compounds may dissolve in water, but they remain intact as chemical compounds. By testing the water in many places where it enters the ground, and then where water flows in the stream below, scientists can identify where the streamwater originated.

Thinking About the Environment

The water cycle describes the movement of water from Earth, to the atmosphere, and back (figure 1). You can see the water cycle at work in rainfall and snowfall, in rivers and streams, and in the oceans. You can observe evaporation by watching water slowly disappear from a wet roadway.

An illustration of the water cycle — **Figure 1**. The water cycle. Illustration by Stephanie Pfeiffer.

You cannot, however, see one mysterious part of the water cycle. Much of Earth’s precipitation moves into the soil, and, without your noticing, it flows underground as groundwater (figures 2, 3, 4a, 4b, and 5). This water can surface quickly or stay underground for thousands of years.

An illustration of how water moves underground during the water cycle — **Figure 2**. Water moves underground as part of the water cycle. Notice that some water stays near the soil surface. This shallow groundwater, or soil water, may be a few feet deep or up to 20 feet deep
below the soil surface. Deeper underground water is called deep groundwater or just groundwater.
Illustration by Stephanie Pfeiffer.

An illustration showing how groundwater fills the spaces between soil particles and fractured rock underground. — **Figure 3**. Groundwater fills the spaces between soil particles and fractured rock underground. Notice that below the water table, all openings between soil particles and rocks are full of groundwater. Above the water table, some water, held by molecular attraction, may surround particles and rocks. Illustration by Stephanie Pfeiffer, adapted from the Groundwater Foundation and the U.S. Geological
Survey.

An illustration showing a coastal aquifer — **Figure 4a.** Aquifers are natural underground water storage areas. This is an illustration of a coastal aquifer. Illustrations by Stephanie Pfeiffer.

An illustration showing a mountain area aquifer — **Figure 4b.** Aquifers are natural underground water storage areas. Coastal aquifers (4a) are
different than aquifers found in hilly or mountainous areas (4b). Illustrations by Stephanie Pfeiffer.

Underground water comes to the surface naturally through artesian wells, springs, and through seepage to streams and rivers. People bring groundwater to the surface by digging wells that pump water upward for their use. People use groundwater for irrigation, livestock, mining, public use (such as public swimming pools or water in public buildings), and individual household uses. Surface water, such as water in reservoirs, streams, rivers, and lakes, is also used for a variety of similar purposes. Plants use the water in the top several feet of soil for growth. This water is called shallow groundwater, or soil water.

A map showing the primary aquifers of the United States

Introduction

When snow melts or rain falls, some of the water runs across the ground’s surface to nearby streams and rivers. This water movement is called surface flow. Much of the water, however, goes into the soil, and then seeps downward due to the force of gravity. The entrance of water into the soil is called infiltration, and the downward flow is called percolation (pər kə lā shən). Some of the water stays in the soil near the soil’s surface, instead of percolating. This soil water flows laterally and down hillsides, especially in small, steep, forested watersheds called catchments (figure 6). This shallow underground water flow is called interflow. (See figure 2 in “Thinking About the Environment.”)

An illustration of the Mississippi river network — **Figure 6**. Smaller watersheds may be contained within larger watersheds. The scientists in this study were interested in very small, steep, forested watersheds in the Sierra Nevada of California (**figures 7 and 8**). These small watersheds are called catchments. Illustration by Stephanie Pfeiffer.

A map highlighting the Sierra Nevada mountain range in California — **Figure 7**. The Sierra Nevada is a mountain range in California. Map by Carey Burda.

A rocky mountain stream — **Figure 8**. The Sierra Nevada has steep, forested slopes and clear mountain streams. Photo courtesy of the Forest Service, Region 5.

Snow is the main source of water in some of these catchments. These catchments are at higher elevations, where snow occurs more frequently (figures 9 and 10). In catchments at lower elevations, rain is the main source of water. As the global climate becomes warmer, the percent of total precipitation falling as snow will become less at these higher elevations.

An illustration of above and below sea level — **Figure 9**. Elevation is a measure of the height above the level of the sea.
Illustration by Stephanie Pfeiffer.

AN illustration showing how higher elevations experience colder temperatures — **Figure 10**. As elevation increases, an area’s climate gets cooler and snow may fall often in the winter months. Illustration by Stephanie Pfeiffer.

