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Getting to the Core: Understanding Lakes through Sediment Coring

Jeremy Wang Gillian Roehrig

Amy Myrbo

University of Minnesota STEM Education Center1

Limnology Resource Center-LacCore2 NASA SMD Division Earth Science Audience/Grade Level Earth science, environmental science, and biology classes

Grades 7-10 (primary audience); Grades 11-14 (with modification) Subject Lake structure, history, and biology Class Time

2-3 weeks, depending on class length Length/Format Approximately 30 pages; PDF, Powerpoint

                                                                                                               1 http://www.cehd.umn.edu/stem/ 2 http://lrc.geo.umn.edu/laccore/

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Introduction/Overview The goal of this curriculum is to introduce students to limnology, the study of lakes. Through the lessons and activities, students develop a broad understanding of the structure of lakes and how they form, with a focus on how scientists understand the history of lakes by gathering and analyzing core samples from lake floors. In addition, students develop engineering design skills through an extended problem-solving activity. The curriculum consists of 5 activities:

• In Activity 1, students use Internet resources to gather information about lakes around the world in order to develop an understanding of the unity and diversity of lakes.

• In Activity 2, students model water inputs and outputs to lakes using a physical model. Students use models to explain changes observed in lakes via satellite images.

• In Activity 3, students create a miniature lake and a corresponding bathymetric map. Students discuss the relationship between geological features of lakes and the history and formation of lakes.

• In Activity 4, students conduct a case study of a lake from which sediment cores have been taken. Students analyze the lake core sample, correlating changes in the lake core sediment with other data sources to reconstruct past environments.

• In Activity 5, students engage in an engineering activity, working in small groups to develop a device prototype for collecting lake core sediments.

The activities are intended to be used successively in the order presented, but can be used selectively or rearranged based on classroom constraints and student characteristics. In each activity, key questions for teachers to ask students are written in italics. These materials were developed to support on-site school visits from LacCore researchers. During these visits, students use coring equipment to collect sediment samples from a local lake and conduct initial core description. For more information about lake coring at or near your school site, contact LacCore at laccore@umn.edu. Background Information for Educators Lakes and reservoirs play a vital role in humans’ lives. Over 70% of Earth’s surface is covered in water. When seen from space, it is clear why Earth is known as the “Blue Planet.” While the vast majority of water on Earth is found in oceans, fresh water for human use is mostly found in lakes and rivers. Scientists estimate that there are somewhere in the neighborhood of 304 million lakes and ponds in the world. Thus, an understanding of lakes, their properties, is important

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for both scientists and society. Moreover, lakes can tell us about past changes in the environment, giving clues to how current actions can impact the future environment. Activity 1: Lakes of the World Information Search Lakes are bodies of water that can be described by features and characteristics, such as location, area, depth, inflows, outflows, and the living things that are found in and around them. Each lake has unique features that reflect the history and characteristics of the surrounding area. Lakes can be categorized into different types based on defining characteristics, such as location, drainage, and mixing of water layers. One way in which lakes are categorized into different types is based on the processes by which they are formed.3 Glacial lakes formed as a result of glaciers receding after the last ice age, roughly 10,000 years ago. As the glaciers receded, the scouring action of the ice movement pulverized rock into sediment and carved out basins that became lakes. The most prominent examples of glacial lakes are the Great Lakes in North America. Rift lakes occur along geologic faults between tectonic plates that are moving apart. Examples of rift lakes include Lake Baikal in Siberia, and Lake Malawi and other Rift Valley lakes in eastern Africa. Crater lakes, such as Crater Lake in Oregon, USA, occur in the caldera of inactive volcanoes. Lakes can also be man-made; most reservoirs are created behind dams that humans have built to control the flow of water in rivers. Activity 2: Modeling Lake Dynamics Lakes can be thought of as systems that have inputs and outputs. Lakes form in basins and depressions in land where water collects. Scientists typically think about lake inputs in terms of drainage basins or watersheds (also known as hydrologic units), which are the areas of land where surface water from precipitation or snow and ice melt converges to a single point. This point can be a lake or other body of water. Water leaves lakes via seepage into groundwater, drainage via rivers, and evaporation. Changes to water levels in lakes can occur over time when there is imbalance between the inputs and outputs. Some of these changes occur quickly (several years), while others occur over a longer time period (several decades). Models are a good way of understanding the dynamics of lakes. Models are created to be representations of things that are too small, too large, too dangerous, or that happen too slowly or quickly to be directly observed. A good model accurately represents critical aspects of the phenomena it is meant to represent. Models cannot capture all aspects of the phenomena they represent, and it is important to consider these shortcomings.                                                                                                                3 For a list of types of lakes, see: http://en.wikipedia.org/wiki/Lake#Types_of_lakes

