Module 1
Introducing Water
Water is our most valuable renewable resource. It is necessary for all forms of life, particularly humans, whose needs encompass domestic use, fishing, irrigation for growing crops, manufacturing, and power. Many industries have been built next to large sources of water, such as rivers or ocean. Rivers are dammed to store the energy in their flow as electric power, and most agriculturalists construct dams to store rainfall. An understanding of the cycling of this precious resource and how it underpins the plant and animal life on Earth is the basis of this module.
Where is Earth’s Water?
Most water (96.5%) is in the oceans as salt (or saline) water.
• Along the equatorial belt, heat from the sun evaporates the water, carrying it upwards as water vapour both north and south of the equator by warm and cool air currents.
• As the water vapour cools, it precipitates as fresh water, in the form of rain, hail, sleet, or snow.
• Some of the water soaks into the ground, leaving the rest to flow over land into streams, lakes, and into the ocean as runoff.
• This cycle, which has no beginning or ending, is known as the water cycle.
Nearly 70% of freshwater is contained in the glaciers and icecaps, and only 30%, mainly as rainfall, sinks into the soil. Mortlock River, tributary of the Avon R.
• Water percolates underground through rock fractures, or cracks, and unconsolidated materials like gravel, sand, or silt, until it reaches a confining layer – such as solid rock. This is called groundwater. The underground level where the spaces, fractures, and voids in the rock become completely saturated with water is called the Water Table.
For an overview of how water cycles through the upper layers of Earth’s surface, visit
https://www.usgs.gov/special-topics/water-science-school/science/groundwater-flow-and-water-cycle
Water Cycle and Energy
The water cycle is driven by energy from the sun. Energy from the sun is continuously moving through the water cycle; it is being absorbed, carried, and released through different processes.
Draw a picture to illustrate what you understand about the processes described above. Include the following components:
• water stored in earth’s oceans
• energy from the sun warming ocean water
• water molecules evaporating from the ocean into the atmosphere
Energy is not created or destroyed; it simply moves through different states.
• Describe what is happening to the sun’s energy during the process of evaporation?
• Describe how the mass of the water in each container changed
• Use what you know about evaporation to explain your observations
• Describe what happened to the temperature of the water in each container
• What conclusions can you draw from these changes
• Experimental results are never perfect; sometimes results aren’t exactly how we measure things; our instruments may not be precise enough
• Does any of the data you collected surprise you
• How could measurement uncertainties insert blips in your data
Water in the Wheatbelt
There are 14 river systems in the Wheatbelt. To the east, there is an extensive system of streams, or drainage lines. These are ancient remnants that now only flow during wet years, draining into chains of saltlakes.
Wetlands
In the past, wetlands were viewed as wastelands and were often reclaimed for farming, housing, and waste infill. Today, they are recognised as one of the most important and productive ecosystems on Earth.
• They provide habitat, water, and an abundant food source for a diverse range of animals including birds, frogs, invertebrates, and fish. They are nurseries for fish and migratory bird populations, and in times of drought, they provide vital refuge areas for plants and animals.
• The food supply in these waters consists of micro and macro-invertebrates, insects, crustaceans, molluscs, and worms; all are a vital part of the food chain. Together with bacteria and unicellular organisms, they help to break down leaves, bark and twigs that fall into the water, and can even change their environments by moving soil, sand, or pebbles around.
• Scientists use the number and types of aquatic macroinvertebrates in a waterway to determine how healthy it is.
Toolibin Lake is the only remaining example of a permanent wetland in the Wheatbelt.
Situated in the upper Blackwood River catchment, near Narrogin, it is surrounded by extensive woodlands, principally sheoak (Casuarina obesa) and paperbark (Melaleuca strobophylla) trees.
• The lake was once a freshwater wetland, and home to rich plant and animal communities.
• Clearing for agriculture has brought marked changes. By 1972, 91% of the total catchment area had been cleared for agriculture, changing deep rooted native plants to shallow-rooted crops that don’t use all the rainfall.
• As a result, this unused rainwater either runs off or percolates below the root zone into the groundwater.
• Rising groundwater levels have caused the saline groundwater under Toolibin Lake to rise virtually to the floor of the lake.
• Evaporation further concentrates the salts at the surface.
https://www.agric.wa.gov.au/soil-salinity/dryland salinity-western-australia-0
Activity
Demonstrate the Proportion of Earth’s Water that is Fresh:
This simple group exercise demonstrates the proportion of Earth’s water that is fresh and available for humans to use.
MATERIALS
• 10L bucket
• 300ml beakers (5)
• 100ml measuring cylinder
• 5ml pipette
• 1ml pipette
METHOD
1. Fill the 10L bucket to the 10L mark.
2. From the 10L, remove 300ml to beaker (1). This represents the volume of fresh water on the planet. There remains 9.7L in the bucket, representing the volume of water in the oceans.
3. From beaker (1), using the measuring cylinder and the pipette, remove 204 ml into beaker (2). This represents the volume of water in icecaps and glaciers.
4. From beaker (1), using the measuring cylinder, remove 90ml into beaker (3). This represents the volume of groundwater.
5. From beaker (1), using 5ml pipette, pipette 4.5 ml into beaker (4). This represents permafrost (underground ice).
6. From beaker (1), pipette 1.5ml into beaker (5).This represents available surface fresh water.
7. A careful pipetting of 1.33ml from beaker (5) into a small test-tube represents the volume of surface water used for agriculture (horticulture and pasture) in the southwest of WA (see link below).
8. The volume, 0.17ml, remaining in beaker (5) represents the volume of fresh water available for other human uses.
9. Write up this activity with students presenting their data in tabular format, identifying the nature of each water source and expressing all volumes as percentages of Earth’s total water of 10L (i.e. 0.0017% is water for human use).
10. Students may research how humans use the tiny fraction of available surface fresh water remaining after agricultural usage.
DISCUSS
Why it is important to save fresh water?
• How would students do this?
• Do they know what happens to fresh water that falls as rain? Where does it go?
• Comparing the volume 0.17ml, representing fresh water available for humans, with the 9,700ml (9.7L) remaining in the bucket as ocean water, what might humans do to increase the amount of fresh water for humans?
Activity
Draw a Water Cycle:
Using the information provided, and calculations in the prior Activity, have students represent all proportions of Earth’s water in a Water Cycle, adding their calculations to the diagram.