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Lake Turnover: Why Lakes Mix Twice a Year

5th grade nonfiction passage about how lakes mix: 198 words, six questions, an answer key and vocabulary.

5th grade nonfiction how lakes mix 198 words

Lake Turnover: Why Lakes Mix Twice a Year

In summer, a deep lake in a cool place is a bit like a layered drink. The sun warms the top, and warm water is lighter, so it floats above the cold, heavy water below. A calm line between the layers keeps them apart. Down in the cold layer, fish and other animals slowly use up the oxygen, and very little new oxygen can reach them.

Then autumn comes. The air turns cool, and the top layer cools too. Cooler water is heavier, so it begins to sink. Wind pushes the surface around and helps to stir the whole lake. Soon the layers blend together, and the lake turns over. Fresh oxygen from the surface travels to the bottom, and nutrients from the muddy bottom are stirred upward.

Winter brings a second change. Water is heaviest at a temperature just above freezing. That heaviest water stays near the bottom, while colder water and ice float above it. In spring, the ice melts, the top water warms to that heavy point, and it sinks. This mixes the lake a second time. The two turnovers each year keep a lake healthy for the plants, fish, and insects that live there.

Questions

  1. Why does warm water float on top of the lake in summer? in the text

  2. What happens to the oxygen in the cold bottom layer during summer? in the text

  3. What two things help mix the layers together in autumn? in the text

  4. In which two seasons does a lake turn over? in the text

  5. Why does the water just above freezing stay near the bottom in winter? think about it

  6. Why are the two turnovers good for the animals in a lake? think about it

Words to know

layers
levels of something stacked one above another
oxygen
a gas in air and water that animals need to breathe
nutrients
materials that living things need in order to grow
surface
the top of the water, where it meets the air
turnovers
times when a lake's layers flip and mix together
Share

One passage, three levels

The same topic and facts written three ways, so a mixed class can read and talk about one text. Each group’s sheet shows only a shape; the key says which is which.

● Easier · 139 words · Flesch-Kincaid grade 1.4

In summer, a deep lake has layers. The sun warms the top. Warm water is light, so it stays on top. The cold, heavy water stays below. The layers do not mix. Fish at the bottom use up the oxygen. Not much new oxygen can reach them.

Then autumn comes. The air gets cool. The top water gets cool, too. Cool water is heavy, so it sinks. Wind stirs the lake. The layers mix. The lake turns over. Oxygen goes down to the bottom. Nutrients rise up from the mud.

In winter, the heaviest water is just above freezing. It stays at the bottom. Colder water and ice float on top. In spring, the ice melts. The top water warms up and sinks. The lake mixes again. The two turnovers help the plants, fish, and insects in the lake.

▲ This passage · 198 words · Flesch-Kincaid grade 4.9

In summer, a deep lake in a cool place is a bit like a layered drink. The sun warms the top, and warm water is lighter, so it floats above the cold, heavy water below. A calm line between the layers keeps them apart. Down in the cold layer, fish and other animals slowly use up the oxygen, and very little new oxygen can reach them.

Then autumn comes. The air turns cool, and the top layer cools too. Cooler water is heavier, so it begins to sink. Wind pushes the surface around and helps to stir the whole lake. Soon the layers blend together, and the lake turns over. Fresh oxygen from the surface travels to the bottom, and nutrients from the muddy bottom are stirred upward.

Winter brings a second change. Water is heaviest at a temperature just above freezing. That heaviest water stays near the bottom, while colder water and ice float above it. In spring, the ice melts, the top water warms to that heavy point, and it sinks. This mixes the lake a second time. The two turnovers each year keep a lake healthy for the plants, fish, and insects that live there.

■ Harder · 236 words · Flesch-Kincaid grade 7.7

During the summer, a deep lake in a cool region separates into distinct layers, much like a layered drink. The sun warms the surface, and because warm water is lighter than cold water, it floats on top of the heavy, chilly water beneath it. A steady boundary between the layers keeps them from blending. Down in the cold layer, fish and other animals gradually use up the oxygen, and very little fresh oxygen can make its way down to replace it.

Autumn changes everything. As the air turns cool, the surface layer cools as well. Cooler water is heavier, so it begins to sink, and the wind churns the surface and helps to stir the entire lake. Before long the layers have blended together, and the lake has turned over. Fresh oxygen from the surface is carried all the way to the bottom, while nutrients from the muddy lake floor are stirred upward into the water above.

Winter brings a second change. Water is at its heaviest at a temperature just above freezing, so that heaviest water remains near the bottom, while colder water and ice float above it. When spring arrives, the ice melts, the top water warms to that same heavy point, and it sinks, which mixes the lake for a second time. These two turnovers each year keep the lake healthy for the plants, fish, and insects that make their homes in it.

Download as one PDF

How to use it

  1. Press Read it big (or B) to put the text on the projector, or Full screen (F) to fill the whole screen.
  2. Ask the questions one at a time and use Show answer when the class has decided. A shows or hides every answer.
  3. Print student copy for the class, or Print with answers for yourself.

Ideas for class

  • Before reading, put layers, oxygen, nutrients, surface and turnovers on the board with their meanings from the Words to know section and have students predict what the text will be about.
  • Read it aloud once while students follow along, then have them reread it alone or with a partner. At a calm 100 words a minute it takes about 2 minutes to read aloud.
  • Use the Read it big button (or B) to put the text on the projector, and Show answer on one question at a time so the class commits to an answer first.
  • Question 5 asks the reader to infer. Ask students to point to the words in the passage that led them to their answer.
  • Ask students to write one question the passage did not answer, then look for the answer in a book or on a classroom screen.
  • Print the student copy for independent work and keep the answer-key copy for yourself.

Related

Questions

What reading level is "Lake Turnover: Why Lakes Mix Twice a Year"?

It was written for 5th grade. It has 198 words and works out to a Flesch-Kincaid grade level of about 4.8. That is a formula's estimate from sentence length and syllables, and it is not a Lexile or a guided reading level, so check it against your students.

What do the questions ask?

There are six. 4 ask for something the text says directly and 2 ask the reader to work something out from clues. Each has an answer in the key, and the answers are written as a teacher would accept them, not as the only possible wording.

How long does it take to read?

About 2 minutes read aloud at 100 words a minute. For a one-minute fluency check, paste it into the fluency timer and use the word count.

Can I print it?

Yes. Print student copy gives the passage, the questions with lines to write on, and the word meanings. Print with answers gives the same page with the answers filled in. Both are made in your browser.

Is this passage from a published book?

No. It was written for Peabody Teach, so there is no book to buy and no login to read it.

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