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Activity 3: Mini-Lake Bathymetry The bottom surface of a lake shows a lot about its history and formation. The shape and features of a lake bottom can provide clues to human and geological processes that have shaped a lake over time. Different types of lakes generally have different shapes and depth features. For example, rift lakes (such as Lake Baikal and Lake Malawi) are usually long, narrow, and very deep with steep sides; crater lakes formed in former volcanoes are round and deep with steep sides and have volcanic outcroppings; glacial lakes have more gentle sloping bottoms, caused by the scouring that occurs as glaciers recede. In order to study lake floors, scientists create bathymetric maps, which are the equivalent to underwater topographic maps. These maps are made by sampling different areas of a lake surface using a depth gauge. Modern methods involve using echo sounding techniques to survey lakes and other bodies of water. Bathymetric maps are not only important for navigation, but also for observing changes in lakes over time through processes such as sedimentation and human development. Activity 4: 20th Century History of an Urban Lake The study of lakes is called limnology, and the study of past conditions of the environment through lakes is called paleolimnology. Much of what scientists learn about lakes comes from studying the sediments that collect at the bottom of a lake. The sediment deposited at the bottoms of lakes is made up of small particles (typically <0.1 mm) of various compositions, including material that washes into the lake, the remains of plants and animals that lived in the lake, and minerals that form in the lake. Sediment sinking from above builds up over time, so that newer (younger) sediment lies on top of older sediment. Over time, the sources, types, and amounts of sediment being deposited can change. These changes can reflect changes in the lake itself and in the landscape around it. The lake sediment actually records these changes by storing particles derived from all of these different sources and processes. For instance, over many hundreds of years, climate may change - get wetter or drier, warmer or colder. The new climate may no longer be favorable for the trees and plants that previously lived around the lake, and so a different suite of vegetation may move in. Spruce and pine, which favor cold, wet climates, may be replaced by oaks and grasses, which grow in warmer, drier climates. Each year when these trees release their pollen, some is blown into nearby lakes and becomes part of the lake sediment. Pollen grains have complex shapes and textures, so they can be identified by experts, and they are also very resistant to decomposition, so they last a long time in the sediments. By looking at what

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pollen types are present at different levels (ages) in the core, we can “reconstruct” past vegetation. Similarly, the algae living in the lake change depending on climate, because climate can change lake salinity and nutrient levels. The minerals that form in the lake also depend on salinity (and more generally, lake water chemistry), and thus are also affected by climate. Many other factors are also dependent on climate, such as the amount of erosion into the lake, the amount of water flowing into the lake each year, the summer temperature of the lake water, etc. Each of these parameters is represented in some chemical or biological way in lake sediments, and scientists can reconstruct how they change over thousands of years by analyzing lake sediment core samples. Human impacts can dramatically change lakes. When people start living around a lake, they usually change the landscape. Some of the ways they do this are by clearing forests and prairies, planting crops, building houses, building roads, fertilizing crops and lawns, putting salt and sand on roads, or manufacturing. These and other activities can affect the amount and type of sediment entering the lake, and can change the kinds of animals and plants that can live in the lake by altering lake water quality. Material sinking through the water column is deposited seasonally – some components are produced in the summer, and some in the winter. Annual layers or laminations of sediments are called varves, and they also contain their own chronology – that is, a researcher can count the number of years in a core just like counting tree rings. All lake sediments should, in theory, show those clear layers (laminations) of material. However, burrowing animals can stir up the sediments looking for food, and blend these layers into a homogeneous mass. But when bottom water is anoxic (no oxygen), these organisms can’t live there, and the laminations are preserved intact. This type of preservation is not common – it takes a certain kind of lake, usually a deep lake – but it is sought-after by scientists because these laminations are frequently annual in scale, and so detailed analysis of laminations can actually produce an annual record of changes in a lake. Activity 5: Engineering a Lake Sediment Coring Device Researchers go to great lengths to gather sediments samples from lakes around the world. Collecting these samples is not easy; conditions can be harsh and in most cases they must design and build their own tools. Since there are many different kinds of lake sediment, scientists must be prepared to use different tools and make modifications in order to successfully collect a sediment core. While some of these involve large motors and heavy equipment, the majority of lake sediment cores can be collected using tools operated by hand. In order for sediment samples to be understandable, scientists need to know the location,

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depth (of the water and the sediment), and orientation of the samples they collect. There are many other engineering design constraints that scientists must consider when developing sampling devices, such as cost, transportation, and reliability. National Science Education Standards (1998)

CONTENT STANDARD: K–12 Unifying Concepts and Processes Standard: As a result of activities in grades K–12, all students should develop understanding and abilities aligned with the following concepts and processes:

• Systems, orders, and organization • Evidence, models, and explanation • Constancy, change, and measurement

CONTENT STANDARDS: 5–8 Science as Inquiry Content Standard A: As a result of activities in grades 5–8, all students should develop:

• Abilities necessary to do scientific inquiry • Understandings about scientific inquiry

Earth and Space Science Content Standard D: As a result of activities in grades 5–8, all students should develop an understanding of:

• Structure of the Earth system Science and Technology Content Standard E: As a result of activities in grades 5–8, all students should develop:

• Abilities of technological design CONTENT STANDARDS: 9–12 Science as Inquiry Content Standard A: As a result of activities in grades 9–12, all students should develop:

• Abilities necessary to do scientific inquiry • Understandings about scientific inquiry

Earth and Space Science Content Standard D: As a result of activities in grades 9–12, all students should develop an understanding of:

• Energy in the Earth system • Geochemical cycles

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Science and Technology Content Standard E: As a result of activities in grades 9–12, all students should develop:

• Abilities of technological design

Minnesota State Science Standards (2012) Grade 8:

• 8.1.1.2 Scientific inquiry uses multiple interrelated processes to investigate questions and propose explanations about the natural world. ◦ 8.1.1.2.1 Use logical reasoning and imagination to develop

descriptions, explanations, predictions and models based on evidence.

