Transcript Do Now 11/3/2009

1. How are lakes and streams similar? How are they
different?
2. How do people use lakes?
3. What are some ways lakes are formed?
Lakes
How does water enter into lakes?
 Rainfall (Precipitation)
 Runoff- The water that does not sink into the ground, yet
flows along the surface.
How do lakes form?
- Glaciers: Glaciers scoured out depressions that over time
fill in with runoff water.
- Natural Lakes:
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Ex. Great Lakes- They hold 18 percent of Earth’s freshwater.
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http://upload.wikimedia.org/wikipedia/commons/c/c3/Great_Lakes_from_space.jpg
- Crustal Movement: The Earth’s crust can move and create
depressions that fill in with water.
- Volcanic Eruption: After a volcanic eruption the top of the
volcano can fill with water.
- Caldera: http://www.gvb-csic.es/CCDB/iamgenes/KatmaiCaldera.jpg
- Formation of a dam:
- Human-made lake
-
Ex. Hoover dam
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http://philip.greenspun.com/images/pcd2882/hoover-dam-aerial-91.4.jpg
What is found in lakes?
 Plant Life: Plant life near a lake is usually found near the shallow parts.
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Why?
 Because, plants need sunlight to live and produce.
Amphibians: Organisms that use both the land and the water.
 Ex. Frogs, Ducks, Turtles, etc.
Fish
Plankton: small organisms found near the surface of the water.
Sediment and Nutrients:
 Nutrients: Compounds such as nitrates and phosphates that are
used by plants and algae to grow.
 Sediment: Can a lake be the same depth forever?
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No, sediment will build and over time the lake will decrease in depth. Eventually
becoming dry.
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http://techalive.mtu.edu/meec/module08/FoodWeb.htm
Lake Math
Bay depth: A small bay in a large lake is filling at a rate of 0.01 cm per year.
If the water in the bay averages 100 cm deep, how long will it take for
the bay to become land.
Solution:
1. This is what you know:
Infill rate- r= 0.01 cm/y
2. Average depth- d= 100 com
1.
2. What you need to find:
1.
Time: t
3. This is the procedure you need to use:
1.
time= depth / infill rate
4. Solve:
1.
Time= 100cm / 0.01cm/y = 1000 years
Practice:
A different bay in the same lake is filling at a rate of 0.3 cm/y. This bay averages 150
cm deep. How long will it take to fill in?
How does a lake turnover?
 Turnover- The mixing of lake water, which causes
nutrients from deep in the lake to move to the surface.
 Summer Lake:
 Nutrients are concentrated on the bottom with the more dense colder
water.
 Low nutrient count on top with the less dense water .
 There is a separation of nutrients due to water density.
 Autumn Lake:
 The top layer of water becomes colder and more dense.
 The top layer sinks and mixes with the nutrient rich water from the
bottom.
* Turnover causes nutrients from deep in the lake to move upward toward
the surface.
Vocabulary
 Nutrient
 Eutrophication
 Turnover