Lakes and reservoir

Lakes and ponds are bodies of relatively still, or standing, water.
Although no definite size distinguishes a lake from a pond, lakes generally are larger and deeper than ponds.
Water enters lakes from streams and rivers, by rain or snow falling on or near the depression, and from groundwater.

1. LAKES AND RESERVOIR PREPARED BY: MUHAMMAD MUSAAB

2. WHAT ARE LAKES? Lakes and ponds are bodies of relatively still, or standing, water. Although no definite size distinguishes a lake from a pond, lakes generally are larger and deeper than ponds. Water enters lakes from streams and rivers, by rain or snow falling on or near the depression, and from groundwater.

3. Natural Lakes Many North American lakes, including the Great Lakes, formed when glaciers scoured out depressions that filled with rainwater, groundwater, or water from melting ice. Lakes also formed when sediment that was deposited by glaciers dammed the flow of streams.

4. Crustal Movements Movement of Earth's crust can create depressions that fill with water. These lakes often form along faults— surfaces along which rocks break and move. • Rock lying between two faults can sink to form a depression. • If Earth's crust continues to move along the faults, the lake will deepen.

5. CONT…. Lakes also can form after a volcanic eruption. The top of the volcano then might collapse into the partially emptied magma chamber and form a large depression called a caldera. Rainwater and runoff later fill the caldera.

6. Human-Made Lakes When a dam is built within a stream, a human-made lake forms. When water in a natural or artificially created lake is used for human consumption, the lake is called a reservoir.

7. Life in Lakes Many types of organisms can be found in different arts of lakes. Near a shallow, gently sloping shoreline, light penetrates to the lake bottom, allowing many types of rooted aquatic plants to grow.

8. CONT….. As plants use sunlight to make food, they produce oxygen that other organisms need. Plants also provide many places for small organisms to hide from hungry predators. Organisms that use land and water, such as amphibians, also are found here. 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. Wormlike organisms, bacteria and animal wastes that fall from higher layers of the lake are found on the lake bottom. Some fish species are found in deep waters of large lakes.

9. Sediment and Nutrients When streams and rivers empty into lakes, they deposit sediment on the lake bottom. 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. Over time, the deposited sediment decreases the depth of the lake so sunlight can penetrate more of the lake bottom. More plants grow, so more organisms can hide in them and use the oxygen they produce. As organisms die, they sink and decay, adding more material to the lake bottom and releasing more nutrients into the water.

10. CONT…. This cycle continues until the lake becomes eutrophic. Eutrophication is an increase in nutrients and organisms that is a normal part of a lake's life. Eventually, the lake will become dry land.

11. Turnover When organisms die, they sink to the lake bottom, decay, and nutrients are released into the water. In deep lakes these nutrients are concentrated at the bottom of the lake during summer. The water in the lakes upper layer warms during summer and becomes less dense than the layers below. Because of the different densities, little mixing occurs between layers. 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.

12. CONT….. 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.

13. What process eventually can turn a lake into dry land? Eutrophication is when a lake experiences an increase in nutrients through the process of decaying organisms. Eventually, the lake will become dry land.

14. 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.

15. How did the lake in this photo form? 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.

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