• 8.1.3.4 Current and emerging technologies have enabled humans to develop and use models to understand and communicate how natural and designed systems work and interact. ◦ 8.1.3.4.1 Use maps, satellite images and other data sets to

describe patterns and make predictions about local and global systems in Earth science contexts. For example: Use data or satellite images to identify locations of earthquakes and volcanoes, ocean surface temperatures, or weather patterns.

◦ 8.1.3.4.2 Determine and use appropriate safety procedures, tools, measurements, graphs and mathematical analyses to describe and investigate natural and designed systems in Earth and physical science contexts.

• 8.3.1.2 Landforms are the result of the combination of constructive and destructive processes ◦ 8.3.1.2.2 Explain the role of weathering, erosion, and glacial

activity in shaping Minnesota's current landscape. • 8.3.1.3 Rocks and rock formations indicate evidence of the materials and

conditions that produced them. ◦ 8.3.1.3.1 Interpret successive layers of sedimentary rocks and their

fossils to infer relative ages of rock sequences, past geologic events, changes in environmental conditions, and the appearance and extinction of life forms.

• 8.3.2.3 Water, which covers the majority of the Earth’s surface, circulates through the crust, oceans and atmosphere in what is known as the water cycle. ◦ 8.3.2.3.1 Describe the location, composition and use of major

water reservoirs on the Earth, and the transfer of water among them.

◦ 8.3.2.3.2 Describe how the water cycle distributes materials and purifies water. For example: Dissolved gases in rain can change the chemical composition of substances on Earth. Another example: Waterborne disease.

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• 8.3.4.1 In order to maintain and improve their existence, humans interact with and influence Earth systems. ◦ 8.3.4.1.2 Recognize that land and water use practices can affect

natural processes and that natural processes interfere and interact with human systems. For example: Levees change the natural flooding process of a river. Another example: Agricultural runoff influences natural systems far from the source.

Grade 9: • 9.1.3.1 Natural and designed systems are made up of components that

act within a system and interact with other systems. ◦ 9.1.3.1.1 Describe a system, including specifications of boundaries

and subsystems, relationships to other systems, and identification of inputs and expected outputs. For example: A power plant or ecosystem.

• 9.1.3.3 Science and engineering operate in the context of society and both influence and are influenced by this context. ◦ 9.1.3.3.2 Communicate, justify and defend the procedures and

results of a scientific inquiry or engineering design project using verbal, graphic, quantitative, virtual or written means.

• 9.1.3.4 Science, technology, engineering and mathematics rely on each other to enhance knowledge and understanding. ◦ 9.1.3.4.6 Analyze the strengths and limitations of physical,

conceptual, mathematical and computer models used by scientists and engineers.

• 9.1.2.1 Engineering is a way of addressing human needs by applying science concepts and mathematical techniques to develop new products, tools, processes and systems. ◦ 9.1.2.1.1 Understand that engineering designs and products are

often continually checked and critiqued for alternatives, risks, costs and benefits, so that subsequent designs are refined and improved. For example: If the price of an essential raw material changes, the product design may need to be changed.

• 9.1.2.2 Engineering design is an analytical and creative process of devising a solution to meet a need or solve a specific problem. ◦ 9.1.2.2.1 Identify a problem and the associated constraints on

possible design solutions. For example: Constraints can include time, money, scientific knowledge and available technology.

◦ 9.1.2.2.2 Develop possible solutions to an engineering problem and evaluate them using conceptual, physical and mathematical models to determine the extent to which the solutions meet the design specifications.

• 9.1.3.3 Science and engineering operate in the context of society and both influence and are influenced by this context. ◦ 9.1.3.3.2 Communicate, justify and defend the procedures and

results of a scientific inquiry or engineering design project using verbal, graphic, quantitative, virtual or written means.

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• 9.1.3.4 Science, technology, engineering and mathematics rely on each other to enhance knowledge and understanding. ◦ 9.1.3.4.2 Determine and use appropriate safety procedures, tools,

computers and measurement instruments in science and engineering contexts.

• 9.4.4.1 Human activity has consequences on living organisms and ecosystems. ◦ 9.4.4.1.2 Describe the social, economic and ecological risks and

benefits of changing a natural ecosystem as a result of human activity. For example: Changing the temperature or composition of water, air or soil; altering populations and communities; developing artificial ecosystems; or changing the use of land or water.

Key Terms limnology tectonic

glacier evaporation precipitation drainage basin / watershed reservoir dam

bathymetry / bathymetric map contour lines

varve Appendices

Appendix A – Lake Information Search Handout Appendix B – Types of Lakes Appendix C – State of Flux Lake Images Appendix D – Bathymetry Maps of Lakes Appendix E – Lake McCarrons Sediment Core Image Appendix F – Lake McCarrons Activity Handout Appendix G – Lake McCarrons Historical Data Appendix H – Lake Stratification and Chemistry Appendix I – Lake Coring Devices Appendix J – Pre/Post-Assessment

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Activity 1: Lakes Information Search Focus Questions

What do all lakes have in common? What makes lakes different?

Learner Objective(s)

Understand the characteristics and measurements used to describe lakes such as location, size, depth, bottom composition, aquatic life, inflow and outflows, clarity.

Understand the variability of these characteristics among lakes around the world.

