Today's lesson is about Saltwater vs. Freshwater and what can and can not drink or live there. There are 2 Activities and a story slide with this lesson. If time permits, there is a video at the end of this lesson.
In this presentation, we will discuss how saltwater intrusion affects small islands freshwater supplies, and how tourism is a significant part of this. In Zanzibar fresh water for drinking and other purposes come from rain that replenishes the island’s groundwater reservoir and in many cases freshwater is a scarce resource. On top of this, the excessive pumping in groundwater for the tourist industry increases the risk of salt water seeping into the freshwater magazine from the sea, thereby destroying the freshwater resource.
Students use a thermal process approach to design, build and test a small-scale desalination plant that is capable of significantly removing the salt content from a saltwater solution. Students use a saltwater circuit to test the efficiency of their model desalination plant and learn how the water cycle is the basis for the thermal processes that drive their desalination plant.
With an often unexpected outcome from a simple experiment, students can discover the factors that cause and influence thermohaline circulation in our oceans. In two 45 minute class periods, students complete activities where they observe the melting of ice cubes in saltwater and freshwater, using basic materials: clear plastic cups, ice cubes, water, salt, food coloring, and thermometers. There are no prerequisites for this lesson but it is helpful if students are familiar with the concepts of density and buoyancy as well as the salinity of seawater. It is also helpful if students understand that dissolving salt in water will lower the freezing point of water. There are additional follow up investigations that help students appreciate and understand the importance of the ocean’s influence on Earth’s climate.