Lesson 9: Experiment

Estuary in a test tube

Here is what you do:

1. Fill a test tube half full of water. Pour the water into a measuring cup.
2. Add ¼ teaspoon of salt and three drops of food coloring to the water in the measuring cup. Mix well. This represents salt water flowing into an estuary.
3. Pour the mixture into the test tube. Place the test tube in a holder.
4. Rinse colored water from the measuring cup and fill it half full of water. This represents freshwater flowing into an estuary. You’ll add some of this water to the test tube. Fill a dropper with freshwater from the cup.
5. Hold the dropper at an angle so the open end touches the inside of the test tube. Tilt the tube and squeeze the dropper very slowly and carefully. Let the water trickle down the side of the test tube. Do not shake or move the test tube when you are adding freshwater.
6. Continue adding freshwater until you have about a 1-inch layer on top of the salt water. Allow the water in the test tube to sit for a few minutes. Are there more than two layers of water?
7. Cover the test tube opening and shake. Observe what happens.

What do you think?

1. Which is more dense, salt water or freshwater? How do you know?
2. In an estuary, does freshwater float on top of salt water? Why or why not?
3. Compare this experiment to what happens in an estuary. What do we call a mixture of salt water and freshwater?
4. Where do freshwater and salt water in an estuary come from? Why are estuaries important?

Make a difference.

Sometimes marine wildlife become entangled in discarded fishing line. The line is made of plastic and is very strong. Once a sea turtle or a bird becomes tangled in the line, it is almost impossible for it to get free. Some marine animals can even get caught in plastic rope or plastic six-pack rings.

How do the animals get caught in this floating trash? Most of the time they just don’t see it. Sometimes tiny fish gather around the plastic trash. Then when birds come by to feed, they become entangled.

When birds get caught in the plastic, they often can’t fly away. They may drown or become food for a larger animal.

Sometimes animals eat small pieces of plastic. Most plastics will not digest in an animal’s stomach. The animal may not be able to eat properly and could die.

If you go to the beach, pick up all your litter. Don’t let it float out to sea. A sea turtle may even mistake a plastic bag for a jellyfish. It may become its last meal.

 

Return to:
WaterWays student index