Time Required

1-2 class periods Materials

Demonstration Materials • Large water-filled bucket or aquarium with sand or gravel in bottom

Activity Materials • Computers/Laptops with Internet access • Lake research information grids (Appendix A – printouts or electronic files)

Websites • Students should be encouraged to search for Internet information on their

own, determining the quality of the sources. • Examples of potential sources of information:

o Wikipedia: http://www.wikipedia.org/ o NASA Visible Earth: http://visibleearth.nasa.gov/ o NASA Earth Observatory: http://earthobservatory.nasa.gov/ o Google Maps: http://maps.google.com/ o World Lakes Database: http://wldb.ilec.or.jp/ o State DNR Websites, for example:

MN Lake Finder: http://www.dnr.state.mn.us/lakefind/index.html

WI Lake Finder: http://dnr.wi.gov/lakes/findalake/

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Procedure Teacher Note: Prior to Activity 1, students may be given the Pre/Post-Assessment (Appendix J) to determine prior knowledge and monitor learning objectives. Engagement: Present students with a large, water-filled tub, bucket, or aquarium filled with water and with sand or gravel in the bottom. Have students consider the following question: “Is this a lake?” Using this question as a starting point, students will generate as many questions about lakes as possible. They should NOT try to develop an argument or figure out who is “right.”4 Examples of questions that students might come up with:

• How do lakes form? Where do lakes come from? • What materials is a lake made of? • How does water get into lakes? How does it leave? • What is the biggest lake in the world? Smallest? • How small can a lake be? Does it have to be smaller than

a certain size? • Can a lake be man-made? • What makes a lake ‘natural’? • How does water get in and out of a lake? • Does the same water stay in a lake? For how long? • Do all lakes contain living things? What kinds? • Do lakes have a bottom? What would you find there? • Are there lakes on other planets?

Consolidate students’ questions and as a class choose the 3 most important questions to answer about lakes. Exploration: Students will gather information about selected lakes using Internet resources (see Appendix A). Before students work on this independently, the teacher begins by modeling how to find the information and fill out each column of the table. 1. Hand out lake information grids to students (printout or electronic copy).

                                                                                                               4 For more tips on generating questions, see the Right Question Institute: http://rightquestion.org/educators/resources/

Tips for producing questions (based on the Question Formulation Technique developed by the Right Question Institute): • Have students ask as many

questions as they can • Do not stop to discuss, judge,

or answer questions • Write down every question

exactly as it is stated • Change any statement into a

question  

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2. Using Google Earth or Google Maps projected for the class, teacher begins at school location and zooms out to find nearby lakes. Choose a lake that is likely familiar to most students. This may be the largest lake in the state or region. 3. After taking a look at the lake, do an Internet search for information about that lake. Teacher may gather information from websites like Wikipedia, state DNR websites, and the NASA Visible Earth website (see Materials section above) to fill in one of the rows in the grid. Teacher should explain each column and discuss proper units for each characteristic. Students should fill out row as teacher gathers this information. 4. Students will follow the procedure modeled above to gather information about other lakes listed in the grid. Allow 15-25 minutes for students to work independently, depending on grade level. 5. If students finish early, they may attempt to search for information to answer questions generated at the beginning of class. Explanation:

After students have completed lake information table, have a classroom discussion around the following questions: • What are the units for the dimensions being used to compare lakes? • What was the largest lake found? Smallest? • What was the deepest lake? • Did you find any lakes with interesting shapes? Why do you think that

shape occurred? • What color were the lakes? Why do you think that they were that color? • Are there saltwater lakes? • How can you tell whether or not a lake freezes over during the winter? Discuss different types of lakes, based on formation, using images in Appendix B.

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Extension: Review the questions generated at the beginning of the lesson. Have any of the questions been answered? What other questions do students have after gathering information about lakes? Write down any additional questions that students have based on the activity. Advanced: What is the relationship between latitude, longitude, elevation, and where lakes are located around the world? The image below can be used to guide this discussion.

Figure 1. Predicted distribution of lakes around the world. Colors represent the density of lakes (dL; number of lakes per area – 106 km2) around the world, with yellow areas having few lakes and blue areas having many lakes (Downing et al., 2006)5.

Evaluation: Students are encouraged to share answers gathered during lake

information grid. Teacher may lead discussion about answers, focusing on aspects of measurement (units), approximation, and consensus.

Additional questions: What do all lakes have in common? What are some things that make lakes different?

                                                                                                               5 Downing, J. A. et al. (2006). The global abundance and size distribution of lakes, ponds, and impoundments. Limnology and Oceanography, 51 (5).

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Activity 2: Modeling Lake Dynamics In this activity, students use a physical model of a lake to discuss the inflows and outflows of water and how they contribute to changes in lakes over time. A key to understanding lake dynamics is the balance between inputs and outputs of water and nutrients. The goal of this activity is to help students develop a sense of lakes as systems, and to develop an appreciation of how models can be used to describe complex systems. Focus Questions

How do lakes form? What causes lakes to change?

Learner Objectives

Explain how water flows into and out of lakes Describe changes that occur in lakes and explain what causes these changes

in terms of input and output Understand lakes as systems

Time Required

1-2 class periods Materials

Engagement • Computer • Projector • Color printouts of satellite images from NASA State of Flux website

o OR Computers with Internet access Exploration

• Several tubs or buckets o One with holes and/or overflow cutout

• Watering cans • Tape or putty (for blocking holes) • Ice • Funnel • Rulers • Crayons/wax pencils/dry erase markers

Explanation • Pencils and paper • Colored pencils / markers

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Procedure Engagement: Show students satellite images of changes in lakes from the NASA State of Flux website6. These images may be printed out, or students may access them on computers, if available.

