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
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http://www.cehd.umn.edu/stem/ 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
[email protected]. 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