The scientists in this study wanted to answer the following questions: (1) How much does soil water, compared with other water sources, such as rapid snowmelt, rainfall runoff, and groundwater, contribute to streamflow in these catchments? (2) Could underground water’s contribution to stream flow change as less snow falls in higher elevation catchments?

Reflection Section

Methods

The scientists studied eight catchments in the Sierra Nevada. In particular, they studied catchments within the Kings River Experimental Watersheds. This area has been set aside especially to investigate watershed ecology in the Sierra National Forest in California (see figure 7). Four of the catchments were at high elevations in the mountains, and four were located at lower elevations (table 1).

Table 1

Table 1. Characteristics of the catchments studied by the scientists.
Watershed Name	Elevation Range (in m)	Size Range (in km2)	Percentage of Precipitation as Snowfall	Percentage of Precipitation as Rainfall	Average Annual Air Temperature (in °C)
Providence (four catchments)	1,479–2,113	0.49–1.32	20	80	7.8
Bull (four catchments)	2,055–2,490	0.55–2.28	75-90	10-25	6.8

The scientists collected water samples from the streams at each of the streams’ outlets within each catchment (figures 11 and 12).

Dr. Hunsaker testing the water acidity, temperature, and amount of dissolved sunstances in a stream — **Figure 11**. Dr. Hunsaker holds an instrument that measures water acidity, water temperature, and the amount of dissolved substances in a stream within the Kings River Experimental Watersheds. A flume sits in the stream behind her. The flume creates a uniform streamflow so that scientists can measure the amount of water flowing in the stream. Solar-powered instruments automatically
measure and record the amount of streamflow
every 15 minutes. Photo courtesy of Dr. Carolyn
Hunsaker.

An illustration of a catchment and streamflow — **Figure 12**. All streamwater flowed to one stream outlet in each catchment. Illustration by Stephanie Pfeiffer.

How Do You Convert the Characteristics of the Catchments to the U.S. Imperial System?

They collected these samples every other week from the fall of 2003 until the fall of 2007. The scientists collected soil water samples using pumps at depths of 13 cm and 26 cm into the soil (figure 13).

A scientist preparing a vacuum pump — **Figure 13**. This scientist is preparing vacuum pumps that enable him to collect soil water. The tip shown in the inset is inserted into the soil to collect the water. Photo courtesy of Dr. Carolyn Hunsaker.

These samples were taken upslope from the streams and at various locations throughout each catchment. The scientists collected snowfall samples using plastic bottles with funnels (figure 14).

A snowmelt sampler — **Figure 14**. This snowmelt sampler is used to collect snowmelt. These samplers are buried in the soil up to the base of the funnel. An air line and a sample line are connected to the funnel. When it snows and the snow melts, the water sample is pumped out by hand. Photo courtesy of Dr. Carolyn Hunsaker.

They installed these plastic bottles before winter and collected the melted snow water every other week after snowfall (figure 15).

A scientist pumping snowmelt into a sampler — **Figure 15**. This scientist is pumping the
snowmelt out of the sampler. Photo courtesy of Dr. Carolyn Hunsaker.

The scientists collected 2,239 streamflow, snowmelt, soil water, spring water, and groundwater samples (table 2). The scientists analyzed all the samples to determine which
chemical compounds, and how much of each chemical compound, each sample contained scientists analyzed all the samples to determine which chemical compounds, and how much of each chemical compound, each sample contained.

Table 2. The scientists collected five different types of water samples.
Type of Water Sample	Number of Water Samples Collected
Streamflow (collected at the outlets)	1,342
Snowmelt	83
Soil Water	803
Spring Water	1
Groundwater (collected from drinking water wells)	10
Total Samples Collected	2,239

The scientists used math to analyze the chemical characteristics of the water. This analysis enabled them to compare the water samples collected away from the streams
with the streamflow samples collected at each catchment’s outlet. This procedure enabled the scientists to compare the chemical content of the water samples and to identify how much snowmelt and rainwater contributed to each stream.

Number Crunches

Reflection Section

Findings

The scientists found that during the study period, over 60 percent of the streamflow came from water flowing underground (table 3). Snowmelt and rainwater moved rapidly through the soil to streams following a snowfall or rainfall. This rapid movement of groundwater to streams was likely due to the shallowness of the bedrock in this region of the Sierra Nevada.