Examples: • “Lake Changes Uganda” • “Dam Impact Kansas” • “Lake Shrinkage Utah” • “Lake Shrinkage Africa” • “Expanding Lake China” • “Reservoir Shrinkage, Nevada / Arizona”

Students work in small groups (2-4) to view images and answer the following questions:

1. What is the lake’s name and where is it located? 2. When were the satellite images taken? 3. What changes can you see from the satellite images? 4. Why do you think the changes in the lake occurred?

Have students share out answers and discuss different types of changes that occur in lakes (expansion, shrinkage) and their possible causes. Exploration:

1. Set up shallow tub with water and output holes covered. Fill the tub with water and explain to students that the tub will serve as a model for a lake.

2. Discuss the parts of the lake model, focusing on inputs (watering cans) and outputs (drain holes and overflow cutout) and what they correspond to in real lakes (rivers, precipitation, evaporation, glaciers, irrigation, etc.), as well as limitations of the model.

3. Mark the starting water level in the tub. Unplug drain and begin pouring water into the system. Attempt to keep the water level relatively constant at the starting water level. Discuss the relative rates of input and output and how the model aligns with what happens in the real world. For example, “Are the rates of input and output for a lake relatively constant or do they change?” [Optional: Use beakers and a stopwatch to measure the rates of outflow and inflow.

4. Discuss the following scenarios and how they could be translated to the model. Be sure to describe (1) whether it changes the input, output, or both; (2) how the rate of input/output is changed; and (3) the short-term and long-term impact on the water level of the “lake.”

• Precipitation

                                                                                                               6 Images available in Appendix or NASA State of Flux website: http://climate.nasa.gov/state_of_flux

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• Large storm events • Seasonal drought • Dam impact • Increased irrigation and water usage • Glacier/snow melting

5. Conduct experiments and describe changes that can be made to the model corresponding to each of the above scenarios to demonstrate how these effects the level of the water in the reservoir.

Explanation:

1. In small groups, have students choose one of the scenarios from the Engagement activity (i.e. one of the State of Flux image sets) and describe how a lake model that would the change observed in the satellite images.

2. Each student group creates a diagram of their model, including a container/reservoir, inputs and outputs, and what each part represents. Encourage students to be creative in their models and to consider how other analogs can be used to model the phenomena observed on the satellite images.

3. Each group will explain and defend their model to the class. Evaluate students based on the rubric below.

Extension:

Discuss the following questions How could you model evaporation in this system? How do you model seasonal changes in this system? What are some limitations of the model? How does the movement of water into and out of lakes influence the movement of other things into and out of lakes (nutrients, organic material, sediment)? What is ‘lake retention time’ (or ‘residence time’) and how can it be calculated?

Use calculations of the rates of input and output to make predictions about how long it will take the lake to drain or overflow based on a given set of inputs and outputs.

Evaluation:

Evaluate each group’s model diagram and presentation based on the rubric at the end of this lesson.

Conclusion

Describe the major inputs and outputs of a lake (for example, a lake discussed in in Activity 1). Explain recent or past changes in lake water levels in terms of changes to inputs and outputs.

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Rubric for Explanation Activity

Excellent (4) Good (3) Satisfactory (2)

Needs Improvement (1)

Diagram Includes reservoir, inputs, outputs, and additional equipment needed to model the lake system

Includes most parts of system, but one part is missing

Includes parts of system, but two parts are missing

Includes parts of system, but three or more parts missing, or a critical part is missing

Inputs Appropriately models the types of and changes in water input in terms of amount and rate

Models types and changes in water input, in terms of amount

Models types or changes in water input, in terms of amount

Models types or changes in water input, but does not specify amount or rate

Outputs Appropriately models the types of and changes in water output in terms of amount and rate

Models types and changes in water output, in terms of amount

Models types or changes in water output, in terms of amount

Models types or changes in water output, but does not specify amount or rate

Explanation of Model

Justify all parts of model and explain why the expected change will occur. Includes quantitative measures to support model.

Justify most parts of model and explain why the expected change will occur qualitatively

Justify some parts of model and predict what changes will occur

Justify a few parts of the model and predict

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Activity 3: Mini-Lake Bathymetry In this activity, students develop an understanding of what lies below the surface and at the bottom of a lake. By creating their own miniature lake and corresponding bathymetric map, they will gain an understanding of the significance of what lies at the bottom of lakes and how it reflects the formation and geologic processes that shape the lake. Focus Questions

What does the bottom of a lake look like? What can the bottom of a lake tell us about the history of a lake?

Learner Objectives

Explain what a bathymetric map is and how they are made. Explain how geologic processes (sedimentation, tectonic movement, volcanic

activity) and human activities can influence the formation and structure of lakes.

Time Required

2-3 class periods Materials

Bathymetric maps of relevant lakes Small plastic boxes with lids (1 for every 2 students) (24oz reusable

containers work well) Modeling clay (approximately 1 lb per group) Food coloring Straws / skewers / chopsticks (for depth gauge) Transparency sheets, cut in half Dry-erase markers Permanent markers Beakers for distributing water

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Procedure Engagement: Question: “If you empty all of the water out of a lake, what would it look like?” As a class, look at bathymetry maps for the lakes below7. Discuss the significance of lake floor features in relation to lake formation and/or history.

