Chapter 6.2 - Lakes and Reservoirs


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Chapter 6.2 - Lakes and Reservoirs

  1. 2. Chapter: Freshwater at Earth’s Surface Table of Contents Section 3: Wetlands Section 1: Streams Section 2: Lakes and Reservoirs Section 4: Pollution of Freshwater
  2. 3. Formation of Lakes <ul><li>Lakes and ponds are bodies of relatively still, or standing, water. </li></ul><ul><li>Although no definite size distinguishes a lake from a pond, lakes generally are larger and deeper than ponds. </li></ul><ul><li>Water enters lakes from streams and rivers, by rain or snow falling on or near the depression, and from groundwater. </li></ul>Lakes and Reservoirs 2
  3. 4. Natural Lakes Lakes and Reservoirs 2 <ul><li>Many North American lakes, including the Great Lakes, formed when glaciers scoured </li></ul>out depressions that filled with rainwater, groundwater, or water from melting ice.
  4. 5. Natural Lakes <ul><li>Lakes also formed when sediment that was deposited by glaciers dammed the flow of streams. </li></ul>Lakes and Reservoirs 2
  5. 6. Crustal Movements <ul><li>Movement of Earth’s crust can create depressions that fill with water. </li></ul><ul><li>These lakes often form along faults— surfaces along which rocks break and move. </li></ul>Lakes and Reservoirs 2 <ul><li>Rock lying between two faults can sink to form a depression. </li></ul><ul><li>If Earth’s crust continues to move along the faults, the lake will deepen. </li></ul>
  6. 7. Crustal Movements <ul><li>Lakes also can form after a volcanic eruption. </li></ul>Lakes and Reservoirs 2 <ul><li>Rainwater and runoff later fill the caldera. </li></ul><ul><li>The top of the volcano then might collapse </li></ul>into the partially emptied magma chamber and form a large depression called a caldera .
  7. 8. Human-Made Lakes <ul><li>When a dam is built within a stream, a human-made lake forms. </li></ul>Lakes and Reservoirs 2 <ul><li>When water in a natural or artificially created lake is used for human consumption , the lake is called a reservoir . </li></ul>
  8. 9. Life in Lakes <ul><li>Many types of organisms can be found in different parts of lakes. (Copy into your notes from page 174.) </li></ul>Lakes and Reservoirs 2
  9. 10. Life in Lakes Lakes and Reservoirs 2 <ul><li>Near a shallow, gently sloping shoreline, light penetrates to the lake bottom, allowing </li></ul>many types of rooted aquatic plants to grow.
  10. 11. Life in Lakes <ul><li>As plants use sunlight to make food , they produce oxygen that other organisms need. </li></ul>Lakes and Reservoirs 2 <ul><li>Plants also provide many places for small organisms to hide from hungry predators. </li></ul><ul><li>Organisms that use land and water, such as amphibians, also are found here. </li></ul>
  11. 12. Life in Lakes <ul><li>Because sunlight cannot penetrate to the bottom of a deep lake, rooted plants cannot survive there, so frogs and small fish have nowhere to hide. </li></ul>Lakes and Reservoirs 2 <ul><li>Wormlike organisms, bacteria and animal wastes that fall from higher layers of the lake are found on the lake bottom. </li></ul><ul><li>Some fish species are found in deep waters of large lakes. </li></ul>
  12. 13. Sediment and Nutrients <ul><li>When streams and rivers empty into lakes, they deposit sediment on the lake bottom. </li></ul>Lakes and Reservoirs 2 <ul><li>A lake might fill more quickly if nutrients —compounds such as nitrates and phosphates that are used by plants, algae, and some plankton to help them grow— are in the water . </li></ul>
  13. 14. Sediment and Nutrients <ul><li>Over time, the deposited sediment decreases the depth of the lake so sunlight can penetrate more of the lake bottom. </li></ul>Lakes and Reservoirs 2 <ul><li>More plants grow, so more organisms can hide in them and use the oxygen they produce. </li></ul><ul><li>As organisms die, they sink and decay, adding more material to the lake bottom and releasing more nutrients into the water. </li></ul>
  14. 15. Sediment and Nutrients <ul><li>This cycle continues until the lake becomes eutrophic. </li></ul>Lakes and Reservoirs 2 <ul><li>Eutrophication ( yew troh fuh KAY shun ) is an increase in nutrients and organisms that is a normal part of a lake’s life. </li></ul><ul><li>Eventually, the lake will become dry land. </li></ul>
  15. 16. Turnover <ul><li>When organisms die, they sink to the lake bottom, decay, and nutrients are released into the water. </li></ul>Lakes and Reservoirs 2 <ul><li>In deep lakes these nutrients are concentrated at the bottom of the lake during summer. </li></ul><ul><li>The water in the lakes upper layer warms during summer and becomes less dense than the layers below. </li></ul>
  16. 17. Turnover <ul><li>Because of the different densities, little mixing occurs between layers. </li></ul>Lakes and Reservoirs 2 <ul><li>When summer ends, the surface water becomes cooler and denser. It sinks and mixes with nutrient-rich water. This mixing of lake water, is called turnover . </li></ul>
  17. 18. Turnover <ul><li>Turnover causes nutrients from deep in the lake to move upward toward the surface. </li></ul>Lakes and Reservoirs 2 <ul><li>This process circulates nutrients at the lake bottom to the shallow areas and surface water, where organisms use them to grow and reproduce. </li></ul>
  18. 19. Section Check 2 Question 1 What process eventually can turn a lake into dry land? A. crustal movements B. eutrophication C. turnover D. upwelling NC: 3.02
  19. 20. Section Check 2 Answer The correct answer is B. Eutrophication is when a lake experiences an increase in nutrients through the process of decaying organisms. Eventually, the lake will become dry land. NC: 3.02
  20. 21. Section Check 2 Question 2 What is a lake called when the water is used for human consumption? When a dam is built a human-made lake, or reservoir , forms. The reservoir is used to supply drinking water to nearby communities. Answer NC: 3.02
  21. 22. Section Check 2 Question 3 How did the lake in this photo form?
  22. 23. Section Check 2 Answer This lake formed after a volcanic eruption occurred causing the top of the volcano to sink into itself. The depression, called a caldera, has filled with rainwater and runoff.