Table 3. The percentage of streamflow coming from underground water in each of the eight small catchments.
Watershed	Percent of Streamflow Coming From Underground Water
1	63
2	61
3	69
4	66
5	42
6	65
7	60
8	66

Soil water above the water table (interflow) did not contribute much water to the streamflow. This finding was consistent with other studies that have found that soil water within 1 meter of the soil surface is taken up by trees and used for transpiration (tran(t) spə rā shən) (figure 16).

An illustration showing how Carbon dioxide enters a plant and water and oxygen leave

Figure 16. Transpiration involves the flow of water into tree roots, up tree trunks, into branches, and out through pores in tree leaves. Illustrations by Stephanie Pfeiffer and Nickola Dudley (inset).

The scientists found that the proportion of groundwater contributing to streamflow compared with surface flow was about the same for snowmelt water and rainwater.

Number Crunches

Reflection Section

Discussion

The scientists guessed that the shallow bedrock in this region contains large depressions. These depressions are like dimples in the bedrock. The depressions hold groundwater. Following a rainfall or snowfall, water percolates downward and the depressions fill up and spill over. Water then runs along the bedrock underground and into streambeds.

The total amount of streamflow coming from groundwater originating from snow and rain was about the same. The scientists expect, therefore, that a lower percentage of snowfall and a greater percentage of rainfall in the future will not affect streamflow in the higher elevation catchments.

Reflection Section

Adapted from Liu, F.; Hunsaker, C.; Bales, R.C. 2012. Controls of streamflow generation in small catchments across the snow—rain transition in the Southern Sierra Nevada, California. Hydrological Process, published online in Wiley Online Library, DOI: 10-1002/hyp.9304, http://www.fs.fed.us/psw/publications/hunsaker/psw_2012_hunsaker002_lui.pdf.

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What Is a Natural Inquirer Journal?

Three Natural Inquirer journal covers with NI bee

A Natural Inquirer journal is a collection of 4-8 articles on a related science topic. Journals are written for a middle school audience, but they can also be adapted for both high school students and advanced upper elementary students. Some journals are particularly suited to high school students; you can find our grade level recommendations in the tags on the product page or by filtering journals by grade level.

Journals include:

Four to eight articles based on published, peer-reviewed research papers; the articles keep the research paper format (see more below) but are written in language students can understand.
A FACTivity for each article, which is an activity to complete after reading the article. The FACTivity helps reinforce major science concepts from the article. These activities are designed to be easy to implement, with few material requirements and options for adapting them for your audience or available resources. Some articles in a journal may have two FACTivities.
A short “Welcome to the journal” article about key background information and science concepts that unify the articles included in the journal
A glossary of new terms for each article and the introductory materials.
A list of related Natural Inquirer publications for each article as well as outside references.
Standards correlations, including Next Generation Science Standards, addressed in the articles and the FACTivities.

Journals may also include additional essays (called spotlights), other activities (like crossword puzzles or vocabulary challenges), and more.

A screenshot of the article resource tile for "A Flame Changer" showing the three different format option buttons.

Reading Modes

Journals are available in three different formats:

Hard copies can be ordered from the website and shipped, all free of charge.
PDF versions of the printed journal can be downloaded free on the website. The PDF version directly replicates the content and layout of the printed version. You can also download individual articles as pdfs.
The “Read Distraction Free” option allows the individual articles to open in their own window, without the rest of the website being visible. These articles can be found under the “Articles” tab. This version allows readers to scroll to particular sections of the article using the sidebar menu on the left side of the screen. This version also has interactive Reflection Sections and Number Crunches. Students can enter their answers, submit them, and then receive the correct answers to double-check their work. Submitted answers are not saved on the website and will disappear once the window is closed.

What's in a Natural Inquirer Article?

Here, we'll go into more detail about the parts of a Natural Inquirer article and give you some ideas about how they can be used.

Meet the Scientists
This section introduces the scientists (and others) who worked on the study. In their own words, they each share a memorable science experience, a favorite research project, or something they learned during the course of their education or research.

Use this section to:
- Introduce kids to the variety of people who work in science
- Introduce kids to the variety of scientific fields and give brief descriptions of science-related jobs
- Explore ways that people interact with science every day
Next Generation Science Standards (NGSS) applications:
- Science and Engineering Practices
- Crosscutting Concepts: Influence of Science, Engineering, and Technology on Society and the Natural World
Note that specific standards for this particular journal are linked on this educator guide tab.