Crater Lake The deepest lake in the US and one of the clearest in the world; the lake was formed after a volcanic eruption; the lake has not inlets or outlets.

Superior Shoal (Lake Superior) A shallow area (like a sandbar) in Lake Superior that is only 6m from the surface at shallowest; the shoal was left behind during glacial recession; it has been suggested as the cause of several shipwrecks.

Lake Mead A reservoir formed behind the Hoover Dam; the cross-sections show sedimentation of the lake that is the result of the rivers that flow into the reservoir; sedimentation has occurred at a greater rate where the river enters the reservoir.

Exploration: 1. Students will work in pairs to create a “mini-lake” in a small plastic

container. The lake floor will be formed using modeling clay. Each pair’s/group’s miniature lake should be unique, but include some specific features: a shore, a deepest point, and at least one input or output location. Provide students with time to plan and create their lake. Students may name lakes and label features.

2. After students have created their lake bottom with clay, they will develop a bathymetric map of their lake. To do this, students will fill the container with water at various levels. Food coloring can be added to the water to make it more visible against the clay. Distribute water with food coloring, clear mapping surface, markers, and depth gauge materials.

3. To create a depth gauge: on a wooden stick or straw, mark off regular intervals of 1-5cm (depending on size of container) with a marker. Students will use this as a guide to raise the water level by one mark for each contour line.

4. Place the depth gauge at the lowest point of the mini-lake. Fill water up to first mark on the depth gauge.

5. Place transparency over the top of the container (have students make alignment marks so that transparency is replaced in the correct location). Outline the area filled with water on the transparency.

6. Fill the mini-lake with water to the next mark on the depth gauge and repeat Step 5 until the lake has been filled and the bathymetry map has been completed.

                                                                                                               7 See Appendix C. Local examples may be used instead.

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Tips for creating good “mini-lakes”:

• The deepest point(s) of the lake should be at the bottom of the container

• Include at least one steep drop-off and one gentle slope • Make the surfaces of the lake bottom smooth • Do not create “overhangs”

Explanation:

1. Once students have created both the lakes and corresponding bathymetric maps, set up a matching game where students attempt to determine which map corresponds to each lake.

2. Each group should name their lake and create a nametag on a piece of paper to place next to their model. Assign each group a number or letter to write on their map transparency.

3. Have students number a sheet of paper with the set of numbers or letters assigned and set up the models and transparencies in different areas of the room. Allow students 10-15 minutes to circulate around the room to determine which lake corresponds with each map.

4. As a class, go through answers. When students choose a match between a lake and a map, ask them to justify their answer by referring to contour lines and corresponding features in the mini-lakes.

Extension:

Discuss the geologic processes (sedimentation, tectonic shifts, volcanic activity, human development) that could potentially create the lake floor features students created.

Discuss methods that scientists use to create bathymetric maps. Watch the TV documentary Drain the Great Lakes (National Geographic TV)

and discuss modern methods for creating bathymetric models Evaluation:

Find a bathymetric lake map for a lake that has significance for students. Have students find a set of landmarks on the map, based on contour lines. For example, the lowest point, a steep drop off, a shallow area, an island, etc.

Conclusion

What is a bathymetric map? What can a bathymetric map tell you about a lake?

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Activity 4: 20th Century History of an Urban Lake In this lesson, students analyze a sediment core from an urban lake. The lake sediment found on the bottom of a lake is related to processes in and around the lake. Natural changes in the environment, as well as changes made by humans to the landscape, can have effects on lakes that are recorded in the sediment. Lake sediments can be used to learn about changes in and around lakes over time. Human development (building, land use, etc.) during the 20th century had an effect on the lake used in this study. In the past few decades, improvements have occurred in this lake. Focus Questions

How do sediments record the history of a lake? How do humans change the type and amount of sediment deposited in a lake over time?

Learner Objectives

Collaborate with others in a small group to estimate number and thicknesses of sediment layers in a lake core sample.

Make an argument for your group’s answers to the rest of the class. Relate layer properties to time scale in the 20th century. Think about how rates of sediment deposition can be affected by humans.

Time Required

1-2 class periods Materials

Posters of full-sized core image (1 for every ~4 students Print posters in color and laminate OR Open in PDF viewer on computers Pencils, pens Post-it notes

Procedure Engagement: Divide class into 4 groups, assigning each group a season – summer, fall, winter, and spring. Each group should discuss and describe what happens to a lake during each of those seasons. Each group reports back to the group. Guide a classroom discussion about how these changes relate to sediments at the bottom of the lake (see Background Information).8 A useful analogy for                                                                                                                8 More information about lake sediments and coring methods is available from http://www.stolaf.edu/academics/nicollet/methods_sediment.html

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helping students understand sedimentary layers is layers of dirty clothes in a laundry hamper (or a pile on the floor!). By making some assumptions, such as that one outfit represents one day, you can use the order of the outfits to determine when the clothes were worn. As you go deeper into the hamper, you go further back in time. Different types of clothing may indicate what the weather was like in the past (i.e. sweaters on cold days, shorts on warm days). Exploration:

1. Divide students into small groups (2-5 students) and hand out laminated images of sediment cores from Lake McCarrons. Provide students with some background about the lake core, including how the core was collected (sediment coring device), when it was collected (in the year 2000), and the definition of a varve (see Background Information).

2. Hand out student worksheets that includes instructions and questions to answer related to the sediment core (see Appendix F). Review the directions with students.

