St Lawrence Estuary - STEM Challenge

Written By Shannon Hardy
 

Investigating Brackish Water in Estuaries

Today we are going to explore estuaries and brackish water. Estuaries are where freshwater meets saltwater, creating a very unique ecosystem that is home to many different plants and animals. Brackish water is a mixture of that freshwater and saltwater and can be found in estuaries like the St. Lawrence. Let’s investigate brackish water and learn about what makes it so special.

Suggested Materials:

  • A clear glass jar or cup

  • A clear container, or bin

  • Water

  • Salt

  • Measuring spoon

  • Food colouring of different colours

  • Stirring spoon


    Optional Materials:

  • Glue gun

  • Duct tape

  • Plasticine

  • Paper cups

  • Push pins

  • Small drink bottles with lids


Phase 1: Research and Design

As a group or individual, brainstorm and design a water mixing container to represent your estuary. The goal is to have 2 separate liquids slowly mix together in one container.

There are a few different ways you can build this. We suggest doing some research to come up with a solution.


Phase 2: Begin Construction

Build your mixing container.

Phase 3: Mix up Your Water Solutions

Add one teaspoon of salt to one cup of freshwater and stir until the salt dissolves.

Next, add a few drops of food colouring to the salt water.

Measure out 1 cup of fresh water and add a different colour.

Adding food colouring to the different mixtures will help you observe the properties of the water more clearly when mixing.

Phase 4: Create an Estuary

Add your salty solution and freshwater to the divided mixing container, and remove the barrier slowly.

Be very careful not to mix the 2 liquids too quickly. What do you observe? If you remove the barrier too quickly make note of the outcome and start again if necessary.

Phase 5: Observe and reflect

Replace the barrier and stir the water on one side, this will create brackish water (saltwater and freshwater mixed together). Saltwater is denser (heavier) than freshwater because of the salt it contains. When fresh river water pours into an estuary it will sit on top of the salt water until the ocean or tidal currents mix the two. Once the two waters are mixed they are known as brackish water.

BUILD YOUR ESTUARY

Discussion:

What did you observe when you added the salt water solution to the freshwater?

Why do you think the different layers form?

How do the properties of freshwater differ from saltwater?

What kind of plants and animals do you think would be able to survive in brackish water?

 Spark curiosity and inspire kids to take action with Live It Earth STEM Challenges that are learner-driven and problem-based. If you enjoyed this STEM challenge, here are 3 of our favourite past STEM Challenges: Make Your Own Dog Treats in our Dogs STEM Challenge, Grow Your Own Fungi in our Fungi STEM Challenge, or Design and Build an ROV in our Deep Sea STEM Challenge.

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Shannon Hardy
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