Other resources:

Many of the scientists and engineers featured in this section are also featured on our collector cards. Learn more about their work, how they got interested in their fields, and interesting projects they worked on. Cards can be printed as posters, too.
Thinking About Science
This section briefly describes a concept about science or scientific research. This overview can touch on topics like
- study type (longitudinal study, quantitative vs. qualitative data),
- behaviors of scientists (conducting literature reviews, collaborating with other specialists, replicating earlier studies),
- the practice of science (the scientific method, engineering design, data collection, randomization, controls and variables),
- or other aspects of science (bias, correlation vs. causation).
Use this section to:
- Reinforce steps in the scientific method and the process of science
- Encourage students to think about the practice of science and what it can and cannot tell us
- Consider the many types of scientific study and what information each type can provide
Next Generation Science Standards applications:
- Science and Engineering Practices
- Life Science Disciplinary Core Ideas (depending on topic)
- Most Crosscutting Concepts (depending on topic)
Note that specific standards for this particular journal are linked on this educator guide tab.

Other resources:

You can use key words to search for other or related scientific topics on our website (e.g. “longitudinal study,” “bias,” or “sampling”).
Thinking About the Environment
This section provides a brief overview of a topic or concept in environmental/life science. The topic or concept is directly related to the research study that follows. Examples of topics include the carbon cycle, the water cycle, habitat fragmentation, phenology, biodiversity, and ecosystem services.

Use this section to:
- Provide important background information to help students understand the research study
- Serve as a quick reference during reading or class instruction
- Connect the research article with other activities or media on the same topic
Next Generation Science Standards applications:
- Life Science and some Earth Science Disciplinary Core Ideas (depending on topic)
- Most Crosscutting Concepts (depending on topic)
Note that specific standards for this particular journal are linked on this educator guide tab.

Other resources:

You can use key words to search for more resources on life or earth science topics on our website (e.g. “habitat,” “carbon,” or “genetics”).
Introduction
This section begins the scientific article format. Much like the published, peer-reviewed study this article is based on, the introduction provides background information for the study – what is currently known and what remains unknown. The introduction culminates in the question(s) the study hopes to answer.

The introduction is also the first section with a Reflection Section. This section includes two or three questions to help kids reflect on what they’ve just learned in the Introduction. If they are using the online distraction-free reading mode, they can answer these questions directly on the website.

Use this section to:
- Review important background information that kids need to understand the study
- Connect the study to the concepts addressed in the Thinking About Science and Thinking About the Environment sections
- Understand research questions and hypotheses, including generating their own hypotheses given what they already know
Next Generation Science Standards applications:
- Life Science and some Earth Science Disciplinary Core Ideas (depending on topic)
- Most Crosscutting Concepts (depending on topic)
Note that specific standards for this particular journal are linked on this educator guide tab.

Other resources:

Use one of the guided reading lesson plans to help kids follow the format of a scientific paper.
Methods
This section is the nuts and bolts of the study design – the who, what, when, where, why, and how of the research. Contained within the Methods section are usually maps of the study location or the set-up of study plots, as well as details about what data was collected and how.

The Methods section also ends with a Reflection Section – two or three questions to help students think through what they just read. These questions are interactive on the distraction-free reading mode.

Use this section to:
- Show students how experiments and studies are designed and carried out
- Explore sampling methods and randomization
- Introduce various data collection tools (e.g. camera traps, surveys, insect collection tools, weather stations, etc.)
- Explain bias and how studies are designed to remove bias
- Help students gain experience with map reading
Next Generation Science Standards applications:
- Life Science and some Earth Science Disciplinary Core Ideas (depending on topic)
- Most Crosscutting Concepts (depending on topic)
Note that specific standards for this particular journal are linked on this educator guide tab.

Other resources:

Many Methods and Findings sections contain Number Crunches, which are simple math exercises designed to help students interact with the data from the study.
Findings
This section summarizes the data collected during the study. The Findings section usually includes data tables or graphs and highlights the significant data points from the study. This section often mentions statistical analysis or the use of computer programs to model or analyze the data, though these methods are only discussed generally.

The Findings section also ends with a Reflection Section – two or three questions to help students think through what they just read. These questions are interactive on the distraction-free reading mode.

Use this section to:
- Have students practice reading and interpreting graphs and tables
- Compare results between variables and controls
- Explain the concept of statistical significance
- Discuss how no data or negative results still provide valuable information
Next Generation Science Standards applications:
- Life Science and some Earth Science Disciplinary Core Ideas (depending on topic)
- Most Crosscutting Concepts (depending on topic)
Note that specific standards for this particular journal are linked on this educator guide tab.