3. Using the sediment core images, students work in groups to come up with an estimate of the number of varves in the core and answer related questions provided on the worksheet (answers below).

4. Discuss the estimates that each group came up with and the process that they used to come to an agreement on their estimate. Below are some methods and/or issues that may be presented:

Weighted average of group counts Votes among the group for certain layer counts Time-depth relationship Using prior knowledge Arguing, compromising Splitting up work (“let’s each count 10 cm”) Judgment calls Searching for additional information Setting thresholds and rules for consistency Pulling in other subdisciplines Speculation

5. Based on this discussion, relate the methods and issues that came up in this activity relate to how scientists interpret sediment core samples, namely, the uncertainties inherent in the interpretations scientists make about the age and environmental conditions from sediment core samples.9

Answers to worksheet questions:                                                                                                                9 For an in-depth discussion, see http://www.ncdc.noaa.gov/paleo/reports/trieste2008/lake-sediments.pdf

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1. Count the layers! How many years does the clearly layered portion represent? Approximately 86 years (+/- 5 years)

a. Given that the top is the year 2000, what year did laminations start to form? Around 1914

b. [Alt language: The top layer represents the year 2000. About what year does the bottom layer represent?]

2. Are there any years that are represented by particularly thick layers? Yes. a. What years are those, approximately? Those areas of the core

correspond with the 1930s and 1950s. b. Why do you think that some layers are thicker than others? What

do you think thicker layers might tell you about the environment around the lake? Thicker layers mean more material being deposited in the lake, due to increased erosion of material from the landscape into the lake, and/or increased algae growth (the result of increased nutrients). Thicker layers probably mean more activity (development etc.) on the landscape around the lake.

3. Given your answer in (2), the laminated portion is 43 cm long and represents (______) years, about how much time does this whole core, 129 cm long, represent?

If 43 cm represents 86 years, 129 cm represents about 258 years. So it’s closer to the Revolutionary War than the Civil War or Columbus’s voyage. The core actually represents closer to 500 years based on other dating methods. This is primary explained by the sedimentation rate before European settlement, which is only about 20% the rate after human impact. Compaction is also a factor – over long periods of time, the added weight of sediments on top will squeeze the water out, and the mud will slowly turn into rock - a process known as “lithification.”

Explanation:

1. Discuss the environment surrounding Lake McCarrons, emphasizing the role of humans. Lake McCarrons is an urban lake; discuss local examples of urban lakes and how they might differ from lakes that are relatively unaffected by human activities. “What are some ways in which humans might effect lakes?”

2. Discuss the causes of the thick layers found in the sediment core (question 2). Label these years on the core. “What kind of evidence could help us understand the past changes in the lake?”

3. Using climate and population data and historical photos of Lake McCarrons (see Appendix H), have students explain how changes in the environment correlate with changes in the core sample. Specifically, look at data around the times that correlate with the 1930s and 1950s. These times correlate with some major events, such as the Dust Bowl, the

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introduction of a swimming beach, and development of housing and roads in the surrounding areas (indicated by increasing population).

Extension:

Explain how lake stratification occurs in more detail using the slides found in the Appendix H. Discuss other ways in which core samples are analyzed (e.g. composition, chemical makeup, carbon dating). More information about initial core description can be found here: http://lrc.geo.umn.edu/laccore/icd.html For an in-depth discussion of the human impacts on Lake McCarrons, see Myrrbo (2008).10

Evaluation:

What influences the amount of sediment deposited in a lake over time? What can sediments at the bottom of a lake tell you about the history of a lake?

Conclusion Lake sediments can provide information about the past conditions of the areas surrounding them, such as climate, human impact, and geological processes and events. Using information from multiple sources, scientists make inferences and estimates about the environment during the near and distant past.

                                                                                                               10 Available at http://www.myrbo.com/amy/Myrbo_2008_Urban_McCarrons.pdf

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Activity 5: Engineering a Lake Sediment Coring Device In this lesson, students work in small groups to design and engineer a device that can be used to collect sediment samples from the bottom of a lake. Students will be given materials to build a scaled prototype of a device for collecting lake sediment in a simulated lake environment. Each group will be given time to design and test their ideas prior to presenting their solution to their peers. Focus Question

What are the challenges and limitations associated with collecting sediment from the bottom of a lake?

How do scientists design tools to collect sediment cores from the bottom of a lake?

Learner Objectives

Identify challenges and limitations associated with collecting sediment samples from the bottom of a lake.

Develop possible solutions to collect core samples from the bottom of a lake. Create, test, and improve lake core sampling tools based on an engineering

design cycle. Understand how lake sediment coring equipment used by scientists works.

Time Required

3-4 class periods Materials The following materials are needed to make the simulated lake that will be used to test students’ coring devices:

• Zorbitrol, Instant-Snow, or other Super Absorbent Polymer (SAP)11 • water • food coloring • 1 PVC tube 3” x 24” (Diameter x Length) • 1 PVC endcap 3”(Be sure to get a flat endcap as the tube needs to stand

upright.) • PVC primer and cement (to glue endcap onto tube) • cups (1 for each group) • lake bucket

Provide students with materials for creating a coring device prototype. The following materials are examples of materials that can be provided:

• tape • straws

                                                                                                               11 A commonly available SAP is sodium polyacrylate; Zorbitrol may be purchased via Shilog Medical Supply at: http://www.shilog.com/Store/Pages/548.html; Instant-Snow can be purchased via Steve Spangler Science at: http://www.stevespanglerscience.com/category/instant-snow

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• InstaMorph Moldable Plastic12 (http://amzn.com/B003QKLJKQ) • string • metal washers • rubber washers • erasers • paperclips • rubber bands • scissors • zip ties • chop sticks • balloons

Safety/Special Considerations

• Remind students of safe handling of classroom materials • Zorbitrol®/Instant Snow/SAP should be handled by teacher

Preparation To setup the testing “lake” – “Lake PVC” – which students will use to test their lake coring devices:

1. Glue the end cap onto one end of the PVC tube. 2. In 5 cups mix 1 gram of Zorbitrol® powder with 200 mL of colored water

(per cup)13. Each cup should be a different color. 3. Layer the Zorbitrol® “sediment” into the PVC tube by pouring it down the

side of the tube slowly, trying to avoid mixing of different colored layers. Keep track of the order of colors. You will be able to tell how much sediment each coring device recovers by what color sediment is at the bottom.

4. Next, make 1 cup of Zorbitrol® (same recipe, color optional) for each group to use for experimenting while designing their coring devices.

Procedure Engagement Present a lake model (bucket or tub) from Activities 1 and 2. Without showing the students the supplies, ask students to draw a picture of possible ways to collect a sediment core from this lake without putting a hand in the water. Have students make a list of supplies needed to build the device. This activity is intended to get students to begin thinking about how they would collect samples and what                                                                                                                12 A moldable plastic that can be melted in hot water and hardens at room temperature; available from Amazon (http://amzn.com/B003QKLJKQ) and other retailers. 13 Recipe may need to be adjusted depending on product used. In order to mimic lake sediment, the Zorbitrol®/SAP should have a consistency such that when a straw is inserted and withdrawn the gel does not stay inside, unless the straw is covered by your thumb. If the gel has too much water, the layers will mix.  

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supplies they would use. Have students share their initial design in pairs, then share out some of the solutions that they came up with. Lead a discussion around the following questions:

• How will the sediment stay in the coring devices on the way up to the surface?

• How will you preserve the order of layers in a sample? • How would your device work if the lake model were deeper? 3 ft? 10 ft?

100ft? • Would your device still work with different types of sediment, such as mud,

sand, or gravel? • Would your device work in a real lake?

Exploration:

1. Explain to students the goal of the following activity: To design and create a device that can reach the bottom of a lake, retrieve “sediment” samples, and return it to the surface. Students will build scale prototypes to gather sediment from a simulated lake bottom.

2. Present “Lake PVC” to the students, explaining the features of the model that will influence how the must construct their coring device. Students should be aware of the composition of the “sediment” and the distance between the lake “surface” and “bottom,” and the fact that there is no water between the surface and bottom in this model.

3. Explain the design constraints for developing the device prototype: • Each coring device can use only 1 straw • Students hands cannot dip below the “lake surface” (top of the

container) • The collected core must preserve sediment layers in the correct

order 4. Divide students into groups of 3 or 4 and present the available supplies to

students. In groups, give students ample work time (2-3 days, depending on class time) to build and test a coring device out of the available supplies. Group roles may be assigned at this time.14

5. Each group may make multiple coring devices during development. They can test each device in the test cup of SAP sediment. When testing in the cup, remind students that the device must be able to operate from approximately 24” above the cup. Ultimately, each group must choose 1 design to take to the final test in “Lake PVC.”

6. Successful coring devices will need to have some way to keep the sediment inside the straw when drawing it back to the surface. An analogy that may be useful during the development of the design is putting a straw in a glass of water then putting your thumb over the top to keep the water in as you lift the straw out of the glass. Other coring device designs might close the bottom of the straw to keep the sediment inside.

                                                                                                               14 Suggested group roles: materials manager, designer/documenter, builder/manufacturer, tester/experimenter

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Explanation: 1. After students have designed and built their coring device prototypes,

each group will put their device to the test in “Lake PVC.” Each group will be given 2 attempts to collect a core sample in Lake PVC.

2. Before attempting to recover sediment, each group should give a brief presentation about their device to their peers. The presentation may include all or any of the following: (1) the name of their final prototype, (2) the other designs/prototypes the group tested before arriving to the final design, (3) a description of the key components of the design, and (4) a demonstration of how the prototype is operated.

3. A winning design may be determined by the color of the deepest sediment recovered, by the length of the recovered core, and/or the most accurately preserved sediment layers. Other design aspects may also be considered, such as “most innovative” and “people’s choice.”

Elaboration: Discuss the following questions as a class or in groups:

What were some challenges that your group faced? How did you address those challenges?

How well did your design work? What were some strengths of the design? What were some shortcomings?

How did you choose the final design? What criteria were most influential in making this decision?

Were there any surprises in how your design performed? What types of lakes would your design be appropriate for? How would you adapt your design for use in a deeper “lake”? Could you collect a longer straw of “sediment” using the same design? What might be some practical challenges to adapting this design to a full-

scale model?

Conclusion

Show and discuss images of actual coring equipment used by scientists (see slideshow in Appendix I).15

Final Evaluation: Administer the Pre/Post Assessment (Appendix J) to determine whether learning goals were met.

                                                                                                               15 If you have questions or are curious to learn more about lake coring, contact the LacCore Laboratory via email at laccore@umn.edu.