Other resources:

Search the website for “map” or “graph” to find activities where students can practice making and reading maps and graphs.
Discussion
This section concludes each article. In it, we summarize the main findings of the scientists’ study. Additionally, we present the scientists’ ideas about the limitations of their study, the big-picture impacts of their research, and the scientists’ plans for future study or action.

The Discussion section ends with a Reflection Section – two or three questions to help students think through what they just read, especially general take-aways from the study. These questions are interactive on the distraction-free reading mode.

Use this section to:
- Discuss what conclusions can and cannot be drawn from the available data
- Explain the difference between correlation and causation
- Explore study limitations and opportunities for further study
- Brainstorm ways the study findings could be applied to real-world situations
Next Generation Science Standards applications:
- Life Science and some Earth Science Disciplinary Core Ideas (depending on topic)
- Most Crosscutting Concepts (depending on topic)
Note that specific standards for this particular journal are linked on this educator guide tab.

Other resources:

Use the “Designing Your Own Study” resource page for videos of scientists discussing their own research studies. The page also includes educator resources to help students plan their own scientific studies.

Additional Resources on the Website

A screenshot of the product tabs for an NI monograph On the website, we pair each journal with a variety of other resources, as well. Use the tabs on the product page to browse through the following:

Related activities, including the FACTivity for each article
An “About” essay that gives some larger context for the research the scientists conducted or more information about the science topic from the journal
A glossary of all boldfaced terms from the journal
A “Scientists and Collaborators” page that lists the people involved in the studies in the journal; click on a researcher to reach their bio page and see what other articles they might be featured in
A “Related Content” page that lists both Natural Inquirer resources about similar topics and also outside reference materials

Article Selection and Review

Natural Inquirer partners with the USDA Forest Service, so we source research studies by Forest Service scientists that have been peer-reviewed and published in reputable journals. Some of our articles have also been created in collaboration with scientists from other Federal agencies, such as U.S. Geological Survey and the United Nations Food and Agriculture Organization, universities, and other non-profits.

All journal articles are reviewed by scientists who conducted the original research study to verify scientific accuracy. Journals are also reviewed by student editorial review boards of middle or high school students before publication. Additionally, all journals are reviewed by the Forest Service and the U.S. Department of Agriculture before publication.

A screenshot of the citation for "Lights, Camera, Tracks" Every journal article includes a citation of its source study. Many educators pair the original research paper with our article to help more advanced students learn how to read formal research papers. The journal article then serves as adapted primary literature, bridging the two articles.

Lessons

In this lesson, students will create a storyboard to graphically represent the main points from the research article they read. This lesson plan can be used with any Natural Inquirer...
Lesson Plan – Storyboard
In this lesson, students will create a storyboard to graphically represent the main points from the research article they read. This lesson plan can be used with any Natural Inquirer...
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Freshwater - Vol. 18 No. 1
This lesson plan introduces students to the different sections of a Natural Inquirer article. Additionally, it helps the students understand the content of the article through the use of graphic...
Lesson Plan – Reading a Natural Inquirer Article – FACELook
This lesson plan introduces students to the different sections of a Natural Inquirer article. Additionally, it helps the students understand the content of the article through the use of graphic...
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FACELook! Exploring the Relationship Between Carbon, Photosynthesis, and the Roots of Trees
In small groups (or individually), students will read a Natural Inquirer or Investi-gator article and write a letter to the scientist, asking for clarification on at least four questions. This...
Lesson Plan – Letter to a Scientist
In small groups (or individually), students will read a Natural Inquirer or Investi-gator article and write a letter to the scientist, asking for clarification on at least four questions. This...
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Wildland Fire 2 - Vol. 13 No. 1

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If you are a trained Project Learning Tree educator, you may use “Rain Reasons” and “Water Wonders” as additional resources.

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Standards addressed in this Article:

What Is a Natural Inquirer Journal?

Reading Modes

What's in a Natural Inquirer Article?

Meet the Scientists

Thinking About Science

Thinking About the Environment

Introduction

Methods

Findings

Discussion

Additional Resources on the Website

Article Selection and Review

Lessons

Education Files

Project Learning Tree

Glossary

intact

land cover

laterally

localized

precipitation

reservoir

runoff

snowmelt

snowpack

streamflow

turbidity

upslope

watershed

Fengjing Liu

Carolyn Hunsaker

Roger Bales

Related Resources from the Natural Inquirer

Additional Resources